Takatomo Yoshioka

Radiographic evaluation of root canal multiplicity in mandibular first premolars

The purpose of this study was to examine the accuracy of radiographic evaluation of root canal multiplicity in mandibular first premolars in vitro. One hundred thirty-nine extracted human mandibular premolars were used. Buccolingual radiographs were taken, and the number of canals in each tooth was determined on radiographs by four dentists using a view box. A sudden narrowing of the main canal was interpreted as a sign of multiple canals. After the radiographic evaluation, the tooth crown was removed. India ink was injected into the root canal system, and the root was cleared to observe the canal morphology. There was no statistically significant difference among the four dentists with respect to the coincidence rate (93%-96%) of the canal number evaluated on radiographs with that identified by cleared teeth observation (p > 0.05, one-way analysis of variance). A sudden narrowing of the main canal on the radiograph was a good criterion to judge root canal multiplicity.

Crack Initiation on the Apical Root Surface Caused by Three Different Nickel-Titanium Rotary Files at Different Working Lengths

INTRODUCTION The aim of this study was to compare the effects of three brands of nickel-titanium (NiTi) rotary files with different designs on the initiation of apical root cracks when working short, at, and beyond the apical foramen. METHODS One-hundred eight teeth with straight single canals were selected and mounted on resin blocks with simulated periodontal ligaments, and the apex was exposed. The teeth were divided into 9 groups of 12 teeth according to the NiTi rotary file type used (Profile [Dentsply Maillefer, Ballaigues, Switzerland], K3 [SybronEndo, West Collins, CA], and EndoWave [FKG Dentaire, La-Chaux-de-Fonds, Switzerland]) and working length (at CL, 1 mm short of [CL - 1 mm], and 1 mm beyond [CL + 1 mm] the apical foramen). Digital images of the apical surface of every tooth were taken during the apical enlargement sequence at each file change. These images were compared with the baseline image, and the presence of a crack was noted. RESULTS Significantly less cracks were observed in the CL - 1 mm group than in the CL and CL + 1 mm groups. No significant difference was found between the file types used. CONCLUSIONS Working 1 mm short of the apical foramen caused less cracks on the apical surface. In addition, more cracks were observed when using larger file sizes. Instrumentation with NiTi rotary files could potentially cause cracks on the apical root surface.

A new engine-driven canal preparation system with electronic canal measuring capability.

A new cordless engine-driven root canal preparation system has been developed that electronically monitors the location of the file tip and the torque applied to the file during all instrumentation procedures. The Root ZX is mounted inside the handpiece to measure the canal length. The engine is driven with a rechargeable battery, and it works more than 40 minutes without a recharge. Nickel-titanium files are used for this preparation system. The file is rotated at 240 to 280 rpms. When the file tip reaches the apical constriction, the revolution of the file can be automatically reversed (Auto-apical-reverse mechanism). If there is too much torque, the rotation is automatically reversed (Auto-torque-reverse mechanism). These automatic functions promise a safer engine preparation of the canal with nickel-titanium files.

Detection rate of root canal orifices with a microscope

The purpose of this study was to compare the detection rate of root canal orifices by three different methods: naked eye, with surgical loupes, and under a microscope. Two undergraduate dental students located the orifices of 260 teeth by using the above-mentioned methods. Then, India ink was injected into the pulp chamber and all teeth were cleared to determine the actual number of the orifices. There was a significant difference in the detection rate among the three methods (p < 0.01, chi-square test); the microscopic method could more accurately detect orifices than the others could. Surgical loupes were relatively ineffective compared with the microscopic method for detecting orifices.

The Effect of Root Preparation Technique and Instrumentation Length on the Development of Apical Root Cracks

The purpose of this study was to compare the effects of root canal preparation techniques and instrumentation length on the development of apical root cracks. Forty extracted mandibular premolars with straight roots were randomly selected and mounted on resin blocks with simulated periodontal ligaments, and the apex was exposed. The teeth were divided into four groups of 10 teeth each for different canal preparation techniques and instrumentation lengths: group A: step-back preparation (SB) with stainless steel files (SF) using root canal length (RCL) to guide instrumentation length; group B: SB using RCL - 1 mm; group C: crown-down preparation (CD) with Profile using RCL; and group D: CD with PF using RCL - 1 mm. Digital images of the instrumentation sequence were compared for each tooth. Statistical analysis revealed a significant effect of instrumentation length (p < 0.05) but no significant effect of preparation technique (p > 0.05) on the development of apical cracks.

