Document:

EXHIBIT 10.26

          FOURTH AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT

      This FOURTH AMENDMENT to AMENDED AND RESTATED CREDIT AGREEMENT (this
"FOURTH AMENDMENT") effective as of December 31, 1999 (the "EFFECTIVE DATE" and
to continue to be effective to and including December 31, 2000 as provided in
Section 15 below), 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, as Amended by Third Amendment to
Amended and Restated Credit Agreement dated as of January 31, 2000 (such Amended
and Restated Credit Agreement as amended and as the same may be further amended
from time to time, the "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 Agreement, and the Agent and the Lenders have agreed to amend the 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 Fourth Amendment, each of the terms
"Agent," "Bank of America," "Borrower," "Agreement," "Effective Date,"
"Lenders," and "Fourth Amendment" shall have the meaning assigned to such term
herein above.

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

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

4.    AMENDMENTS AND SUPPLEMENTS TO DEFINITIONS.

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

            "APPLICABLE MARGIN" effective as of April 1, 2000, the applicable
      per annum percentage set forth at the appropriate intersection in the
      table shown below, based on the ratio of Total Funded Debt to EBITDA,
      determined as of the end of the most recent fiscal quarter (beginning with
      the fiscal quarter ended March 31, 2000) of the Borrower:

           ------------------------------------------------------------
                                     APPLICABLE     APPLICABLE MARGIN
            TOTAL FUNDED DEBT TO       MARGIN         ALTERNATE BASE
                   EBITDA            EURODOLLAR            RATE
           ------------------------------------------------------------
           Less than 1.0                2.25%              0.00%
           ------------------------------------------------------------
           Greater than or equal to
           1.0 but less than 1.5        2.5%               .25%
           ------------------------------------------------------------
           Greater than or equal to
           1.5 but less than 2.0        2.75%              .25%
           ------------------------------------------------------------
           Greater than or equal to
           2.0 but less than 2.5        3.0%               .50%
           ------------------------------------------------------------
           Greater than or equal to
           2.5 but less than 4.0        3.5%               1.00%
           ------------------------------------------------------------
           Greater than or
           equal to 4.0                 4.5%               2.00%
           ------------------------------------------------------------

      Each change in the Applicable Margin resulting from a change in the ratio
      of Total Funded Debt to EBITDA shall take effect as of the date of
      determination of the ratio of Total Funded Debt to EBITDA. For clarity
      purposes it is understood and agreed that Total Funded Debt includes,
      without limitation, any and all deferred interest under any Subordinated
      Debt.

            "BORROWING BASE" shall mean (i) for the period from December 31,
      1999 through January 31, 2000, the amount equal to three and three
      quarters (3.75) times EBITDA as of the end of the most recent fiscal
      quarter of the Borrower (calculated on a rolling four quarter basis), (ii)
      for the period from February 1, 2000 through December 30, 2000, the amount
      equal to three and four tenths (3.40) times EBITDA as of the end of the
      most recent fiscal quarter of the Borrower (calculated on a rolling four
      quarter basis), (iii) and (iii) on December 31, 2000, three (3.00) times
      EBITDA as of the end of the most recent fiscal quarter of the Borrower
      (calculated on a rolling four quarter basis). For any calculation period
      which would include one or more quarters prior to any Stock Purchase or
      any Asset Purchase or any other future acquisition of an entity occurring
      during the quarter, the "rolling four quarters" shall include the "pro
      forma" EBITDA of the applicable Acquired Entity for such prior periods
      adjusted to reflect the costs and expenses which such Acquired Entity
      would have incurred had the Management Services Agreements between the
      Borrower and/or any Subsidiary and such Acquired Entity been in effect
      (adding back appropriate executive salaries and non-cash charge offs
      relating to this transaction).

            "CLOSING DATE" shall mean the date that this Fourth Amendment shall
      be executed by the Lenders and the Borrower.

                                     Page 2
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            "EBITDA" shall mean, for any period, the sum of Consolidated Net
      Income for such period plus the following expenses or charges to the
      extent deducted from Consolidated Net Income in such period: interest,
      taxes, depreciation, depletion, amortization, the amount of the settlement
      of the lawsuit with Joseph Bonola, D.D.S. up but not to exceed $1,372,743
      as reflected on Schedule 1 to the Second Amendment, and the amount of
      legal fees and expenses related to the arbitration with Dr. Leon Roisman,
      D.M.D. that was expensed in Fiscal year 1999, up to but not to exceed
      $541,000.

