This doctoral thesis has been done due to the big prevalence of upper cuspid impaction in general population. In the second phase of dental replacement, the tooth that causes more eruptive problems is the upper permanent cuspid. If this tooth modifies its eruptive path, the consequence can be either an ectopic eruption or its palatine retention. In both cases the patient will require orthodontic treatment that usually is long and complex. For this reason, it is important to be able of predicting upper permanent cuspid impaction. OBJECTIVES: The objectives of this doctoral thesis were to develop a precise method to measure with accuracy the angulation of the upper permanent cuspid, to determine which reference angles are more reliable at measuring this angulation, to compare the angulation of cuspid which erupt normally with those cuspids who become palatally impacted, to evaluate if the different preventive treatments improve the cuspid´s eruption, to analyze if the cuspid´s sectorial position and height are related to the final eruptive result, to evaluate if the upper first bicuspids inclination can influence the cuspid´s eruptive route and last of all to determine if dental alterations are related to the lack of eruption of the upper permanent cuspid. MATERIALS AND METHODS: A retrospective study was done with patients of a private dental office of Valencia specialized in Pediatric Dentistry and Orthodontics. We had the approval of the Ethics Committee of Research in Humans of the University of Valencia. A sample of 356 patients was compiled with a minimum of 2 panoramic radiographs in which the upper permanent cuspids weren´t erupted in the initial radiograph. All patients who lacked data in the clinical history or had any disease affecting dental eruption were discarded. The radiographs were compiled until orthodontic fixed appliances were placed. In the radiographs, a series of measurements were made with specifically designed software for this study. Finally the sample was divided into 4 groups depending if the cuspids erupted without any treatment, if the cuspids erupted with a light treatment, needed a fenestration when cuspids were diagnosed as impacted or cuspids without reference (those which we had no clinical evidence of its final oral eruption). RESULTS: The cuspid´s inclination change with age gave statistically significant differences between the group of impacted cuspids and the rest of groups from age 9 in the 3 angles used in this study. The impacted canines were located between sectors 2, 3 and 4 but only since age 10. The height of the impacted canines was statistically different from the rest of groups since age 13. The first upper bicuspid´s inclination changed in time in a similar way in all study groups. 78 % of the treated cuspids erupted normally. Between the light treatments done, the biggest success rate was found in the combination of maxillary expansion with primary predecessor cuspid extraction, followed by primary predecessor cuspid extraction and last maxillary expansion. There was a statistically significant relation between upper lateral incisors and the group of impacted canines. DISCUSSION: The cuspid´s inclination change with age of each study group showed very similar results with other studies in literature. The cuspid´s sectorial position also showed very similar results with other studies but only after age 10. The cuspid´s height gave statistically significant differences at a very late age so showing a very low clinical importance for an early diagnosis that agrees with most studies of literature. At the treatment part, our study differs from other studies due to the fact that the temporary cuspid extraction was not always done to restore the permanent cuspid´s eruption path. The relation obtained between upper lateral incisors agenesis and impacted canines is highly obtained in orthodontic literature. CONCLUSIONS: An accurate method of measurement of the upper permanent cuspid inclination based on 3 angles has been obtained with specifically designed software for this study. The angles C2 (angle between suborbitary line and the upper permanent cuspid axis), C3 (angle between occlusal plane and the upper permanent cuspid axis) and C4 (angle between midline and the upper permanent cuspid axis) showed very reliable results in the measurement of upper permanent cuspid inclination. The upper permanent cuspid angulation is a very important prognosis factor to predict its palatal impaction because at age 9 it can differentiate cuspids with a normal eruptive path from cuspids that will need any preventive treatment. The preventive treatment of maxillary expansion and primary predecessor cuspid extraction improves an anomalous inclination of an upper cuspid preventing a palatal impaction and making easier its eruption. The sectorial position of the upper permanent cuspid from age 10 on can be a prognosis factor to prevent its palatal impaction. Also, the upper permanent cuspid´s height at age 12 with respect to the occlusal plane can be a prognosis factor to prevent its palatal impaction. The first upper premolar´s inclination doesn´t have influence on the adjacent permanent cuspid´s eruptive path. The upper lateral incisors agenesia is a dental alteration related with the lack of eruption of the upper permanent cuspid.
