<PAGE>   1
                                                                   EXHIBIT 10.28

                               FIRST AMENDMENT TO
                   SECOND AMENDED AND RESTATED LOAN AGREEMENT



         THIS FIRST AMENDMENT TO SECOND AMENDED AND RESTATED LOAN AGREEMENT
(this "Amendment") is executed as of December 30, 1999, by and among MONARCH
DENTAL CORPORATION, a Delaware corporation ("Borrower"), BANK OF AMERICA, N.A.,
a national banking association ("Administrative Agent"), as administrative
agent, and the entities from time to time designated as "Lenders" under the Loan
Agreement (herein defined) ("Lenders"), and is consented to by the GUARANTORS
listed on the signature pages attached hereto.


                              W I T N E S S E T H:


         WHEREAS, Borrower, Administrative Agent and Lenders entered into that
certain Second Amended and Restated Loan Agreement, dated as of June 30, 1999,
pursuant to which Lenders agreed to make the Credit Facility (as therein
defined) available to Borrower (as heretofore or hereafter amended, the "Loan
Agreement")(each capitalized term used but not otherwise defined herein shall
have the same meaning given to it in the Loan Agreement); and

         WHEREAS, Borrower has requested that Administrative Agent and Lenders
modify certain covenants, terms and conditions contained in the Loan Agreement;
and

         WHEREAS, subject to the terms and conditions contained herein,
Administrative Agent and the Lenders have agreed to such request.

         NOW, THEREFORE, in consideration of the covenants, conditions and
agreements hereinafter set forth, and for other good and valuable consideration,
the receipt and adequacy of which are all hereby acknowledged, Borrower,
Administrative Agent and Lenders hereby covenant and agree as follows:

                             ARTICLE I - AMENDMENTS

         Section 1.1. Modification of Definitions. The following definitions
contained in Section 1.1 of the Loan Agreement are hereby deleted and replaced
with the following:

                  Default Rate means the fluctuating per annum rate of interest
         equal to the lesser of (a) the Variable Rate plus 6% or (b) the Maximum
         Lawful Rate.


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 1



<PAGE>   2

                  Fixed Charge Coverage Ratio means, for any date of
         determination and computed for the immediately preceding twelve month
         period, the ratio of (a) the difference between (i) the sum of (A)
         Consolidated EBITDA plus (B) Consolidated Lease Expense, and (ii) the
         sum of (X) Maintenance Capital Expenditures, plus (Y) payments made to
         the other owners of partially-owned subsidiaries which constitute such
         other owner's portion of net earnings of such partially-owned
         subsidiaries (to the extent that such amounts are included in
         Consolidated EBITDA), plus (Z) all "earnout payments" made during such
         period, to (b) the sum of (i) Consolidated Interest Expense (excluding
         any non-cash amortization of capitalized financing fees included in
         Consolidated Interest Expense, including, without limitation, the
         Warrants (as defined in Section 2.2(b) of this Amendment)), plus (ii)
         Consolidated Current Maturities, plus (iii) Consolidated Lease Expense,
         plus (iv) Consolidated Capital Lease Expense, plus (v) Actual Taxes.
         The amount of the Consolidated Net Income, Consolidated Lease Expense
         and Consolidated Interest Expense to be included in computing the Fixed
         Charge Coverage Ratio shall be the actual amount of such items incurred
         during the relevant periods. The term "earnout payments" means any
         amount payable by Borrower or any Subsidiary of Borrower under any
         agreement for an Acquisition by Borrower or any Subsidiary of Borrower
         other than the consideration paid at the closing of such Acquisition.

         Section 1.2. New Definitions. The following definitions are hereby
added to Section 1.1 of the Loan Agreement:

                  Change in Control means the acquisition, after the date
         hereof, by any Person, or two or more Persons acting in concert, of
         beneficial ownership (within the meaning of Rule 13d-3 of the
         Securities and Exchange Commission under the Securities Exchange Act of
         1934) of 20% or more of the outstanding shares of voting stock of
         Borrower.

                  Change in Management means that any of the following Persons
         shall cease to be employed by Borrower in the capacity in which they
         are employed as of the date of this Amendment: Lisa Peterson as Chief
         Financial Officer and Gary Cage as Chief Executive Officer.