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

            "FOURTH AMENDMENT" shall mean that certain Fourth Amendment to
      Amended and Restated Credit Agreement dated effective as of the December
      31, 1999, by and among the Borrower, the Agent and Lenders.

5.    AMENDMENT TO SECTION 8.01. Section 8.01 of the Agreement is hereby amended
by adding the following to the end of Section 8.01(a):

      "As soon as available, and in any event on or before two weeks after the
      Closing Date, Borrower shall deliver to the Agent the audited annual
      financial statements for fiscal year 1999 prepared in accordance with this
      Section 8.01(a) accompanied by the related opinion of independent public
      accountants as called for in this Section 8.01(a)."

6.    AMENDMENT TO SECTION 8.01. Section 8.01 of the Agreement is hereby amended
by deleting the paragraph after Section 8.01(o) in its entirety and replacing it
with the following:

      The Borrower shall furnish to the Lenders, at the time it furnishes
      financial statements pursuant to paragraph (a) above and within 45 days of
      the end of each of the first three fiscal quarters of the Borrower, a
      certificate substantially in the form of EXHIBIT C hereto executed by a
      Responsible Officer (i) certifying as to the matters set forth therein and
      stating that no Default has occurred and is continuing (or, if any Default
      has occurred and is continuing, describing the same is reasonable detail),
      and (ii) setting forth in reasonable detail the computations necessary to
      determine the Borrower's Total Funded Debt, Senior Funded Debt and EBITDA
      and whether the Borrower is in compliance with Sections 9.11, 9.12, 9.13,
      9.14, 9.15, 9.16, and 9.24 as of the end of the respective fiscal quarter
      or fiscal year.

7.    AMENDMENT TO SECTION 8.01. Section 8.01 of the Agreement is hereby amended
by adding the following new subsections:

            (p) MONTHLY FINANCIAL STATEMENTS. As soon as available and in any
      event within 45 days after the end of each calendar month, the
      Borrower-prepared consolidated and consolidating statements of income,
      cash flow of the Borrower and its Consolidated Subsidiaries for such
      period and for the period from the beginning

                                     Page 3
<PAGE>
      of the respective fiscal year to the end of such period, and the related
      consolidated and consolidating balance sheets as at the end of such
      period, and setting forth in each case in comparative form the
      corresponding figures for the corresponding period in the preceding fiscal
      year, accompanied by the certificate of a Responsible Officer, which
      certificate shall state that said financial statements fairly present the
      consolidated and consolidating financial condition and results of
      operations of the Borrower and its Consolidated Subsidiaries in accordance
      with GAAP, as at the end of, and for, such period (subject to normal
      year-end audit adjustments).

            (q) MANAGEMENT LETTER. As soon as available and in any event by no
      later than two weeks after the Closing Date, an auditor-prepared Fiscal
      1999 management letter.

            (r) ACCOUNTS RECEIVABLE. As soon as available and in any event
      within 45 days after the end of each calendar month, (i) a report in form
      reasonably satisfactory to the Agent reflecting the aging and collection
      of the receivables of the Borrower and its Subsidiaries, each such aging
      report to show in reasonable detail, calculations reflecting compliance
      with Section 9.24 and (ii) such other reports as deemed necessary by the
      Agent.

8.    AMENDMENT TO SECTION 8. Section 8 of the Agreement is hereby amended by
adding a new Section 8.13 to read as follows:

            Section 8.13 FIELD EXAM. The Borrower and its Subsidiaries shall
      permit the Agent and its representatives to have access, during normal
      business hours, to their records of accounts and appropriate personnel for
      purpose of conducting an examination of accounts receivable. Such field
      exam shall be completed and a report provided to the Agent within 45 days
      after the Closing Date.

9.    AMENDMENT TO SECTION 9.13. Section 9.13 of the Agreement is hereby amended
in its entirety to read as follows:

            9.13 LEVERAGE RATIO. The Borrower will not permit its Leverage Ratio
      as of the end of any fiscal quarter (calculated on a rolling four quarter
      basis) to be greater than the ratio indicated in the chart below. For any
      calculation period which would include one or more quarters prior to any
      Stock Purchase or any Asset Purchase or any other future acquisition of an
      entity, the "rolling four quarters" shall include the "pro forma" EBITDA
      of the applicable Acquired Entity for such prior periods adjusted to
      reflect costs and expenses which such Acquired Entity would have included
      had the Management Services Agreements between Borrower and/or any
      Subsidiary and such Acquired Entity been in effect (adding back
      appropriate executive salaries and non-cash charge offs relating to this
      transaction). As used in this Section 9.13, "Leverage Ratio" shall mean
      the ratio of (i) Senior Funded Debt to (ii) EBITDA.

