[The effect of different gutta-percha master cones on first penetration depth of spreader and apical microleakage].

PURPOSE: This study was to evaluate the effect of different master cones on apical microleakage through comparing first penetration depth of spreader and the leakage concentration of glucose in the curved root canal of the extracted posterior teeth filled with different gutta-percha master cones. METHODS: Sixty-six extracted roots of human posterior teeth with a single, curved canal were collected and divided into five experimental groups of 11 roots in each group (Group A:master cone 0.06 tapered, 25#; Group B: 0.06 tapered, 20#; Group C: 0.04 tapered, 30#; Group D: 0.04 tapered, 25#; Group E: 0.02 tapered, 25#) using cold lateral condensation as positive control group(group F, AH-PLUS sealer) of 5 roots and negative control (group G, integrated teeth) of 6 roots. The first penetration depth of spreader and the concentration of glucose in apical reservoir at 1, 2, 4, 7, 10, 15, 20 and 30 days were measured, respectively. The data was analysed with ANOVA and LSD test using SPSS 16.0 software package. RESULTS: The value of working length minus the first penetration depth of spreader in group D was significantly smaller than that in group A and group C(P<0.05),and that in group E was significantly smaller than that in group A ,B,C(P<0.05), but no significant difference(P>0.05) in other groups. The concentration of leakage glucose in group F was significantly higher than that in the other six groups(P<0.05),and there were no significant difference in the five experimental groups (P>0.05),which had no significant difference from the negative control group G(P>0.05). CONCLUSIONS: Choosing smaller tapered master cone could get better apical filling in curved canals, but it has no superiority in apical sealing in short time.

[Experimental study of preparing curved root canals with different instrument].

OBJECTIVE: To compare the shaping ability and the influence on apical foramen among hand ProTaper, stainless steel K-files and rotary ProTaper in preparing different curved root canal. METHODS: Forty simulated resin root canal blocks were randomly divided into four groups and prepared by hand ProTaper, stainless steel K-file and rotary ProTaper, respectively. Of them, 12 blocks in group A, B, C consist of six 200 curved root canals and six 30 degrees curved root canals each group. The curvature of the other 4 blocks in group D was less than 5 degrees. Taking photos of the models to the root canal orthotopically and apical foramen using digital camera before and after instrumentation. Finally, the transportation of root canal and the size of apical foramen were analyzed using special image software Auto-CAD. RESULTS: The transportation of center in group B was the highest than that in group A and group C (P<0.05). In some portions of root canal, the transportation of center in group C was higher than that in group A. The size of the apical foramen in group B was significantly bigger than the other groups and the size of the apical foramen in 30 degrees root canal was significantly bigger than that in 20 degrees root canal after instrumentation (P<0.05). There was no significantly different between group A and group C, though the size of apical foramen in group C was bigger than that in group A at the same curvature, and that in 30 degrees root canal was bigger than in 20 degrees root canal (P>0.05). CONCLUSION: Both of the two instruments engender root canal transportation, and curvature is the main reason of transportation. Comparing with stainless steel K-files, NiTi files can maintain the shape of the root canal and apical foramen well.

[The effect of smear layer on apical microleakage].

PURPOSE: To evaluate the effect of smear layer on apical microleakage in extracted root-filled teeth by SEM and glucose penetration model. METHODS: 51 straight single-rooted human teeth were randomly divided into 5 groups, instrumented and irrigated differently by groups. 11 teeth in group A were irrigated with 17% EDTA and 1% NaClO,11 teeth in group B with 1% tetracycline hydrochloride and 1% NaClO,11 teeth in group C with 10% citric acid and 1% NaClO, 9 teeth in group D with 1% NaClO only and 9 teeth in group E with 0.9% NaCl. One tooth in each group was observed under scanning electron microscopy. The other teeth were obturated using lateral condensation technique. Leakage along the root filling was measured by the concentration of glucose in apical reservoir at 1, 2, 4, 7, 10, 15, 20 and 30 days respectively with glucose oxidase method. The data were analyzed with repeated measure ANOVA and SNK-q test using SPSS 16.0 software package. RESULTS: No smear layer on the root canal wall was observed in group A, B and C, the leakage was lower than that in group D and E (P<0.05). The smear layer occurred in quantity in group D, E and their leakage increased. The microleakage was higher in group E than that in group D (P<0.05). CONCLUSION: Removal of smear layer on the root canal wall could reduce the root apical microleakage.