Letter to the Editor

To: Editor, The Angle Orthodontist

Re: Effect of injectable platelet-rich fibrin (i-PRF) on the rate of tooth movement. Emire Aybuke Erdur, Kotter Karakaslı, Elif Oncu, Bahadir Ozturk, Sema Hakkı. Angle Orthod. 2021;91:285-292.

Thank you for publishing this interesting study. However, we would like further clarification regarding some aspects of the study.

1. Why was i-PRF injected only on the distal aspect of the canine being retracted and not also on the mesial aspect? At what vertical level were the injections performed and how did you determine the level? Also, please describe the timeline for the two i-PRF injections and why that timeline was selected. It was unclear whether space closure began immediately following extraction and the first i-PRF injection, or whether there was a delay.

2. The timelines of assessment were one-week post receiving the i-PRF, 4^th week, 8^th week and 12^th week, while the i-PRF was injected just after extraction and 1 week later. What was the expected duration of action of i-PRF and the subsequent rationale behind assessing the movements at T3 and T4?

3. The GCF samples were collected at mesiobuccal and distobuccal points of the canine at T0, T1 and T2. If no i-PRF was injected on the mesiobuccal aspect, how can the differences in the results on the mesial surface between the study and the control group be explained? It was stated that “i-PRF stimulated the expression of inflammatory cytokines, which indicated osteoclastic activity and an increased rate of tooth movement.”

4. The paper reported a significant decrease in the OPG levels on the mesial side of the canine. However, this was in contrast to a previous study by Nishijima Y et al (Orthod Craniofac Res. 2006 May;9(2):63-70) finding that the levels increased on the tension side (mesial) and decreased on the compression side (distal). Please explain why OPG levels decreased on the mesial side of the canine.

We would appreciate your further comments on the details of the study.