[In vitro study of shaping ability of single-file techniques in curved canals]

To compare the shaping quality in curved canals of two single-file technique systems with other two traditional full-sequential systems.

Eighty mature molar canals with the curvature between 20 and 45 degrees were randomly divided into four groups. Specimens in each group were prepared to size 25 at working length using A (Reciproc), B (OneShape), C (MTwo) and D (Revo S), respectively. Each canal was scanned by micro-computed tomography before and after preparation. Parameters including changes in dentine volume, percentage of uninstrumented area, degree and tendency of transportation were analyzed. The operating time was also recorded.

In full canal length, there was no difference in canal dentine removal, instrumented percentage and transportation degree among four groups (P > 0.05). In the apical 4 mm region, group A removed more dentine [(2.14±0.76) mm(2) of canal surface area and (0.38 ± 0.15) mm(3) of canal volume] than groups B and C(P < 0.05). At 1 mm level, median of transportation degree of group A was 0.05 (0.03)mm, which was smaller than other groups (P < 0.05). Groups A and B took (86.3±24.6) s and (85.9±21.3) s, while groups C and D took (147.4±28.3) s and (126.3±27.7) s srespectively to finish preparation. Single file techniques were significantly faster than the two full-sequential systems (P < 0.01).

Compared with the continuous rotary systems, the reciprocating single-file system A showed better apical shaping ability. Both single-file techniques were more efficient than full-sequential systems for curved canal preparation. Single-file techniques appear to be the effective and efficient method for curved canal preparation.