The purpose of this study is to determine if the injection of Platelet-rich plasma (PRP) is effective in reducing alveolar bone loss that happens after each rapid maxillary expansion (RME) on the buccal aspect of the posterior teeth.

16 patients with a skeletal maxillary constriction aged between 10-16 years old will get into orthodontic treatment to widen the maxilla using Hyrax appliance.

An amount of patient blood will be withdrawn and centrifuged to get PRP. Then the PRP will be injected in one half of each patient mouth in a split-mouth design, beneath the buccal periosteal of the first molars and first premolars, the halves will be chosen randomly.

High resolution CBCT images will be taken before and after orthodontic treatment to analyze buccal bone thickness and height changes.

Correction of the maxillary transverse discrepancy is essential for treatment of various types of malocclusions. Palatal expansion is the most common method used to improve the transverse dimensions of the maxilla especially Rapid maxillary expansion (RME) . RME is associated with intermittent high force systems which cause lateral flexion of the alveolar processes and buccal displacement of the anchorage teeth . Displacement of these teeth outside the alveolar anatomic limits can damage the periodontium and finally compromising tooth longevity.

Several researchers have studied the incidence of buccal dehiscence and fenestrations after RME , using CBCT Images.

From here It was thought about using a method to eliminate these dangerous side effects. It was found that platelet rich plasma (PRP) has the ability to enhance tissue regeneration, accelerate wound healing and inducing stem cells differentiation through its growth factors (GFs).

This is the first study in the world that will use PRP with orthodontic treatment, because of its benefits and easiness of using in dental clinic.

Study sample, that consists of 16 patients, was calculated using (G-power sample size calculator) depending on the buccal alveolar bone thickness changes, with a study power of 95%.

Sample will be chosen from the patients who are coming to Orthodontic department in the Faculty of dentistry - Damascus university.

Allocation of the sides of intervention (PRP injection) and control sides is made by letting the participants to withdraw a closed envelop from a dark black box. Each envelop in the box contain either (R letter) for the right side or (L letter) for the left side that will be the intervention side for that patient.

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.

High resolution CBCT will be taken before the beginning of treatment (T0). Hyrax appliance will be applied on the first molars and first premolars and cemented using GIC.

After one day of cementation, 20ml of patients' blood will be withdrawn and centrifuged to get 4 ml of PRP.

The buccal soft tissue will be anesthetized (sub-mucosal) in the intervention side , then the PRP will be injected at the buccal area of the first molar and first premolar in that side using insulin syringe , 2 ml for each tooth mentioned in two points. The first point place is in the middle of the attached gingiva over the mesial root of the first molar and buccal root of the first premolar. The second point is in the mucosal-gingival junction over the same root of each tooth.

Starting of expansion will be done in the same day of injection, twice a day until getting an over correction of 2-3 mm.

After one week, the injection of prp will be repeated in the same way (T1) High resolution CBCT for the maxilla will be taken 3 months after the beginning of treatment (T2).

All measures will be analyzed before and after treatment between two sides. A questionnaire will be given to the patients to study pain level accompanying PRP 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:

• 10-16 years old patients
• Complete emergence of first molars and first premolars
• Clinical maxillary transverse deficiency
• Good oral hygiene (Gingival index <1) according to Silness & loe 1964
• ( Plaque index <1)

Exclusion Criteria:

• The presence of a medical situations that affects orthodontic treatment and periodontal health
• The presence of drug therapy affect orthodontic treatment and periodontal health
• Bad oral hygiene (gingival and plaque index >1)
• Patient with physical and psychological limitations
• Metallic restorations or endodontic treatments on the appliance supporting teeth (first molars and first premolars)
• Craniofacial anomalies
• Previous orthodontic treatment
• Patients who did not correctly follow the protocol of activation
• Patients who did not return for control dental appointments
• Patients whose cementation of the appliance failed
• Patients whose dental structures were difficult to visualize on the CBCT scans as a result of artifact