A comparison of space closure rates between preactivated nickel-titanium and titanium-molybdenum alloy T-loops: a randomized controlled clinical trial

Abstract

The purpose of this study was to conduct a prospective randomized controlled clinical trial to evaluate the rate of space closure and tooth angulation during maxillary canine retraction using preactivated T-loops made from titanium-molybdenum alloy (TMA) and nickel-titanium (NiTi). Twelve patients (six males and six females) aged between 13 and 20 years who had upper premolar extractions were included, and each acted as their own control, with a NiTi T-loop allocated to one quadrant and TMA to the other using a split mouth block randomization design. The loops were activated 3 mm at each visit to deliver a load of approximately 150 g to the upper canine teeth. Maxillary dental casts, taken at the first and each subsequent monthly visit, were used to evaluate changes in extraction space and canine angulation. All used T-loops were compared with unused loops in order to assess distortion. Mixed model statistical analysis was used to adjust for confounding variables. The mean rate of canine retraction using preactivated NiTi and TMA T-loops was 0.91 mm/month (±0.46) and 0.87 mm/month (±0.34), respectively. The canine tipping rates were 0.71 degrees/month (±2.34) for NiTi and 1.15 degrees/month (±2.86) for TMA. Both the rate of space closure and the tipping were not significantly different between the two wire types. The average percentage distortion of the TMA T-loop was 10 times greater than that of the NiTi loops when all other variables were matched. There was no difference in the rate of space closure or tooth angulation between preactivated TMA or NiTi T-loops when used to retract upper canines. The NiTi loops possessed a greater ability to retain and return to their original shapes following cyclical activation.

Nickel titanium T-loop wire dimensions for en masse retraction

“…This was expected since it has already been shown that betatitanium T-loops produced with larger wire sizes produced more force. 18 The NiTi T-loops previously shown in the literature produced lower force levels [10][11][12] than was found in our study but were probably adequate for canine retraction. This study, however, aimed to evaluate springs for en masse retraction, where a force twice as large is generally suggested.…”

“…Even though the use of NiTi T-loops has already been shown in attempts to maintain the force upon deactivation, [9][10][11][12] it appears that they were designed for canine retraction. Because recent studies have shown that there is no difference in the rates of anterior retraction and loss of anchorage between that and en masse retraction, [13][14][15] it makes sense that the latter method would be clinically more practical and save chair time.…”

“…The issue is that previously described available NiTi T-loop9 designs produce low forces for that purpose (below 250 gf at the beginning of deactivation), either because they were made from a small dimension wire, such as 0.016" 3 0.022", 9 or because they were possibly not activated enough. [10][11][12] Another issue with the proposed NiTi T-loops is that they are too large, with heights above 8 mm, which could cause impingements clinically.…”

Initial forces experienced by the anterior and posterior teeth during dental-anchored or skeletal-anchored en masse retraction in vitro

“…En masse retraction studies have traditionally evaluated rates of tooth movement in vivo, relying on cephalometric measurements 10,11 and dental cast measurements 12,13 with applied forces being measured via force gauges. 14 Due to the inherent difficulty in accurate force measurements in vivo, studies using in vitro or numerical methods are considered.…”

The Role of Loop Height and Design on its Force Characteristics in Alignment of Teeth: A Finite Element Analysis

“…However, a high loop may irritate oral structures. Accordingly this is prudent to measure the load components produced by different design parameters of loops (6)(7)(8).…”