Effect of dentin bonding agent diffusing through dentin slices on the reactive oxygen species production and apoptosis of pulpal cells.

BACKGROUND/PURPOSE: Dentin bonding agents (DBAs) are cytotoxic to dental pulp cells. This study aimed to evaluate the effects of three DBAs (Optibond Solo Plus, Op; Clearfil SE Bond, SE; and Xeno III, Xe) after diffusion through 0.2-mm or 0.5-mm dentin slices on reactive oxygen species (ROS) production and apoptosis in dental pulp cells. METHODS: The amounts of DBAs diffusing through 0.2-mm or 0.5-mm dentin slices were quantified using a UV-Vis spectrophotometer. The effects of diffused DBAs on ROS production and viability of dental pulp cells were investigated using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay on Days 1 and 2. Flow cytometric analysis and double staining of treated dental pulp cells with Annexin V-fluorescein isothiocyanate (V-FITC) and propidium iodide (PI) were performed on Day 2. RESULTS: Xe showed greatest diffusion through dentin slices after 8-hour period, followed by SE and Op. Dental pulp cells produced a lesser amount of ROS, when treated with DBAs diffusing through a 0.5-mm dentin slice than through a 0.2-mm dentin slice for the same period of time. A small proportion of cells were TUNEL-positive after treatment with any of the three diffused DBAs. Annexin V-FITC/PI staining identified apoptotic cells; cell survival was higher in those cells treated with DBAs diffusing through a 0.5-mm dentin slice than through a 0.2-mm dentin slice. CONCLUSION: The three DBAs after diffusion through 0.2- or 0.5-mm dentin slice still exhibit cytotoxicity to dental pulp cells. However, the 0.5-mm dentin slice is found to be a better barrier than the 0.2-mm dentin slice to protect dental pulp cells from DBA-induced cytotoxicity.

Biocompatibility and cytotoxicity of two novel low-shrinkage dental resin matrices.

BACKGROUND/PURPOSE: To reduce the polymerization shrinkage of dental composite resin, we used two different ratios of toluene 2,4-diisocyanate (TDI) or 1,6-hexamethylene diisocyanate (HDI) as functional side chains of bisphenol A-glycidyl methacrylate (bis-GMA) to synthesize two series of new dental resin matrices. This study evaluated the biocompatibility and cytotoxicity of these two series of new resin matrices. METHODS: Two series of new dental resin matrices with the ratios of TDI or HDI functional side chain to bis-GMA (defined as B group) being 1:4, 1:2, 1:1 and 3:2 (defined as T1/4, T1/2, T1, T3/2, and H1/4, H1/2, H1, H3/2 groups, respectively) were synthesized. Each resin sample was light cured and immersed in the culture medium for 24 hours to make the extract solution. Then, human gingival fibroblasts were cultured in different extract solutions for 72 hours. The cytotoxicities of different resins were evaluated by microtitertetrazolium (MTT) assay, the levels of cell-produced reactive oxygen species (ROS) induced by different extract solutions was measured. RESULTS: Resins of the T1/4 and B groups revealed significantly higher cytotoxicity than resins of other groups. However, resins of the T1 and T3/2 groups exhibited less cytotoxicity. In general, resins of the TDI-modified groups showed equal or less cytotoxicity and induced equal or lower levels of ROS than the corresponding resins of the HDI-modified and B groups. CONCLUSION: Our results showed that the TDI-modified resin matrices containing more functional side chains were less cytotoxic than the corresponding HDI-modified resin matrices. When the ratio of functional side chain to bis-GMA is increased, the stereo hindrance of resin structure is increased, more toxic resin monomers are trapped in the complicated resin structure, and thus the resin matrix reveals less cytotoxicity. The TDI-modified resin matrices exhibit higher stereo hindrance of resin structure and thus show less cytotoxicity than the corresponding HDI-modified resin matrices.

Conjugation of diisocyanate side chains to dimethacrylate reduces polymerization shrinkage and increases the hardness of composite resins.

BACKGROUND/PURPOSE: Polymerization shrinkage is one of the main causes of dental restoration failure. This study tried to conjugate two diisocyanate side chains to dimethacrylate resins in order to reduce polymerization shrinkage and increase the hardness of composite resins. METHODS: Diisocyanate, 2-hydroxyethyl methacrylate, and bisphenol A dimethacrylate were reacted in different ratios to form urethane-modified new resin matrices, and then mixed with 50 wt.% silica fillers. The viscosities of matrices, polymerization shrinkage, surface hardness, and degrees of conversion of experimental composite resins were then evaluated and compared with a non-modified control group. RESULTS: The viscosities of resin matrices increased with increasing diisocyanate side chain density. Polymerization shrinkage and degree of conversion, however, decreased with increasing diisocyanate side chain density. The surface hardness of all diisocyanate-modified groups was equal to or significantly higher than that of the control group. CONCLUSION: Conjugation of diisocyanate side chains to dimethacrylate represents an effective means of reducing polymerization shrinkage and increasing the surface hardness of dental composite resins.