THE EFFECT OF SEMICONDUCTOR LASER TREATMENT ON RAT PULP TISSUE MORPHOLOGY AND THE LEVEL OF DAMAGE REPAIR FACTORS

Wenshang Song, Suna Li, Zilue Liu, Shixin Cai^*

Department of Orthodontics and Prosthodontics, Hengshui People’s Hospital, Hengshui, Hebei 053000, China

Objective: To investigate the impact of semiconductor laser treatment on the morphology of rat pulp tissues and the level of damage repair factors. 

Methods: The 7-week-old Sprague-Dawley rats (n=60) were randomly divided into 4 groups: control group (n=15), low power group (n=15) with 1.0w, Continuous-wave mode, irradiated for 30s; medium power group (n=15) with 1.5w, Continuous-wave mode, irradiated for 30s and high power group (n=15) with 2.0w, Continuous-wave mode, irradiated for 30s. Animals were randomly selected, killed, and tissue samples were collected on d 1, d 7, and d 14 after irradiation. The morphological and pathological changes of the pulp tissues were observed. In addition, six mice in the medium power group were randomly selected, and the cytokine expression on d 1, d 7, and d 14 in the pulp tissues were detected. 

Results: H&E staining showed no inflammatory cells or other pathological changes in the pulp tissues of the control group, and clear morphological structures were observed. On d 1 after laser irradiation, the pulp vessels were slightly dilated, while there were no significant pathological changes in other areas in the low power group. In the medium power group, the arrangement of odontoblast layer was slightly disordered, and the vascular dilation of pulp was more obvious than that of the low-dose group. In the high power group, the dentin cell layer was disordered, the vascular dilation of the pulp was the most obvious, and a few inflammatory cells infiltrated in other areas. After laser irradiation for 14 d, the pulp tissue in the low power group and medium power group was basically restored to health, and there was no significant difference from normal pulp tissue. There was no obvious inflammatory area, and the pulp vessels were slightly dilated in the high power group. Overall, higher laser power caused more serious tissue damage. After laser irradiation for 14 d, inflammation in pulp tissues of all groups was improved. The PCR results showed that the expression of CXCR4 was time-dependently increased by irradiation, while SDF1 expression was increased by irradiation on day 1 followed by decreased expression on day 7 and 14. SDF1 expression on day 7 and 14 was still higher than that in the control group. However, the expression of DMP1 mRNA showed gradual increase from d 1 to d 14; by d 14, DMP1 showed highest expression, with statistical difference compared with the control and d 1 groups (P<0.05), while the other groups were not statistically different compared with each other (P>0.05). TNF-α mRNA expression increased on d 1 after laser irradiation compared to the control group, and then gradually decreased until it reached almost the same expression as the control group on d 14. 

Conclusion: In pilot clinical and dental studies, semiconductor laser teeth whitening is non-invasive with few side effects. However, in order to reduce the irritation to the dental pulp and achieve significant long-term results, it is necessary to select proper semiconductor laser whitening procedures. Their increasing application in clinical dentistry may provide better cosmetic dental treatment for patients.