PubMed · 1506574
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S C Rhodes, L K Branham. 1992. Handpieces.. https://doi.org/10.14219/jada.archive.1992.0201
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This article is the second in a series of three compiling the results of the 1995 Managed Care Marketplace Information Survey conducted by the ADA Council on Dental Practice. This article addresses dentists' opinions on various statements regarding managed care. Most dentists had similar opinions regardless of whether they participated in managed care.
STATEMENT OF PROBLEM: The use of endosseous implants to support and retain dental prostheses has become a routine treatment option in many dental practices. Although physical, mechanical, and chemical differences exist among implant systems, survival claims are similar. PURPOSE OF STUDY: This review solicited literature from six implant manufacturers that was thought, by their standards, to be pertinent to the validation of their implant system. METHODS: The literature was reviewed and categorized. CONCLUSION: On the basis of the literature supplied by the manufacturers, only one implant system demonstrated scientifically valid long-term success.
Cyclic fatigue of nickel-titanium, engine-driven instruments was studied by determining the effect of canal curvature and operating speed on the breakage of Lightspeed instruments. A new method of canal curvature evaluation that addressed both angle and abruptness of curvature was introduced. Canal curvature was simulated by constructing six curved stainless-steel guide tubes with angles of curvature of 30, 45, or 60 degrees, and radii of curvature of 2 or 5 mm. Size #30 and #40 Light-speed instruments were placed through the guide tubes and the heads secured in the collet of a Mangtrol Dynamometer. A simulated operating load of 10 g-cm was applied. Instruments were able to rotate freely in the test apparatus at speeds of 750, 1300, or 2000 rpm until separation occurred. Cycles to failure were determined. Cycles to failure were not affected by rpm. Instruments did not separate at the head, but rather at the point of maximum flexure of the shaft, corresponding to the midpoint of curvature within the guide tube. The instruments with larger diameter shafts, #40, failed after significantly fewer cycles than did #30 instruments under identical test conditions. Multivariable analysis of variance indicated that cycles to failure significantly decreased as the radius of curvature decreased from 5 mm to 2 mm and as the angle of curvature increased greater than 30 degrees (p < 0.05, power = 0.9). Scanning electron microscopic evaluation revealed ductile fracture as the fatigue failure mode. These results indicate that, for nickel-titanium, engine-driven rotary instruments, the radius of curvature, angle of curvature, and instrument size are more important than operating speed for predicting separation. This study supports engineering concepts of cyclic fatigue failure and suggests that standardized fatigue tests of nickel-titanium rotary instruments should include dynamic operation in a flexed state. The results also suggest that the effect of the radius of curvature as an independent variable should be considered when evaluating studies of root canal instrumentation.