Correction of unilateral posterior crossbite in the mixed dentition : studies of treatment effects, stability and cost-effectiveness

Abstract: Unilateral posterior crossbite of dento-alveolar origin is a trans-verse discrepancy of the maxillo-mandibular relationship and is one of the most common malocclusions in the mixed dentition. If untreated, the crossbite and the abnormal lateral movement of the lower jaw may strain the orofacial structures, causing adverse ef-fects on the temporomandibular joints, the masticatory system and facial growth. Thus, early orthodontic intervention is usually un-dertaken to correct the condition at the mixed dentition stage and the orthodontist may choose from a range of treatment methods. The method of choice for orthodontic treatment should not only be clinically effective, with long-term stability, but also cost-effective. The overall aim of this thesis was to compare and evaluate dif-ferent methods of correcting unilateral posterior crossbite, in terms of clinical effectiveness, stability and cost-effectiveness. The ap-proach was evidence-based; RCT-methodology was used in order to generate a high level of evidence. This thesis is based on four studies: Paper I comprise a systematic review of the scientific literature and evaluation of the quality of the retrieved studies from an evidence-based perspective. The literature search spanned from January 1966 to October 2002 and was subsequently expanded to Decem-ber 2010. Papers II, III and IV were randomized controlled trials. Paper II compared and evaluated different strategies (Quad Helix, expan-sion plate, composite onlay and expectance for possible spontane-ous correction) for correcting posterior crossbite in the mixed den-tition. Paper III compared and evaluated the long-term stability and post-treatment changes associated with the Quad Helix and expansion plate methods, compared to normal controls. In paper IV, the cost-effectiveness of the Quad Helix and expansion plate methods was evaluated, using a cost-minimization analysis. The following conclusions were drawn: Paper I The systematic review, including the supplementary literature search, disclosed that: • There is moderately strong evidence to support the clinical ef-fectiveness of both Quad Helix and RME. However, to date there is insufficient evidence to indicate that either method is superior. • There is moderately strong scientific evidence that Quad Helix is more effective than the expansion plate for correcting poste-rior crossbite in the mixed dentition. • Because there is currently limited or insufficient scientific evi-dence, further well-designed studies are needed to address the following questions: long-term stability, possible space gain, cost-effectiveness, treatment-related discomfort or pain affect-ing quality of life and possible effects on the orofacial struc-tures, for example temporomandibular disorders and facial asymmetry. Papers II and III • Quad Helix is an appropriate and successful method and supe-rior to expansion plate in terms of clinical effectiveness and cost-effectiveness; the major disadvantage of the expansion plate method is the dependence on patient compliance. • The composite onlay method is not effective for correction of posterior crossbite in the mixed dentition. Spontaneous correc-tion does not occur. • In cases of successful crossbite correction by Quad Helix or expansion plate appliances, both methods achieve similar long-term stability and the prognosis is favourable. • Despite active transverse expansion, the width of the maxilla in the former crossbite patient group never reached the mean maxillary width of the normal group. Paper IV • Quad Helix offers significant economic benefits over the ex-pansion plate appliance for correction of posterior crossbite. • Quad Helix has lower direct and indirect costs and fewer fail-ures needing re-treatment. • Even with full compliance, i.e. when only successful treatments are considered, expansion plate treatment is more expensive than Quad Helix treatment. Key conclusions and clinical implications For correction of posterior crossbite in the mixed dentition, the Quad Helix appliance is superior to the expansion plate in terms of clinical effectiveness and cost-minimization and is thereby the pre-ferred method of treatment. Both methods, provided that the out-come has been successful, show similar long-term stability.