What percentage of mineral loss must occur before a carious lesion becomes visible on a conventional radiograph?

Conventional dental radiographs (periapical and bitewing) require approximately 40-50% demineralization of the tooth structure before a caries lesion becomes radiographically detectable. This is because the X-ray beam must traverse the lesion from multiple angles, and the remaining mineral density must differ sufficiently from healthy enamel or dentin to create a visible radiolucency. This significant threshold means that many early-stage caries lesions are not detectable radiographically and require clinical examination and other diagnostic tools (e.g., DIAGNOdent, transillumination). This limitation reinforces the importance of combining radiographic findings with clinical examination in caries diagnosis.