Friction behavior of self-ligating and conventional brackets with different ligature systems

Self-ligating brackets are widely believed to offer better clinical efficiency and, in particular, less friction. Thus, the goal of this in vitro investigation was to assess the friction behavior of different bracket/archwire/ligature combinations during simulated canine retraction. An important aspect of this work was to determine whether conventional bracket systems behave differently in passive or active self-ligating brackets used with a Slide™ ligature, an elastic ligature, or a steel ligature.

Three conventional (Contour, Class One; Discovery^®, Dentaurum; Mystique MB, GAC) and six self-ligating (Carriere SL, Class One; Clarity™ SL, 3M Unitek; Damon3, Ormco; In-Ovation^® C, GAC; Speed Appliance, Speed System™; QuicKlear^®, Forestadent^®) bracket systems were analyzed. All brackets featured a 0.022″ slot (0.56 mm). Each conventional system was tested with a steel ligature (0.25 mm; Remanium^®, Dentaurum), an elastic ligature (1.3 mm in diameter; Dentalastics, Dentaurum), and a modified elastic ligature (Slide™; Leone^®). Each combination was used with four archwires, including rectangular stainless steel (0.46 × 0.64 mm, 0.018 × 0.025″, Dentaurum), rectangular nickel–titanium with Teflon coating (0.46 × 0.64 mm, 0.018 × 0.025″, Forestadent^®), round coaxial nickel–titanium (0.46 mm, 0.018″, Speed), and half-round/half-square (D-profile) stainless steel (0.46 mm, 0.018″, Speed). In the orthodontic measurement and simulation system (OMSS), retraction of a canine was simulated on a Frasaco model replicated in resin. Based on the force systems, the respective friction values were determined. For each combination of materials, five brackets of the same type were tested and five single measurements performed.

Friction values were found to vary distinctly with the different combinations, modifiers being the ligature systems and the archwire types. Any significant friction differences between the steel-ligated, Slide™-ligated, and self-ligated brackets were sporadic. All three systems were associated with average friction values of 40 %. Active self-ligating brackets and elastic-ligated conventional brackets, by contrast, generally differed significantly from the three above-mentioned bracket systems and showed distinctly higher friction values averaging 59 and 67 %, respectively.

While passive self-ligating bracket systems have frequently been touted as advantageous in the literature, they should not be regarded as the only favorable system. Steel-ligated and Slide™-ligated conventional bracket systems are capable of offering similar friction performance.