The influence of mandibular deformation, implant numbers, and loading position on detected forces in abutments supporting fixed implant superstructures.

STATEMENT OF PROBLEM Forces may arise in association with the use of implant stabilized mandibular fixed partial dentures as a result of functional jaw deformation, yet the phenomenon has received little attention and is rarely included as a variable when investigating implant biomechanics. PURPOSE This in vitro investigation tested the hypothesis that functional mandibular deformation influences force distribution in the jaw/implant/superstructure complex. MATERIAL AND METHODS Six Brånemark implants were mounted in an acrylic resin replica of an edentulous human mandible. Applied forces were measured with 4-element resistance strain gauges mounted on each of 6 standard titanium abutments. The mandible was supported either on its lower border or suspended in a frame that simulated the natural situation. A cast gold superstructure was a mounted on varying combinations of implants, loaded occlusally in different locations, and the resultant forces at each supporting transmucosal abutment measured. RESULTS The suspended ("natural") support configuration was associated with considerable differences in patterns of force transmission as compared with bench support. Loads were more widely spread, and large extrusion forces were detected, particularly where several implants were connected. CONCLUSIONS Functional mandibular deformation is a significant factor in the design of mandibular implant stabilized prostheses, and calls into doubt the value of modeling techniques that do not allow for this phenomenon.