         Section 1.3. Interest Rate. Section 3.3 of the Loan Agreement is hereby
amended and replaced with the following Section 3.3:


                  SECTION 3.3. Interest Rate. Interest on the Advances shall
         accrue at a rate per annum equal to the lesser of (a) at Borrower's
         option, the applicable Variable Rate or the applicable Adjusted LIBOR
         Rate, subject, however, to the provisions of Section 10.8 (the
         "Applicable Rate"), or (b) the Maximum Lawful Rate; provided, however,
         if at any time the Applicable Rate exceeds the Maximum Lawful Rate,
         resulting in the charging of interest hereunder to be limited to the
         Maximum Lawful Rate, then any subsequent reduction in the Applicable
         Rate shall not reduce the rate of interest below the Maximum Lawful
         Rate until the total amount of interest accrued on the indebtedness
         evidenced

FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 2

<PAGE>   3

         hereby equals the amount of interest which would have accrued on such
         indebtedness if the Applicable Rate had at all times been in effect.

                  Without notice to Borrower or anyone else, the Variable Rate
         and the Maximum Lawful Rate shall each automatically fluctuate upward
         and downward as and in the amount by which the Base Rate and Maximum
         Lawful Rate, respectively, fluctuate, subject always to limitations
         contained in this Agreement. In addition, without notice to Borrower or
         anyone else, the Variable Rate and the Adjusted LIBOR Rate initially
         provided for under this Agreement shall fluctuate upward or downward
         from time to time based on changes in the Consolidated Funded Debt to
         Consolidated EBITDA ratio, pursuant to Schedule II. Such changes shall
         occur on the first day of the calendar month following the month in
         which Administrative Agent receives the quarterly financial statements
         and related officer's certificate required to be delivered by Borrower
         pursuant to Sections 6.1 (b) and (d) hereof showing that such
         adjustment is appropriate (except that with respect to any Adjusted
         LIBOR Rate then in effect, such change shall occur at the end of the
         applicable Interest Period).

         Section 1.4. Principal Payments. Subsection (c) of Section 3.4 of the
Loan Agreement is hereby amended and replaced with the following subsection (c):

                  (c) Upon any debt or equity offering by Borrower or any
         Guarantor (other than the Required Institutional Debt), Borrower shall
         make a principal payment in an amount equal to one-hundred percent
         (100%) of the net proceeds to Borrower or such Guarantor from such
         offering as such amount is approved by Administrative Agent for the
         purpose of reducing the amount outstanding under the Credit Facility.

A new subsection (e) is hereby added to Section 3.4 of the Loan Agreement as
follows:

                  (e) In addition to any other payments required hereunder,
         Borrower shall pay to Administrative Agent, for the ratable benefit of
         the Lenders, on the same date as interest payments are required to be
         made under subsection (a) above, a principal payment under the Credit
         Facility in an amount equal to the product of (i) 0.75 multiplied by
         (ii) the unpaid amount of payments of any kind scheduled to be made
         during the calendar quarter then ended under Debt of Borrower or any
         Subsidiary (including, without limitation, any Subordinate Acquisition
         Debt and "earnout payments" owing by Borrower or such Subsidiary, but
         excluding the Credit Facility and the Short Term Debt) which was not
         paid as a result of a permanent reduction or forgiveness of such Debt.
         As used in this Section 3.4(e) only, the term "earnout payments" means
         "earnout payments" (as defined in the definition of Fixed Charge
         Coverage Ratio) which are guaranteed to be paid by Borrower or the
         applicable Subsidiary, without the satisfaction of any condition to
         such payment.

FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 3

<PAGE>   4

         Section 1.5. Coverage Ratio. Section 7.3 of the Loan Agreement is
hereby amended and replaced with the following Section 7.3:

                  SECTION 7.3. Coverage Ratio. Borrower shall not permit its
         Fixed Charge Coverage Ratio to be, as of the end of any calendar
         quarter, (i) prior to and including June 30, 2000, less than 1.00 to
         1.00, and (ii) thereafter, less than 1.20 to 1.00.

