Biological apatite crystallite alignment analysis of human maxillary molar region cortical bone with microbeam X-ray diffraction

The jaw bone is a specialized bone which in association with the masticatory muscles, moderates the occlusal forces transmitted to the jaw via teeth. It is suggested that there is a strong relationship between the structural characteristics of the jaw bone and occlusal force. Earlier studies involving bone density have shown clear differences between the properties of the maxilla and those of the mandible. We believe that assessment of the bone is also necessary to gain a better understanding of the material properties of the jaw bone, which maintains sufficient strength to withstand mechanical stress. In the present study, the authors conducted a quantitative assessment of biological apatite (BAp) crystallite alignment, which is an indicator used in bone quality assessment, with the aim of clarifying the structural characteristics of the human maxilla. Using dentulous maxillae from Japanese cadavers, we measured the bone mineral density (BMD) and BAp crystallite alignment of first molar cortical bone, which was the area of interest. For measurement, the maxilla was classified into a total of four regions, consisting of cortical bone surrounding the alveolar process and cortical bone surrounding the root, on both the buccal and palatal sides, and each of these regions was assessed. The results indicated no significant differences in BMD values based on site, but in the buccal cortical bone surrounding the root, strong alignment was observed in the vertical direction (Y-axis) in relation to the occlusal plane. Moreover, strong alignment was seen in the mesiodistal direction for palatal cortical bone compared to buccal cortical bone. At the same time, however, all of the measurement regions in the buccopalatal direction (Z-axis) showed low values for both buccal and palatal cortical bone. Based on the results of the present study, it was confirmed that buccal cortical bone in the maxillary first molar cortical bone region has a strong mechanical characteristic in the Y-axis direction. This suggests that buccal cortical bone is more strongly affected by occlusal force, and it is surmised that it plays a significant role in transmitting stress generated primarily by the buccal root.