J Korean Dent Sci.  2023 Jun;16(1):23-34. 10.5856/JKDS.2023.16.1.23.

Force Assessment of Thermoformed and Direct-printed Aligners in a Lingual Bodily Movement of a Central Incisor Over Time: A 14-day In Vitro Study

• Remley ML
• Miranda GFPC
• Bankhead B
• McCray J
• Kim KB

• KMID: 2549598
• DOI: http://doi.org/10.5856/JKDS.2023.16.1.23

Abstract

Purpose
This study aims to investigate the force delivery profile of thermoformed aligners (TFA) compared with direct-printed aligners (DPA) and to explore the effect of different activation amounts on forces and moments of respective groups. A secondary objective is to observe the amount of stress relaxation that occurs over the 7~14 days when aligners are maintained in a simulated intraoral environment.
Materials and Methods
An in vitro setup was created to quantify forces and moments. It consisted of a three dimensional-printed base plate and segmented maxillary teeth, placed in a semi-enclosed chamber to maintain a temperature of 37°C. Ninety clear aligners were divided into nine groups of ten aligners each based on material types (Zendura, ATMOS, TC-85) and activation amounts. Aligners were created with 0.00, 0.25- and 0.50-mm activations for lingual bodily movement of the upper left central incisor and kept on models in the “stressed” position in a 37°C water bath. Three force components acting on the upper left lateral incisor, upper left central incisor, and upper right central incisor were measured for each time point, beginning from the initial baseline measurement, 8 hours, 16 hours, 24 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, and lastly, 14 days. Result: TC-85 aligners in every activation group showed less force on teeth than Zendura and ATMOS. Significant force levels from 0.0 mm activation were present and stayed consistent over the course of 14 days. Comparisons made for baseline measurements to 7-days and 14-days showed statistically significant change from the baseline force level.
Conclusion
TC-85 aligners demonstrated lower, more consistent forces with fewer side effects. Aligners can generate forces even when no activation is programmed. No major decreases in force levels over time were observed; the intra-oral clinical simulated environment and length of observation time could contribute to this.

Keyword

Clear aligners; Orthodontic tooth movement; Shape memory polymer