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 the upper dentition and the nasomaxillary complex as a result of different directions of force application, and to determine the initial centres of resistance for both the upper dentition and the nasomaxillary complex. A macerated human skull with a well-aligned upper arch was used as one experimental model and Araldit 208 as a substitute for the periodontal ligament (PDL). Specifically designed 'antenna-headgear' was developed in an attempt 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 holography 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 transmitted by the headgear resulted in complex displacement of facial bones. Pure translation of the maxilla and the upper dentition was observed when the force vector passed by in the area of the key-ridge. No obvious difference was found between the centre of resistance of the upper dentition and the nasomaxillary complex. The location of two different centres of resistance could not be confirmed by measuring initial displacements on this macerated human skull.