Method and apparatus for determining the preload for screws for dental implant systems

Abstract

A method and apparatus are provided for determining the preload in a dental implant system. The preload is determined by transmitting a sonic impulse, which is preferably an ultrasonic impulse, at a predetermined frequency to the head of the implant screw through a transducer, which may be incorporated into the head of the screw, the head of a wand which generates the sonic impulse, or the transducer and pulse-generating instrumentation may be incorporated into a torque generating instrument used to tighten the screw. The preload is determined by measuring the delay between the first and second reflections through the preloaded screw to determine a preload value and comparing that value with a pre-established baseline value for the screw, and comparing the difference with a predetermined table of values to determine the preload on the screw.

We claim:  
     
         1 . A method of determining the pre-load on a screw that secures a component to other components in a dental implant system comprising: 
 a. Transmitting a sonic impulse at a predetermined frequency to the head of the screw through a transducer when the screw is in an unstressed condition;    b. Measuring a first delay between first and second reflections through the unstressed screw, and establishing a baseline value for the unstressed screw;    c. Applying a preload of a predetermined value to the screw to secure implant components together;    d. Transmitting a sonic impulse at a predetermined frequency to the head of the preloaded screw through a transducer;    e. Measuring a second delay between the first and second reflections through the preloaded screw to establish a preload value; and    f. Determining the difference between the first delay and the second delay to establish a difference between the baseline value and the preload value, and comparing the difference with a predetermined table of values to determine the preload on the screw.    
     
     
         2 . The method of  claim 1  wherein the sonic impulse is an ultrasonic impulse.  
     
     
         3 . The method of  claim 1  wherein the screw secures an abutment to an implant.  
     
     
         4 . The method of  claim 1  wherein the screw secures a dental prosthesis to an abutment.  
     
     
         5 . The method of  claim 1  wherein the screw secures a dental prosthesis directly to an implant.  
     
     
         6 . Apparatus for determining the preload on a screw in a dental implant system that includes at least one screw for securing components of the dental implant system together, wherein the dental implant system includes at least a fixture having one end adapted for osseointegration into a jawbone, the other end adapted to receive an abutment, and the abutment adapted to receive and support a dental prosthesis, the apparatus further comprising 
 a. Means for applying a preload to the screw to secure at least some components of the implant system together;    b. Means for transmitting a sonic impulse at a predetermined frequency to the head of the screw;    c. Means for transmitting the sonic impulse through the screw and detecting first and second reflections of the pulses;    d. Means for measuring the delay between the first and second reflections through the preloaded screw to determine a preload value; and    e. Means for determining the difference in the delay between a pre-established baseline value for the screw and the preload value, and comparing the difference with a predetermined table of values to determine the preload on the screw.    
     
     
         7 . The apparatus of  claim 1  wherein the sonic impulse is an ultrasonic impulse.  
     
     
         8 . The apparatus of  claim 1  wherein the screw secures an abutment to an implant.  
     
     
         9 . The apparatus of  claim 1  wherein the screw secures a dental prosthesis to an abutment.  
     
     
         10 . The apparatus of  claim 1  wherein the screw secures a dental prosthesis directly to an implant.  
     
     
         11 . The apparatus of  claim 1  wherein the means for transmitting a sonic impulse is an apparatus that produces an ultrasonic impulse.  
     
     
         12 . The apparatus of  claim 1  wherein the means for transmitting the sonic impulse through the screw and detecting first and second reflections of the pulses is a transducer.  
     
     
         13 . The apparatus of  claim 12  wherein the transducer is affixed to the head of the screw.  
     
     
         14 . The apparatus of  claim 12  wherein the transducer is affixed to a wand, and the wand is in electronic communication with an electronic control and measurement circuit.