Dentists are advised to use sterile water for patients with weakened immune systems and for those who undergo surgery where the gum line is cut.

BBC: Bacteria found in dentists' sprays

You should always introduce the floss at the top of the tooth, in the gum line, and bring it down, then remove it and find an unused length for the next tooth.

WSJ: How to Be a Better Flosser

Rather than just pulling the shears out, the surgeons decided to make an incision from his upper gum line on the right side of his upper lip to the anterior maxillary wall, which is in the middle of the cheek.

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