Control of Cariogenic Bacteria Using Lethal Laser Photosensitization Therapy

Objectives: Residual infected dentin is a common cause of recurrent caries at base of deep cavity restoration. Since there is not yet a recognized method of detecting residual bacteria in the dentinal tissue, it seems appropriate to develop a method of ensuring a bacteria-free tissue before cavity restoration. The present study aimed to determine the optimum conditions (photosensitizer’s concentration/ laser wavelength) for use of laser beam in combination with photosensitizers to inhibit or reduce the growth of Streptococcus mutans (SM). Methods: Two experiments (A and B) were devised. In A, 4 groups corresponding to four concentrations of Tolonium Chloride dye (TC) (mg/ml); 0 (control), 0.191, 1.91 and 5 were created. Suspensions of SM (NCTC 10449) in Brain Heart Infusion (BHI) broth were assigned to the groups. Following a 4-fold serial dilution, the groups were stained with their respective dye. Dilutions in each group were subsequently plated in BHI agar, incubated aerobically at 37°C for 48 hours, and bacteria growth measured by a count of colony forming unit per milliliter (cfu/ml). In experiment B, suspensions of SM stained with TC (0.191mg/ml as determined in experiment A) were respectively irradiated with laser beams of varying wavelengths to give 5 experimental groups; unstained/non-irradiated (control), stained/non-irradiated, 488 nm, 543 nm, and 633 nm. Following irradiation, the suspensions were plated in BHI agar, incubated aerobically at 37°C for 48 hours, and bacterial growth was determined as in experiment A. Results: In A, paired t-test indicated significant (n=5, a=0.05) growth inhibition with 0.191(p<0.01), 1.91(p<0.01), and 5.0(p<0.001) when compared with the control. In B, significant growth inhibition was observed in all groups (p<0.001) when compared with the control. Conclusion: Tolonium Chloride alone and in combination with low power laser beam inhibited the growth of cariogenic bacteria, thus highlighting its potential usefulness for treatment of residual infected dentin.