Influence of Screw Access Hole Diameter and Preparation Method on the Fit and Fracture Resistance of Implant-Supported Monolithic Zirconia Crowns.

Abstract

Purpose: To evaluate how screw access hole (SAH) presence, diameter, and preparation method affect marginal and internal fit and fracture resistance of implant-supported monolithic zirconia crowns.

Materials and methods: Seventy-two crowns were assigned to six groups (n=12): no SAH; 1-, 2-, or 3-mm presintered SAHs; a 1-mm SAH enlarged to 3 mm after cementation; or a 3-mm SAH prepared after cementation in crowns without an initial SAH. Marginal and internal fit was assessed in the first four groups by the silicone replica technique. After thermocycling and cyclic loading, fracture load, Weibull parameters, fracture patterns, and scanning electron microscopy findings were evaluated.

Results: Overall discrepancy and internal gap were greater without an SAH (184.7 and 182.1 μm) than with an SAH (54.7-65.9 and 60.1-71.1 μm) (P<.05), with no differences among SAH diameters (P>.05). Fracture loads were higher for no SAH and a 1-mm SAH than for all groups with 2- or 3-mm openings (P<.001). Among final 3-mm openings, preparation method did not affect mean fracture load (P>.05), although handpiece-prepared groups had lower Weibull moduli.

Conclusions: The 1-mm SAH improved crown fit without reducing fracture resistance, whereas openings of 2 mm or larger reduced fracture resistance. For 3-mm SAHs, preparation method did not affect mean fracture load.