Effect of Cortical Shell and Bone Quality on the Pullout Comparison of Mini-Implants

Abstract

Anchorage, which is defined as resistance against undesired tooth movements, is one of the most important factors in orthodontic treatments. In recent years, mini-implants have been started to use instead of uncomfortable headgears and nance appliance etc. Mini-implants are the small sized screws with 1 to 2.5 mm in diameter and 4 to 21 mm in length. Anchorage capacity of a mini-implant can be measured with pullout tests. The main factors that affecting the implant’s pullout performance are bone mineral density (BMD), thickness of the cortical bone and implant design. There are several studies in literature that are investigating these factors. On the comparison of pullout performance for mini-implants, human and animal cadavers were used as test medium in recent studies. In addition to this, there are also several studies that the tests had been conducted on polyurethane (PU) foams as a standard testing material. The main advantage of using synthetic foam is omitting the bone quality bias via using a uniform and standard material. In this study, cortical shells including PU foams were produced with several cortical thicknesses and foam densities. Aim of this study was to determine the effect of cortical shell’s thickness and density on the pullout performance of the mini-implants. Results showed that cortical shell thickness is directly correlated with the pullout strength and although the density of the cortical shell has an effect on pullout the most dominant factor is the cortical shell thickness.