Relationship between cariogenic bacteria and molar incisor hypomineralization in Brazilian schoolchildren

Background: Teeth with defects in their structure, such as the ones affected by molar-incisor hypomineralization (MIH), are more susceptible to carious lesions. Caries is a complex and multifactorial disease highly prevalent in childhood. The present research evaluated the relationship between the stages of MIH and cariogenic bacteria in children.Methods: After examining 566 schoolchildren, four groups of 10 children each were formed: healthy (G1), mild MIH (G2 and G3), and severe MIH + caries (G4). Dental biofilm was assessed to quantify Streptococcus mutans (SM) and Lactobacillus spp. (LB) using real-time polymerase chain reaction (RT-PCR).Results: LB counting in biofilm samples of healthy children (G1) and those with mild MIH characterized by white opacities (G2) were not significantly different. The same happened when the ones with yellow opacities (G3) were compared with severe MIH + caries (G4) (P>0.05). The post hoc Tukey test proved that G4 had greater levels of SM and LB when compared with G2 (P<0.05); however, the control group did not diverge from the others considering SM (P>0.05). Increased LB enhanced the severity of MIH [rate ratio (RR): 7.706; P=0.035].Conclusions: LB was influenced by different degrees of MIH and the presence of caries and could guide clinical decisions and patients' recommendations to prevent carious lesions in MIH children.