<PAGE>   1
                                                                EXHIBIT 10.48

                                   AMENDMENT
                                       TO
                              EMPLOYMENT AGREEMENT



         This Amendment to Employment Agreement ("Amendment") is made as of the
1st day of June, 1996 by and among Gary A. Lockwood (the "Employee"), Mason
Dental Midwest, Inc., a Michigan corporation (the "Company"), and Princeton
Dental Management Corporation, a Delaware corporation ("Princeton"). The
Employee, the Company and Princeton are herein collectively referred to as the
"Parties".

                                    RECITALS

         A. The Parties have previously entered into that certain Employment
Agreement dated December 31, 1993 (the "Employment Agreement").

         B. The Parties desire to amend the Employment Agreement to reflect
certain agreements among the Parties.

                                   AGREEMENTS

         NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Parties hereto agree as
follows:

                 1. Unless otherwise defined herein, all capitalized terms used
herein which are defined in the Employment Agreement shall have the meanings
assigned to them in the Employment Agreement.

                 2. The Employment Agreement is amended as follows:

                          A. Term of Agreement. Section 1 of the Employment
Agreement is deleted in its entirety and replaced by the following:

         " 1.    Term of Agreement. Subject to the terms and conditions hereof,
this Agreement shall commence as of January 1, 1994 and shall continue in
effect until May 30, 2001."


                          B. Compensation. Subsections (i), (ii) and (iv) of
Section 3 are deleted in their entirety and replaced by the following:

         " 3.    Compensation.  (i) Base Salary. As compensation for Employee's
services under this Agreement, Employee shall be entitled to receive a base
salary of $97,000.00 per
<PAGE>   2

annum, to be paid in accordance with the current payroll practices of the
Company. Effective June 1, 1996, Employee's base salary shall be increased to
$106,150.18 [BASED ON CPI INCREASES OF 2.6% IN '94, 2.8% IN '95, 1.8% FOR THE
FIRST FIVE MONTHS OF '96 AND $2,000 FOR PAYMENT OF WHOLE LIFE PREMIUMS.]
Beginning January 1, 1997, Employee shall be entitled to annual increases in
such base salary equal to the average annual increase in the Consumer Price
Index [INSERT SPECIFIC CPI INDICATOR],  as determined by the United States
Department of Labor; provided, however, that any such increase for 1997 shall
be pro-rated to account for the fact that Employee has, effective June 1, 1996,
been granted such an increase through May 31, 1996.

                 (ii) Bonuses and Stock Options. The Company may, at its sole
discretion, pay Employee an annual performance award ("Annual Performance
Award") during each year of the Term as determined by the Board of Directors at
its sole and exclusive discretion from time to time. As of the date hereof,
Princeton has also agreed to grant Employee a stock option as set forth on
Exhibit A. Effective June 1, 1996, the Employee shall also be entitled to
receive, pursuant to the provisions of Princeton's 1993 Incentive and
Non-Statutory Stock Option Plan, options to purchase up to 50,000 shares of
Princeton common stock as set forth on Exhibit B attached hereto and
incorporated herein.

                 (iv) Reimbursement of Expenses. In addition to compensation,
Employee shall be entitled to reimbursement of ordinary and necessary
out-of-pocket trade or business expenses reasonably incurred in the ordinary
course of employment duties and paid by Employee on behalf of the Company. Such
reimbursement shall not constitute compensation. Reimbursement shall be made
following submission by the Employee to the Company of such vouchers as may be
reasonably satisfactory to the Company and as may be in compliance with
Internal Revenue Service guidelines, rulings and requirements regarding valid
business expenses. Princeton shall acquire for Employee a credit card having a
$10,000.00 credit limit, which credit card Employee shall use for Company and
Princeton business purposes only, and not for any other use whatsoever. All
expenses charged to such credit card must be in compliance with nternal
Revenue Service guidelines, rulings and requirements regarding valid business
expenses. If Employee breaches this Agreement and uses a Company credit card
for personal use then the Company shall have the right to withhold such amount
from the Employee's paycheck as an offset. Notwithstanding anything contained
in this Section 3(iv) to the contrary, Employee shall be required to submit a
written budget on a monthly basis of anticipated expenses to the Board of
Directors of Princeton for its approval and Employee shall adhere to such
approved budget.

         C. Termination of Employment. Section 4 of the Employment Agreement is
deleted in its entirety and replaced by the following:

         " 4.    Termination of Employment.  This Agreement may be terminated
by either the Employee, the Company or Princeton upon ninety (90) days written
notice."





