An ex vivo laboratory study to determine the static frictional resistance of a variable ligation orthodontic bracket system

Abstract

Objective: To determine the effects of static frictional resistance on varying the ligation technique in a Delta Force bracket system (Ortho Organizers Ltd, Hampton, UK) and using increasing degrees of bracket/archwire angulation to simulate binding.

Design: An ex vivo laboratory investigation using the Instron Universal Testing Machine (Instron Ltd, High Wycombe, UK) to generate sliding forces on an archwire through the Delta Force bracket. The system was lubricated with Saliva Orthana artificial saliva (Nycomed Ltd, Buckinghamshire, UK).

Setting: Biomaterials Laboratory, Eastman Dental Institute, London, UK.

Materials and method: Ninety Delta Force brackets were tested against 0.018-inch stainless steel wire. Three modes of ligation were tested with three different angulations: 0, 5 and 10° to simulate increasing levels of binding.

Results: The average static frictional resistance went from 0.20 N, at 0° angulation and minimum ligation, to 2.37 N with 10° angulation and maximum ligation. Results revealed that the ligation pattern was found to be highly statistically significant (P<0.001) in influencing frictional force. The binding angle showed a trend of increasing frictional force with increasing bracket/archwire angulation. Repeatability testing showed no evidence of bias (P=0.171).

Conclusions: These results suggest that the Delta Force variable ligation system does in fact enable friction to be varied, which may have implications in clinical application.

Keywords:

• Variable ligation brackets
• static frictional resistance
• Delta Force brackets

Acknowledgments

The authors wish to thank Precision Orthodontics Ltd (Mr Mike Debenham) for the generous donation of brackets, archwires and elastic modules used in the study. Statistical advice was provided by Dr David Moles, for which we are extremely grateful.