Does Preheating Influence the Cytotoxic Potential of Dental Resin Composites?

Abstract

Resin-based dental composites (RBC) release cytotoxic components, however the extent of the elution from preheated RBCs is barely investigated. The aim was therefore to determine the cytotoxic effect of preheated conventional, bulk, and thermoviscous RBCs of clinically relevant sizes using different cell viability methods in a contact-free model. Samples (6 × 4 mm) were prepared from conventional [Estelite Sigma Quick (ESQ), Filtek Z250 (FZ)] and bulk-filled [Filtek One BulkFill Restorative (FOB), SDR Plus Bulk Flow (SDR), VisCalor Bulk (VCB)] RBCs. The pre-polymerization temperature was set to room temperature (RT) and 55/65 °C. Pulp cells were cultured, followed by a 2-day exposure to monomers released from solid RBC specimens suspended in the culture medium. Cytotoxicity was assessed using a WST-1, MTT, and LDH colorimetric viability assays. Data were analyzed using one-way ANOVA, Tukey's post hoc test, multivariate analysis, and independent t-test. The effect size (ƞp²) of material and temperature factors was also assessed. All the RBCs demonstrated cytotoxic effect upon exposure to pulp cells, but to a varying extent (ESQ >> VCB > FZ = FOB = SDR). The effect of pre-polymerization temperature was insignificant (ƞp² < 0.03), except for the thermoviscous RBC, which showed inconsistent findings when subjected to distinct viability tests. Cell viability was predominantly dependent on the type of material used (p < 0.001) which showed a large effect size (ƞp² > 0.90). Irrespective of the pre-polymerization temperature, RBC samples in a clinically relevant size can release monomers to such an extent, which can substantially decrease the cytocompatibility.

Keywords: bulk-fill; cytotoxicity; dental composite; preheated.

Figure 1

Resin-based composite (RBC) specimen preparation. The 6 × 4 mm RBC specimens were suspended in the cell culture medium using a polyethylene suture to prevent direct contact to the pulp cells.

Figure 2

Illustration of changes in cell proliferation as detected by the water-soluble tetrazolium salt (WST-1) staining at 48 h upon exposure to the released monomers from the investigated resin-based composites (RBC). Optical densities were normed to the negative control. The graph represents the WST-1 values as a ratio compared with the average value of the untreated control. (A) (WST-1 RT) shows the cell viability upon exposure to RBC specimens polymerized in a room-temperature (RT) condition. (B) (WST-1 PH) shows the cell viability upon exposure to RBC specimens polymerized in a preheated (PH) condition. Different capital letters on (A,B) indicate a statistically significant difference according to the one-way ANOVA and Tukey’s post hoc tests. (C) (WST-1 RT vs. PH) illustrates the comparison of cell proliferation upon exposure to RBC specimens polymerized in RT and PH conditions. * indicates a statistically significant difference between the RT vs. PH groups according to the pairwise comparison using the independent sample t-test. The investigated RBCs were applied in layered [Estelite Sigma Quick (ESQ) and Filtek Z250 (FZ)] or bulk-fill [Filtek One Bulk Restorative (FOB), SDR Plus Bulk Flow (SDR), and VisCalor Bulk (VCB)] method.

Figure 3

Illustration of changes in cell viability as detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay at 48 h upon exposure to the released monomers from the investigated resin-based composites (RBC). Optical densities were normed to the negative control. The graph represents the MTT values as a ratio compared with the average value of the untreated control. (A) (MTT RT) shows the cell viability upon exposure to RBC specimens polymerized at room-temperature (RT). (B) (MTT RT) shows the cell viability upon exposure to RBC specimens polymerized in a preheated (PH) condition. Different capital letters on (A,B) indicate a statistically significant difference according to the one-way ANOVA and Tukey’s post hoc tests. (C) (MTT RT vs. PH) illustrates the pairwise comparison of cell viability upon exposure to RBC specimens polymerized in RT and PH conditions using the independent sample t-test. No statistically significant difference was found between the RT vs. PH groups. The investigated RBCs were applied in layered [Estelite Sigma Quick (ESQ) and Filtek Z250 (FZ)] or bulk-fill [Filtek One Bulk Restorative (FOB), SDR Plus Bulk Flow (SDR), and VisCalor Bulk (VCB)] method.

Figure 4

Illustration of cytotoxicity as measured by lactate dehydrogenase (LDH) assay at 48 h upon exposure to the released monomers from the investigated resin-based composites (RBC). Optical densities were normed to the negative control. The graph represents the LDH values as a ratio compared with the average value of the untreated control. (A) (LDH RT) shows the cytotoxicity upon exposure to RBC specimens polymerized at room-temperature (RT). (B) (LDH PH) shows the cytotoxicity upon exposure to RBC specimens polymerized in a preheated (PH) condition. Different capital letters on (A,B) indicate a statistically significant difference according to the one-way ANOVA and Tukey’s post hoc tests. (C) (LDH RT vs. PH) illustrates the comparison of cytotoxicity upon exposure to RBC specimens polymerized in RT and PH conditions. * indicates a statistically significant difference between the RT vs. PH groups according to the pairwise comparison using the independent sample t-test. The investigated RBCs were applied in layered [Estelite Sigma Quick (ESQ) and Filtek Z250 (FZ)] or bulk-fill [Filtek One Bulk Restorative (FOB), SDR Plus Bulk Flow (SDR), and VisCalor Bulk (VCB)] method.