         Section 1.6. Leverage Ratio. Section 7.5 of the Loan Agreement is
hereby amended and replaced with the following Section 7.5:

                  SECTION 7.5. Consolidated Senior Funded Debt to Consolidated
         EBITDA. As of the end of any calendar quarter, Borrower shall not
         permit the ratio of Consolidated Senior Funded Debt to Consolidated
         EBITDA for the immediately preceding twelve months to be (a) prior to
         the earlier of (i) June 30, 2000 or (ii) the closing of the Required
         Institutional Debt (such date, the "Ratio Reduction Date"), more than
         3.60 to 1.00, (b) for the period from the Ratio Reduction Date through
         and including December 31, 2000, more than 3.00 to 1.00, and (c)
         thereafter, more than 2.50 to 1.00; provided that the Target Company
         EBITDA attributable to any Acquisition, for purposes of calculating
         Consolidated EBITDA, shall, for the twelve (12) month period commencing
         on the Acquisition Date, be computed by annualizing the actual Target
         Company EBITDA for the period since the Acquisition Date.

         Section 1.7. Limitation on Debt. Section 7.6 of the Loan Agreement is
hereby amended and replaced with the following Section 7.6:

                  SECTION 7.6. Limitation on Debt. Neither Borrower nor any
         Guarantor shall incur any Debt, except for (a) the Obligations, (b)
         trade payables incurred in the ordinary course of business, (c) the
         Debt described on Schedule III hereto, (d) Debt in respect of (i)
         taxes, assessments, governmental charges or levies and claims for
         labor, materials and supplies, (ii) judgments or awards which have been
         in force for less than the applicable appeal period so long as
         execution is not levied thereunder or in respect of which Borrower or
         Guarantor shall at the time in good faith be prosecuting an appeal or
         proceedings for review and in respect of which a stay of execution
         shall have been obtained pending such appeal or review, and (iii)
         endorsements made in connection with the deposits of items for credit
         or collection in the ordinary course of business, (e) capitalized lease
         obligations related to capital expenditures made by Borrower as
         permitted by Section 7.19 hereof (and so long as such capitalized lease
         obligations do not cause Borrower to be in violation of any other
         covenant of this Agreement), (f) Subordinate Acquisition Debt, (g)
         Permitted Institutional Debt, provided that, (1) the amount of the
         Permitted Senior Institutional Debt outstanding at any time cannot
         exceed the lesser of 70% of the aggregate amount of Permitted
         Institutional Debt outstanding at the time of determination or
         $17,500,000.00, (2) the amount of Permitted Subordinate Institutional
         Debt outstanding at any time cannot be less than $7,500,000.00, and (3)
         the


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 4

<PAGE>   5

         issuance of said Permitted Institutional Debt would otherwise be
         permitted by the other terms and conditions of the Credit Facility, (h)
         the Short Term Debt in existence on the date of the execution of this
         Agreement (Lenders hereby agreeing that (1) Administrative Agent shall
         be entitled to execute on behalf of Lenders any documents or agreements
         approved by Administrative Agent acknowledging that the Short Term Debt
         is included in the Obligations and secured by the Collateral, subject,
         however, to the provisions of Section 9.6 hereof and (2) all or any
         portion of the proceeds of the Permitted Institutional Debt shall be
         used to repay the Short Term Debt and then to pay down the Credit
         Facility), and (i) refinancings, renewals or extensions of the Debt
         permitted under the foregoing clauses provided that such refinancings,
         renewals or extensions do not result in an increase in the aggregate
         unpaid principal amount of the Debt so refinanced, renewed or extended.

         Section 1.8. Acquisitions. Section 7.9 of the Loan Agreement is hereby
amended and replaced with the following Section 7.9:


                  SECTION 7.9. Consolidations, Mergers, Acquisitions, Sales of
         Assets, and Maintenance. Neither Borrower nor any Guarantor shall,
         without prior approval of Required Lenders, (a) consolidate or merge
         with or into any other Person, (b) sell, lease, abandon or otherwise
         transfer all or any material part of its assets to any Person, in one
         or a series of related transactions, or (c) terminate, or fail to
         maintain, its good standing and qualification to transact business in
         all jurisdictions where the failure to maintain its good standing or
         qualification to transact business would reasonably be expected to have
         a Material Adverse Effect; provided, however, that any Guarantor may
         merge with or into Borrower or any other Guarantor. Borrower shall not
         make any Acquisitions or open any new offices or branches, without the
         prior written consent of Required Lenders (other than the new office in
         Decatur, Georgia which is scheduled to open in January, 2000).

