Students' perceptions of pre-clinical endodontic training with artificial teeth compared to extracted human teeth.

PURPOSE: Artificial teeth have several advantages in pre-clinical endodontics training. This study aimed to compare artificial resin teeth with extracted human teeth, from a student's perspective, during a pre-clinical undergraduate endodontic course for three consecutive academic years (2011-2014). METHODS: At the end of the course, students completed a questionnaire that included questions about their perceptions of the difficulty of artificial teeth vs. natural teeth and ranked the perceived advantages of artificial teeth. RESULTS: Participants expressed that all procedures, except obturation, were more difficult to perform on artificial teeth than on natural teeth, a result that was due to the hardness of the resin. They ranked the fairness and availability as the best advantages. CONCLUSION: Artificial teeth have multiple advantages but cannot replace natural teeth. The physical characteristics through the manufacturing material of artificial teeth should be enhanced to increase wider use and acceptance.

Cyclic fatigue analysis of twisted file rotary NiTi instruments used in reciprocating motion.

AIM: To evaluate the cyclic fatigue fracture resistance of engine-driven twisted file (TF) instruments under reciprocating movement. METHODOLOGY: A sample of 30 size 25, 0.08 taper NiTi TF instruments was tested in a simulated canal with 60˚ angle of curvature and a 3 mm radius. During mechanical testing, different movement kinematics were used at a constant speed, which resulted in three experimental groups (each group n = 10). The instruments from the first group (G1) were rotated until fracture occurred. The instruments in the second (G2) and third group (G3) were driven under reciprocating movement with different angles of reciprocation. The time of fracture for each instrument was measured, and statistical analysis was performed using one-way analysis of variance followed by Tukey's Honestly Significant Different test. RESULTS: Reciprocating movement resulted in a significantly longer cyclic fatigue life (P < 0.0001) when compared with continuous rotation. No difference was found between reciprocation 150° clockwise/30° counterclockwise (CW/CCW) and 30° CW/150° CCW. CONCLUSIONS: The reciprocating movement was associated with an extended cyclic fatigue life of the TF size 0.25, 0.08 taper instruments in comparison with conventional rotation.

Mechanical properties of nickel-titanium rotary instruments produced with a new manufacturing technique.

AIM: To investigate whether flexibility and cyclic fatigue resistance was increased for nickel-titanium instruments produced by a new manufacturing technique. METHODOLOGY: Forty K3 tip size 25, 0.06 taper (SybronEndo) nickel-titanium rotary instruments were randomly selected and divided into two groups (n = 20). One group served as control, being the commercially available instruments produced with a traditional grinding process (K3). The second group of instruments (K4 prototypes) were then subjected to a proprietary thermal treatment after the grinding process. Finally, each group was randomly divided into two subgroups of 10 instruments each, to perform the stiffness test and the cyclic fatigue test. All data were recorded and subjected to statistical evaluation using Student's t-test. Significance was set at the 95% confidence level. RESULTS: For the stiffness test, a statistically significant difference (P < 0.05) was noted between K3 and K4 prototype instruments. K4 prototype instruments were significantly more flexible when compared to K3 instruments (59.3 ± 4.3 vs. 98.1 ± 6.4 g cm(-1) ). For the cyclic fatigue test, a significant difference (P < 0.05) was noted between K3 and K4 prototype instruments. K4 prototype instruments demonstrated a significant increase in the mean number of cycles to failure (NCF) when compared to K3 instruments (1198 ± 279 vs. 542 ± 81 NCF). CONCLUSIONS: The new manufacturing technique resulted in the K4 prototype instruments having enhanced mechanical properties, compared to K3 instruments, manufactured with a traditional grinding process.