# The Pathology of the First Permanent Molar during the Mixed Dentition Stage--Review
## 3 Results and Discussion
### Eruption Pathology
#### 3.1.1 Ectopic Eruption
The irreversible type has been significantly correlated with a larger FPM width and a more mesial angle of eruption; a tendency toward a shorter maxilla has also been associated with the irreversible category [19]. [PERSON] et al., 2005, determined a ratio of reversible versus irreversible ectopic eruption of 2.27:1 [17]. Significant correlations were found between spontaneous self-correction and bilateral locations (\(p<0.05\)). The average magnitude of impaction (MOI) was 2.91 mm on the right side and 1.6 mm on the left side, and this difference was found to be statistically significant (\(p<0.05\)). The MOI was higher in the irreversible group than in the reversible one. Therefore an increasing value of MOI was considered a reliable predictor for the irreversible outcome, although the correlation between the MOI and the type of ectopy (reversible versus irreversible) was not assessed. Classes I and II resorption cases got self-corrected, and classes III and IV resorption cases remained impacted. No statistically significant correlation was found between the degree of resorption of the primary second molar and the MOI of the FPM [17]. In another study that evaluated the predicting factors for the irreversible outcome of ectopic eruption of maxillary FPM, [PERSON] et al., 2017, identified positive correlations between increased MOI, resorption class of the primary second molar, severe lock, bilateral location, and irreversible ectopic eruption [26]. The authors showed that increased MOI was the most reliable predictor for irreversible outcomes [26]. In their 2021 research on 419 teeth, out of which 257 (61.3%) presented reversible and 162 (38.7%) irreversible ectopic eruptions, [PERSON] et al. found Class III resorption in the majority (84.2%) of the cases [31]. A statistically significant difference was determined between the reversible and irreversible groups (\(p=0.022\)). The more severe the root resorption, the more inclined the outcome was toward the irreversible type [31]. The mean value for the magnitude of the impaction index (MOII) was calculated by dividing the value of FPM impaction magnitude by the value representing the crown width of the second primary molar. The mean value of MOII was 0.198 \(\pm\) 0.077 in the reversible group and 0.282 \(\pm\) 0.115 in the irreversible group. A statistically significant difference was found between the two groups (\(p<0.001\)) [31]. Concerning the eruption angulation, the critical value determined was 73.05\({}^{\circ}\). Therefore a greater value was correlated with an irreversible outcome. No statistically significant difference was found between the groups [31]. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Stability**} & \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Number of**} & \multirow{2}{*}{**Number of**} & \multirow{2}{*}{**Emopic Volume**} & \multirow{2}{*}{**Number of**} & \multirow{2}{*}{**Emopic Volume**} & \multirow{2}{*}{**Prevalence in Relation to Dental Arch Performance in Relation to State**} \\  & & & & & & & & \\ \hline Crown [25] & 2018 & 7649 & 203 (2.6\%) & average age in the affected group & F45-(81.7\%) & F45-(81.7\%) & F45-(81.6\%) & B-(21.8\%) \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & & \\ \hline [PERSON] et al. [30] & 2021 & 772 & 79 (10.2\%) & F5-(9.0\%) & F48-(81.7\%) & & Mo-190\% & NS \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\ \hline [PERSON] et al. [31] & 2021 & 11,403 & 409 (8.5\%) & mostly \(p\)\(\times\)6-7 & F44 (35.2) & 634 & Mo-69.7\% & mostly symmetrically \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._Associated Anomalies  
[PERSON] and [PERSON] found a posteriorly positioned maxilla relative to the cranial base, a tendency to dolichocephaly, and a posterior rotation of the chin in cases of ectopic eruption of the maxillary FPM [32].