         Section 1.9. Distributions. Section 7.11 of the Loan Agreement is
hereby amended and replaced with the following Section 7.11:

                  SECTION 7.11. Distributions. Neither Borrower nor any
         Guarantor shall make or declare any Distributions until the Obligations
         have been paid in full.

         Section 1.10. Repurchase of Stock. Section 7.18 of the Loan Agreement
is hereby amended and replaced with the following Section 7.18:

                  SECTION 7.18. Repurchase of Stock. Neither Borrower nor any
         Guarantor shall purchase any of the stock of any of the Guarantors or
         Borrower during the term of the Credit Facility without prior notice to
         and approval of Required Lenders.

         Section 1.11. Capital Expenditures. Section 7.19 of the Loan Agreement
is hereby amended and replaced with the following Section 7.19:


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 5

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                  SECTION 7.19. Capital Expenditures. Borrower and Guarantors
         shall not make capital expenditures, in the aggregate, in excess of (a)
         during calendar year 2000, $5,000,000 plus $1,121,000 (representing
         capital expenditures incurred in 1999 but which have not yet been
         paid), and (b) during each calendar year thereafter, the lesser of (i)
         2.5% of gross revenues for Borrower and the Guarantors on a
         consolidated basis (calculated in accordance with GAAP) for the
         previous calendar year or (ii) 115% of the budgeted amount for capital
         expenditures in Borrower's operating budget for such year.

         Section 1.12. Defaults. Subsection (k) of Section 8.1 of the Loan
Agreement is hereby deleted.

A new subsection (l) is hereby added to Section 8.1 of the Loan Agreement as
follows:

                  (l) The occurrence of (i) any Change in Control or, (ii) a
         Change in Management prior to the closing and funding of either (i)
         Permitted Institutional Debt in an amount not less than $25,000,000 (at
         least $10,000,000 of which shall be Permitted Subordinate Institutional
         Debt), or (ii) Permitted Subordinate Institutional Debt in an amount
         not less than $15,000,000.

         Section 1.13. Replacement Schedule. Schedule II to the Loan Agreement
is hereby deleted and replaced with Schedule II hereto.

                           ARTICLE II - MISCELLANEOUS

         Section 2.1. Closing. The closing (the "Closing") of the transactions
contemplated by this Amendment shall occur on and as of the date that all
conditions hereto contained in Section 2.2 of this Amendment have been satisfied
(the "Modification Closing Date").

         Section 2.2. Conditions to the Closing. As conditions precedent to the
Closing, all of the following shall have been satisfied:

                  (a) Borrower, each Guarantor and Required Lenders shall have
executed and delivered this Amendment; and

                  (b) Borrower shall execute and deliver to Administrative Agent
(i) that certain Fee Letter (herein so called) from Administrative Agent to
Borrower and shall have paid to Administrative Agent, for the benefit of the
Lenders, all fees payable in cash as provided therein and (ii) that certain
Warrant Agreement (herein so called) in the form attached hereto as Exhibit "A"
and the Warrant Certificates (as defined in the Warrant Agreement).

         Section 2.3. Continuing Effect. Except as modified and amended hereby,
the Loan Agreement and other Loan Documents are and shall remain in full force
and effect in accordance with their terms.


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 6
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         Section 2.4. Representations and Warranties. Borrower hereby represents
and warrants to Administrative Agent and the Lenders that (i) except as has been
disclosed by Borrower to Administrative Agent in writing, all representations
and warranties made by Borrower in the Loan Agreement as of the date thereof are
true and correct as of the date hereof, as if such representations and
warranties were recited herein in their entirety and (ii) Borrower is not in
default of any covenant or agreement contained in the Loan Agreement.

         Section 2.5. Payment of Expenses. Borrower agrees to pay to
Administrative Agent the reasonable attorneys' fees and expenses of
Administrative Agent's counsel and other expenses incurred by Administrative
Agent in connection with this Amendment.

         Section 2.6. Binding Agreement. This Amendment shall be binding upon,
and shall inure to the benefit of, the parties' respective representatives,
successors and assigns.

