Exhibit 4.13

AMENDMENT NO. 4 TO  ASSET PURCHASE AGREEMENT

AMENDMENT
NO. 4 TO ASSET PURCHASE AGREEMENT (the "Fourth Amendment"), dated as of November 26, 2001, among CORE-VENT CORPORATION, d/b/a Paragon Implant Company, a
Nevada corporation ("Paragon"), CORE-VENT BIOENGINEERING, INC., a California corporation ("C-V BioEngineering"), CORE-VENT PARAGON BIO, a California
corporation ("C-V Paragon"), PARAGON ADMINISTRATION, INC., a California corporation ("Paragon Administration"), CORE-VENT GmbH, a corporation organized under the laws of
the Federal Republic of Germany ("C-V GmbH"), CORE-VENT ISRAEL (1997), a PARAGON Company Ltd., a corporation organized under the laws of Israel ("C-V
Israel"; and together with Paragon, C-V BioEngineering, C-V Paragon, Paragon Administration, C-V GmbH and C-V Israel, the "Seller"), the shareholders of
Paragon identified on the signature page hereof (the "Paragon Shareholders"), the shareholders of C-V BioEngineering identified on the signature page hereof (the "C-V
BioEngineering Shareholders"), the Niznick Family Foundation (the "Niznick Foundation"), a California not-for-profit corporation, DR. GERALD A. NIZNICK, an individual
("Dr. Niznick"; and together with the Paragon Shareholders, the C-V BioEngineering Shareholders and the Niznick Foundation, the "Shareholders"), SULZER MEDICA USA INC., a
Delaware corporation ("Parent"), SULZER DENTAL INC. (formerly known as Sulzer Calcitek Inc.), a Delaware corporation ("Calcitek") and SULZER DENTAL GmbH (formerly known as Sulzer
Calcitek GmbH.), a corporation organized under the laws of the Federal Republic of Germany ("Calcitek GmbH"), SULZER DENTAL LTD., a corporation organized under the laws of Israel ("Calcitek
Israel") and SULZER DENTAL CORP, a corporation organized under the laws of Canada ("Calcitek Canada" and together with Calcitek, and Calcitek GmbH and Calcitek Israel, the "Purchaser").

W
I T N E S S E T H:

WHEREAS,
the Seller, the Shareholders, Parent and Purchaser entered into (i) the Asset Purchase Agreement dated November 1, 2000, pursuant to which Seller agreed to sell
and Purchaser agreed to purchase the Assets, all as more particularly set forth therein; (ii) Amendment No. 1 to Asset Purchase Agreement dated January 8, 2001;
(iii) Amendment No. 2 to Asset Purchase Agreement and (iv) Amendment No. 3 to Asset Purchase Agreement (as so amended, the "Asset Purchase Agreement")
pursuant to which Seller agreed to modify certain of the terms of the original Asset Purchase Agreement, all as more particularly set forth therein;

WHEREAS,
the parties hereto wish to further amend the Asset Purchase Agreement by executing this Amendment No. 4 to Asset Purchase Agreement all as more particularly set forth
herein.

NOW,
THEREFORE, in consideration of the premises and the mutual agreements and covenants hereinafter set forth, and intending to be legally bound hereby, the parties hereby agree as
follows:

1.Definitions.Capitalized terms used herein without definition shall have the meanings ascribed to such terms
in the Asset Purchase Agreement.

2.Amendments.The parties hereby agree to amend the Asset Purchase Agreement by deleting the text of
Section 2.08 in its entirety and substituting therefor the following:

"(a)
In full and final satisfaction of any obligation to pay a post-Closing Purchase Price adjustment and provided that the conditions set forth in subsection 2.08(b) herein
are satisfied prior to or contemporaneous with the execution of this Amendment No. 4, Seller shall receive by wire transfer a Purchase Price adjustment equal to $1,824,055.56 (calculated as
$2,000,000 less $175,944.44, the amount previously paid to Seller pursuant to the previous Section 2.08, as amended by Amendment No. 2). No interest will be due on the amount paid
pursuant to this provision."

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(b)
The payment outlined in subsection 2.08(a) is subject to the satisfaction of the following conditions:



3.Further Agreement.Purchaser and Seller specifically agree that: (a) Purchaser has no liability for
the payment of any Israeli taxes which may be or are due as a result of the transaction reflected in the Agreement (the "Israeli Taxes"); (b) Seller acknowledges the liability for the payment
of the Israeli Taxes and agrees to pay same; (c) to the extent that Purchaser receives any funds from the Israeli tax authorities as a result of Seller's payment of the Israeli Taxes, Purchaser
shall remit same on a dollar-per-dollar basis to Seller; and (d) to the extent that Purchaser receives tax credits from the Israeli tax authority as a result of Seller's
payment of the Israeli Taxes, Purchaser shall transfer said tax credit to Seller.

4.No Further Modifications.Except as expressly set forth herein, the terms and provisions of the Asset
Purchase Agreement remain unmodified and in full force and affect.

5.Miscellaneous.

