Objective: To establish a system for quantitatively measuring alveolar bone density and to test its precision and validity.
Methods: With the aid of computer technique, the system measured the average gray level intensity of regions of interest (ROIs) on standardized exposed direct digital periapical radiograph. To correct the variation resulting from exposure condition, an aluminum stepwedge was exposed simultaneously. By referring the image of aluminum stepwedge on each radiograph the equivalent aluminum thickness(EAT)and corrected gray level intensity(CGL)of the ROIs could be calculated as indicators of alveolar bone density. Nineteen specimens containing different amounts of hydroxy-phosphorite were radiographed. The precision of the system was tested by repeatedly measuring 2 of the specimens. The set of specimens was exposed under two different exposure time in order to test the system's validity to correct the gray level difference caused by different exposure time.
Results: After repeated measurement of specimens, we found the Relative Standard Deviation(RSD) of EAT and CGL was between 0.83%-2.15%; At the level of 95%, if the difference of EAT between the two ROIs was larger than 0.05 mm or the difference of CGL was larger than 3, the content of hydroxy-phosphorite in them was different; The two sets of data during different exposure time were processed with Wilcoxon Signed Ranks Test, and the result showed effective correction of the variation caused by different exposure time.
Conclusion: The precision and validity of the quantitative alveolar bone density measuring system are acceptable. The system can be used to compare alveolar bone density longitudinally and cross-sectionally.