<PAGE>   1

                                                                   EXHIBIT 10.33

                            STOCK PURCHASE AGREEMENT

     This Stock Purchase Agreement (this "AGREEMENT") is made and entered into
as of the 2nd day of October, 1998 by and between Dental/Medical Diagnostic
Systems, Inc., a Delaware corporation, ("DMD" or the "COMPANY"), and Chrysalis
Dental, Inc. ("CHRYSALIS") on the following terms and conditions:

     1.   PURCHASE AND SALE OF STOCK. On the terms and subject to the
conditions set forth in this Agreement, DMD agrees to sell and deliver to
Chrysalis, and Chrysalis agrees to purchase and acquire from DMD, 100,000
shares of the Common Stock of the Company, par value $0.01 per share (the
"SHARES"), free and clear of any and all liens, claims and encumbrances of any
kind.

     2.   CONSIDERATION. The consideration for the Shares (the "PURCHASE
PRICE") consists of an exclusive world wide license to a tooth whitening
formula designed and developed by Chrysalis, as provided for in that certain
Licenses Agreement, by and between the Company and Chrysalis, dated October 2,
1998.

     3.   THE CLOSING. The closing (the "CLOSING") of the purchase and sale of
the Shares shall take place on October 2, 1998 at the offices of Chrysalis
Dental, Inc., 11322 South O'Henry Road, Sandy, UT 84070. All documents and
other deliveries at the Closing may be exchanged by mail. The date of the
Closing is referred to herein as the Closing Date.

     4.   REPRESENTATIONS AND WARRANTIES OF CHRYSALIS. Chrysalis represents and
warrants to the Company as follows:

          4.1  It understands an investment in the Shares involves a high
degree of risk, and it is able to bear the risk of an entire loss of the
investment, it has such knowledge and experience in financial and business
matters that it is capable of evaluating the merits and risks of an investment
in the Shares.

          4.2  It understands that the Shares have not been registered under
the Securities Act or under any state securities laws. It is familiar with the
provisions of the Securities Act and Rule 144 thereunder and understands that
the restrictions on transfer placed on the Shares may result in it being
required to hold the Shares for a certain period of time.

          4.3  It is acquiring the Shares for its own account, and not as a
nominee or agent for others, and not with a view to resale or distribution of
any part thereof, and it has no present intention of selling or distributing
the Shares.

          4.4  It is, and each of its shareholders is, an "accredited" investor
for purposes of Regulation D promulgated by the Securities and Exchange
Commission under the Securities Act of 1933.

                                       1
<PAGE>   2
          4.5  It believes that it has received all the information it
considers necessary or appropriate for deciding whether to purchase the Shares,
and it has had an opportunity to ask questions and receive answers from the
Company and its officers and directors regarding the business, prospects and
financial condition of the Company.

          4.6  It agrees not to sell, assign, transfer or otherwise dispose of
(collectively, "Transfer") any of the Shares except pursuant to an effective
registration statement under the Securities Act or an exemption from
registration. As a further condition to any such Transfer, except in the event
that such Transfer is made pursuant to an effective registration statement
under the Securities Act, if in the reasonable opinion of counsel to the
Company any Transfer of the Shares by the contemplated transferee thereof would
not be exempt from the registration and prospectus delivery requirements of the
Securities Act, the Company may require the contemplated transferee to furnish
the Company with an investment letter setting forth such information and
agreements as may be reasonably requested by the Company to ensure compliance
by such transferee with the Securities Act.

          4.7  Each certificate evidencing the Shares will bear the following
legend:

"THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933 (THE "ACT") OR STATE SECURITIES LAWS AND NO TRANSFER
OF THESE SECURITIES MAY BE MADE EXCEPT (A) PURSUANT TO AN EFFECTIVE
REGISTRATION STATEMENT UNDER THE ACT, OR (B) PURSUANT TO AN EXEMPTION THEREFROM
WITH RESPECT TO WHICH THE COMPANY MAY, UPON REQUEST, REQUIRE A SATISFACTORY
OPINION OF COUNSEL FOR THE HOLDER THAT SUCH TRANSFER IS EXEMPT FROM THE
REQUIREMENTS OF THE ACT."

     5.   REGISTRATION RIGHTS

          5.1  Registration Procedures and Expenses. DMD shall use commercially
reasonable efforts to effect the registration of the Shares on Form S-3 under
the Securities Act within six months of the date hereof by performing the
following:

               5.1.1  DMD shall use all best efforts to cause to be prepared
and filed with the Commission a registration statement with respect to the
Shares, and use all reasonable efforts to cause such registration statement to
become and remain effective for a period of not less than twelve months
following the effective date of such registration statement or, if shorter,
until all of the Shares have been sold.

