AbstractThe purpose of this investigation was to histologically determine the position of the periodontal probe tip when probing the deepest in terra dicular pocket depth in grade II and III facial molar furcation sites. Facial furcation pockets (5.8 mm+ 1.3) were probed with a pressure‐sensitive probe set at 50 g pressure. The probe tip was attached to the tooth with an acid etched composite resin. Surgical block biopsies were removed, fixed, decalcified and processed for histological sectioning. Buccolingual serial sections (6 μ) were cut from 9 biopsies and apicocoronal serial sections were cut from 3 biopsies. The sections were histometrically analyzed. The probe tip penetrated the inflamed furcation connective tissue an average depth of 2.1 mm (±0.6), The probe tip was located 0.4 mm (± 1.4) apical to the crest of the interradicular bone. The % of inflammatory cell infiltrate in the connective tissue (ICT) around the probe tip was 56% (± 15%). There was no correlation between the % of ICT and the depth of probe penetration. This investigation demonstrated that probing of untreated facial molar furcation sites does not measure the attachment level of the interradicular root surfaces, but rather records the depth of probe penetration into the inflamed furcation connective t