<PAGE>   1
EXHIBIT 10.26                                                        [EXECUTION]


                       THIRD AMENDMENT TO CREDIT AGREEMENT


         THIS THIRD AMENDMENT TO CREDIT AGREEMENT (herein called this
"Amendment") made as of June 1, 2000 by and among Pentegra Dental Group, Inc., a
Delaware corporation (herein called "Borrower"), and Bank One, Texas, N.A.,
individually and as Agent (herein called "Agent"), and the Lenders, including
Agent, party to the Original Agreement ("Lenders"), defined below.

                              W I T N E S S E T H:

         WHEREAS, Borrower, Agent and Lenders have entered into that certain
Credit Agreement dated as of June 1, 1998 (as amended, supplemented, or restated
to the date hereof, the "Original Agreement"), for the purposes and
consideration therein expressed, pursuant to which Lenders became obligated to
make loans to Borrower as therein provided; and

         WHEREAS, Borrower and Lenders desire to amend the Original Agreement to
modify certain terms and provisions thereof;

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein and in the Original Agreement, in
consideration of the loans which may hereafter be made by Lender to Borrower,
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto do hereby agree as follows:


                                   ARTICLE I.

                           Definitions and References

         Section 1.1. Terms Defined in the Original Agreement. Unless the
context otherwise requires or unless otherwise expressly defined herein, the
terms defined in the Original Agreement shall have the same meanings whenever
used in this Amendment.

         Section 1.2. Other Defined Terms. Unless the context otherwise
requires, the following terms when used in this Amendment shall have the
meanings assigned to them in this Section 1.2.

         "Amendment" means this Third Amendment to Credit Agreement.

         "Credit Agreement" means the Original Agreement as amended hereby.

<PAGE>   2

                                   ARTICLE II.

                        Amendments to Original Agreement

         Section 2.1. Defined Terms. (a) The following defined terms in Section
1.1. of the Original Agreement are hereby amended in their entirety to read as
follows:

                      " 'Commitment' means the amount of $10,100,000, as from
         time to time reduced by Borrower pursuant to Section 2.2."

                      " 'Eurodollar Margin' means:

                         (i) with respect to Eurodollar Loan 1 for each day
         during any Fiscal Quarter on or before September 30, 2000, the
         Eurodollar Margin shall be 2.5% per annum;

                         (ii) with respect to Eurodollar Loan 1 for each day
         during any Fiscal Quarter on or after October 1, 2000, the Eurodollar
         Margin shall be 3.0% per annum; and

                         (iii) with respect to Eurodollar Loan 2 for each day
         during any Fiscal Quarter, the Eurodollar Margin shall be 4.5% per
         annum.

                         " 'Maturity Date' means July 31, 2001."

                         " 'Permitted Investments' means Investments in:

                         (a) marketable obligations, maturing within 12 months
         after acquisition thereof, issued or unconditionally guaranteed by the
         United States of America or an instrumentality or agency thereof and
         entitled to the full faith and credit of the United States of America.

                         (b) demand deposits, and time deposits (including
         certificates of deposit) maturing within 12 months from the date of
         deposit thereof, with any office of any Lender or with a domestic
         office of any national or state bank or trust company which is
         organized under the Laws of the United States of America or any state
         therein, which has capital, surplus and undivided profits of at least
         $500,000,000, and whose certificates of deposit have at least the third
         highest credit rating given by either Rating Agency.

                         (c) repurchase obligations with a term of not more than
         seven days for underlying securities of the types described in clause
         (a) above entered into with any commercial bank meeting the
         specifications of clause (b) above

                         (d) open market commercial paper, maturing within 270
         days after acquisition thereof, which has the highest or second highest
         credit rating given by either Rating Agency.


                                       2
<PAGE>   3
                         (e) investments in money market or other mutual funds
         substantially all of whose assets comprise securities of the types
         described in clauses (a) through (d) above.

                         (f) investments in acquisitions of any Person, provided
         that (i) the consideration for any such acquisition shall consist
         solely of common stock of Borrower and capital securities of the Person
         so acquired, (ii) after giving effect to such acquisition, the Person
         so acquired shall not be liable for any Indebtedness, (iii) Borrower
         shall neither assume nor in any way become obligated or liable for any
         additional Indebtedness relating to or resulting from any such
         acquisition, and (iv) Borrower shall neither expend or pay any of
         Borrower's Cash and Cash Equivalents in connection with any such
         acquisition.

