Thank you for reaching out to us.

The halacha is that there should be no barrier (chatzitzah) between one’s body and the mikveh waters. Food residue on the teeth would be such a barrier.

At the same time, the mikveh waters do not have to be in actual contact with inner surfaces of the body, such as the inside of the mouth. Rather, the water must have the theoretical potential to reach these inner surfaces, if they were exposed. A foreign body stuck on a tooth, or between teeth, would eliminate that potential.

For these reasons, the teeth are cleaned prior to immersion, and during immersion the lips should be lightly closed but not tightly clenched.

Please let us know if we can be of further assistance.