Document:

Exhibit 4.4

                        REGISTRATION RIGHTS AGREEMENT

      REGISTRATION RIGHTS AGREEMENT (this "AGREEMENT"), dated as of January 31,
2000, by and between CASTLE DENTAL CENTERS, INC., a Delaware corporation (the
"COMPANY"), HELLER FINANCIAL, INC., a Delaware corporation ("HELLER") and
MIDWEST MEZZANINE FUND II, L.P., a Delaware limited partnership ("MIDWEST")
(Heller and Midwest are sometimes referred to individually as a "HOLDER" and
together, as the "HOLDERS"). Capitalized terms used and not other defined herein
have the respective meanings ascribed thereto in Article I.

                                   RECITALS

      WHEREAS, contemporaneously with the execution and delivery of this
Agreement, the Holders and the Company will enter into a Subordinated Note
Purchase Agreement (the "PURCHASE AGREEMENT");

      WHEREAS, pursuant to the Purchase Agreement, the each Holder will purchase
a note or notes convertible into shares of Common Stock of the Company; and

      WHEREAS, each of the Holders and the Company desire to enter into this
Agreement to provide the Holders with certain rights with respect to their
ownership of the Company's Common Stock issuable upon conversion of the
Convertible Note.

      NOW, THEREFORE, the parties hereto hereby agree as follows:

                                  ARTICLE I
                              CERTAIN DEFINITIONS

      1.1 DEFINED TERMS. The following capitalized terms, when used in this
Agreement, have the respective meanings set forth below:

            "COMMISSION" means the Securities and Exchange Commission or any
      other federal agency at the time administering the Securities Act.

            "COMMON STOCK" means the common stock of the Company, par value
      $.001 per share, any securities into which such Common Stock shall have
      been changed or any securities resulting from any reclassification or
      recapitalization of such Common Stock and all other securities of any
      class or classes (however designated) of the Company the holders of which
      have the right, without limitation as to amount, after payment on any
      securities entitled to a preference on dividends or other distributions
      upon any dissolution, liquidation

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      or winding up, either to all or to a share of the balance of payments upon
      such dissolution, liquidation or winding up.

            "CONVERTIBLE NOTES" means the notes dated the date hereof initially
      convertible for an aggregate of 442,880 shares of Common Stock, issued to
      the Holders, and any securities issued upon subdivision or combination, or
      in substitution, thereof.

            "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
      amended, and the rules and regulations promulgated thereunder.

            "EXISTING REGISTRABLE SECURITIES" means the 2,969,822 shares of
      Common Stock defined as "Registrable Securities" and "Registrable inside
      Shareholder Securities" pursuant to that certain Amended and Restated
      Registration Rights Agreement, dated as of June 16, 1997, among the
      Company and those Persons whose names appear thereon, as such agreement
      exists as of the date hereof, without giving effect to any further
      amendment or modifications thereto, so long as such shares remain
      "Registrable Securities" or "Registrable inside Shareholder Securities"
      thereunder.

            "FULLY DILUTED BASIS" means, with respect to the calculation of the
      number of shares of Common Stock, (i) all shares of Common Stock
      outstanding at the time of determination, and (ii) all shares of Common
      Stock issuable upon the conversion, exchange or exercise of all securities
      (including the Convertible Notes) convertible, exchangeable or exercisable
      for or into shares of Common Stock regardless of whether such securities
      are then convertible, exchangeable or exercisable.

            "HOLDERS" means the Holders and any permitted successors or assigns,
      so long as such Persons are the owners of record of any Registrable
      Securities or any Convertible Notes pursuant to which any Registrable
      Securities may be issued.

            "MAJORITY HOLDERS" means, as of any particular date, the holders of
      a majority of the outstanding Registrable Securities based upon the sum of
      the total number of shares of Registrable Securities then outstanding and
      the total number of shares of Registrable Securities issuable with respect
      to any Convertible Notes then outstanding.

            "PERSON" means an individual, partnership, corporation, trust,
      unincorporated organization, joint venture, government (or agency or
      political subdivision thereof) or any other entity of any kind.

            "REGISTRABLE SECURITIES" means any shares of Common Stock issuable
      upon conversion of the Convertible Note or securities issued or issuable
      with respect to such Convertible Note or Common Stock by way of stock
      dividend or stock split or in connection with a combination of shares,
      recapitalization, merger, consolidation or other reorganization or
      otherwise upon any required adjustments. As to any particular Registrable
      Securities, such securities shall cease to be Registrable Securities when
      (a)

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      a registration statement with respect to the sale of such securities shall
      have become effective under the Securities Act and such securities shall
      have been disposed of in accordance with such registration statement, or
      (b) they shall have been distributed to the public pursuant to Rule 144
      (or any successor provision) under the Securities Act.

            "REGISTRATION EXPENSES" means all expenses incident to the Company's
      performance of or compliance with SECTION 2, including, without
      limitation, all registration, filing and National Association of
      Securities Dealers, Inc. fees, all fees and expenses of complying with
      securities or blue sky laws, all word processing, duplicating and printing
      expenses, messenger and delivery expenses, the fees and disbursements of
      counsel for the Company and of its independent public accountants,
      including the expenses of any special audits or "comfort" letters required
      by or incident to such performance and compliance, the reasonable fees and
      disbursements of one counsel (except in the event of a conflict of
      interest, then such number of counsel as is appropriate to resolve such
      conflict) retained by the holder or holders of a majority of the
      Registrable Securities being registered, premiums and other costs of
      policies of insurance, if any, obtained by the Company against liabilities
      arising out of the public offering of the Registrable Securities being
      registered and any fees and disbursements of underwriters customarily paid
      by issuers or sellers of securities, including reasonable fees of
      underwriters counsel including qualification of securities under blue sky
      laws, but excluding all agency fees and commissions, underwriting
      discounts and commissions and transfer taxes, if any.

            "SECURITIES ACT" means the Securities Act of 1933, as amended, and
      the rules and regulations promulgated thereunder.

                                  ARTICLE II
                       REGISTRATION UNDER SECURITIES ACT

      2.1   REGISTRATION OF REGISTRABLE SECURITIES ON REQUEST.

            (a) REQUEST. The Majority Holders shall have the right to request in
writing that the Company effect one registration under the Securities Act of
1933, as amended (the "SECURITIES ACT") of all or part of such Holders'
Registrable Securities pursuant to this SECTION 2.1. Within ten days after
receipt of any such request, the Company will give written notice of such
requested registration to all other Holders of Registrable Securities, which
Holders shall be entitled to include their Registrable Securities in such
registration subject to SECTION 2.1(F). Thereupon the Company will use its best
efforts to effect, as expeditiously as possible, the registrations under the
Securities Act on the form requested by the Holders of Registrable Securities
requesting registration of the following securities, subject to SECTIONS 2.1(F):

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                  (i)   the Registrable Securities which the Company has been so
      requested to register by the Majority Holders; and

                  (ii) all other Registrable Securities which the Company has
      been requested to register by the Holders thereof by written request given
      to the Company within thirty (30) days after the giving of such written
      notice by the Company (which request shall specify the intended method of
      disposition of such Registrable Securities).

      The Holders of a majority of the Registrable Securities requesting a
registration under this ARTICLE II may, at any time prior to the effective date
of the registration statement relating to such registration, revoke, without
liability, such request by providing written notice to the Company. The Company
will pay all Registration Expenses in connection with any registration pursuant
to this SECTION 2.1.

            (b) REGISTRATION OF OTHER SECURITIES. Whenever the Company shall
effect a registration pursuant to this SECTION 2.1, no securities other than
Registrable Securities shall be included among the securities covered by such
registration unless (i) the managing underwriter of such offering shall have
advised each Holder of Registrable Securities to be covered by such registration
in writing that the inclusion of such other securities would not in the
underwriter's reasonable judgment adversely affect such offering or (ii) the
Holders of a majority of Registrable Securities to be covered by such
registration shall have consented in writing to the inclusion of such other
securities. The Company has not granted, and the Company will not grant to any
person at any time on or after the date hereof, the right to be included among
the securities registered pursuant to this SECTION 2.1 that is inconsistent with
the provisions of this SECTION 2.1(B).

            (c) REGISTRATION STATEMENT FORM. Registrations under this SECTION
2.1 shall be on such appropriate registration form of the Commission (i) as
shall be selected by the Holders of a majority of the Registrable Securities so
to be registered and (ii) as shall permit the disposition of such Registrable
Securities in accordance with the intended method or methods of disposition
specified in their request for such registration. The Company agrees to include
in any such registration statement all information which Holders of Registrable
Securities being registered shall reasonably request.

            (d) EFFECTIVE REGISTRATION STATEMENT. A registration requested
pursuant to this SECTION 2.1 shall not be deemed to have been effected and shall
not count as a requested registration pursuant to SECTION 2.1(A) hereof (i)
unless a registration statement with respect thereto has become effective under
the Securities Act and has remained effective for a period of at least 180 days
(or such shorter period in which all Registrable Securities included in such
registration have actually been sold thereunder, but subject to extension
pursuant to SECTION 2.4(B)), (ii) if after it has become effective, such
registration is interfered with by any stop order, injunction or other order or
requirement of the Commission or other governmental agency or court for any
reason not the fault of a Holder of Registrable Securities covered thereby have
not been sold, or (iii) if the conditions to closing specified in the selling
agreement or

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underwriting agreement entered into in connection with such registration are not
satisfied or waived by the parties thereto other than a Holder of Registrable
Securities. Notwithstanding the foregoing, the Company will pay all Registration
Expenses in connection with any registration that is not deemed to have been
effected pursuant to SECTION 2.1(A) as a result of the terms of this SECTION
2.1(D).

