# The Pathology of the First Permanent Molar during the Mixed Dentition Stage--Review
## 3 Results and Discussion
### Pathology of the Dental Hard Tissues
#### 3.2.1 Molar Incisor Hypomineralization
MIH cases were found in 58 children examined, resulting in an overall prevalence of 2.9% (1.65% in male and 1.25% in female patients) [56]. The most common lesions found were demarcated opacities (71.5%), followed by posteruptive enamel breakdown (19.6%) and atypical restorations (8.9%). The highest prevalence was found in the youngest group of age, eight-year-olds (n = 19; 32.8%), followed by 12-year-old children (n = 12; 20.7%) and nine-year-olds (n = 10; 17.2%) [56]. In another study investigating 659 Lebanon children 7-9 years old, the MIH recorded prevalence was 26.7% (176 subjects) [79]. The distribution of MIH patients according to gender was 80 boys (45.45%) and 96 girls (54.55%). In what concerns the distribution of MIH lesions in relation to age, a higher percentage was found in nine-year-old patients (29.8%), followed by the eight-year-old group (20.7%) and seven-year-old group (25%). The majority of cases (52.8%) showed only FPM affection, while in 47.2% of cases, both molars and incisors were involved [79]. [PERSON] et al., in a group of 5318 Indian children, revealed a number of 216 patients with MIH defects, representing a prevalence of 4.1% [80]. MIH lesions were found more frequently in males (120 subjects) than in females (96 subjects), but no statistically significant differences were determined. The majority of MIH lesions were in the maxilla (619 teeth) compared to the mandible (589 teeth) [80]. In another 2020 study investigating 407 Brazilian children aged 7-14 years old by [PERSON] et al., MIH prevalence was 14.5% (59 subjects), with a higher distribution among male patients (n = 33; 55.9%) compared to female patients (n = 26; 44.1%), but no statistically significant difference was found [81]. Most of the MIH teeth presented mild defects (n = 202; 77.4%). Of the 261 MIH affected teeth, the maxillary FPMs represented 33% (n = 86) and the mandibular FPMs 28.3% (n = 74) [81]. Table 2 summarizes the main studies regarding the occurrence of MIH. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Study**} & \multicolumn{1}{c}{**Year**} & \multicolumn{1}{c}{**Sample**} & \multicolumn{1}{c}{**Prevalence of**} & \multicolumn{3}{c}{**Gender**} & \multicolumn{3}{c}{**Degree of Severity of Affected Molas**} \\ \cline{4-7} \multicolumn{1}{c}{} & & & **MIH** & **Distribution** & **Mild** & **Moderate** & **Severe** \\ \hline [PERSON] et al. [73] & 2012 & 505 & 90 & F-45 (50\%) & 45 (50\%) & 26 & 19 \\  & & & (17.88\%) & M-45 (50\%) & (50\%) & (28.89\%) & (21.11\%) \\ \hline [PERSON] et al. [74] & 2014 & 810 & 164 & F-96 (85.85\%) & 17.1\% C/W & 31.3\% & 10\% \\  & & & (20.27\%) & M-68 (41.5\%) & 41.6\% Y/B & 31.3\% & 10\% \\ \hline [PERSON] et al. [75] & 2018 & 1511 & 215 & F-113 (52.6\% & & \\  & & (14.2\%) & M-102 (47.4\%) & NS & NS & NS \\ \hline [PERSON] et al. [76] & 2018 & 705 & 56 & F-34 (60.7\%) & M-22 (39.3\%) & NS & NS \\ \hline [PERSON] et al. [77] & 2019 & 686 & 248 & F-120 (49.4\%) & 45 & 163 & 35 \\  & & & (35.4\%) & M-123 (50.6\%) & (18.5\%) & (67.1\%) & (14.4\%) \\ \hline [PERSON] et al. [56] & 2020 & 2000 & 58 & NS & 70.8\% & 20.6\% & 8.6\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Occurrence of MIH as described by different authors. F—female; M—male; NS—not specified; C/W—creamy/white; Y/B—yellow/brown. In a 2017 systematic review of 61 publications, the overall prevalence of MIH was 11.24%, with a high degree of geographic variations and mild variation according to gender [82]. A higher prevalence in European and South American countries than in Asian countries was found. The highest prevalence estimate was for middle social class school children in Brazil, and the lowest prevalence estimate was for urban school children in India [82]. In another 2018 systematic review and meta-analysis of 99 studies on 113,144 participants from 43 countries, the number of prevalent cases in 2015 was 878 (791-971) million, and the number of incident cases in 2016 was 17.5 (15.8-19.4) million [83]. The mean prevalence identified by meta-analysis was 13.1%.