The Photobiomodulation Effect of 940nm Laser Irradiation on Enterococcus faecalis in Human Root Dentin Slices of Varying Thicknesses

Introduction: An increase in dentine thickness could result in an inadequate depth of laser energy penetration. This study aimed to evaluate the effect of a 940 nm laser on Enterococcus faecalis through varying thicknesses of human root dentin slices. Methods: Thirty-five dentin slices of root dentin with thicknesses ranging between 500 and 3000 μm were produced. Six experimental groups (500, 1000, 1500, 2000, 2500, and 3000 μm (n=5 each) were lased and the seventh, non-lased group served as the positive control with a dentine thickness of 2000 μm. The slices were inoculated with 2 μL of E. faecalis suspension of 1.5 × 108 E. faecalis cells/mL. All the lased slices were lased from the opposing side of the inoculation. A non-initiated 200 μm bare end fibre at the power of 1 W, in a continuous wave was used. Four doses of laser irradiation of 5 seconds with a side to side movement with the tip held at a 5o angle to the dentine slice were performed. The colony-forming units of E. faecalis were determined and the bacterial photobiomodulation effect analysed using one-way ANOVA with a Bonferroni and Holm post hoc test at a significance level of P>0.05. Results: There were statistical differences between the dentin slices of 500, 1000, and 1500 μm treated with the laser compared to the positive control (P<0.01). However, there were no statistical differences between the lased 2000 and 2500 μm slices compared to the positive control. There was significantly more photobiomodulation of the E. faecalis for the dentine slices of 3000 μm than the positive control (P<0.01). Conclusion: Laser treatment through dentine slices of 2000 μm and thinner significantly reduced bacterial growth. The photobiomodulation effects started to occur in dentine slices thicker than 2500 μm compared to the positive control.