Evaluation of the effects of fluoride-releasing varnish on dentin demineralization using optical coherence tomography

Optimal Surface Pre-Reacted Glass Filler Ratio in a Dental Varnish Effective for Inhibition of Biofilm-Induced Root Dentin Demineralization

A unique type of dental varnish (DV) containing surface pre-reacted glass (S-PRG) fillers of different concentrations was evaluated to determine the unpresented optimal ratio for inhibiting root dentin bio-demineralization. S-PRG DVs (10% to 40%)—10%-S, 20%-S, 30%-S, and 40%-S—were applied to bovine root dentin blocks and compared with controls—0%-f (no S-PRG) and 5%-NaF (5%-NaF). The Streptococcus mutans biofilm challenge was executed inside and outside an oral biofilm reactor for 7 days. The specimens were examined using a confocal laser scanning microscope and swept-source optical coherence tomography. Furthermore, they were observed using a scanning electron microscope and analyzed using energy-dispersive X-ray spectroscopy. The roughness (SzJIS) due to leaching of DV materials and demineralization depth were significantly less in the S-PRG groups than the control groups (p < 0.05). Complete or partially plugged dentinal tubules (DTs) were observed in 20%-S, 30%-S, and 40%-S, while wide-open DTs were observed more in controls. Cylindrical tags were present in groups containing more than 20% S-PRG. F, Na, Al, and Sr were detected in a higher percentile ratio in the 20%-S, 30%-S, and 40%-S groups compared to 0%-f and 10%-S. Nonetheless, it is suggested that incorporating 20% to 30% S-PRG fillers in DVs would be effective enough as an anti-demineralization coating, together with supplementing minerals; further evaluation is required to validate these findings.

Inhibitory activity of S-PRG filler on collagen-bound MMPs and dentin matrix degradation

OBJECTIVES

To evaluate the inhibitory activity of an ion-releasing filler (S-PRG) eluate on dentin collagen-bound metalloproteinases (MMPs) and dentin matrix degradation.

METHODS

Dentin beams (5 × 2 × 0.5 mm) from human molars were completely demineralized to produce dentin matrix specimens. The dry mass was measured, and a colorimetric assay (Sensolyte) determined the initial total MMP activity to allocate the beams into four treatment groups (n = 10/group): 1) water for 1 min (negative control); 2) 2% chlorhexidine digluconate (CHX - inhibitor control) for 1 min; 3) S-PRG eluate for 1 min; 4) S-PRG eluate for 30 min. After the treatments, the total MMP activity was reassessed. The specimens were stored in simulated body fluid (SBF) at 37 °C for up to 21 days. The dry mass was reassessed weekly. On day 7, the dentin matrix degradation was analyzed for the presence of collagen fragments (CF; Sirius Red) and hydroxyproline (Hyp) in the SBF. Statistical analyses were performed with ANOVA/Tukey, paired t-tests, and RM-ANOVA/Sidak (α = 5%).

RESULTS

S-PRG eluate exposure for 1 and 30 min reduced (p < 0.0001) MMP activity. S-PRG exposure for 30 min presented MMP activity inhibition equivalent to CHX (p = 0.061). S-PRG and CHX decreased CF (p ≤ 0.007) and Hyp (p < 0.046) release. After 21 days of storage, S-PRG-treated beams, regardless of exposure time, presented a reduced (p ≤ 0.017) mass loss, intermediate between CHX and control.

CONCLUSION

Treating demineralized dentin with S-PRG eluate for 1 or 30 min reduced matrix-bound MMP activity and dentin matrix degradation for up to 21 days.

CLINICAL SIGNIFICANCE

S-PRG filler may hinder the progression of dentin carious/erosive lesions and enhance the stabilization of dentin bonding interfaces.