            (e) UNDERWRITERS. Any registration effected pursuant to this SECTION
2.1 shall, at the election of the Holders of a majority of the Registrable
Securities to be so registered, be an underwritten public offering on a firm
commitment basis or a best efforts basis. The managing underwriter or
underwriters thereof shall be selected by the Company, subject to the approval
of such selection by the Holders of a majority of the Registrable Securities to
be so registered, and the price, terms and provisions of the offering shall be
subject to the approval of the Company and the Holders of a majority of the
Registrable Securities to be so registered.

            (f) APPORTIONMENT IN REGISTRATIONS REQUESTED. If, in connection with
a registration requested pursuant to this SECTION 2.1, the managing underwriter
shall advise the Company in writing (with a copy to each Holder of Registrable
Securities requesting registration) that, in its opinion, the number of
securities requested to be included in such registration exceeds the number
which can be sold in such offering within a price range acceptable to the
Holders of a majority of the Registrable Securities requested to be included in
such registration, the number of securities that are otherwise entitled to be
included in such registration shall be allocated in the following manner: the
Registrable Securities requested to be included in such registration shall be
reduced, on a pro rata basis among the Holders thereof requesting such
registration on the basis of the percentage of the Registrable Securities held
by the Holders of Registrable Securities which have requested that such
Registrable Securities be included.

      2.2 REGISTRATIONS ON FORM S-3. Anything contained in SECTION 2.1 to the
contrary notwithstanding, the Holder or Holders of the Registrable Securities
shall have the right to request in writing an unlimited number of registrations
on Form S-3 (or any successor or similar short- form registration statement), of
Registrable Securities, which request or requests shall (i) specify the number
of Registrable Securities intended to be sold or disposed of and the Holders
thereof, and (ii) state the intended method of disposition of such Registrable
Securities. A requested registration in compliance with this SECTION 2.2 shall
not count as a registration statement initiated pursuant to SECTION 2.1 but
shall otherwise be treated as a registration initiated pursuant to, and shall,
except as otherwise expressly provided in this SECTION 2.2, be subject to
SECTION 2.1. In addition, the Company may at any time initiate a registration on
Form S-3 (or any successor or similar short-form registration statement) of the
Registrable Securities. The Holder or Holders of such Registrable Securities
shall cooperate with such registration, including providing the information
regarding such Holder or Holders required to be included in the Prospectus by
the Securities Act. The Company will pay all Registration Expenses in connection
with any registration on Form S-3 (or any successor or similar short-form
registration statement).

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      2.3   "PIGGYBACK" REGISTRATIONS.

            (a) RIGHT TO INCLUDE REGISTRABLE SECURITIES. If the Company at any
time proposes to register any Common Stock under the Securities Act (other than
by a registration on Form S-4, Form S-8 or any successor or similar form, or in
connection with a tender offer, merger, or other acquisition, and other than
pursuant to SECTION 2.1 or SECTION 2.2), whether or not for sale for its own
account, and the registration form to be used may be used for the registration
of Registrable Securities, the Company will give prompt written notice (in any
event within ten (10) business days after its receipt of any notice of exercise
of other demand registration rights and at least thirty (30) days prior to the
anticipated filing date of the registration statement relating to such
registration) to all Holders of Registrable Securities of its intention to do so
and of such Holders' rights under this SECTION 2.3. Upon the written request of
any such Holder made within twenty (20) days after the date of any such notice,
the Company will include in such registration all Registrable Securities which
the Company has been so requested to register by the Holders thereof, PROVIDED
that if, at any time after giving written notice of its intention to register
its Common Stock and prior to the effective date of the registration statement
filed in connection with such registration, the Company shall determine for any
reason not to register or to delay registration of its Common Stock, the Company
may, at its election, give written notice of such determination to each Holder
of Registrable Securities and, thereupon, (i) in the case of a determination not
to register, shall be relieved of its obligation to register any Registrable
Securities in connection with such registration (but not from its obligation to
pay the Registration Expenses in connection therewith or to include any
Registrable Securities in subsequent registrations), without prejudice, however,
to the rights of any Holder of Registrable Securities entitled to do so to
request that such registration be effected as a registration under SECTION 2.1
or SECTION 2.2, and (ii) in the case of a determination to delay registering,
shall be permitted to delay registering any Registrable Securities for the same
period as the delay in registering its Common Stock. No registration effected
under this SECTION 2.3 shall relieve the Company of its obligation to effect any
registration upon request under SECTION 2.1 or SECTION 2.2. The Company will pay
all Registration Expenses in connection with each registration of Registrable
Securities requested pursuant to this SECTION 2.3.

            (b)   APPORTIONMENT IN "PIGGYBACK" REGISTRATIONS.

                  (i) If a registration under this SECTION 2.3 is an
      underwritten primary registration on behalf of the Company and the
      managing underwriter of such underwritten offering advises the Company in
      writing of its belief that the aggregate number of shares of Common Stock
      requested to be included in such registration exceeds the number which can
      be sold in such offering, then the Company will include in such
      registration, (A) first, the securities proposed by the Company to be sold
      for its own account, (B) second, the Registrable Securities and Existing
      Registrable Securities requested to be included in such registration;
      PROVIDED, THAT if the managing underwriter advises the Company in writing
      of its belief that a lower number of Registrable Securities and Existing
      Registrable Securities should be included, then the Company shall be
      required to include in the underwriting only that lower number of
      Registrable Securities and Existing Registrable Securities, and the
      holders of Registrable Securities and Existing Registrable Securities

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                                     -6-
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      who have requested registration shall participate in the underwriting in
      accordance with the terms of SECTION 2.3(B)(III) below, and (C) third, if
      all of the Registrable Securities and Existing Registrable Securities
      requested to be included in such registration have been included therein,
      then any other securities requested to be included in such registration.

                  (ii) If a registration under this SECTION 2.3 is an
      underwritten secondary registration on behalf of holders of the Company's
      Securities, and the managing underwriter advises the Company in writing of
      its belief that the aggregate number of shares of Common Stock requested
      to be included in such registration exceeds the number which can be sold
      in such offering, then the Company will include in such registration (A)
      first, the securities requested to be included therein by the holders
      requesting such registration, (B) second, the Registrable Securities and
      Existing Registrable Securities requested to be included in such
      registration; PROVIDED, THAT if the managing underwriter advises the
      Company in writing of its belief that a lower number of Registrable
      Securities and Existing Registrable Securities should be included, then
      the Company shall be required to include in the underwriting only that
      lower number of Registrable Securities and Existing Registrable
      Securities, and the holders of Registrable Securities and Existing
      Registrable Securities who have requested registration shall participate
      in the underwriting in accordance with the terms of SECTION 2.3(B)(III)
      below, and (C) third, if all of the Registrable Securities and Existing
      Registrable Securities requested to be included in such registration have
      been included therein, then any other securities requested to be included
      in such registration.

                  (iii) If the number of Registrable Securities and Existing
      Registrable Securities to be included in a registration are to be reduced
      pursuant to either SECTION 2.3(B)(I)(B) or SECTION 2.3(B)(II)(B), the
      maximum number of Registrable Securities and Existing Registrable
      Securities that are entitled to be included in such registration (other
      than Registrable Securities included pursuant to SECTION 2.3(B)(II)(A),
      which shall not be reduced) (the "MAXIMUM NUMBER OF SHARES") shall be
      allocated among the holders of Registrable Securities and Existing
      Registrable Securities in the following manner:

                  (A) first, each Holder of Registrable Securities shall be
      entitled to include in such registration a number of shares of Registrable
      Securities determined in accordance with the following formula:

                       1 degree = 2 x (H/R x M)

      Where:

      1 degree  = the number of shares of Registrable Securities that such
                  Holder shall be entitled to include in such registration
                  pursuant to this clause (A).

      H         = the number of shares of Registrable Securities owned by such
                  Holder.

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      R         = the total number of shares of Registrable Securities and
                  Existing Registrable Securities for which registration has
                  been requested.

      M         = the Maximum Number of Shares.

                  (B) second, each Holder of Registrable Securities and each
      holder of Existing Registrable Securities shall be entitled to include in
      such registration a portion of the remaining Maximum Number of Shares
      determined in accordance with the following formula:

                       2 degree =  H/R x (M-I)

      Where:

      2 degree  = the number of shares of Registrable Securities or Existing
                  Registrable Securities that such Holder shall be entitled to
                  include in such registration pursuant to this clause (B).

      H         = the number of shares of Registrable Securities and Existing
                  Registrable Securities owned by such Holder.

      R         = the aggregate number of shares of Registrable Securities and
                  Existing Registrable Securities for which registration has
                  been requested.

      M         = the Maximum Number of Shares.

      I         = the aggregate number of shares of Registrable Securities to be
                  included in such registration pursuant to clause (A) above.

