In vitro Evaluation of Biomechanics of Orthodontic Aligners
Creators: Kaur, Harsimrat
Publisher: name: University of Alberta Library
Year: 2024

<p>In 2020, the dental care cost in Canada was approximately $13.89 billion and 20% of Canadians underwent orthodontic treatment. Patients seek orthodontic treatment to improve their oral functionality, psychosocial well-being, appearance, and quality of life. Aligner mechanotherapy is gaining popularity as an esthetic alternative to fixed labial mechanotherapy. However, the literature has reported limited treatment outcome with aligner mechanotherapy where 70-80% of orthodontic patients undergoing aligner treatment require midcourse correction, case refinement, or conversion to a fixed labial mechanotherapy before the end of treatment. This could be attributed to gaps in knowledge regarding aligner biomechanics that limits the predictability of orthodontic treatment outcome pointing towards the need to investigate biomechanics of the aligner mechanotherapy.</p>

<p>The objective of the present thesis was to utilize in vitro methods (Orthodontic Simulator) to study the force system of aligners towards gaining a foundational understanding of their expected behavior in full arch treatments. Specifically, the fundamental factors such as tooth anatomy and position, aligner materials, and auxiliaries that could influence the biomechanics of aligner mechanotherapy were evaluated in this thesis. The initial experiments assessed the force system for different teeth (central incisor, canine and second premolar) by utilizing the most used aligner materials (polyethylene terephthalate, polyethylene terephthalate glycol, and polyurethane). The biomechanical knowledge was further advanced by subsequent experiments to evaluate the effect of varying the location of auxiliaries such as divots and attachments on aligner force system for bodily tooth movement and extrusion movement, respectively.</p>

<p>There were several key observations made by series of biomechanical experiments. The initial experiment introduced the implication of tooth anatomy and tooth position in aligner biomechanics where mean buccal force and moment (that could tip teeth buccally/lingually) were significantly more for canine than for central incisor and premolar at 0.20 mm of lingual displacement. The similar trend was observed for other most used aligner materials: polyethylene terephthalate and polyurethane that exerted different force system on tested teeth. This experiment results highlighted the role of distinct underlying mechanical properties and variance in response of different materials to thermoforming process in aligner biomechanics.  The results obtained from the experiments involving auxiliaries with aligner suggest that tactical placement of auxiliaries on buccal and lingual aspect of crown of incisors could improve the force system of aligners. This could mean possibility of extending the utility and application of aligners to difficult tooth movement such as bodily movement and extrusion. </p>

<p>Overall, this in vitro evidence will improve understanding of force system of aligner mechanotherapy. The results will be instrumental in guiding the future research, influence the design and protocol of the aligner mechanotherapy that will improve the delivery of care by improving treatment outcome, and reducing the treatment time for orthodontic patients.  </p>