               5.1.2  DMD shall cause to be prepared and filed with the
Commission such amendments and supplements to such registration statement and
the prospectus used in connection therewith as may be necessary to update and
keep such registration statement effective for the period set forth in Section
5.1.1. above and to comply with the provisions of the Securities Act with
respect to the sale of all securities covered by such registration statement.
Notwithstanding anything else to the contrary contained herein, neither DMD or
any of its affiliates



                                       2

<PAGE>   3
shall be required to disclose any confidential information concerning pending
acquisitions not otherwise required to be disclosed.

                  5.1.3 DMD shall cause to be furnished to Chrysalis such
number of copies of the final prospectus as Chrysalis may reasonably request in
order to facilitate the sale of the Shares. Chrysalis shall comply with all
prospectus delivery requirements under the Securities Act. It shall be a
condition to DMD's obligations to effect registration of the Shares that
Chrysalis and others participating in such registration provide DMD and any
underwriter identified by Chrysalis, with all material facts including, without
limitation, furnishing such certificates, questionnaires and legal opinions as
may be required by DMD or such underwriter concerning such participating
sellers and the Shares to be registered which are reasonably required to be
stated in the registration statement or in the prospectus or are otherwise
required in connection with the offering.

                  5.1.4 Allocation of Expenses. All expenses incurred by DMD or
its affiliates in complying with this Section, including, without limitation,
all registration and filing fees, printing expenses, and fees and disbursements
of counsel for DMD and its affiliates, are herein called Registration Expenses.
All selling commissions applicable to the sales of the Shares and all fees and
disbursements of counsel for Chrysalis are herein called Selling Expenses. DMD
will pay all Registration Expenses in connection with registration pursuant to
this Section 5.1. All Selling Expenses in connection with such registration
shall be borne by Chrysalis.

      6.    REPRESENTATIONS AND WARRANTIES OF DMD.

            6.1   Organization, Standing and Corporate Power. DMD is a
corporation duly organized, validly existing and in good standing under the
laws of the State of Delaware, with adequate corporate power and authority to
own its properties and carry on its business as presently conducted. DMD has
the corporate power to enter into, execute and deliver this Agreement and the
agreements referred to herein and to consummate the transactions contemplated
hereby and thereby.

            6.2   Execution, Delivery and Performance. The execution, delivery
and performance of this Agreement and the other agreements referred to herein
and the consummation of the transactions contemplated hereby and thereby have
been or will prior to the Closing be duly authorized by the Board of Directors
of DMD, and DMD has taken all other actions required by law, its Articles of
Incorporation and its Bylaws in order to consummate the transactions
contemplated by this Agreement and the other agreements referred to herein.
This Agreement and the other agreements referred to herein constitute the valid
and binding obligations of DMD and are enforceable in accordance with their
respective terms, except as enforceability may be subject to or limited by
bankruptcy, insolvency, reorganization, moratorium or other similar laws
relating to or affecting creditors' rights generally.

            6.3   Authorized and Outstanding Stock. The Shares, when issued in
accordance with the provisions of this Agreement, will be duly authorized and
validly issued and fully paid and nonassessable and, assuming the accuracy of
Chrysalis' representations and warranties contained elsewhere herein, will be
issued in compliance with federal securities laws.

                                       3

<PAGE>   4
     7.   MISCELLANEOUS.

          7.1  Successors and Assigns. This Agreement shall be binding upon and
inure to the benefit of the parties hereto and their respective successors and
assigns. No party other than DMD may assign any of its rights, or delegate
any of its duties or obligation, under this Agreement without the prior written
consent of the other parties, and any such purported assignment or delegation
shall be void ab initio. Notwithstanding the foregoing, DMD, its affiliates,
and its successors and assigns, may assign its rights and delegate its duties
to any successor entity resulting from any liquidation, merger, consolidation,
reorganization, or transfer of all or substantially all of the assets or stock
of DMD.

