Self-ligating brackets

Abstract

We appreciate the efforts of Dr Tae-Kyung Kim and his colleagues and congratulate them for their work on self-ligating brackets; it has enriched the orthodontic literature. We followed with great interest their article, “Comparison of frictional forces during the initial leveling stage in various combinations of self-ligating brackets and archwires with a custom-designed typodont system” (Kim TK, Kim KD, Baek SH. Am J Orthod Dentofacial Orthop 2008;133:187.e15-24). Recently, miniscrews and self-ligating brackets (SLBs) have been the greatest buzz in orthodontics. Now, with many commercial products available, their work will help orthodontic professionals to choose the appropriate SLB and archwire combination. But we think that some points in the study need further clarification. The points are as follows. Regarding the classification of self-ligating brackets used in the study, the authors stated “The SLBs tested in this study were as follows: (1) 3 ASLBs (active self-ligating brackets): In-Ovation R, SPEED, and Time 2; (2) 2 PSLBs (passive self-ligating brackets): Damon 2 and Damon 3; and (3) a new type of SLB, SmartClip.” The SmartClip is definitively a new self-ligating bracket introduced by 3M Unitek in 2004, but it is classified as a passive self-ligating bracket. According to Miles,1Miles P.G. SmartClip versus conventional twin brackets for initial alignment: is there a difference?.Aust Orthod J. 2005; 21: 123-127PubMed Google Scholar “In the case of the SmartClip, the archwire is ‘passively’ held in the bracket by means of the programmed nickel-titanium clip and subsequently there is no constant normal force of ligation.” These nickel-titanium clips release the wire if the force of ligation needed to keep the wire in the slot exceeds a certain limit, and that's why the combinations of the SmartClip, .014-in austenitic nickel-titanium (A-Ni-Ti) or copper nickel-titanium (Cu-Ni-Ti) archwire, and a 3-mm displacement of the mandibular lateral incisors, and the SmartClip, .014 Cu-Ni-Ti archwire, and a 2-mm displacement of the mandibular lateral incisors could not be tested and had to be excluded from the study. Moreover, according to Valant,2Valant J.R. Time: a self-ligating interactive bracket system.Semin Orthod. 2008; 14: 46-53Abstract Full Text Full Text PDF Scopus (6) Google Scholar 3 types of self-ligating bracket systems are used in contemporary orthodontic practices: completely passive through all stages of treatment (Damon 2 and Damon 3), completely active through all stages of treatment (SPEED), and interactive−ie, they can have either passive or active properties during any stage of treatment at the discretion and direction of the clinician (In-Ovation R and Time). Although it does not make a difference in the results of the study, it might be misleading to some readers. About friction force values in the maxillary and mandibular arches, the authors stated “In the combination of bracket and displacement, Damon 2 and Damon 3 in the maxillary typodont system and In-Ovation R, Damon 2, and Damon 3 in the mandibular typodont system produced significantly lower frictional force (FF) values than the other brackets. The PSLB showed significantly lower levels of FF when compared with the ASLB. These findings suggest that, regardless of the amount of tooth displacement, the PSLB produced a lower FF than the ASLB.” The authors found the lowest static and kinetic FF values in the mandibular arch with the In-Ovation R bracket, which, according to them, is an active self-ligating bracket. This finding needs more clarification. Spring clips of ASLB are made of different materials and can produce different amounts of force for the same amount of flexion: eg, in the SPEED system, the spring is made of super-elastic nickel titanium, and the In-Ovation R system has a spring that is designed to apply 250 g of force at maximum flexion.3Alpern M.C. Gaining control with self-ligation.Semin Orthod. 2008; 14: 73-86Abstract Full Text Full Text PDF Scopus (4) Google Scholar These materials have different physical properties that probably affected the FF value and substantially affected the results of the study. Author's responseAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 134Issue 1PreviewWe thank Drs Agarwal, Valiathan, and Shah for their interest in our article. In our study, the self -ligating bracket (SLB) was classified according to Voudouris.1 Although Smartclip was classified as a passive SLB by Miles,2,3 we do not agree with that opinion. We think that a true passive SLB does not apply a ligation force to the archwire. When the archwire contacts the clip of Smartclip, some ligation force could be exerted. Therefore, the Smartclip bracket was classified as a new SLB. The types and properties of SLBs that are commercially available might need to be reevaluated. Full-Text PDF