Effects of Length and Width of Microimplants on Stress Generation

Objective: The relative effect of implant length and width to screw design has been well evaluated with conventional integrated implants. Non-integrated implants used as temporary anchorage devices differ in application, use and design requirements. The purpose of this study was to evaluate the effect of differential length versus width for a single orthodontic implant design.

Methods: Composite photoelastic rectangular blocks were fabricated with individual simulants for cortical and trabecular bone. Self-drilling implants of 1.6 mm diameter and 2.0mm diameter (Rocky Mountain Orthodontics) were tested. Mircoimplant lengths of 6mm, 8mm and 10mm diameters were tested. The implants were inserted into the blocks according to manufacturers' recommendations. Stresses generated from the different microimplant designs were analyzed immediately after insertion. Stresses were digitally photographed in the field of a circular polariscope and analyzed to quantify stress intensity. Implants were not loaded as previous studies have shown that stresses generated from a loaded microimplant were largely installation stresses.

Results: All implants produced similar patterns of installation stress distribution. A localized higher intensity stress pattern was generated immediately adjacent to the lateral and apical aspects of the implants. The localized intensity increased as the implants increased in diameter and length. The outer lateral and apical fringes were the same on all microimplants.

Conclusion: No critical diameter or length was determined with this study. Installation stresses remained relatively constant regardless of length or width. The lateral and apical stress intensity increases with increasing length and diameter while the stress distribution remains relatively constant.