2501 Int. J. Environ. Res. Public Health 2009, 6 1. Introduction Visual caries detection and diagnosis is a key area for each dental practitioners, epidemiologists, teachers and scientists. While the application of the WHO´s DMF index [1] as a basic oral health measure will continue, due to its worldwide acceptance, its convenience and the possibility to compare past dental data with future findings, due to their high frequency there is a strong need to consider non-cavitated caries lesions as a relevant dental health indicator [2]. As such lesions will not be registered with the DMF index, new and more precise visual caries detection and diagnostic methods should be used to record the overall dental health status of a patient. Recently introduced diagnostic systems, e.g., the criteria by Ekstrand et al. [3], Nyvad et al. [4] and the ICDAS (International Caries Detection and Assessment System) group [5,6], have included non-cavitated caries lesions, but classify the caries process with only a few criteria [5,6]. However, due to the fact that the clinical appearance of carious lesions is complex, a limited set of criteria seems to be unlikely to describe the clinical appearance as precisely as possible. The ICDAS II criteria do no longer, for example, distinguish between white and brown discolorations [5,6], which, in fact, provide important information about lesion activity [7] and are essential for comprehensive caries monitoring in longitudinal studies. The previously used differentiation according to Ekstrand et al. [3,8] nevertheless proved useful and practicable in own investigations [9]. Further, the classification of lesions with both white opacities and brown discolorations on the other hand was difficult, as was distinguishing precisely between brown discolorations and microcavities. These clinical experiences, as well as the fact that adjunct diagnostic methods, e.g., laser fluorescence measurements, electrical resistance measurements and quantitative light-induced fluorescence measurements do not perform as satisfactorily on non-cavitated occlusal surfaces as was hoped [10-14] constitute the main drivers for the development of the Universal Visual Scoring System (UniViSS). Furthermore, the system should compensate for inaccuracies of existing scoring systems, fulfill the current requirements for caries detection and diagnostic methods as well as be adjustable [15]. Hence the first aim of the present work was to describe the development and methodology of UniViSS for occlusal and smooth surfaces in primary and permanent teeth. Our second aim was to analyse the validity and reproducibility of UniViSS on occlusal surfaces for the first time as both issues are of clinical importance to verify the potential of this new visual caries detection and diagnostic system on the most caries susceptible sites. 2. Material and Methods 2.1. Selection of the Diagnostic Criteria The methodical development of UniViSS took into consideration basic diagnostic principles and well-accepted caries detection and diagnostic criteria, e.g., WHO basic methods [1], the criteria given by Ekstrand et al. [3], Nyvad et al. [4], as well as the recently introduced ICDAS criteria [5,6]. Furthermore, Ismail’s [16] systematic review on visual caries detection and diagnostic methods provided valuable information. This means that UniViSS uses clinically accepted and validated criteria such as white and brown opacities, microcavities, occurrences of enamel breakdowns and grey