Bracket slot and archwire dimensions: manufacturing precision and third order clearance

Abstract

Objective: To determine the accuracy of different manufacturer’s dimensions of bracket slots and stainless steel archwires and compare these against the tolerance limits given by DIN 13971 and 13971‐2. Further to calculate torque play and effective torque and to compare the results to nominal torque.

Design: A laboratory investigation.

Setting: The Department of Orthodontics and Dentofacial Orthopedics at Medical University of Graz, Austria.

Materials and methods: Ten upper central incisor brackets (0·022 inch) from five different bracket systems were investigated. Bracket slot height was measured with leaf gauges. The height and width of 10 stainless steel archwires with dimensions either 0·019×0·022 or 0·020×0·025 inch were measured using a micrometer.

Results: All measured bracket slot heights were within the upper and lower tolerance limits given by DIN 13971‐2. Archwires showed measurements outside the upper and lower tolerance limits given by DIN 13971. The smallest effective torque loss (4·5°) resulted from the combination of the 0·022‐inch SPEED System bracket with the 0·020×0·025‐inch SPEED Wire small upper. The highest torque loss (11·7°) was found with the 0·022‐inch Damon 2 bracket and the 0·019×0·025‐inch ECO Charge 1 archwire.

Conclusion: The accuracy of the manufacturers dimension is not to be taken for granted. A perfect ‘finishing’ still requires correction bends put in by the orthodontist.

Keywords:

• Nominal torque
• effective torque
• torque loss
• bracket slot dimension
• archwire dimensions

Acknowledgments

The authors would like to thank Irene Mischak, a mathematician at the School of Dentistry, University of Graz, for support with the statistical analysis.