Tooth-level outcomes in molar incisor hypomineralisation affected molars with post-eruptive breakdown: a randomized clinical trial comparing glass ionomer and resin composite.

OBJECTIVE: To evaluate the survival of restorations with glass ionomer cement (GIC) and resin composite (RC) in molar incisor hypomineralisation (MIH)-affected molars, residual opacity behavior, and tooth survival. MATERIALS AND METHODS: This randomized clinical trial included 72 restorations followed for 12 months. Teeth with MIH-associated post-eruptive breakdown (PEB) involving up to four surfaces were restored using GIC (Equia Forte®) or RC (Clearfil SE Bond® + Filtek Z350XT®). Outcomes included restoration survival (modified ART criteria), new post-eruptive breakdown in residual opacities, and overall tooth survival. Cluster-robust Cox regression and Kaplan-Meier analyses were performed. RESULTS: At 12 months, no statistically significant difference was detected in restoration survival between GIC and RC (91.7% and 88.9%, respectively; p = 0.690). A considerable proportion of failures was attributable to PEB in residual enamel opacities adjacent to restorations (GIC: 30.6%; RC: 25.0%), with no significant difference in survival between groups (p = 0.499). In the regression analyses, absolute isolation was identified as an independent predictor of all outcomes. CONCLUSION: No statistically significant difference was detected in the 12-month survival of GIC and RC restorations in MIH-affected molars. A substantial proportion of treatment failures was associated with PEB of residual opacities adjacent to restorations. The absence of absolute isolation showed an exploratory association with all evaluated outcomes, including overall treatment failure. CLINICAL SIGNIFICANCE: Even when restorations remain clinically successful, residual hypomineralised enamel may continue to fracture, highlighting the need for longitudinal follow-up and treatment strategies focused on preservation of the tooth as a whole.