Defense Date


Document Type


Degree Name

Master of Science in Dentistry



First Advisor

Dr. Janina Golob Deeb

Second Advisor

Dr. Thomas Waldrop

Third Advisor

Dr. Caroline Carrico

Fourth Advisor

Dr. Todd Kitten

Fifth Advisor

Dr. Kinga Grzech-Leśniak


Purpose: Lasers have been used for treatment of dentinal hypersensitivity and for various bacterial reduction indications in periodontology. Their effectiveness in killing oral bacteria is not well known. The compounding effect of the combination of a laser treatment and adjunct antimicrobial agent use on bacterial viability is still evolving. The purpose of this in vitro study was to evaluate the effect of three lasers commonly used in dentistry in conjunction with chlorhexidine (CHX), hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl), or sodium fluoride (NaF) on viability of oral bacteria associated with root caries.

Methods: Three bacterial species were used in our study: Streptococcus mutans (Sm), Streptococcus sanguinis (Ss), and Enterococcus faecalis (Ef). Bacteria were grown in BHI broth and incubated at 37°C. Bacterial samples were irradiated with the Er:YAG, Nd:YAG and CO2 lasers for 30 secs. The experiment was repeated three times for each treatment modality. Treatment groups consisted of: 1: no treatment, 2: 0.5% H2O2 alone, 3: 0.5% NaOCl alone, 4: .12% CHX alone, 5. 2% NaF alone, 6: Laser irradiation alone, 7: Laser irradiation with 0.5% H2O2, 8: Laser irradiation with 0.5% NaOCl, 9: Laser irradiation with .12% CHX, 10: Laser irradiation with 2% NaF for all three lasers. Microbial viability was determined through plating and colony counts. Viable colonies were counted, converted into CFU/ml and transformed into log form for statistical analysis. Statistical analysis was done using a two-tailed paired t-test.

Results: The use of CO2, Nd:YAG, and Erb:YAG lasers alone failed to show statistically significant antibacterial activity against any of the bacteria. The only effective mono-treatment with irrigation solutions was CHX for Sm. The combined treatment of 0.5% NaOCl with Erb:YAG and Nd:YAG showed the greatest and most significant reduction of all three bacterial viability compared to any other treatment group.

Conclusion: The combination of irradiation with Nd:YAG or Erb:YAG laser with the addition of 0.5% NaOCl resulted in the largest reduction of bacterial survival when compared to monotherapies with antimicrobial solutions or lasers.


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