The aim of the present study is to evaluate the efficacy of a novel fluoride varnish (NFV) in preventing white spot lesion development in adolescents during and after treatment with fixed orthodontic appliances.

The study will employ a double-blind, randomized placebo-controlled design with two parallel groups. The intervention will start at onset of the fixed appliances and will be finalized one year after debonding. The primary outcome will be incidence of white spot lesions on the labial surfaces of the maxillary incisors, canines and premolars, as assessed from high-resolution digital photos. The secondary outcome is the prevalence of WSLs at debonding.

During the course of the orthodontic treatment, the patients are regularly checked every 6th week. At the end of each such occasion, the clinical staff will apply either the test or the placebo varnish with a small brush in a thin layer around the base of the braces on the maxillary teeth.

The pre- and post-treatment photos are projected on a screen (Hewlett Packard ProBook 6650b, Palo Alto CA, USA) in a dark room and the incidence and severity of enamel demineralization will be registered independently by two experienced and calibrated orthodontists according to the index of Gorelick et al. (1982).

Inclusion Criteria:

• The inclusion criterion is a scheduled treatment with fixed maxillary appliances according a standard straight-wire concept (McLaughlin et al., 2001) during a period of at least 12 months

Exclusion Criteria:

• In the event of long-term prescriptions of general antibiotics during the course of the study, this should be recorded separately