Biomechanical evaluation of the effects of thread parameters on dental implant stability: a systematic review

The threads of dental implants are critical components that transfer occlusal loads to the surrounding bone. The appropriate size of thread parameters can influence the stability of the implant after implantation. Despite several research studies on the effectiveness of implant thread parameters, there is limited structured information available. This study aims to conduct a systematic review to evaluate the biomechanical effects of thread parameters, namely, thread depth, thread width, thread pitch, and thread angle on implant stability. A comprehensive literature review was conducted in PubMed/MEDLINE, Scopus, ScienceDirect, and Web of Science for research published in English in the last two decades according to the PRISMA protocols. The extracted data were organized in the following order: area, bone layers, bone type, implant design, implant material, failure criteria/unit, loading type, statistical analysis/optimization, experimental validation, convergence analysis, boundary conditions, parts of the Finite Element Model, studied variables, and main findings. The search yielded 580 records, with 39 studies meeting the selection criteria and being chosen for the review. All four thread parameters were found to affect the stress and strain distribution in cancellous and cortical bones. Thread pitch and depth are more important for implant primary stability as they are directly correlated with the functional surface area between the implant and bone. Moreover, thread pitch, depth, and width can increase the insertion torque, which is favorable for implant primary stability, especially in low-quality bones. The thread angle can also direct occlusal forces to the bone more smoothly to prevent bone overloading and destructive shear stresses, which cause bone resorption. This structured review provides valuable insights into the biomechanical effects of thread parameters on implant stability.