                         (g) credit extensions permitted by Section 7.8."

                         " 'Prime Rate' means

                         (a) with respect to Eurodollar Loan 1, on or before
         September 30, 2000, the base commercial rate of interest as announced
         from time to time by Agent (which may not be the lowest, best or most
         favorable rate of interest which Agent may charge on loans to its
         customers), and

                         (b) with respect to Eurodollar Loan 1, on or after
         October 1, 2000, the per annum rate of interest .50% above the base
         commercial rate of interest as announced from time to time by Agent
         (which may not be the lowest, best or most favorable rate of interest
         which Agent may charge on loans to its customers), and

                         (c) with respect to Eurodollar Loan 2, the per annum
         rate of interest 2.00% above the base commercial rate of interest as
         announced from time to time by Agent (which may not be the lowest, best
         or most favorable rate of interest which Agent may charge on loans to
         its customers)."

         (b)             The following new defined terms are hereby added to
                         Section 1.1. of the Original Agreement in appropriate
                         alphabetical order:

                         " 'Cash and Cash Equivalents' means all of Borrower's
         demand deposits and time deposits (including certificates of deposit)
         maturing within 12 months from the date of deposit thereof with Bank
         One, Arizona, N.A., but excluding any such deposits in the Remittance
         Account."

                         " 'Covenant Period' means a six-month period ending on
         March 31 and September 30 of any year."


                         " 'Dental Practice Advances' means all loans or
         advances by Borrower to Dental Practice Groups to provide working
         capital for the operations of Dental Practice Groups

                                       3
<PAGE>   4
         and for other general business purposes, an itemized listing of which
         is attached hereto as Schedule 1."

                  " 'Dental Practice Notes' means all promissory notes executed
         by Dental Practice Groups payable to Borrower to evidence their
         respective obligations to repay Dental Practice Advances, each note
         shall be due and payable in thirty-six (36) equal monthly installments
         over a three (3) year period and bear interest at the per annum rate of
         ten percent (10%) and may not be renewed, extended, or increased by
         Borrower."

                  " 'Dental Practice Payments' means all payments received by
         Borrower in respect of the Dental Practice Notes and all payments
         received from Non-Conforming Dental Practice Groups (as defined in
         Section 6.18) in respect of Dental Practice Advances."

                  " 'Eurodollar Loan No. 1' means the Eurodollar Loan in the
         principal amount of $8,000,000 bearing interest at a rate of 8.78% per
         annum on June 1, 2000 and having an original Interest Period which
         began on June 1, 1998, as continued by successive Interest Periods or
         converted to a Base Rate Loan."

                  " 'Eurodollar Loan No. 2' means the Eurodollar Loan in the
         principal amount of $2,100,000 bearing interest at a rate of 10.78% per
         annum on June 1, 2000 and having an original Interest Period which
         began on April 6, 1999, as continued by successive Interest Periods or
         converted to a Base Rate Loan."

                  " 'Quarterly Note Collections' means, for any Fiscal Quarter,
         the aggregate amount of Dental Practice Payments deposited in the
         Remittance Account and applied by Agent against the Obligations
         pursuant to Section 6.18(b)."

                  " 'Remittance Account' means account number 4848-6521
         established at Bank One, Arizona, N.A. in the name of Borrower, which
         is a restricted account, from which Borrower may not withdraw funds
         except as expressly set forth herein, and which has been pledged to
         Agent."

         Section 2.2. Commitments to Lend; Notes. The last sentence in Section
2.1 of the Original Agreement is hereby amended in its entirety to read as
follows:

         "After June 1, 2000, no new Loans shall be made under this Agreement."

         Section 2.3. Scheduled Principal and Interest Payments. Section 2.7 of
the Original Agreement is hereby amended in its entirety to read as follows:

                  "Section 2.7. Scheduled Principal and Interest Payments. The
         principal amount of the Loans shall be due and payable as follows: (i)
         $250,000 of the principal amount of Eurodollar Loan 2 shall be due and
         payable on or before July 14, 2000, and (ii) the remainder of the
         principal amount of the Loans shall be due and payable in quarterly
         installments (subject to the proviso at

