Effect of Screw-access Channels on the Fracture Resistance of 3 Types of Ceramic Implant-supported Crowns

Statement Of Problem: Access channels for retrieving ceramic implant-supported screw-retained crowns may decrease their fracture resistance.

Purpose: The purpose of this in vitro study was to evaluate the effect of screw-access channels on 3 types of ceramic implant-supported crowns.

Material And Methods: Sixty computer-aided designed and computer-aided manufactured (CAD-CAM) ceramic implant-supported screw-retained maxillary premolar crowns were fabricated, 30 with an occlusal screw-access channel and 30 without access channels. Each group was further divided into the following 3 subgroups of 10 specimens each: monolithic zirconia, veneered zirconia, and lithium disilicate. Identical milled titanium implant abutments were fabricated. Crowns were fabricated with standardized thicknesses and subjected to cyclic loading until failure occurred. Data analysis was performed using 1-way analysis of variance test of significance followed by Tukey honest significant difference (HSD) test (α=.05).

Results: No significant differences in fracture resistance were found between access channel groups and corresponding groups without access channels (P>.05). Among the subgroups, monolithic zirconia recorded the highest fatigue failure mean load values (2047.8 ±83.2 N for crowns with access channels and 2028.7 ±104.5 N for crowns without access channels), which was significantly higher (P<.05) than values for the lithium disilicate group (605.4 ±37.9 N for crowns with access channels and 615.3 ±76.6 N for crowns without access channels) and the veneered zirconia group (411 ±34.4 N for crowns with access channels and 461.2 ±72.7 N for crowns without access channels), which recorded the lowest fatigue failure load mean values.

Conclusions: Screw-access channels did not affect the fatigue failure load of monolithic zirconia, monolithic lithium disilicate, or veneered zirconia ceramic crowns. Monolithic zirconia crowns recorded significantly higher fatigue failure load among the 3 types of crowns tested.