What is a contraindication for placing a sealant?

A tooth with a complete restoration is indeed a contraindication for placing a sealant. Sealants are designed to protect teeth that have natural grooves, pits, and fissures, which are susceptible to decay. However, if a tooth has already been completely restored—typically through a filling, crown, or other restorative procedure—it no longer has the same surface characteristics that sealants provide protection for. Therefore, placing a sealant on a tooth that is already restored would not be appropriate since the sealant would not adhere effectively or serve any purpose.

In contrast, other scenarios such as a recently cleaned tooth surface, a tooth with no visible pits and fissures, and a tooth that has been previously sealed do not present the same contraindication. A recently cleaned tooth is usually an ideal candidate for sealant application, as it allows for better adhesion. A tooth with no visible pits and fissures may not require a sealant, but it doesn’t preclude its potential placement. Lastly, previously sealed teeth can sometimes be re-sealed if necessary, depending on the condition of the existing sealant and the tooth's surface.