EXHIBIT 10.24

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE UNITED STATES SECURITIES ACT OF
1933, AS AMENDED, NOR THE SECURITIES LAWS OF ANY STATE. THIS NOTE MAY NOT BE
SOLD, PLEDGED, HYPOTHECATED OR OTHERWISE TRANSFERRED AT ANY TIME, EXCEPT UPON
(1) SUCH REGISTRATION, OR (2) DELIVERY TO THE ISSUER OF THIS NOTE OF AN OPINION
OF COUNSEL REASONABLY ACCEPTABLE TO THE ISSUER THAT REGISTRATION IS NOT REQUIRED
FOR SUCH TRANSFER, OR (3) THE SUBMISSION TO THE ISSUER OF THIS NOTE OF OTHER
EVIDENCE, REASONABLY ACCEPTABLE TO THE ISSUER, TO THE EFFECT THAT ANY SUCH SALE,
PLEDGE, HYPOTHECATION OR TRANSFER WILL NOT BE IN VIOLATION OF THE UNITED STATES
SECURITIES ACT OF 1933, AS AMENDED, OR OTHER APPLICABLE SECURITIES LAWS OF ANY
STATE, OR ANY RULES OR REGULATIONS PROMULGATED THEREUNDER.

THE PAYMENT OF THE PRINCIPAL OF, AND INTEREST ON, AND ALL OTHER AMOUNTS OWING IN
RESPECT OF THE INDEBTEDNESS EVIDENCED BY, THIS NOTE, IS AND SHALL BE EXPRESSLY
SUBORDINATED, TO THE EXTENT AND IN THE MANNER SET FORTH HEREIN AND, IF
APPLICABLE, IN THAT CERTAIN SUBORDINATION AGREEMENT, OR ANY OTHER SUBORDINATION
AGREEMENT NOW OR HEREAFTER EXECUTED, AMONG THE ISSUER OF THE NOTE, THE HOLDER,
BANK OF AMERICA, N.A., FORMERLY KNOWN AS NATIONSBANK OF TEXAS, N.A., ITS
SUCCESSORS OR ASSIGNS, OR ANY OTHER HOLDER OF SENIOR DEBT (COLLECTIVELY, "SENIOR
CREDITOR"), (IN ANY SUCH EVENT, THE "SUBORDINATION AGREEMENT").


                       SENIOR SUBORDINATED PROMISSORY NOTE

$13,621,536.00                                                 JANUARY 31, 2000
                                                               CHICAGO, ILLINOIS

      FOR VALUE RECEIVED, the undersigned, CASTLE DENTAL CENTERS, INC., a
Delaware corporation ("Company"), hereby unconditionally promises to pay to the
order of ________________________________ ("Holder"), at Holder's office at
_____________________ or at such other place as Holder may from time to time
designate in writing, in lawful money of the United States of America and in
immediately available funds, the principal sum of THIRTEEN MILLION SIX HUNDRED
TWENTY ONE THOUSAND FIVE HUNDRED THIRTY SIX AND NO/100 DOLLARS ($13,621,536.00),
or, if less, the aggregate unpaid principal amount hereof, at such times as are
specified in, and in accordance with the provisions of, the Senior Note Purchase
Agreement (or hereinafter defined). This Senior Subordinated Promissory Note is
referred to in and was executed and delivered pursuant to that certain Senior
Subordinated Note Purchase Agreement of even date herewith (the "Note Purchase
Agreement") among the Company, Holder and ________________________________, to
which reference is hereby made for a statement of the terms and conditions under
which the senior subordinated loan evidenced hereby was made and is to be
repaid. All terms which are capitalized and used herein (which are not otherwise
specifically defined herein) and which are defined in the Note Purchase
Agreement shall be used in this Senior Subordinated Promissory Note as defined
in the Note Purchase Agreement.
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      The Company further promises to pay interest on the outstanding unpaid
principal amount hereof, as provided in the Note Purchase Agreement, from the
date hereof until payment in full hereof at the applicable rate specified in
subsection 3.02(a) of the Note Purchase Agreement; provided, however, that if
Holder so elects, following the occurrence and during the continuance of an
Event of Default, the Company promises to pay to Holder interest on the unpaid
principal amount hereof at the applicable rate specified in subsection 3.02(b)
of the Note Purchase Agreement. Interest shall be payable in accordance with the
provisions specified in subsection 3.02(c) of the Note Purchase Agreement, which
specifies that accrued interest on the subordinated Notes shall be payable on
each Quarterly Date, except that interest payable at the Post-Default Rate shall
be payable from time to time on demand.

      If a payment hereunder becomes due and payable on a day that is not a
Business Day, the payment may be made on the next succeeding Business Day, and
such extension of time shall be included in the computation of the amount of
interest due on such succeeding Business Day. Checks, drafts or similar items of
payment received by Holder shall not constitute payment, but credit therefor
shall, solely for the purpose of computing interest earned by Holder, be given
in accordance with the Note Purchase Agreement. In no contingency or event
whatsoever shall interest charged hereunder, however such interest may be
characterized or computed, exceed the highest rate permissible under any law
which a court of competent jurisdiction determines is applicable hereto. In the
event of any such determination, the provisions of subsection 5.03 of the Note
Purchase Agreement shall govern and control.

      If any suit or action is instituted or attorneys are employed to collect
this Senior Subordinated Promissory Note or any part thereof, the Company hereby
promises and agrees to pay all costs of collection, including attorneys' fees
and court costs.

      The Company and each endorser, guarantor and surety of this Senior
Subordinated Promissory Note hereby waives presentment for payment, protest and
demand, and notice of demand, protest, dishonor and nonpayment of this Senior
Subordinated Promissory Note.

      THIS SENIOR SUBORDINATED PROMISSORY NOTE HAS BEEN DELIVERED AT AND SHALL
BE DEEMED TO HAVE BEEN MADE AT CHICAGO, ILLINOIS AND SHALL BE INTERPRETED AND
THE RIGHTS AND LIABILITIES OF THE PARTIES HERETO SHALL BE DETERMINED IN
ACCORDANCE WITH THE INTERNAL LAWS AND DECISIONS OF THE STATE OF ILLINOIS WITHOUT
REGARD TO CONFLICTS OF LAW PROVISIONS. Whenever possible each provision of this
Senior Subordinated Promissory Note shall be interpreted in such manner as to be
effective and valid under applicable law, but if any provision of this Senior
Subordinated Promissory Note shall be prohibited by or invalid under applicable
law, such provision shall be ineffective to the extent of such prohibition or
invalidity, without invalidating the remainder of such provision or the
remaining provisions of this Senior Subordinated Promissory Note. Whenever in
this Senior Subordinated Promissory Note reference is made to Holder or the
Company, such reference shall be deemed to include, as applicable, a reference
to their respective successors and assigns. The provisions of this Senior
Subordinated Promissory Note shall be binding upon and shall inure to the
benefit of such successors and assigns. The Company's successors and assigns
shall include, without limitation, a receiver, trustee or debtor in possession
of or for the Company.

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      IN WITNESS WHEREOF, the Company has executed this Senior Subordinated
Promissory Note as of the day and year first written above.

                                    CASTLE DENTAL CENTERS, INC., a Delaware
                                    corporation

                                    By:   _______________________________
                                    Name: Jack H. Castle, Jr.
                                    Title: Chairman and Chief Executive
                                           Officer