Friction in fixed appliance systems has received considerable attention in recent literature, although that attributable to varying second order (tip) and third order (torque) adjustments in either the bracket or the archwire has not been fully investigated. The ex vivo study of 0·022 × 0·028-inch slot Minitwin ® , Activa ® , and Standard Straight Wire ® brackets investigates friction when known values of tip or torque were applied to 0·018 × 0·025-inch stainless steel wires. The resistance to sliding of the wire through the ligated brackets was measured on a vertically-mounted Instron testing machine. The results showed that the self-ligating Activa ® brackets consistently produced less friction than the other conventionally tied brackets. Minitwin ® brackets were slightly more resistant to movement than the Standard ® brackets during torquing, but the converse was found when tip was applied. Increasing tip and torque (ranges tested 0–6 degrees and 0–25 degrees, respectively) produced almost linear increases in friction for all brackets, although increasing tip had the more profound effect on friction, particularly in Activa brackets.
A basic on-line digitizing system is described. The design and writing of cephalometric programs and the limitations imposed by the amount of memory available are discussed together with the principal advantages and disadvantages of the system.
The impacted palatal canine requires a combination of both surgical and orthodontic management. Two types of approach are commonly used: simple exposure, or exposure with bracketing at the time of surgery. In this study 104 consecutively treated patients with palatally impacted canines were examined at two centres, one at which the ectopic tooth was surgically exposed alone and the other where an orthodontic bracket was bonded to facilitate early traction, and the flap replaced. The aim was to compare the outcome and complication rate for each type of procedure. In 30.7 per cent of all cases exposed and bracketed a second surgical intervention was required, compared with 15.3 per cent in the simple exposure group. Bracketing, though effective, is a more costly and time-consuming procedure, and it is suggested that simple exposure provides an equally efficient and predictable method of managing the palatally impacted canine with obvious clinical and financial benefits. The long-term periodontal status of the teeth which have been exposed in these two ways, however, needs further investigation.
A mathematical and computational approach to some of the common problems found in writing digitizing programs for cephalometric analysis is described. The paper is aimed at those with access to a microcomputer and digitizer, some knowledge of the BASIC computer language and simple mathematics but little experience of writing digitizing programs.
The principles of prefabricating round and edgewise archwires using a wax bite technique and their specific application to prescriptions for upper and lower archwire designs are described. The technique has proved particularly useful both in teaching beginners the elements of fixed appliance therapy and in reducing the length of patient appointments.
The design, construction and clinical management of the quadhelix appliance are discussed. Clinically, the appliance has a useful role to play in malocclusions where moderate expansion of the upper arch is required; the appliance may be modified to act as a space maintainer or to provide additional minor tooth movements.
A questionnaire sent to all U.K. hospital orthodontic consultants resulted in an 88 per cent response rate. The average waiting time for initial consultation was 31·6 weeks for routine cases and 3·6 weeks for urgent cases. The average waiting time for out patient treatment was 68·7 weeks for routine cases and 7·5 weeks for urgent cases. Nearly 33 per cent of hospitals used the Dental Health Component of the Index of Orthodontic Treatment need (IOTN) as a guide to placing patients on waiting lists. ‘Urgency’ and ‘Complexity’ were used more frequently than indices. Sixty-nine per cent of hospitals exclude some categories of malocclusion from treatment in their departments. A prospective survey reported on 2480 completed treatments over a six week period and there was an average discontinuation rate of 9·2 per cent of all cases finished during the period. Comparison of the completed and discontinued groups revealed few significant treatment-related factors. There was some evidence that the more senior and experienced the operator, the less the rate of discontinuation. A greater rate of discontinuation was seen in removable appliance cases when compared with fixed appliance cases.
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