This study aims to assess the effect of PRP on the rate and type of OTM during en-masse frictionless retraction of maxillary anterior teeth using a segmental arch technique.

Thirty adult patients exhibiting class II division 1 malocclusion requiring upper first premolar extractions followed by en-masse retraction will participate in the study. They will be randomly and equally distributed into the PRP group (G1) and the control group (G2). The injection of PRP will be performed pre-retraction. The rate of orthodontic tooth movement will be assessed clinically by measuring the extraction space with a digital caliper. The cephalometric radiographs will evaluate the type of OTM at the beginning of en-masse retraction (T0) and at the middle of en-masse retraction (T1).

One of the most important challenges in daily practice is prolonged orthodontic treatment duration. Many therapeutic procedures, such as chemical interventions, have been introduced to minimize orthodontic treatment time. Even though all the methods of chemically assisted acceleration of OTM increase the rate of bone turnover and increase the rate of tooth movement, however, these chemical agents, i.e., hormones or vitamin D3, have many problems such as systemic effects and short half-life which make them not practical in clinical orthodontic. Therefore, the injection of PRP has been proposed.

-In both groups, two first upper premolars were extracted. In all patients, fixed metal orthodontic brackets with MBT prescription 0.022 were bonded. After the arches were leveled and aligned, a rigid sectional archwire (0.021 x 0.025 in stainless steel) was used for the anterior six teeth. To strengthen anchorage, microscrews (diameter 1.6 mm; length 10 mm) were inserted at 8mm from the archwire into the inter-radicular space between the maxillary first molar and second premolar.

Two crimpable hooks were used with a height of 8 mm between the lateral incisor and canine on both sides of the sectional wire 0.021x0.025 to pass the force vector as close as possible to the center of resistance. En-masse retraction began one week after premolar extraction, using calibrated nickel-titanium coil springs with 175 g force per side.

-In PRP, 48 ml of blood was collected from the patient in sterile tubes with ACD-A as an anticoagulant. PRP was prepared as follows: Initially, the blood was centrifuged at 2000 rpm for 6 minutes. After separation of the blood, PRP and some Platelet-Poor Plasma (PPP) were collected and mixed in a dry tube, and then a second centrifugation was done at 2700 rpm for 3 minutes. After the second centrifugation, the lower 1/3rd of the tube is PRP. About 4 ml of PRP was collected from the tube, and then the patient was injected with it. After regional anesthesia for pain control, 0.5 ml of PRP was slowly injected submucosally palatal to each tooth from the right canine to the left canine using a 1cc syringe. Paracetamol was described for the patient to control pain and ensure confirming not to use ibuprofen or another NSAIDS. The injection was applied one time.

Inclusion Criteria:

1. age range between 16 and 27 years
2. Class II division I malocclusion in which extraction of upper first premolars is indicated
3. skeletal class II relationships (4°<ANB<10°),
4. Non-growing patients
5. No maxillary constriction
6. overjet >5 and <10 mm
7. normal overbite of 0-50%
8. normal anterior facial height
9. No systemic disease.

Exclusion Criteria:

1. patients who have undergone previous orthodontic treatment
2. patients who need orthopedic surgery
3. moderate to severe anterior crowding (Disharmony Dento-Maxillary (DDM≥3)
4. Poor oral hygiene,
5. long-term use of medical drugs, especially NSAIDs