| Besides the third molar, maxillary canine, which plays an important role in oral function and aesthetic appearance, has a high prevalence of being impacted. This may cause the displacement and root resorption of adjacent teeth, ruin the integrity of denture, give rise to disorders of occlusion relation and has a negative effect on masticatory function, upper jaw development and so on. Clinically, impacted canine is among the toughest problems in the field of orthodontics. The keys of a successful treatment to an impacted canine include early diagnose, exact locating of the canines, and correct assessment of prognosis, time and complication.Panoramic radiograph is the most common method to diagnose the impacted tooth. Imaging parameters in panoramic radiograph which affect the time of treatment are evaluated in this study, in the help of giving some clinical reference.Since the most common complication is root resorption of adjacent incisors. In this study, spiral computed tomography is used to precisely determine the degree and location of root resorption, and to decide the validity of the panoramic radiograph in diagnosing the spatial relationship between impacted canine and adjacent incisors.Here are the two parts of this study:Part 1: 25 cases of maxillary impacted canines which are treated with artificial eruption are selected and panoramic radiographs before and after the treatment obtained. The inclination, distance to the occlusion plate, position of the apex and root deviations of the impacted canine are measured. The length of active treatment was recorded and analyzed statistically in relation to the degree of displacement and incidence of root deviation. Finally, pre- and post-therapeutic panoramic radiographs were compared to determine the incidence of root resorptions and marginal bone defects.Part 2: 19 maxillary impacted canine cases which have both the panoramic radiograph and spiral CT test were selected 10 orthodontics researchers were invited to decide the degree and location of incisor root resorption caused by impacted canines on panoramic radiograph. Taking the results of CT scan as the actual amount of root resorption, we calculated the sensitivity and specificity of the panoramic radiograph, and did consistency analysis to the overlap range of impacted canine and the root of incisors and actual extent of root resoption.The results are as below:1. The results indicated a inverse correlation of the duration of active treatment time with angle of inclination(r =-0.76,P<0.001), and a direct correlation of time with the distance between impacted canine to occlusion plate(r=0.59,P<0.01). 2. The sensitivity and specificity of diagnosing the incisor root resorption caused by impacted canine on panoramic radiograph is 46.3% and 86.5% respectively. There is a low consistency (kappa test, k=0.2576<0.40) between the overlap range of impacted canine and incisor root on panoramic radiograph and actual amount of resorption obtained by CT scan.Based on the inclination and the distance between impacted canine and occlusion plate, primary assessment can be made about orthodontic treatment prognosis and time span from the panoramic radiograph. That may be helpful in the negative diagnose of incisor root resorption caused by impacted canine, but the accuracy of positive conclusion is low because of the lack of a reliable parameter of root resorption. The overlap range of impacted canine and the root of incisors can't be used as an indicator of the extent of the incisor root resorption.Spiral CT is advanced in diagnosing, locating and assessment of the complication of the impacted tooth. However, due to the high radiation dose, high costs and complicated procedures, it can only be a second means applied to the cases selected by panoramic radiograph and periapical film. |
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