Effects of a Four vs. Two-Band Hyrax-Type Rapid Palatal Expander.

The use of an expansion screw fixed to dental units across the mid-palatal suture has been used for over a century to eliminate maxillary transverse deficiency. The presence or absence of certain teeth and the stage of dental development have dictated the number of bands as part of the design of this appliance. Classically, four bands have been cemented onto the four anchor maxillary teeth for the appliance. However, it has been claimed that the same clinical result can be achieved using a two-band system. The study group consisted of 31 subjects between the ages of 9 and 16 requiring maxillary expansion who were being treated at the Department of Orthodontics. They were randomly divided into two groups. The first group was treated with a two-band hyrax device placed on the first permanent molars (G₁); the second group was treated with a four-band hyrax device placed on the first premolars and first permanent molars (G₂). Baseline and treatment progress records consisting of standardized maxillary occlusal radiograph, and dental casts were taken in a standardized and serial fashion. Comparison of the data collected from each group led to the following conclusions: G₂ showed greater skeletal expansion, but underwent slightly greater relapse during post retention. The two-band system (G₁) showed residual expansion during the retention phase, but was less effective in older subjects. Therefore, both appliance systems produced similar skeletal responses over time, but behaved differently during active expansion which was dependent on subject age.