Measurement of the distortion of the human mandible in function

Objectives: to record the change in spatial relationship between 2 osseointegrated implants placed in the parasympheseal region of the human mandible during posturing and functional loading of the lower jaw in vivo. Methods: The development of a sensitive intra oral transducer capable of being accurately connected between 2 implants in the human subject was fundamental to this study. A low voltage Transducer capable of recording linear movements of up to 200 microns (accurate to < 5microns) was developed. The implants were themselves not loaded readings being taken from rest position to protrusive, to lateral excursions and also with loading of the jaws posterior to the implants by the means of custom built bite blocks fitted between the mandible and maxilla. Results: Readings from a number of subjects, all of whom were wearing lower full implant retained overdentures, demonstrated a reduction in the distance between 2 anterior implants during various functional movements of between 10 and 150 microns. Conclusion: Any functional activity of the human mandible from rest appears to reduce the arch width and the resultant distortion of the lower jaw across the midline can be recorded using unloaded bilaterally placed implants as ‘markers’ of the underlying bone position. The distortion of the mandible in function, in a clinical situation where 2 or more implants are connected via a fixed prosthesis across the midline, may produce stresses that will have biomechanical implications regardless of the passivity of fit of any superstructure.