Stability of screw-retention in two-piece zirconia implants: An in vitro study.

Abstract

To compare the stability of a screw-retained connection in a novel two-piece zirconia implant to a conventional titanium-based connection in an in vitro chewing simulation including artificial ageing. Incisor (I) and molar (M) shaped monolithic zirconia crowns were screw-retained on either two-piece zirconia (test) or two-piece titanium (control) implants resulting in 4 groups of 8 samples (titanium implants with incisor-shaped crowns (T-I), titanium implants with molar-shaped crowns (T-M), zirconia implants with incisor-shaped crowns (Z-I) and zirconia implants with molar-shaped crowns (Z-M). These were subjected to artificial ageing by thermal cycling (TC: 2×3000×5°C/55°C cycles of 2min) and mechanical loading (ML: 1.2×106 cycles of 50N, f=1Hz). Surviving samples additionally underwent a fracture force test. Kaplan-Meier plots were drawn, and two-way ANOVA was calculated taking anatomical localisation and material variables as factors. The mean corresponding survival times were lower for T-M (0.86×106 ±0.31×106 cycles) and Z-I (0.84×106 ±0.21×106 cycles) compared to T-I (1.14×106 ±0.10×106 cycles) and Z-M (1.20×106 ±0.10×106 cycles). In one-way ANOVAs for survival time dependent on either location or material, no statistically significant differences could be found (location: p=.31; material: p=.62) in one-way ANOVAs. The interaction of location and material showed significant differences (F=21.3, p<.001). The connection of the tested screw-retained zirconia crowns in two-piece zirconia implants is comparable to standard titanium implants in the specific in vitro testing.