Effect of a screw-access channel on the fracture resistance of monolithic zirconia crowns

Abstract

Purpose This in-vitro study was designed from a clinical case and investigated the effect of the presence of a screw assess channel, created either during the milling phase or following cementation, on the fracture strength of a monolithic zirconia cement-retained implant-supported fixed prosthesis (ISFP). Material & Methods A definitive cast from a clinical case restoring a mandibular right first molar implant was utilized to fabricate three different styles of monolithic zirconia cement-retained ISFP. Group 1 had no screw-access channel (CR), Group 2 had a screw-access channel milled in the green phase (MA), and Group 3 had a screw-access channel created by hand preparation after cementation (HA). With 3 groups and 5 samples in each group, there were a total of 15 monolithic zirconia crowns fabricated on custom abutments in preparation for testing. The maximum force required for crown fracture was measured using a universal testing machine. Results The mean loads to fracture from highest to lowest were: the milled screw-access channel group (MA), followed by the hand-made screw-access channel group (HA), and lastly by the cement-retained group without a screw-access channel (CR). One-way ANOVA analysis indicated the fracture strength of the MA was statistically significantly different than the cement-retained samples (P<0.05). No statistically significant differences were found between the milled screw-access channel and the access channel created by hand. Conclusion The presence of a screw-access channel, whether milled or prepared by hand, does not negatively affect the fracture strength of a monolithic zirconia ISFP.