Elastic response of the temporo-mandibular joint to very small forces.

The mechanical mobility of the temporo-mandibular joint (TMJ) was measured by applying small sinusoidal forces at different frequencies to the teeth and measuring the resultant motion of the teeth. Velocity/force ratios were recorded versus frequency at maxillary and mandibular teeth and the results were interpreted in terms of linear spring-mass-dashpot models. Differences in results obtained at maxillary and mandibular teeth indicate that the TMJ has an effective spring constant of 9 X 10(7) dynes/cm when excited by forces of approximately 2 X 10(3) dynes. Displacements occurring in the TMJ due to orthodontic elastics will be in the order of 20 mum which is between one and two orders of magnitude smaller than could be detected by radiography.