Photoactivated disinfection of Streptococcus intermedius through dentin disc at clinically relevant intervals: An in vitro study

In this present study we have tested the impact of porfimer sodium (Photofrin®, AXCAN PHARMA Inc., Quebec, Canada) photoactivated disinfection (PD) on cells of Streptococcus intermedius in suspension. In order to provide basic data to support future clinical studies of PD in dentistry the study used exposure to Quartz-tungsten-halogen (QTH) dental curing light for clinically relevant time periods to activate Photofrin® and measured its effectiveness under a variety of conditions including activation through dentin hard tissue. S. intermedius was grown in planktonic suspension for 48 h. Nine groups were formed: three control groups (1-3) and six experimental groups (4-9). Groups 4-6 tested the use of Photofrin® treatment combined with QTH light at various intervals of irradiation (5, 15 and 60 s). Groups 7-9 were similar to groups 4-6 with the exception that irradiation commenced through a dentin disc. Following treatment, bacteria were plated. Colony counts were measured following 72 h incubation at 37 °C. Statistical analysis was carried out by one-way ANOVA at a 95% confidence level. A significant reduction in S. intermedius colony counts was observed for all experimental groups and one control group. The reduction in numbers of colonies in the experimental groups varied from 79.28 to 99.40% with an average of 94.61%. Reduction in viable bacterial cells indicated a strong relationship between power density and irradiation interval. When curing light energy density was lower due to the irradiation through the 1 mm dentin disc, prolonged irradiation interval enhanced bacterial kill. In conclusion, where direct irradiation is not possible for PD treatment, irradiation through dentin may still be done successfully within a clinically relevant interval.