Twenty patients need therapeutic extraction of the maxillary first premolars with subsequent retraction of the maxillary canines, will be divided randomly into two groups, and will randomly assigned to one side of the maxillary arch at the first premolar region , and the other side served as the control. canine retraction will be initiated after completion of the leveling and alignment phase via closed nickel-titanium coil springs applying 150 g of force per side , soldered transpalatal arch will be used as an anchor unit.

Pre- and post distalization dental casts will be evaluated to study rate of canine distalization, over a follow-up period until a Class I canine relationship will be achieved. The levels of Pain and discomfort will be monitored using a questionnaire with a VAS scale administered three times during the first day after prf injection.

Reduced orthodontic treatment duration is important for care providers and orthodontic patients.it is also desirable that aesthetic concerns and time dependent adverse events such as discomfort, pain, external root resorption, suboptimal oral hygiene, white spot lesions and dental caries are held to the minimum. Although the surgical assisted accelerated orthodontic tooth movement (such as distraction of periodontal ligament, distraction of dentoalveolus, periodontally accelerated osteogenic orthodontics (PAOO),Corticision, orthognathic surgery, piezocision, piezopuncture and micro osteoperforation). It has been proved to be the most effective one currently, its disadvantages are: it is a bone surgery, and it causes loss of alveolar bone that undermines the periodontal support of the target teeth.

Noninvasive and nonsurgical methods have always been preferred by both the clinicians and the patients. These techniques have ranged from application of biological molecules to innovative technologies such as resonance vibration, cyclic forces, light electrical currents, magnetic field forces, low-intensity laser irradiation and low-level light therapy. Endogenously produced biologicals have been tested based on their roles in the turnover of alveolar bone in response to orthodontic tooth movement as well as during wound healing.

That's why the submucosal injection of platelet rich plasma (PRP) is a technique developed for accelerating orthodontic tooth movement by simulating the effects of bone insult without surgery and loss of alveolar bone, Some researchers found that prp injection created a regional acceleratory phenomenon-like effect which forms the basis of rapid tooth movement compared with conventional orthodontic treatment.

From here it has been thought about using a method to eliminate the surgical techniques' side effects. It has been found that platelet rich fibrin (PRF) has the ability to enhance tissue regeneration, accelerate wound healing and inducing stem cells differentiation through its growth factors (GFs).

PRF characteristics in comparison to platelet rich plasma PRP are:

1. its preparation is completely natural and there is no need for thrombin addition so there isn't immune reaction
2. it contains stem cells
3. it requires one stage centrifugation
4. PRF has been reported to gradually release autologous growth factors and expressed stronger and more durable effect on the cellular proliferation and differentiation than PRP in vitro This is the first study in the world that will use i-PRF with Orthodontic treatment, because of its benefits and easiness of using in dental clinic Study sample that consists of 20 patients, was calculated using (G-power sample size calculator), depending on the rate of canine retraction with a study power of 95%.

Allocation of the sides of intervention (PRF injection) and control sides is made by computer program (Excel).

After ensuring of the patients compliance with the terms and conditions of this study, the purpose and methods of the study will be explained to the patients using Information Sheet. In case of approval to participate, the patients asked to sign the Informed Consent.

Extra & Intra-oral photographs, impressions and clinical examination will be made.

Canine retraction will be initiated after completion of the leveling and alignment phase via closed nickel-titanium coil springs applying 150 g of force per side at the same time 20ml of patients' blood will be withdrawn and centrifuged (700 rpm within 3 minutes) to get 4ml i-PRF. PRF will be injected at the area of the extracted first premolar, The first point place is in the buccal interventional side (supra periosteal injection) and the second point place is in the palatal interventional side(sub periosteal injection). PRF will be injected twice at the beginning and at the middle of the canine retraction.

All measures will be analyzed before and after canine retraction between two sides.

A questionnaire will be given to the patients to study pain level accompanying PRF injection compared to the control side. Pain will be assessed using Visual Analogue Scale (VAS) 1 (No Pain) - 10 (Worst Pain).

A questionnaire will be given to the patients to study their acceptance of new treatment approach with comprehensive orthodontic treatments.

Inclusion Criteria:

1. Adult healthy patients, Male and female, Age range: 15-27 years.

2. Class II Division 1 malocclusion:

   Mild / moderate skeletal Class II (ANB ≤7) Overjet ≤10 Normal or excessive facial height (Clinically and then cephalometry assessed using these angles : SN-MP , MM , Y axis) Mild to moderate crowding ≤ 4

3. permanent occlusion.

4. Exist all the upper teeth (except third molars).

5. Good oral and periodontal health:

Probing depth < 4 mm No radiographic evidence of bone loss. Gingival index ≤ 1 Plaque index ≤ 1

Exclusion Criteria:

1. Medical problems that affect tooth movement (corticosteroid, NSAIDs, …)

2. patients have anti indication for oral surgery ( medical - social - psycho)

3. Presence of primary teeth in the maxillary arch

4. Missing permanent maxillary teeth (except third molars).

5. Poor oral hygiene or Current periodontal disease:

   Probing depth ≥ 4 mm radiographic evidence of bone loss Gingival index > 1 Plaque index > 1

6. Patient had previous orthodontic treatment

7. Craniofacial anomalies (cleft lip and palate patients)

8. Smokers

9. coagulation disorders and patients treated with anticoagulants.

10. patients with immunodeficiency disorders

The Individual participant data will be only available for the researchers in the department of Orthodontics, Damascus University

One blinded