Effect of material composition and thickness of orthodontic aligners on the transmission and distribution of forces: an in vitro study.

Abstract

To investigate the effects of material type and thickness on force generation and distribution by aligners. Sixty aligners were divided into six groups (n = 10): one group with a thickness of 0.89mm using Zendura Viva (Multi-layer), four groups with a thickness of 0.75mm using Zendura FLX (Multi-layer), CA Pro (Multi-layer), Zendura (Single-layer), and Duran (Single-layer) sheets, and one group with a thickness of 0.50mm using Duran sheets. Force measurements were conducted using Fuji® pressure-sensitive films. The lowest force values, both active and passive, were recorded for the multi-layered sheets: CA Pro (83.1N, 50.5N), Zendura FLX (88.9N, 60.7N), and Zendura Viva (92.5N, 68.5N). Conversely, the highest values were recorded for the single-layered sheets: Duran (131.9N, 71.8N) and Zendura (149.7N, 89.8N). The highest force was recorded at the middle third of the aligner, followed by the incisal third, and then the cervical third. The net force between the incisal and cervical thirds (FI-FC) showed insignificant difference across different materials. However, when comparing the incisal and middle thirds, the net force (FI-FM) was higher with single-layered materials. Both overall force and net force (FI-FM) were significantly higher with 0.75mm compared to those with a thickness of 0.50mm. Multi-layered aligner materials exert lower forces compared to their single-layered counterparts. Additionally, increased thickness in aligners results in enhanced retention and greater force generation. For effective bodily tooth movement, thicker and single-layered rigid materials are preferred. This research provides valuable insights into the biomechanics of orthodontic aligners, which could have significant clinical implications for orthodontists. Orthodontists might use this information to more effectively tailor aligner treatments, considering the specific tooth movement required for each individual patient. In light of these findings, an exchangeable protocol for aligner treatment is suggested, which however needs to be proven clinically. This protocol proposes alternating between multi-layered and single-layered materials within the same treatment phase. This strategy is suggested to optimize treatment outcomes, particularly when planning for a bodily tooth movement.