Resistance to Sliding with Self-Ligating Brackets: The Effect of Moment

Objectives:  The purpose of this study is to investigate and compare the resistance to sliding (RS) between a conventionally-ligated (CL) and various self-ligating (SL) brackets under a dynamically increasing applied moment, and different archwire materials.

Methods: Three different SL brackets and one CL bracket were mounted on a custom-built device to simulate canine retraction mechanics. The archwire was pulled (5mm/min) through the bracket by a load cell attached to the crosshead of an Instron testing machine, while a second load cell simultaneously recorded the force required to rotate the test bracket, thus allowing the moment applied to the archwire to be calculated. The three SL brackets tested were Damon3 (D), InnovationR (I), and Smartclip (S); the CL bracket used was Victory (V). All brackets were tested on both 0.019x0.025" stainless steel (SS) and nickel-titanium (NT) archwires. (n=10 for each archwire-bracket combination) The RS at calculated moments of 2000gm-mm and 4000gm-mm was determined and compared between the various brackets with both archwire types. Descriptive measures and two-way ANOVA analysis were used to calculate the means and statistical differences amongst the different samples.

Results: Results are presented as means±SD

	Moment	D/SS	I/SS	S/SS	V/SS	D/NT	I/NT	S/NT	V/NT
RS (gm)	2000gm.mm	175.3±22.2	212.7±28.5	173.3±50.5	200.4±17.6	196.8±7.0	260.8±10.5	210.1±28.9	227.0±9.6
	4000gm.mm	331.5±24.9	351.2±31.7	357.1±24.3	340.0±28.7	364.9±25.7	458.2±18.8	424.3±33.8	398.1±26.8

The CL bracket was similar (p<0.05) to SL brackets on SS archwire, though some statistical differences were present between the CL and SL brackets when NT archwire was used. At none of the variables tested did the CL bracket display the greatest amount of RS.

Conclusions: All brackets tested displayed a greater amount of RS with NiTi than SS archwires. At clinically relevant amounts of applied moment, the difference in total RS amongst the various SL and CL brackets tested was not clinically significant.