Bactericidal Effect of Er,Cr:YSGG Laser on Caries-Affected Dentin

Objectives: The purpose of this in vitro study was to investigate the effectiveness of Er,Cr:YSGG laser for disinfection of affected dentin.

Methods: Freshly extracted molars (n=20) with caries reaching inner half of dentin were selected and divided into two groups. Group 1 was disinfected with 2% chlorhexidine gluconate (60s, Consepsis, Ultradent) and Group 2 with Er,Cr:YSGG laser (37,5 J/cm², Waterlase, Biolase). Three dentin biopsies were performed on each tooth: B1- before caries removal, B2- after selective caries removal using the SmartPrep Instrument, and B3- after disinfection with chlorhexidine or laser. Biopsies were stored in reduced transport fluid, plated using a spiral plater (Spiral Systems, Cincinnati, Ohio) and incubated anaerobically (37^oC, 5d) to assess total bacteria and Streptococcus mutans counts (CFU). Quantitative PCR was performed using S. mutans-specific primers on total DNA isolated from biopsy samples

Results: After selective caries removal the chlorhexidine group (B2), the mean proportion of total bacteria showed 98.7% reduction based on plating and 98.1% and 97.6% reduction in S. mutans based on plating and DNA quantification, respectively. In the laser group, 98.7% reduction in total bacteria and 99.6% reduction in S. mutans were detected by plating and 68.4% reduction in S. mutans by DNA quantification. After disinfection with either chlorhexidine or laser (B3), 100% reduction of total bacteria and S. mutans occurred in both groups. qPCR revealed 95.2% decrease in S. mutans in chlorhexidine group and 94.8% in laser group.

Conclusion: Standardized selective caries removal using SmartPrep Instrument showed statistically significant reduction of both total and S. mutans bacterial counts. Disinfecting the affected dentin surface with chlorhexidine or Er,Cr:YSGG laser showed further decrease in bacterial counts. However, no significant difference was found between the antimicrobial treatments applied.

In part sponsored by the University of Michigan School of Dentistry and by NIDCR DE007057.