Assessment of the Efficacy of Twin Arch Brackets in the Control of Orthodontic Tooth Movement: A Randomized Controlled Clinical Study

Alignment and leveling of teeth generally constitute the most important preliminary clinical phase of any orthodontic treatment with fixed orthodontic appliances.

During the leveling and alignment stage, tooth movement is directly affected by many factors, such as interbracket distance, bracket width, archwire selection and the friction generated between the bracket and the archwire. It is critical that the force moment which generated by interaction between the bracket slot and the archwire to be transferred from the archwire to the malpositioned tooth.

While it is widely recognized that the geometric structure of the bracket, especially the slot width, determines the efficiency of the force moment, the interbracket span, on the other hand, remains another crucial factor affecting the effectiveness of tooth displacement. It has been established that a sufficient interbracket span enables the flexible archwire to activate its springiness caused by deflection. A wider bracket is favorable to develop an adequate force moment, but the subsequent decrease in the space between the brackets will reduce the effective length of the archwire segments between the supports. As a matter of fact, the efficiency of treatment mechanics is a major focus in modern orthodontics.The advancement of bracket design began with the vertically positioned slot in the ribbon arch appliance to the pure rectangular horizontal slot in the traditional standard edgewise to the modern preadjusted brackets in the straight wire technique, and to the current design of the self-ligating brackets system. It is interesting to note that despite the numerous bracket designs, one feature has remained unchanged: there is only one single horizontal slot on the facial surface of the bracket. In some design variations, such as the Tip- Edge Plus, In-Ovation and " R " brackets, an additional horizontal slot is enclosed within the bracket base and is not open to the labial surface, therefore only allowing for engagement of segmental auxiliary archwires. However some inventors design bracket system called "the twin wire appliance or twin arch wire appliance " which can fit two archwires simultaneously by incorporating two horizontal slots in the design of single brackets. In twin arch appliance design, the bracket width is doubled without decreasing the interbracket span.

The treatment technique to work with two arch wires simultaneously is not new. The idea behind the invention of twin arch appliance was to achieve a better control over orthodontics tooth movements. In the orthodontic literature a very little knowledge and research can be found concerning the use of Twin arch appliance in orthodontic treatment. In the 1930s attempts were made to develop a new treatment method with this concept. Spencer Atkinson was the pioneer, Spencer created a bracket with a vertical and a horizontal slot, positioned one on top of the other. Then in 2008 an experimental study for the efficiency of double slot brackets in correction of malposed teeth when placed in wax typodont was established. The study revealed that twin slot bracket doubles the rate of teeth alignment. The reason behind this phenomenon that the twin-slot bracket doubles the rate of alignment may be attributed to fact that the force applied on the tooth bonded with the twin-slot bracket is doubled and the rate of wax flow is likely to be proportional to load .

Because of the promising results obtained from the previous experimental study and the lack of clinical study results, it will be beneficial to study and compare clinically the effectiveness of twin arch appliance in control of orthodontic tooth movements as well as the comfort of patient during the initial leveling and alignment stage of treatment in relation to other conventional bracket systems.