To study the incidence and reasons of image distortion of incisors on panoramic photography of orthodontic patients.

The panoramic and cephalometric photography of 500 orthodontic patients were evaluated retrospectively. All of the photography was gotten from the department of radiology, Hospital of Stomatology, Sun Yat-sen University and was taken with bite rod. The image amplifying, shrinking, shortening, and blurring were used as evaluation indicators to analyze the incidence of image distortion of upper and lower incisors. In order to explore the reasons of image distortion, the distance from the root apex of the incisor to the edge of opposite incisor was measured. The One-way ANOVA was used as statistic method to analyze the data with SPSS 19.0.

There were 417 patients who had normal incisor image, and 83 patients with incisor image distortion. The incidence of image distortion was 16.6%. There were 17 patients with amplified incisor image. None of the patient had image shrinking. There were 30 patients with shorten incisor image, and 36 patients with blurred image incisor. The distance from the root apex of the incisor to the edge of opposite incisor of the patients with incisor image distortion was significant greater than the patients with normal incisor image. The One-way ANOVA results shown that the F value was 5 187.18, P value was 0. The overjet of upper and lower incisors of the patients with image distortion was greater than the patients with normal incisor image. The One-way ANOVA results shown that the F value was larger than 477, P value was 0.

Serious dental and maxillofacial malformation such as serious anterior crossbite and deep overjet was one of the main reasons which caused the incisor image distortion on panoramic photography.