Objectives: Measuring peak insertion torque in relation to different bone densities, the present study seeks to determine whether micromotion at the interface is related to primary stability achieved by increasing insertion torque.
Material and methods: A total of 120 Ti-Bone implants were placed in fresh bovine bone samples representing three density categories: hard, normal and soft (HNS). Five groups of peak insertion torque (20, 35, 45, 70 and 100 N/cm) were evaluated in the three bone density categories noted. Customized electronic equipment connected to a PC was used to register the peak and other insertion torque data. A loading device, consisting of a digital force gauge and a digital micrometer, was used to measure the micromovements of the implant during the application of 20, 25 and 30 N lateral forces. The data were analyzed for statistical significance by ANOVA and Spearman's rank correlation coefficient tests.
Results: A statistically significant difference between implant micromobility placed with different levels of torque and in different bone densities was demonstrated by ANOVA. Spearman's rank correlation coefficient showed a high dependency between the peak insertion torque and the observed micromovement. Particularly, in soft bone, it was not possible to achieve more than 35 N/cm of peak insertion torque.
Conclusions: Results showed that increasing the peak insertion torque reduces the level of implant micromotion. In addition, micromotion in soft bone was found to be consistently high, which could lead to the failure of osseointegration. Thus, immediate functional loading of implants in soft bone should be considered with caution.