Class I furcation involvement is defined as what?

• A. Horizontal attachment loss greater than 3 mm but not through entire furcation
• B. Horizontal attachment loss less than 3 mm into furcation
• C. Through-and-through destruction
• D. No furcation involvement

Answer: (B)

Furcation involvement is graded by how far the horizontal bone loss extends into the space between the roots of a multirooted tooth. In Class I, the involvement is shallow: there is horizontal bone loss into the furcation, but it is less than 3 millimeters. There is no through-and-through defect, meaning the loss does not extend all the way between the buccal and lingual aspects of the furcation. This level of involvement can often be detected with a Nabers furcation probe and may not be evident on radiographs.

If the horizontal loss into the furcation were 3 millimeters or more, that would describe a different class, typically more advanced, where the defect may become more extensive or even through-and-through. If there were a through-and-through communication between the buccal and lingual sides, that would be a further class. If there is no furcation involvement at all, that would be described as no furcation involvement.