Factors affecting spontaneous eruption of impacted mandibular first molars after surgical exposure

Abstract Objectives The purpose of this study was to investigate factors, such as the status of impaction, root developmental stage, depth of impaction, tooth angulation and eruption space, which can influence the spontaneous eruption of impacted mandibular first molars after surgical exposure. Material and methods Clinical dental records and panoramic radiographs of children aged 6 years or older were studied. In total, 59 impacted mandibular first molars of 54 children had undergone surgical exposure to induce eruption and were followed for more than 6 months. Fisher's exact test and independent-sample t -tests were used for analysis. Results The failure rates of tooth eruption in type I and type II cases were significantly higher than those in type III and IV cases ( p  = 0.012). Regarding the degree of root development, the failure rate of spontaneous eruption increased as root formation approached completion, but this trend was statistically insignificant ( p  = 0.275). Failure rate was higher in the cases of shallow impaction than cases of deep impaction ( p  = 0.011). The angulation of impacted teeth did not influence the spontaneous eruption after surgical exposure ( p  = 0.394). Spontaneous eruption failure was significantly more likely when the eruption space between the adjacent second premolar and the second molar was smaller than the crown width of the impacted tooth ( p  = 0.002). Conclusion The results showed that spontaneous eruption by surgical exposure occurred well when the impaction type was distally angulation, the depth of the impaction was deep, or eruption space was sufficient.