"The Doctor", a 1967 short story by Theodore L. Thomas. You may have read it in one of these compilations. I read it in the anthology Alpha One (Robert Silverberg, ed.), which can be borrowed (for free but registration required) from the Internet Archive.
Not a dentist, a medical doctor:
When Gant first opened his eyes he thought for an instant he was back in his home in Pennsylvania. He sat up suddenly and looked wildly around in the dark of the cave, and then he remembered where he was. The noise he made frightened his wife and his son, Dun, and they rolled to their feet, crouched, ready to leap. Gant grunted reassuringly at them and climbed off the moss-packed platform he had built for a bed. The barest glimmerings of dawn filtered into the cave, and the remnants of the fire glowed at the mouth. Gant went to the fire and poked it and put some chips on it and blew on them. It had been a long time since he had had such a vivid memory of his old life half a million years away. He looked at the wall of the cave, at the place where he kept his calendar, painfully scratched into the rock. It had been ten years ago today when he had stepped into that molybdenum-steel cylinder in the Bancroft Building at Pennsylvania State University. What was it he had said? "Sure, I'll try it. You ought to have a medical doctor in it on the first trial run. You physicists could not learn anything about the physiological effects of time travel. Besides, this will make history, and I want to be in on it."
With no real dentists around, he also practices dentistry:
He walked along the foot of the cliffs, looking in on the caves. In one he found a woman with a swollen jaw, in pain. She let him look in her mouth, and he saw a rotted molar. He sat down with her and with gestures tried to explain that it would be painful at first if he removed the tooth, but that it would soon be better. The woman seemed to understand. Gant took up a fresh branch and scraped a rounded point on one end. He picked up a rock twice the size of his fist, and placed the woman in a sitting position with her head resting on his thigh. He placed the end of the stick low on the gum to make sure he got the root. Carefully he raised the rock, knowing he would have but one try. He smashed the rock down and felt the tooth give way and saw the blood spout from her mouth. She screamed and leaped to her feet and turned on Gant, but he jumped away. Then something struck him from behind and he found himself pinned to the ground by two men sitting on him. They growled at him and one picked up a rock and the stick and smashed a front tooth from Grant's mouth. Then they threw him out of the cave.
At the end Gant buries his son, not his wife:
He stared down in the dim light of the cave. It ws Dun, and he was dead. His head had been crushed. Gant cried out and leaned against the wall. He knelt and hugged Dun's warm body to him, pushing his wife aside. He pressed his face into the boy's neck and thought of the years that he had planned to spend in teaching Dun the healing arts. He felt a heavy pat on his shoulder and looked up. His wife was there, awkwardly patting him on the shoulder, trying to comfort him. Then he remembered the woman who had killed his son.
