Rapid maxillary expansion (RME) in the initial stages of occlusal development has become a routine procedure in orthodontic practice. The increase of the transverse dimensions of the maxilla in the mixed dentition can be carried out by a rapid palatal expander that exploits primary teeth as anchorage to minimize any negative effects on permanent teeth. This case report demonstrates the use of a modified Haas-type RME appliance in a Caucasian girl 7 years 6 months of age with a maxillary transverse deficiency, unilateral crossbite, dental midline deviation, and maxillary anterior dental crowding. The patient was treated with a modified Haas-type RME appliance composed of a six-band metal-cast structure with a partial occlusal covering that was bonded to the primary teeth using glass-ionomer cement. Clinicians see advantages in terms of speed of application and patient compliance by taking a single impression. Stability and retention of the appliance improve thanks to custom-made metal casting and the risks of decementation minimize via the use of glass-ionomer cement. Moreover, the fabrication in inert titanium, hypoallergenic resin, and laser soldering means patients with allergies can use it. The results demonstrate that the expansion carried out on primary teeth is followed by permanent molars and remains stable. Orthodontics (Chic) 2011;12:252–259.
Key words: cast Haas-type RME appliance, expansion stability of permanent dentition, maxillary incisor alignment, mixed dentition, rapid palatal expansion