S-PRG Filler Eluate Induces Oxidative Stress in Oral Microorganism: Suppression of Growth and Pathogenicity, and Possible Clinical Application

Controlling the oral microbial flora is putatively thought to prevent not only oral diseases, but also systemic diseases caused by oral diseases. This study establishes the antibacterial effect of the novel bioactive substance “S-PRG filler” on oral bacteria. We examined the state of oxidative stress caused by the six types of ions released in eluate from the S-PRG filler in oral bacterial cells. Moreover, we investigated the effects of these ions on the growth and pathogenicity of Gram-positive and Gram-negative bacteria. We found that the released ions affected SOD amount and hydrogen peroxide in bacterial cells insinuating oxidative stress occurrence. In bacterial culture, growth inhibition was observed depending on the ion concentration in the medium. Additionally, released ions suppressed Streptococcus mutans adhesion to hydroxyapatite, S. oralis neuraminidase activity, and Porphyromonas gingivalis hemagglutination and gingipain activity in a concentration-dependent manner. From these results, it was suggested that the ions released from the S-PRG filler may suppress the growth and pathogenicity of the oral bacterial flora. This bioactive material is potentially useful to prevent the onset of diseases inside and outside of the oral cavity, which in turn may have possible applications for oral care and QOL improvement.

Characteristics of biofilm-induced degradation at resin-dentin interfaces using multiple combinations of adhesives and resins

OBJECTIVE

We aimed to evaluate morphological, mechanical and chemical characteristics at resin-dentin interfaces using multiple combinations of adhesives and resins after a short-term biofilm-induced degradation.

METHODS

Cervical cavities were prepared in bovine incisors, treated by Clearfil SE Bond 2 (SE) or FL-Bond II (FL), restored by Clearfil Majesty ES Flow (ES) or Beautifil Flow Plus (BFP) and grouped into SE-ES, SE-BFP, FL-ES and FL-BFP. After biofilm challenge, interfacial gaps and dentin wall lesions were examined by optical coherence tomography (OCT). Gap depth (GD), gap pattern scale (GPS) and dentin wall lesion depth (WLD) were evaluated from confocal laser scanning microscope. Microhardness of dentin lesions was measured with a Vickers microhardness tester. Chemical elements in resins and dentin wall lesions were analyzed by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDS). Morphological structures of interfacial gaps were observed by SEM.

RESULTS

OCT could detect adhesive-dentin-bonded and adhesive-dentin-debonded gaps. SE-containing groups showed significantly lower GPS than FL-containing groups. FL-BFP showed significantly lower WLD than FL-ES. Microhardness of dentin wall lesions was higher than that of outer lesions and they showed significant differences in FL-BFP. SE-BFP showed a lower GPS curve and higher intensities of Ca and P in the upper half of dentin wall lesions than other groups. From SEM, microgaps between filler and matrix, break and loss of matrix, separation of adhesive matrix with hybrid layer occurred at interfacial gaps.

SIGNIFICANCE

The morphological, mechanical and chemical characteristics of resin-dentin interfacial degradation depend on the component and chemistry of restorative materials.

Detection and analysis of early degradation at resin-dentin interface by optical coherence tomography (OCT) and confocal laser scanning microscope (CLSM)

OBJECTIVE

To evaluate early degradation at resin-dentin interface using non-invasive swept-source optical coherence tomography (SS-OCT) and confocal laser scanning microscope (CLSM).

METHODS

Self-etch adhesives and resin-composites containing bisphenol-glycidyl-dimethacrylate (Bis-GMA), which is one of the most widely used monomers in restorative materials, were investigated in this study. Forty cervical cavities were prepared in bovine incisors and applied by the adhesive with/without Bis-GMA (AdhesiveBG/Adhesive), filled by the resin with/without Bis-GMA (ResinBG/Resin) and then challenged by cariogenic biofilm (37 °C, 24 h). Gap Formation and dentin demineralization around resin-composites were observed by SS-OCT and CLSM.

