title: Computer-assisted orientation of dental periapical radiographs to the occlusal plane.
abstract: OBJECTIVE
  This study describes a computer assisted orientation method for digital dental periapical radiographs.
  
  
  METHODS
  Four hundred twenty dental periapical radiographs were collected for this experiment. To locate the air space for orientation, they were processed by dedicated computer software. The program included binary image transformations, thresholding segmentation, quartering, characterization, and label interpretation. The results were then compared with those of an experienced dentist.
  
  
  RESULTS
  The most accurate threshold values for locating the air space can be obtained between gray levels 45 and 47, with an accuracy of 98.10% (412 out of 420) and no uninterpretable images. The accuracy did not drop unless the threshold value was adjusted to 25 (91.67%) or 75 (91.90%).
  
  
  CONCLUSIONS
  The strategy adopted in this study proved to be an effective and simple approach to orient the dental periapical radiographs to the occlusal plane. Errors in interpretation in a small percentage of the radiographs were caused by anatomic variations of the patients.
authors.affiliation: Department of Dentistry, Buddhist Tzu-Chi General Hospital, and Tzu-Chi University, Hualien, Taiwan.
authors.forename: Chih-Hao
authors.initials: CH
authors.lastname: Huang
authors.forename: Chih-Yu
authors.initials: CY
authors.lastname: Hsu
mesh_terms: D000465:Algorithms; D003768:Dental Occlusion, Centric; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods*; D019252:Radiography, Dental, Digital; D012984:Software; D014092:Tooth Root / Q000000981:diagnostic imaging*