A measurement of clasp forces on teeth

Abstract

A method that measures the force which clasps transmit to abutment teeth was developed and a comparative study was made between the effectiveness of a wrought wire clasp and that of a cast bar clasp. A transducer, using a resistance strain gauge, measured the flexure of clasps and the forces exerted by the clasps on abutment teeth. The cast bar clasps were more flexible than the wrought wire clasps of equal length. All of the clasps tested exerted forces against the teeth when the removable partial denture bases were at rest. The wrought wire clasps flexed a greater distance and exerted more force against the abutment teeth when the casting was seated and removed from the model. The forces exerted by the clasps when the casting bases were moved were different from each other and yet followed a pattern. The force increased for both types of clasps as the bases were depressed; however, the wrought wire clasp exerted more force than the cast bar clasps. The forces measured could be significant when the direction and the result of the forces were examined. The wrought wire clasps may tilt the abutment tooth distolingually and the cast bar clasp may force the tooth mesiolingually. The results of this study question some of the empirical theories used today to substantiate extension partial denture clasp designs. It appears that the theoretical and the practical do not always agree; therefore, the theoretical should be tested further.