Int. J. Environ. Res. Public Health 2009, 6 2506 According to the second aim of this study, the validity and reproducibility of UniViSS on occlusal surfaces was tested. Histological validation revealed that 12 teeth (18%) showed no signs of demineralization, 30 teeth (46%) had a caries in the enamel (D1-2), 17 teeth (26%) showed a lesion limited to the outer half of the dentin (D3), whereas in six teeth (10%) caries had already spread into the inner half of the dentin (D4). After correlating the histological findings with UniViSS the following data were obtained for the caries detection level (D0 vs. D1-4): SE 100.0%, SP 58.3% and Az 0.841. For dentine caries detection (D0-2 vs. D3-4) the parameters were SE 62.5%, SP 97.6 and Az 0.816. The intra-examiner wK values/ coincident readings were found within a range between 0.90/ 93% (D1, D2) and 0.98/98% (J.K.); the inter-examiner reproducibility amounted to 0.89/91% (D2), 0.97/98% (D1) and 0.93/95% (J.K.). 4. Conclusions This manuscript describes the development and methodology of UniViSS. Firstly validity and reproducibility data for occlusal surfaces is presented. The development of UniViSS was mainly influenced by the results of previous epidemiological and diagnostic caries studies by the authors [2,9,10,12-14,21-23], the huge data base of high-quality photographs from caries lesions, the clinical experience of the authors as well as the empirical data obtained during the tests on practicability. Using this methodology, the inaccuracies of existing visual diagnostic systems mentioned in the introductory section were compensated. Another advantage worth stressing is the consistency of the criteria for occlusal and smooth surfaces, as well as for primary and permanent teeth. For smooth surfaces the system’s availability extends to the freely accessible vestibular and oral as well as to the approximal surfaces. It also enables the visual caries detection and diagnosis of caries-related cervical defects in older patients. This means that the system can non-restrictively be used in all age groups. After analyzing the diagnostic performance it can be concluded that the validity and reproducibility results are very encouraging. Considering the registered validity data in comparison to previously published results of different visual caries detection and diagnostic systems [4-6,8,24], the documented Az values for the overall caries detection level (0.84) and for the dentine caries detection level (0.82) are in the same range. According to our results the intra- and inter-examiner-reproducibility can be assessed as excellent after an extensive theoretical and practical training. The registered wK values were found to be in the same order of magnitude that was obtained for the visual criteria by Ekstrand et al. [3,8] or the ICDAS [5,6]. When reflecting of the methodology and potential of UniViSS for dental practice, clinical studies and epidemiological trials the new visual caries detection and diagnostic system allow a precise description of non-cavitated and cavitated caries lesions alike. To make examination data comparable UniViSS follows basic principles [1] and is considering most frequently used and validated criteria [3,5,6,8,20], too. In this context, UniViSS should be understood as an addition to existing methods, used to visually describe the clinical appearance of (non-)cavitated carious lesions as precise as possible. According to the authors, it is only possible under this assumption that (non-)cavitated lesions can be detected and diagnosed reliably, that the diagnostic performance of visual methods can be improved, that changes of carious lesions can be detected as part of a caries monitoring and that caries