Insertion and Loading Characteristics of Three Different Bone-Level Implants

Purpose: While primary stability still constitutes an important factor for implant success, high levels of insertion torque resulting from bone compression are controversial and may constitute a co-factor in peri-implant bone loss. Materials and Methods: Adhering to the manufacturers' protocols for medium-quality bone, implant surgery was performed in polyurethane foam blocks equipped with strain gauges attached to the buccal aspect. Following insertion and attachment of provisional abutments, oblique loading was performed. The following parameters were recorded for three different implant types (Straumann Bone Level Tapered [BLT], MIS V3 [V3], Dentsply Sirona ASTRA TX [ASTRA]): maximum insertion and removal torque, maximum strain during insertion and loading, and implant stability before and after loading (resonance frequency analysis [RFA]). Statistical analysis was based on analysis of variance (ANOVA), Tukey honest significant difference test, and Pearson's product moment correlation (α = .05). Results: Maximum insertion torque (59.9 ± 4.94 Ncm) was recorded for BLT followed by V3 and ASTRA (P .01 for all comparisons). Maximum removal torque (43.7 ± 9.69 Ncm) was also recorded for BLT, but the pairwise comparisons reached significance only for BLT vs ASTRA (P .01) and V3 vs BLT (P = .03). Implant stability differed among groups only after loading, where the pairwise comparison between BLT and ASTRA reached significance (P = .02). Maximum strain during insertion was caused by BLT reaching 19,482.62 μm/m, whereas ASTRA implants only caused 6,169.84 μm/m. Strain development during insertion differed significantly among groups (P .05 for all comparisons). Maximum strain during loading was observed in V3 (646.44 ± 204 μm/m), while only a nonsignificant difference existed between ASTRA and BLT. Insertion torque correlated significantly with strain development (r = 0.68; P .01), implant stability after loading (r = 0.46; P = .01), and removal torque (r = 0.54; P .01). Also, implant stability after loading correlated with removal torque (r = 0.86; P .01). Conclusion: Different implant designs and surgical protocols result in varying levels of bone compression. Implants with a triangular shape do not seem to solve this problem. Keywords: implant insertion torque, removal torque, resonance frequency analysis, strain development