[Treatment of crossbite with the quadhelix appliance and lower lingual arch to maintain constant lower intermolar width].

The quadhelix appliance is often recommended for the treatment of children with crossbite. It is characterized by high effectiveness, low cost and short treatment time. Its modification with asymmetric arms enables asymmetric expansion of the upper arch. However, no clinical studies confirming such action are known. During maxillary expansion the lower arch tends to follow the maxillary teeth by tipping laterally. This phenomenon hinders crossbite treatment. The aim of the present study was to evaluate the effect of asymmetric arms of the quadhelix appliance during treatment of crossbite and to assess the effectiveness of the lower lingual arch in maintaining lower intermolar width. The study group included 20 children with crossbite. The treatment procedure comprised slow maxillary expansion with the quadhelix appliance. A lower lingual arch activated 1 mm inwards was simultaneously used in order to prevent increase in the lower intermolar width through occlusal contacts. The maxillary intermolar widths were measured between the central fossae of the right and left first permanent upper molars. Mandibular intermolar widths were measured between medial buccal cusps. The mean increase in upper intermolar width was 4.1 mm. The mean change in the lower intermolar width was -0.1 mm and was statistically insignificant. Posterior crossbite was eliminated in 16 children (80%). In 20% of children an improvement (e.g. reduction of the number of teeth in crossbite) was noted. The subtraction sum of the upper and lower intermolar widths was -5.7 mm before treatment and -1.4 mm after treatment. The upper dental arch before treatment had an asymmetric shape in all subjects. The width of the more deficient side was 19.65 mm and the wider side measured 22.3 mm. This difference was statistically highly significant (p < 0.0001). After treatment, the width of the side where the shorter arm was used was 22 mm. The width of the opposite side was 23.7 mm. The difference was statistically significant (p < 0.003). The width of the palate increased on the average by 3.5 mm. The change in overbite was statistically insignificant, enabling safe application of this method in patients with crossbite and open vertical skeletal configuration. The length of the upper arch increased by 0.2 mm (p < 0.01). The average treatment time was 17 weeks, depending on the number of teeth in crossbite before treatment (Rs = 0.58; p < 0.007). Longer treatment times (6-7 months) were reported in other studies describing patients of the same age. The quadhelix with asymmetric lateral arms is recommended for the treatment of crossbite with an asymmetric upper dental arch. The simultaneous application of lower lingual arch prevents lower intermolar expansion, thus shortening the time of treatment.