What is the main concern when placing sealants on teeth with carious lesions?

The primary concern when placing sealants on teeth with carious lesions is that bacteria may remain encapsulated under the sealant. This is significant because if carious lesions are present, it indicates that there is decay and potential bacterial activity within the tooth structure. When a sealant is applied over these affected areas, it can create a barrier that traps bacteria, preventing them from being removed or treated. This encapsulation can lead to further decay, as the bacteria continue to produce acids that can worsen the carious lesion over time.

The other concerns, while relevant in broader contexts, do not represent the main issue with sealant placement over carious lesions. For instance, issues with adhesion and discoloration are important for the integrity and aesthetic of the sealant but do not have the same immediate implications for oral health as the encapsulation of bacteria. Allergic reactions are rare and generally not a significant risk associated with sealants compared to the consequences of sealing over active decay.