                                       4
<PAGE>   5
         the end of this sentence), each of which shall be equal to the lesser
         of (a) $50,000 and (b) $350,000 minus the Quarterly Note Collections
         and shall be due and payable on the fifteenth day of October, January,
         April and July of each year, beginning October 15, 2000 (the "Quarterly
         Payments"), and continuing regularly thereafter until the Maturity
         Date, on which date all unpaid principal of and accrued interest on the
         Loans shall be due and payable; provided that after giving effect to
         the payment thereof, no Quarterly Payment shall cause the aggregate
         amount of Borrower's Cash and Cash Equivalents as of the last day of
         the Fiscal Quarter immediately preceding the date of such Quarterly
         Payment to be less than the amount of $750,000. Payments of principal
         shall first be applied to Eurodollar Loan 2. In addition to principal
         installments described above, interest shall be due and payable
         quarterly as it accrues on the last day of each September, December,
         March and June of each year, said installments of interest beginning
         June 30, 2000. As soon as available, and in any event within five (5)
         Business Days after the end of each Fiscal Quarter, Borrower will
         deliver to Agent a certificate certifying the amount of Borrower's Cash
         and Cash Equivalents as of the end of such Fiscal Quarter, in form,
         substance, and detail acceptable to Agent."

         Section 2.4. Mandatory Prepayments. Section 2.8(b) of the Original
Agreement is hereby deleted in its entirety.

         Section 2.5. Dental Practice Advances. The Original Agreement is hereby
amended to add Section 6.18 thereto immediately following Section 6.17 thereof
to read as follows:

         "Section 6.18. Dental Practice Advances.

                                       5
<PAGE>   6

                  (a) Prior to June 1, 2000, Borrower has made Dental Practice
         Advances which are not evidenced by promissory notes and which were
         accounted for by Borrower as accounts receivable created in the
         ordinary course of its business. Borrower agrees to require each Dental
         Practice Group to which it has made a Dental Practice Advance to either
         (i) pay in full the principal amount plus all accrued interest in
         respect of such Dental Practice Advance on or before August 31, 2000 or
         (ii) execute and deliver to Borrower a Dental Practice Note
         (collectively, the "Repayment Options"). Borrower will use its best
         efforts to obtain the agreement of each such Dental Practice Group to
         one of the Repayment Options. In the event that any such Dental
         Practice Group does not agree to a Repayment Option (a "Non-Conforming
         Dental Practice Group"), Borrower will develop a plan to pursue
         collection remedies against such Non-Conforming Dental Practice Group
         that is reasonably acceptable to Agent. On or before July 30, 2000,
         Borrower shall deliver to Agent a certificate signed by the chief
         financial officer of Borrower which (i) certifies that Borrower has
         required each Dental Practice Group to which Borrower has made a Dental
         Practice Advance to agree to a Repayment Option, (ii) attaches a
         schedule which lists each Dental Practice Group that has elected to
         execute and deliver a Dental Practice Note, and (iii) attaches a
         schedule which lists each Non-Conforming Dental Practice Group and the
         collection remedies to be pursued by Borrower, all in form, substance
         and detail acceptable to Agent. Borrower hereby agrees (i) to hold all
         Dental Practice Payments received by it in trust for the benefit of
         Agent and to deposit all Dental Practice Payments into the Remittance
         Account weekly on the last Business Day of each week and (ii) at the
         request of Agent, to direct all Dental Practice Groups to which it has
         made a Dental Practice Advance to make all Dental Practice Payments
         directly to the Remittance Account. As soon as available, and in any
         event within thirty (30) days after the end of each month, Borrower
         will deliver to Agent (at Borrower's expense) a certificate (i)
         itemizing the current balance of the Dental Practice Notes and all
         Dental Practice Payments received in respect thereof during such month,
         (ii) providing a current status of the collection efforts relating to
         each Non-Conforming Dental Practice Group, and (iii) providing such
         other information relating to the Dental Practice Advances as may be
         requested by Agent, all in form, substance, and detail acceptable to
         Agent.

