title: Quantitative pixel grey measurement of the "high-risk" sign, darkening of third molar roots: a pilot study.
abstract: OBJECTIVE
  Our aim was to examine the panoramic darkening of the root, which is a "high-risk" sign, using quantitative measurements of pixel grey values to determine different aetiological backgrounds, namely inferior alveolar nerve (IAN) exposure with or without groove formation of the third molar roots or thinning/fenestration of the lingual cortex (LCTF).
  
  
  METHODS
  38 impacted third molars that had been surgically removed and had darkened roots on panoramic radiographs were included in this retrospective case-control study. 15 IAN exposure cases were selected for the case group, and 23 cases with proven lingual cortical thinning or fenestration were chosen for the control group. The mean pixel grey values of selected areas in the dark band (D) and control areas within the same roots (R) were determined with the ImageTool (University of Texas Health Science Center, San Antonio, TX) software. The differences in pixel values (R-D) of the IAN and LCTF groups were analysed using the Mann-Whitney U-test and Pearson's χ(2) test.
  
  
  RESULTS
  The medians of the R-D pixel values were 45.7 in the IAN group and 34.3 in the LCTF group, whereas the interquartile ranges were 12.0 (IAN) and 18.3 (LCTF) (p < 0.001). The R-D critical value at which the outcomes differed significantly was 38. If the differences in pixel grey values (R-D) were higher than 38, the chance of IAN exposure was approximately 32 times higher than the chance of LCTF (χ(2) test, p < 0.001; odds ratio, 32.0; 95% confidence interval, 3.5-293.1).
  
  
  CONCLUSIONS
  The pre-operative prediction of IAN exposure or lingual cortical thinning in cases with "darkening" is possible based on pixel grey measurements of digital panoramic radiographs.
authors.affiliation: Department of Oral and Maxillofacial Surgery, University of Pécs, Pécs, Hungary. jozsef.szalma@aok.pte.hu
authors.forename: J
authors.initials: J
authors.lastname: Szalma
authors.forename: Z
authors.initials: Z
authors.lastname: Bata
authors.forename: E
authors.initials: E
authors.lastname: Lempel
authors.forename: S
authors.initials: S
authors.lastname: Jeges
authors.forename: L
authors.initials: L
authors.lastname: Olasz
mesh_terms: D000539:Alveolar Process / Q000000981:diagnostic imaging; D001862:Bone Resorption / Q000000981:diagnostic imaging; D016022:Case-Control Studies; D005544:Forecasting; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008340:Mandibular Nerve / Q000000981:diagnostic imaging; D008964:Molar, Third / Q000000981:diagnostic imaging*; D010865:Pilot Projects; D019252:Radiography, Dental, Digital / Q000379:methods*; D011862:Radiography, Panoramic / Q000379:methods*; D012189:Retrospective Studies; D012307:Risk Factors; D012680:Sensitivity and Specificity; D014092:Tooth Root / Q000000981:diagnostic imaging*; D014095:Tooth, Impacted / Q000000981:diagnostic imaging*
keywords: darkening; inferior alveolar nerve; panoramic radiography; third molar