FURCATION INVOLVEMENT

A furcation is the branching point
 between roots on a multirooted tooth. 
In the absence of disease, furcations
cannot be clinically probed because
 they are filled in with bone and 
periodontal attachment. With advancing
 periodontal disease, however, attachment
 loss and bone loss may reach a furcation 
area resulting in a furcation involvement.28,29 
Pockets that extend into the furcation create
 areas with difficult access for the dentist

 and dental hygienist to clean during regular
 office visits, and are a real challenge for
 patients to reach and clean during
their normal home care. Therefore, these areas of
furcation involvement readily accumulate soft plaque
deposits and mineralized calculus .
These deposits frequently become
impossible to remove and may provide a pathway for
periodontal disease to continue to progress.
Initially, there may be an incipient (initial or beginning)
furcation involvement. As disease progresses into
the furcation (interradicular) area, attachment loss and
bone loss will begin to progress horizontally between
the roots. At that point, a furcation probe (such as a
Nabor’s probe with a blunt end and curved design) can
probe into a subgingival furcation area. It can be used
to detect the concavity between roots. The first sign of
 detectable furcation involvement is termed
grade I and can progress to a grade II involvement
when the probe can hook the furcation roof (the part
of the root forming the most coronal portion of the furcal
area). In the most extreme circumstances, the furcation
 probe may actually extend from the furcation of one tooth
 aspect to the furcation on another tooth aspect.
 This is referred to as athrough-and-through (grade III) furcation involvement . 
(A summary of the grades of furcationinvolvement 
It is important to remember where to insert a probe in
order to confirm furcation involvement .
 Recall that mandibular molar furcations are
located between mesial and distal roots near the middle
of the buccal surface (midbuccal) and middle of the lingual
surface (midlingual)