         Section 2.7. Ratification. Except as otherwise expressly modified by
this Amendment, all terms and provisions of the Loan Agreement, the Notes and
the other Loan Documents, shall remain unchanged and hereby are ratified and
confirmed and shall be and shall remain in full force and effect, enforceable in
accordance with their terms.

         Section 2.8. No Defenses. Borrower and each Guarantor, by its execution
of this Amendment, hereby declares that it has no set-offs, counterclaims,
defenses or other causes of action against Administrative Agent or any Lender
arising out of the Credit Facility, the modification of the Credit Facility, any
documents mentioned herein or otherwise; and, to the extent any such set-offs,
counterclaims, defenses or other causes of action may exist, whether known or
unknown, such items are hereby waived by Borrower and each Guarantor.

         Section 2.9. Further Assurances. The parties hereto shall execute such
other documents as may be necessary or as may be required, in the opinion of
counsel to Administrative Agent, to effect the transactions contemplated hereby
and the liens and/or security interests of all other collateral instruments, as
modified by this Amendment. Borrower also agrees to provide to Administrative
Agent such other documents and instruments as Lenders reasonably may request in
connection with the modification of the Credit Facility effected hereby.

         Section 2.10. Usury Savings Clause. Notwithstanding anything to the
contrary in this Amendment, the Notes or any other Loan Document, or in any
other agreement entered into in connection with the Notes or securing the
indebtedness evidenced by the Notes, whether now existing or hereafter arising
and whether written or oral, it is agreed that the aggregate of all interest and
other charges constituting interest, or adjudicated as constituting interest,
and contracted for, chargeable or receivable under the Notes or otherwise in
connection with the Notes shall under no circumstances exceed the maximum rate
of interest permitted by applicable law. In the event the maturity of the Notes
is accelerated by reason of an election by any of the



FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 7

<PAGE>   8


holders thereof resulting from a default thereunder or under any other document
executed as security therefor or in connection therewith, or by voluntary
prepayment by the maker, or otherwise, then earned interest may never include
more than the maximum rate of interest permitted by applicable law. If from any
circumstance any holder of any of the Notes shall ever receive interest or any
other charges constituting interest, or adjudicated as constituting interest,
the amount, if any, which would exceed the maximum rate of interest permitted by
applicable law shall be applied to the reduction of the principal amount owing
on such Notes or on account of any other principal indebtedness of the maker to
the holders of such Notes, and not to the payment of interest, or if such
excessive interest exceeds the unpaid balance of principal thereof and such
other indebtedness, the amount of such excessive interest that exceeds the
unpaid balance of principal thereof and such other indebtedness shall be
refunded to the maker. All sums paid or agreed to be paid to the holders of the
Notes for the use, forbearance or detention of the indebtedness of the maker to
the holders of such Notes shall be amortized, prorated, allocated and spread
throughout the full term of such indebtedness until payment in full for the
purpose of determining the actual rate on such indebtedness is uniform
throughout the term thereof.

                  The terms "maximum amount" or "maximum rate" as used in this
Amendment or the Notes, or in any other agreement entered into in connection
with the Notes or securing the indebtedness evidenced by the Notes, whether now
existing or hereafter arising and whether written or oral, include, as to
Chapter 303 of the Texas Finance Code (and as same may be incorporated by
reference in other statutes of the State of Texas), but otherwise without
limitation, that rate based upon the "weekly ceiling"; provided, however, that
this designation shall not preclude the rate of interest contracted for, charged
or received in connection with the Credit Facility from being governed by, or
construed in accordance with, any other state or federal law, including but not
limited to, Public Law 96-221.

         Section 2.11. Non-Waiver of Events of Default. Neither this Amendment
nor any other document executed in connection herewith constitutes or shall be
deemed (a) a waiver of, or consent by Administrative Agent or any Lender to, any
default or event of default which may exist or hereafter occur under any of the
Loan Documents, (b) a waiver by Administrative Agent or any Lender of any of
Borrower's obligations under the Loan Documents, or (c) a waiver by
Administrative Agent or any Lender of any rights, offsets, claims, or other
causes of action that any Lender may have against Borrower.

