Lateral force in relation to the denture base and clasp design

Abstract

Lateral force on a partial denture initiates vertical and horizontal rotational components. If the framework and abutments are rigid to each other, the occlusal rests on the side opposite the application of lateral force tend to resist the vertical rotation. This helps prevent the harmful tipping action of the abutments on the side of the lateral force application. Lack of rigidity allows a tipping action of the teeth and prevents the proportionate sharing of the load by the opposite side. The horizontal rotational pattern depends on the denture base location, the area of the application of the lateral force, and the relative location of the abutments. There are many variable factors, but some general principles can be outlined. Flexibility in the framework or clasping design places most of the rotational stress on one or two abutments. With rigidity, we can rationalize the pattern of horizontal rotation and plan a better design to help resist this tendency and, by so doing, spread the stress to all the abutments. Unfortunately, variations in tooth mobility that we cannot perceive or measure further complicate every case. It is hoped that this presentation does not seem to oversimplify the problem or claim any panacea, but rather to show some of the torques that are likely to effect the prognosis of our treatment and to point out a rational direction toward which we can work. With the aid of good roentgenograms, study casts, and accurate clinical examination, we can evaluate the relative resistance of each abutment to the various types of forces that may be exerted on them. Provision can be made then, in the partial design, to prevent overloading and to give a more equal distribution of lateral stress.