                                     Page 4
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               -------------------------------------------------
                   PERIOD (QUARTER END DATE)          RATIO
               -------------------------------------------------
               December 31, 1999                     3.75 to 1.0
               -------------------------------------------------
               March 31, 2000                        3.40 to 1.0
               -------------------------------------------------
               -------------------------------------------------
               June 30, 2000                         3.40 to 1.0
               -------------------------------------------------
               -------------------------------------------------
               September 30, 2000                    3.40 to 1.0
               -------------------------------------------------
               -------------------------------------------------
                                                     3.00 to
               December 31, 2000                     1.0
               -------------------------------------------------

10.   AMENDMENT TO SECTION 9.14. Section 9.14 of the Agreement is hereby amended
in its entirety to read as follows:

            Section 9.14. FIXED CHARGE COVERAGE RATIO. The Borrower will not
      permit its Fixed Charge Coverage Ratio as of the end of any fiscal quarter
      (calculated on a rolling four quarter basis) to be less than the ratio for
      the relevant periods set forth below.

               -------------------------------------------------
                              PERIOD                   RATIO
               -------------------------------------------------
               December 31, 1999 through
               December 31, 2000                     1.30 to 1.0
               -------------------------------------------------

      For purposes of this Section 9.14, "Fixed Charge Coverage Ratio" shall
      mean the ratio for the relevant period of (i) EBITDA, less taxes payable
      in cash, plus lease and rental expense to (ii) lease and rental expense,
      plus cash and deferred interest, plus senior and subordinate principal
      payments scheduled during the period, plus actual capital lease payments.
      The ratio will be determined quarterly on a rolling twelve-month basis.
      For any calculation period which would include one or more quarters prior
      to any Stock Purchase or any Asset Purchase or any other future
      acquisition of an entity, the "rolling four quarters" shall include the
      "pro forma" EBITDA of the applicable Acquired Entity for such prior
      periods adjusted to reflect costs and expenses which such Acquired Entity
      would have included had the Management Services Agreements between
      Borrower and/or any Subsidiary and such Acquired Entity been in effect
      (adding back appropriate executive salaries and non-cash charge offs
      relating to this transaction).

11.   AMENDMENT TO SECTION 9.15. Section 9.15 of the Agreement is hereby amended
in its entirety to read as follows:

            Section 9.15. RATIO OF TOTAL FUNDED DEBT TO EBITDA. The Borrower
      will not permit its ratio of Total Funded Debt as of the end of any fiscal
      quarter to EBITDA for the four fiscal quarters ending on such date to be
      greater than the ratio indicated in the chart below. For purposes hereof,
      EBITDA shall be calculated as provided in Section 9.13 above. For clarity
      purposes it is understood and agreed that Total Funded Debt includes,
      without limitation, any and all deferred interest under any Subordinated
      Debt.

               -------------------------------------------------
                   PERIOD (QUARTER END DATE)          RATIO
               -------------------------------------------------

               December 31, 1999                     4.25 to 1.0
               -------------------------------------------------
               March 31, 2000                        4.75 to 1.0
               -------------------------------------------------
               June 30, 2000                         4.75 to 1.0
               -------------------------------------------------
               September 30, 2000                    4.60 to 1.0
               -------------------------------------------------
               December 31, 2000                     4.15 to 1.0
               -------------------------------------------------

                                     Page 5
<PAGE>
12.   AMENDMENT TO SECTION 9.16. Section 9.16 of the Agreement is hereby amended
in its entirety to 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 exceed $3,500,000 during
      fiscal year 2000 (January 1, 2000 through December 31, 2000), as outlined
      in SCHEDULE 9.16.

13.   AMENDMENT TO SECTION 9. Section 9 of the Agreement is hereby amended by
adding the following new Sections:

            Section 9.24 ACCOUNTS RECEIVABLE. Neither the Borrower nor any
      Subsidiary will permit its Average Accounts Receivable Days [at the end of
      any calendar month] to exceed 80 days. For purposes of this Section 9.24,
      "Average Accounts Receivable Days" shall mean the (i) net patient
      receivables plus net unbilled patient receivables, divided by (ii) net
      patient revenues for the 12-month period ending on such date, multiplied
      by (iii) 365 days.

