Abstract
The purpose of this study was to measure the long-term growth of the mandible in miniature pigs using 3D Cone-Beam Computerized Tomography (CBCT). The mandibles of the pigs were scanned monthly over 12 months using CBCT and the 3D mandibular models were reconstructed from the data. Seventeen anatomical landmarks were identified and classified into four groups of line segments, namely anteroposterior, superoinferior, mediolateral and anteroinferior. The inter-marker distances, inter-segmental angles, volume, monthly distance changes and percentage of changes were calculated to describe mandibular growth. The total changes of inter-marker distances were normalized to the initial values. All inter-marker distances increased over time, with the greatest mean normalized total changes in the superoinferior and anteroposterior groups (p<0.05). Monthly distance changes were greatest during the first four months and then reduced over time. Percentages of inter-marker distance changes were similar among the groups, reaching half of the overall growth around the 4th month. The mandibular volume growth increased non-linearly with time, accelerating during the first five months and slowing during the remaining months. The growth of the mandible was found to be anisotropic and non-homogeneous within the bone and non-linear over time, with faster growth in the ramus than in the body. These growth patterns appeared to be related to the development of the dentition, providing necessary space for the teeth to grow upward for occlusion and for the posterior teeth to erupt.
Highlights
The growth and the associated morphological changes of the mandible has long been an interesting research subject for orthodontists [1]
If treatments are needed during the growth period, the factor of the mandibular growth should be taken into account
Kim et al [5] studied mandibular growth in New Zealand white rabbits using cone-beam computed tomography (CT) (CBCT), but measurements were performed with relatively large time intervals with a limited number of variables for describing the bone geometry
Summary
The growth and the associated morphological changes of the mandible has long been an interesting research subject for orthodontists [1]. In contrast to cephalometric radiographs, computed tomography (CT) can accurately measure the three-dimensional (3D) geometry of bones, but requires relatively high doses of radiation, limiting its use in in vivo studies. The development of cone-beam CT (CBCT) has enabled the accurate measurement of the 3D geometry of bones at relatively low radiation levels. This has opened up the possibility of long-term monitoring of the mandibular growth on animal models. Kim et al [5] studied mandibular growth in New Zealand white rabbits using CBCT, but measurements were performed with relatively large time intervals with a limited number of variables for describing the bone geometry. Since the mandibles in these children are CT scanned at a limited number of instances unevenly spread over a period of time (about five times over 14 years), the descriptions of the patterns of mandible growth in this particular group of subjects are limited to the selected time instances
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