Patients at the Orthodontic Department of University of Aleppo Dental School will be selected if they meet the inclusion criteria then fixed orthodontic treatment with 0.018-inch slot MBT appliances will be applied for those patients.

The aim of this study is to compare Two rebonding procedures by applying a split-mouth design. The clinical failure rates of the two rebonding procedures will be evaluated.

The sample of this study will be chosen after examination of patients referred to the Department of Orthodontics at the University of Aleppo Dental School then subjects who meet the inclusion criteria will be included in this trial.

An information sheet will be given to each possible candidate. Then consent forms will be obtained.

All patients will receive both rebonding procedures by applying split-mouth design. Each patient will be asked to select an opaque sealed envelope from a box with 20 ones. Ten envelopes will Include instructions for applying sandblasting prior to acid-etching on the right upper premolars and acid-etching alone on the left upper premolars. In contrast, the other ten envelopes will include opposite instructions.

A total sample of 80 premolars will be obtained to study the clinical failure rates of the two rebonding procedures.

The 80 premolars will be randomly divided into two groups:

• The first group in which the enamel will be prepared using sandblasting prior to acid-etching.
• The second group in which the enamel will be prepared using acid-etching alone.

Inclusion Criteria:

1. good general health and oral hygiene
2. willing and able to comply with the trial procedures
3. No crossbite, scissor bite, or occlusal interferences with the bonded/rebonded brackets in the premolars region (to prevent any potential early bond failure)
4. no craniofacial anomalies.

Exclusion Criteria:

1. any type of pervious orthodontic therapy
2. any need for ortho-surgical treatment or teeth extraction.