M Beerens

11 GENERAL INTRODUCTION 1 GENERAL INTRODUCTION AND OUTLINE OF THE THESIS Orthodontics Orthodontics and dentofacial orthopaedics is a specialty field of dentistry that deals primarily with the diagnosis, prevention and correction of malpositioned teeth and the jaws ( Mosby’s Medical Dictionary , 2012). Malocclusions may cause problems with the oral function, for example temporo-mandibular joint dysfunction, mastication, swallowing and speech problems. Greater susceptibility to trauma, periodontal disease and tooth decay are also related to malocclusions (Proffit et al. , 2013). However, the principal objective for most patients seeking orthodontic treatment is to achieve a detectable improvement in their dentofacial appearance while their secondary goal of treatment is an oral health benefit (Ackerman, 2010). Therefore, most orthodontic patients are treated for esthetic reasons, with only a small number of patients receiving treatment for primarily a medical or dental indication (van der Kaaij et al. , 2015). Orthodontics and white spot lesions Three main types of appliances are used in orthodontic therapy: active, passive and functional. These can be fixed or removable. Particularly fixed active appliance treatment has become an integral part of modern orthodontics (Graber et al. , 2011). Unfortunately, this type of treatment can cause adverse effects. Among these, white spot lesions (WSL) are prominent. These lesions have a negative effect on the esthetic outcome of orthodontic treatment (Gorelick et al. , 1982). These WSL manifest themselves as subsurface enamel porosities that might progress into carious lesions and are therefore a problem of clinical relevance. The overall prevalence of WSL in orthodontic patients was reported between 2% and 97% (Boersma et al. , 2005; Chapman et al. , 2010; Julien et al. , 2013). The highest incidence occurs on the maxillary lateral incisors followed by the maxillary canine, premolar, and central incisors, respectively (Chapman et al. , 2010). WSL are the result of prolonged accumulation of bacterial plaque on the enamel surface adjacent to the fixed appliances (O’Reilly and Featherstone, 1987), commonly due to inadequate oral hygiene (Chapman et al. , 2010), and a frequent intake of carbohydrates (Feyerskov and Kidd, 2008; Maltz et al. , 2017), resulting in a disbalance between remineralization and demineralization with