Purpose: Nickel-titanium (NiTi) rotary files are becoming more popular and an important part of the equipment for root canal treatment. The superelasticity and shape memory of the instruments have improved the shaping procedures in root canal preparation, making it easier and faster. In this study, we assessed the educational effectiveness of J- and S-shaped root canal preparation with FKG Race in dental students’ hands-on practical classes.

 Methods: Fifty-six third-year students in the School of Dentistry, Osaka University performed J- and S-shaped root canal preparation in transparent epoxy resin blocks with FKG Race twice each. After penetration with a #15 K-file, root canal length was measured. Cervical preflaring and glide path preparation were performed with PreRace and #15 K-file, respectively. Then, the working length was determined by subtracting 1 mm from the root canal length. Root canal preparation was performed with Race (#30/6%, #30/4%, #25/4%, and #20/4%) in order and the final preparation was carried out with #30/6%. In order to evaluate the quality of root canal preparation, we photographed the epoxy resin blocks before and after the instrumentation by micro-computed tomography and measured the root canal width perpendicular to the long axis of the root canal at 1, 2, 3, 4, 5, and 6 mm from the root apex. The increase in root canal width and the time for preparation were compared between the students and specialists certified by the Japanese Society of Conservative Dentistry.

 Results: In the J-shaped root canal preparation by the students for the first time, 62.5% of the students had apical perforation and 5.4% had ledge formation. In the second-time preparation of the J-shaped root canal, 30.4% of the students had apical perforation, 3.6% had separated files, and 3.6% had ledge formation. In the S-shaped root canal preparation by the students for the first time, 23.2% of the students had apical perforation and 7.1% had separated file. In the second-time preparation of the S-shaped root canal, separated file occurred in 7.1%. In terms of speed of root canal preparation, the second try at S-shaped preparation by the students was significantly faster than the first try. The distances between pre- and post-instrumentation at the different levels showed no significant differences among the first and second trials by the students and specialists.

 Conclusion: In the practice of curved-root canal preparation using NiTi files, students can quickly and accurately achieve successful preparation even for difficult S-shaped root canals, especially by paying attention when preparing a root apex.

 Objective: Aside from their biocompatibility, hops also exhibit bioactivity, such as antibacterial effects against oral bacteria that cause dental plaques and anti-inflammatory action in the host. Therefore, hops are expected to have protective activity against periodontitis. However, the mechanism by which hops act on the periodontal bacterial pathogen Porphyromonas gingivalis has not been elucidated. In this study, using RNA-Seq, we performed a comprehensive analysis of the activity of xanthohumol (XN), a component of hops, against P. gingivalis.

 Materials and methods: RNA-Seq transcriptome analysis of the effects of XN on P. gingivalis was conducted using next-generation sequencing. After culturing P. gingivalis strain W83 anaerobically in the presence of XN, RNA was extracted from the bacterial cells for RNA-Seq analysis and confirmation of reproducibility by real-time PCR.

 Results: The transcriptome analysis revealed the increased expression of genes related to heat shock proteins, namely, molecular chaperone GroES, nucleotide exchange factor GrpE, and molecular chaperone HtpG. Meanwhile, there was decreased expression of the Fe-S cluster assembly proteins, SufB and SufD, and the Fe-S cluster assembly ATPase SufC. The SufB, SufD, and SufC genes play major roles in the uptake of iron and formation of iron-sulfur clusters. Therefore, XN likely inhibits the uptake of iron that is necessary for P. gingivalis growth.

 Conclusion: The hop component XN has an inhibitory effect on the growth of P. gingivalis in vitro.

 Purpose: MetaSEAL Soft is a self-adhesive root canal sealer that is easy to use, less susceptible to root canal irrigants and moisture, and advantageously starts polymerization from the root canal wall, so high sealing ability can be expected. The purpose of this study was to evaluate the outcomes of root canal filling using MetaSEAL Soft.

