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

PURPOSE: 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, preexisting CBCT data sets were imported into image-processing software (Mimics and 3-matic, Materialise) to create accurate 3D mandibular contours using finite element analysis (FEA). A total of 18 models for the reconstruction of the mandibular first and second molars were created based on the implant diameter, crown height, and splinted or nonsplinted form, with a 100-N load applied at a 30-degree angle. Two extra-short implants with a length of 4 mm and a diameter of 4.1 mm and/or 4.8 mm were used; the crown heights were 15 mm, 12.5 mm, and 10 mm, depending on the model.

RESULTS

The study of stresses in cortical bone, trabecular bone, implants, and crowns revealed that the highest stress levels (ie, 118.27 MPa in cortical bone) were associated with the treatment plan involving two implants with a diameter of 4.1 mm without a splint and a crown height of 15 mm. Conversely, the lowest amount of stress (ie, 29.12 MPa in cortical bone) was observed in the treatment plan with two implants with a diameter of 4.8 mm without a splint and a crown height of 10 mm. Crown height influenced stress the most (≤ 237.6% increase), followed by diameter (≤ 63.7% reduction, weakened at higher crowns), while the type of splinting effects varied (ie, +122.7% crown stress increase in specific cases); cortical bone stayed below a 130 MPa safe zone, but trabecular bone often exceeded 10 MPa.

CONCLUSIONS

Increasing the height of the crown in nonsplinted implants leads to an increase in stress distribution in all cases of the treatment plan outlined in this study, with statistical analysis suggesting trabecular bone risk and a need for fatigue studies.