In which type of interaction do both species benefit?

Mutualism  interaction do both species benefit?

Mutualism

This is because of these things

Bee on a spring flower collecting pollen and nectar

A honeybee moves from flower to flower. The honeybee benefits as it gathers nectar to make honey. The flower benefits from the transfer of pollen that sticks to the bee's feet as it moves from one flower to the next.

An oxpecker bird eats insects off of a cape buffalo

The oxpecker eats insects and parasites off of a cape buffalo. The oxpecker benefits by getting a meal, while the cape buffalo benefits from being cleaned of insects and parasites.

the answer to your question is tooth decay.