Osteoporosis is a common disease , and problems associated with age-related osteopenia have received wide attention. Bone mineral density (BMD) is an important parameter of bone status . The vertebrae, forearm and hip are often associated with fractures in patients with osteoporosis, so they are popular sites for BMD measurements . Jaw bone is one of the most active parts of human skeleton, the relationship between jaw bone loss and general osteoporosis was reported in 1960 .

In recent years, methods for measuring general BMD have developed rapidly. Quantitative computed tomography (QCT) , digital panoramic tomography and dual-energy X ray absorptiometry (DXA) have been used to examine BMD of the jaw bone. Currently, DXA technology is widely used to measure BMD because it has high scan speed, high precision and accuracy, and uses a low radiation dose .

The decrease of BMD is more obvious in the mandible than in the maxilla, so the BMD of the mandible is usually measured. BMD attenuation can be monitored through measuring the mandibular BMD to prevent osteoporosis and reduce the risk of fractures in the elderly. BMD measurement can also aid in the diagnosis and treatment of some mandibular diseases and simultaneous tooth implantation. Mandibular bone loss is a significant factor that affects the preservation of teeth and denture construction. BMD measurement can provide references for the evaluation of dental implant indications and the effect of titanium implants on mandible fracture reconstruction.

Conclusions about the association between osteoporosis and BMD of jaw bone remain controversial . Most studies used DXA technology to measure skeletal BMD (femur and lumbar vertebrae), whereas standard digital panoramic tomography (SDPTG) was used to measure mandible BMD (cortical, alveolar bone and trabecular). The disparity may result from different methods, standards, or test locations.

The physical characteristics and BMD of different races also vary significantly due to heredity, living environment, living styles and habits. Even in those of the same race, there are differences between regions. In order to provide a normal reference for mandibular BMD, which is absent in China, and study the correlation between the BMD of the mandible and the lumbar vertebrae, the authors measured the BMD of the lumbar vertebrae and the mandible of normal adults in China with DXA.

Subjects and methods

224 healthy adult volunteers (111 males and 113 females) were recruited in China. None had any known medical conditions or were taking any medication that affected bone metabolism. The participants were divided into 6 age groups: 20–29, 30–39, 40–49, 50–59, 60–69 and over 70 years ( Table 1 ). A local ethics committee approved this study and informed consent was obtained from all volunteers.

Table 1

Number of study population in each group.

Age (years)	Males ( n )	Females ( n )
20–29	21	23
30–39	20	21
40–49	21	22
50–59	20	21
60–69	17	15
70–	12	11
Total	111	113

 

The DXA scans were performed on a GE LUNAR (DPX-L or other model number) (GE LUNAR Company, USA). The BMD measurements were obtained from mandibular chin, bilateral mandibular angles and lumbar vertebrae (L1–L4). The positioning for the DXA scan of the mandibular chin was similar to that described by H orner et al. . For mandibular angle scanning, the participant laid horizontally on the bed with the head in the middle. The anterior DXA images of L1–L4, and the combined vertebral segments (L1–L4), of the lumbar spine were acquired with the region of interest (ROI) isolated for quantification of BMD and generation of the T- and Z-scores by the combined GE Lunar/NHANES III software. DXA-derived BMD values are expressed as areal density (areal BMD in g/cm ² ). Quality assurance was performed by calibrating the DXA system with a spine phantom supplied by the manufacturer. According to the adsorption of low energy photos in different tissues, the DXA images of mandibular chin and mandibular angles were acquired at l46.8 keV and 100 keV. The area for BMD measurement was mapped manually on the mandibular chin ( Fig. 1 a ) and mandibular angle ( Fig. 1 b and 1c). 10 ROI were placed over each measurement area without overlapping. The size of each ROI was 1 cm ² . The BMD values of each ROI were measured and averaged. The ROI excluded the area of impacted teeth that may introduce error in BMD measurement. The BMD of the lumbar vertebrae was analysed with DXA instrument software ( Fig. 1 d) and the results were used as standard reference.

The area for BMD measurement in (a) mandibular chin, (b and c) mandibular angle, and (d) lumbar vertebrae.