Motion Analysis of the Mandible during Low-Speed, Rear-End Impacts using High-Speed X-rays.

There has been much debate over "whiplash"-induced temporomandibular joint (TMJ) dysfunction following low-speed, rear-end automobile collisions. While several authors have reported TMJ injury based on case studies post collision, there has been little biomechanical evidence showing that rear-end impact was the primary cause of such injury. The purpose of this study was to measure the relative translation between the upper and lower incisors in cadavers subjected to low-speed, rearend impacts. High-speed x-ray images used for this analysis were reported previously for the analysis of cadaveric cervical spine kinematics during low-speed, rear-end impacts. The cadavers were positioned at various seatback angles and body postures, producing an overall picture of various seating scenarios. Of the 38 tests conducted using 10 cadavers, there were seven tests from three cadavers in which the positions of the upper and lower incisors could be tracked with precision using imageprocessing software. The relative protrusion, retrusion, and mouth opening were computed from these seven sets of data, providing a better understanding of TMJ motion. Based on this limited data, the average maximum protrusion, retrusion and mouth opening were 1.6+/-1.8, 1.1+/-0.7, and 1.2+/-1.2 mm, respectively. These values appear to fall within normal physiological limits experienced during daily activities such as mastication. It is concluded that low-speed, rear-end automobile collisions do not appear to create the motion required to initiate injury to the TMJ.