Vectorial analysis of the instantaneous equilibrium of forces between incisal and condylar guidances

Protrusive functional relationships between the upper and lower jaws are constrained by the structures of the temporomandibular joints (TMJs) and the opposing contacting surfaces of the anterior teeth. To check these biomechanical relationships, the link quadrilateral bell crank model was assumed in order to compute the instantaneous equilibrium of forces using vectorial analysis. Four anterior teeth configurations were analyzed to study the distribution of force components. The first represented normal bite (used as control), the second represented long anterior overjet, the third represented deep anterior overbite, and the fourth one represented freedom in centric. When three different interincisal contact positions were assumed, functional compromises concerning load/reaction between the TMJ and anterior dentition were found. In centric occlusion there was a tendency toward less loading in the joints and increased loading on the dentition. In intermediate positions and close to the edge-to-edge position, the mechanical tendencies were toward increased loading in the joints and decreased loading on the dentition.