            Section 9.25 ACQUISITIONS. Neither the Borrower nor any Subsidiary
      will, during fiscal year 2000, make any New Acquisition (whether or not
      proceeds of any Loans are utilized therefor), unless such New Acquisition
      is approved of in advance by all of the Lenders.

            Section 9.26 ADVANCES. Unless the Borrower or its Subsidiary
      receives prior written consent from all of the Lenders, neither the
      Borrower nor any Subsidiary will, during fiscal year 2000, use the
      proceeds of any Loan to settle any lawsuit or arbitration if any such
      settlement exceeds $100,000, or the aggregate of all settlements for
      fiscal year 2000 exceeds $250,000.

14.   AMENDMENT TO SECTION 10.01. The period at the end of clause (o) in Section
10.01 is changed to "; or" and a new clause (p) is hereby added to Section 10.01
to read as follows:

            "(p) the field exam conducted pursuant to Section 8.13 is determined
      by the Majority Lenders in their sole reasonable discretion to be less
      than satisfactory.

15. EFFECTIVENESS OF THIS FOURTH AMENDMENT. Except for the definition of
"Applicable Margin", which shall be effective as of December 31, 1999 and
continuing until the Final Maturity Date, this Fourth Amendment shall be
effective as of December 31, 1999 through December 31, 2000. Thereafter, the
terms and conditions of the Agreement as in effect prior to the execution of
this Fourth Amendment shall govern as if this Fourth Amendment had not been
executed.

16. TEMPORARY WAIVER. Borrower's covenant in Section 8.11 is hereby temporarily
waived. This temporary waiver shall terminate 30 days after the Closing Date and
shall not be deemed to be a consent to, or waiver or modification or, any other
term or condition of the Agreement, the Security Agreement, the Guarantee
Agreement, or any other Loan Document.

                                     Page 6
<PAGE>
17. AMENDMENT FEE. The Borrower shall pay to the Agent for the account of each
Lender an amendment fee equal to .5% of the Aggregate Maximum Commitment Amounts
(the "AMENDMENT FEE"). Borrower shall pay (i) 33.34 % of the Amendment Fee on
Borrower's execution hereof, (ii) 33.33% of the Amendment Fee on September 29,
2000, and (iii) 33.33% of the Amendment Fee on December 29, 2000. If the Loans
are completely paid prior to December 29, 2000, then the balance of the
Amendment Fee shall be due and payable at such time the loans are completely
paid.

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

      (1) the Agent's receipt of Borrower-prepared financial statements (in form
      of the financial statements called for in Section 8.01(b)), at least two
      days prior to the Closing Date, for the period ending March 31, 2000;

      (2) the Agent's receipt of the reports reflecting compliance (as waived by
      the letter dated May 19, 2000 from Agent to Borower) with all financial
      covenants as of September 30, 1999, December 31, 1999 and March 31, 2000
      applying the terms and conditions of the Agreement as amended by this
      Fourth Amendment;

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

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

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

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

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

22. COUNTERPARTS. This Fourth 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 Fourth Amendment containing a set of counterpart execution pages reflecting
the execution of each party hereto shall be

                                     Page 7
<PAGE>
sufficient to reflect the execution of this Fourth Amendment by each necessary
party hereto and shall constitute one instrument.

23. ENTIRE AGREEMENT. This Fourth 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 Fourth Amendment.

24. GOVERNING LAW. This Fourth 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 FOURTH AMENDMENT, THE 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]

                                     Page 8
<PAGE>
      IN WITNESS WHEREOF, the parties hereto have caused this Fourth 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: ________________________________________

                                    Name: ______________________________________
                                    Title: _____________________________________

LENDERS:                            FLEET NATIONAL BANK (FORMERLY KNOWN AS
                                    BANK BOSTON, N.A.)

                                    By: ________________________________________

                                    Name: ______________________________________
                                    Title: _____________________________________

                                    AMSOUTH BANK

                                    By: ________________________________________

                                    Name: ______________________________________
                                    Title: _____________________________________

                                    HELLER FINANCIAL, INC.

                                    By: ________________________________________

                                    Name: ______________________________________
                                    Title: _____________________________________

                                     Page 9
<PAGE>
                                RATIFICATION

      Each of the Guarantors hereby expressly (i) acknowledges the terms of this
Fourth 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

                                    Page 10
<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

                                      CASTLE TEXAS HOLDINGS, INC.

