Evaluation of antibacterial photodynamic therapy effects on human dental pulp cell cultures

• We assess an antibacterial photodynamic therapy (aPDT) protocol on dental pulp cells.
• We examine cell viability, metabolism and cell death type after the aPDT protocol.
• aPDT was able to kill pulp cells in a dye concentration-dependent manner.
• aPDT-induced cell death occurred mostly by necrosis.
• aPDT associating MB at low concentration is a low-risk therapy for caries treatment.

SummaryBackgroundThe antibacterial photodynamic therapy (aPDT) has been used in dentistry against oral microorganisms because of its excellent biocide effect. However, for carious lesions applications, there is little evidence that this therapy is safe for the pulp tissue.ObjectiveThis study evaluates the effects of an aPDT protocol on human pulp cells in vitro.MethodsPulp cells isolated from dental pulp were exposed to an aPDT protocol associating methylene blue (MB) at concentrations of 0.0125, 0.025 and 0.050 mg/ml and red laser irradiation using a continuous-wave indium-gallium-aluminum-phosphide (InGaAlP) diode laser (λ = 660 nm, 40 mW, 2.4 J, 60 J/cm2 for 1 min). Pre-irradiation time was 5 min for each MB concentration. Cell viability was determined by MTT assay and activity of alkaline phosphatase was assessed by BCIP-NBT assay. Type of aPDT-induced cell death was assessed by flow cytometry. Data was statistically compared (ANOVA followed by Tukey’ or Bonferroni's post hoc tests).ResultsaPDT was able to kill pulp cells in a dye concentration-dependent manner. The cellular viability was significantly reduced when used MB at 0.025 or 0.050 mg/ml concentrations (p < 0.0001). At these concentrations, aPDT-induced cell death occurred mostly by necrosis. Alkaline phosphatase activity was significantly reduced in all experimental groups (p < 0.001). Pulp cells showed suitable viability when MB at 0.0125 mg/ml was exposed to laser irradiation.ConclusionsaPDT with MB at 0.0125 mg/ml may represent a low-risk therapy for restorative dentistry applications. aPDT protocol using concentrations above 0.025 mg/ml of MB associating red laser irradiation may be harmful for dental pulp cells.