Glass hybrid, but not calcium hydroxide, remineralized artificial residual caries lesions in vitro

In vitro remineralization by various ion-releasing materials of artificially demineralized dentin: A micro-CT study

OBJECTIVE

The aim of this study was to evaluate the remineralizing properties of ion-releasing restorative materials on pH cycling-induced carious dentin.

METHODS

Fifty sound molars were freshly extracted. The occlusal surfaces were abraded using water-cooled sandpaper (800 grit). The residual crowns were embedded in self-cured acrylic resin with the flat dentin surface exposed. A mesio-distal trench was created using a calibrated 0.5 mm deep occlusal reduction burr, and artificial dentin caries were generated by pH cycling. Then, teeth were randomly assigned to five groups according to the ion-releasing material used. For each sample, micro-CT acquisitions were performed at various intervals. Remineralization was assessed by mean gray value (MGV) measurements after registration and segmentation of the region of interest with 3D Slicer software. One-way repeated-measures ANOVA followed by Tukey's post hoc test was used to investigate the difference in MGVs among the various groups.

RESULTS

Only Cention Forte showed significantly increased MGVs after 4 weeks compared to demineralized dentin. MGVs were higher, but not significantly, after placement of the restorative materials, including in the resin composite control group. These results can be explained by the radiopacity of the materials.

SIGNIFICANCE

Cention Forte, the material with the highest radiopacity, showed a significant increase in the MGVs of artificially carious dentin after 4 weeks. However, the study of dentin remineralization by micro-CT could be impacted by the radiopacity of the restorative materials used. The relevance of this examination for the study of dentinal remineralization should be investigated.

Efficacy of bioactive materials in preventing Streptococcus mutans-induced caries on enamel and dentine

The study investigated the ability of bioactive materials used to restore enamel and dentine specimens to prevent caries. Enamel (n = 50) and dentine (n = 50) specimens were obtained from bovine incisors, prepared, and randomly allocated to one of five groups according to the restorative treatment: alkasite without adhesive system; alkasite with adhesive system; high viscosity glass ionomer cement; resin composite; no restoration; negative control group. Specimens were restored, exposed to a thermal cycling aging protocol, sterilized, and exposed to a cariogenic challenge induced by Streptococcus mutans and then submitted to surface and subsurface microhardness tests and polarized light microscopy to verify the caries lesion development in enamel or dentine surrounding the restorative materials. Data were analyzed using one-way ANOVA. In enamel and dentine, glass ionomer cement, alkasite without and with adhesive system presented a lower percentage surface microhardness loss than resin composite and negative control. Enamel subsurface microhardness presented no statistically significant differences between glass ionomer cement, alkasite without and with adhesive system. Glass ionomer cement also did not present statistically significant differences from resin composite and the negative control. In dentine, glass ionomer cement showed the highest subsurface microhardness values. In conclusion, bioactive restorative materials provide greater protection to enamel and dentine against surface caries development than resin composite.

Bacterial reduction in sealed caries lesions is strain- and material-specific

Sealing can arrest caries lesions. We aimed to evaluate if sealing effects and kinetics are bacterial-strain and sealing-material specific. Human dentin discs were mounted in a dual-chamber device. Caries lesions were induced chemically and contaminated with either Lactobacillus rhamnosus (LR) or Streptococcus sobrinus (SS). For (1) kinetics assessment, the initial bacterial load and the sealing period were varied, and lesions sealed using a self-etch adhesive and composite. For (2) comparing materials, six sealing protocols (#1-#6) were evaluated: 1# Self-etch adhesive plus composite placed without a liner, or #2 calcium hydroxide, or #3 mineral trioxide aggregate, or #4 Biodentine liners; #5 antibacterial adhesive plus composite; #6 glass ionomer cement. Pulpal fluid flow was simulated during sealing. The outcome was the number of surviving bacteria (CFU) per g dentin. For LR, bacterial survival increased significantly with increasing initial bacterial load and decreased with longer sealing periods. The relative reduction followed a first-order kinetics. More LR survived under calcium hydroxide or MTA than other materials (p < 0.001). For SS, nearly no bacteria survived sealing regardless of sealing period, initial bacterial load or sealing material. In conclusion, sealing effects and kinetics were strain- and material-specific.

Margin Integrity and Secondary Caries of Lined or Non-lined Composite and Glass Hybrid Restorations After Selective Excavation In Vitro

OBJECTIVES

For deep carious lesions, selective carious tissue removal (leaving soft dentin close to the pulp) is suggested. Afterward, different restoration materials, such as resin composites or glass hybrids (GHs), can be placed. Many dentists also apply setting or non-setting calcium hydroxide liners before restoration. We compared margin integrity and susceptibility for secondary caries in differently restored premolars in vitro.

METHODS

In 48 extracted human premolars, artificial residual lesions were induced on pulpo-axial walls of standardized cavities. Teeth were restored using a GH (Equia Forte) or adhesively placed resin composite restoration (OptiBond FL and Tetric EvoCeram) without any liner (RC), resin composite restoration with a non-setting calcium hydroxide liner (RC_NCH), or resin composite restoration with a setting calcium hydroxide liner (RC_SCH). After thermomechanical cycling, groups (n=12) were compared regarding their gingivocervical margin integrity (proportion of irregularities, microgaps, gaps >5 μm, overhangs). Teeth were then submitted to a continuous culture Lactobacillus rhamnosus biofilm model. After 14 days, bacterial numbers in biofilms, along tooth-restoration margins and mineral loss (ΔZ) of secondary lesions, were determined.

RESULTS

GH and RC_NCH showed significantly higher proportions of irregularities than RC and RC_SCH (p<0.05/Mann-Whitney). GH also showed significantly more gaps than alternative restorations (p<0.05). Bacterial numbers and ΔZ did not differ significantly between groups (p>0.05).

CONCLUSIONS

GH and composites lined with non-setting calcium hydroxide showed reduced margin integrity compared with non-lined composites or composites lined with setting calcium hydroxide. This did not increase susceptibility for secondary caries.