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

                                      ACADEMY FOR DENTAL ASSISTANTS, INC.

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

                                    Page 11
<PAGE>
                                  SCHEDULE 9.16

                             Schedule 9.16, Page 1EXHIBIT 10.27

                     FIRST AMENDMENT TO SENIOR SUBORDINATED

                             NOTE PURCHASE AGREEMENT

      This FIRST AMENDMENT TO SENIOR SUBORDINATED NOTE PURCHASE AGREEMENT
("AMENDMENT") is dated as of May 19, 2000, and is entered into by and among
CASTLE DENTAL CENTERS, INC., a corporation formed under the laws of Delaware
(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").

      WHEREAS, the Company and the Holders are parties to a certain Senior
Subordinated Note Purchase Agreement dated January 31, 2000 (as such agreement
has from time to time been amended, supplemented or otherwise modified, the
"AGREEMENT"); and

      WHEREAS, the parties desire to amend the Agreement as hereinafter set
forth.

      NOW THEREFORE, in consideration of the mutual conditions and agreements
set forth in the Agreement and this Amendment, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto hereby agree as follows:

      1. DEFINITIONS. Capitalized terms used in this Amendment, unless otherwise
defined herein, shall have the meaning ascribed to such terms in the Agreement.

      2. AMENDMENTS. Subject to the conditions set forth below, the Agreement is
hereby amended as follows:

            (a) Subsection 1.02 is amended by deleting the definition of
      "Applicable Margin" in its entirety and inserting the following in lieu
      thereof:

                  "APPLICABLE MARGIN" shall mean (a) with respect to interest
            calculated by reference to the Eurodollar Rate, (i) from January 31,
            2000 through April 30, 2000, four percent (4.0%) and (ii) from May
            1, 2000 and thereafter, five and one half percent (5.5%) and (b)
            with respect to interest calculated by reference to the Base Rate,
            (i) from January 31, 2000 through April 30, 2000, two and three
            quarters percent (2.75%) and (ii) from May 1, 2000 and thereafter,
            four and one quarter percent (4.25%).

            (b) Subsection 1.02 is further amended by deleting the definition of
      "EBITDA" in its entirety and inserting the following in lieu thereof:

                  "EBITDA" shall mean, for any period, the sum of Consolidated
            Net Income for such period plus the following expenses or charges to
            the extent deducted from Consolidated Net Income in such period:
            interest, taxes, depreciation, depletion, amortization, the amount
            of the settlement of the lawsuit with Joseph Bonola, D.D.S. up to
            but not to exceed $1,372,743 as reflected on
<PAGE>
            Schedule 1 to the Second Amendment to the Senior Credit Agreement,
            dated as of September 30, 1999 and the amount of the unreimbursed
            (whether by insurance or otherwise) legal feesand expenses related
            to the arbitration with Dr. Leon Roisman, D.M.D. that was expensed
            in Fiscal year 1999, up to but not to exceed $541,000.

            (c) Subsection 1.02 is further amended by inserting the definition
      of "Payment Rate" in its entirety and in the proper alphabetical order:

                  "PAYMENT RATE" shall mean the Eurodollar or Base Rate, as
            applicable, PLUS appropriate Applicable Margin in effect from time
            to time, LESS, in any case, from May 1, 2000 through December 31,
            2000, one and one half percent (1.5%).

            (d) Subsection 1.02 is further amended by inserting the definition
      of "PIK Interest" in its entirety and in the proper alphabetical order:

                  "PIK INTEREST" shall mean that interest computed on the unpaid
            principal amount of the Notes at one and one-half percent (1.5%)
            from May 1, 2000 through December 31, 2000.

            (e)  Subsection  2.03(a)  is hereby  amended  in its  entirety  to
      hereafter read as follows:

            " (a) VOLUNTARY PREPAYMENTS. Subject to the terms of the
            Subordination Agreement, the Company may prepay the outstanding
            principal of (together with accrued interest on and, if applicable,
            the prepayment fee described below) the Subordinated Notes in full
            or in part (in minimum amounts of $1,000,000), at any time and from
            time to time on any Quarterly Date as applicable, upon not less than
            three (3) Business Days' prior notice to Holders. The Company shall
            not be permitted to prepay voluntarily the Convertible Notes. Any
            prepayment in full of the Subordinated Notes shall be accompanied by
            all PIK Interest accrued to date."