                  (b) If no Default or Event of Default has occurred and is
         continuing, on the last Business Day of each week, Borrower hereby
         irrevocably directs Bank One, Arizona, N.A. to transfer all funds on
         deposit in the Remittance Account to Agent, to be applied by Agent as a
         payment (or a prepayment, as applicable) of the Obligations in
         accordance with Section 3.1. If a Default or Event of Default has
         occurred and is continuing, Agent may at any time and from time to time
         direct Bank One, Arizona, N.A. to transfer any funds on deposit in the
         Remittance Account to Agent, to be applied by Agent as a payment (or a
         prepayment, as applicable) of the Obligations in accordance with
         Section 3.1, and Borrower hereby irrevocably directs Bank One, Arizona,
         N.A. to strictly follow any such directions received from Agent. If a
         Default or Event of Default has occurred and is continuing, Agent will
         direct the transfer of funds and apply such funds pursuant to the
         immediately preceding sentence at least once per week. All principal or
         interest
                                      6
<PAGE>   7
         prepaid pursuant to this section shall be in addition to, and not in
         lieu of, all payments otherwise required to be paid under the Loan
         Documents at the time of such prepayment.

                  (c) Borrower hereby agrees to deliver all Dental Practice
         Notes to Agent on July 31, 2000, August 31, 2000 and thereafter
         promptly upon its receipt thereof in accordance with the requirements
         of the Security Documents. All such Dental Practice Notes shall be
         delivered in suitable form for transfer by delivery with any necessary
         endorsement or shall be accompanied by fully executed instruments of
         transfer or assignment in blank, all in form and substance satisfactory
         to Agent."

         Section 2.6. Indebtedness. Section 7.1 of the Original Agreement is
hereby amended in its entirety to read as follows:

                       "Section 7.1. Indebtedness. No Restricted Person will in
         any manner owe or be liable for Indebtedness except:

                  (i)      the Obligations.

                  (ii)     Subordinated Debt.

                  (iii) Indebtedness outstanding under the instruments and
         agreements described on the Disclosure Schedule, excluding any renewals
         or extensions of such Indebtedness.
                  (iv) purchase money Indebtedness or other acquired or assumed
         Indebtedness in connection with Dental Practice Acquisitions
         consummated on or before June 1, 2000 in an aggregate principal amount
         not to exceed the amount of such Indebtedness outstanding as of June 1,
         2000, excluding any renewals or extensions of such Indebtedness."

         Section 2.7. Limitation on Investments and New Businesses. Section 7.7
of the Original Agreement is hereby amended in its entirety to read as follows:

                       "Section 7.7. Limitation on Investments and New
         Businesses. No Restricted Person will (i) make any expenditure or
         commitment or incur any obligation or enter into or engage in any
         transaction except in the ordinary course of business, (ii) engage
         directly or indirectly in any business or conduct any operations except
         in connection with or incidental to its present businesses and
         operations, or (iii) make any acquisitions of or capital contributions
         to or other investments in any Person, other than Permitted Investments
         and Dental Practice Advances existing as of June 1, 2000 (which Dental
         Practice Advances may not be renewed, extended, or increased)."

         Section 2.8. Limitation on Investments and New Businesses. Section 7.9
of the Original Agreement is hereby amended in its entirety to read as follows:

                       "Section 7.9. Transactions with Affiliates. No Restricted
         Person will engage in any material transaction with any of its
         Affiliates on terms which are less favorable to it

                                       7
<PAGE>   8
         than those which would have been obtainable at the time in arm's-length
         dealing with Persons other than such Affiliates, provided that Borrower
         shall not extend credit or make any advances or loans to any
         Subsidiary, any Affiliate, or any Dental Practice Group."

         Section 2.9. Dental Base. Section 7.11 of the Original Agreement is
hereby deleted in its entirety.

         Section 2.10. Continuity of Founding Practices and Affiliated
Practices. Section 7.12 of the Original Agreement is hereby deleted in its
entirety.

         Section 2.11. Capital Expenditures. Section 7.13 of the Original
Agreement is hereby deleted in its entirety.

         Section 2.12. Current Ratio. Section 7.14 of the Original Agreement is
hereby amended in its entirety to read as follows:

                    "Section 7.14. Current Ratio. As of the end of each Covenant
         Period, the ratio of Borrower's Consolidated current assets to
         Borrower's Consolidated current liabilities (excluding any current
         liabilities from litigation, the Obligations and any other
         non-operational, non-recurring charge), all determined in accordance
         with GAAP, shall not be less than 1.0 to 1.0."

         Section 2.13. Total Funded Debt to Capitalization Ratio. Section 7.15
of the Original Agreement is hereby deleted in its entirety.

         Section 2.14. Total Funded Debt to EBITDA Ratio. Section 7.16 of the
Original Agreement is hereby deleted in its entirety.

         Section 2.15. Total Senior Funded Debt to EBITDA Ratio. Section 7.17 of
the Original Agreement is hereby deleted in its entirety.

