Evaluation of the Effects of Diameter, Length, Splinted or Non- Splinted Forms, and Crown-to-Implant Ratio on the Stress Distribution around Extra-Short Implants in the Posterior Mandible: Finite Element Analysis

Purpose: Significant advancements in implantology over the past decade have expanded treatment options for maxillofacial reconstructions. This study aimed to investigate the distribution of stress in the bone around extra-short posterior mandibular implants to replace two molar teeth in six different treatment plans. Materials and Methods: In this experimental study, pre-existing cone beam computed tomography (CBCT) data sets were imported into image processing software (Mimics and 3-matic) to create accurate three-dimensional (3D) mandibular contours using finite element analysis (FEA). A total of 18 models for the reconstruction of the first and second mandibular molars were defined based on the implant diameter, crown height, and splinted or non-splinted forms, with a 100 N load applied at a 30- degree angle. Two extra-short implants with a length of 4mm and diameters of 4.1mm or 4.8mm were utilized. The crown heights were also 15mm, 12.5mm, and 10mm. Results: The study of stresses in cortical bone, trabecular bone, fixture, and crown revealed that the highest stress levels (e.g., 118.27 MPa in cortical bone) were associated with the treatment pla involving two implants with a diameter of 4.1mm without a splint and a crown height of 15mm. Conversely, the lowest amount of stress (e.g., 29.12 MPa in cortical bone) was observed in the treatment plan with two implants with a diameter of 4.8mm without a splint and a crown height of 10mm. Crown height most influenced stress (up to 237.6% increase), followed by diameter (up to 63.7% reduction, weakened at higher crowns), while splinting effects varied (e.g., +122.7% crown stress increase in specific cases); cortical bone stayed below a 130 MPa safe zone, but trabecular bone often exceeded 10 MPa. Conclusion: Increasing the height of the crown in non-splinted implants leads to an increase in stress distribution in all cases of the treatment plan outlined in this study, with static analysis suggesting trabecular bone risk and a need for fatigue studies.