Therefore the aim of the current randomized controlled clinical trial is to investigate the effect of gradually increasing force magnitude versus constant force magnitude on the rate of tooth movement in a canine retraction model, furthermore investigate the effect of the two force systems on the ratio of cytokines and the pain experienced by the patient.

Research question:

In adult orthodontic patients requiring bilateral maxillary canines retraction, will gradually increasing force magnitudes accelerate the rate of canine retraction in the experimental side when compared to the control side?

A. -Patient preparation:

1. After patient selection, routine orthodontic records will be collected (study models, panoramic, lateral cephalometric radiographs, and intra-oral and extra-oral photographs).
2. The orthodontic treatment: All subjects will receive a Straight Wire Appliance (SWA); Roth prescription slot 0.022 × 0.028 inch. The brackets will be bonded to the tooth surface using orthodontic light cured composite resin. Ready-made molar bands with 2 buccal tubes (main and auxiliary)1 will be selected, fitted, and cemented on the upper first molars using glass ionomer cement. The arch wire sequence in the initial levelling and alignment stage will be tailored according to the severity of crowding of each case.
3. Just before canine retraction, alginate impressions will be made for the maxillary arch, CGF sample will be taken as described later in the same section, stainless steel arch wire 0.017 x 0.025 mil will be inserted.

B. Canine Retraction:

1. The active group (gradually increasing force magnitude) will be randomly assigned to either the patients' left or right sides only (split mouth design).
2. At the start of canine retraction, Nickel-titanium closed-coil springs applying 50 g and 150 g measured using Correx tension gauge will be used in the active side and control sides respectively on each side, stretched bilaterally from the hook on the first molar band to the hook of canine brackets(19).
3. Activation will be done every 4 weeks.
4. The impressions will be poured with dental stone within 15 minutes to ensure its accuracy.
5. Visual analogue scale (VAS) will be explained to the patient and used to measure pain intensity in the postoperative period: immediately after the commencement of canine retraction and at each visit. The patient is asked to make three pain ratings each time to take an average. (one day, second day and one week after)

Inclusion Criteria:

1. Males and Females with an age ranging between 16-30 years (Adult patients since cooperation increases with age) (17).
2. Malocclusion that requires extraction of the maxillary first premolars and canines retraction with moderate anchorage.
3. Full permanent dentition with exception of the third molars.
4. Good oral hygiene and periodontal condition (Probing depth< 4 mm in all teeth), since the periodontal condition affects the amount and type of tooth movement.
5. Absence of untreated caries which may worsen during the study time.

Exclusion Criteria:

1. Medically compromised patients.
2. Patients suffering from any congenital or hereditary diseases.
3. Smoking or any systemic diseases.
4. Chronic use of any medications including antibiotics, phenytoin, cyclosporine, anti-inflammatory drugs, systemic corticosteroids, and calcium channel blockers. All the above factors affect the rate of tooth movement