[Effect of different root canal file tapers on fracture strength of root canal wall].

PURPOSE: To compare the effects of different nickel-titanium rotary tapers on fracture strength of root canal and the application value of finite element analysis in root canal therapy.

METHODS

Twenty four mandibular premolars were selected and all crowns were removed. All samples were randomly divided into 4 groups: A, B, C and D. Group A and C were instrumented with Z-K3 nickel titanium file as 0.04 taper for root canal preparation. Group B and D were instrumented with Z-K3 nickel titanium file as 0.06 taper. Group C and D were sliced into 2 mm thick slices 3 times after root canal preparation. Two teeth were selected from group A and group B and scanned with micro-CT. The model was imported into different softwares to optimize. The assembly model was built and imported into ANSYS for finite element analysis. Universal testing machine and force bar were used to apply 100 N force to samples until fracture occurring at any place of tooth sample. The fracture load was recorded and comparative analysis was conducted.

RESULTS

The results of finite element analysis showed that the maximum stress of 0.04, 0.06 taper models was 138.88 MPa and 78.812 MPa, respectively. The average fracture load of group A, B was 490.12 N and 501.83 N, respectively. In group C and D, the maximum average fracture load was 93.61 N and 141.53 N, respectively. From the neck to the middle and then to the tip, the average fracture load of root canal decreased in turn.

CONCLUSIONS

For normal form mandibular premolars, the fracture strength of the root instrumented with 0.06 taper nickel titanium rotary file was significantly higher than that instrumented with 0.04 taper. Three dimensional finite element analysis could guide dentists to choose a suitable taper file in root canal treatment to reduce the incidence of root fracture.