Accuracy of three corrective techniques for implant bar fabrication

Statement of the problem. Numerous articles emphasize the importance of pas sivity of inplant-prosthetic component interfaces. Nonpassive interfaces ca n lead to bone loss, abutment fracture, and connecting screw breakage. Purpose. The purpose of this study was to evaluate 3 postcasting techniques for the correction of non passive fit between a cast bar superstructure an d its interface with an implant abutment. Material and methods. Thirty implant Hader bars were fabricated based on a metal model composed of two 3.8/4.5 HL PME titanium implant abutments. Init ial measurements were collected on the y-axis of the left implant abutment- bar interface by using a M2001ARS toolmaker microscope. Means were calculat ed from buccal, distal, and lingual measurements on each specimen. Ten spec imens were sectioned, indexed, and corrected by casting the same alloy(grou p 1). Ten specimens were sectioned, indexed, and corrected by soldering (gr oup 2). The last 10 specimens were submitted to 2 cycles of electrical disc harge machining on a MedArc M-2 EDM machine (group 3). Postcorrection measu rements were collected on the 3 groups. A 1-way ANOVA and a Tukey-Kramer te st at a .05 significance level were performed on the 3 groups after the cor rective techniques. Results. Initial gap means were 192 mum for group 1, 190 mum for group 2, a nd 198 mum for group 3. There was a significant difference (P<.05) in gap m eans between group 1 (15 <mu>m) and group 2 (72 mum) as well as between gro up 2 and group 3 (7.5 mum) after each correction technique. No difference w as detected between group I and group 3. Conclusion. The electrical discharge machining group resulted in the smalle st mean gap distance of 7.5 pm, thus meeting the criteria of passive fit (w ithin 10 mum) described in the literature.