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Examination of alveolar and trabecular morphology and how it relates to masticatory forces

Final Report Summary - EAT (Examination of alveolar and trabecular morphology and how it relates to masticatory forces)

OVERVIEW
Detailed characterization of the geometry of the alveolar and trabecular bone in the mandibles of the cat, rabbit, sheep, pig, cercocebus and human have been undertaken. In addition, dynamic musculoskeletal models of the rabbit, sheep and pig have been developed to provide the most accurate simulations and predictions of tooth loading in these species. The effects of including fibrous periodontal ligaments on the load transfer from teeth to the alveolar bone were also examined thoroughly by finite element (FE) analysis. Overall, a large volume of data has been produced – a small sample of which is discussed below. A further substantial publication is in preparation to report all the data.

VARIATION IN CORTICAL AND TRABECULAR BONE MORPHOLOGY.
High resolution microCT of 12 mandible samples of each animal type have been performed and analysed. New techniques to reliably segment out the trabecular bone and new methods to characterise the trabecular network and cortical bone morphologies have been developed. These methods and sample will be presented in a forthcoming publication.
Variation of cortical bone thickness over all the surface of the mandibles has been determined. For example, for the rabbit, the length and orientation of the (single root) molars and pre-molars are clearly reflected in the plots, with the variation in bone distribution providing an indication of load transfer paths. This method provides an easy visual way to compare mandibles of the same species, and those of different species.
Variations in trabecular bone properties along the length of the human mandible have also been determined and compared, in particular comparing the variation and differences in the basal bone (within the tooth roots) and alveolar bone (between the teeth).

INVESTIGATION OF MASTICATORY FORCES AND LOAD TRANSFER IN THE MANDIBLE.
Detailed dissections of a number of pig, sheep and rabbit heads were undertaken, after being scanned by MRI. The MRI data was reconstructed and used to extract muscle details, including points of attachment and the muscles’ lines of action for comparison to the dissection work, and to construct highly detailed musculoskeletal models. These allow accurate predictions of tooth loading during mastication. In the case of the rabbit model, we also collected in vivo bite force data that was used to successfully validate the model predictions. A paper describing this work has been published.

MODELLING OF TOOTH-BONE LOAD TRANSFER
Three-dimensional FE analyses have been carried out to investigate the role of the periodontal ligament (PDL), especially the ligament fibres, in transferring the load from the teeth to the alveolar bone. The model results confirm that inclusion of the PDL fibres is important to reliably predict load transfer to the bone. These results also have direct implications for the current debate about the mechanism underlying orthodontic tooth movement. By modelling the fibrous structure of the PDL, we have shown that the fibres lead to strain distributions in the alveolar bone that are not predicted by current hypotheses about the mechanical stimuli for orthodontic tooth movement. This work has been published recently. FE modelling of mandible segments has also been undertaken, and is being analysed further.

CONTINUING WORK AND APPLICATION OF THE RESULTS
Detailed interpretation of the FE results and investigation of the overall role of the trabecular and cortical bone on mandible performance is being completed now, and a number of papers are in preparation. The models developed have significant future potential. In particular: the sheep and pig models will be applied in further research into animal health; the work on characterization of bone details in the human mandible and role of the PDL will be of interest for dental applications; all the models will be used in future research to understand skull development and medical conditions affecting that development.