The primary aim of the current study was to evaluate three dimensionally, using digital models and cone beam computed tomography imaging, the effect of micro-osteoperforations on the rate of tooth movement in the first molar distalization.

The design of this randomized controlled clinical trial is a parallel group, two arms trial

• Preparatory phase

  • Self-drilling mini-screws will be placed buccally between upper 2nd premolar and 1st molar bilaterally in the last NiTi wire insertion visit.
  • After the completion of levelling and alignment phase an intra oral scan will be made for the upper arch and a rigid stainless-steel retraction arch wire 0.017" x 0.025" will be inserted.
  • The patient will then be referred to the radiology center and a pre-retraction cone beam computed tomography (CBCT) image will be taken for the maxillary arch (T0).

• Experimental phase

  • Subjects will receive MOPs randomly to either the left or right maxillary molar buccal alveolar regions. MOPs will be performed at the first day of the distalization treatment (T0) and will repeated every 2 months.
  • Molar distalization will started immediately after performing the MOPs using sliding jig distalizer.
  • The force will be applied to the mini-screw with the sliding jig mechanics on average 300 gm using Nickel-titanium closing coil springs.
  • Before leaving the clinic, the patient will be asked to:
  • Use chlorhexidine three times per day for 3 days after MOP applications.
  • avoid using pain killers (except Panadol when needed).
  • fill in a Numeric pain rating scale.

• Follow up phase

  • Follow up visits will be scheduled every 4 weeks for reactivation coil spring and check TADs stability.
  • An intra oral scan for the upper arch will made every visit.
  • The study time will be continued for 6 months (T1, T2, T3, T4, T5, T6).
  • The same technique of MOP will be repeated after 2 and 4 months of follow up (T2,T4).
  • After 6 months of follow up, the final dental model will made, and the patient will be referred to the same radiology center to acquire the post-distalization CBCT.

Inclusion Criteria:

1. Adult patients
2. Skeletal Class I or mild Class II relationship
3. Dental class II bilaterally (non-extraction cases)
4. Full permanent dentition including 2nd maxillary molars
5. Good oral hygiene
6. Medically free

Exclusion Criteria:

1. Systemic diseases that may interfere with the treatment
2. Use of any medications that might have affected the biology of tooth movement
3. unilateral Class II molar relationship
4. extreme skeletal Class II relationship (ANB >7°)
5. periodontal disease or alveolar bone loss
6. Patients with dental anomalies in maxillary 1st molar

The first assessor will perform the digital models & CBCT measurements blindly for each patient. The second assessor will perform the same measurements blindly to calculate the inter-observer error