Evaluation of the preparation of the coronal part of the mesial canals of lower molars.

Canal entrances can be flared using specific, low speed, continuously rotating Ni-Ti instruments. Two such instruments were evaluated for their capacity to flare the canal entrance while respecting the initial canal axis. Lower molars (n = 20) with two distinct mesial canals were prepared to within 2.5 mm of the pulp chamber floor using Bramante's technique. Canal entrances were flared with a QUANTEC FLARE LX or an ENDOFLARE. They both had a 0.12 taper and a #25 tip diameter. The instruments were first inserted in the canals using an axial movement and then withdrawn with a selective circumferential brushing action. Photographs taken before and after each preparation were compared. No ledging or significant modification of the working length was noted. The centre of mass was displaced on average by 0.138 mm with no brushing action and 0.274 mm with brushing action. In most cases (87.5%), the centre of mass was displaced mesially. The two instruments behaved in an identical mode, both before (p = 0.3497) and after (p = 0.9304) the brushing action. Ni-Ti flaring instruments can be used to flare the canal entrance with little displacement of the initial canal axis, even when a brushing action is used.