The influence of functional loading on bone remodelling in the human mandible
Cioffi, Iacopo (2008) The influence of functional loading on bone remodelling in the human mandible. [Tesi di dottorato] (Inedito)
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The strain (i.e. deformation) history influences the degree of mineralization of cortical bone (DMB) as well as its osteonal microstructure. This study aimed first to examine the relationships of stress and strain distributions with the variations in DMB and the osteonal orientations in the cortical bone of the human mandibular condyle. It was hypothesized that strains are inversely proportional to local DMB and that the principal strains are oriented parallel to the osteons. To test this, ten human mandibular condyles were scanned in a microCT system. Finite element models were created in order to simulate static clenching. Within each condyle, 18 volumes of interest were selected to analyze regional differences in DMB, stress and strains. Subchondral bone showed a lower equivalent strain (2652±612 με) as compared to the anterior (p=0.030) and posterior cortex (p=0.007) and was less mineralized. Contrary to our hypothesis, the results show that strains correlated positively with regional variations in DMB (r=0.750, pb0.001). In the anterior and the posterior cortex, the first principal strain was parallel to the cortical surface and oriented supero-inferiorly with a fan-like shape. In subchondral bone, the first and the second principal strain were parallel to the surface and oriented antero-posteriorly and medio- laterally, respectively. It was concluded that the strain distributions, by themselves, cannot explain the regional differences found in DMB. In agreement with our second hypothesis, the orientation of the osteonal network of the mandibular condyle was closely related to the strain orientations. The results of this study suggest that the subchondral and the cortical bone are structured to ensure an optimal load distribution within the mandibular condyle and have a different mechanical behaviour. Subchondral bone plays a major role in the transmission of the strains to the anterior and posterior cortex, while these ensure an optimal transmission of the strains within the condylar neck and, eventually, to the mandibular ramus. Bone remodelling is also affected by muscular activity. Bone remodelling at the attachment site of the lateral pterygoid muscles was also assessed, by measuring the degree of mineralization of bone (DMB), in order to test to which extent muscular activity might influence bone turnover in a certain location. Ten left mandibular condyles were obtained from ten embalmed human male cadavers (mean age ± SD: 69.8±14.4 years, range: 43 to 92 years). A high-resolution microCT system was used to obtain three-dimensional reconstructions of the condyles. For each condyle the attachment site of the lateral pterygoid muscle was identified, and the degree of mineralization measured in that location and compared to a control region were no muscle was attached. At the attachment site the DMB was lower (1036.5±70.3 mg HA/cm3) than in the posterior control region (1079.3±62.3 mg HA/cm3, p=0.003). The mineralization in the lateral subregions of the attachment(1052.2±74 mg HA/cm3) was significantly higher (p=0.016) than in the medial subregions (1004±66.8 mg HA/cm3). The result of this study show that bone remodelling is higher at the attachment site of the lateral pterygoid muscle. Hence, muscular activity sensibly affect bone turnover.
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