Experimental study on central location ability and clearance rate of three nickel-titanium instruments for root canal retreatment

Comparision of the central location ability and clearance rate of ProTaper retreatment, Fengdu O-file and M3-RT three kinds of nickel-titanium instruments and hand stainless instruments K-file, H-file. Observe the form of the root canal wall. To provide experimental basis and reference for the clinical application of nickel-titanium instruments for root canal retreatment.

40 simulated resin blocks with the same specification were randomly divided into four groups (n＝10). Each group was separately prepared with hand stainless instruments K-file and H-file (group A₁), ProTaper retreatment (group B₁), Fengdu O-file (group C₁), and M3-RT (group D₁). Using scanner to obtain the pre- and post-operative images and overlapping the images through Photoshop. Measuring the root canal inner and outer wall resin removal with Image J, compared the central location ability of the four group. A total of 60 mandibular single canal premolars extracted due to orthodontics were collected. The teeth were randomly divided into four groups (n＝15) after filling the root canal. Use hand stainless instruments K-file,H-file(group A₂), ProTaper retreatment(group B₂), Fengdu O-file(group C₂), M3-RT(group D₂) to remove the filling materials. The roots were longitudinally sectioned, and the image of the root surface was photographed under the 10 × magnification microscope. The software was used to trace the area of the root canal wall and residual root filling, and the root filling clearance rate of each group was calculated. Two teeth were randomly selected in each group and observed under scanning electron microscope.

Within 9 mm from the root tip hole, the central location ability of group B₁, C₁, D₁ was better than that of group A₁(P < 0.05). At 4 mm from the root tip hole, group D₁ has the best central location ability(P < 0.05). There was no difference of the four instruments at a distance of 10 mm from the root tip hole(P > 0.05). There were various degree of filling material remained in the root canal after the four groups of instruments for retreatment canal preparation. There was no significant difference between group B₂, C₂, D₂(P > 0.05), and both were higher than group A₂(P < 0.05). Scanning electron microscope observation results shown that the root canal wall prepared by group B₂, C₂, D₂ was more smooth and continuous than group A₂, and the residual filling material was less.

The central location ability of three kinds of nickel-titanium root canal retreatment instruments were significantly better than that of hand stainless instruments. ProTaper retreatment, Fengdu O-file and M3-RT three kinds of nickel-titanium root canal retreatment instruments showed good performance, the central location ability of M3-RT was slightly better. Nickel-titanium root canal retreatment instruments are more efficient than traditional hand stainless instruments in removing root fillings and the root canal wall after preparation is smoother and has good continuity.