Achievable convergence angle and the effect of preparation design on the clinical outcome of full veneer crowns in dogs.
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It is widely accepted that the convergence angle of a full veneer crown preparation should be as close to parallel as possible to attain adequate retention/resistance. The shape of the dog's canine tooth limits the veterinary dentists' ability to achieve the recommended convergence angle. However, the clinically achievable convergence angle of the canine tooth in dogs has not been evaluated. In addition, the convergence angle and other physical properties of a preparation, such as height and base diameter, have been shown to affect the retention/resistance of full veneer crowns, in vitro. This effect has not been evaluated clinically in the dog. Physical properties of 32 stone dies from full veneer crowns of canine teeth were studied to evaluate the clinically achievable convergence angle and the potential effect physical properties of the preparation had on the clinical outcome of the restoration. The clinically achievable convergence angle was much higher than the current recommendation. There was an association, albeit not statistically significant, between physical properties of a preparation (convergence angle, height, base diameter) and the clinical outcome of the restoration. (+info)
Optimum design for glass fiber-reinforced composite clasps using nonlinear finite element analysis.
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The purpose of this study was to design an optimum glass fiber-reinforced composite (FRC) clasp. Three-dimensional finite element models were constructed of FRC circumferential clasp arms and an abutment tooth. The basic clasp arm was half-oval, without a taper, 2.60 mm wide and 1.30 mm thick. Four modified clasp arms were prepared by changing the width or thickness of the basic clasp (width/thickness: 2.60 mm/0.65 mm, 2.60 mm/1.95 mm, 1.30 mm/1.30 mm, and 3.90 mm/1.30 mm). Forced displacements of 5 mm in the removal direction were applied to the nodes at the base of the clasp arm. The retentive forces and maximum tensile stresses of the five FRC clasp arms ranged from 1.00-16.30 N and from 58.9-151 MPa, respectively. Results showed that an optimum FRC clasp was a circumferential clasp with 2.60 mm width and 1.30 mm thickness, which had sufficient retentive force and low risk of tensile failure. (+info)
Effects of surface roughness and tapered angle of cone crown telescopic system on retentive force.
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This study evaluated the effect of surface roughness and tapered angle of cone crowns on retentive force (RF). Cone crowns from Ti-6Al-7Nb alloy with a tapered angle of 4, 5, or 6 degrees were fabricated using a milling machine and a finishing machine to produce a smooth surface. Cone crowns of 6 degrees with a rough surface were also prepared. The RF during 1,000 cycles of insertion/separation was recorded. The first RF of the 6 degrees cone crowns was 24.2-27.7 N, and the surface roughness was not significant. The RF of all specimens decreased at 100 cycles, then those of inner and outer crowns with the same roughness remained unchanged, but those of different roughnesses increased with number of cycles. The RF of cone crowns with a smaller tapered angle was significantly greater than with a larger angle at any measured cycles. (+info)
Validation of implant stability: a measure of implant permanence.
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