THE INFLUENCE OF MANDIBULAR DEFORMATION, IMPLANT NUMBERS, AND LOADINGPOSITION 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 fu nctional jaw deformation, yet the phenomenon has received little atten tion and is rarely included as a variable when investigating implant b iomechanics. Purpose. This in vitro investigation tested the hypothesi s that functional mandibular deformation influences force distribution in the jaw/implant/superstructure complex. Material and methods. Six Branemark implants were mounted in an acrylic resin replica of an eden tuous human mandible. Applied forces were measured with 4-element resi stance strain gauges mount-ed on each of 6 standard titanium abutments . The mandible was supported either on its lower border or suspended i n a frame that simulated the natural situation. A cast gold superstruc ture was mounted on varying combinations of implants, loaded occlusall y in different locations, and the resultant forces at each supporting transmucosal abutment measured. Results. The suspended (''natural'') s upport configuration was associated with considerable differences in p atterns of force transmission as compared with bench support. Loads we re more widely spread, and large extrusion forces were detected, parti cularly where several implants were connected. Conclusions. Functional mandibular deformation is a significant factor in the design of mandi bular implant stabilized prostheses, and calls into doubt the value of modeling techniques that do not allow for this phenomenon.