Purpose: to examine the danger zone and to evaluate the effectiveness of filing technique in reducing perforation.
•n: 41 human mandibular 1st and 2nd molars ( Asians) mean curvature 25⁰ MD (10⁰ -42⁰)
•Hemi-section at the bifurcation level, examining only M root (MR). MD and BL radiographs of MR and curvature was measured using Schneider’s technique.
•Anticurvature filing was first introduced by AbuRass
• 2 groups (A: n=30 teeth; 60 canals; no canal preparation, B: n=11 teeth; 30 canals n=15 stepback tech (SB), n=15 anticurvature filing (AC)) •Anticurvature filing: preparation of the bulkier walls M,B,L walls and avoiding the furcal walls in 3:1 ratio (M,B,L : Furcal walls).
•Roots were sectioned at 5 and 8 mm level.
•Mesial canal wall was thicker than furcal wall although not significant; 20% thicker at 8 mm level and 14% thicker at 5 mm level (the canals are actually closer to the furcal area i.e canals are not perfectly centered) Table.1.
•There were no significant difference between AC and SB at the 5 mm level but significant with the 8 mm level in thickness of furcal wall (AC 41%, SB 56% thinner) Fig.3.36% perforation using SB due to 0.2-0.3 thickness at 8 mm level
after preparation of the root canals by both SB and AC filing techniques, significantly more dentine had been removed from the furcal Wall than the mesial wall of the root at the 8 mm level.