Abdel Latif, Hind Hassan; (1996) Functional mandibular deformation in edentulous subjects treated with dental implants. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The purpose of this investigation was to study functional mandibular deformation in edentulous subjects who had been treated with osseointegrated implants. The orientation of the muscles of mastication was determined in a series of 34 Caucasian skulls. This data was then used to construct a test loading rig in which a human mandible was mounted and could be loaded in a simulated physiological manner. The mandible contained dental implants, and baseline data on its functional deformation were obtained using photoelastic stress coating. A range of electronic displacement transducers was then developed on the rig for subsequent mounting intra-orally on dental implants. These measured corporal rotation, dorso-ventral shear and approximation of the corpora in real time, via a multi channel data logging system. This was combined with a strain gauge loading beam and a Mandibular Kinesiograph, to enable simultaneous recording of jaw positions and the loads applied to the implant fixtures. The effects on jaw deformation of loading various implants and of contraction of different jaw closing muscles were then studied in the test rig. The clinical study was conducted in a group of subjects who had been treated successfully with mandibular dental implants. Patient variables measured were relative mandibular bone density (using periapical radiographs and aluminium step wedges), jaw shape and dimension as well as implant sizes and positions. Medial convergence, dorso-ventral shear and corporal rotation were then measured in relation to jaw position and a range of loading modalities. The in vitro investigation using the photoelastic coating, showed deformation to occur in the region anterior to the mental foramina, near the condyles and along the external oblique ridges. The transducers showed that deformation was markedly related to the point of loading, depending on whether a force was applied to the symphysis, or any particular implant. A scheme for describing corporal rotation and dorso-ventral shear has been developed. The clinical investigation demonstrated these deformations and approximation of the corpora. Jaw deformation took place immediately on the commencement of jaw opening, and was related to muscle activity and bone variables. The degree of approximation was less than that recorded in previous studies. The existence and dimensions of corporal rotation and dorso-ventral shear have never been reported for in human subjects. Mandibular deformations occurring during lateral excursions were considerably less than those during jaw opening.

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