(a)
This Amendment No. 4 shall be governed by, and construed in accordance with, the laws of the State of California, applicable to contracts executed in and to be performed
entirely in that state.

(b)
This Amendment No. 4 may be executed in one or more counterparts, and by the different parties hereto in separate counterparts, each of which when executed shall be deemed to
be an original but all of which taken together shall constitute one and the same agreement.

IN
WITNESS WHEREOF, the parties hereto have executed, or have caused this Agreement to be executed by their respective officers thereunto duly authorized, as of the date first written
above.

| |  | CORE-VENT CORPORATION, d/b/a Paragon Implant Company                    
| |  | ------------------------------------------------------------------------
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President
| |  | CORE-VENT BIOENGINEERING, INC.                                          
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President
| |  | CORE-VENT PARAGON BIO                                                   
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President

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| |  | PARAGON ADMINISTRATION, INC.                                            
| |  | ------------------------------------------------------------------------
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President
| |  | CORE-VENT GmbH                                                          
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President
| |  | CVPBE, Inc.                                                             
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President
| |  | CV Equipment, Inc.                                                      
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President
| |  | PARAGON DENTAL IMPLANT, LTD.                                            
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: President
| |  | THE PARAGON SHAREHOLDERS                                                
| |  | By: /s/DR. GERALD A. NIZNICKDr. Gerald A. Niznick                       
| |  | THE C-V BIOENGINEERING STOCKHOLDERS                                     
| |  | By: /s/DR. GERALD A. NIZNICKDr. Gerald A. Niznick                       
| |  | THE NIZNICK FOUNDATION                                                  
| |  | By: /s/DR. GERALD A. NIZNICKName: Dr. Gerald A. Niznick
Title: Director 
| |  | SULZER MEDICA USA INC.                                                  
| |  | By: /s/RICHARD J. MAYName: Richard J. May
Title: Treasurer              

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| |  | SULZER DENTAL INC.                                            
| |  | --------------------------------------------------------------
| |  | By: /s/STEVEN E. HANSONName: Steven E. Hanson
Title: President
| |  | SULZER DENTAL GmbH                                            
| |  | By: /s/STEVEN E. HANSONName: Steven E. Hanson
Title: President
| |  | SULZER DENTAL LTD.                                            
| |  | By: /s/STEVEN E. HANSONName: Steven E. Hanson
Title: President
| |  | SULZER DENTAL CORP.                                           
| |  | By: /s/STEVEN E. HANSONName: Steven E. Hanson
Title: President

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EXHIBIT 4A    AMENDMENT TO INTELLECTUAL PROPERTY LITIGATION AGREEMENT

This
Amendment is entered into and is effective as of the 26th day of November 2001 by and betweenSulzer
Dental Inc.("Dental"), successor-in-interest to Sulzer Calcitek Inc., andDr. Gerald A.
Niznick("Niznick").

WHEREAS,
Dental and Niznick are parties to that certain Intellectual Property Litigation Agreement dated January 8, 2001 (the "Agreement"); and

WHEREAS,
the Agreement remains in full force and effect as of this date; and

WHEREAS,
Dental and Niznick now desire to amend the Agreement to accomplish a modification to their contractual relationship with this document (the "Amendment");

NOW
THEREFORE, the parties agree as follows:



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IN
WITNESS WHEREOF the parties have caused the Amendment to be executed by their duly authorized representative as of the date and year set forth above.

|                                                                                            |  |                                                                                                
|------------------------------------------------------------------------------------------- |  | -----------------------------------------------------------------------------------------------
|Sulzer Dental Inc.
By: /s/ STEVEN E. HANSON
Printed Name: Steven E. Hanson
Title:
President |  | Dr. Gerald Niznick
By: /s/ DR. GERALD NIZNICK
Printed Name: Dr. Gerald Niznick
Title:
President

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EXHIBIT 4B    AMENDMENT TO CONSULTING AND LICENSE AGREEMENT

THIS AMENDMENT is entered into and is effective as of the 26th day of November, 2001 by and betweenSulzer
Dental Inc.("Dental"), successor-in-interest to Sulzer Calcitek Inc., andDr. Gerald A.
Niznick("Niznick").

WHEREAS,
Dental and Niznick are parties to that certain Consulting and License Agreement dated January 8, 2001 (the "Agreement"); and

WHEREAS,
the Agreement remains in full force and effect as of this date; and

WHEREAS,
Dental and Niznick now desire to amend the Agreement to accomplish a modification to their contractual relationship with this document (the "Amendment");

NOW
THEREFORE, the parties agree as follows:





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IN
WITNESS WHEREOF the parties have caused the Amendment to be executed by their duly authorized representative as of the date and year set forth above.

|                                                                                            |  |                                                                                                
|------------------------------------------------------------------------------------------- |  | -----------------------------------------------------------------------------------------------
|Sulzer Dental Inc.
By: /s/ STEVEN E. HANSON
Printed Name: Steven E. Hanson
Title:
President |  | Dr. Gerald Niznick
By: /s/ DR. GERALD NIZNICK
Printed Name: Dr. Gerald Niznick
Title:
President

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