Observational study on primary and secondary stability of two current bone level implant designs

Objective: Achieving high levels of primary implant stability is considered to be desirable, despite some studies warning of the risk of bone damage. It was the goal of this observational clinical study to compare two current bone level implant systems with respect to primary and secondary stability. Method and materials: Data on bone quality, insertion torque, implant stability at insertion and after healing, as well as number of implants lost during healing were obtained from two centers either placing BLT (Bone Level Tapered, Straumann) or Nobel Parallel CC (Nobel Biocare) implants. Statistical analysis was based on Spearman rank correlation tests, analysis of variance, and t tests with the level of significance set at α = .05. Results: A total of 312 BLT and 92 Nobel Parallel CC implants were placed. Ten BLT and two Nobel Parallel CC implants failed resulting in survival rates of 96.79% and 97.83%, respectively. Mean insertion torque recorded in the different bone classes showed large standard deviations, and only torque values for BLT implants recorded in type 3 bone differed significantly from type 2 bone and type 1 bone (P = .024). For BLT implants, bone quality and insertion torque correlated (Spearman rho = -.3326; P = .0023) as did ISQ at insertion (Spearman rho = -.2241; P = .0429). Implant diameter significantly affected primary (P = .0013) and secondary (P = .0050) stability of Nobel Parallel CC implants while for BLT implants a significant effect was only seen for secondary stability (P = .0000). Bone quality had a significant effect on implant insertion torque for BLT implants (P = .0059). Bone quality had no general effect on ISQ changes during healing but 3.3-mm BLT implants showed significantly (P = .0005) lower stability after healing. Conclusion: Huge variation with respect to primary and secondary stability seems to exist among similar looking implant systems clinically used for identical indications.