Which of the following conditions would not be advised for sealant application?

Sealant application is a preventive measure designed to protect the occlusal surfaces of teeth from decay by providing a physical barrier. Healthy teeth are ideal for sealant placement because they have not yet developed any caries or decay, making them prime candidates for preventive care.

Interproximal lesions indicate that there is already some degree of carious activity between teeth, which suggests that the tooth is not healthy enough to receive a sealant. In this case, the presence of decay would necessitate restorative treatment instead of a sealant, as covering the lesion with a sealant could trap bacteria and exacerbate the condition.

In terms of minor surface stains or occasional sensitivity, these conditions do not preclude the application of sealants. Minor stains can often be cleaned, and sensitivity should be evaluated on a case-by-case basis but is typically not a barrier to sealant application. Therefore, the presence of interproximal lesions is the key factor that disqualifies a tooth from receiving a sealant.