Which of the following is a commonly used instrument in endodontics?

In endodontics, the primary goal is to treat the inside of the tooth, specifically the pulp and root canals. A file is a critical instrument used in this specialty. Endodontic files are designed to clean and shape the canals by removing infected pulp tissue and debris while allowing for the proper preparation of the canal for filling and sealing. Files come in various sizes and tapers to accommodate different canal anatomies, making them indispensable for ensuring the success of root canal treatments.

The handpiece is useful in many dental procedures, but it is not specific to endodontics per se, as it is utilized across various disciplines for drilling and cutting. The prophy cup is used primarily for coronal polishing, which is not related to endodontics, while a scaler is used for removing calculus and plaque from tooth surfaces and is more relevant in periodontal treatments rather than endodontic procedures. Thus, the file stands out as the essential tool specifically employed in endodontic treatments.