Molecular insights into hypomineralized enamel

High-Resolution Characterization of Enamel Remineralization Using Time-of-Flight Secondary Ion Mass Spectrometry and Electron Microscopy

INTRODUCTION

The aim of this in vitro study was to assess the suitability of high-resolution time-of-flight secondary ion mass spectrometry (ToF-SIMS) for visualizing cross-sectional changes in human enamel microstructure and chemical composition during treatment and remineralization cycling of artificially generated caries lesions underneath an artificial plaque.

METHODS

Treatments consisted of exposure to twice daily toothpaste/water slurries prepared from 0, 1,100, and 5,000 μg/g fluoride (F) NaF/silica toothpastes. In addition, treatments with slurries prepared from 1,100 μg/g F SnF2/silica toothpastes were done using 44Ca in the remineralization solution to allow for differentiation of newly formed mineral and exploration of incorporated metal dopants using ToF-SIMS. Complementary microhardness, scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM) investigations were performed on enamel cross sections.

RESULTS

HR-TEM was used for the first time to determine the change in crystallinity during remineralization revealing distinct microstructural zones within one lesion. Chemical mapping using ToF-SIMS demonstrated that the distribution of F, while observed primarily in the new mineral phase, was widespread throughout the lesion with 44Ca substantially limited to the remineralizing mineral. Both penetrated the inter-rod spaces of the sound enamel illustrating how acid damage propagates into the native mineral as the caries lesion deepens. HR-TEM examination revealed different regions within the lesion characterized by distinct micro- and ultrastructures. Importantly, HR-TEM revealed a return of crystallinity following remineralization. F dose-response observations verified the ability of these high-resolution techniques to differentiate remineralization efficacy.

CONCLUSION

The collective results provided new insights such as the visualization of F or calcium penetration pathways, as well as new tools to study the caries process.

Multi-scale characterization of Developmental Defects of Enamel and their clinical significance for diagnosis and treatment

Developmental Defects of Enamel (DDE) such as Dental Fluorosis (DF) and Molar Incisor Hypomineralization (MIH) are a major public health problem. Their clinical aspects are extremely variable, challenging their early and specific diagnosis and hindering progresses in restorative treatments. Here, a combination of macro-, micro- and nano-scale structural and chemical methods, including, among others, Atom Probe Tomography recently applied on tooth enamel, were used to study and compare MIH, DF and healthy teeth from 89 patients. Globally, we show that DF is characterized by an homogenous loss of mineral content and crystallinity mainly disrupting outside layer of enamel, whereas MIH is associated with localized defects in the depth of enamel where crystalline mineral particles are embedded in an organic phase. Only minor differences in elemental composition of the mineral phase could be detected at the nanoscale such as increased F and Fe content in both severe DDE. We demonstrate that an improved digital color measurement of clinical relevance can discriminate between DF and MIH lesions, both in mild and severe forms. Such discriminating ability was discussed in the light of enamel composition and structure, especially its microstructure, organics presence and metal content (Fe, Zn). Our results offer additional insights on DDE characterization and pathogenesis, highlight the potentiality of colorimetric measurements in their clinical diagnosis and provide leads to improve the performance of minimally invasive restorative strategies. STATEMENT OF SIGNIFICANCE: Developmental Defects of Enamel (DDE) are associated to caries and tooth loose affecting billions of people worldwide. Their precise characterization for adapted minimally invasive care with optimized materials is highly expected. Here In this study, first we propose the use of color parameters measured by a spectrophotometer as a means of differential clinical diagnosis. Second, we have used state-of-the-art techniques to systematically characterize the structure, chemical composition and mechanical optical properties of dental enamel teeth affected by two major DDE, Dental Fluorosis (DF) or Molar Incisor Hypomineralization (MIH). We evidence specific enamel structural and optical features for DF and MIH while chemical modifications of the mineral nanocrystals were mostly correlated with lesion severity. Our results pave the way of the concept of personalized dentistry. In the light of our results, we propose a new means of clinical diagnosis for an adapted and improved restoration protocol for these patients.

Enamel Fluoride Uptake Determined Using the Microbiopsy Technique and Time-of-Flight Secondary Ion Mass Spectrometry: A Pilot Study

This study evaluated the suitability of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to assess enamel fluoride uptake (EFU) in comparison with the microbiopsy technique. Enamel specimens were exposed to equimolar solutions of fluoride prepared from sodium fluoride (NaF), stannous fluoride (SnF2), or amine fluoride (AmF). EFU was quantified by both techniques on the same specimens. EFU was found to be highest for samples treated with AmF, followed by SnF2 and NaF. Both methods yielded clearly interpretable, highly correlating (r = 0.95) data. ToF-SIMS can be considered a promising alternative to the microbiopsy technique for near-surface EFU assessment.

