title: [A system for quantitatively measurement of alveolar bone density and the evaluation of its precision and validity].
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Stomatology, Peking University Third Hospital, Beijing, China. zhengxu_allen@sina.com
authors.forename: Xu
authors.initials: X
authors.lastname: Zheng
authors.forename: Jiu-xiang
authors.initials: JX
authors.lastname: Lin
mesh_terms: D016301:Alveolar Bone Loss / Q000000981:diagnostic imaging; D000539:Alveolar Process / Q000000981:diagnostic imaging*; D015519:Bone Density / Q000502:physiology; D006801:Humans; D016300:Radiography, Bitewing / Q000295:instrumentation* / Q000592:standards; D019252:Radiography, Dental, Digital