Computer-assisted orientation of dental periapical radiographs to the occlusal plane

Objective. This study describes a computer assisted orientation method for digital dental periapical radiographs. Study design. 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.