 Methods: This study retrospectively investigated patients who had root canals filled with MetaSEAL Soft between October 2013 and May 2019 at six dental clinics. The following data from all patients were analyzed: age, sex, tooth type, diagnosis, treatment history, apical lesions by dental X-ray photograph, spontaneous pain, percussion pain, swelling, tenderness, sinus tract, treatment method, and root canal filling method. The teeth were classified into three groups according to the radiolucency on dental X-ray photographs before and after root canal filling: (1) normal, (2) reduced, (3) increased or no change. Outcomes were defined as success if X-ray examination results were classified as (1) or (2) with normal clinical presentation, or failure if the results were classified as (3), even when the clinical presentation was normal, or clinical signs or symptoms were present, even if the radiographs appeared normal. Success rates were calculated separately for pulpectomy and infected root canal treatment by the Kaplan-Meier method. The success rate of infected root canal treatment was further calculated according to the presence or absence of preoperative lesions and the history of endodontic treatment.

 Results: Data from 197 patients (52.0±15.1 years old) and a total of 381 teeth were analyzed. Pulpectomy was performed for 86 teeth and infected root canal treatment for 295 teeth. Apical radiolucency was observed in 115 teeth before treatment, of which 31 were initial treatment and 84 were retreatment. The observation period was up to 5 years (average, 3.5 years). The success rate of pulpectomy was 97.6% after 1 year, 96.4% after 2 years, and 96.4% after 5 years. The success rates of root canal treatment without lesions were 98.9%, 98.9%, and 95.3%, respectively. The success rates of initial treatment with lesions were 64.5%, 92.9%, and 92.9%, and those of retreatment with lesions were 45.2%, 60.7%, and 75.7% after 1, 2, and 5 years, respectively.

 Conclusion: The success rates of root canal filling using MetaSEAL Soft were high for both pulpectomy and infected root canal treatments, and remained high over a 5-year observation period.

 Purpose: To develop a new toothpaste for preventing root caries, we examined several ingredients based on root caries progression, and found that pyrrolidone carboxylic acid (PCA) can inhibit the development and progression of dentin demineralization. The purpose of this study was to estimate the efficacy of the new toothpaste containing PCA and fluoride (F) to prevent root caries by evaluating its inhibitory effects on dentin demineralization and collagen degradation in vitro. We also investigated the mechanism of the inhibitory effect of PCA on demineralization and collagen degradation.

 Methods:

 1. Toothpaste efficacy; Sound and collagen-exposed dentin blocks were obtained from bovine roots. Sound dentin blocks were treated with diluted toothpastes (1,450 ppm F [TP-1450F], 3,000 ppm F [TP-3000F] or 1,450 ppm F+PCA [TP-1450F+PCA]) and were immersed in artificial saliva. Collagen-exposed dentin blocks were treated with diluted toothpastes and immersed in artificial saliva containing collagenase. The blocks were then immersed in demineralized solution. The amount of released Ca ions was determined by atomic absorption spectroscopy. Furthermore, the amount of hydroxyproline (HYP) in the surface of collagen-exposed dentin blocks was determined by confocal Raman microscopy.

 2. Mechanism of action; Sound and collagen-exposed dentin blocks were treated with diluted 1,450 ppm F (S-1450F) and 1,450 ppm F+PCA (S-1450F+PCA) solutions, respectively. F uptake to the blocks was measured using ion electrodes. Collagen and collagenase were incubated with PCA, and the amount of collagen degradation was determined. Moreover, the amount of PCA adhered to collagen and hydroxyapatite (HAP) before and after washing was examined, and the amount of PCA residues was calculated.

 Results: 1. In the TP-1450F+PCA group, the amount of released Ca ions was significantly smaller than that in the TP-1450F group of both sound and collagen-exposed dentin blocks. The amount of HYP in the TP-1450F+PCA group was significantly larger than that in the TP-1450F and TP-3000F groups. 2. F uptake was larger in the S-1450F+PCA group than that in the S-1450F group of both sound and collagen-exposed dentin blocks. PCA inhibited collagen degradation by collagenase and the amount of PCA residues on collagen was larger than that on HAP.