         Section 2.16. Fixed Charge Ratio. Section 7.18 of the Original
Agreement is hereby deleted in its entirety.

         Section 2.17. Debt Service Coverage Ratio. Section 7.19 of the Original
Agreement is hereby amended in its entirety to read as follows:

                    "Section 7.19. Debt Service Coverage Ratio. As of the end of
       each Covenant Period, the ratio of (a) Borrower's EBITDA for the two
       consecutive Fiscal Quarters then ended, multiplied by two, to (b)
       scheduled principal payments on all other Indebtedness (excluding the
       Obligations) due during the next four Fiscal Quarters, shall not be less
       than 1.50 to 1.0."



                                       8
<PAGE>   9

         Section 2.18. Net Worth. Section 7.20 of the Original Agreement is
hereby amended in its entirety to read as follows:

                    "Section 7.20. Net Worth. Borrower's Consolidated Net Worth
         as of the end of each Fiscal Quarter, shall not be less than $0.00;
         provided that Borrower's Consolidated Net Worth shall be automatically
         increased to reflect non-cash items (including adjustments for
         impairment of goodwill, bad debt reserves, accrual adjustments,
         depreciation, amortization, or other one-time non-cash items) on
         Borrower's Consolidated financial statements."

         Section 2.19. Dental Practice Acquisitions & Dental Practice Advances.
Section 7.21 of the Original Agreement is hereby amended in its entirety to read
as follows:

                       "Section 7.21. Dental Practice Acquisitions & Dental
         Practice Advances. Borrower shall not make any Dental Practice
         Acquisition or make any Dental Practice Advances from and after June 1,
         2000."

         Section 2.20. Bank Accounts. The Original Agreement is hereby amended
to add Section 7.22 thereto immediately following Section 7.21 thereof read as
follows:

                       "Section 7.21. Bank Accounts. Borrower shall not
         establish any demand, time, savings, passbook, or similar account or
         certificate of deposit at any bank or other depository or financial
         institution other than Bank One, Arizona, N.A."


                                   ARTICLE III

                            Fees and Other Agreements

         Section 3.1. No Optional Conversion to Base Rate Loans. After June 1,
2000, Borrower shall not have the option to convert Eurodollar Loan No.1 or
Eurodollar Loan No. 2 to a Base Rate Loan; provided, however, that Eurodollar
Loan No.1 and/or Eurodollar Loan No. 2 may be converted to Base Rate Loans by
Agent pursuant to Sections 3.2 through 3.5.

         Section 3.2. Amendment Fee. In consideration of Agent and each Lenders'
agreement to enter into this Amendment, Borrower will pay to Agent for the
account of Lenders an amendment fee in the aggregate amount of $20,000 (the
"Amendment Fee"), which shall be due and payable on the date of effectiveness of
this Amendment.

         Section 3.3. Additional Security. Pursuant to Section 6.15 of the
Credit Agreement, Lender hereby requests and Borrower hereby agrees to grant
security interests in additional collateral to further secure the Obligations
and to modify existing Security Documents on or before July 31, 2000, each in
form and substance satisfactory to Agent, in order to effect the following:


                                       9
<PAGE>   10
         (a) to grant new liens in all of Borrower's inventory and equipment,
including that inventory and equipment used in all Dental Practice Groups, and
in any of Borrower's other personal property;

         (b) to grant new liens in all of Borrower's stock or other equity
interests in any Dental Practice Groups;

         (c) to modify existing Security Documents to confirm that all right,
title and interest of Borrower in and to all management service agreements and
receivables of the Dental Practice Groups which secure such management service
agreements are covered by the Security Documents;

         (d) to obtain security agreements covering the accounts receivable of
each Dental Practice Group acquired as part of a Dental Practice Acquisition,
and assigning each such agreement to Agent for the benefit of Lenders; and

         (e) to execute and file all necessary UCC-1 and UCC-3 financing
statements covering all additional collateral above and reflecting Borrower's
name change to e-dentist.com upon the occurrence of such change.

         Section 3.4. Waiver of Financial Covenants. In connection with
Borrower's creation of an additional reserve for bad debts totaling $4,200,000,
on Borrower's financial statements as of March 31, 2000 (collectively, the
"Financial Statement Changes"), Agent (on behalf of Lenders) hereby waives any
Default or Event of Default resulting from any violations of Sections 7.14,
7.15, 7.16, 7.17, and 7.19 of the Credit Agreement as of March 31, 2000.


