Abstract
Statement of problem. The clinical long-term success of single-tooth implant restorations depends, in part, on a stable connection between the prosthetic restoration and the implant body. Purpose. The purpose of this experiment was to investigate the fatigue life of UCLA-style abutment screws in wide-diameter versus conventionally sized dental implant restorations. Material and methods. Five 3.75 × 15-mm and five 6.0 × 15-mm hexed dental implants were used. Ten frameworks were fabricated, 5 with a single UCLA-style, 3.75-mm hexed gold alloy cylinder, and 5 with a single UCLA-style, 6.0-mm hexed gold alloy cylinder. To simulate a common laboratory procedure, 2 abutment interfaces were relieved with a one-quarter round bur for both diameters. The 3.75-mm implant used a Gold-Tite central abutment screw torqued to 32 Ncm, and the 6.0-mm implant used a titanium central abutment screw torqued to 25 Ncm. Frameworks were dynamically loaded (~10 Hz) with a 120 ± 10-N, 4-mm off-axis force. Liquid metal strain gauges were used to measure joint opening. Measurements were made at intervals of 103, 104, 105, and 5×105 cycles. Gauge output data were converted to displacement with a conversion factor determined by calibration. Linear regression analysis then was performed. Results. Two observations were made in this study. Two of three 3.75-mm nonadjusted specimens and all three 6.0-mm nonadjusted specimens maintained joint closure (range of opening 0-20 μm) while measured under dynamic loading. The median joint opening at 5×105 cycles for 3.75-mm nonadjusted specimens was 14 ± 7 μm; for 6.0-mm specimens, it was 11 ± 10 μm. Both 3.75-mm adjusted specimens and 1 nonadjusted specimen failed to maintain joint closure (excess joint opening >50 μm). One of the 3.75-mm adjusted specimens had abutment screw fracture. One of two 6.0-mm adjusted specimens failed to maintain joint closure because of screw fracture. Conclusion. The dental implant–abutment interface of 3.75-mm and 6.0-mm externally hexed implants experienced similar joint opening after periods of dynamic loading. Laboratory adjustment of the interface significantly decreased the service life of the abutment screw joint. (J Prosthet Dent 2001;85:599-607.)
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