         Section 2.12. Enforceability. In the event the enforceability or
validity of any portion of this Amendment, the Loan Agreement, the Notes, or any
of the other Loan Documents is challenged or questioned, such provision shall be
construed in accordance with, and shall be governed by, whichever applicable
federal or Texas law would uphold or would enforce such challenged or questioned
provision.

         Section 2.13. Counterparts. This Amendment may be executed in several
counterparts, all of which are identical, each of which shall be deemed an
original, and all of which counterparts together shall constitute one and the
same instrument, it being understood and


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 8


<PAGE>   9

agreed that the signature pages may be detached from one or more of such
counterparts and combined with the signature pages from any other counterpart in
order that one or more fully executed originals may be assembled.

         Section 2.14. Choice of Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF TEXAS, EXCEPT TO THE
EXTENT FEDERAL LAWS PREEMPT THE LAWS OF THE STATE OF TEXAS.

         Section 2.15. Entire Agreement. This Amendment and the other Loan
Documents, contain the entire agreements between the parties relating to the
subject matter hereof and thereof. This Amendment and the other Loan Documents
may be amended, revised, waived, discharged, released or terminated only by a
written instrument or instruments, executed by the party against which
enforcement of the amendment, revision, waiver, discharge, release or
termination is asserted. Any alleged amendment, revision, waiver, discharge,
release or termination which is not so documented shall not be effective as to
any party.

         THIS AMENDMENT AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL
AGREEMENT BETWEEN THE PARTIES RELATED TO THE SUBJECT MATTER HEREIN CONTAINED 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.











                     [REMAINDER OF PAGE INTENTIONALLY BLANK.
                      SIGNATURES FOUND ON FOLLOWING PAGES.]


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 9

<PAGE>   10



         IN WITNESS WHEREOF, this Amendment is executed effective as of the date
first written above.

                                  BORROWER:

                                  MONARCH DENTAL CORPORATION,
                                  a Delaware corporation


                                  By:
                                  Name:
                                  Title:


                                  ADMINISTRATIVE AGENT:

                                  BANK OF AMERICA, N.A., a national
                                  banking association, as Administrative Agent


                                  By:
                                  Name:
                                  Title:


                                  LENDERS:

                                  BANK OF AMERICA, N.A., a national banking
                                  association,



                                  By:
                                  Name:
                                  Title:


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 10


<PAGE>   11



                                  FLEET NATIONAL BANK,
                                  a national banking association


                                  By:
                                  Name:
                                  Title:

                                  COOPERATIEVE CENTRALE RAIFFEISEN-
                                  BOERENLEENBANK B.A., "Rabobank Nederland",
                                  New York Branch


                                  By:
                                  Name:
                                  Title:


                                  By:
                                  Name:
                                  Title:


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 11


<PAGE>   12



         CONSENT OF GUARANTORS


Each Guarantor hereby (a) acknowledges its consent to this Agreement and the
changes to the Credit Facility effected hereby, (b) ratifies and confirms all
terms and provisions of its respective Guaranty and the security instruments
relating to the Collateral , (c) agrees that such Guaranty and security
instruments are and shall remain in full force and effect, (d) acknowledges that
there are no claims or offsets against, or defenses or counterclaims to, the
terms and provisions of and the obligations created and evidenced by such
Guaranty or security instruments, (e) reaffirms all agreements and obligations
under such Guaranty and such security instruments with respect to the Credit
Facility, the Notes, this Agreement and all other documents, instruments or
agreements governing, securing or pertaining to the Credit Facility, as the same
may be modified by this Agreement, (f) and acknowledges that the Obligations
described in this Agreement are the guaranteed obligations under such Guaranty
and are the obligations secured by such security instruments and (g) represents
and warrants that all requisite corporate or partnership action necessary for it
to execute this Agreement has been taken.

         EXECUTED as of the 30th day of December, 1999.

