Functional mandibular deformation in edentulous subjects treated with dental implants.

PURPOSE: The purpose of this study was to measure medial convergence, dorsoventral shear, and corporal rotation in the human mandible. MATERIALS AND METHODS: Measurements were made using custom-fabricated strain gauge displacement transducers in 6 edentulous subjects who had been treated with mandibular endosseous dental implants. These were mounted on the most distal of the mandibular implants on each side, and measurements were made in real time using a multichannel analogue/digital converter and a personal computer for data storage and analysis. Measurements were made while the implants were loaded, and the subjects opened and closed their mouths and made lateral mandibular excursions. Medial convergence was measured as a linear change at the site of the most distal implant. Dorsoventral shear was expressed as a relative rotation of the right and left mandibular bodies projected onto the median sagittal plane, and corporal rotation was expressed as the relative rotation of the most distal implant. RESULTS: Jaw deformation was found to occur immediately on opening and was related to closing forces and jaw position. Medial convergence of up to 41 microns was observed, with values for corporal rotation of up to 6 degrees and dorsoventral shear of up to 19 degrees. CONCLUSION: The study demonstrated clinically for the first time 3 different and simultaneous patterns of functional mandibular deformation.

Effects of superstructure type and design on force transmission via implant-stabilised mandibular prostheses.

Forces to which individual implant units are subjected when an implant-stabilised mandibular over-denture is loaded have been measured using a carbon-fibre reinforced epoxy resin replica of an edentulous mandible mounted in a loading rig which simulated physiological conditions. Three different retentive designs were used; ball attachments, a fixed-fixed bar cranked anteriorly, and a similar design with posterior cantilevers. Forces exerted on the implants were measured using resistance strain gauges mounted on their trans-mucosal abutments and the dentures were loaded at individual tooth positions with a strain gauge beam. Ball attachments were associated with the lowest detected forces on the abutments. It is concluded that variations in superstructure design affect the forces transmitted by implants stabilising a complete mandibular over-denture, when the mandible is suspended and loaded in a physiological manner.

Acrylic denture distortion following double processing with microwaves or heat.

The present study compared the fit of acrylic resin bases subjected to two curing cycles in a water-bath or in a microwave oven. Resin bases were processed on duplicate stone casts prepared from a cobalt chromium master die. Ten bases, composed of conventional polymethylmethacrylate, were cured in a water-bath for 7 h at 70 degrees C and 3 h at 100 degrees C, and a further 10 cured in a domestic microwave oven at 65 W for 25 min. Ten bases composed of polymethylmethacrylate modified by means of a chemical activator were cured at 100 degrees C in a water-bath for 20 min. All bases were then subjected to a second curing cycle following addition of new acrylic resin to the alveolar ridge areas. Following each curing cycle the fit of the posterior border of each base was evaluated. A silicone impression material was used to form indices between the bases and the master die, these were then invested in stone and sectioned to allow cross-sectional measurement by means of an eyepiece micrometer. A one-way analysis of variance and unpaired Student's t tests were employed to compare the differences in distortion of the three groups. The differences in distortion between the first and second curing cycles were significant for all curing methods (P less than 0.001). However, microwave curing caused significantly less distortion of the denture base than short water-bath curing, especially in the centre of the palate (P less than 0.001).