Objectives To examine whether periodontal injection of platelet-rich plasma (PRP) could accelerate orthodontic tooth movement.Methods A split-mouth randomised controlled clinical trial was conducted among 16 female participants. Canines were retracted on 0.017 x 0.025-inch stainless steel archwires through closed-coil springs attached on first molars with mini-screws for anchorage preservation. The intervention side received PRP + CaCl2 solution and the control
side CaCl2 only. Intraligamental injections were performed during the canine retraction period every three weeks (zero, three and six weeks). The rate of canine retraction was assessed through superimposition of digital models every month for a total of four months. Assessment of associated pain was conducted by questionnaire.Results During the four-month period, a faster rate of canine retraction was detected on the intervention side only for the first month. Following cessation of PRP injections, the rate of canine retraction on the intervention side was initially slower than and then similar to that on the control side. An increase of pain was reported on both sides.Conclusions PRP could accelerate orthodontic tooth movement in the short term with no prolonged effects.