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                                                                EXHIBIT 4.11



                              EXTENSION OF LIENS


STATE OF TEXAS                      ss

                                    ss

COUNTY OF NUECES                    ss
          --------

        WHEREAS, TEXAS AIRSONICS, INC., whose successor by merger is AMERICAN
DENTAL TECHNOLOGIES, INC., a Delaware corporation (herein called "Mortgagor",
whether one or more), did execute and deliver a certain Deed of Trust dated
October 17, 1996, recorded in the Office of the County Clerk of Nueces County,
Texas, at Doc. No. 1996041318,  Official Public Records of Nueces County,
Texas, in favor of THE INTERNATIONAL BANK (herein called the "Lender"), whose
mailing address is P.O. Box 4956, Corpus Christi, Texas 78469, in order to
secure the indebtedness evidenced by a Revolving Credit Promissory Note of even
date therewith in the principal amount of $2,500,000.00 executed by TEXAS
AIRSONICS, INC., and AMERICAN DENTAL TECHNOLOGIES, INC., payable to the order
of said Lender, which said Deed of Trust covered the following property in
Nueces County, Texas, to-wit:

                Lot One (1), Block Two (2), INDUSTRIAL TECHNOLOGY PARK
                UNIT 1, a Subdivision of the City of Corpus Christi, Nueces
                County, Texas, as shown by the map or plat thereof recorded in
                Volume 46, Pages 105-107, Map Records, Nueces County, Texas.

        WHEREAS, by an Allonge and Amendment of even date herewith AMERICAN
DENTAL TECHNOLOGIES, INC., and Lender have rearranged the payment of the
indebtedness evidenced by said Note and have extended the maturity thereof to
October 15, 1998;

        WHEREAS, the said Lender and AMERICAN DENTAL TECHNOLOGIES, INC.,
desire to extend the liens of the said Deed of Trust;

        NOW, THEREFORE, the said Lender, as the holder of said indebtedness,
and AMERICAN DENTAL TECHNOLOGIES, INC., hereby agree that the said Deed of
Trust, and the liens thereof, shall be extended in accordance with the
extensions of the said indebtedness pursuant to said Allonge and Amendment of
even date herewith.

        Except as so amended and extended, the said Deed of Trust shall remain
in full force and effect, and is hereby ratified and confirmed.

        DATED effective the 15th day of October 1997.


THE INTERNATIONAL BANK                  AMERICAN DENTAL TECHNOLOGIES, INC.




By:/s/ Scott Heitkamp                   By:/s/ Benjamin J. Gallant
   ---------------------------             ---------------------------------
   SCOTT HEITKAMP                          BENJAMIN J. GALLANT
   Executive Vice President                President



STATE OF TEXAS                      ss

                                    ss

COUNTY OF NUECES                    ss

        
        This instrument was acknowledged before me on the 21st day of November 
1997, by SCOTT HEITKAMP, the Executive Vice President of THE INTERNATIONAL
BANK, a Texas banking association, on behalf of said association.

[SEAL]
ANGIE L. CUEVAS 
Notary Public
STATE OF TEXAS                         /s/ Angie L. Cuevas
My Comm. Exp. March 9, 2001             -----------------------------
                                        Notary Public, State of Texas