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.