      2.4 REGISTRATION PROCEDURES. Whenever the holders of Registrable
Securities have requested that any Registrable Securities be registered pursuant
to this Agreement, the Company will use its best efforts to effect the
registration and the sale of such Registrable Securities in accordance with the
intended method of disposition thereof, and pursuant thereto the Company will as
expeditiously as possible:

         (a) prepare and file with the Commission within 90 days, and use its
best efforts to prepare and so file within 45 days, after receipt of a request
for registration with respect to such Registrable Securities, a registration
statement with respect to such Registrable Securities (such registration
statement to include all information which the holders of the Registrable
Securities to be registered thereby shall reasonably request) and use its best
efforts to cause such registration statement to become and remain effective;
PROVIDED, THAT at least five days before filing a registration statement or
prospectus or any amendments or supplements thereto, the Company will (i)
furnish to counsel selected by the holders of a majority of the Registrable
Securities covered by such registration statement copies of all such documents
proposed to be filed, and the Company

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shall not file any thereof to which such counsel shall have reasonably objected
on the grounds that such document does not comply in all material respects with
the requirements of the Securities Act or of the rules or regulations
thereunder, and (ii) notify each holder of Registrable Securities covered by
such registration statement of (x) any request by the Commission to amend such
registration statement or amend or supplement any prospectus, or (y) any stop
order issued or threatened by the Commission, and take all reasonable actions
required to prevent the entry of such stop order or to remove it if entered;

         (b) (i) prepare and file with the Commission such amendments and
supplements to such registration statement and the prospectus used in connection
therewith as may be necessary to keep such registration statement effective for
a period of not less than 180 days (except that such 180 day period shall be
extended (x) by the length of any period that a stop order or similar proceeding
is in effect which prohibits the distribution of the Registrable Securities, and
(y) by the number of days during the period from and including the date on which
each seller of Registrable Securities shall have received a notice delivered
pursuant to clause (g) below until the date when such seller shall have received
a copy of the supplemented or amended prospectus contemplated by clause (g)
below), and (ii) comply with the provisions of the Securities Act with respect
to the disposition of all securities covered by such registration statement
during such period in accordance with the intended methods of disposition by the
sellers thereof set forth in such registration statement;

         (c) furnish to each seller and each underwriter, if any, of Registrable
Securities, without charge, such number of conformed copies of such registration
statement, each amendment and supplement thereto, the prospectus included in
such registration statement (including each preliminary prospectus and, in each
case including all exhibits) and such other documents as such seller may
reasonably request in order to facilitate the disposition of the Registrable
Securities owned by such seller;

         (d) use its best efforts to register or qualify such Registrable
Securities under such other securities or blue sky laws of such jurisdictions as
any seller thereof shall reasonably request, to keep such registration or
qualification in effect for so long as such registration statement remains in
effect and do any and all other acts and things which may be reasonably
necessary or advisable to enable such seller to consummate the disposition in
such jurisdictions of the Registrable Securities owned by such Seller; PROVIDED,
HOWEVER, that the Company will not be required to (i) qualify generally to do
business in any jurisdiction where it would not otherwise be required to qualify
but for this clause (d), (ii) subject itself to taxation in any such
jurisdiction or (iii) consent to general service of process in any such
jurisdiction;

         (e) furnish to each seller of Registrable Securities a signed copy,
addressed to such seller (and the underwriters, if any) of an opinion of counsel
for the Company, dated the effective date of such registration statement (and,
if such registration statement includes an underwritten public offering, dated
the date of the closing under the underwriting agreement), reasonably
satisfactory in form and substance to such seller, covering substantially the
same matters with respect to such registration statement (and the prospectus
included therein) as are customarily

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covered in opinions of issuer's counsel delivered to the underwriters in
underwritten public offerings, and such other legal matters as the seller (or
the underwriters, if any) may reasonably request;

         (f) furnish to each seller of Registrable Securities a signed copy,
addressed to such seller (and the underwriters, if any) of a "comfort" letter,
dated the effective date of such registration statement signed by the
independent public accountants who have certified the Company's financial
statements, covering substantially the same matters with respect to such
registration statement (and the prospectus included therein) and with respect to
events subsequent to the date of such financial statements, as are customarily
covered in accountants' letters delivered to the underwriters in underwritten
public offerings of securities and such other financial matters as the
underwriters may reasonably request;

         (g) immediately notify the managing underwriter, if any, and each
seller of Registrable Securities, at a time when a prospectus relating thereto
is required to be delivered under the Securities Act, of the happening of any
event known to the Company as a result of which the prospectus included in such
registration statement, as then in effect, contains an untrue statement of a
material fact or omits to state any fact required to be stated therein or
necessary to make the statements therein not misleading in light of the
circumstances under which they were made, and, at the request of any such
seller, the Company will prepare and furnish such seller, as soon as
practicable, a reasonable number of copies of a supplement to or an amendment of
such prospectus as may be necessary so that, as thereafter delivered to the
purchasers of such Registrable Securities, such prospectus shall not include an
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein not misleading in
the light of the circumstances under which they were made; PROVIDED THAT, if (i)
the providing of copies of such supplement or amendment would require the
Company to publicly disclose information sooner than it otherwise would be
required to disclose such information and (ii) the Board of Directors of the
Company determines, in its reasonable business judgment, that the disclosure of
such information would interfere with any material financing, acquisition,
corporate reorganization or other material transaction or development involving
the Company, then the Company may postpone providing copies of such supplement
or amendment until the earlier of (x) the date 30 days after the occurrence of
the event necessitating such supplement or amendment and (y) a date as soon as
practicable after the date on which the Board of Directors determines, in its
reasonable business judgment, that the disclosure of such information would not
interfere with any material financing, acquisition, corporate reorganization or
other material transaction or development involving the Company;

         (h) cause all such Registrable Securities to be listed on each
securities exchange on which similar securities issued by the Company are then
listed and on any Securities Exchange or National Automated Quotation System
requested by the holders of a majority (by number of shares) of such Registrable
Securities, provided that the Company then meets or is reasonably capable of
meeting the eligibility requirements for such exchange or system and such
exchange or system is reasonably satisfactory to the managing underwriters, and
to enter into such

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customary agreements as may be required in furtherance thereof, including,
without limitation, listing applications and indemnification agreements in
customary form;

         (i) retain a transfer agent and registrar for all such Registrable
Securities not later than the effective date of such registration statement;

         (j) make available for inspection by any seller of Registrable
Securities, any underwriter participating in any disposition pursuant to such
registration statement and any attorney, accountant or other agent retained by
any such seller or underwriter, all financial and other records, pertinent
corporate documents and properties of the Company and its subsidiaries, if any,
and cause the Company's and its affiliates' and subsidiaries' officers,
directors, employees and independent accountants to supply all information
reasonably requested by any such seller, underwriter, attorney, accountant or
agent in connection with such registration statement to enable them to conduct a
reasonable investigation within the meaning of the Securities Act;

         (k) subject to other provisions hereof, use its best efforts to cause
such Registrable Securities covered by such registration statement to be
registered with or approved by such other governmental agencies or authorities
or self-regulatory organizations as may be necessary to enable the sellers
thereof to consummate the disposition of such Registrable Securities;

         (l) otherwise use its best efforts to comply with all applicable rules
and regulations of the Commission and make available to its security holders, in
each case as soon as practicable, an earnings statement covering a period of at
least twelve months, beginning with the first month after the effective date (as
the term "effective date" is defined in Rule 158(c) under the Securities Act) of
the registration statement, which earnings statement shall satisfy the
provisions of SECTION 11(A) of the Securities Act and Rule 158 thereunder;

         (m) permit any holder of Registrable Securities, which holder, in the
sole judgment, exercised in good faith, of such holder might be deemed to be a
controlling person of the Company (within the meaning of the Securities Act or
the Exchange Act) to participate in the preparation of any registration
statement covering such holder's Registrable Securities and to include therein
material, furnished to the Company in writing, which in the reasonable judgment
of such holder should be included and which is reasonably acceptable to the
Company; and

         (n) use every reasonable effort to obtain the lifting at the earliest
possible time of any stop order suspending the effectiveness of any registration
statement or of any order preventing or suspending the use of any preliminary
prospectus.

      2.5 REGISTRATION EXPENSES. All expenses incident to the Company's
performance of or compliance with this Agreement, including without limitation,
all Registration Expenses will be borne by the Company.

                                                 Registration Rights Agreement

                                     -11-
<PAGE>
                                 ARTICLE III
                                INDEMNIFICATION

      3.1 INDEMNIFICATION BY THE COMPANY. In the event of any registration of
any securities by the Company under the Securities Act, the Company agrees to
indemnify and hold harmless, to the fullest extent permitted by law, each of the
holders of any Registrable Securities covered by such registration statement,
each other Person, if any, who controls such holder within the meaning of the
Securities Act or the Exchange Act, and each of their respective directors,
officers, general partners, limited partners and managing directors and each
other person who participates as an underwriter in the offering or sale of such
securities as follows:

         (a) against any and all loss, liability, claim, damage or expense
arising out of or based upon an untrue statement or alleged untrue statement of
a material fact contained in any registration statement (or any amendment or
supplement thereto), including all documents incorporated therein by reference,
or in any preliminary prospectus or prospectus (or any amendment or supplement
thereto) or the omission or alleged omission therefrom of a material fact
required to be stated therein or necessary to make the statements therein, in
light of the circumstances under which they were made, not misleading, or any
violation by the Company of any federal, state or common law rule or regulation
applicable to the Company and relating to action required of or inaction by the
Company in connection with any such registration;

         (b) against any and all loss, liability, claim, damage and expense to
the extent of the aggregate amount paid in settlement of any litigation,
investigation or proceeding by any governmental agency or body, commenced or
threatened, or of any claim whatsoever based upon any such untrue statement or
omission or any such alleged untrue statement or omission, or any violation by
the Company of any federal, state or common law rule or regulation applicable to
the Company and relating to action required of or inaction by the Company in
connection with any such registration, if such settlement is effected with the
written consent of the Company, which consent shall not be unreasonably
withheld; and

         (c) against any and all expense incurred by them in connection with
investigating, preparing or defending against any litigation, or investigation
or proceeding by any governmental agency or body, commenced or threatened, or
any claim whatsoever based upon any such untrue statement or omission or any
such alleged untrue statement or omission, or any violation by the Company of
any federal, state or common law rule or regulation applicable to the Company
and relating to action required of or inaction by the Company in connection with
any such registration, to the extent that any such expense is not paid under
SECTION 3.1 (A) or (B) above;

PROVIDED, THAT this indemnity does not apply with respect to any particular
holder, to any loss, liability, claim, damage or expense to the extent arising
out of an untrue statement or alleged untrue statement or omission or alleged
omission made in reliance upon and in conformity with written information
furnished to the Company by or on behalf of that holder expressly for use in the
preparation of any registration statement (or any amendment or supplement
thereto), including all documents incorporated therein by reference, or in any
preliminary prospectus or prospectus

                                                 Registration Rights Agreement

                                     -12-
<PAGE>
(or any amendment or supplement thereto); PROVIDED, FURTHER, that the Company
will not be liable to any holder or any person who participates as an
underwriter in the offer or sale of Registrable Securities, if any, under the
indemnity agreement in this SECTION 3.1, with respect to any preliminary
prospectus or the final prospectus or the final prospectus as amended or
supplemented, as the case may be, to the extent that any such loss, liability,
claim, damage or expense of such underwriter, controlling Person or holder
results from the fact that such underwriter sold Registrable Securities to a
Person to whom there was not sent or given, at or prior to the written
confirmation of such sale, a copy of the final prospectus or of the final
prospectus as then amended or supplemented, whichever is most recent, if the
Company has previously and timely furnished copies thereof to such underwriter
and such final prospectus, as then amended or supplemented, has corrected any
such misstatement or omission. Such indemnity shall remain in full force and
effect regardless of any investigation made by or on behalf of such holder or
any such director, officer, general partner, underwriter or other controlling
person and shall survive the transfer of such securities by such seller.

