Unilateral posterior crossbite (UPC) with functional shift is one ofthe most common malocclusions in mixed dentition. Left untreated,it may cause long-term effects on the growth and development of thejaws and teeth. Early orthodontic intervention is usually undertakento correct the condition at the primary or mixed dentition stage.Quad-helix (QH) or removable expansion plates (EP) are commontreatment alternatives to correct crossbites and treatment ofcrossbite may consume a relatively large part of the total resourcesin orthodontic care. In Sweden the treatment can be performed eitherin specialist orthodontic clinics or in general dentistry. The role ofthe orthodontist in general dental care is essential in diagnostics andtreatment planning, whereas general dentists may often provide apart of the treatment after consultation with, or under the supervisionof, an orthodontist. Economic evaluations have become an integral component of healthservices. The main reason is that resources within the health sector(personnel, time, facilities, equipment, and knowledge) are limited.Nevertheless, studies comparing the costs of orthodontic treatmentsperformed in general versus specialist dentistry are virtuallynon-existent.To date there are no studies evaluating the oral health related qualityof life (OHRQoL) in children with unilateral posterior crossbite. Itis thus important to analyse and compare the OHRQoL betweenchildren with and without malocclusions (children with normalocclusion). When treatment effects of unilateral crossbite correction have beenassessed, most studies have used two-dimensional evaluations suchas linear measurements. However, orthodontic treatment effectsincluding crossbite correction may, if possible, be described in allthree planes. There are no studies in the literature that have explicitlyinvestigated the three-dimensional treatment effects of unilateralcrossbite correction between different appliances and, in this context,related the treatment changes to growth changes associated withuntreated subjects with unilateral posterior crossbite as well as insubjects with normal occlusion and with no or mild orthodontictreatment need. The research questions addressed in this thesis originate fromidentified knowledge gaps and clinical needs in orthodontic care,and to provide as high clinical evidence as possible a multi-centrerandomised control trial (RCT) has been performed as well as acontrolled trial regarding comparisons and the impact differentmalocclusions may have on OHRQoL.The results are expected to be beneficial for the patients who willbe offered the most widely accepted and effective treatment, which isof importance for the dentists for decisions as to which treatment willgive the best outcome, and beneficial for both dental care providersand society in care planning and the allocation of resources.Therefore, this thesis was based on four studies: Paper I: a systematic literature review was undertaken to answer thefollowing questions:• Are there any articles regarding health economics in orthodonticsand is it possible to make any conclusions from thearticles?The literature search spanned from January 1966 to September2014 and was later supplemented and extended to April 2019.Paper II: the aims were to investigate:• The OHRQoL using the Child Perceptions Questionnaire(CPQ8-10) in 93 children with unilateral posterior crossbite,71 children with excessive overjet and 65 children with normalocclusion with no or mild orthodontic treatment need. Paper III and IV: these two papers originated from a multi-centreRCT. The aims were to investigate:• Clinical effectiveness and cost-analysis in specialist and generaldentistry (Paper III)• Three-dimensional evaluations of crossbite correction (PaperIV)Key findings in Paper I and the supplementary search:• Few orthodontic studies have presented both economic andclinical outcomes. There is currently insufficient evidence availableabout the health economics of orthodontic interventions.• Further studies are still warranted and preferably using thesame clinical outcomes. Key findings in Paper II• Children with excessive overjet reported significantly lowerOHRQoL compared to children with unilateral posteriorcrossbite or normal occlusion.• The children generally reported low CPQ scores that imply anoverall fairly good OHRQoL.Key findings in Paper III• Treatment of unilateral posterior crossbite in mixed dentitionis recommended to be performed by a specialist orthodontistusing the quad-helix appliance since the quad-helix treatmentperformed in specialist orthodontic clinics had the highest costeffectiveness. Key findings in Paper IV• Crossbite children had, before treatment, significantly smallerpalatal surface and volume than normal control children.• After treatment, there were no significant differences betweenthe treatment groups and the normal group, which impliesthat the palatal surface and projection area together with thepalatal shell volume for the treatment groups and the normalgroup were equivalent. Conclusions and clinical implications:With a superior success rate and cost-effectiveness, it is concludedthat treatment of unilateral posterior crossbite in mixed dentition isrecommended to be performed by specialist orthodontists using thequad-helix appliance.The unilateral posterior crossbite correction resulted in a normalisationof the occlusion, palatal area and volume.

