Prevalence and characteristics of ectopic eruption of the first permanent molar and predictive factors for clinical outcome

The primary objective of this study was to assess the occurrence, distribution, and features of ectopic first permanent molars (FPMs), as well as to investigate the clinical outcomes associated with ectopic eruption based on the degree of root resorption observed in primary second molars. This study was performed retrospectively by examining panoramic radiographs of 7070 patients aged 5 to 12 years. The gender and age of the patients, the number, location, and distribution mode of ectopic FPMs, the resorption degree of the distal roots of primary second molars, and the clinical outcome of ectopic eruption were evaluated. Descriptive statistics and chi-square test were performed on the obtained data using SPSS version 22 (SPSS Inc, Chicago, IL, USA). In 144 of 7070 cases, a total of 221 ectopic permanent first molar teeth were detected (2% prevalence). The mean age of the 144 patients was 8.04 years. Ectopic eruption was most common in patients aged 7–8 years (48.63%), which was statistically significant (P < 0.05). Ectopic eruptions were more common in females (58.30%) than males (41.70%; P < 0.05). Of the ectopic permanent first molars, 78 (35.30%) were in the mandible, and 143 (64.70%) were in the maxilla. The relationship between the degree of resorption and the type of ectopic eruption was statistically significant (P < 0.05). The increase in the severity of root resorption in the primary second molars was a significant predictor for the prognosis of ectopic eruption in the present study. Early diagnosis and treatment of ectopic FPMs are of great importance to preventing premature loss of primary second molars resulting in malocclusion.