The challenges of validating diagnostic methods and selecting appropriate gold standards.

Caries diagnostic methods are usually methods for caries lesion detection and measurement. Caries lesions occur on a continuous scale of tissue damage, from subclinical surface changes to macroscopic cavities reaching the pulp. Any change of a lesion on this continuous scale offers the opportunity for the diagnosis of disease activity or remission. Research aimed at remineralizing agents may focus on lesions that are amenable to remineralization, and select a method that will measure small changes in early lesions. General caries management strategies depend on detecting all stages of lesion development, and methods covering early to late stages are preferred. This paper addresses some methodological issues in validating caries diagnostic methods. The available gold standards for caries lesions are discussed, with their suitability in different applications, and their "validity" as far as it is known or can be inferred. The gold standards are compared as far as their measurement of lesion parameters and reproducibility is concerned. Tentative conclusions are formulated, and recommendations for future research are given.