Influence of Restoration Type on the Cytotoxicity of a 35% Hydrogen Peroxide Bleaching Gel.

OBJECTIVES: The tooth/restoration interface may act as a pathway for hydrogen peroxide (H2O2) diffusion into the pulp chamber. Therefore, the influence of resin-modified glass ionomer cement (RMGIC) and resin composite simulated restorations on the cytotoxicity of an in-office bleaching gel was assessed in vitro. MATERIALS AND METHODS: Cavities in enamel/dentin discs restored with RMGIC Vitremer (3M ESPE) or Single Bond/Filtek Z350 (3M ESPE) resin composite (RC) were subjected or not subjected to hydrolytic degradation (HD). A 35%-H2O2 bleaching gel was applied to simulated restored and nonrestored enamel surfaces, and culture medium in contact with the dentin substrate (extract) was collected and applied to MDPC-23 cells. Nonrestored discs subjected or not subjected to bleaching were used as positive and negative controls, respectively. Cell viability, oxidative stress, interleukin (IL)-1ß expression, alkaline phosphatase (ALP) activity, and mineralized nodule deposition were evaluated. The H2O2 in the extracts was quantified. Data were subjected to statistical analysis. RESULTS: Higher oxidative stress associated with reduced cell viability, ALP activity, and mineralized nodule deposition was observed for all bleached groups compared with the negative control group. The RMGIC/HD group, which presented the highest H2O2 diffusion, had the lowest values of cell viability, ALP activity, and mineralized nodule deposition, as well as significantly increased IL-1ß expression. CONCLUSIONS: Dental cavities restored with the RMGIC subjected to hydrolytic degradation allowed for more intense diffusion of H2O2 into the pulp chamber, intensifying the toxicity of a 35%-H2O2 bleaching gel to pulp cells.

Indirect cytocompatibility of a low-concentration hydrogen peroxide bleaching gel to odontoblast-like cells.

AIM: To assess the initial cytotoxicity and the late phenotype marker expression of odontoblast-like cells (MDPC-23) subjected to less aggressive in-office bleaching therapies. METHODOLOGY: A 17.5% hydrogen peroxide (H2O2) gel was applied for 45, 15 or 5 min to enamel/dentine discs adapted to trans-wells positioned over cultured MDPC-23 cells. No treatment was performed on the negative control. Immediately after bleaching, the cell viability, gene expression of inflammatory mediators and quantification of H2O2 diffusion were evaluated. The ALP activity, DSPP and DMP-1 gene expression and mineralized nodule deposition (MND) were assessed at 7, 14 or 21 days post-bleaching and analysed statistically with Mann-Whitney U-tests (α = 5%). RESULTS: H2O2 diffusion, proportional to treatment time, was observed in all bleached groups. Reductions of approximately 31%, 21% and 13% in cell viability were observed for the 45-, 15- and 5-min groups, respectively. This reduction was significant (P < 0.05) for the 45- and 15-min groups, which also presented significant (P < 0.05) over-expression of inflammatory mediators. The 45-min group was associated with significant (P < 0.05) reductions in DMP-1/DSPP expression at all periods, relative to control. The ALP activity and MND were reduced only in initial periods. The 15-min group had less intense reduction of all markers, with no difference to control at 21 days. CONCLUSIONS: The 17.5% H2O2 applied to tooth specimens for 5 min caused no alteration in the odontoblast-like cells. When this gel was applied for 45 or 15 min, a slight cytotoxicity, associated with alterations in phenotypic markers, was observed. However, cells were able to recover their functions up to 21 days post-bleaching.

Effect of LPS treatment on the viability and chemokine synthesis by epithelial cells and gingival fibroblasts.

OBJECTIVE: Several local factors can affect the wound-healing process, delaying its progression and postponing tissue homeostasis. It is known that local inflammation is related to wound healing; however, the maintenance of the inflammatory reaction can impair the proliferation and migration of oral mucosal cells. The aim of this study was to evaluate the viability and chemokine expression of epithelial cells and gingival fibroblasts exposed to long-term lipopolysaccharide (LPS) treatment. DESIGN: Epithelial cells (HaCaT, Cell Lines Service, 300493) and human gingival fibroblasts (HGFs) were seeded (1×10(5) cells/well) in 24-well plates and incubated for 24h. To simulate the responses of cells to a local chronic oral mucosal inflammation, we added LPS of Escherichia coli (10 µg/ml) to Dulbecco's modified Eagle's medium (DMEM), kept in contact with fibroblasts and epithelial cells for 24, 48, and 72h. Then the cells were assessed for viability (alamarBlue assay), number (trypan blue assay), and expression of CCL2 and CCL5 inflammatory chemokines (enzyme-linked immunosorbent assay (ELISA)). Data were statistically analyzed by nonparametric Kruskal-Wallis and Mann-Whitney tests at a significance level of 5%. RESULTS: Cell treatment with LPS caused significant decrease in viability for both cell lines. No time-dependent effect was observed for epithelial cells. However, reduction in fibroblast viability was greater at 48 and 72 h. CCL2 and CCL5 synthesis was significantly increased for both LPS-treated cells, and this expression decreased with time. CONCLUSION: The maintenance of an inflammatory cell stimulus by LPS decreases the number and viability of cultured oral mucosal cells, which may be related to delayed wound healing.