      3.2 INDEMNIFICATION BY HOLDERS OF REGISTRABLE SECURITIES. In connection
with any registration statement in which a holder of Registrable Securities is
participating, each such holder agrees to indemnify and hold harmless (in the
same manner and to the same extent as set forth in SECTION 3.1 of this
Agreement), to the extent permitted by law, the Company and its directors,
officers and controlling Persons, and their respective directors, officers and
general partners, with respect to any statement or alleged statement in or
omission or alleged omission from such registration statement, any preliminary,
final or summary prospectus contained therein, or any amendment or supplement
thereto, if such statement or alleged statement or omission or alleged omission
was made in reliance upon and in conformity with written information furnished
to the Company by or on behalf of such holder, specifically stating that it is
for use in the preparation of such registration statement, preliminary, final or
summary prospectus or amendment or supplement. Such indemnity shall remain in
full force and effect regardless of any investigation made by or on behalf of
the Company, or such holder, as the case may be, or any of their respective
directors, officers, controlling Persons or general partners and shall survive
the transfer of such securities by such holder; PROVIDED that no such holder
shall be liable under SECTION 3.2 for any amounts exceeding the product of the
purchase price per Registrable Security and the number of Registrable Securities
being sold pursuant to such registration statement or prospectus by such holder.

      3.3 WRITTEN NOTICE. Promptly after receipt by an indemnified party
hereunder of written notice of the commencement of any action or proceeding
involving a claim referred to in SECTION 3.1 or SECTION 3.2 of this Agreement,
such indemnified party will, if a claim in respect thereof is to be made against
an indemnifying party, give written notice to the latter of the commencement of
such action; PROVIDED, THAT the failure of any indemnified party to give notice
as provided herein shall not relieve the indemnifying party of its obligations
under SECTION 3.1 or SECTION 3.2 of this Agreement except to the extent that the
indemnifying party is actually materially prejudiced by such failure to give
notice. In case any such action is brought against an indemnified party, the
indemnifying party will be entitled to participate in and to assume the defense
thereof, jointly with any other indemnifying party similarly notified, to the
extent that it

                                                 Registration Rights Agreement

                                     -13-
<PAGE>
may wish, with counsel reasonably satisfactory to such indemnified party, and
after notice from the indemnifying party to such indemnified party of its
election so to assume the defense thereof, the indemnifying party will not be
liable to such indemnified party for any legal or other expenses subsequently
incurred by the latter in connection with the defense thereof, unless in such
indemnified party's reasonable judgment a conflict of interest between such
indemnified and indemnifying parties may exist in respect of such claim, in
which case the indemnifying party shall not be liable for the fees and expenses
of (i) more than one counsel for all holders of Registrable Securities, selected
by a majority (by number of shares) of the holders of Registrable Securities
(which choice shall be reasonably satisfactory to the Company), or (ii) more
than one counsel for the Company in connection with any one action or separate
but similar or related actions. An indemnifying party who is not entitled to, or
elects not to, assume the defense of a claim will not be obligated to pay the
fees and expenses of more than one counsel for all parties indemnified by such
indemnifying party with respect to such claim, unless in the reasonable judgment
of any indemnified party a conflict of interest may exist between such
indemnified party and any other of such indemnified parties with respect to such
claim, in which event the indemnifying party shall be obligated to pay the fees
and expenses of such additional counsel or counsels. The indemnifying party will
not, without the prior written consent of each indemnified party, settle or
compromise or consent to the entry of any judgment in any pending or threatened
claim, action, suit or proceeding in respect of which indemnification may be
sought hereunder (whether or not such indemnified party or any Person who
controls such indemnified party is a party to such claim, action, suit or
proceeding), unless such settlement, compromise or consent includes an
unconditional release of such indemnified party from all liability arising out
of such claim, action, suit or proceeding. Notwithstanding anything to the
contrary set forth herein, and without limiting any of the rights set forth
above, in any event any party will have the right to retain, at its own expense,
counsel with respect to the defense of a claim.

      3.4 UNDERWRITING AGREEMENT. The Company and each holder of Registrable
Securities requesting registration shall provide for the foregoing indemnity
(with appropriate modifications) in any underwriting agreement with respect to
any required registration or other qualification of securities under any Federal
or state law or regulation of any governmental authority other than the
Securities Act.

      3.5 CONTRIBUTIONS. If the indemnification provided for in SECTIONS 3.1 and
3.2 of this Agreement is unavailable or insufficient to hold harmless an
indemnified party under such Sections, then each indemnifying party shall
contribute to the amount paid or payable by such indemnified party as a result
of the losses, claims, damages or liabilities referred to in SECTION 3.1 or
SECTION 3.2 of this Agreement in such proportion as is appropriate to reflect
the relative fault of the indemnifying party on the one hand, and the
indemnified party on the other, in connection with statements or omissions which
resulted in such losses, liabilities, claims, damages or expenses, as well as
any other relevant equitable considerations, including, without limitation, the
relative benefits received by each party from the offering of the securities
covered by such registration statement, the parties' relative knowledge and
access to information concerning the matter with respect to which the claim was
asserted and the opportunity to correct and prevent any statement or omission.
The relative fault shall be determined by reference to,

                                                 Registration Rights Agreement

                                     -14-
<PAGE>
among other things, whether the untrue or alleged untrue statement of a material
fact or the omission or alleged omission to state a material fact relates to
information supplied by the indemnifying party or the indemnified party and the
parties' relative intent, knowledge, access to information and opportunity to
correct or prevent such untrue statements or omission. The parties hereto agree
that it would not be just and equitable if contributions pursuant to this
SECTION 3.5 were to be determined by pro rata or per capita allocation (even if
the underwriters, if any, were treated as one entity for such purpose) or by any
other method of allocation which does not take account of the equitable
considerations referred to in the first sentence of this SECTION 3.5. The amount
paid by an indemnified party as a result of the losses, claims, damages or
liabilities referred to in the first sentence of this SECTION 3.5 shall be
deemed to include any legal or other expenses reasonably incurred by such
indemnified party in connection with investigating or defending any action or
claim (which shall be limited as provided in SECTION 3.3 of this Agreement if
the indemnifying party has assumed the defense of any such action in accordance
with the provisions thereof) which is the subject of this SECTION 3.5. Promptly
after receipt by an indemnified party under this SECTION 3.5 of notice of the
commencement of any action against such party in respect of which a claim for
contribution may be made against an indemnifying party under this SECTION 3.5,
such indemnified party shall notify the indemnifying party in writing of the
commencement thereof if the notice specified in SECTION 3.3 of this Agreement
has not been given with respect to such action; PROVIDED, THAT the omission to
so notify the indemnifying party shall not relieve the indemnifying party from
any liability which it may otherwise have to any indemnified party under this
SECTION 3.5, except to the extent that the indemnifying party is actually
materially prejudiced by such failure to give notice. The Company and each
holder of Registrable Securities agrees with each other and the underwriters of
the Registrable Securities, if requested by such underwriters, that (i) the
underwriters' portion of such contribution shall not exceed the underwriting
discount and (ii) that the amount of such contribution shall not exceed an
amount equal to the net proceeds actually received by such indemnifying party
from the sale of Registrable Securities in the offering to which the losses,
liabilities, claims, damages or expenses of the indemnified parties relate. No
Person guilty of fraudulent misrepresentation (within the meaning of SECTION
11(F) of the Securities Act) shall be entitled to contribution from any Person
who was not guilty of such fraudulent misrepresentation.

      3.6 PERIODIC PAYMENTS. The indemnification required by this Article III
shall be made by periodic payments of the amount thereof during the course of
the investigation or defense, as and when bills are received or expense, loss,
damage or liability is incurred.

                                  ARTICLE IV
                               OTHER AGREEMENTS

      4.1   HOLDBACK AGREEMENTS.

         (a) HOLDERS OF REGISTRABLE SECURITIES. Each holder of Registrable
Securities agrees not to sell, make any short sale of, loan, grant any option
for the purchase of, effect any public sale or distribution of or otherwise
dispose of any securities of the Company, during the seven days

                                                 Registration Rights Agreement

                                     -15-
<PAGE>
prior to, and the 90-day period beginning on, the effective date of any
underwritten registration pursuant to Article II hereof (except as part of such
underwritten registration), unless the managing underwriters of the registered
public offering otherwise agree.

         (b) THE COMPANY. The Company agrees (i) not to sell, make any short
sale of, loan, grant any option for the purchase of, effect any public sale or
distribution of its securities, during the seven days prior to, and during the
90-day period beginning on, the effective date of any underwritten registration
pursuant to Article II hereof in which holders of Registrable Securities are
selling stockholders (except as part of such underwritten registration or
pursuant to registrations on Form S-4 or Form S-8 or any successor form), unless
the managing underwriters of the registered public offering otherwise agree, and
(ii) to use all reasonable efforts to cause each holder of at least 5% (on a
fully-diluted basis) of its equity securities, or any securities convertible,
exchangeable or exercisable for or into such securities, to agree not to sell,
make any short sale of, loan, grant any option for the purchase of, or effect
any public sale or distribution of any such securities during such period
(except as part of such underwritten registration, if otherwise permitted),
unless the managing underwriters of the registered public offering otherwise
agree.

