Experimental and numerical investigation of atraumatic tooth extraction biomechanics in an ex vivo swine model
Creators: Gadzella, Timothy J.
Publisher: name: University of Alberta Library
Year: 2024

<p>Tooth extraction (exodontia) is among the most common surgical procedures in healthcare, driven by the prevalence of tooth decay and periodontal disease. Traditionally, tooth extraction is completed with forceps and the exertion of combined loads about the tooth’s centre of rotation. This approach widens bone surrounding the tooth root, but also may cause damage to the surrounding tissues which strongly influences patient recovery and is hypothesized to impact the survivability of implants and the remaining natural dentition. Different atraumatic extraction techniques have been developed to minimize damage, but the altered loading they impose relative to routine forceps extraction and the connection to patient outcomes is unclear. The biomechanics of the dental complex under extraction must be better understood in order to make these connections between mechanical loading and patient outcomes.<br>
Experimental ex vivo and numerical computer models of the dental complex (a single tooth unit comprised of the tooth, periodontal ligament (PDL), and supporting bone) under vertical extraction load are proposed using partial swine incisors. First, an experimental method is developed with a novel process for preparing the swine mandibles and performing simulated extractions using a custom self-aligning experimental apparatus. Second, a generalized axisymmetric model of the swine incisor is developed using a visco-damage hyperelastic model of the PDL to represent the extraction experiments. A multi-curve inverse finite element approach is proposed to determine parameters of the PDL model from the experimental data. Both the experimental and numerical methods are then applied in a characterisation study of the biomechanics of vertical tooth extraction in relation to varying load regimes, imposed damage states, and tooth geometry. Finally, a new software interface for prescribing and recording extraction load applied during vertical tooth extraction is proposed to facilitate implementation of the study findings with a commercially available Benex® extraction device.<br>
Key findings from the thesis research are presented describing both a fundamental characterisation of dental complex biomechanics and applications of the developed models. The mechanical response of the dental complex to extraction load depended on both tooth geometry (root surface attachment area) and the applied extraction load, with higher loading rates and larger root surface areas causing greater peak extraction forces. The stiffness of the dental complex and tooth fracture rate also increased with load rate. A set of PDL parameters were found as a solution to the inverse finite element problem that, when implemented in the axisymmetric finite element model, predicted the stiffness and peak force of three displacement-controlled data sets from the experimental data. The application of this numerical model as a predictive tool was demonstrated for predicting new force-hold loading schemes and the predictions were validated experimentally. The model was also adapted to different geometric conditions by predicting the change in dental complex response when the PDL was damaged with a dental instrument. A proof-of-concept for the software interface was used in a benchtop ex vivo study that demonstrated the successful use of a clinical extraction device in following a prescribed load scheme. <br>
The combined findings of the presented thesis demonstrate the importance of biomechanics in characterizing vertical tooth extraction, provide modeling tools for the development of biomechanically-based extraction procedure guidelines, and initiate the technological advancements needed to clinically implement these guidelines. Outcomes from this thesis can be directly applied to the development of improved vertical tooth extraction procedures and further investigation of the biomechanical predictors of dental complex injury.</p>