An in vivo quantitative analysis of the fit of Nobel Biocare implant superstructures

LOSS Of osseointegration of implant fixtures and mechanical failure of superstructures have been attributed to failure to achieve a passive fit between the superstructure and the transmucosal abutment (TMA). The fit of five mandibular superstructures, fabricated on Nobel Biocare implants, was investigated in vivo, using a polyvinyl siloxane impression material to record the discrepancies. Following sectioning of the impressions, the vertical and horizontal discrepancies were analysed at four locations using a travelling microscope. The discrepancies obtained were measured both when the gold cylinder screws were maximally tightened by hand and when tightened with a torque driver to the recommended value of 10 Ncm. The vertical discrepancies for the hand tightened abutments ranged from 0 mu m to 63 mu m with a mean of 14 mu m. In the mechanically tightened group, the vertical discrepancies ranged from 0 mu m to 130 mu m with a mean of 21 mu m. The horizontal discrepancies for the mechanically tightened abutments ranged from 0 mu m to 140 mu m with a mean of 31 mu m, compared with a mean of 46 mu m and range of 0 mu m to 113 mu m, for the hand-tightened abutments. A close fit was seldom achieved. It is concluded that considerable discrepancies existed around superstructures that had been judged to have a clinically acceptable fit. These were reduced in the vertical direction by hand tightening of the gold screws.