Journal of Orthodontics

Variation in head position in the cephalostat is a potential source of error in cephalometrics as it causes distortion of the radiographic projection of the head. Image subtraction is an electronic technique enabling images to be superimposed and which highlights any differences. Using this method, a study was carried out to assess the reproducibility of the position of the head in the cephalostat. It was also used to find out whether subjects could improve their own head relocation by looking at the monitor and trying to achieve the best possible fit on the original image.

In clinical use polycarbonate edgewise bracket designs, patterned on metallic predecessors, have demonstrated slot-wing fracture. A preliminary two-dimensional photoelastic stress investigation is described in which two bracket designs, without angles in the edgewise slot component, are subjected to simulated palatal root torque mechanics.

Cases of severely displaced unerupted maxillary canines are presented, related to disturbance of the follicle. Removal of the deciduous predecessor produced favourable eruption of the permanent canine and should be considered as a treatment option in similar cases.

Longitudinal records, in the form of study casts, of 35 Class I cases were examined for factors associated with changes of sagittal molar relationship during childhood. These were studied at two phases: between the deciduous and mixed dentitions, and between the mixed and permanent dentitions. During the first of these periods, there was a small, but general move to a less post-normal occlusion, although some cases were found to show a slight reverse trend. In the second period, the permanent molar relationship became less post-normal, but this was reflected only weakly in that of the canines. Throughout development, asymmetry of occlusal relation became more marked with age, an unexplained bias towards less post-normal occlusion on the left side developing in the second phase. The amount of change in this period was related to variations of deciduous molar size, especially that of the upper second molar.

This cephalometric study was undertaken to compare and contrast the errors involved in taking linear and angular measurements using three different methods; hand instruments on tracing, digitization of tracings, and direct digitization of the radiographs. Of the three methods direct digitization of the radiographs proved to be the most reproducible particularly with angular measurements, although statistically significant differences were rarely found. Tracings were advantageous only with linear measurements involving constructed points such as Gonion and Articulare. Traditional methods of measurement using a ruler and protractor compared well with computer based methods involving the digitizer.

Clinical and practical features are described for an operator changing fixed appliance technique from a standard edgewise system to one using pretorqued and preangulated brackets, with generally flat archwires.

Two instances are described in which the cutting of distal sections of archwires using current clinical methods has proved hazardous.

The Waveney Goal Post Appliance was designed to stabilize the second supportive phase of Clark's Twin Block therapy (1982). It is to be worn full time and is simple to construct, and well tolerated. It can be used to stabilize the dentition following most forms of functional treatment.

A useful modification of the Barrer appliance is described to enable final positioning and retention following treatment in both upper and lower arches.