Mechanical stress during implant surgery and its effects on marginal bone: a literature review

Objective: High levels of primary implant stability have been advocated particularly for immediate loading protocols. Current implant systems and drill protocols are intended not to cause excessive stress on bone during implant insertion as resorptive processes might compromise esthetics and function. The goal of this narrative review was to summarize current data on the effect of mechanical stress on alveolar bone. Method and materials: PubMed was searched (final search conducted on 30 September 2019) applying the user query "(dental implant insertion) AND (mechanical stress) AND (bone)." The papers identified were grouped according to the research methodology applied (in vitro studies and finite element analysis, animal studies, and clinical trials). Results: In total, 176 articles were identified, of which 58 were included. A clear tendency towards increased stress in bone resulting from the use of undersized osteotomies was shown. Depending on the degree of undersizing, the inner parts of implant threads create healing chambers in which bone formation seems to progress very well, while areas of direct contact between implant body and alveolar bone experience resorption during healing. More resorption seems to occur when implants have been placed with higher insertion torque, although these implants maintain greater total bone-to-implant contact during initial healing. Clinically, mobile implants seem to have a compromised prognosis and high insertion torques seem not to guarantee successful osseointegration. Marginal bone level changes obviously have a tendency of being greater in implants inserted with high levels of torque. Conclusion: Clinicians should be cautious during implant surgery not to overstress bone. Future implant systems should focus on optimized drill protocols and apply macrodesigns that also derive stability from trabecular bone as well, instead of merely compressing the cortical layer. Keywords: alveolar bone, compression, implant insertion, marginal bone level change, mechanical stress