                                   ARTICLE IV.

                           Conditions of Effectiveness

         Section 4.1. Effective Date. This Amendment shall become effective as
of the date first above written when and only when:

             (a) Agent shall have received all of the following, at Agent's
office, duly executed and delivered and in form and substance satisfactory to
Agent, all of the following:

                (i)   this Amendment;

                (ii)  a Consent of Guarantor in the form attached hereto;

                (iii) a certificate of the President and Secretary of Borrower
                      dated the date of this Amendment certifying as to certain
                      corporate matters and that all of the representations and
                      warranties set forth in Article IV hereof are true and
                      correct at and as of the time of such effectiveness;

                                       10
<PAGE>   11
                (iv)  the Amendment Fee described in Section 3.1;

                (v)   a First Amendment to Security Agreement dated the date of
                      this Amendment;

                (vi)  UCC-1 financing statements naming Borrower, as debtor, and
                      Agent, as secured party, covering the Remittance Account,
                      to be filed with the Secretary of State of Arizona and the
                      Secretary of State of Texas;

                (vii) an Acknowledgment Agreement among Borrower, Agent, and
                      Bank One, Arizona, N.A.;

                (viii) such other supporting documents as Agent may reasonably
                      request;

         (b) Borrower shall have paid, in connection with such Loan Documents,
all recording, handling, amendment and other fees required to be paid to Agent
pursuant to any Loan Documents; and

         (c) Borrower shall have paid, in connection with such Loan Documents,
all other fees and reimbursements to be paid to Agent pursuant to any Loan
Documents, or otherwise due Agent and including fees and disbursements of
Agent's attorneys.


                                   ARTICLE V.

                         Representations and Warranties

                Section 5.1. Representations and Warranties of Borrower. In
order to induce Agent to enter into this Amendment, Borrower represents and
warrants to Agent that:

                             (a) The representations and warranties contained in
                Article V of the Original Agreement, are true and correct at and
                as of the time of the effectiveness hereof except to the extent
                that the facts upon which such representations are based have
                been changed by transactions and events expressly permitted by
                the Credit Agreement.

                             (b) Borrower is duly authorized to execute and
                deliver this Amendment and will continue to be duly authorized
                to borrow and to perform its obligations under the Credit
                Agreement. Borrower has duly taken all corporate action
                necessary to authorize the execution and delivery of this
                Amendment and to authorize the performance of its obligations
                hereunder and thereunder.

                             (c) The execution and delivery by Borrower of this
                Amendment, the performance by Borrower of its obligations
                hereunder and the consummation of the transactions contemplated
                hereby do not and will not conflict with any provision of law,
                statute, rule or any of its organizational documents, or of any
                material agreement,


                                       11
<PAGE>   12
                judgment, license, order or permit applicable to or binding upon
                it, or result in the creation of any lien, charge or encumbrance
                upon any assets or properties or any of its assets. Except for
                those which have been duly obtained, no consent, approval,
                authorization or order of any court or governmental authority or
                third party is required in connection with the execution and
                delivery by Borrower of this Amendment or to consummate the
                transactions contemplated hereby.

                             (d) When duly executed and delivered, each of this
                Amendment and the Credit Agreement will be a legal and binding
                obligation of Borrower, enforceable in accordance with its
                terms, except as limited by bankruptcy, insolvency and similar
                laws applying to creditors' rights generally and by principles
                of equity applying to creditors' rights generally.

                             (e) The audited annual Consolidated financial
                statements of Borrower dated as of March 31, 1999 and the
                unaudited quarterly Consolidated financial statements of
                Borrower dated as of December 31, 1999 fairly present the
                Consolidated financial position at such dates and the
                Consolidated statement of operations and the changes in
                Consolidated financial position for the periods ending on such
                dates for Borrower. Copies of such financial statements have
                heretofore been delivered to each Lender. Since such dates no
                Material Adverse Change has occurred in the financial condition
                or businesses or in the Consolidated financial condition or
                businesses of Borrower.

                             (f) Attached hereto as Schedule 1 is a true,
                correct, and complete list of each Dental Practice Advance made
                by Borrower on or prior to the date hereof which has not been
                repaid in full.


                                   ARTICLE VI.

