Due to recent advent of microscopic endodontic treatment, flexible Ni-Ti rotary instruments, and sophisticated irrigation system, the conventional root canal treatment has achieved fairly high success rate of above 95%.

However, conventional, orthograde endodontic treatment may not always work, considering the complexity of the pulp system, hence the result may not be 100% successful.

In this article, 3 cases are presented in which conventional root canal treatment failed to achieve favorable outcome due to lateral canals, but was successfully managed by endodontic micro surgery.

The purpose of this study was to investigate the influence of phase transformation behavior of R-phase Ni-Ti file on its cyclic fatigue resistance and the root canal shaping ability.

The pre-treated NRT (NRT-N) and NRT files (MANI, Tochigi, Japan) were examined. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were performed to analyze the phase- transformation behavior. The numbers of rotations until fracture for the 06/#25 and 06/#40 files were determined by performing cyclic fatigue resistance tests. A curved root canal model was apically enlarged using the 06/#25, 06/#30, 06/#35, and 06/#40 files. Next, pre- and post-operative images of the model were superimposed. The increases in the outer and inner canal widths of the curvature were measured at 0, 1, 2, 3, 4, and 5 mm from the apex, in order to determine the canal centering abilities of the files.

The XRD patterns showed that the predominant phases in NRT-N and NRT at room temperature were the austenite phase and the R-phase, respectively. The DSC results showed that the reverse transformation finish temperature from the R-phase to the austenite phase in the case of NRT was 40.45±2.63℃, while it was 23.20±3.33℃ for NRT-N. The NRT files exhibited superior cyclic fatigue resistance regardless of the instrument size. When the #40 files were used for apical enlargement, the increase in the outer canal width at 0 mm in the case of the NRT file was smaller than that in the case of the NRT-N file (p < 0.05). When the #30 and #35 files were used, the NRT file exhibited a higher centering ability at 0 mm than did the NRT-N file variety (p < 0.05).

Thus, it was concluded that Ni-Ti file exhibited R-phase had better cyclic fatigue resistance and shaping ability than Ni-Ti files exhibit austenite phase at clinical temperature.

For successful endodontic treatment, it is important to have proper understanding of the anatomical features of teeth, such as the roots and root canals. The maxillary first molar (M1) in particular is reported to have a complex mesiobuccal root (MBR) canal morphology, while the maxillary second molar (M2) has complex root fusion. The relationship between these roots and their root canal morphology and the differences between men and women are, however, not fully understood. Understanding this complex anatomical morphology in three dimensions using computed tomography (CT) should greatly improve the success rate of endodontic therapy. In this study, root fusion and root canal morphology in M1 and M2 were analyzed in a Japanese population.

Multi-detector CT (MDCT) images of M1 and M2 in 443 Japanese subjects (220 men and 223 women), aged 20 to 29 years, who visited Nihon University Matsudo Hospital between January 2010 and March 2014 were examined. The MDCT images were used to observe the roots and root canals and classify root fusion and root canal morphology by sex.

The rate of root fusion in M1 was low at approximately 5% and the majority of roots were of 3 separate roots, much like in other races. Two root canals in the MBR were observed at the middle part in 62.3% of men and 59.6% of women, and at the apical third in 60.9% of men and 59.6% of women. Two root canals were seen to the same extent in both men and women, which agreed with the results of an identical Mongoloid population.

Approximately 45% of individuals had root fusion in M2, which was at least twice as prevalent as in other races. The rate of root fusion was approximately 33% in men and approximately 54% in women, indicating a higher rate in women (P < 0.01). The rate of fusion of the MBR and palatal root was highest at approximately 14% in both sexes, followed by fusion of the MBR and distobuccal root at approximately 10%. While uncommon, a C-shaped root resulting from root fusion was seen in M1s in approximately 0.5% of men and 0.4% of women, and a little more commonly in M2s in 4.1% of men and 6.7% of women. As for the relationship between fused roots and root canals, a higher tendency was seen in both sexes for 3 separate root canals despite root fusion. All the fused roots had a complex root canal morphology.

No difference was seen between men and women in terms of root and root canal morphology of fused roots in M1. However, the rate of root fusion in M2 was significantly higher in women (P < 0.01). No differences in root and root canal morphology patterns of fused roots were seen between men and women, and many root and root canal morphologies were seen in both sexes. Performing endodontic therapy in maxillary molars based on the information on root fusion, root canal morphology and other features gleaned from CT images as well as microscopic images would improve the success rate of endodontic therapy.