                           GUARANTORS:

                           Managed Dental Care Centers, Inc., a Texas
                           corporation
                           Monarch Dental Associates (Arkansas), Inc., an
                           Arkansas corporation (f/k/a United Dental Care, Inc.)
                           Dental Care One (Monarch), Inc., an Ohio corporation
                           Midwest Dental Management, Inc., a Wisconsin
                           corporation
                           Dental Centers of Indiana (Monarch), Inc., an Indiana
                           corporation;
                           Midwest Dental Care, Mondovi, Inc., a Wisconsin
                           corporation;
                           Midwest Dental Care, Sheboygan, Inc., a Wisconsin
                           corporation;
                           Monarch Dental Management, Inc., a Texas corporation;
                           Three Peaks Dental Management, Inc., a Colorado
                           corporation;
                           Monarch Dental Associates (Utah), Inc., a Utah
                           corporation




                           By:
                               -------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


                           MacGregor Dental Associates, L.P., a Texas limited
                           partnership

                           By:      Monarch Dental Management, Inc., a Texas
                                    corporation, its general partner


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 12

<PAGE>   13



                           Monarch Dental Associates, L.P., a Texas limited
                           partnership

                           By:      Monarch Dental Management, Inc., a Texas
                                    corporation, its general partner


                           By:
                               -------------------------------------------------
                           Name:
                                 -----------------------------------------------
                           Title:
                                  ----------------------------------------------

                           Monarch Dental (Press) Associates, L.P., a Texas
                           limited partnership

                           By:      Monarch Dental Management, Inc., a Texas
                                    corporation, its general partner


                           By:
                               -------------------------------------------------
                           Name:
                                 -----------------------------------------------
                           Title:
                                  ----------------------------------------------

                           Monarch Dental Associates (Midland/Odessa), L.P., a
                           Texas limited partnership

                           By:      Monarch Dental Management, Inc., a Texas
                                    corporation, its general partner


                           By:
                               -------------------------------------------------
                           Name:
                                 -----------------------------------------------
                           Title:
                                  ----------------------------------------------


                           Monarch Dental Associates (Abilene), L.P., a Texas
                           limited partnership

                           By:      Monarch Dental Management, Inc., a Texas
                                    corporation, its general partner


                           By:
                               -------------------------------------------------
                           Name:
                                 -----------------------------------------------
                           Title:
                                  ----------------------------------------------


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 13


<PAGE>   14



                           Monarch Dental Associates (Arizona), L.L.C.,  an
                           Arizona limited liability company

                           By:      Monarch Dental Associates (Utah), Inc., a
                                    Utah corporation, its manager


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------


                           Partners Dental Corporation, a Delaware corporation


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------


                           Valley Forge Dental Associates, Inc.,
                           a Delaware corporation


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------

                           VFD of Pennsylvania, Inc.,
                           a Delaware corporation


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------

                           Horizon Group International, Inc.,
                           an Ohio corporation


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 14


<PAGE>   15



                           Precise Dental Lab, Inc.,
                           an Ohio corporation

                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------

                           VFD of Georgia, Inc.,
                           a Delaware corporation


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------

                           VFD of Pittsburgh, Inc.,
                           a Pennsylvania corporation


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------

                           Pro Dent, Inc.,
                           a Pennsylvania corporation


                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------


                           VFD Realty, Inc.,
                           a Delaware corporation

                           By:
                              -------------------------------------------------
                           Name:
                                -----------------------------------------------
                           Title:
                                 ----------------------------------------------


FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental)         Page 15



<PAGE>   16



                                                                               1


                                   Schedule II
<TABLE>
<CAPTION>

====================================================================================================================
         If Borrower's Consolidated              Base Rate           LIBOR          Letter of          Unused
        Funded Debt to Consolidated               Spread             Margin         Credit Fee           Fee
               EBITDA Ratio is:                                                     Percentage
<S>                                              <C>               <C>              <C>               <C>
 Greater than or equal to 3.50 to 1.00, but        2.10%             4.10%            2.00%             0.50%
           less than 4.00 to 1.00
 Greater than or equal to 3.00 to 1.00, but        1.50%             3.70%            2.00%             0.50%
           less than 3.50 to 1.00
 Greater than or equal to 2.50 to 1.00, but        1.00%             3.30%            2.00%            0.375%
           less than 3.00 to 1.00
 Greater than or equal to 2.00 to 1.00, but        1.00%             2.90%            2.00%            0.375%
           less than 2.50 to 1.00
 Less than 2.00 to 1.00                            0.50%             2.50%            2.00%             0.25%
====================================================================================================================
</TABLE>

FIRST AMENDMENT TO SECOND AMENDED
AND RESTATED LOAN AGREEMENT (Monarch Dental) Page 1