Class II malocclusion with excessive overjet is one of the most common malocclusions among children and adolescents. In addition to increasing the risk for dental trauma, the malocclusion can also be related to bullying due to the prominent maxillary incisors. The treatment for a Class II malocclusion can be initiated at different ages and with different treatment strategies, but the treatment timing has often been, and still is, discussed within the orthodontic profession and literature. Research reports that an early treatment approach, initiated in mixed dentition and often including an additional phase of treatment in permanent dentition, reduces the incidence of dental trauma. Otherwise, no differences in treatment effects have yet been seen between treatment that is started early in mixed dentition or treatment initiated later in permanent dentition. 

During the last decades, there has been an increased focus on patient-reported outcomes within orthodontic research. The patient perspective and economic evaluations of performed treatment are areas where knowledge gaps can be found in the available research. 

This thesis is based on four studies. The studies were designed with high level of methodology and validity as a priority and with the objective to identify and address knowledge gaps related to the impact of Class II malocclusion with excessive overjet and a subsequent early treatment with headgear activator. Firstly, a systematic review addressing treatment effects was performed. This was followed by the implementation of two randomised controlled trials (RCTs) with the aims to evaluate treatment effects and self-perceived oral health-related quality of life (OHRQoL) as well as the cost associated with treatment. In addition, a clinical controlled trial was performed to assess the self-perceived OHRQoL for children with Class II malocclusion with excessive overjet, and compare to children with unilateral posterior crossbite or normal occlusion with no or mild orthodontic treatment need.  

The papers referred to in this thesis:  

Paper I. A systematic literature review performed to evaluate the evidence supporting early treatment (before the age of 10) of Class II malocclusion. The search included four data bases and spanned from January 1960 to October 2017.  

Paper II. A clinical controlled multicenter trial with the objective to investigate the OHRQoL among 9-year-old children in mixed dentition and to compare the self-perceived OHRQoL by the use of the Child Perceptions Questionnaire (CPQ). Evaluation and comparisons were made for children with Class II malocclusion with excessive overjet (EO), children with unilateral posterior crossbite (UPC), and children with normal occlusion (NO) presenting with no or mild orthodontic treatment need.  The sample consisted of 229 children, sourced from 19 Public Dental Service Clinics in Sweden and covering a range of demographic areas.

A single centre RCT designed to evaluate the effects of headgear activator treatment and the associated costs forms the basis of the final two papers: 

Paper III. The effects of early headgear activator treatment was compared to an untreated control group. The sample consisted of 60 children presenting with a Class II malocclusion with excessive overjet. Primary outcome was the reduction of overjet and overbite as well as effects regarding oral health-related quality of life, lip closure, incidence of trauma, and skeletal changes.

Paper IV. The costs and treatment effects of headgear activator treatment started in the mixed or late mixed dentition was registered and compared. The sample consisted of 51 children starting treatment at 9 or 11 years of age. The primary outcome measure was comparison of the treatment costs between the two groups. Secondary outcomes were comparisons of oral health-related quality of life, dental and skeletal treatment effects, lip closure, and trauma incidence. 

The following conclusions were drawn: 

• There is medium to high level of evidence, depending on treatment appliance, that early treatment reduces overjet and improves antero-posterior skeletal relationship, but currently, insufficient evidence is available regarding the effects of early treatment on OHRQoL, incidence of trauma, soft tissue profile, or treatment-related costs. There is a knowledge gap with respect to long-term outcome and the stability of early treatment.
• Children with Class II malocclusion with excessive overjet report significantly lower self-perceived OHRQoL compared to children with unilateral posterior crossbite or normal occlusion, with the domains of social and emotional well-being being most affected. The children in all three groups reported generally low CPQ scores, which implies an overall fairly good self-perceived OHRQoL.
• Early treatment with headgear activator was successful in reducing overjet and correcting molar relationship. Early treatment did not result in any significant difference regarding self-reported OHRQoL, lip closure, or incidence of trauma when compared to the untreated control group.
• The costs associated with headgear activator treatment, as well as the treatment effects, were equivalent regardless of whether treatment was started at 9 or 11 years of age. The most pronounced treatment effects were reduction of overjet and correction of molar relationship, whereas the treatment effects regarding OHRQoL, lip closure, and trauma incidences were found to be modest.
• With costs and treatment effects being equivalent, an early treatment approach can be advocated to enhance trauma prevention.