Furcation grooves on the palatal aspect of the buccal roots of 35 maxillary
first premolars, randomly selected, were assessed and found to exist in 97
% of the sample. The buccal roots were sectioned into slices, 1 mm thick, a
nd morphometric horizontal and vertical measurements were taken by a Toolma
ker Microscope. The slice with the deepest invaginations served as the refe
rence plane. The deepest invaginations were found to be at a mean distance
of 1.18 mm from the bifurcation, with a mean depth of 0.4 mm, The canal had
a kidney-shaped appearance in cross-section, and the mean distance from th
e invagination to the canal wall was 0.81 mm. It is thus hazardous to use r
otary instruments for flaring these roots and any circular-shaped post spac
e preparation at this level is contraindicated, The outcome of such procedu
res might be root thinning, perforation, or vertical root fracture, thus ca
using a poor prognosis.