# 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  
Molar incisor hypomineralization (MIH) is the name assigned by [PERSON], [PERSON], and [PERSON] in 2001 to a pathologic condition characterized by \"a hypomineralisation of systemic origin of one to four FPMs frequently associated with affected incisors\" [43]. Mandibular incisors are more rarely involved than maxillary ones [43; 44]. The condition was first reported in the late 1970s by Swedish dentists, worried because of its particular, destructive behavior and its increasing incidence [42]. From then until the consensus adopted in 2001 [43], large defects in FPMs during or soon after the eruption were referred to in the literature as non-fluoride enamel opacities, idiopathic enamel opacities, internal enamel hypoplasia, mottling of enamel, cheese molars, etc. [45]. MIH represents a major concern for the child's oral health due to the rapid destruction of the dental tissue it generates soon after the eruption of FPM. Etiology  
Enamel is formed through the process called amelogenesis, carried out by ameloblasts [46]. Amelogenesis comprises two sequential stages, the matrix secretion stage and the calcification (maturation) stage [47; 48; 49]. Disturbances during the maturation stage are responsible for enamel hypomineralisation [47; 49; 50; 51]. Amelogenesis is completed at the time of tooth eruption, and the ameloblasts die after the end of this process [46]. Therefore, no secondary or regenerative enamel is produced afterward [46], no metabolic activity exists once the enamel is formed, and disturbances during enamel formation are expressed as permanent defects in the erupted tooth [50]. Enamel formation is a sensitive process; thereby, systemic and environmental factors can affect it [44; 47; 49; 51; 50]. The unique combination of affected molars and incisors indicates that a specific influence on enamel development during a limited period of time is responsible for MIH lesion occurrence [44]. The period of amelogenesis of the FPM starts from the eighth month of intrauterine life and continues until the age of four; the risk factors associated with MIH act during this period, the first ten months of life being critical [52; 53]. Prenatal, perinatal, and postnatal medical conditions were associated with MIH lesions. Among prenatal medical conditions, [PERSON] and [PERSON], 2000, found the mother's chronic diseases like syphilis, high blood pressure, hyperglycemia, and prolonged use of drugs to be related to MIH [42]. Hypocalcemia due to maternal diabetes and vitamin D deficiency can also be associated with MIH occurrence [51]. [PERSON] et al., 2008 identified multiple maternal episodes of high fever due to cold and infections during the last pregnancy months in association with MIH and emphasized on the harmful influence of maternal pyrexia on amelogenesis, ranging from dysfunction to complete degeneration of the ameloblasts [54]. Other maternal medical conditions reported by [PERSON] et al.,2008, were diabetes, prolonged vomiting, and use of spasmolytic medication in late pregnancy [54]. [PERSON] et al., 2013, found no association between maternal health problems during the third trimester of pregnancy and MIH [49]. [PERSON] et al., 2022, identified significant correlations between smoking during pregnancy and MIH (\(p=0.0005\)) [55]. Perinatal medical conditions include premature birth, prolonged delivery, and low birth weight. All these generate hypoxia, and lack of oxygen in active ameloblasts seems to be one of the most plausible causative factors for MIH [51]. [PERSON] et al., 2013, determined correlations between MIH occurrence and prematurity and no associations of MIH with low and very low birth weights [49]. [PERSON] et al., 2008 determined cesarean section, prolonged delivery, premature birth, and twining in association with MIH [54]. [PERSON] et al., 2020, ascertained significant correlations between low birth weight and MIH [56].