Original Article
Effect of archwire size and material on the resistance to sliding of self-ligating brackets with second-order angulation in the dry state*,**,*,**,*

https://doi.org/10.1067/mod.2002.126156Get rights and content

Abstract

When paired with a particular self-ligating bracket design, the material and the geometric characteristics of an archwire influence its resistance to sliding. Four designs of self-ligating brackets (1 with a slide, 3 with clips) were coupled with 5 types of archwires: 14-mil round austenitic nickel-titanium, 16 × 22-mil rectangular austenitic nickel-titanium, 19 × 25-mil rectangular austenitic nickel-titanium, 19 × 25-mil rectangular martensitic nickel-titanium, and 19 × 25-mil rectangular stainless steel. The resistance to sliding (RS) of each archwire-bracket couple was measured at second-order angles between −9° and 9°. Interbracket distances of 8 and 18 mm between the test bracket and the adjacent brackets mimicked closure of a premolar extraction. When clearance exists, the RS is negligible for self-ligating brackets with slides coupled to any size of wire as well as for those with clips when coupled to wires that do not contact the clip. Once the wire attains a certain size and contacts the clip, the RS depends on the archwire size, the bracket design, and the materials of the couple. When coupled with the 16 × 22-mil wire, the brackets with clips applied normal forces ranging from a low of 5.6 centi-Newtons (cN) (1 cN = 1 g) to a high of 230 cN. When clearance disappears, the RS increased proportionally with the second-order angle. The 19 × 25-mil stainless steel wires, which were the most stiff, increased at rates between 75 and 84 cN/degree; the 14-mil austenitic nickel-titanium wires, which were the least stiff, increased at rates from 2.6 to 5.4 cN/degree. The treatment objectives for a particular patient at a specific stage should determine the appropriate archwire-bracket combination. (Am J Orthod Dentofacial Orthop 2002;122:295-305)

Section snippets

Material and dimensions

Of the 4 types of 22-mil upper left premolar self-ligating brackets (Table I), 1 bracket design (Damon 2) had a slide, and 3 had clips (In-Ovation, SPEED, and Time) (Fig 2).

. Scanning electron micrographs of different bracket designs coupled with 14-mil active NiTi A archwires (upper row) and 19 × 25-mil SS archwires (bottom row). Damon 2 brackets (far left column) have slides, and In-Ovation, SPEED, and Time brackets have clips.

The Damon 2 and the SPEED brackets had prescriptions of −7° torque

Results

When paired with 4 different self-ligating bracket designs, the RS values of 3 different archwire sizes and 3 different archwire materials were compared after tipping at various degrees of second-order angulation.

Dimensions of archwires and brackets

For the brackets with clips, the heights (Y) of the slots (Fig 3, bottom) changed from 1 wall of the slot to the other (Fig 2). At a distance (X) equal to the SIZE of the archwire, Y was estimated by solving the equation, Y = MX + B, that describes the lumen. If the HEIGHT of the archwire was greater than the estimated Y value, the deflection of the slide or the clip was estimated by subtracting Y from the HEIGHT (Table V, last column). The 14-mil NiTi A archwires were not predicted to deflect

Conclusions

When clearance existed between the archwire and the walls of the bracket's slot, the ligation force applied by the slide or the clip to the archwire was estimated by dividing the measured resistance to sliding by the coefficient of friction (which depended on the materials of the archwire-bracket couple). When brackets with slides were used, no ligation force was produced, but, when brackets with clips were used, the amount of ligation force appeared proportional to the dimensions of the

Acknowledgements

The authors appreciate the generous donation of the materials by 3M/Unitek, American Orthodontics, Dentaurum, Forestadent USA, GAC International, RMO, Strite Industries Limited, and Sybron Dental Supply Ormco.

References (31)

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aDepartment of Biomedical Engineering.

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bDepartment of Orthodontics.

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cDental Research Center.

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dCurriculum in Applied and Materials Science.

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Reprint requests to: Robert P. Kusy, University of North Carolina, DRC Building 210H, CB#7455, Chapel Hill, NC 27599; e-mail, [email protected].

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