Effects of CO2 Laser Irradiation During Experimental Tooth Movement

Objectives: Patients often feel pain or discomfort when exposed to orthodontic forces. One recently suggested method to control pain is laser therapy. In the present study, we demonstrated the efficacy of CO2 laser irradiation in reducing pain during experimental tooth movement by evaluating the distribution of c-fos-immunoreactivity (Fos-IR) neurons in the medullary dorsal horn (MDH).

Methods: Forty 7-week-old male Wistar rats were used. The experimental animals were randomly divided into four groups: control group (n=5), tooth movement group (n=5), laser irradiation group (n=10), and tooth movement with laser irradiation group (n=20). Two hours after experimental treatment, the difference in distribution of Fos-IR was assessed in the MDH. To evaluate the damage to nerve fibers of the dental pulp and the periodontal ligament (PDL) by the laser irradiation, the calcitonin gene related peptide (CGRP)-containing nerve fibers were examined. In addition, to test thermal effects on the CO2 laser irradiation, a thermocouple probe was inserted below the mucosa and measured the temperature change when the laser is irradiated.

Results: The number of Fos-IR neurons in the MDH increased significantly two hours after the start of the tooth movement. Treatment with CO2 laser irradiation significantly reduced the induction of Fos-IR neurons in the MDH. The CGRP immunoreactivity in the dental pulp or apical area was observed in all the study groups. No tissue injury due to CO2 laser irradiation was observed in the hematoxylin-eosin (H-E) staining. The maximum temperatures measured below the mucosa were less than 40°C.

Conclusion: These findings suggested that CO2 laser irradiation had the analgesic effects on the initial pain associated with orthodontic force. Furthermore, no tissue injury by laser irradiation was observed, which suggests that CO2 laser irradiation may be an effective measure to relieve pain.