            (f)  Subsection  2.03(b)(ii)  is hereby amended in its entirety to
      hereafter read as follows:

            " (ii) concurrently with the consummation of a Change in Control,
            Company shall pay the outstanding principal of the Subordinated
            Notes (together with accrued interest and, if applicable, the
            prepayment fee described below). Any prepayment in full of the
            subordinated Notes shall be accompanied by all PIK Interest accrued
            to date."

            (g)  Subsection  3.02(c)  is hereby  amended  in its  entirety  to
      hereafter read as follows:

            " DUE DATES. Accrued interest on the Notes shall be payable at the
            Payment Rate on each Quarterly Date, except that interest payable at
            the Post-Default Rate shall be payable from time to time on demand.
            The PIK Interest shall accrue from

                                       2
<PAGE>
            May 1, 2000 through December 31, 2000 and shall be payable in full
            on the first Quarterly Date in the year 2001 and shall also be
            payable on demand upon the occurrence of an Event of Default. In
            addition, accrued interest on Convertible Notes shall be payable on
            the date of conversion of all or any part of such Convertible Note."

            (h) Section 9.13 is amended by deleting the first sentence thereof
      and inserting the following in lieu thereof:

            "The Company will not permit its Leverage Ratio as of the end of any
            fiscal quarter (calculated on a rolling four quarter basis) to be
            greater than the ratio on the relevant dates set forth below:

                  DATE                                               RATIO
                  ------------------------------------------------------------
                  March 31, 2000                                  3.65 to 1.00
                  June 30, 2000                                   3.65 to 1.00
                  September 30, 2000                              3.50 to 1.00
                  December 31, 2000 and thereafter                3.25 to 1.00."

            (i) Section 9.14 is amended in its  entirety to hereafter  read as
      follows:

                  "Section 9.14 FIXED CHARGE COVERAGE RATIO . The Company will
            not permit its Fixed Charge Coverage Ratio as of the end of any
            fiscal quarter (calculated on a rolling four quarter basis) to be
            less than the ratio on the relevant dates set forth below.

                  DATE                                               RATIO
                  ------------------------------------------------------------
                  March 31, 2000                                  1.15 to 1.00
                  June 30, 2000                                   1.15 to 1.00
                  September 30, 2000                              1.15 to 1.00
                  December 31, 2000                               1.15 to 1.00
                  March 31, 2001                                  1.00 to 1.00
                  June 30, 2001 and thereafter                    1.05 to 1.00

            For purposes of this Section 9.14, "FIXED CHARGE COVERAGE RATIO"
            shall mean (a) with respect to all calculations of Fixed Charge
            Coverage Ratio through and including December 31, 2000, the ratio
            for the relevant period of (i) EBITDA, LESS taxes payable in cash,
            PLUS lease and rental expense to the extent deducted in computing
            net income to (ii) lease and rental expense, PLUS interest expense,
            PLUS, scheduled senior and subordinate principal payments including
            Senior Funded Debt, capital leases, the Indebtedness, Junior
            Subordinated Debt, Debt described on Schedule 9.01 and other Debt
            subordinated or required to be subordinated to the Indebtedness and
            (b) with respect to all calculations of Fixed Charge Coverage Ratio
            on January 1, 2001 and thereafter, the ratio for the relevant period

                                       3
<PAGE>
            of (i) EBITDA, LESS taxes payable in cash, PLUS lease and rental
            expense to the extent deducted in computing net income to (ii) lease
            and rental expense, PLUS interest, PLUS, during the Revolving Credit
            Period (as defined in the Senior Credit Agreement), one-seventh
            (1/7) of the then-outstanding principal balance of the Senior Loans,
            PLUS, without duplication, current maturities of long-term debt,
            PLUS capital leases PLUS, from and after Revolving Credit Period
            scheduled payments of principal on Debt of the Company and its
            Subsidiaries. For any calculation period which would include one or
            more quarters prior to any Stock Purchase or any Asset Purchase or
            any other future acquisition of an entity, the "rolling four
            quarters" shall include the "pro forma" EBITDA of the applicable
            Acquired Entity for such prior periods as approved by Holders,
            adjusted to reflect costs and expenses which such Acquired Entity
            would have included had the Management Services Agreements between
            Company and/or any Subsidiary and such Acquired Entity been in
            effect (adding back appropriate executive salaries and non-cash
            charge offs relating to this transaction), in each instance, as
            approved by Holders."

