# Comparison of Energy and Frequency of Nanosecond Q-switched ND-YAG Laser and Chlorhexidine on Reducing the Number of Oral Streptococcus Mutans Isolates: In Vitro Study: -

## TL;DR

This study compares the effectiveness of a laser and chlorhexidine in reducing Streptococcus mutans bacteria in the mouth.

## Contribution

The study demonstrates that high-energy Q-switched Nd:YAG laser therapy is as effective as chlorhexidine in reducing S. mutans in vitro.

## Key findings

- Laser energy and frequency significantly reduced S. mutans counts, with complete elimination at 30 mJ.
- Inhibition zones were largest at 30 mJ/10 Hz, but chlorhexidine showed slightly larger zones without statistical significance.
- Both laser therapy and chlorhexidine showed comparable antimicrobial efficacy against S. mutans.

## Abstract

Streptococcus mutans is a facultative anaerobic coccus that is a part of the
oral flora of humans. chlorhexidine also has some side effects. Today, Nd:
YAG lasers have become very popular in dentistry and are used for various
types of treatment. Therefore, this study aims to compare the effects of
Chlorhexidine 2% and nanosecond (Nd: YAG) laser in reducing the number of
oral Streptococcus mutans bacteria in the oral cavity.

An in vitro experimental design was conducted using S. mutans ATCC 35668
cultured on Mueller-Hinton agar. Bacterial suspensions were standardized to
a half-McFarland turbidity and distributed in 96-well plates. The
antimicrobial activity of 2% CHX was assessed via the well-diffusion method.
Laser irradiation was applied at varying energies (10, 20, 30 mJ) and
frequencies (5, 10 Hz). Bacterial counts and inhibition zone diameters were
measured, and data were analyzed using two-way ANOVA followed by Tukey post
hoc tests (α=0.05).

Bacterial counts decreased with increasing laser energy and frequency, with
complete elimination observed at 30 mJ (both frequencies) and at 20 mJ/10
Hz. Inhibition zone diameters were largest at 30 mJ/10 Hz (8.6 ± 0.39 mm),
while 2% CHX produced a slightly larger, but not statistically significant,
inhibition zone (13 ± 2.9 mm vs. 11.5 ± 14.4 mm; P.05). Both laser
parameters and CHX significantly reduced S. mutans populations,
demonstrating comparable antimicrobial efficacy at higher laser energies.

High-energy 1064 nm Q-switched Nd:YAG laser therapy effectively reduces S.
mutans counts in vitro, with results comparable to 2% CHX. Laser application
may serve as an alternative or adjunctive strategy for microbial control in
dental treatments, particularly in cases where chemical antiseptics are
limited or contraindicated.