Orthopedic jaw movement observations. Part II: The rotational capacity of the mandible

Using computerized axiography, particularly the electronic mandibular position indicator (EMPI), the mandibular opening movement was measured in 86 asymptomatic volunteers and temporomandibular joint (TMJ) patients. Terminal hinge-axis movement and hinge-axis rotation at maximum-guided mouth opening were recorded. The angle of hinge-axis rotation was used as a parameter for both movements, in accordance with the neutral-zero method. This is a well-established technique in orthopedics and is the standard tool for quantitative functional analysis of joints. An average group was defined, 50% being volunteers. The interquartile range for terminal hinge-axis movement in this study was 5.42 degrees-7.41 degrees in the volunteers and 4.73 degrees-7.25 degrees in the patients. The interquartile range for hinge-axis rotation at maximum opening was from 29.09 degrees-34.87 degrees in the volunteers and from 26.7 degrees-35 degrees in the patients. Computerized axiography is a refined tool for analyzing rotational and translational capacities of the mandible. It is a valid and practical method for orthopedic-diagnostic evaluation of mandibular movements and gives objective criteria for diagnosis in accident victims.