RESULTS

Three types of resin-dentin interfacial degradation could be detected from SS-OCT. Type I-dentin demineralization around resin without gap, showing feather-shaped dark zones without bright scattered lines at resin-dentin interfaces. Type II-dentin demineralization around resin with adhesive-dentin bonded gaps, showing feather-shaped dark zones with bright scattered lines at resin-dentin interfaces. Type III-dentin demineralization around resin with adhesive-dentin debonded gaps, showing edge-shaped dark zones with bright scattered lines at resin-dentin interface. From CLSM, the groups were compared in gap scale (GS), gap depth (GD), gap width (GW) and dentin wall lesion depth (WLD). Bis-GMA-containing adhesive groups showed significantly lower GS than Bis-GMA-free adhesive groups. Bis-GMA-containing resin groups showed significantly lower WLD than Bis-GMA-free resin groups. However, they did not show significant differences in GD and GW.

CONCLUSION

Three types of early degradation at resin-dentin interface can be noninvasively detected by SS-OCT. Bis-GMA-containing and Bis-GMA-free restorative materials show differences in gap scale and dentin wall lesion depth.

CLINICAL SIGNIFICANCE

SS-OCT can nondestructively detect early resin-dentin interfacial degradation. Gap scale can be used as a parameter to evaluate the risk factor of gaps.

Efficacy of S-PRG filler containing varnishes on enamel demineralization prevention

This study evaluated the efficacy of S-PRG vanishes on preventing enamel demineralization. Bovine enamel specimens were obtained, polished and the baseline Knoop microhardness was evaluated. Specimens were stratified into six groups (n = 15), according to the varnish applied: S10—experimental varnish containing 10% of S-PRG fillers, S20—20% of S-PRG fillers, S30—30% of S-PRG fillers; S40—40% of S-PRG fillers; PC (positive control)—5% of NaF; NC (negative control)—no treatment was performed. Half of enamel surfaces were protected to work as a control and varnishes were applied over the unprotected area. A demineralizing pH-cycling was performed, and surface and cross-sectional microhardness were measured. The percentage of microhardness of the treated area was calculated comparing with the untreated area. Statistical analysis was performed by one-way ANOVA and Tukey’s test (p = 5%). All experimental S-PRG varnishes protected against demineralization in relation to no treatment, but S40 was the most effective on the surface. For all depths, S30 and S40 were superior in enamel demineralization prevention than other S-PRG filler concentrations and 5% NaF. It was concluded that S-RPG filler containing varnishes were effective to prevent enamel demineralization. The higher concentrated products were more effective than 5% sodium fluoride on surface demineralization prevention.

Efficacy of S-PRG filler containing varnishes on enamel demineralization prevention

This study evaluated the efficacy of S-PRG vanishes on preventing enamel demineralization. Bovine enamel specimens were obtained, polished and the baseline Knoop microhardness was evaluated. Specimens were stratified into six groups (n = 15), according to the varnish applied: S10—experimental varnish containing 10% of S-PRG fillers, S20—20% of S-PRG fillers, S30—30% of S-PRG fillers; S40—40% of S-PRG fillers; PC (positive control)—5% of NaF; NC (negative control)—no treatment was performed. Half of enamel surfaces were protected to work as a control and varnishes were applied over the unprotected area. A demineralizing pH-cycling was performed, and surface and cross-sectional microhardness were measured. The percentage of microhardness of the treated area was calculated comparing with the untreated area. Statistical analysis was performed by one-way ANOVA and Tukey’s test (p = 5%). All experimental S-PRG varnishes protected against demineralization in relation to no treatment, but S40 was the most effective on the surface. For all depths, S30 and S40 were superior in enamel demineralization prevention than other S-PRG filler concentrations and 5% NaF. It was concluded that S-RPG filler containing varnishes were effective to prevent enamel demineralization. The higher concentrated products were more effective than 5% sodium fluoride on surface demineralization prevention.

