Dimensional Accuracy Analysis of Implant Framework Castings from Two Casting Systems

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Dimensional Accuracy Analysis of Implant Framework Castings from Two Casting Systems
28 June 2003
T.L. CHANG, C. MARUYAMA, S.N. WHITE, S. SON, and A.A. CAPUTO, UCLA School of Dentistry, Los Angeles, CA, USA
IADR
Objectives: The importance of passive fit of implant-prosthetic component interfaces has been amply documented. Misfitting implant prostheses can lead to screw loosening, component fracture, or bone loss. The purpose of this investigation was to compare the dimensional accuracy of implant framework castings from an argon vacuum casting machine with those from a centrifugal casting machine. Methods: Three 4 x 10 mm external hex type implants (3i) were embedded in an acrylic block. Implants were 7 mm apart with 2 mm offset of the middle implant. Eight reference points were marked on the collar of the implants. Twenty implant bar frameworks were waxed with UCLA abutments, invested with a ringless system, and subjected to the same thermal cycle. Ten wax patterns were cast in gold alloy (550, Leach & Dillon) using an oxygen-propane torch and centrifugal casting system. The other 10 patterns were cast using an argon vacuum casting machine (KDF, Denken Co.). The White one screw technique was applied after sequentially tightening the mesial and distal abutment screws to 10 Ncm. Fit of the implant framework castings was evaluated by measuring the vertical discrepancy at the reference points between the UCLA abutment and implant fixture under a microscope at 80X. The vertical discrepancies at each of the implants for the two casting systems were averaged and statistically compared for differences. Results: The mean discrepancy at the distal implant from the tightened mesial abutment screw was 96.4¨±5.8 mm for the centrifugal system compared to 27.5¨±7.2 mm for KDF (p<0.05). For distal screw tightened, the mesial discrepancy was 36.6¨±11.6 mm for the centrifugal system compared to 55.4¨±9.2 mm for KDF (p>0.05). Conclusions: Utilizing the one screw technique to evaluate casting fit, the results indicate that the KDF argon vacuum casting machine may produce more accurate castings than the conventional centrifugal casting system.