Application of "cusp writer" findings to practical and theoretical occlusal problems. Part II

The cusp writer is a teaching aid to facilitate understanding of the correlation between cusp angulations and the various occlusal determinants. The cusp writer provides graphic evidence that the occlusal determinants which influence configurations (i.e., incisal guidance, condylar guidance, plane [curve] of occlusion, curve of Spee [compensating curve], and plane of motion) are reciprocal, one tempering the value of the other. Cusp writings demonstrate the following: (1) The angle of the plane (curve) of occlusion to the plane of motion in concert with the other occlusal infuluence determines the optimal height and angulation of the cusps. (2) Cusps appear to be steep or shallow relative to each other, to the plane of occlusion, and to the plane of motion. (3) The steepness of the curve of Spee determines the relative cusp height and angulation of one tooth to another, from an anterior to a posterior direction in the dental arch. (4) The angle of the tangent to any segment of the curve of Spee to the plane of motion determines the optimal height and angulation of the cusps of the segment. (5) The graphs show that the flatter the curve of Spee, the more uniform the cusp height and angulations are from anterior to posterior teeth. The steeper the curve of Spee, the more irregular the cusp height and angulations are with steeper anterior cusps and flatter posterior cusps. (6) The steeper the curve of Spee, the flatter the molar cusp angulations must be to avoid deflective and/or interceptive occlusal contacts on the balancing side. (7) With the syndrome of a steepening curve of Spee due to the loss of one or more lower posterior teeth, the cusps of the remaining opposing teeth must be constantly flattened by wear or selective grinding and reshaping to avoid traumatic occlusion, unless the drifting is interrupted by restorative dentistry. (8) Cusp angulation of artificial teeth should be chosen to harmonize with the angle of incidence of the compensating curve tangents to the plane of motion. (9) Condylar guidance has less influence on cusp angulation in comparison to incisal guidance and the other occlusal determinants. (10) Changing the hinge axis location 1/2 inch (12.5 mm.) distally and/or superiorly has very little effect on the influence of the above occlusal determinants on cusp configuration, if the vertical dimension of occlusion remains constant.