A strain gauge analysis comparing 4-unit veneered zirconium dioxide implant-borne fixed dental prosthesis on engaging and non-engaging abutments before and after torque application

This study quantified the strain development after inserting implant-borne fixed dental prosthesis (FDP) to various implant-abutment joints. Two bone-level implants (empty set = 4.1 mm, RC, SLA 10 mm, Ti, Straumann) were inserted in polyurethane models (N = 3) in the area of tooth nos 44 and 47. Four-unit veneered zirconium dioxide FDPs (n = 2) were fabricated, one of which was fixed on engaging (E; RC Variobase, empty set = 4.5 mm, H = 3.5 mm) and the other on non-engaging (NE) abutments (RC Variobase, empty set = 4.5 mm, H = 5.5 mm). One strain gauge was bonded to the occlusal surface of pontic no. 46 on the FDP and the other two on the polyurethane model. Before (baseline) and after torque (35 Ncm), strain values were recorded three times. Data were analyzed using Kruskal-Wallis and Mann-Whitney U tests (alpha = 0.05). Mean strain values presented significant increase after torque for both E and NE implant-abutment connection type (baseline: E = 4.33 +/- 4.38; NE = 4.85 +/- 4.85; torque: E = 196.56 +/- 188.02; NE = 275.63 +/- 407.7; p<.05). Mean strain values based on implant level presented significant increase after torque for both E and NE implant-abutment connection (baseline: E = 4.94 +/- 5.29; NE = 5.78 +/- 5.69; torque: E = 253.78 +/- 178.14; NE = 347.72 +/- 493.06; p < .05). The position of the strain gauge on implants (p = .895), FDP (p = .275), and abutment connection type (p = .873) did not significantly affect the strain values. Strain levels for zirconium dioxide implant-borne FDPs were not affected by the implant-abutment connection type.