Clear Aligner Therapy CAT is a method used to straighten teeth using clear custom made plastic aligners that apply light pressure to gradually move teeth into the desired position. Compared with fixed orthodontic appliances clear aligners are more comfortable and aesthetically acceptable which has increased their popularity. The treatment is based on computer aided design where a three dimensional digital model of the dental arches is created and tooth movements are planned using specialized software. Initially clear aligners were used mainly for simple malocclusion cases such as mild crowding or small space closure but their application has expanded to treat more complex cases including extraction cases open bites and Class II malocclusions.

Maxillary molar distalization is a common non extraction method used to correct Class II molar relationships particularly in patients with mild skeletal discrepancies or maxillary dentoalveolar protrusion. Traditionally molar distalization was achieved using extraoral appliances such as headgear which require high patient compliance. To reduce dependence on compliance several intraoral appliances and skeletal anchorage methods have been introduced. However these methods may produce unwanted effects such as reduction in facial height clockwise rotation of the mandible premolar extrusion molar tipping and loss of anterior anchorage.

Clear aligners can also achieve Class II correction through sequential maxillary molar distalization with good predictability when attachments are placed on the teeth. V- staging patterns are used for distalization with clear aligners sequential distalization and simultaneous distalization. Sequential distalization is considered more effective and is commonly used in clinical practice. In this approach the second molars are distalized first followed by the first molars once the second molars have moved halfway and then the premolars move sequentially. The effectiveness of this movement is influenced by staging strategy and the design position and shape of attachments.

There is limited clinical evidence comparing the effectiveness of different staging approaches in maxillary molar distalization with clear aligners. Therefore the purpose of this study is to compare the efficacy of V- staging patterns for maxillary molar distalization in two study groups using clear aligner therapy.

In this study patients were instructed to change aligners every week and wear them for twenty two hours per day while maintaining a daily compliance log to record the duration of aligner wear.

Digital intraoral scans were obtained for each participant and digital dental models were generated. These models were used to plan treatment and fabricate thermoplastic clear aligners using a pressure molding machine. Attachments were bonded to the teeth to facilitate the required tooth movements.

For each patient three digital models of the maxillary arch were collected including pre treatment model T0 virtual treatment plan model T1 and post treatment model at the end of distalization phase T2. These models were used to assess the predicted and achieved tooth movements.

The digital models were imported into software to perform superimposition and measurements. Initially T0 and T1 were compared to determine the prescribed movement. The buccal cusp tips of the first and second molars were used as landmarks to measure distalization. T0 and T2 were then compared to evaluate the achieved movement after treatment.

The distal movement of the mesiobuccal cusp and distobuccal cusp of each molar was analyzed. Prescription referred to the amount of movement planned between T0 and T1 while achieved movement referred to the movement observed between T0 and T2. Accuracy was calculated as the percentage of achieved movement compared with the planned movement.

A reference coordinate system was established to describe tooth movement in three spatial dimensions and to allow comparison between predicted and achieved tooth movements.