the aim of this study is to assess and compare the effect of PRF and vitamin Dꝫ injection on the rate of canine retraction and to determine the bone thickness changes correlated with the two techniques.

• Participants will be recruited from the Faculty of Dentistry, Beni-Suef University. All subjects will be informed of the treatment procedures and will sign a consent form.
• Subjects will be randomly divided into two groups:

Group 1 (PRF group): upper canine retraction will be facilitated by PRF injection that will be randomly assigned to one side (experimental side). The contralateral side will serve as the control one.

Group II (Vitamin Dꝫ group): canine retraction will be facilitated by Vitamin Dꝫ injection that will be randomly assigned to one side (experimental side). The contralateral side will serve as the control one.

• The predicted sample size (n) was a total of (28) cases (i.e. 14 cases per group). Sample size calculation was performed using G*Power version 3.1.9.7
• Randomization:

Simple randomization will be designed with the aid of a computer-generated schedule with 1:1 allocation ratio. Allocation concealment will be achieved using identical opaque, sealed envelopes. Randomization and allocation concealment will be performed by one of the academic staff who will not be involved in the study and will keep the allocation table away from the operators. The operator will shuffle the sealed envelopes and will ask the patient to pick one envelope at the time of recruitment. In each group, a randomly selected side will act as the experimental side while the contralateral side will serve as the control. Blinding of the operators will not be applicable and so blinding will be limited to the outcome assessment.

Methodology:

All patients will be treated with a 0.022-inch MBT bracket system. Leveling and alignment phase will be completed until a 0.017 X 0.025'' stainless steel wire will be inserted passively into the bracket slot. Before canine retraction, the subject will be randomly assigned to one of the groups (PRF or Vitamin Dꝫ group). In both groups, canine retraction will be performed with closed Ni-Ti coil springs with a force of 150 g per side that will be adjusted by the use of a force gauge.

PRF group:

A 20 ml blood sample will be drawn from the median cubital vein into a PRF tube. Centrifugation will be done at 700 rpm for 3 minutes and the liquid of PRF will be suctioned out using a separate syringe. PRF will be injected distal to the canine on the experimental side three times; at the beginning of canine retraction (T0), 1 month after the start of canine retraction (T1), and 2 months after the start of canine retraction (T2).

Vitamin Dꝫ group:

Subjects will receive vitamin Dꝫ injection distal to the canine on the experimental side three times; at the beginning of canine retraction (T0), 1 month after the start of canine retraction (T1), and 2 months after the start of canine retraction (T2).

• For both groups, alginate impressions will be taken just before canine retraction and at a monthly rate till the end of the canine retraction phase. Study casts will be obtained, and the rate of canine movement will be measured every month.
• Cone beam computed tomography (CBCT) will be obtained before treatment and after canine retraction to evaluate the bone thickness changes associated with the two techniques.
• The results will be obtained and statistically evaluated.

Inclusion Criteria:

1. Age: 18- 40 years old.
2. Angle Class I or Class II dental malocclusion that required bilateral maxillary first premolar extraction and upper canine retraction as a part of the treatment plan.
3. Good to fair oral hygiene.
4. Normal probing depth.

Exclusion Criteria:

1. Active periodontal disease.
2. Poor oral hygiene.
3. Systemic diseases or medications that alter bone metabolism or tooth movement.
4. Craniofacial anomalies.

single-blinded limited to the outcome assessment