The overall aim of this thesis was to evaluate methods used to identify individuals with increased risk of coronal caries lesion development. The specific aims were to:•evaluate the accuracy of different methods used to identify individuals with increased risk of developing dental coronal caries lesions (study I)•design and pilot a novel classification system for the assessment of caries lesion progression in bitewing radiography and to report rater agreement of the system (study II)•assess intra-individual differences in biofilm acid-tolerance between different tooth surfaces and inter-individual variation as well as stability of acid tolerance over time (study III)•assess diagnostic accuracy of two established methods and a candidate method to identify adolescents with increased risk of dental coronal caries lesion development (study IV).Study I comprised a systematic review of caries risk assessment methods, following methods were included for final analysis: previous caries experience, tests using microbiota, buffering capacity, salivary flow rate, dental plaque, dietary habits and sociodemographic variables. Assessment of risk of bias with the aid of Quadas-2 resulted in identification of methodological limitations concerning study design, test technology and reporting. Evidence for methods using previous caries experience and salivary mutans streptococci was low and evidence regarding other methods was lacking. The overall evidence on the validity of analysed methods used for caries risk assessment is limited. As methodological quality was low, there is a need to improve study design. In study II a classification system with drawings and text was designed to assess caries lesion progression in bitewing radiographs. Guidelines for Reporting Reliability and Agreement Studies, GRRAS were used to design and report the study. Pairs of posterior bitewing radiographs (baseline and 1-year follow-up) with different status concerning caries lesion progression were selected and 10 raters assessed the radiographs with the aid of the classification system. Seven raters repeated their assessments. Kappa for the interrater agreement of 10 raters assessing progression was 0.61, indicating substantial agreement. Corresponding intrarater agreement was substantial (kappa 0.66–0.82). This system can provide a common framework for clinical decision-making on caries interventional methods and patient visiting intervals. Scientifically, the system allows for a comparative analysis of different methods of prevention and treatment of caries as well as of different caries risk assessment methods.In study III dental biofilms were collected from supragingival approximal surfaces of canines and first premolars, second premolar and first molars, and between the central incisors of both jaws in adolescents at baseline, day 3, after 1 month as well as after 6- and 12 months for the approximal surfaces of second molars and first molars. After exposure to pH 3.5 for 2 hours, biofilm cells were visualized using LiveDead® BacLightTM staining and each sample was examined using an inverted confocal scanning laser microscope. Live bacteria (acid-tolerant) appeared green while dead (non acid-tolerant) bacteria appeared red. Images of the biofilm were compared with a scale (score 1-5) to assess the proportion acid-tolerant bacteria in each sample. A majority of the adolescents were assessed with low scores of biofilm acid tolerance. In 14 of 20 individuals, no differences were seen between the three dental sites. At 51 of total 60 sites, assessed score of acid tolerance at baseline was unchanged after one month. However, scores for acid tolerance changed over a 1-year period in 50% of the individuals. Results should be interpreted with caution because of the limitation in sample size. Acid tolerance of dental biofilm is a candidate method that may be implement in caries risk assessment methods. It needs to be scientifically evaluated in clinical prospective studies as a biomarker for caries development. For the purpose of study IV, the STARD-statement “Standards for Reporting of Diagnostic Accuracy” was implemented for design and reporting of the study. Adolescents, aged 12, visiting two public dental clinics were examined by visual/tactile examination and bitewing radiography of posterior teeth at baseline and after 1 year. Two established methods (previous caries experience and dentists’ risk assessment) and one candidate method (acid tolerance in dental biofilm) were applied with pre-specified thresholds. The reference standard comprised coronal caries lesion development after 1 year. Caries lesion progression occurred in 29% of the adolescents, mainly approximal lesions within enamel. Diagnostic test accuracy varies with thresholds of the index tests, reference standard and with different caries status and caries lesion progression. Most positive likelihood ratios for the methods were