Canine retraction rate with self-ligating brackets vs conventional edgewise brackets

Abstract

Objective: To compare the rates of retraction down an archwire of maxillary canine teeth when bracketed with a self-ligating bracket was used on one side and a conventional bracket on the other.

Materials and methods: In 43 patients requiring maxillary premolar extraction, a self-ligating bracket (Damon3, SmartClip) was used on the maxillary canine on one side and a conventional bracket (Victory Series) on the other. The teeth were retracted down a 0.018-inch stainless steel archwire, using a medium Sentalloy retraction spring (150 g). The rates of retraction were analyzed using a paired t-test.

Results: The mean movement per 28 days for the conventional bracket was 1.17 mm. For the Damon bracket it was 0.9 mm and for the SmartClip bracket it was 1.10 mm. The differences between the conventional and self-ligating brackets were statistically significant: paired t-test, SmartClip, P < .0043; Damon3, P < .0001).

Conclusion: The retraction rate is faster with the conventional bracket, probably because of the narrower bracket width of the self-ligating brackets.

Figure 1

Wire-bracket interface. The surface is not smooth, but irregular. The areas of contact between the wire surface and bracket surface is determined by asperities.

Figure 2

Notching occurring when the wire catches due to deformation of the wire, ie, contact of a notch in the wire against the edge of the bracket: or, when binding reaches an angle in which plastic deformation occurs (θ > θ_z). When binding becomes sufficient to cause notching, sliding mechanics cease.

Figure 3

(A) Passive stage of orthodontic tooth movement when the contact angle, θ, is less than the critical angle, θ_c. In the passive stage, the wire does not touch the edges. (B) In an experimental design, the wire can be stabilized so it does not move, and the wire can be stabilized so it cannot flex. The wire can actually be positioned so there are no forces whatsoever on the bracket-wire interface. This, however, never happens in clinical orthodontics. (C) This represents the active stage of orthodontic tooth movement when θ is more than θ_c, and the wires start to contact the corners of the bracket and binding starts.

Figure 4

Classical friction results when only friction is involved.

Figure 5

Coefficient of binding data.

Figure 6

(A) Maxillary right canine retracted using GAC retraction spring (150 g). Canine in final position (SmartClip). (B) Maxillary right canine in final position (Damon). (C) Maxillary canine is retracted with conventional bracket (Victory Series).

Figure 7

The beam illustration demonstrates the position of the maximum bending moment (M_BM). The maximum bending moment is M_BM  =  (FWX)/L.