Final answer:
The best device to remove subgingival calculus on this client is a Gracey curette.
Step-by-step explanation:
The BEST device to remove subgingival calculus on this client would be a Gracey curette.
Unlike an ultrasonic scaler or a scaler, a Gracey curette has a curved, rounded blade that can effectively reach and remove calculus below the gumline without causing damage to the surrounding tissues.
A universal curette may be used for supragingival calculus removal, but it is not as effective for subgingival calculus.