Abstract : This study aimed to evaluate the influence of heat application on the sealing ability and apatite-like precipitate-forming ability of a bioactive glass-containing root canal sealer (Nishika Canal Sealer^TM BG ; BG). Simulated root canals prepared in bovine dentin blocks were filled with either warm-vertical compaction or single cone technique using either BG or a zinc oxide non-eugenol-based sealer, and apical leakage of bovine serum albumin was quantified. Canals filled with gutta-percha without sealer served as positive controls. To evaluate precipitate formation, set BG specimens with or without heat application (200°C, 5 seconds) were immersed in a simulated body fluid (SBF) and analyzed with scanning electron microscopy and energy dispersive X-ray analysis (EDX). Significantly more leakage was detected in the positive control group compared with the other groups (p<0.00001), whereas no significant difference was found among the experimental groups (p>0.05). Apatite-like precipitates were observed on the surface of heat-applied and non-heat-applied BG specimens after 1 week of SBF immersion. EDX revealed that the elemental composition of SBF-immersed BG was similar regardless of heat application. In conclusion, under the present experimental conditions, heat application did not influence the sealing ability and apatite-like precipitate-forming ability of BG.

Abstract : Purpose : The aim of this study was to evaluate the distance between the terminal position and anatomical apical foramen after root canal preparation using tri-auto ZX2 with two different methods : the position at ‘0.5’ and the position of 1.0 mm subtracted from ‘Apex’ as the working length.

 Methods : Thirty J-shaped simulated resin canals were randomly divided into two groups (N=15 in each group). Group 1 was set at the position when the flashing bar of tri-auto ZX2 with apical action reached the level at which the word ‘0.5’ appeared on its LCD screen during root canal preparation. Group 2 was prepared with the position of 1.0 mm subtracted from ‘Apex’ as the working length without apical action. All canals were prepared with NEX files with tri-auto ZX2. The distance between the apical foramen and terminal position after final preparation was measured by stereomicroscope. The data was analyzed using Student’s t-test.

 Results : The distance was 0.50±0.24 mm in Group 1 and 1.10±0.28 mm in Group 2 and the difference was significant (p<0.05).

 Conclusion : The distance between the working terminal position and apical foramen after root canal preparation was significantly shorter in Group 1 than in Group 2.

Abstract : This study aimed to evaluate the canal-centering ability and instrumentation time of different nickel-titanium (NiTi) rotary preparation techniques performed by undergraduate students. Simulated J-shaped resin canals were instrumented by undergraduate students with no clinical experience of NiTi rotary instrumentation, using (1) the single-length technique with Optimal Torque Reverse (OTR) motion ; (2) the crown-down technique with rotary motion ; or (3) the step-back technique with manual stainless-steel K-files (Zipperer). The rotary instrumentation was done using EndoWave instruments (FKG) and TriAuto ZX2 motor (J. Morita). Canal-centering ratios were determined after superimposition of pre- and post-instrumentation images. Instrumentation time was measured and ledge formation was recorded. At ≥ 1 mm from the apex, the single-length and crown-down groups showed significantly lower canal-centering ratio (i. e., less deviation) than the step-back group (p<0.05). The length of instrumentation time was single-length group=crown-down group<step-back group (p<0.05). Ledge formation occurred in 2, 1 and 10 canals in the single-length, crown-down, and step-back groups, respectively. Within the limitation of this study, EndoWave rotary instrumentation with the single-length technique (in OTR motion) and crown-down technique exhibited superior canal-shaping ability compared with the manual step-back technique with K-files, when the instrumentation was performed by novice undergraduate students.