Trends in the prevalence of Molar Incisor Hypomineralisation between 2018 and 2023: A comparison of two cross-sectional studies in elementary schools Mexico.

Purpose : The aim of this study was to compare the prevalence of Molar Incisor Hypomineralisation (MIH) in schoolchildren in Tepatitlán de Morelos (Mexico) between 2018 and 2023. Furthermore, the association of MIH with other variables was investigated. Methods : Children (5-13 years old) enrolled in elementary schools in Tepatitlán de Morelos, Mexico, were evaluated. Intra-oral examinations were performed on schoolgrounds by calibrated examiners. In both cohorts, the presence and characteristics of MIH and Hypomineralised Second Primary Molars (HSPM) were scored according to the scoring system from the European Academy of Paediatric Dentistry (EAPD). Also, the severity of MIH was evaluated. In 2023, dental plaque and dental caries were additionally scored. Descriptive and statistical analyses were performed (α=5%, 95%CI). Results : In both cohorts together, 959 schoolchildren were evaluated. The prevalence of MIH was 35.78% in 2018, and 26.58% in 2023 (p=0.002). Also, the tooth level prevalence of MIH decreased significantly from 12.71% to 8% when comparing the two cohorts (p<0.001). Higher prevalence of HSPM was observed in children with MIH, compared to children without MIH in both cohorts (p<0.001). Neither the number of teeth presenting cavitated caries lesions (p=0.193), nor the plaque score (p=0.061) was associated with the presence of MIH in 2023. Children with severe MIH had a higher likelihood to present cavitated caries lesions compared to children with mild MIH (p=0.001). Conclusion : The findings in the present study portray a statistically significant decrease in the MIH prevalence at both child and tooth level in the period 2018-2023.