REACTION STRAINS ON THE CONDYLAR NECK DURING MASTICATION AND MAXIMUM MUSCLE STIMULATION IN DIFFERENT CONDYLAR POSITIONS - AN EXPERIMENTAL-STUDY IN THE MINIATURE PIG

Most researchers agree that the primate temporomandibular joint (TMJ) is loaded compressively during function and that condylar position mus t play a role in mediating such loads. However, the precise nature of that role remains unclear. Using a pig model in this study, we attempt ed to analyze strain on the neck of the condyle during normal masticat ion and during simulated function in different condylar positions. Min iature three-element rosette strain gauges were bonded to the lateral surface of the condylar neck in 4 female miniature pigs (one per condy le). Measurements of strain were made during normal mastication and wi th the pigs under general anesthesia during maximum stimulation of the masseter and temporalis muscles in each of five condylar positions-ce ntric occlusion, centric relation, anterior, relaxed and wide open-est ablished through use of acrylic splints. Condylar position was evaluat ed by superimposition of lateral and dorsoventral cephalograms, with m easurement of horizontal and vertical changes in location of implants placed on the neck of the condyle relative to implants placed on the z ygomatic arch. As in primates, the TMJ was found to be load-bearing du ring mastication, with compressive strain oriented approximately perpe ndicular to the occlusal plane. In 3 pigs, strain was higher during ba lancing than during working function. During stimulation, the TMJ reac tion strains were significantly lower with the condyles in the anterio r position compared with the other positions, and the compressive stra in was directed more anteriorly along the neck of the condyle in that position.