            (j) Section 9.15 is amended in its  entirety to hereafter  read as
      follows:

            "9.15 RATIO OF TOTAL FUNDED DEBT TO EBITDA. The Company will not
            permit its ratio of Total Funded Debt as of the end of any fiscal
            quarter to EBITDA for the four fiscal quarters ending on such date
            to be greater than the ratio for the relevant periods set forth
            below:

                  PERIOD ENDING                                       RATIO
                  --------------------------------------------------------------
                  March 31, 2000                                  5.00 to 1.00
                  June 30, 2000                                   5.00 to 1.00
                  September 30, 2000                              4.75 to 1.00
                  December 31, 2000 and thereafter                4.25 to 1.00.

            For purposes hereof, EBITDA shall be calculated as provided in
            section 9.13. For clarity purposes, it is understood and agreed that
            Total Funded Debt includes, without limitation, any and all deferred
            interest under all Total Funded Indebtedness."

      3. AMENDMENT FEES. In connection with the execution of this Amendment, the
Company shall pay to Holders, for their ratable benefit, a fee of $37,500
("AMENDMENT FEE"), which Amendment Fee shall be deemed to be earned on the
Effective Date and shall be due and payable on the following dates in the
following amounts:

                  DATE                          AMOUNT
                  ----------------------------------------
                  Effective Date                $12,502.50
                  September 29, 2000            $12,498.75
                  December 29, 2000             $12,498.75

                                       4
<PAGE>
;provided, however, in the event the Company pays to Holders the entire
principal balance of the Subordinated Notes prior to December 29, 2000, the
entire unpaid amount of the Amendment Fee shall become immediately due and
payable.

      4. CONDITIONS. The effectiveness of this Amendment (the date on which this
Amendment becomes effective shall referred to as the "EFFECTIVE DATE") is
subject to the following conditions precedent (unless specifically waived in
writing by the Holders):

            (a) The Company shall have executed and delivered this Amendment,
      and such other documents and instruments as the Holders may reasonably
      require shall have been executed and/or delivered to the Holders;

            (b) All proceedings taken in connection with the transactions
      contemplated by this Amendment and all documents, instruments and other
      legal matters incident thereto shall be satisfactory to the Holders and
      their legal counsel;

            (c)   Holders  shall have  received  all  deliquent  payments  due
      under the Agreement;

            (d)   After giving effect to this  Amendment,  no Default or Event
      of Default shall have occurred and be continuing;

            (e) Each of the Holders shall have received (and the Company
      covenants and agrees to deliver to Holders), by May __, 2000 [TWO WEEKS
      FROM EFFECTIVE DATE], the documents referred to in Section 8.01(a) of the
      Agreement for the fiscal year ended December 31, 1999 and Section 8.01(b)
      for the fiscal quarter ended March 31, 2000;

            (f) Each of the Holders shall have received consolidated and
      consolidating statements of income, stockholders' equity, changes in
      financial position and cash flow of the Company and its Consolidated
      Subsidiaries for the months ending January 31, 2000 and February 29, 2000,
      in each case prepared by the Company and accompanied by the certificate of
      a Responsible Officer stating that such financial statements fairly
      present the consolidated and consolidating financial condition of the
      Company and its Consolidated Subsidiaries in accordance with GAAP, as at
      the end of, and for, each such month;

            (g) Each of the Holders shall have received evidence that the
      requisite number of Senior Lenders have consented to the execution of this
      Amendment; and

            (h) The Senior Credit Documents shall have been amended in a manner
      satisfactory to Holders and such amendment shall have become effective.

      5. REPRESENTATIONS AND WARRANTIES. To induce Holders to enter into this
Amendment, the Company represents and warrants to Holders:

                                       5
<PAGE>
            (a) that the execution, delivery and performance of this Amendment
      has been duly authorized by all requisite corporate action on the part of
      the Company and that this Amendment has been duly executed and delivered
      by the Company;

            (b) that each of the representations and warranties set forth in
      Article VII of the Agreement (other than those which, by their terms,
      specifically are made as of certain date prior to the date hereof) are
      true and correct in all material respects as of the date hereof; and

      6. SEVERABILITY. Any provision of this Amendment held by a court of
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

      7. REFERENCES. Any reference to the Agreement contained in any document,
instrument or agreement executed in connection with the Agreement shall be
deemed to be a reference to the Agreement as modified by this Amendment.

