Effect of Slot Dimensions on Aligner Retention

Introduction: Orthodontic brackets with rectangular arch wire slots have been historically used for fixed orthodontic treatment and remain as the industry standard. In light of the biomechanical disadvantages of rectangular slot design and the tremendous market demand for clear aligner therapy, a novel orthodontic device system was designed and evaluated. Clear aligner therapy (CAT) as a solo system has another host of compromises and disadvantages which include lesser treatment outcomes and lack of tooth movement accuracy. A novel 3D printed orthodontic trapezoidal slot twin bracket was fabricated to be used as a fixed appliance, as a clear aligner system, and/or a combination of both. Research on this alternative slot form was conducted on aligner retention utilizing varying slot dimensions with the base of slot ranging from 0.014” to 0.018” and top of slot ranging from 0.040” to 0.060”. A 2mm retention attachment and no attachment model were used as an industry comparison/control. Methods: The trapezoidal slot twin bracket (UL5) was fabricated in composite/ceramic hybrid via 3D printed technology. The brackets were bonded to a 3D printed model and scanned using a Trios 3 intraoral scanner. The STL file was then 3D printed using Sprintray 3D printing technology. A vacuum-form using Zendura Flex aligner material was fabricated on the model using a Ministar S pressure forming machine. The aligner was trimmed equal-gingival. A custom uniaxial tensile testing machine was used to measure the force required to remove the aligner from the testing model. Results: The data collected was compared to each top of slot dimension (0.040”, 0.050”, 0.060”), each base of slot dimension (0.014” or 0.018”), no attachment, and 2mm retention attachment. Two-tailed T-tests showed clinical significance among all categories tested. An ANOVA was conducted to confirm clinical significance among the different slot configurations. Conclusion: From the data collected, researchers were able to select a slot dimension of choice for further testing of the system.