Analysis of Human and Microbial Salivary Proteomes in Children Offers Insights on the Molecular Pathogenesis of Molar-Incisor Hypomineralization

Comparative analysis of oral microbiome in molar-incisor-hypomineralization vs healthy age-matched controls

Molar-incisor-hypomineralization (MIH) is one of the most challenging dental diseases in children. While the association of oral microbiomes with caries and periodontitis has been studied thoroughly, limited data on the microbial composition in MIH and its clinical significance exist. This cross-sectional study aimed to compare the supragingival plaque microbiome between children and adolescents affected by MIH and a healthy age-matched control group. Ninety-five patients aged 7-17 years were recruited at the Department of Conservative Dentistry, Heidelberg University Hospital. The final sample included 29 participants with a confirmed diagnosis of MIH, treated preventively and restoratively, and 35 orally healthy controls. Clinical data were obtained, and supragingival plaque samples were collected using OMNIgene ORAL OMR-110 (DNA Genotek Inc.), followed by 16S rRNA amplicon sequencing. The microbiome composition was analyzed using α-diversity (Shannon index) and evenness (Pielou index), with group differences assessed using permutational multivariate analysis of variance (PERMANOVA) and MaAsLin2. The overall microbiome composition showed mostly similarities between both groups (PERMANOVA: R² = 0.019, P-value = 0.287), indicating no major dysbiosis. However, a significant decrease in α-diversity and evenness was observed with an increasing number of MIH-affected teeth. Pronounced positive correlations were found between ASV0055 (Streptococcus spp.), caries experience, and MIH severity. ASV0100 (Mannheimia sp.) increased significantly with the increasing number of MIH-affected teeth, whereas ASV0053 (Bergeyella sp.) decreased with higher caries experience. In summary, the oral microbiome of children and adolescents with MIH exhibits no significant differences from healthy children and adolescents of the same age group. Depending on MIH severity, the presence of early plaque-forming species and cariogenic biofilm may increase, requiring intensive, tailored preventive care and appropriate restorative treatment to achieve microbial homeostasis.

IMPORTANCE

Molar-incisor-hypomineralization (MIH) represents a significant burden for affected children and adolescents, playing an increasingly important role in pediatric dentistry worldwide. Despite its high global prevalence, data on the microbiome of MIH patients remains limited. This study is the first to compare the oral microbiome composition of MIH patients with a healthy control group, making a significant contribution to pediatric dentistry and microbiology. Our results indicate that the oral microbiome of children with MIH is similar to that of healthy children of the same age. Although this structural anomaly predisposes patients to caries, effective preventive and restorative treatments can help maintain microbial homeostasis. However, MIH-affected children remain high-risk patients, as the disease severity may reduce microbial diversity. Furthermore, the increased abundance of Streptococcus spp. in MIH patients indicates a higher caries susceptibility, emphasizing the need for targeted dental care focusing on plaque control and topical fluoride use.

Salivary proteomics as signature for molar incisor hypomineralization stages

OBJECTIVE

Saliva is a rich-bodily fluid with recognized clinical diagnosis roles. This research aimed to investigate the salivary proteomic signatures for MIH in children with distinct degrees of severity.

MATERIALS AND METHODS

In this cross-sectional study, 50 schoolers (8-13 years) were equally assigned into the following groups: G1 (Control group-Healthy first permanent molars), G2 (Mild MIH with white/creamy opacity and free of caries), G3 (Mild MIH with yellow/brown opacity and free of caries), G4 (Severe MIH with white/creamy, yellow/brown opacities including post-eruptive fracture and free of caries), G5 (Severe MIH with white/creamy, yellow/brown opacities, post-eruptive fracture, and caries). Unstimulated saliva samples were collected and later explored using mass spectrometry analysis.

RESULTS

In total, 6,471 proteins were found, 5,073 exclusively from MIH children, and 778 overlapping among the different degrees of the disturb. The biological pathways displayed distinct patterns among the groups, which differed according to the MIH degrees. Gene-Ontology differences might not be verified regarding the biological processes and cellular components. Conversely, concerning molecular function, alterations among groups were evident, with proteins that would contribute to MIH in children with the severe condition (i.e., calcium ion binding, microtubule binding, platelet-derived growth factor binding).

CONCLUSION

The results of this study support important salivary proteomics changes in MIH children according to distinct degrees of severity, reinforcing the interplay between the clinical characteristics and changes in the salivary proteome.

CLINICAL RELEVANCE

Changes occurring in the salivary proteomics of children with distinct degrees of severity of Molar Incisor Hypomineralization (MIH) might be promising biomarkers and valuable information in clinical care, helping professionals make better clinical decisions and helping patients to understand their disturbance.

Metagenomic Analysis of the Buccal Microbiome by Nanopore Sequencing Reveals Structural Differences in the Microbiome of a Patient with Molar Incisor Hypomineralization (MIH) Compared to a Healthy Child-Case Study

Molar incisor hypomineralization (MIH) is a qualitative developmental defect that affects the enamel tissue of permanent molars and can also occur in permanent incisors. Enamel affected by MIH has reduced hardness, increased porosity, and a higher organic content than unaffected enamel. These characteristics predispose the enamel to accumulation of bacteria and a higher prevalence of caries lesions. Through a groundbreaking metagenomic analysis of the buccal mucosal sample from a patient with MIH, we explored the intricacies of its microbiome compared to a healthy control using state-of-the-art nanopore long-read sequencing. Out of the 210 bacterial taxa identified in the MIH microbiome, we found Streptococcus and Haemophilus to be the most abundant genera. The bacteria with the highest read counts in the patient with MIH included Streptococcus mitis, Haemophilus parainfluenzae, Streptococcus pneumoniae, Rothia dentocariosa, and Gemella haemolysans. Our results revealed a striking contrast between healthy and MIH affected children, with a higher dominance and number of pathogenic species (S. pneumoniae, H. influenzae, and N. meningitidis) and reduced diversity in the MIH-affected patient. This distinct microbial profile not only sheds light on MIH-affected patients, but paves the way for future research, inspiring deeper understanding and larger scale studies.

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.

Qualitative and Quantitative Mass Spectrometry in Salivary Metabolomics and Proteomics

The metabolomics and proteomics analysis of saliva, an excellent biofluid that is a rich source of biological compounds, allows for the safe and frequent screening of drugs, their metabolites, and molecular biomarkers of various diseases. One of the most frequently used analytical methods in saliva analysis is liquid chromatography coupled with mass spectrometry (LC-MS) and tandem mass spectrometry. The low ionisation efficiency of some compounds and a complex matrix makes their identification by MS difficult. Furthermore, quantitative analysis by LC-MS frequently cannot be performed without isotopically labelled standards, which usually have to be specially synthesised. This review presented reports on qualitative and quantitative approaches in salivary metabolomics and proteomics. The purpose of this manuscript was to present the challenges, advances, and future prospects of mass spectrometry, both in the analysis of salivary metabolites and proteins. The presented review should appeal to those interested in the recent advances and trends in qualitative and quantitative mass spectrometry in salivary metabolomics and proteomics, which may facilitate a diagnostic accuracy, the evaluation of treatment efficacy, the early diagnosis of disease, and a forensic investigation of some unapproved drugs for any medical or dietary administration.