Preparing the S-Shape Canal: Does Coronal Enlargement Prevent Transportation?

Purpose: This study evaluated the effects of coronal enlargement files with different tapers, apical diameters, and heat treatments on canal transportation in standardized S-shaped simulated canals.
Methods: Sixty resin blocks with a 50° double curvature were assigned to four groups (n=15): UniGold Sx, UniBlue Sx, N1, and Control. All canals were prepared to size 25/.04 using the K7 system. Pre- and post-instrumentation images were superimposed in Fiji, and transportation was measured at five levels. ANOVA and Bonferroni tests were used (α=0.05).
Results: No significant differences were observed at the apical constriction. At 2 mm, coronal enlargement groups showed transportation opposite the furcation, whereas the control group showed transportation toward it (p<0.05). At 5 and 8 mm, the N1 group exhibited the least transportation (p<0.05). UniGold Sx showed the highest transportation at 11 mm (p<0.05).
Conclusion: Minimally invasive, flexible files reduced transportation in critical areas, while all forms of
coronal preparation improved apical shaping safety.

Keywords: Canal transportation, coronal enlargement, root canal preparation, S-shaped canal.