                                      -2-
<PAGE>   3


         D. Compensation Upon Termination or During Disability. Section 5 of
the Employment Agreement is deleted in its entirety and replaced by the
following:

         " 5.    Compensation Upon Termination or During Disability. Upon
termination of Employee's employment with the Company for any reason other than
for cause, Employee shall be entitled to receive a severance allowance equal to
ninety (90) days of Employee's base compensation, payable in accordance with
the payroll practices of the Company."

         E. Chief Operating Officer. The following new Section 16 is added to
the Employment Agreement:

         " 16.   Chief Operating Officer. Notwithstanding anything in this
Agreement to the contrary, effective June 1, 1996, the Employee is appointed as
the Chief Operating Officer of Princeton, with such duties and responsibilities
as are customary with respect to such position and as may be determined by the
Board of Directors of Princeton. As full compensation for Employee's fulfilling
the duties of Chief Operating Officer, in addition to any other compensation
provided for in this Agreement, Employee shall receive the sum of $12,000.00
per annum, to be paid in accordance with the current payroll practices of
Princeton. Effective June 1, 1996, the Employee shall also be entitled to
receive, pursuant to the provisions of Princeton's 1993 Incentive and
Non-Statutory Stock Option Plan, options to purchase up to 50,000 shares of
Princeton common stock as set forth on Exhibit C attached hereto and
incorporated herein." [YOU INDICATED YOU ARE CONSIDERING A MORE AGGRESSIVE,
PERFORMANCE-BASED, OPTION PROGRAM, BUT WE HAVE NOT YET DISCUSSED WHAT THAT
MIGHT BE.]

         Except as specifically amended by this Amendment, the Employment
Agreement shall remain in full force and effect.


                            END OF TEXT ON THIS PAGE





                                      -3-
<PAGE>   4

         IN WITNESS WHEREOF, the parties have executed this Amendment to
Employment Agreement as of the date first written above.


PRINCETON DENTAL MANAGEMENT CORPORATION



By:
   -----------------------------------
Printed Name:
             -------------------------
Its:
    ----------------------------------

MASON DENTAL MIDWEST, INC.



By:
   -----------------------------------

Printed Name:
             -------------------------

Its:
    ----------------------------------




----------------------------------
Gary A. Lockwood, individually





                                      -4-
<PAGE>   5

                                   EXHIBIT B

                             STOCK OPTION AGREEMENT

         This Stock Option Agreement ("Agreement") is made this 1st day of
June, 1996 by and among Princeton Dental Management Corporation, a Delaware
corporation (the "Company"), and Gary A. Lockwood, an employee of the Company
or a subsidiary thereof (the "Employee").

         The Company and the Employee agree as follows:

         1. 1993 Incentive and Non-Statutory Stock Option Plan. This Agreement,
executed on behalf of the Company by its President, evidences the grant of an
Incentive Stock Option to purchase Common Stock of the Company (the "Option")
for services anticipated to be rendered by Employee. The Option is subject in
its entirety to the terms and conditions of the Princeton Dental Management
Corporation 1993 Incentive and Non-Statutory Stock Option Plan (the "Plan")
adopted by the Board of Directors June 3, 1993 and approved by the Shareholders
on July 12, 1993.  A copy of the Plan is annexed to this Agreement.

         2. Date of Grant. The date of the grant of the Option is June 1, 1996.

         3. Number and Price of Shares. The total number of shares granted is
50,000. The purchase price per share shall be the average Company trading price
based on the trading days contained in the 61 day period beginning on June 1,
1996 and running through July 31, 1996.

         4. Option Period and Time of Exercise. The number of shares specified
in Paragraph 3 above are divided into four parts which may be exercisable
within the Option period as follows:

<TABLE>
<CAPTION>
Part     No. of Shares    Date Exercisable         Expiration Date
----     -------------    ----------------         ---------------
<S>      <C>                      <C>              <C>
1        15,000                   1/1/97           1/1/2003
2        15,000                   1/1/98           1/1/2003
3        10,000                   1/1/99           1/1/2003
4        10,000                   1/1/2000         1/1/2003
</TABLE>


         (i) The Board may, in its sole discretion, cancel Options granted to
the Employee if the employment of Employee is terminated for cause. Upon the
termination of employment other than for cause, Options granted under the Plan
shall be cancelled only to the extent that such Options were not exercisable as
of the date of such termination.





                                      -5-
<PAGE>   6

         (ii) In no event shall the Options be exercisable after the expiration
date of the Option period.

