- "Are you all right?"
"I think I chipped a tooth. Did I chip a tooth? Am I bleeding?" - ―Teyla Emmagan and Dr. Rodney McKay[src]
Teeth are a type of biological structure used to break down food. They are part of the anatomy of humans and other organisms.
Overview
Tau'ri

Tau'ri can have molars called wisdom teeth. Sometimes they need to be removed. When John Sheppard had his removed, he was put on codeine for a full seven days. (SGA: "Conversion")
Wraith

While Wraith get their sustenance from the life force of others through their feeding hand, they do possess teeth and all the organs necessary to digest food. Eating this way provides adult wraith a moment of pleasure but it doesn't sustain them. (SGA: "Condemned", "Instinct", "The Queen")

This might be different for children Wraith. As when Ellia was young, she had been fed like a normal human child by Zaddik and that had seemed to suffice for a time. (SGA: "Instinct")
Unnatural

When Ellia mutated after taking the unfinished Iratus bug retrovirus, both of her hands contained small teeth-like structures which made her an excellent climber.[1] (SGA: "Instinct")

Michael's genetically engineered experiment, which combined various life forms, had teeth. (SGA: "Whispers")
The Goa'uld had a deadly biological weapon that utilized two fake hollow teeth. Inside each had a different biological organism similar to a virus that, after breaking the teeth, would combine and multiple exponentially, releasing themselves into the atmosphere. When Rya'c of Chulak was brainwashed by Apophis in 1998, he had these teeth, though they were removed before Rya'c could break them while on Earth. (SG1: "Family")