Location of the centre of resistance of the upper dentition and the nasomaxillary complex. An experimental study

The purpose of this study was to investigate the initial displacement of th e upper dentition and the nasomaxillary complex as a result of different di rections of force application, and to determine the initial centres of resi stance for both the upper dentition and the nasomaxillary complex. A macerated human skull with a well-aligned upper arch was used as one expe rimental model and Araldit 208 as a substitute for the periodontal ligament (PDL). Specifically designed 'antenna-headgear' was developed in an attemp t to create different points of force application to simulate high-pull and horizontal traction, and orthopaedic force magnitudes of 8 N were applied to the upper dentition and the nasomaxillary complex. Double exposure holog raphy was used to measure the initial displacement. Reproducibility of the technique was tested and found to be reliable. According to the registered fringe patterns, the force application transmit ted by the headgear resulted in complex displacement of facial bones. Pure translation of the maxilla and the upper dentition was observed when the fo rce vector passed by in the area of the key-ridge. No obvious difference wa s found between the centre of resistance of the upper dentition and the nas omaxillary complex. The location of two different centres of resistance cou ld not be confirmed by measuring initial displacements on this macerated hu man skull.