         5. Manner of Exercise. Subject to the conditions and restrictions
contained in the Plan and Paragraph 6 below, the Options shall be exercised by
delivering written notice of exercise to the Secretary of the Company.

         6. Non-Transferability. This Agreement and Option granted may not be
assigned or transferred by the Employee except as provided in the Plan.

         7. Amendment. Neither this Agreement or the Option may be amended or
modified or revoked except by agreement in writing and signed by the Company
and the Employee.

         8. Interpretation. The Board has the sole power to interpret the Plan
and to resolve any questions arising under the Plan or this Agreement.

         9. Entire Agreement. Except as specifically referenced in Employee's
Employment Agreement, this Agreement constitutes the entire agreement under the
Plan between the Company and the Employee and supersedes all other agreements
under the Plan heretofore entered into.

         IN WITNESS WHEREOF, the Company and the Employee have executed this
Agreement as of the 1st day of June, 1996.


PRINCETON DENTAL MANAGEMENT CORPORATION



By:
   -----------------------------------

Printed Name:
             -------------------------

Its:
    ----------------------------------




----------------------------------
Gary A. Lockwood, individually






                                      -6-
<PAGE>   7

                                   EXHIBIT C

                             STOCK OPTION AGREEMENT

         This Stock Option Agreement ("Agreement") is made this 1st day of
June, 1996 by and among Princeton Dental Management Corporation, a Delaware
corporation (the "Company"), and Gary A. Lockwood, an employee of the Company
or a subsidiary thereof (the "Employee").

         The Company and the Employee agree as follows:

         1. 1993 Incentive and Non-Statutory Stock Option Plan. This Agreement,
executed on behalf of the Company by its President, evidences the grant of an
Incentive Stock Option to purchase Common Stock of the Company (the "Option")
for services anticipated to be rendered by the Employee. The Option is subject
in its entirety to the terms and conditions of the Princeton Dental Management
Corporation 1993 Incentive and Non-Statutory Stock Option Plan (the "Plan")
adopted by the Board of Directors June 3, 1993 and approved by the Shareholders
on July 12, 1993. A copy of the Plan is annexed to this Agreement.

         2. Date of Grant. The date of the grant of the Option is June 1, 1996.

         3. Number and Price of Shares. The total number of shares granted is
50,000. The purchase price per share shall be the average Company trading price
based on the trading days contained in the 61 day period beginning on June 1,
1996 and running through July 31, 1996.

         4. Option Period and Time of Exercise. The number of shares specified
in Paragraph 3 above are divided into four parts which may be exercisable
within the Option period as follows:

<TABLE>
<CAPTION>
Part     No. of Shares    Date Exercisable         Expiration Date
----     -------------    ----------------         ---------------
<S>      <C>                      <C>              <C>
1        10,000                   1/1/97           1/1/2003
2        10,000                   1/1/98           1/1/2003
3        15,000                   1/1/99           1/1/2003
4        15,000                   1/1/2000         1/1/2003
</TABLE>


         (i) The Board may, in its sole discretion, cancel Options granted to
the Employee if the employment of Employee is terminated for cause. Upon the
termination of employment other than for cause, Options granted under the Plan
shall be cancelled only to the extent that such Options were not exercisable as
of the date of such termination.





                                      -7-
<PAGE>   8

         (ii) In no event shall the Options be exercisable after the expiration
date of the Option period.

         5. Manner of Exercise. Subject to the conditions and restrictions
contained in the Plan and Paragraph 6 below, the Options shall be exercised by
delivering written notice of exercise to the Secretary of the Company.

         6. Non-Transferability. This Agreement and Option granted may not be
assigned or transferred by the Employee except as provided in the Plan.

         7. Amendment. Neither this Agreement or the Option may be amended or
modified or revoked except by agreement in writing and signed by the Company
and the Employee.

         8. Interpretation. The Board has the sole power to interpret the Plan
and to resolve any questions arising under the Plan or this Agreement.

         9. Entire Agreement. Except as specifically referenced in Employee's
Employment Agreement, this Agreement constitutes the entire agreement under the
Plan between the Company and the Employee and supersedes all other agreements
under the Plan heretofore entered into.

         IN WITNESS WHEREOF, the Company and the Employee have executed this
Agreement as of the 1st day of June, 1996.


PRINCETON DENTAL MANAGEMENT CORPORATION





By:
   -----------------------------------

Printed Name:
             -------------------------

Its:
    ----------------------------------




----------------------------------
Gary A. Lockwood, individually





                                      -8-