      4.2   UNDERWRITTEN OFFERINGS.

         (a) DEMAND UNDERWRITTEN OFFERINGS. If requested by the managing
underwriter for any underwritten offering of Registrable Securities pursuant to
a registration pursuant to SECTION 2.1 or 2.2 above, the Company will enter into
an underwriting agreement with such underwriters for such offering, such
agreement to be reasonably satisfactory in substance and form to the Company,
and to contain such representations and warranties by the Company and such other
terms as are generally included in agreements of this type, including, without
limitation, indemnities customarily included in such agreements. The holders of
the Registrable Securities will cooperate with the Company in the negotiation of
the underwriting agreement. The holders of Registrable Securities to be
distributed by such underwriters shall be parties to such underwriting
agreement. The Company shall cooperate with any such holder of Registrable
Securities in order to limit any representations or warranties to, or agreements
with, the Company or the underwriters to be made by such holder only to those
representations, warranties or agreements regarding such holder, such holder's
Registrable Securities and such holder's intended method of distribution and any
other representation required by law.

         (b) INCIDENTAL UNDERWRITTEN OFFERINGS. If the Company at any time
proposes to register any of its securities under the Securities Act as
contemplated by SECTION 2.3 of this Agreement and such securities are to be
distributed by or through one or more underwriters, the Company will, if
requested by any holder of Registrable Securities as provided in SECTION 2.3 of
this Agreement, arrange for such underwriters to include all the Registrable
Securities to be offered and sold by such holder, subject to the limitations set
forth in SECTION 2.3 hereof, among the securities to be distributed by such
underwriters. The holders of Registrable Securities to be distributed by such
underwriters shall be parties to the underwriting agreement between the Company
and such underwriters. The Company shall cooperate with any such holder of

                                                 Registration Rights Agreement

                                     -16-
<PAGE>
Registrable Securities in order to limit any representations or warranties to,
or agreements with, the Company or the underwriters to be made by such holder
only to those representations, warranties or agreements regarding such holder,
such holder's Registrable Securities and such holder's intended method of
distribution and any other representation required by law.

      4.3 ADJUSTMENTS AFFECTING REGISTRABLE SECURITIES. The Company will not
take any action, or fail to take any action which it may properly take, with
respect to its securities which would adversely affect the ability of the
holders of Registrable Securities to include such Registrable Securities in any
registration of its securities contemplated by this Agreement or the
marketability of such Registrable Securities under any such registration
(including, without limitation, effecting a stock split or a combination of
shares).

      4.4 RULE 144. The Company covenants that it will file the reports required
to be filed by it under the Securities Act and the Exchange Act and the rules
and regulations adopted by the Commission thereunder (or, if the Company is not
required to file such reports, it will, upon the request of any holder of
Registrable Securities, make publicly available other information), and it will
take such further action as any holder of Registrable Securities may reasonably
request, all to the extent required from time to time to enable such holder to
sell shares of Registrable Securities without registration under the Securities
Act within the limitation of the exemption provided by (i) Rule 144 under the
Securities Act, as such Rule may be amended from time to time, or (ii) any
similar rule or regulation hereafter adopted by the Commission. Upon the request
of any holder of Registrable Securities, the Company will deliver to such holder
a written statement as to whether it has complied with such requirements.

                                  ARTICLE V
                                 MISCELLANEOUS

      5.1 NOMINEES FOR BENEFICIAL OWNERS. In the event that any Registrable
Securities are held by a nominee for the beneficial owner thereof, the
beneficial owner thereof may upon the giving of written notice to the Company,
at its election, be treated as the Holder of such Registrable Securities for
purposes of any request or other action by any Holder or Holders of Registrable
Securities pursuant to this Agreement or any determination of any number or
percentage of shares of Registrable Securities held by any Holder or Holders of
Registrable Securities contemplated by this Agreement. The Company may require
assurances reasonably satisfactory to it of such owner's beneficial ownership of
such Registrable Securities.

      5.2   GOVERNING LAW; SUBMISSION TO JURISDICTION.

         (a) This Agreement shall be governed by, and construed in accordance
with, the laws of the State of Illinois.

         (b) Any legal action or proceeding with respect to this agreement shall
be brought in the courts of the State of Illinois or of the United States of
America for the northern district of Illinois,

                                                 Registration Rights Agreement

                                     -17-
<PAGE>
and, by execution and delivery of this agreement, each of the Company and the
Holder hereby accepts for itself and (to the extent permitted by law) in respect
of its property, generally and unconditionally, the jurisdiction of the
aforesaid courts. Each of the Company and the Holder hereby irrevocably waives
any objection, including, without limitation, any objection to the laying of
venue or based on the grounds of FORUM NON CONVENIENS, which it may now or
hereafter have to the bringing of any such action or proceeding in such
respective jurisdictions.

         (c) Nothing herein shall affect the right of any holder to serve
process in any other manner permitted by law.

         (d) The Company and the Holder hereby (i) irrevocably and
unconditionally waive, to the fullest extent permitted by law, trial by jury in
any legal action or proceeding relating to this agreement and for any
counterclaim therein; (ii) irrevocably waive, to the maximum extent not
prohibited by law, any right it may have to claim or recover in any such
litigation any special, exemplary, punitive or consequential damages, or damages
other than, or in addition to, actual damages; (iii) certify that no party
hereto nor any representative or agent of counsel for any party hereto has
represented, expressly or otherwise, or implied that such party would not, in
the event of litigation, seek to enforce the foregoing waivers, and (iv)
acknowledge that it has been induced to enter into this agreement and the
transactions contemplated hereby among other things, the mutual waivers and
certifications contained in this SECTION 5.2.

      5.3 ENTIRE AGREEMENT; AMENDMENTS. This Agreement constitutes the entire
agreement of the parties with respect to the subject matter hereof and
supersedes any and all previous oral or written communications, representations
or agreements. This Agreement may be amended, modified or supplemented only by a
written instrument duly executed by the Company, the Holders of a majority of
the outstanding Registrable Securities, and each of Heller and Midwest so long
as such Holders own any Registrable Securities.

      5.4 TERM. This Agreement will terminate at such time as the Registrable
Securities, in the aggregate, represent less than both (i) 1% of the Company's
outstanding shares of Common Stock on a fully diluted basis, and (ii) the
average weekly trading volume of the Company's Common Stock for four consecutive
calendar weeks.

      5.5 WAIVER. No waiver by any party of any term or condition of this
Agreement, in one or more instances, shall be valid unless in writing, and no
such waiver shall be deemed to be construed as a waiver of any subsequent breach
or default of the same or similar nature.

      5.6 SUCCESSORS AND ASSIGNS. Except as otherwise expressly provided herein,
this Agreement shall be binding upon and inure to the benefit of the parties
hereto and their respective heirs, personal representatives, successors and
permitted assigns, as the case may be.

      5.7 REMEDIES. In the event of a breach by any party to this Agreement of
its obligations under this Agreement, the loss of any right as provided in this
Agreement as a result of such breach shall not be the sole and exclusive remedy
of any party injured by such breach. Any such injured

                                                 Registration Rights Agreement

                                     -18-
<PAGE>
party will be entitled to specific performance of its rights under this
Agreement, in addition to being entitled to exercise all rights granted by law,
including recovery of damages. The parties agree that the provisions of this
Agreement shall be specifically enforceable, it being agreed by the parties that
the remedy at law, including monetary damages, for breach of any such provision
will be inadequate compensation for any loss and that any defense in any action
for specific performance that a remedy at law would be adequate is waived.

      5.8 INVALID PROVISIONS. If any provision of this Agreement is held to be
illegal, invalid or unenforceable under any present or future law, and if the
rights or obligations of any party hereto under this Agreement will not be
materially and adversely affected thereby, (i) such provision will be fully
severable, (ii) this Agreement will be construed and enforced as if such
illegal, invalid or unenforceable provision had never comprised a part hereof,
(iii) the remaining provisions of this Agreement will remain in full force and
effect and will not be affected by the illegal, invalid or unenforceable
provision or by its severance herefrom and (iv) in lieu of such illegal, invalid
or unenforceable provision, there will be added automatically as a part of this
Agreement a legal, valid and enforceable provision as similar in terms to such
illegal, invalid or unenforceable provision as may be possible.

      5.9 HEADINGS. The headings used in this Agreement have been inserted for
convenience of reference only and do not define or limit the provisions hereof.

      5.10 FURTHER ASSURANCES. Each party hereto shall cooperate and shall take
such further action and shall execute and deliver such further documents as may
be reasonably requested by any other party in order to carry out the provisions
and purposes of this Agreement.

      5.11 GENDER. Whenever the pronouns "he" or "his" are used herein they
shall also be deemed to mean "she" or "hers" or "it" or "its" whenever
applicable words in the singular shall be read and construed as though in the
plural and words in the plural shall be construed as though in the singular in
all cases where they would so apply.

      5.12 COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which will be deemed an original, but all of which
together will constitute one and the same instrument.

