Friction in fixed appliance systems has received considerable attention in the recent literature, although that attributable to the type of ligation used has not been fully investigated. This in vitro study of 0.022 x 0.028 inch slot Minitwin, Activa ('A' Company, San Diego, California, USA), and SPEED brackets (Strite Industries Ltd., Cambridge, Ontario, Canada), investigates friction in two forms of self-ligating brackets and in two methods of ligating Minitwin straight wire brackets with polyurethane elastomeric ligatures. The resistance to sliding of rectangular archwires through the ligated brackets was measured on a vertically mounted Instron testing machine. The stainless steel archwires used were straight lengths of 0.016" x 0.022", 0.017" x 0.025", 0.018" x 0.025", and 0.019" x 0.025" Nubryte Gold (GAC International Inc., Central Islip, New York, USA). The results showed a significant reduction (P < 0.01) in frictional resistance in the Activa brackets compared with SPEED brackets by a factor of approximately 15. When the SPEED brackets were compared to Minitwin brackets, the reduction in friction was by 50-70 per cent (P < 0.01). The placing of 'figure-of-eight' elastomeric ties increased friction by a factor of 70-220 per cent compared to conventional elastomeric ties (P < 0.01) except for 0.016" x 0.022" archwires. The results indicate that self-ligating brackets require less force to produce tooth movement because they apply less frictional contact to the archwire than conventionally tied siamese brackets.

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 postal survey was conducted to determine the use of eye protection and incidence of ocular trauma in orthodontic practice. One-hundred-and-fifty-nine NHS orthodontic consultants and 203 specialist orthodontic practitioners were surveyed. Two-hundred-and-forty-one(66·5 per cent) replies were received. Some form of eye protection was routinely worn by 66·8 per cent of orthodontists, 64·3 per cent of patients, but only 33·6 per cent of DSAs. Eye protection was not offered to DSAs in 31·9 per cent of practices or to patients in 22·1 per cent. Forty-three per cent of orthodontists reported instances of ocular injury in their practices. The majority of these injuries (n = 104) occurred during debonding or trimming acrylic. Other incidents involved ligating materials, intra-oral polishing, and acid etching. Most injuries (83·5 per cent) were treated in the surgery without any long-term effects. The routine use of goggles or spectacles with side-pieces and plastic lenses, which conform to British Standard BS 2092, is recommended for staff and patients during all operative procedures in orthodontic practice.