[Effects of Nd: YAG laser irradiation on the root surfaces and adhesion of Streptococcus mutans].
OBJECTIVE
This study aimed to evaluate the effects of treatment with different powers of Nd: YAG laser irradiation on root surfaces and Streptococcus mutans (S. mutans) adhesion.


METHODS
Extracted teeth because of severe periodontal disease were divided into the following four groups: control group, laser group 1, laser group 2, and laser group 3. After scaling and root planning, laser group 1, laser group 2, and laser group 3 were separately treated with Nd: YAG laser irradiation (4/6/8 W, 60 s); however, the control group did not receive the treatment. Scanning electron microscopy (SEM) was used to determine the morphology. S. mutans were cultured with root slices from each group. Colony forming unit per mL (CFU·mL⁻¹) was used to count and compare the amounts of bacteria adhesion among groups. SEM was used to observe the difference of bacteria adhesion to root surfaces between control group (scaling) and laser group 2 (6 W, 60 s), thereby indicating the different bacteria adhesions because of different treatments.


RESULTS
Morphology alterations indicated that root surfaces in control group contain obvious smear layer, debris, and biofilm; whereas the root surfaces in laser group contain more cracks with less smear layer and debris. The bacteria counting indicated that S. mutans adhesion to laser group was weaker than that of control group (P<0.05). No statistical significance among the laser groups (P>0.05) was observed. Morphology alterations also verified that S. mutans adhesion to laser group 2 (6 W, 60 s) was weaker than that of control group (scaling).


CONCLUSIONS
This study demonstrated that Nd: YAG laser irradiation treatment after scaling can reduce smear layer, debris, and biofilm on the root surfaces as compared with conventional scaling. The laser treatment reduces the adhesion of S. mutans as well. However, Nd: YAG laser irradiation can cause cracks on the root surfaces. In this experiment, the optimum laser power of 6 W can thoroughly remove the smear layer and debris, as well as relatively improve the control of thermal damagee.
State Key Laboratory of Oral Diseases, Dept. of Periodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
Li
L
Yuanhong
State Key Laboratory of Oral Diseases, Dept. of Periodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
Li
L
Zhongcheng
State Key Laboratory of Oral Diseases, Dept. of Periodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
Luo
L
Mengqi
State Key Laboratory of Oral Diseases, Dept. of Periodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
Shen
S
Daonan
State Key Laboratory of Oral Diseases, Dept. of Periodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
Zhang
Z
Shu
State Key Laboratory of Oral Diseases, Dept. of Periodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
Meng
M
Shu
D001422:Bacterial Adhesion; D003804:Dentin; D006801:Humans; D053844:Lasers, Solid-State; D008855:Microscopy, Electron, Scanning; D009354:Neodymium; D016369:Smear Layer; D013295:Streptococcus mutans; D014092:Tooth Root
D009354:Neodymium
Nd: YAG laser; Streptococcus mutans; root surfaces