M Beerens

EFFECTS OF MI PASTE PLUS ® : A 3-MONTHS FOLLOW-UP 4 57 INTRODUCTION Changes of the enamel surface as a result of decalcification, or development of so called multiple white spot lesion (WSL) is by far the most important visible iatrogenic effect of orthodontic fixed appliance treatment (Wisth and Nord, 1977; Gorelick et al. , 1982; Øgaard et al. , 1988a; Øgaard et al. , 2004; Bishara and Ostby, 2008; Øgaard, 2008). The prevalence of WSL on at least one tooth surface of patients who undergo fixed appliance therapy has been found to vary from 4.9% (Gorelick et al. , 1982) to 97% (Boersma et al. , 2005). The incidence is higher in patients treated with orthodontic fixed appliance, than in non-orthodontic individuals (Zachrisson and Zachrisson, 1971). White spot lesions are defined as subsurface enamel porosities caused by an imbalance between demineralisation and remineralisation. When WSL are located on smooth surfaces they present as milky-white opacities (Bishara and Ostby, 2008). Demineralisation of enamel around brackets can be a very rapid process (Gorelick et al. , 1982; Øgaard et al. , 1988a) Frequent exposure to fermentable carbohydrates accelerates the rate of plaque accumulation and maturation, and leads to lower plaque pH and colonization of aciduric bacteria. Together this favours increased proportions and absolute numbers of Streptococcus mutans and Lactobacillus spp. in saliva and plaque (Scheie et al. , 1984; Rosenbloom and Tinanoff, 1991; Ahn et al. , 2007; Kim et al. , 2010). After removal of the fixed appliance, the numbers of S. mutans and Lactobacillus spp. decrease to the amounts and proportions observed before the orthodontic treatment without additional prophylactic measures (Rosenbloom and Tinanoff, 1991). With respect to remineralisation of WSL, removing the fixed appliance as an aetiological factor contributes to a favourable balance between demineralisation and re- mineralisation. This is observed especially in combination with good oral hygiene (Willmot, 2008). Clinically, it has been observed that these WSL can disappear (Backer, 1966). Nevertheless, post- orthodontic patients still have a higher prevalence of WSL when compared with untreated age-matched controls, even 5 years after the removal of the fixed appliance (Øgaard, 1989). Removal of the appliance appears to be insufficient to completely remineralise the softened enamel. A clinical trial performed at the Academic Centre for Dentistry (ACTA) department of Orthodontics using quantitative light-induced fluorescence (QLF) showed that natural repair was limited. The majority of WSL remained unchanged, while 10% had progressed in severity 6 months after debonding.