Study on machine learning of molar incisor hypomineralization in an endemic fluorosis region in central China

Objectives: The aim of the present study was to develop a machine learning model to predict the risk of molar incisor hypomineralization (MIH) and to identify factors associated with MIH in an endemic fluorosis region in central China.

Methods: A cross-sectional study was conducted with 1,568 schoolchildren from selected regions. The clinical examination included an investigation of MIH based on the European Academy of Paediatric Dentistry (EAPD) criteria. In this study, supervised machine learning (e.g., logistic regression) and correlation analysis (e.g., Spearman correlation analysis) were used for classification and prediction.

Results: The overall prevalence of MIH was 13.7%. The nomograph showed that non-dental fluorosis (DF) had a considerable influence on the early occurrence of MIH and that this influence became weaker as DF severity increased. We examined the association between MIH and DF and found that DF had a protective correlation with MIH; the protective effect became stronger as DF severity increased. Furthermore, children with defective enamel were more likely to experience caries, and dental caries were positively correlated with MIH (OR = 1.843; 95% CI: 1.260–2.694). However, gender, oral hygiene, and exposure to poor-quality shallow underground water did not increase the likelihood of developing MIH.

Conclusions: DF should be considered a protective factor within the multifactorial etiology of MIH.

Molar-incisor hypomineralization (MIH), dental fluorosis, and caries in rural areas with different fluoride levels in the drinking water

AIM

This study determined the prevalence of molar-incisor hypomineralization (MIH) and its association with dental fluorosis and caries in children living in rural areas in north-eastern Brazil who are exposed to residual fluoride (F) levels in the drinking water.

DESIGN

A census was carried out with 610 schoolchildren aged 6 to 12 years. The European Academy of Paediatric Dentistry criteria, Thysltrup and Fejerskov index, and World Health Organization index were used for diagnosis of MIH, dental fluorosis, and caries detection, respectively. The association between the outcome and exposure variables was determined by robust Poisson regression (P < .05).

RESULTS

Water F-levels varied from 0.06 to 1.98 ppm. MIH was not related to fluoride levels in the drinking water, but it showed an inverse and direct correlation with dental caries and fluorosis, respectively. Children with MIH had a higher DMFT, and severe MIH cases were most frequent in children with dental fluorosis.

CONCLUSION

Drinking water F-levels were not directly related to the occurrence of MIH in schoolchildren. The severity of MIH, however, was likely to be associated with dental fluorosis in areas with moderate to high fluoride levels in the drinking water.

Adhesive luting of orthodontic devices to silica-based ceramic crowns-comparison of shear bond strength and surface properties

OBJECTIVES

The aim of this study was to analyse the impact of different clinical conditioning approaches and an ammonium polyfluoride- and trimethoxysilylpropyl methacrylate-based experimental primer for intraoral luting of buccal tubes on silica-based ceramic surfaces.

MATERIALS AND METHODS

A total of 60 leucite-reinforced glass ceramic molar crowns were conditioned using different methods (n = 10): I-roughening, hydrofluoric acid, silane; II-roughening, silane; III-roughening, experimental coupling agent; IV-experimental coupling agent; V-roughening; VI-no treatment. A buccal tube was adhesively luted to the ceramic surface. Subsequently, water storage, thermocycling and chewing simulation were carried out. The shear bond strength (SBS) was determined, and changes in the surface were assessed.

RESULTS

All tubes of the control group (group VI) debonded after incubation. The conditioning methods using coupling agents revealed mean values for SBS of 61.56 MPa (group I), 45.53 MPa (group III), 41.65 MPa (group II), and 23.14 MPa (group IV). In groups I-III, both composite residues and cracks/tear-outs were detected.

CONCLUSIONS

The conditioning of silicate ceramic surfaces with a suitable coupling agent system appears to allow sufficient adhesive luting of buccal tubes. The intraoral luting of fixed appliance elements on silicate ceramic surfaces using an ammonium polyfluoride- and trimethoxysilylpropyl methacrylate-based ceramic primer can withstand orthodontic forces.

CLINICAL RELEVANCE

Ammonium polyfluoride- and trimethoxysilylpropyl methacrylate-based ceramic primers revealed promising results for the intraoral adhesive luting of orthodontic devices to silica-based ceramic crowns.