      5.13 NOTICES. All notices and other communications provided for herein
(including, without limitation, any modifications of, or waivers or consents
under, this Agreement) shall be given or made by telex, telecopy, courier or
U.S. Mail or in writing and telexed, telecopied, mailed or delivered to the
intended recipient at the address specified below; or, as to any party, at such
other address as shall be designated by such party in a notice to each other
party:

                                                 Registration Rights Agreement

                                     -19-
<PAGE>
         If to the Company:

            Castle Dental Centers, Inc.
            1360 Post Oak Boulevard
            Suite 1300
            Houston, Texas  77056
            Attention: Jack H. Castle, Jr.
            Telecopy: (713) 513-1401

         If to Heller:

            Heller Financial, Inc.
            500 West Monroe Street
            Chicago, Illinois  60661
            Attention:  Account Manager
                        Corporate Finance
            Telecopy: (312) 441-7367

         with a copy to:

            Heller Financial, Inc.
            500 West Monroe Street
            Chicago, Illinois 60661
            Attention:  Legal Services
                        Corporate Finance Group
            Telecopy: (312) 441-6876

         If to Midwest:

            Midwest Mezzanine Fund II, L.P.
            208 South LaSalle Street, 10th floor
            Chicago, Illinois 60604-1003
            Attention: J. Allan Kayler
            Telecopy: (312) 553-6647

Except as otherwise provided in this Agreement, all such communications shall be
deemed to have been duly given when transmitted, if transmitted before 1:00 p.m.
local time on a business day (otherwise on the next succeeding business day) by
telex or telecopier and evidence or confirmation of receipt is obtained, or
personally delivered or, in the case of a mailed notice, three (3) business days
after the date deposited in the mails, postage prepaid, in each case given or
addressed as aforesaid.

                                                 Registration Rights Agreement

                                     -20-
<PAGE>
      IN WITNESS WHEREOF, the parties have executed and delivered this
Registration Rights Agreement as of the date first above written.

HELLER FINANCIAL, INC.,                CASTLE DENTAL CENTERS, INC.,
A DELAWARE CORPORATION                 A DELAWARE CORPORATION

By_________________________________    By_________________________________
                                           Jack H. Castle, Jr.
                                           Chairman and Chief Executive
MIDWEST MEZZANINE FUND II, L.P.              Officer

By:  ABN AMRO Mezzanine Management
     II, L.P., its general partner

By:  ABN AMRO Mezzanine Management
     II, Inc.,  its general partner

By_________________________________
    J. Allan Kayler, Senior Vice
      President

                                                 Registration Rights AgreementEXHIBIT 10.21

            THIRD AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT

      This THIRD AMENDMENT to AMENDED AND RESTATED CREDIT AGREEMENT (this "THIRD
Amendment") executed effective as of January 31, 2000 (the "EFFECTIVE DATE"), is
by and among CASTLE DENTAL CENTERS, INC., a Delaware corporation ("BORROWER"),
and BANK OF AMERICA, N.A. (formerly known as NationsBank, N.A.), a national
banking association (in its individual capacity, "BANK OF AMERICA"), as agent
(in such capacity, "AGENT") for each of the lenders that is a signatory hereto
(individually, together with its successors and assigns, "LENDER" and
collectively, "LENDERS") and such Lenders.

                             W I T N E S S E T H:

      WHEREAS, the Borrower, the Agent and the Lenders are parties to that
certain Amended and Restated Credit Agreement dated as of December 18, 1998, as
amended by First Amendment to Amended and Restated Credit Agreement dated as of
July 20, 1999, as amended by Second Amendment to Amended and Restated Credit
Agreement dated as of September 30, 1999 (such Amended and Restated Credit
Agreement as amended and as the same may be further amended from time to time,
the "CREDIT AGREEMENT"), pursuant to which the Lenders agreed to make loans to
and extensions of credit on behalf of the Borrower; and

      WHEREAS, the Borrower has requested that the Agent and the Lenders amend
the Credit Agreement, and the Agent and the Lenders have agreed to amend the
Credit Agreement in the particulars hereinafter provided.

      NOW, THEREFORE, in consideration of the premises and the mutual covenants
herein contained, the parties hereto agree as follows:

      1. TERMS DEFINED ABOVE. As used in this Third Amendment, each of the terms
"Agent," "Bank of America," "Borrower," "Credit Agreement," "Effective Date,"
"Lenders," and "Third Amendment" shall have the meaning assigned to such term
herein above.

      2. TERMS DEFINED IN CREDIT AGREEMENT. Each term defined in the Credit
Agreement and used herein without definition shall have the meaning assigned to
such term in the Credit Agreement, unless expressly provided to the contrary.

      3. OTHER DEFINITIONAL PROVISIONS. The words "hereby," "herein,"
"hereinafter," "hereof," "hereto," and "hereunder" when used in this Third
Amendment shall refer to this Third Amendment as a whole and not to any
particular paragraph or provision of this Third Amendment.

      4. AMENDMENTS AND SUPPLEMENTS TO DEFINITIONS.

      (1) The following terms, which are defined in Section 1.02 of the Credit
      Agreement, are hereby amended in their entirety to read as follows:

                                       1
<PAGE>
            "AGREEMENT" shall mean this Amended and Restated Credit Agreement,
      as amended and supplemented by the First Amendment, the Second Amendment,
      and the Third Amendment and as the same may from time to time be further
      amended or supplemented.

            "SUBORDINATED DEBT" shall mean the Debt of the Borrower or any
      Subsidiary that is subordinated to the Indebtedness pursuant to a
      subordination agreement substantially in the form of Exhibit H or
      otherwise on terms satisfactory to the Majority Lenders.

      (2) Section 1.02 of the Credit Agreement is hereby further amended and
      supplemented by adding the following new definitions where alphabetically
      appropriate, which read in their entirety as follows:

            "EFFECTIVE DATE" shall mean the Effective Date of this Third
      Amendment.

            "THIRD AMENDMENT" shall mean that certain Third Amendment to Amended
      and Restated Credit Agreement dated as of the Effective Date, by and among
      the Borrower, the Agent and Lenders.

            "NEW MEZZANINE FINANCING" shall mean Subordinated Debt issued by the
      Borrower pursuant to which net cash proceeds to the Borrower shall be up
      to but not to exceed $20,000,000, provided such New Mezzanine Financing is
      upon terms satisfactory to the Majority Lenders.

            "SETTLEMENT AGREEMENT" shall mean that certain letter agreement
      dated as of January 28, 2000 among the Company, Castle Dental Centers of
      California, Inc. and the Persons referred to therein as the "DCS Parties".

5.    AMENDMENT TO SECTION 2.03(A). Section 2.03(a) of the Credit Agreement is
hereby amended in its entirety to read as follows:

            "The Aggregate Commitments shall at all times be equal to the lesser
      of (i) the Aggregate Maximum Credit Amounts after adjustments resulting
      from reductions pursuant to Section 2.03(b) or increases pursuant to
      Section 2.03(d) or (ii) the Borrowing Base as determined from time to
      time."

6.    AMENDMENT TO SECTION 8.01(H). Section 8.01(h) of the Credit Agreement is
hereby amended by adding the following sentence at the end thereof:

            "Borrower shall issue an additional borrowing base report as of
      September 30, 1999 on January 20, 2000 which shall reflect on a pro forma
      basis all Debt outstanding on January 20, 2000 and include, without
      limitation, the effects of the New Mezzanine Financing."

                                       2
<PAGE>
7.    AMENDMENT TO SECTION 8.11. Section 8.11 of the Credit Agreement is hereby
amended in its entirety to read as follows:

            "The Borrower hereby covenants and agrees that, beginning 20
      Business Days after the Effective Date, Borrower shall maintain at all
      times Hedging Agreements with one of the Lenders, or with another party
      reasonably acceptable to the Majority Lenders, whereby the Borrower will
      swap the floating interest rate relating to 50% of Borrower's Total Funded
      Debt for a fixed rate relating to such amount."

8.    AMENDMENT TO SECTION 9.11. Section 9.11 of the Credit Agreement is hereby
amended in its entirety to read as follows:

            "Section 9.11 RATIO OF TOTAL FUNDED DEBT TO CAPITALIZATION. For the
      four fiscal quarters ending on December 31, 1999, March 31, 2000, June 30,
      2000, and September 30, 2000, the Borrower will not permit its ratio of
      Total Funded Debt to Capitalization to be greater than .65 to 1.0. For the
      one fiscal quarter ending on December 31, 2000, the Borrower will not
      permit its ratio of Total Funded Debt to Capitalization to be greater than
      .625 to 1.0. For each fiscal quarter thereafter, the Borrower will not
      permit its ratio of Total Funded Debt to Capitalization as of the end of
      any fiscal quarter to be greater than .60 to 1.0."

9.    AMENDMENT TO SECTION 9.14. Section 9.14 of the Credit Agreement is hereby
amended by deleting the chart contained therein in its entirety and replacing it
with the following:

             ------------- ---------------------------------
                 RATIO                  PERIOD
             ------------- ---------------------------------
             1.10 to 1.00  from the Effective Date through
                           and including 3/31/2001
             ------------- ---------------------------------
             1.15 to 1.00  from 6/30/2001 and thereafter
             ------------- ---------------------------------

10.   AMENDMENT TO SECTION 9.16. Section 9.16 of the Credit Agreement is hereby
amended in its entirety to hereafter read as follows:

            "Section 9.16 CAPITAL EXPENDITURES. Without the prior written
      consent of the Majority Lenders, the Borrower will not make any
      expenditures for fixed or capital assets if, after giving effect thereto,
      the aggregate of all such expenditures would, in the case of the 12 month
      periods ending at the end of the fiscal quarters ending on December 31,
      1999, March 31, 2000 and June 30, 2000 respectively, exceed $11,000,000,
      and in the case of each 12 month period ending at the end of each fiscal
      quarter thereafter, exceed $10,000,000."

11.   AMENDMENT - NEW SECTION 9.24. A new Section 9.24 to Article IX is hereby
added to read as follows:

                                       3
<PAGE>
      "Section 9.24 PRE-PAYMENT OF NEW MEZZANINE FINANCING. Neither the Borrower
      nor any Subsidiary will directly or indirectly prepay any sums outstanding
      on the New Mezzanine Financing whether voluntarily, mandatorily or through
      any redemption pursuant to the Stockholders Agreement dated January 31,
      2000, between the Borrower, Heller Financial, Inc. and Midwest Mezzanine
      Fund II, L.P. (the "STOCKHOLDERS AGREEMENT") or otherwise without the
      express written consent of the Majority Lenders. In furtherance hereof and
      in addition, the Borrower will not redeem any "Redeemable Securities" (as
      defined in the Stockholders Agreement) without the express written consent
      of the Majority Lenders."