                                  Miscellaneous

         Section 6.1. Ratification of Agreements. The Original Agreement as
hereby amended is hereby ratified and confirmed in all respects. The Loan
Documents, as they may be amended or affected by this Amendment are hereby
ratified and confirmed in all respects. Any reference to the Credit Agreement in
any Loan Document shall be deemed to refer to this Amendment also. The
execution, delivery and effectiveness of this Amendment shall not, except as
expressly provided herein, operate as a waiver of any right, power or remedy of
Agent under the Credit Agreement or any other Loan Document nor constitute a
waiver of any provision of the Credit Agreement or any other Loan Document.

         Section 6.2. Survival of Agreements. All representations, warranties,
covenants and agreements of Borrower herein shall survive the execution and
delivery of this Amendment and the performance hereof, including without
limitation the making or granting of the Loan, and shall further survive until
all of the Obligations are paid in full. All statements and agreements contained
in any certificate or instrument delivered by Guarantor or Borrower hereunder or
under

                                       12
<PAGE>   13
the Credit Agreement to Agent shall be deemed to constitute representations and
warranties by, or agreements and covenants of, such Person under this Amendment
and under the Credit Agreement.

         Section 6.3. Release of Claims. Borrower hereby releases and forever
discharges Agent, together with its employees, agents, attorneys, officers, and
directors (all of the foregoing hereinafter called the "Released Parties"), from
any and all actions and causes of action, judgments, executions, suits, debts,
claims, demands, liabilities, obligations, damages and expenses of any and every
character, known or unknown, direct and/or indirect, at law or in equity, of
whatsoever kind or nature, whether heretofore or hereafter accruing, for or
because of any matter or things done, omitted or suffered to be done by any of
the Released Parties prior to and including the date hereof, and in any way
directly or indirectly arising out of or in any way connected to the Original
Agreement, including but not limited to claims of usury (although no such claims
are known to exist) (all of the foregoing hereinafter called the "Released
Matters"). Borrower acknowledges that the agreements in this Section 5.3 are
intended to cover and be in full satisfaction for all or any alleged injuries or
damages arising in connection with the Released Matters herein compromised and
settled.

         Section 6.4. Loan Documents. This Amendment is a Loan Document, and all
provisions in the Credit Agreement pertaining to Loan Documents apply hereto and
thereto.

         Section 6.5. Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of Texas and any applicable
laws of the United States of America in all respects, including construction,
validity and performance.

         Section 6.6. Counterparts; fax. This Amendment may be separately
executed in counterparts and by the different parties hereto in separate
counterparts, each of which when so executed shall be deemed to constitute one
and the same Amendment. This Amendment may be validly executed by facsimile or
other electronic transmission.

         THIS AMENDMENT AND THE OTHER LOAN DOCUMENTS 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 OF THE PARTIES.


            [THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]



                                       13
<PAGE>   14
         IN WITNESS WHEREOF, this Amendment is executed as of the date first
above written.


                                    PENTEGRA DENTAL GROUP, INC.
                                    Borrower


                                    By: _________________________________
                                           James M. Powers, Jr.
                                           President & Chief Executive Officer



                                    BANK ONE, TEXAS, N.A.
                                    Agent and Lender


                                    By: _________________________________
                                           Bonnie D. Wilson
                                           Vice President
<PAGE>   15


                                                                      SCHEDULE 1

                            DENTAL PRACTICE ADVANCES



<PAGE>   16



                                                               [THIRD AMENDMENT]

                              CONSENT AND AGREEMENT

         Pentegra Investments, Inc., a Delaware corporation, hereby (i) consents
to the provisions of this Amendment and the transactions contemplated herein and
(ii) ratifies and confirms the Guaranty dated as of June 1, 1998 made by it for
the benefit of Bank One Texas, N.A. and any other Lenders that become parties to
the Credit Agreement ("Guaranty") and (iii) agrees that all of its respective
obligations and covenants thereunder (to the extent it is a party thereto) shall
remain unimpaired by the execution and delivery of the Amendment and the other
documents and instruments executed in connection therewith and that the Guaranty
shall remain in full force and effect.

         THIS CONSENT AND AGREEMENT AND THE OTHER LOAN DOCUMENTS 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 OF THE PARTIES.

         IN WITNESS WHEREOF, this Consent and Agreement is executed by the
undersigned and is made effective as of June 1, 2000.



                                           PENTEGRA INVESTMENTS, INC.




                                           By: ________________________________
                                               Sam H. Carr
                                               Senior Vice President