Obturation of Accessory Canals After Four Different Final Irrigation Regimes

The aim of this study was to evaluate accessory canal obturation after four different final irrigation regimes. Sixty-four extracted human lower premolars were instrumented, divided randomly into four groups, and finally irrigated as follows: no irrigation (NO), distilled water (WA), sodium hypochlorite ([SH] 6%, 20 ml for 15 min), and EDTA (15%, 8 ml for 3 min) combined with the SH regimen (ES). The System B and the Obtura II were used to fill the canals. The teeth were cleared and observed under a digital microscope. Obturation material penetration rates in length into the accessory canals were measured and the following values were obtained: 22.3% in group NO, 21.8% in group WA, 53.5% and 68.1% in groups SH and ES, respectively. Statistically significant differences were found when comparing each of the first two groups (NO and WA) with SH and ES groups (p < 0.05). The use of sodium hypochlorite alone or in combination with EDTA in final irrigation flushes may enhance a better obturation material penetration into the accessory canals.

An Observation of the Healing Process of Periapical Lesions by Digital Subtraction Radiography

The purpose of this study was to evaluate the efficacy of digital subtraction radiography using a direct digital imaging system in the follow-up study of endodontically treated teeth. The RVG-S was used as a direct digital imaging system. The intraimage variation of the original RVG-S image caused by dark current and sensitivity variations among pixels was corrected by pixel-to-pixel. The interimage variation was further corrected using a copper step-wedge attached to the sensor. Standardized images were obtained from the same geometrical setup during the follow-up. Pixel values at the regions of interest positioned on the periapical lesion increased after the endodontic treatment, and this change continued during the observation period up to 545 days. The subtraction method with direct digital radiography will be a useful tool to evaluate the healing process in endodontic treatments.

Importance of clinical examination and diagnosis: A case of dens invaginatus

A case report is presented that shows a radiolucent lesion between the maxillary left lateral incisor and canine tooth, both of which were vital. The cause of the lesion was initially unclear. The patient was to be treated surgically, however, precise examination made it clear that the cause of the radiolucent lesion was due to the exposure of a second canal because of attrition of the lateral incisor crown. The final diagnosis of the tooth was dens invaginatus. This case highlights the importance of careful examination and correct diagnosis.

Electronic detection of root canal constrictions.

The aim of this study was to investigate the possibility of detecting root canal constrictions by using an apex locator. Seventy impenetrable canals in extracted human teeth were used. Based on contact microradiographic findings, they were divided into three groups: group A (constricted within 3 mm of the radiographic apex, 23 canals), group B (nonconstricted within 3 mm of the radiographic apex, 28 canals), and group C (constricted more than 3-mm short of the radiographic apex, 19 canals). Electrical impedances at two different frequencies (8 kHz and 0.4 kHz), as well as the meter values of the Root ZX were recorded at the position where a file tip could reach. The impedance ratios (Z8kHZ:Z0.4kHz) and the meter values of the Root ZX showed a statistically significant difference between groups A and B. It was suggested that the Root ZX might be useful for detecting root canal constrictions.

Effects of new adhesive resin root canal filling materials on vertical root fractures.

The aim of this study was to compare the fracture resistance of roots following root canal therapy using the RC Sealer system, the Epiphany system and the conventional system of gutta-percha and Sealapex. Fifty-six maxillary central incisors were divided into eight groups of seven teeth each, according to master apical file size and obturation systems. Obturation materials in the root canal were vertically loaded using a universal testing machine. Fracture loads were analysed by ANOVA and Tukey comparison, and fracture patterns were analysed with ordinal logistic regression. Master apical file size 80 had a significantly lower fracture load than size 40 (P < 0.05). The groups obturated using the Resilon Cone and the Epiphany Sealer had significantly lower fracture loads than the other groups (P < 0.05). There was no significant improvement in resistance to vertical root fractures using the examined adhesive resin root canal filling systems, compared with conventional gutta-percha and sealer.