Effects of surface roughness and tapered angle of cone crown telescopic system on retentive force.

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° were fabricated using a milling machine and a finishing machine to produce a smooth surface. Cone crowns of 6° with a rough surface were also prepared. The RF during 1,000 cycles of insertion/separation was recorded. The first RF of the 6° 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.