What symbiotic relationship is the nile crocodile and Egyptian plover?

A mutualistic relationship, that is, both species benefit. The bird gets food, and the crocodile gets its teeth cleaned.

The Egyptian plover hops right into the open mouth of the Nile crocodile to remove parasites. After the job is done, whether the crocodile is hungry or not the bird always leaves unharmed.

This symbiotic relationship is actually not proven to be factual at all.