Anterior crossbite with functional shift also called pseudo Class III isa malocclusion in which the incisal edges of one or more maxillaryincisors occlude with the incisal edges of the mandibular incisorsin centric relationship: the mandible and mandibular incisors arethen guided anteriorly in central occlusion resulting in an anteriorcrossbite.Early correction, at the mixed dentition stage, is recommended,in order to avoid a compromising dentofacial condition whichcould result in the development of a true Class III malocclusionand temporomandibular symptoms. Various treatment options areavailable. The method of choice for orthodontic correction of thiscondition should not only be clinically effective, with long-termstability, but also cost-effective and have high patient acceptance, i.e.minimal perceived pain and discomfort. At the mixed dentition stage,the condition may be treated by fixed (FA) or removable appliance(RA). To date there is insufficient evidence to determine the preferredmethod.The overall aim of this thesis was therefore to compare andevaluate the use of FA and RA for correcting anterior crossbitewith functional shift in the mixed dentition, with special referenceto clinical effectiveness, stability, cost-effectiveness and patientperceptions. Evidence-based, randomized controlled trial (RCT)methodology was used, in order to generate a high level of evidence.The thesis is based on the following studies:The material comprised 64 patients, consecutively recruited fromthe Department of Orthodontics, Faculty of Odontology, Malmö University, Sweden and from one Public Dental Health Service Clinicin Malmö, Skane County Council, Sweden. The patients were nosyndrome and no cleft patients. The following inclusion criteria wereapplied: early to late mixed dentition, anterior crossbite affecting oneor more incisors with functional shift, moderate space deficiency inthe maxilla, no inherent skeletal Class III discrepancy, ANB angle>0º, and no previous orthodontic treatment. Sixty-two patients agreedto participate and were randomly allocated for treatment either withFA with brackets and wires, or RA, comprising acrylic plates withprotruding springs. Paper I compared and evaluated the efficiency of the two differenttreatment strategies to correct the anterior crossbite with anteriorshift in mixed dentition. Paper II compared and evaluated thestability of the results of the two treatment methods two years afterthe appliances were removed. In Paper III, the cost-effectiveness ofthe two treatment methods was compared and evaluated by costminimizationanalysis. Paper IV evaluated and compared the patient´sperceptions of the two treatment methods, in terms of perceived pain,discomfort and impairment of jaw function. The following conclusions were drawn from the results:Paper I• Anterior crossbite with functional shift in the mixed dentitioncan be successfully corrected by either fixed or removableappliance therapy in a short-term perspective.• Treatment time for correction of anterior crossbite withfunctional shift was significantly shorter for FA compared toRA but the difference had minor clinical relevance. Paper II• In the mixed dentition, anterior crossbite affecting one ormore incisors can be successfully corrected by either fixedor removable appliances, with similarly stable outcomes andequally favourable prognoses.• Either type of appliance can be recommended. Paper III• Correction of anterior crossbite with functional shift usingfixed appliance offers significant economic benefits overremovable appliances, including lower direct costs formaterials and lower indirect costs. Even when only successfuloutcomes are considered, treatment with removable applianceis more expensive. Paper IV• The general levels of pain intensity and discomfort were lowto moderate in both groups.• The level of pain and discomfort intensity was higher for thefirst three days in the fixed appliance group, and peaked onday two for both appliances.• Adverse effects on school and leisure activities as well asspeech difficulties were more pronounced in the removablethan in the fixed appliance group, whereas in the fixedappliance group, patients reported more difficulty eatingdifferent kinds of hard food.• Thus, while there were some statistically significant differences between patients´ perceptions of fixed and removableappliances but these differences were only minor and seemsto have minor clinical relevance. As fixed and removableappliances were generally well accepted by the patients, bothmethods of treatment can be recommended. Key conclusions and clinical implicationsFour outcome measures were evaluated: -success rate oftreatment, treatment stability, cost-effectiveness and patientacceptance, which is important from both patient and caregiver perspectives. It is concluded that both methods have highsuccess rates, demonstrate good long-term stability and are wellaccepted by the patients. Treatment by removable appliance isthe more expensive alternative. Thus, in the studies on whichthis thesis is based, fixed appliance emerges as the preferredapproach to correction of anterior crossbite with functionalshift in the mixed dentition.