          7.2  Notices. All notices, demands and other communications
(collectively, "Notices") given or made pursuant to this Agreement shall be in
writing and shall be deemed to have been duly given if sent by registered or
certified mail, return receipt requested, postage and fees prepaid, by
overnight service with a nationally recognized "next day delivery company such
as Federal Express or United Parcel Service, by facsimile transmission, or
otherwise actually delivered to the following addresses:

          (a)  if to DMD:

               Dental/Medical Diagnostic Systems, Inc.
               200 North Westlake Boulevard, Suite 202
               Westlake Village, California 91362
               Fax No. (805) 374-2137
               Attn: Robert H. Gurevitch

          (b)  if to Chrysalis:

               Chrysalis Dental, Inc.
               11322 South O'Henry Road
               Sandy, Utah 84070
               Attention: Dr. Alan H. Anderson

Any Notice shall be deemed duly given when received by the addressee thereof,
provided that any Notice sent by registered or certified mail shall be deemed
to have been duly given two business days from the date of deposit in the United
States, unless sooner received and any notice sent by overnight service as
provided above shall be deemed to have been duly given the next business day
from the date of deposit with the service. Any of the parties to this Agreement
may from time to time change its address for receiving notices by giving
written notice thereof in the manner set forth above.

          7.3  Amendment Waiver. No provision of this Agreement may be waived
unless in writing signed by all of the parties to this Agreement, and the
waiver of any one provision of this Agreement shall not be deemed to be a
waiver of any other provision. This Agreement may be amended only by written
agreement executed by all of the parties to this Agreement.

                                       4
<PAGE>   5
          7.4  Dispute Resolution. Any dispute or claim arising hereunder shall
be settled by arbitration. Any party may commence arbitration by sending a
written notice of arbitration to the other party. The notice will state the
dispute with particularity. The arbitration hearing shall be commenced thirty
(30) days following the date of delivery of notice of arbitration by one party
to the other, by the American Arbitration Association ("AAA") as arbitrator.
The arbitration shall be conducted in Los Angeles, California in accordance
with the commercial arbitration rules promulgated by AAA, and each party shall
retain the right to cross-examine the opposing party's witnesses, either
through legal counsel, expert witnesses or both. The decision of the arbitrator
shall be final, binding and conclusive on all parties (without any right of
appeal therefrom) and shall not be subject to judicial review. As part of his
decision, the arbitrator may allocate the cost of arbitration, including fees
of attorneys and experts, as he or she deems fair and equitable in light of all
relevant circumstances. Judgment on the award rendered by the arbitrator may be
entered in any court of competent jurisdiction.

          7.5  Governing Law. This Agreement shall be governed by and construed
both as to validity and performance and enforced in accordance with the laws of
the State of California without giving effect to the choice of law principles
thereof.

          7.6  Remedies Cumulative. Each of the various rights, powers and
remedies shall be deemed to be cumulative with, and in addition to, all the
rights, powers and remedies which DMD may have hereunder or under applicable
law relating hereto or to the subject matter hereof, and the exercise or
partial exercise of any such right, power or remedy shall constitute neither an
exclusive election thereof nor a waiver of any other such right, power or
remedy.

          7.7  Headings. The section and subsection headings contained in this
Agreement are included for convenience only and form no part of the agreement
between the parties.

          7.8  Severability. Whenever possible, each provision of this Agreement
shall be interpreted in such a manner as to be effective and valid under
applicable law, but if any provision of this Agreement shall be or become
prohibited or invalid under applicable law, such provision shall be ineffective
to the extent of such prohibition or invalidity without invalidating the
remainder of such provision or the remaining provisions of this Agreement.

          7.9  Expenses. Each party shall pay its own costs, expenses,
including without limitation, the fees and expenses of their respective counsel
and financial advisors.

          7.10 Entire Agreement. This Agreement, including the other agreements
and schedules to be entered into in connection with the transactions
contemplated by the License Agreement constitutes and embodies the entire
understanding and agreement of the parties hereto relating to the subject
matter hereof and there are no other agreements or understandings, written or
oral, in effect between the parties relating to such subject matter except as
expressly referred to herein.





<PAGE>   6

     IN WITNESS WHEREOF, this Stock Purchase Agreement has been executed as of
the date first set forth above.

DENTAL/MEDICAL DIAGNOSTIC SYSTEMS, INC.
200 North Westlake Boulevard, Suite 202
Westlake Village, California 91362


By:  /s/ [SIGNATURE ILLEGIBLE]
   --------------------------------------

Its:   C.F.O.
    -------------------------------------


CHRYSALIS DENTAL, INC.
11322 South O'Henry Road
Sandy, Utah 84070


By: /s/ [SIGNATURE ILLEGIBLE]
   ---------------------------------------

Its:  President
    --------------------------------------