Ultrastructural Images of Enamel Tufts in Human Permanent Teeth

Confocal Raman data analysis of tufts and spindles at the human dentin-enamel junction

OBJECTIVE

The aim of this article is to analyze the chemical mapping of tufts and spindles of the human dental enamel using confocal Raman microscopy measuring length, structuration and composition of spindles and tufts.

DESIGN

we used Raman diffusion, based on the interaction between photons and optic phonons, to reveal chemical bound. Adult molars were selected and longitudinally sectioned. Areas of 120 * 120 μm were scanned near the dentin-enamel junction and grooves. Spectra were collected and phosphate and proteins peak intensities images were reconstructed, related to HPA concentration. Images of Phosphate (PO₄^3-, 960 cm^-1) and protein (CH, 2800/3000 cm^-1) intensities have been reconstructed. K-mean cluster has been calculated to compare centroid spectra from enamel, dentin and tuft or spindle.

RESULTS

intensity profile revealed spindles as less mineralized areas than enamel, from 5 to 10 µm large. In the groove of molar, long tufts were found, more than 150 µm.

CONCLUSIONS

Confocal Raman microscopy is a very interesting tool to characterize chemically secondary structure of enamel. The size of a tuft in the groove allows us make the hypothesis that they could play a role in long term resilience of mechanical stress.

Dental abrasion as a cutting process

A mammalian tooth is abraded when a sliding contact between a particle and the tooth surface leads to an immediate loss of tooth tissue. Over time, these contacts can lead to wear serious enough to impair the oral processing of food. Both anatomical and physiological mechanisms have evolved in mammals to try to prevent wear, indicating its evolutionary importance, but it is still an established survival threat. Here we consider that many wear marks result from a cutting action whereby the contacting tip(s) of such wear particles acts akin to a tool tip. Recent theoretical developments show that it is possible to estimate the toughness of abraded materials via cutting tests. Here, we report experiments intended to establish the wear resistance of enamel in terms of its toughness and how friction varies. Imaging via atomic force microscopy (AFM) was used to assess the damage involved. Damage ranged from pure plastic deformation to fracture with and without lateral microcracks. Grooves cut with a Berkovich diamond were the most consistent, suggesting that the toughness of enamel in cutting is 244 J m(-2), which is very high. Friction was higher in the presence of a polyphenolic compound, indicating that this could increase wear potential.

Tooth enamel properties and morphology after microabrasion: an in situ study

AIM

This study evaluated the effect of saliva on enamel after microabrasion with different microabrasive compounds under in situ conditions.

METHODS

Enamel/dentin blocks (16 mm² ) from bovine incisors were divided into nine groups (n = 19): one control group (no treatment), four groups treated with microabrasion using 35% phosphoric acid (H₃ PO₄ ) + pumice, and the last four groups treated with microabrasion using 6.6% hydrochloric acid (HCl) + silica. The treated groups were subdivided according to the in situ regimen: without salivary exposure, 1 h, 24 h, or 7 days of saliva exposure. Surface microhardness (SMH) and cross-sectional microhardness (CSMH) were tested. Scanning electron microscopy (SEM) was used to evaluate enamel morphology. Microhardness data were tested by analysis of variance, and Tukey's and Dunnett's tests (α = 0.05).

RESULTS

The SMH analysis revealed that all the microabrasion-treated groups presented significantly-reduced SMH values when compared to the control group (P < 0.05). Treatment with HCl + silica was more prone to the effect of saliva than H₃ PO₄ + pumice, even for CSMH analysis, once the superficial layers reached the same microhardness of that of the control group (P > 0.05). These results were confirmed by SEM, which demonstrated the mineral recovery effect over time.

CONCLUSION

Saliva was effective in promoting the rehardening of enamel after microabrasion, mainly for the surfaces treated with HCl + silica.