Photoactivated disinfection of Streptococcus intermedius through dentin disc

Objectives: The purpose of this study was to evaluate the antimicrobial effect of Photofrin combined with dental curing light irradiation on the viability of S. intermedius. The study further examined the effect of this combination treatment when irradiation was commenced through 1mm dentin disc.

Methods: S. intermedius was grown in planktonic suspension for 48h. Nine groups were formed. The Photoactivated Disinfection (PAD) treatment consisted of Photofrin that was activated by quartz-tungsten-halogen (QTH) dental curing device. Following treatment, bacteria was plated. Colony counts were measured following 72h incubation at 37C. Statistical analysis was carried out by one-way ANOVA at a 95% confidence level.

Results: A significant reduction in S. intermedius colony counts was observed for all experimental groups. The reduction in numbers of colonies varied from 79.28%-99.40% with an average of 94.61%. Reduction in viable bacterial cells indicated a strong relationship between irradiation intensity and irradiation interval. When irradiation intensity was lower prolonged irradiation interval enhanced bacterial kill.

In Conclusions: where direct irradiation is not possible for PAD treatment, indirect irradiation through dentin may still be done successfully within a clinically relevant interval. Lower irradiation intensities can be compensated by longer irradiation intervals thus PAD treatment may be further developed for clinical dental use.