What is typically a sign that a sealant may fail?

A sign that a sealant may fail is visible contamination on the enamel surface. For a sealant to adhere properly, the tooth surface must be clean and free of debris, saliva, or any other contaminants that can interfere with adhesion. Contamination can prevent the sealant from forming a proper bond with the enamel, leading to premature failure of the sealant.

In contrast, excessive viscosity during application may affect the ease of application but does not directly indicate a risk of sealant failure. While poor bonding agent selection can influence the effectiveness of the sealant, it is less about current surface condition and more about the choice made prior to application. Inadequate lighting during application may hinder the operator’s ability to see the surface properly, but it does not directly contribute to the sealant's inherent adhesion properties. Therefore, visible contamination is the most direct indication that a sealant may be at risk of failing.