Final answer:
Reamers are instruments used to remove dentin and increase the size of the canal in dentistry.
Step-by-step explanation:
The instrument used to remove dentin and smooth and increase the size of the canal in dentistry is the reamer. Reamers are dental instruments that have multiple cutting edges and helical flutes to efficiently remove dentin during root canal treatment. They come in various sizes and shapes to suit different canal shapes and sizes.