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Objective: A tooth with a dentigerous cyst (DC) does not always erupt by marsupialization. The eruption duration and conditions of DC-associated premolars were examined to predict such eruption following marsupialization., Study Design: The eruption and conditions including depth, root formation, inclination, and eruption space were examined retrospectively in 21 DC-associated mandibular premolars using dental and panoramic radiograms., Results: Fifteen of 21 premolars erupted half within 3 months and all 15 erupted completely within 10 months after marsupialization, without orthodontic traction. The age of the patients, tooth depth, and inclination were significantly different between the erupted and non-erupted groups, whereas there was no significant difference in the root formation or the eruption space between the 2 groups., Conclusions: The successful eruption of a DC-associated premolar can be predicted within 3 months after marsupialization. Furthermore, the eruption may be affected by the patient's age, tooth depth, and tooth inclination.

Objective: To evaluate the possibility of applying the Third Molar Eruption Predictor to all panoramic radiographs., Study Design: Panoramic radiographs were retrospectively analyzed from a 4-year follow-up study of third molars carried out at the University of Copenhagen, Denmark. The radiographs, taken at a mean age of 20.6 years, included 45 unerupted or partially erupted mandibular third molars in 28 subjects. Because the device was calibrated both with simple proportions and by use of the methods of Bayes' Decision Theory, the separation point of the device was therefore adjusted at 12 mm from the distal surface of the second molar., Results: The predictions of future eruption or impaction made with the calibrated device and the actual clinical outcome 4 years later were in conformity for 80% of the mandibular third molars., Conclusion: The Third Molar Eruption Predictor may be applied to all panoramic radiographs, but it seems to require calibration before use.

Objective: To measure changes in angular position and eruption status of mesially impacted mandibular third molars (M3) during 4-year follow-up period., Study Design: Standardized panoramic radiographs were taken at the start of the study (the average age of the subjects was 19.7 years) and 4 years later. Angulation and degree of impaction of M3 were determined by their sagittal relationships to the adjacent second molars. The impacted M3 were either partially erupted or unerupted., Results: Initial examination showed that among a total of 59 mesioangular M3, 49 (83%) had inclination between 5 and 30 degrees. The proportion of M3 that became upright (zero tilt) was 76% (13/17) with initial angulations of 5 to 10 degrees, 61% (11/18) with initial angulations of 15 to 20 degrees, and 14% (2/14) with initial angulations of 25 to 30 degrees. None of the M3 originally presented at 35 degrees or more became upright, but an average decrease of 12 degrees in angulation was registered. In total, 26 M3 of 59 (44%) became upright during the follow-up period. Initial examination of levels of eruption showed that among 59 M3, 13 (22%) were partially erupted and the rest were unerupted. Of the 46 M3 initially unerupted, 17 (37%) became fully erupted and 7(15%) erupted partially during the 4-year follow-up. Of the total sample, 25 (42%) had erupted to full occlusion during the observation period., Conclusion: A significant proportion of mesially impacted mandibular M3 had changed their angulation and became fully erupted by the time the individual reached 24 years of age. Positional changes and eruption of impacted M3 are unpredictable phenomena.

This study was designed to create a transparent device to be superimposed on a panoramic tomogram taken of a patient at age 20 years to make predictions of future eruption or impaction of lower third molars. The device was developed from data on 40 lower third molars initially retained at age 20 years; one half of these remained impacted, and the other half of them erupted by age 26 years. Tracings were made from panoramic tomograms taken at age 20 years. The critical point for prediction in the overlay was the intersection of a horizontal reference line and the anterior border of the ascending ramus. To estimate this critical separation line, Bayes' Decision Theory was used. The sum of false negatives and false positives was least at a distance of 14.5 mm from the distal surface of the second molar. Mesial from this point, the probability of impaction was 76%; distal from this point, the probability of eruption was 72%. Tested against 35 initially unerupted lower third molars, the predictions made by the device and the actual clinical findings were in conformity in relation to 97% of the test teeth. It could thus be concluded that the method was simple to use and may prove a good addition for predicting lower third molar development.