Pulsed Nd:YAG versus continuous-wave laser photobiomodulation for orthodontic pain: a split-mouth RCT.

Local pain following orthodontic tooth movement negatively affects patients' experience and compliance. Pulsed neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser, based on photobiomodulation therapy (PBMT), can effectively relieve this pain. This study applied pulsed Nd:YAG laser at different frequencies to orthodontic sites and used digital techniques to evaluate differences in pain relief after tooth movement, aiming to screen the optimal frequency, optimize laser parameters, and provide scientific evidence for the analgesic efficacy of pulsed Nd:YAG laser in orthodontics. 96 patients receiving fixed orthodontic appliances for the first time, who met all inclusion criteria and gave informed consent, were enrolled in this randomized, double-blind, controlled trial. Participants were randomly assigned to one of three pulsed Nd:YAG laser groups-low frequency (10 Hz), medium frequency (15 Hz), or high frequency (20 Hz)-or to a continuous-wave semiconductor laser group (n = 24 each). Each participant further served as his or her own control: within each group, one randomly chosen side received active laser treatment while the contralateral side received sham treatment. A digital pressure algometer was used to measure pressure-pain thresholds (PPT) at the crown and the apex of the target teeth at 0 h, 24 h, 72 h, and 7 days after bracket placement, following intra-oral quantitative sensory testing (QST) protocols. Simultaneously, a visual analogue scale (VAS) and questionnaires were employed to record pain onset, peak pain time, pain disappearance time, and daily pain intensity. All data were analyzed using SPSS 27.0. 1. Intra-oral QST findings: Crown PPT on the treated side in the 10 Hz pulsed Nd:YAG group was significantly higher than that on the treated side in the continuous-wave semiconductor laser group (P < 0.05).In the 15 Hz pulsed Nd:YAG group, both apical and crown PPT values on the treated side were significantly higher than the corresponding values in the semiconductor laser group (P < 0.05). For all three pulsed Nd:YAG frequencies and the continuous-wave laser, PPT values on the treated side were significantly higher than those on the non-treated side (P < 0.05). 2. VAS and questionnaire findings: VAS scores on the treated side of the 10 Hz group were lower than those of the semiconductor laser group on days 2 and 3 (P < 0.05). VAS scores on the treated side of the 15 Hz group remained significantly lower than those of the semiconductor laser group throughout the observation period (days 1-6) (P < 0.05). From day 1 to day 6, VAS scores on the treated side were significantly lower than on the non-treated side in all four groups (P < 0.05). The 15 Hz group also exhibited significantly shorter pain disappearance time and overall pain duration compared with the semiconductor laser group (P < 0.05). 1. Under the PBMT paradigm, both pulsed Nd:YAG and continuous-wave semiconductor lasers effectively alleviate pain and associated symptoms after orthodontic tooth movement. 2. When total energy is kept constant (60 J), 15 Hz pulsed Nd:YAG laser shows promising analgesic effects with better reduction in tooth sensitivity and shorter pain duration than 10-20 Hz. Frequency and analgesia are not linearly correlated. The 15 Hz, 150 µs, 0.5 W setting appears to be a potentially optimal parameter for orthodontic pain relief.