12.   AMENDMENT TO EXHIBIT H. Exhibit H to the Credit Agreement is hereby
amended to read as Exhibit H attached hereto.

13.   LIMITED WAIVER. Borrower's Default with respect to Section 8.11 of the
Credit Agreement as it existed prior to the Effective Date is hereby waived.
This waiver is effective as of the Effective Date and does not apply to
compliance with Section 8.11 after the Effective Date. This limited waiver shall
not be deemed to be a consent to, or waiver or modification of, any other term
or condition of the Credit Agreement, the Security Agreement, the Guaranty
Agreement, or any other Loan Document and shall not prejudice any right or
rights which the Lenders may now have or may have in the future under the Credit
Agreement, Security Agreement, Guarantee Agreement, or any other Loan Document.

14.   CONDITIONS. The effectiveness of this Third Amendment against the Agent
and the Lenders is subject to the following conditions precedent:

      (1) the New Mezzanine Financing in an amount of at least $15,000,000 shall
      have been closed and funded;

      (2) the Agent's receipt of multiple original counterparts, as requested by
      the Agent, of this Third Amendment, executed and delivered by a duly
      authorized officer of the Borrower, the Agent, and each Lender, as
      applicable and ratified by the Guarantors;

      (3) the Agent's receipt of a copy of the Subordinated Note and a fully
      executed Subordination Agreement in connection therewith;

      (4) the Agent's receipt of such other instruments or documents as the
      Agent may reasonably request; and

      (5) the "Closing" (as defined in the Settlement Agreement) shall have
      occurred and payment of the "Full Settlement Amount" (as defined in the
      Settlement Agreement) shall occur concurrently herewith.

15.   REPRESENTATIONS AND WARRANTIES. Except as affected by the transactions
contemplated in the Credit Agreement and this Third Amendment, each of the
representations and warranties made by the Borrower in or pursuant to the Credit
Agreement and the Security Instruments shall be true and

                                       4
<PAGE>
correct in all material respects as of the Effective Date, as if made on and as
of such date (except to the extent such representations and warranties are
expressly limited to an earlier date).

16.   ADOPTION, RATIFICATION AND CONFIRMATION OF CREDIT AGREEMENT. Each of the
Borrower, the Agent, and the Lenders does hereby adopt, ratify and confirm the
Credit Agreement, as amended hereby, and acknowledges and agrees that the Credit
Agreement, as amended hereby, is and remains in full force and effect.

17.   SUCCESSORS AND ASSIGNS. This Third Amendment shall be binding upon and
inure to the benefit of the parties hereto and their respective successors and
assigns permitted pursuant to the Credit Agreement.

18.   COUNTERPARTS. This Third Amendment may be executed by one or more of the
parties hereto in any number of separate counterparts, and all of such
counterparts taken together shall be deemed to constitute one and the same
instrument and shall be enforceable as of the Effective Date upon the execution
of one or more counterparts hereof by the Borrower, the Agent and the Lenders.
In this regard, each of the parties hereto acknowledges that a counterpart of
this Third Amendment containing a set of counterpart execution pages reflecting
the execution of each party hereto shall be sufficient to reflect the execution
of this Third Amendment by each necessary party hereto and shall constitute one
instrument.

19.   ENTIRE AGREEMENT. This Third Amendment constitutes the entire agreement
among the parties hereto with respect to the subject hereof. All prior
understandings, statements and agreements, whether written or oral, relating to
the subject hereof are superseded by this Third Amendment.

20.   GOVERNING LAW. This Third Amendment shall be deemed to be a contract made
under and shall be governed by and construed in accordance with the internal
laws of the State of Texas.

      THIS THIRD AMENDMENT, THE CREDIT AGREEMENT, AS SUPPLEMENTED AND AMENDED
      HEREBY, THE NOTES, AND THE OTHER SECURITY INSTRUMENTS REPRESENT THE FINAL
      AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF
      PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

      THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

                         [SIGNATURES BEGIN ON NEXT PAGE]

                                       5
<PAGE>
      IN WITNESS WHEREOF, the parties hereto have caused this Third Amendment to
be duly executed and delivered by their proper and duly authorized officers as
of the Effective Date.

BORROWER:                           CASTLE DENTAL CENTERS, INC.

                                    By: ________________________________________
                                    Name: ______________________________________
                                    Title: _____________________________________

LENDER AND AGENT:                   BANK OF AMERICA, N.A. (formerly known as
                                    NationsBank, N.A.)

                                    By _________________________________________
                                          Matt Bryant, Vice President

LENDERS:                            BANKBOSTON, N.A.

                                    By: ________________________________________
                                    Name: ______________________________________
                                    Title: _____________________________________

                                    AMSOUTH BANK

                                    By: ________________________________________
                                    Name: ______________________________________
                                    Title: _____________________________________

                                    HELLER FINANCIAL, INC.

                                    By: ________________________________________
                                    Name: ______________________________________
                                    Title: _____________________________________

                                       6
<PAGE>
                                  RATIFICATION

      Each of the Guarantors hereby expressly (i) acknowledges the terms of this
Third Amendment, (ii) ratifies and affirms its obligations under its Guaranty
Agreement, in favor of the Agent and the Lenders, as amended, supplemented or
otherwise modified, (iii) acknowledges, renews and extends its continued
liability under its Guaranty Agreement and agrees that said Guaranty Agreement
remains in full force and effect; and (iv) guarantees to the Agent and each
Lender to promptly pay when due all amounts owing or to be owing by it under its
Guaranty Agreement pursuant to the terms and conditions thereof.

GUARANTORS:                         CASTLE DENTAL CENTERS OF FLORIDA, INC.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                    CASTLE DENTAL CENTERS OF TENNESSEE, INC.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                    CASTLE DENTAL CENTERS OF TEXAS, INC.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                    CDC OF CALIFORNIA, INC.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                       7
<PAGE>
                                    CASTLE DENTAL CENTERS OF CALIFORNIA, L.L.C.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                    DENTAL WORLD, INC.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                    CASTLE DENTAL CENTERS OF AUSTIN,  INC.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                    DENTCOR, INC.

                                    By: ________________________________________
                                          Jack H. Castle, Jr.
                                          Chairman & Chief Executive Officer

                                        8
<PAGE>
                                    EXHIBIT H

                        FORM OF SUBORDINATION AGREEMENT

      This Subordination Agreement dated as of _____________ ("AGREEMENT"), is
made by ____________________________ ("SUBORDINATED CREDITOR"), and CASTLE
DENTAL CENTERS, INC., a Delaware corporation ("DEBTOR"), in favor of
NATIONSBANK, N.A., as agent for the senior creditors defined below ("AGENT").

                                 INTRODUCTION

      Reference is made to the Amended and Restated Credit Agreement dated as of
December 18, 1998 (as modified from time to time, the "CREDIT AGREEMENT"), among
the Debtor, the Agent and the banks party thereto ("SENIOR CREDITORS"). It is a
condition precedent to the Senior Creditors' permitting the Debtor to incur the
indebtedness represented by the Subordinated Note that the Subordinated Creditor
enter into this Agreement. In consideration of the foregoing and for other good
and valuable consideration, the Subordinated Creditor, the Debtor, and the
Senior Creditors hereby agree as follows:

Section 1.  DEFINITIONS.  The following terms shall have the following meanings:

      "EVENT OF DEFAULT" means any "Default" or "Event of Default" as defined
in, and which may occur under, the Credit Agreement.

      "LOAN DOCUMENTS" shall have the meaning specified by the Credit Agreement.

      "SENIOR DEBT" means (a) all principal, interest (including interest
accruing after the commencement of a Bankruptcy Event, without regard to whether
or not such interest is an allowed claim), fees, reimbursements,
indemnifications, and other amounts now or hereafter owed by the Debtor and its
Subsidiaries to Senior Creditors under the Credit Agreement, the Loan Documents,
and any other instrument or agreement related thereto and (b) any increases,
extensions, and rearrangements of the foregoing obligations under any
amendments, supplements, and other modifications of the documents and agreements
creating the foregoing obligations.

      "SUBORDINATED DEBT" means all present and future indebtedness,
liabilities, and obligations of any kind owed by the Debtor to the Subordinated
Creditor, including debt obligations, equity obligations, and other contractual
obligations requiring payments of any kind to be made to the Subordinated
Creditor, whether such indebtedness, liabilities, and obligations are absolute
or contingent, joint, several, or independent, arising by operation of law or
contract, created directly with the Subordinated Creditor or acquired by
assignment, participation, or otherwise, or direct or indirect (including
indebtedness, liabilities, and obligations of the Debtor to the Subordinated
Creditor as a result of either's membership in any partnership, syndicate,
association, or other group, and whether incurred by the Debtor as principal,
guarantor, surety, endorser, accommodation party, or otherwise). Subordinated
Debt specifically includes the Subordinated Note.

                                  Exhibit H-1
<PAGE>
      "SUBORDINATED NOTE" means the $___________ Note dated as of
_______________, made by the Debtor and payable to the order of the Subordinated
Creditor, as the same may be increased, extended, rearranged, amended,
supplemented, and otherwise modified from time to time in accordance with this
Agreement.

