Dental holographic interferometryin vivoutilizing a ruby laser system: I. Introduction and development of methods for precision measurements on the functional dynamics of human teeth and prosthodontic appliances

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Abstract
Holographic interferometry, an application of laser technology, was introduced as a non-contact and non-destructive method for investigations concerning the dynamics of human teeth and prosthodontic appliances in function. The method was first tested in a simulator and then used in a number of clinical experiments. A special, totally reflecting paint was used for surface preparation prior to holography. A Q-switched double-pulsed ruby laser with a pulse-length of 24 ns was combined with an electronic subminiature force sensor for pulse triggering which was actuated by the masticatory force of the patient. Force increase and pulse positions were registered synchronously on the screen of an oscilloscope. The applied force exerted by the patient's masticatory muscles could thus be defined according to its point of application, direction, amplitude and duration. The corresponding surface deformation was evaluated by means of a synchronized, double exposed hologram. The measuring range as well as the sensitivity of the method depend on the wavelength of the ruby laser light (0.6943 μm). Conclusions could be drawn regarding the relative and absolute mobility of the teeth and related structures of the holographed jaw section. The technique provided abundant and detailed information, its documentation being facilitated by means of a special photographic method.