Background:The second permanent molar plays an important role when considering extraction of first permanent molars severely affected by molar-incisor hypomineralization (MIH). Aim: To assess the association between MIH and enamel hypomineralization of the second permanent molars in terms of presence and severity. Design: In this retrospective cross-sectional study, permanent teeth were evaluated in 453 patients between the ages of 13 and 16 at a dental clinic, using intraoral photographs. A calibrated examiner classified enamel hypomineralization using the MIH index and dental caries experience using the DMFT and DMFS indices. Statistical analyses were performed using a linear generalized model and ordinal logistic regression. Results:The most commonly affected teeth by enamel hypomineralization were permanent molars, whereas incisors, premolars, and canines were less affected. The presence of severe defects in the first permanent molars was associated with mild defects in the second permanent molars (OR = 4.01; 95% CI: 2.50-7.77). Enamel hypomineralization was associated with increased caries experience (PR = 5.54; 95% CI: 3.81-9.06). Conclusion:Enamel hypomineralization mainly affects the first and second permanent molars. Mild defects in the second permanent molars tend to be more frequent in patients with severe MIH in the first permanent molars. The presence of enamel hypomineralization was associated with higher dental caries experience.

Background Currently, there is no consensus on the superiority of any material for the restorative treatment of molars affected by molar‐incisor hypomineralization (MIH). Aim To evaluate the survival of restorations with stainless‐steel crown (SSC) or composite resin (CR) in first permanent molars affected by MIH for 24 months. Design In this retrospective cohort study, 61 CR and 54 SSC restorations placed on molars affected by MIH of patients, aged between 7 and 10, that were treated and overseen at a university dental clinic in the period of 2017‐2020 were evaluated. The primary outcome was the failure‐free survival time. Parametric survival models were used for data censored by interval, and the comparison between SSC and CR was performed using the hazard ratio function with a 95% confidence interval. Results The survival of SSC and CR restorations after 24 months was 94.4% and 49.2%, respectively. This difference was influenced by the presence of previous restoration (aHR = 3.4; 95% CI: 1.2‐9.4) and cusp involvement (aHR = 4.0; 95% CI: 1.5‐11.2). Conclusion In molars with MIH and the need for restorative treatment, SSC had a significantly higher survival rate than CR over 24 months.

The study of bacterial interaction between Streptococcus mutans and Actinomyces naeslundii may disclose important features of biofilm interspecies relationships. The aim of this study was to characterize—with an emphasis on biofilm formation and composition and metabolic activity—single- and dual-species biofilms of S. mutans or A. naeslundii, and to use a drip flow reactor (DFR) to evaluate biofilm stress responses to 0.2% chlorhexidine diacetate (CHX). Single- and dual-species biofilms were grown for 24 h. The following factors were evaluated: cell viability, biomass and total proteins in the extracellular matrix, 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide—“XTT”—reduction and lactic acid production. To evaluate stress response, biofilms were grown in DFR. Biofilms were treated with CHX or 0.9% sodium chloride (NaCl; control). Biofilms were plated for viability assessment. Confocal laser-scanning microscopy (CLSM) was also performed. Data analysis was carried out at 5% significance level. S. mutans viability and lactic acid production in dual-species biofilms were significantly reduced. S. mutans showed a higher resistance to CHX in dual-species biofilms. Total protein content, biomass and XTT reduction showed no significant differences between single- and dual-species biofilms. CLSM images showed the formation of large clusters in dual-species biofilms. In conclusion, dual-species biofilms reduced S. mutans viability and lactic acid production and increased S. mutans’ resistance to chlorhexidine.

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