Ions released from a S-PRG filler induces oxidative stress in Candida albicans inhibiting its growth and pathogenicity

Candida albicans causes opportunistic fungal infections usually hidden among more dominant bacteria and does not exhibit high pathogenicity in vivo. Among the elderly, due to reduced host resistance to pathogens attributable to immunoscenesence, oral candidiasis is more likely to develop often leading to systemic candidiasis. Surface pre-reacted glass ionomer filler (S-PRG filler) is an ion-releasing functional bioactive glass that can release and recharge six ions which in turn strengthens tooth structure, inhibits demineralization arising from dental caries, and suppresses dental plaque accumulation. However, its effects on C. albicans have never been elucidated. Here, we evaluated the effects of ion released from S-PRG filler on C. albicans. Results show that extraction liquids containing released ions (ELIS) decreased the amount of hydrogen peroxide and catalase activity in C. albicans. Moreover, ELIS presence was found to affect C. albicans: (1) suppression of fungal growth and biofilm formation, (2) prevent adherence to denture base resin, (3) inhibit dimorphism conversion, and (4) hinder the capability to produce secreted aspartyl proteinase. Taken together, our findings suggest that ELIS induces oxidative stress in C. albicans and suppresses its growth and pathogenicity. In this regard, we propose that ELIS has the potential to be clinically used to help prevent the onset and inhibition of oral candidiasis among the elderly population.

Effect of a coating material containing surface reaction-type pre-reacted glass-ionomer filler on prevention of primary enamel demineralization detected by optical coherence tomography

We used optical coherence tomography to examine the effect of a coating material containing surface reaction-type pre-reacted glass-ionomer (S-PRG) filler on primary enamel demineralization in 18 extracted human primary teeth. The pulp was removed, and each tooth was ultrasonically cleaned with distilled water. Six teeth were treated with 0.1-M lactic acid buffer solution (De group). In the second group (n = 6), a thin film of coating material was applied before demineralization (PRG group). A third group (Control group; n = 6) was maintained in artificial saliva. Using optical coherence tomography, we measured peak signal intensity (dB) and width at 1/e² (µm) at predetermined locations on the enamel surface and calculated integrated values. All data were analyzed with ANOVA and the Tukey-Kramer test (α = 0.05). Although changes in integrated values differed between groups, there was a small but significant increase in the Control group and a small but significant decrease in the De group. In the PRG group, integrated values were significantly higher at 7 days after the start of the experiment and significantly increased thereafter. Our findings indicate that a coating material containing S-PRG fillers may prevent primary enamel demineralization.

Enamel remineralization effect of a dentifrice containing calcium sodium phosphosilicate: an optical coherence tomography observation

OBJECTIVE

The purpose of this study was to examine the effects of a dentifrice containing 5% calcium sodium phosphosilicate (CSP) on the remineralization of the enamel using optical coherence tomography (OCT).

MATERIALS AND METHODS

Bovine incisors were sliced and shaped in a rectangular form. One group of five specimens was treated with undersaturated 0.1 M lactic acid buffer solution (pH 4.75) for 10 min and then placed in artificial saliva (pH 7.0) (De group). Other specimens were stored in solutions of toothpaste containing CSP for 10 min, followed by 10-min immersion in the lactic acid buffer solution twice a day before storage in artificial saliva (CSP group). An additional group was stored in only artificial saliva (control group). OCT imaging on the selected location of the enamel surface was performed. The peak intensity and width at 1/e² were recorded in each of the six areas on the sample and averaged, and the sample size of each group was six. The integrated value in units (dB × μm) was calculated in the area of peak intensity. The data for each group was subjected to one-way repeated-measures ANOVA and Tukey HSD tests (α = 0.05).

RESULTS

The changes in integrated values of each group were different. A slight but significant increase in the integrated value was observed in the control group, whereas a slight but significant decrease in the value was observed the De group. Integrated values increased in the CSP group.

CONCLUSIONS

Remineralization occurred upon immersion in the toothpaste containing CSP.