Section 2. TERMS OF SUBORDINATION. Unless and until the Senior Debt shall have
been irrevocably paid in full in cash, and the Senior Creditors shall have no
commitment to extend further Senior Debt, the payment and performance of the
Subordinated Debt is hereby made expressly subordinate and junior in right of
payment and performance to the prior payment in cash and performance of all
obligations and liabilities under the Senior Debt to the extent and in the
manner set forth in this Section 2:

      2.1   LIMITATION ON PAYMENTS.

            (a) No payment or prepayment of any sum on the Subordinated Debt,
whether by acceleration or otherwise, shall be made, if at the time of such
payment, prepayment, or immediately after giving effect thereto there shall
exist a default in the payment or prepayment with respect to any of the Senior
Debt, or immediately after giving effect thereto (i) there shall exist a default
in the payment or prepayment of the principal or interest with respect to any of
the Senior Debt or (ii) there shall have occurred, or after giving effect to
such payment there shall occur, an Event of Default (other than an Event of
Default in the payment of prepayment of principal or interest with respect to
any of the Senior Debt) permitting the Senior Creditors to accelerate the
maturity thereof (with notice, lapse of time, or both) and such Event of Default
shall not have been cured or waived to the satisfaction of the Senior Creditors.

            (b) If at any time there shall occur an Event of Default, the
Subordinated Creditor shall not be entitled to receive any payment on the
Subordinated Debt before the earlier of (i) cure of the Event of Default to the
satisfaction of the Senior Creditors or (ii) the irrevocable payment in full in
cash of the Senior Debt and the termination of all commitments to extend Senior
Debt.

            (c) In the event that any Subordinated Debt is declared due and
payable before their expressed maturity because of the occurrence of an event of
default (under circumstances when the provisions of the foregoing paragraphs (a)
or (b) are not applicable), the Senior Creditors shall be entitled to receive
payment in full of all principal, interest, and other sums outstanding in
connection with the Senior Debt before the Subordinated Creditor is entitled to
receive any payment on account of such Subordinated Debt.

            (d) Any payments received by the Subordinated Creditor in violation
of this Agreement shall be held by the Subordinated Creditor in trust for the
benefit of the Senior Creditors and shall be immediately turned over to the
Agent in the form received (together with any necessary endorsements) for
application to the Senior Debt until all outstanding Senior Debt has been
irrevocably paid in full.

      2.2 SUBORDINATION ON LIQUIDATION. Upon any receivership, insolvency
proceeding, bankruptcy proceeding, assignment for the benefit of creditors,
reorganization, arrangement with creditors, sale of assets for creditors,
dissolution, liquidation, or marshalling of the assets of the Debtor or any of
its Subsidiaries (each, a "BANKRUPTCY EVENT"), all amounts due with respect to
the

                                  Exhibit H-2
<PAGE>
Senior Debt shall be irrevocably paid in full in cash before the Subordinated
Creditor shall be entitled to collect or receive any payment with respect to the
Subordinated Debt. Any payments received by the Subordinated Creditor in such
proceedings shall be held by the Subordinated Creditor in trust for the benefit
of the Senior Creditors and shall be immediately turned over to the Agent in the
form received (together with any necessary endorsements) for application to the
Senior Debt until all outstanding Senior Debt has been irrevocably paid in full
in cash.

      2.3 SUBORDINATION OF LIENS. The Subordinated Creditor will not create,
assume, or suffer to exist any lien, security interest, or assignment of
collateral securing the repayment of the Subordinated Debt. Any such judgment
lien, and any other lien, security interest, or assignment existing in violation
of the foregoing shall be fully subordinate to any lien, security interest, or
assignment in favor of the Senior Creditors which secures any of the Senior
Debt. At the request of the Senior Creditors, the Subordinated Creditor and the
Debtor will take any and all steps necessary to fully effect the release of any
such lien, security interest, assignment, or collateral.

      2.4 LIMITATION OF ACTION. Until the Senior Debt is paid in full in cash,
Subordinated Creditor shall not, without the prior written consent of Senior
Creditors, initiate or participate with others in any suit, action or proceeding
against Debtor or any of its Subsidiaries to enforce payment of or to collect
all or any part of the Subordinated Debt or commence judicial enforcement of any
of its rights or remedies with respect to the Subordinated Debt.

      2.5 FURTHER ASSURANCES. The Subordinated Creditor and the Debtor agree to
execute any and all other instruments requested by the Senior Creditors to
further evidence the subordination of the Subordinated Debt to the Senior Debt
as herein provided.

Section 3. SUBORDINATION ABSOLUTE. This is an irrevocable agreement of
subordination and the Senior Creditors may, without notice to any of the parties
hereto and without impairing or releasing the obligations of the Debtor and the
Subordinated Creditor hereunder, (a) create Senior Debt by extending credit
under the Credit Agreement; (b) change the terms of or increase the amount of
the Senior Debt by increasing, extending, rearranging, amending, supplementing,
or otherwise modifying any of the Loan Documents or other instruments or
agreements creating Senior Debt; (c) sell, exchange, release, or otherwise deal
with any collateral securing any Senior Debt; (d) release anyone, including the
Debtor or any guarantor, liable in any manner for the payment or collection of
any Senior Debt; (e) exercise or refrain from exercising any rights against the
Debtor or any other Person; and (f) apply any sums received by any of the Senior
Creditors, from whatever source, to the payment of the Senior Debt.

Section 4.  PROVISIONS REGARDING SUBORDINATED DEBT.

      4.1 There may be no increases, extensions, rearrangements, amendments,
supplements, or other modifications to the Subordinated Note which increase the
principal amount of, increase the interest rate payable on, or accelerate the
scheduled principal and interest payments on the Subordinated Note, or add or
make more restrictive any default or covenant, without the prior written
permission of the Senior Creditors.

      4.2 The Subordinated Creditor will cause all Subordinated Debt to be
evidenced by a note, debenture, instrument, or other writing evidencing the
Subordinated Debt and will inscribe

                                  Exhibit H-3
<PAGE>
a statement or legend thereon to the effect that such note, debenture,
instrument, or other writing is subordinated to the Senior Debt in favor of the
Senior Creditors in the manner and to the extent set forth in this Agreement.

      4.3 The Subordinated Creditor shall mark the books of Subordinated
Creditor to show that the Subordinated Debt is subordinated to the Senior Debt
in the manner and to the extent set forth in this Agreement and cause all
financial statements of the Subordinated Creditor hereafter prepared for
delivery to any person to make specific reference to the provisions of this
Agreement.

      4.4 The Subordinated Creditor shall not assign or otherwise transfer to
any other person any interest in the Subordinated Debt unless the Subordinated
Creditor causes the assignee or other transferee to execute and deliver to the
Senior Creditors a subordination agreement in substantially the form of this
Agreement or otherwise acknowledges to the reasonable satisfaction of the Senior
Creditors the subordination of the Subordinated Debt in accordance with this
Agreement.

Section 5.  MISCELLANEOUS.

      5.1 To the extent not paid by the Debtor, the Subordinated Creditor shall
reimburse the Senior Creditors for all reasonable expenses of the Senior
Creditors, including reasonable charges and disbursements of legal counsel for
the Senior Creditors, in connection with the execution, amendment, modification,
waiver, and interpretation of this Agreement, and the administration,
preservation, and enforcement of any rights of the Senior Creditors under this
Agreement. To the extent not paid by the Debtor, the Subordinated Creditor shall
indemnify the Senior Creditors against all claims, liabilities, damages, and
expenses in connection with any litigation or proceeding relating to this
Agreement, INCLUDING CLAIMS CAUSED BY THE SENIOR CREDITORS' OWN NEGLIGENCE,
EXCEPT AS A RESULT OF THE SENIOR CREDITORS' GROSS NEGLIGENCE OR WILLFUL
MISCONDUCT. The Senior Creditors are hereby authorized to setoff and apply any
obligations owed by the Senior Creditors to the Debtor against any obligations
of the Debtor under this Agreement. The provisions of this paragraph shall
survive termination of this Agreement.

      5.2 This Agreement shall be governed by the laws of the State of Texas. If
any provision in this Agreement is held to be unenforceable, such provision
shall be severed and the remaining provisions shall remain in full force and
effect. The Senior Creditors' remedies under this Agreement shall be cumulative,
and no delay in enforcing this Agreement shall act as a waiver of the Senior
Creditors' rights hereunder. The provisions of this Agreement may be waived or
amended only in a writing signed by all of the parties hereto. This Agreement
shall bind the Subordinated Creditor and the Debtor and their successors and
assigns and shall inure to the benefit of the Senior Creditors and their
successors and assigns. This Agreement may be executed in multiple counterparts
which together shall constitute one and the same agreement. Unless otherwise
specified, all notices provided for in this Agreement shall be in writing,
delivered to the following addresses:

If to the Subordinated Creditor:

      ______________________________

                                  Exhibit H_4
<PAGE>
      ______________________________
      Telephone: ___________________
      Telecopier: __________________

If to the Debtor:
      Castle Dental Centers, Inc.
      Attn: Jack H. Castle, Jr.
      1360 Post Oak Boulevard
      Houston, Texas  77056
      Telephone:  (713) 513-1401
      Telecopier: (713) 513-1400

If to the Senior Creditors:
      Bank of America, N.A.
      Attn: Matt Bryant
      700 Louisiana, 7th Floor
      Houston, Texas  77002
      Telephone:  713-247-6056
      Telecopier: 713-247-7748

or to such other address as shall be designated by one party in writing to the
other parties. Notice sent by telecopy shall be deemed to be given and received
when receipt of such transmission is acknowledged, and delivered notice shall be
deemed to be given and received when receipted for by, or actually received by,
an authorized officer of the receiving party.

THIS WRITTEN AGREEMENT AND THE RELATED CREDIT DOCUMENTS REPRESENT THE FINAL
AGREEMENT AMONG THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

                                  Exhibit H-5
<PAGE>
      EXECUTED as of the date first above written.

                                    BANK OF AMERICA, N.A. (formerly NationsBank,
                                    N.A.)

                                    By: ________________________________________
                                    Name: ______________________________________
                                    Title: _____________________________________

                                    CASTLE DENTAL CENTERS, INC.

                                    By: ________________________________________
                                    Name: ______________________________________
                                    Title: _____________________________________

                                    [SUBORDINATED CREDITOR]

                                    By: ________________________________________
                                    Name: ______________________________________
                                    Title: _____________________________________

                                  Exhibit H-6

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