Which dental hygiene task involves etching enamel surfaces?

The task that involves etching enamel surfaces is applying pit and fissure sealants. When sealants are applied, the dentist or dental hygienist prepares the tooth by etching the enamel with a mild acidic solution. This process creates small microporosities in the enamel, allowing the sealant resin to bond more effectively to the tooth surface. This is crucial for the longevity and effectiveness of the sealant, as it helps prevent decay in the grooves and pits of the teeth, particularly in molars.

The other tasks listed do not involve this etching process. Taking radiographs focuses on capturing images of the teeth and surrounding structures for diagnostic purposes and does not alter the enamel. Adjusting dental crowns involves the reshaping of existing crowns for a better fit or comfort but does not require etching enamel. Providing local anesthesia is a numbing process that facilitates various dental procedures but does not involve any physical changes to the enamel surface. Thus, the application of pit and fissure sealants is the only task among the options listed that requires etching enamel.