THE PRECISION OF FIT AT THE IMPLANT PROSTHODONTIC INTERFACE

Statement of problem. Percussion, visual observation, and conventional periapical radiographs are the methods most frequently used clinicall y to evaluate the accuracy of implant component assemblies, whereas me thods to measure the: precision of fit are limited. Purpose. In this s tudy the Periotest instrument was used to evaluate the stability of th e interfaces between the implant and the abutment, along with the abut ment and the gold cylinder under a series of assembly conditions. The hypothesis tested is that a more negative Periotest value (PTV) would indicate an accurate fit and a more positive value PTV would correlate with an inaccurate fit. Material and methods. To investigate this hyp othesis in vitro, two bovine ribs were used as patient simulation mode ls. Each model contained three self-tapping Branemark implants placed approximately 7 to 10 mm apart and arranged in a reasonable curvature. A series of component assembly conditions were created as accurate an d inaccurate with thickness gauges of 25.4 mu m, 50.8 mu m, and 101.6 mu m. Results. The mean Periotest values and SDs for accurately assemb led abutments and gold cylinders were 6.0 +/- 0.32 and -3.4 +/- 0.68, respectively. Periotest value data of the assembly conditions were sta tistically analyzed with multiple regression analysis. The misfit in t he implant to abutment interface resulted in a more negative Periotest value trend (r = 0.54) with increases in gauge thickness. However, th e same magnitudes of misfit at the abutment to gold cylinder interface produced a more positive Periotest value trend (r = 0.72). Conclusion . The PTV trends were consistent with increased stability at the abutm ent to implant interface from the increasing magnitude of misfit creat ed with the thickness gauges. In contrast, the measurement trends obse rved for the abutment to gold cylinder interface were consistent with decreased stability with each increase in gauge thickness inserted at the interface.