摘要： Low-level laser irradiation (LLLI) shows effects in orthodontic pain relief and periodontal inflammation control. The aim of this article is to investigate the analgesic and inflammation-modulatory effects of low-level laser irradiation among orthodontic patients with compromised periodontium. A randomised controlled trial with split-mouth design was conducted in 27 adults with treated and controlled chronic periodontitis over 6 months. One side of the dental arch underwent repeated treatment under a 940-nm diode laser (EZlase; Biolase Technology Inc.) with a beam size of 2.8 cm2 for 60 seconds at 8.6 J/cm2, whilst the other side received pseudo-laser treatment. Laser irradiation was applied repeatedly for 8 times during the first 6 weeks after bracket bonding and monthly thereafter until the end of orthodontic treatment. Subjective pain (assessed by visual analogue scale in pain diary and by chairside archwire activation), periodontal status (assessed by periodontal clinical parameters), cytokines in gingival crevicular fluid (interleukin 1β, prostaglandin E2, substance P) and periodontopathic bacteria (Porphyromonas gingivalis and Treponema denticola) in supragingival plaque were assessed. The intensity of pain was lower on the laser-irradiated side at multiple follow-up visits (P < 0.05). The pain subsided 1 day earlier on the laser side, with a lower peak value during the first week after initial archwire placement (P < 0.05). The laser side exhibited a smaller reduction in bite force during the first month (mean difference = 3.17, 95% CI: 2.36–3.98, P < 0.05 at 1-week interval; mean difference = 3.09, 95% CI: 1.87–4.32, P < 0.05 at 1-month interval). A smaller increase was observed in the plaque index scores on the laser side at 1-month (mean difference = 0.19, 95% CI: 0.13–0.24, P < 0.05) and in the gingival index scores at the 3-month follow-up visit (mean difference = 0.18, 95% CI: 0.14–0.21, P < 0.05). Laser irradiation inhibited the elevation of interleukin-1β, prostaglandin E2 and substance P levels during the first month (P < 0.05). However, no intergroup difference was detected in the bacteria levels. Low-level laser irradiation exhibits benefits in pain relief and inflammation control during the early stage of adjunctive orthodontic treatment in periodontally compromised individuals.