      8. COUNTERPARTS. This Amendment may be executed in one or more
counterparts, each of which shall constitute an original, but all of which taken
together shall be one and the same instrument.

      9. RATIFICATION. The terms and provisions set forth in this Amendment
shall modify and supersede all inconsistent terms and provisions of the
Agreement and shall not be deemed to be a consent to the modification or waiver
of any other term or condition of the Agreement. Except as expressly modified
and superseded by this Amendment, the terms and provisions of the Agreement are
ratified and confirmed and shall continue in full force and effect.

      10. WAIVER. The Company and the Holders hereby acknowledge and agree that
prior to the effectiveness hereof, the Company was in default for the months of
January, February, March, April and May 2000 under Sections 3.02, 8.01(a) and
(b), 9.13, 9.14 and 9.15 of the Agreement. Provided that no other defaults by
the Company currently exist and are continuing under the Agreement, and provided
further, the conditions precedent set forth in Section 4 hereof are satisfied,
then the defaults listed above which occurred on or before the date hereof are
hereby waived by the Holders and the Holders' remedies with respect thereto are
hereby waived. Notwithstanding the foregoing, or any other election by the
Holders to date in forgiving any default by the Company or in waiving any
remedies with respect thereto, no such forgiveness or waiver shall affect or be
deemed to affect any default by the Company or any remedy by the Holders
existing after the date hereof, and the Holders shall not be obligated in any
manner to forgive any such defaults, or waive any such remedies. The Holders
hereby reserve, and the Company hereby acknowledges and agrees that the Holders
have effectively preserved, all of their rights, remedies and recourses with
respect to any default under the Agreement except with respect to the defaults
expressly set forth above.

                                       6
<PAGE>
      IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed under seal and delivered by their respective duly authorized
officers on the date first written above.

HELLER FINANCIAL, INC.,                   CASTLE DENTAL CENTERS, INC.,
 a Delaware corporation                    a Delaware corporation

By:   ________________________            By:   ________________________
Name: ________________________            Name: Jack H. Castle, Jr.
Title:________________________            Title: Chief Executive Officer

                                          ATTEST:

MIDWEST MEZZANINE FUND II, L.P.,          ______________________________
 a Delaware limited partnership                 [ASSISTANT] SECRETARY
                                                [CORPORATE SEAL]

By:   ________________________
Name: ________________________
Title:________________________

                                       7
<PAGE>
                            CONSENT AND REAFFIRMATION

      Each of the undersigned (each a "GUARANTOR", collectively the
"GUARANTORS") hereby (i) acknowledges receipt of a copy of the foregoing First
Amendment to Senior Subordinated Note Purchase Agreement; (ii) consents to the
Company's execution and delivery thereof; (iii) agrees to be bound thereby; and
(iv) affirms that nothing contained therein shall modify in any respect
whatsoever its guaranty of the obligations of Company to Heller and Midwest
pursuant to the terms of that certain Subordinated Guaranty Agreement dated
January 31, 2000 (the "GUARANTY") and reaffirms that the Guaranty is and shall
continue to remain in full force and effect. Although each Guarantor has been
informed of the matters set forth herein and has acknowledged and agreed to
same, each Guarantor understands that the Holders have no obligation to inform
any Guarantor of such matters in the future or to seek any Guarantor's
acknowledgment or agreement to future amendments or waivers, and nothing herein
shall create such a duty.

      IN WITNESS WHEREOF, each of the undersigned has executed this Consent and
Reaffirmation on and as of the date of such Amendment.

                                    ACADEMY FOR DENTAL ASSISTANTS, INC.
                                    CASTLE TEXAS HOLDINGS, INC.
                                    CASTLE DENTAL CENTERS OF
                                    CALIFORNIA, L.L.C.
                                    CASTLE DENTAL CENTERS OF TEXAS, INC.
                                    DENTAL WORLD, INC.
                                    CDC OF CALIFORNIA, INC.
                                    CASTLE DENTAL CENTERS OF AUSTIN, INC.
                                    CASTLE DENTAL CENTERS OF FLORIDA, INC.
                                    CASTLE DENTAL CENTERS OF
                                    TENNESSEE, INC., AND
                                    DENTCOR, INC.

                                    By:    ________________________________
                                    Name:  Jack H. Castle, Jr.
                                    Title: Chief Executive Officer

                                       8

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