Abstract : Purpose : The aim of this study was, firstly, to evaluate the canal-centering ability, working time and frequency of procedural errors of different nickel-titanium (NiTi) rotary instruments used by novice undergraduate dental students in curved canals. The second aim was to assess the usability of the instruments for the students.

 Materials and Methods : Simulated J-shaped resin canals were instrumented by undergraduate students (n=13) using JIZAI (MANI) in a single-length technique, WaveOne Gold (Dentsply Sirona ; WOG) in a single-length technique with a reciprocating motion, EndoWave (FKG ; EW) in a crown-down technique, or stainless-steel K-files (Zipperer ; SS) in a manual step-back technique. Canal-centering ratios at 0, 0.5, 1, 2 and 3mm from the apex were calculated after superimposition of pre- and post-instrumentation images. Working time was measured and ledge formation was recorded. After completion of all instrumentation, each student was asked to rank the relative usability of the four instruments using scores 1 (highest) to 4.

 Results and Discussion : All NiTi instruments at all levels, except for EW at 1, 2 and 3mm and JIZAI at 3mm, showed significantly lower centering ratio (i.e., less deviation) than SS (p<0.05). EW showed significantly higher centering ratio than JIZAI at 2 and 3mm and WOG at 3mm (p<0.05). The working time was significantly shorter with the three NiTi instruments than with SS (p<0.05), but similar among the NiTi instruments (p>0.05). Ledge formation occurred in three canals each in EW and SS, and no instrument fractured. The usability scores of NiTi instruments were lower (i.e., higher usability) than SS.

 Conclusion : Under the present experimental conditions where curved resin canals were instrumented by novice undergraduate students, JIZAI, WOG and EW exhibited superior canal-centering ability and shorter working time, and were rated by the students as easier to use, compared with SS. JIZAI and WOG tended to create less canal transportation than EW.

Abstract : Purpose : The aim of this study was to assess the root and root canal morphology of maxillary anterior teeth in a Japanese population using dental cone-beam computed tomography (CBCT).

 Materials and Methods : We analyzed the CBCT images of 263 maxillary central and 269 lateral incisors, and 283 canines from 145 patients. The following parameters were evaluated on CBCT : (1) number of roots and root canals, and (2) the classification of root canal configuration according to Vertucci's criteria.

 Results : All the teeth examined were observed to be single rooted. The majority of the maxillary anterior teeth had a single canal (100% of the central incisors) ; in addition, two canals were identified in 3.0% of lateral incisors and 3.9% of canines. Type Ⅰ Vertucci's classification was the most prevalent canal configuration in the maxillary anterior teeth. Types Ⅲ and Ⅴ of Vertucci's classification were the most frequently observed canal configurations of the teeth with two canals.

 Conclusion : All the maxillary central incisors displayed a single root canal whereas maxillary lateral incisors and canines demonstrated canal variations.

Abstract : Purpose : The aim of this study was to evaluate the push-out bond strength of three types of bio-ceramic sealer : Nishika Canal Sealer^® BG, iRoot SP^® and Well-Pulp ST^®.

 Materials and Methods : Forty human single-rooted teeth were prepared using NiTi-rotary instruments and divided into four groups (N=10) according to the root canal sealer used : Nishika Canal Sealer^® BG, iRoot SP^®, Well-Pulp ST^® and Nishika Canal Sealer^® (control). Then the roots were obturated with each sealer, and the obturated teeth were stored in an incubator for one week. One-mm-thick slices were obtained from each root sample (n=10). The bond strength of each group was measured using a push-out test. The data were analyzed statistically by one-way analysis of variance, followed by Tukey-Kramer multiple tests.

 Results : The Well-Pulp ST^® group showed the highest bond strength and the Nishika Canal Sealer^® BG group showed the lowest. Significant differences of bond strength were found between the iRoot SP^® group and each test group except the Well-Pulp ST^® group (p<0.01).

 Conclusion : Nishika Canal Sealer^® BG showed a significantly lower push-out bond strength than iRoot SP^® and Well-Pulp ST^®.

Abstract : Purpose : The aim of this study was to compare the cyclic fatigue resistance of four different NiTi files on rotary movement within artificial curved canals at simulated body temperature.

 Methods : An NEX NiTi file (NX group) (ISO size=#25, taper=0.06, length=25mm, n=10) and NEX Ms NiTi file (MS group) (ISO size=#25, taper=0.06, length=25mm, n=10), Vortex Blue NiTi file (VB group) (ISO size=#25, taper=0.06, length=25mm, n=10), and RE file CT NiTi file (RE group) (ISO size=#25, taper=0.06, length=25mm, n=10) were tested. All files were tested by rotary movement and the testing device was a stainless-steel artificial canal with a radius of curvature of 5mm and an angle of 45°.

 To simulate the clinical setting, testing was done with up-and-down motion at 0.5 s/4mm. All experiments were conducted at 37±1℃. All samples were subjected to rotary movement until fracture.

 The time to fracture and the lengths of broken fragments were recorded. After the cyclic fatigue resistance tests were completed, the fractured surface was inspected by a scanning electron microscope. The data was analyzed using one-way analysis of variance.

 Results : The time to fracture of the MS group, VB group and RE group were significantly longer than that of the NX group (p<0.01). The average length of broken fragments of the NX group, MS group and VB group were 4.61-4.76mm, and that of the RE group was 2.27-2.68mm. The RE group showed a significantly shorter average length of broken fragments than all other groups (p<0.01).

 Observation of the fractured cross section of the heat-treated NiTi rotary file (MS group, VB group, RE group) with a scanning electron microscope revealed numerous dimples, micro-bubbles and crater-like structures in each.

 Conclusion : The heat-treated NiTi rotary file (MS group, VB group, RE group) showed higher cyclic fatigue resistance than the NEX NiTi rotary file with continuous rotational movement in a body temperature environment.

Abstract : The success rate for treatment of perforated teeth with a periapical lesion is not high (56%). Mandibular molars are reported to have a 10-20% probability of developing a middle mesial canal (MMC), but it is difficult to detect and treat them in the clinic. We report a case of infected root canal treatment for a mandibular first molar with a MMC that had a perforated floor of the pulp chamber. A 35-year-old man presented with apical periodontitis and perforation of the pulp chamber. Perforation was located at the buccal root furcation and was in contact with the periodontal pocket. Root canal treatment with a surgical microscope was started, and the MMC was found. The perforated area was repaired with MTA, the main and MMC were shaped and cleaned, then the root canal was filled. One year after treatment, the clinical symptoms disappeared and the periapical lesion of the apex and root furcation disappeared. The perforation area could be properly identified by optical magnification and pre-treatment, and perforation repair with MTA could be performed. The MMC was found and debridement, which was necessary for the healing of apical periodontitis, was performed, with good results.