The purpose of this study was to evaluate the transportation produced at the apical foramen by the use of stainless steel and nickel-titanium K-files #10, #15, #20, and #25 as a patency file. Thirty human maxillary lateral incisors were transversally cut at 4 mm from the apex and mounted in square pieces of silicone with special marks to ensure repositioning of the specimens. The specimens were randomly divided in two equal groups of 15. In group A, stainless steel K-files #10, #15, #20, and #25 were used as a patency file. In group B, a stainless steel K-file #10 followed by nickel-titanium K-files #15, #20, and #25 were used as in group A. Sodium hypochlorite was used as the irrigating solution. Photographic slides of the apical foramen of each specimen before instrumentation and after the use of each file size were taken. The photographic slides of each specimen were mounted in slide mounts, projected onto the same drawing paper, and superimposed according to the peripheral shape of the root. Transportation of the apical foramen was determined comparing the five drawings of each specimen. Transportation was detected in 18 of the 30 specimens; 9 in group A and 9 in group B. No statistically significant differences were seen between groups (p = 1.00).

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Forty extracted maxillary central incisors were instrumented at the working length to a #50 file. The roots were sectioned transversely with a diamond disk at 7 mm from the anatomical apex. At the opening of the root canal of each section, hemicircular cavities were drilled with a specially designed bur. The corresponding root sections were cemented with glue, thus obtaining root canals with similar cavities that simulated internal resorptions. Teeth were embedded in plaster casts to facilitate their handling. The specimens were randomly separated into four groups of 10. The following obturation techniques were evaluated: lateral compaction (group A), hybrid technique (group B), Obtura II (group C), and Thermafil (group D). AH26 was used as the sealer. After obturation, the plaster was removed and the teeth were radiographed in buccolingual and mesiodistal directions to evaluate the quality of the obturation at the IRC. The incisors were then cut with a scalpel at the same level as the previous section, to examine, under a stereomicroscope, the type of material that filled the IRC. Obtura II gave the best results and in most of the specimens obturated with this technique, the IRC were filled mainly with gutta-percha. Statistical analysis of the data indicated that the differences between group C and the other groups were significant (P < 0.05).

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