 Conclusions: TP-1450F+PCA significantly inhibited demineralization of both sound and collagen-exposed dentin blocks compared with TP-1450F in vitro. TP-1450F+PCA inhibited collagen degradation compared with TP-1450F and TP-3000F. The effects of PCA on F uptake to dentin, collagen degradation by collagenase and adherence to collagen may contribute to the efficacy of TP-1450F+PCA.

 Purpose: Dental caries remains one of the most prevalent diseases in the world. An operative approach with surgical treatment is usually applied to dentin caries with bacterial infection that has progressed into dentin. Accurate diagnosis of caries progression is essential to provide a foundation for selecting the caries treatment. Optical coherence tomography (OCT) is a new diagnostic modality using light, and can create cross-sectional images of biological structures without X-ray exposure. Swept-source OCT (SS-OCT) is a new version of OCT of which the imaging depth is improved over the conventional version of OCT, and is expected to be used in dental clinics. In this study, SS-OCT imaging was performed to dentin caries on the occlusal and proximal surfaces to assess the diagnostic accuracy of SS-OCT.

 Methods: Extracted human teeth with and without dentin caries on occlusal or proximal surfaces were mounted in silicone blocks. SS-OCT scanning (Yoshida Dental OCT, Yoshida Dental) was performed from the occlusal surface of extracted teeth to construct a 3D data set. 2D cross-sectional images were extracted from the 3D data to visualize the caries. After SS-OCT imaging, digital intraoral radiographs (Dentnavi Hands XD35, Yoshida Dental) were captured from the buccal surface of the mounted teeth. The presence and extent of caries were evaluated by 10 dentists and scored using a four-rank depth scale. Sensitivity, specificity and kappa coefficient of SS-OCT and intraoral radiography for the diagnosis of dentin caries on the occlusal and proximal surfaces were calculated and compared at the significance level of α=0.05.

 Results: SS-OCT showed significantly higher sensitivity for the diagnosis of dental caries for both the occlusal and proximal surfaces than intraoral radiography (p<0.05). However, the sensitivity of SS-OCT at the occlusal surfaces was significantly lower than that at the proximal surfaces (p<0.05). Although SS-OCT showed excellent values of the kappa coefficient for both the occlusal and proximal surfaces (p>0.05), intraoral radiography showed significantly lower values at the proximal surfaces (p<0.05).

 Conclusion: SS-OCT is considered to be useful for the diagnosis of dentin caries on occlusal and proximal surfaces. The results of SS-OCT imaging were influenced by the caries location and projection geometry, suggesting the importance of understanding image characteristics in SS-OCT.

 Purpose: Laser-activated root canal irrigation is reported to be efficient for cleaning the root canal system but the risk of irrigant extrusion from the apical foramen remains a concern. This study aimed to evaluate the generation of apical pressure during irrigant activation using a 980-nm diode laser system (Alta Modular Laser System; MLS) with an optothermal converter-coated tip (Thermo-optically Powered tip; TOP tip).

 Methods: Plastic root canal models (0.40-mm inner tip diameter and 6% taper) filled with distilled water were irrigated for 20 s using either the MLS with the TOP tip (Group TOP) or conventional syringe irrigation (Group SI) with different tip/needle insertion depths (2, 5, or 10 mm from the apical foramen). The output power of MLS was set at 2 W (120 mJ, 16 pps). Apical pressure generated during irrigation was measured with a pressure sensor connected to the apex of the model. Statistical analysis was performed using two-way analysis of variance and the Tukey-Kramer post-hoc test. Significance was set at 5%.

 Results: Group SI (−2 mm and−5 mm) showed significantly higher apical pressure compared with the other subgroups (p<0.05). In Group TOP, there were no significant differences among different tip insertion depths (p>0.05).

 Conclusions: Under the present experimental conditions, irrigant activation using the MLS with the TOP tip generated significantly lower apical pressure than syringe irrigation when the tip insertion depth was set deeper in the canal.