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    The effect of sex, age and ethnicity on craniofacial bone mineral density

    Crawford, Susanna Ruth (2014) The effect of sex, age and ethnicity on craniofacial bone mineral density. Doctoral thesis (PhD), Manchester Metropolitan University.


    Available under License Creative Commons Attribution Non-commercial No Derivatives.

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    Bone mineral density (BMD) is a strong indicator of bone strength, which is used to discern between individuals with healthy bones and those with metabolic bone diseases such as osteoporosis. The use of DXA is largely centred around measuring key skeletal sites such as the femoral neck and lumbar spine, however some research has used it to measure BMD in the mandible in older edentulous or osteoporotic sample groups. Within craniofacial research, there is little understanding about the mechanisms used to maintain bone mineral density in the craniofacial skeleton as it only experiences small loads. These loads may be generated through mastication or movement of the head and neck. There is a body of research that uses DXA to measure the BMD of facial bones; however, the studies focus on older, edentulous or osteoporotic individuals and do not include comparisons between sexs, age groups or ethnicities in healthy, dentate sample groups. There is a large body of research that has investigated the differences in bite force and muscle activity between sample groups, however little research has been conducted into ethnic differences in these areas. Furthermore, there is very little research that has explored the force-muscle-bone relationship in the craniofacial skeleton. This study aimed to explore that relationship, and investigate how it is affected by differences in sex, age and ethnicity. In particular, the study measured bilateral bite force, jaw elevator muscle activity and mandibular BMD at the ramus and mandibular body. The present study developed a novel bite force device using existing technologies, it also used a new technique of measuring bite force and muscle activity through computer software, which facilitated synchronisation of the data. Furthermore, this study used a new approach to normalising muscle activity data to a submaximal bite force level, a technique used in other disciplines that measure muscle activity but is not often used in bite force studies. The study also developed a different approach to analysing mandibular BMD from DXA scans, building on the work of previous research. Finally, the study used a new technique for measuring facial dimensions from later photographs rather than radiographs. The present findings indicate no significant differences between males and females in a cohort of young adult Caucasians. The findings indicate a significant effect of age in a cohort of females aged <25yrs compared to >50yrs, but similar differences were not found in males. Significant differences between Caucasian males and African Caribbean males were identified, with particular reference to BMD. Finally, the study reported the significant effect of facial dimensions on the outcome variables bite force, jaw elevator muscle activity and mandibular BMD. The findings are largely concurrent with existing research but also provide new evidence for under investigated areas of research. Overall, this study highlights the use of new techniques for measuring bite force and muscle activity and for analysing BMD from DXA measurements. It has also identified relationships in bite force, muscle activity and mandibular BMD between or within sample groups that have not been reported in previous literature.

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