# The Pathology of the First Permanent Molar during the Mixed Dentition Stage--Review
## 3 Results and Discussion
### Pathology of the Dental Hard Tissues
#### 3.2.2 Dental Caries  
Caries is a chronic infectious disease that leads to destruction by demineralization of the hard dental tissues [88]. The etiology of dental caries is multifactorial and involves the interaction between the host, the oral microflora, the metabolic substrate represented by the diet, and a long period of time in which these factors coexist [88]. It is the result of the imbalance between the demineralization produced by acids and the remineralization carried out, especially by saliva and its components [89]. Although preventable and in increasing decline worldwide, dental caries still represent a serious trait of a child's oral health [90]. FPM Vulnerability to Caries during the Mixed Dentition Stage  
FPM is considered the most caries-sensitive tooth in permanent dentition [91; 92]. After the completion of the increase in enamel thickness, the maturation stage of its development begins, comprising a pre-eruptive and a post-eruptive stage [93]. Post-eruptive maturation of the enamel is characterized by chemical and physical changes in the surface layers of the enamel as a consequence of exposure to the oral environment [94]. Post-eruptive enamel maturation of the FPM takes place during the mixt dentition period, when the FPM cohabits with deciduous teeth, mobile at the time of their exfoliation and sometimes decayed, features which favor biofilm retention and disadvantage self-cleaning [7]. Posteruptive age is considered a predictor for caries on permanent teeth, the FPM being at higher risk of occlusal caries within the first year post-eruption [95; 96]. Therefore, the FPM can serve as \"the first indicator of dental caries activity during the phase of initial mixed dentition\" [97]. Furthermore, the fact that the FPM reveals the progress of caries with high sensitivity determines the use of this tooth as an important tool for establishing programs of preventive maintenance and evaluating their outcome [97]. Its caries status in childhood can reveal the permanent dentition caries distribution in adulthood [98]. From the moment of FPM arising from the oral mucosa until it contacts its antagonist in the occlusal plane, an average time between six months and one year is necessary, which means the existence of a long period without functionality, characterized by occlusal surface massive plaque accumulation [7]. Many authors showed that considerably higher amounts of biofilm accumulate on the occlusal surface of partially erupted FPMs compared to fully erupted FPMs [95; 99; 100; 101]. Moreover, [PERSON] et al. found that lesions initiated during eruption arrest in FPMs which had been in full occlusion for more than one year, due to functional usage and improved conditions for tooth brushing [99]. [PERSON] et al., 2020, showed that FPM's particular vulnerability to caries is due to the eruption age and the position in the dental arch, lack of brushing skills, and parents' ignorance of the permanent nature of this molar [102]. Dental caries of the FPM have a specific profile during the mixed dentition stage: the occlusal surface is the first exposed to risk factors and remains vulnerable until the age of eight, after which the lesions are mostly located on the mesial surface [7]. Researchers showed that mesial surface decay on FPM accounts for the majority of caries experienced in 12-year-old children [91; 103]. Other authors consider that the occlusal surfaces of FPMs and the buccal pit in mandibular FPMs are the most frequent locations for the occurrence of caries during the mixed dentition stage [102; 104]. Epidemiology of FPM Caries in the Mixed Dentition Stage  
Many researchers were concerned with the epidemiology of dental caries on FPM during the mixed dentition phase, focusing on its prevalence, incidence, distribution, associated risk factors, treatment needs, and effectiveness of preventive and curative measures. [PERSON] et al.