Final answer:
A dental assistant's stool has two items not found on the operator's stool: armrests and foot ring.
Step-by-step explanation:
A dental assistant's stool has two items not found on the operator's stool. These items are armrests and foot ring. Armrests provide support and comfort for the dental assistant's arms, while a foot ring helps them maintain proper posture by allowing their feet to rest at a comfortable height.