Coronavirus disease 2019 (COVID-19) has been a social problem since January 2020, and has now affected the entire world. After a state of emergency declaration was extended, the author brought up the issue of the deterioration of the oral environment in elderly residents due to inadequate professional oral care and subsequent illness, including aspiration pneumonia, with the Chairman of the Chiba Dental Association and Professor of Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, and then decided to conduct a questionnaire survey on nursing homes involving both the Yachiyo City and Chiba Dental Associations.

The countermeasures taken against COVID-19 have highlighted the abilities to respond to, judge, and make decisions quickly. Along with these practices, we dentists can help vulnerable people, including the elderly residents of nursing homes. The issue of “oral care at nursing homes” is only one of the triggers. We would like to continue pursuing to the utmost extent what we can do as dentists to help transform the world.

COVID-19 has attracted attention throughout society and led to a focus in dental practice on the risk of airborne infection by bioaerosols. Prevention of spray infection is more difficult in dental therapy with a microscope than dental therapy without one, and as a possibly effective means, we devised a microscope draped shroud (designed by Uchida, Uchida-Drape) composed of a plastic bag and investigated its effect on particle flow with a laser beam and a high-speed camera. The results showed that combined use of a microscope and an Uchida-Drape can reduce the airborne spray exposure of both practitioner and assistant to a level lower than that of ordinary therapy.

In this unprecedented era of Covid-19, “new norm” has to be implemented in the clinical dentistry. This report will describe how the dental office setting should be modified or changed in reference to the recommendation by Center for Disease Control and Prevention (CDC), and will illustrate how microscope can help dentistry in terms of infection control in this “new norm” situation.

Aims: The success of endodontic treatment depends on the knowledge of root canal morphology. However, the incidence of second mesiobuccal root canal in maxillary first permanent molars in Japanese patients has not been clarified. The aim of this study was to clarify the incidence of second mesiobuccal root canal in maxillary first permanent molars in Japanese patients with cone-beam computed tomography (CBCT). Material and Methods: The subjects were 111 patients (male: 45, female: 66; age range, 11 - 74 years) with mesiobuccal root canal in maxillary first permanent molars who underwent CBCT. No root canal fillings, caries, posts, crown restorations, apical periodontitis and resorption were included in this study. Data were recorded and analyzed according to Weine's classification for root canal configuration: type I, a single canal extends from the pulp chamber to the apical foramen; type II, two separate canals leave the chamber but merge before the apex to form one apical foramen; type III, two separate canals leave the chamber and exit the root in separate apical foramina; and type IV, a single canal leaves the chamber, but divides before the apex into two separate canals with separate apical foramina. Results: The incidence of mesiobuccal root canal in maxillary first permanent molars with CBCT were Type I: 23.4%, Type II: 21.6%, Type III: 36.9% and Type IV: 18.0%. Conclusions: The results of the present study indicated the incidence of second mesiobuccal root canal in maxillary first permanent molars in Japanese with CBCT.

Aims: Since the root canal system of the molars is particularly complex, the success of root canal treatment (RCT) depends on knowledge of its morphology. A distolingual root (DLR), which is also called radix entomolaris¹, is a known type of mandibular first molar; however, its incidence and the prevalence of its treatment have not been elucidated in the Japanese population. The purpose of this study was to determine the DLR incidence in mandibular first molars and the prevalence of RCT in mandibular first molars in the Japanese population on cone-beam computed tomography (CBCT). Material and Methods: A total of 150 patients (male: 53, female: 97; age range: 11-85 years) who underwent CBCT examinations at our hospital between November 2019 and February 2020 were included in the study. Images that captured mandibular first molars (n=171) were continuously extracted. The number of three-rooted mandibular first molars with a separate DLR, history of RCT, and presence of radiolucency at the apex were examined to analyze DLR incidence and the prevalence of RCT. Result: The incidence of DLR was 30.4% (male: 30.5%, female: 30.4%) in this patient cohort. A history of RCT was identified in 34.5% of all teeth; of which 24.6% were characterized by radiolucency at the apex. Of the 59 teeth with a history of RCT, 71.2% were treated unsuccessfully, as characterized by the presence of an apical lesion. More specifically, failure of RCT was observed in 47.5% of mesiobuccal (MB) roots, 50.9% of mesiolingual (ML) roots, 50.9% of distal (D) or distobuccal (DB) roots, and 70.0% of DLR alone. Conclusions: The results of the present study show that the incidence of DLR in mandibular first permanent molars on CBCT in a Japanese population was 30.4%. The rate of RCT failure characterized by radiolucency at the apex was 71.2%; specifically, failure rates for MB, ML, D or DB, and DLR alone were 47.5%, 50.9%, 50.9%, and 70.0%, respectively.

Aims: The mandibular canines often survive until a late stage, even in elderly people who have lost many teeth, and they play an important role in occlusion. Canines have long tooth roots and low susceptibility to caries or periodontal disease, giving them a high survival rate. The ability to carry out a detailed evaluation of root morphology of canines in situ in the oral cavity would be extremely useful clinically. The aim of this study was to use cone-beam computed tomography (CBCT) to clarify the rate of occurrence of accessory canals in the mandibular canines of Japanese people. Material and Methods: The subjects were 108 patients (46 men, 62 women, age 14–77 years, mean age 52.8 years) who underwent CBCT between January and April 2020. A total of 108 vital mandibular canines that were completely scanned with CBCT were consecutively selected, and the rate of occurrence of accessory canals in the mandibular canines was evaluated. Results: Accessory canals were present in the mandibular canines of 41 subjects and absent in 67 subjects, a rate of occurrence of 38.0%. Comparing the presence and absence of accessory canals, a significant difference was found; the absence of accessory canals in the mandibular canines was significantly more common (p<0.05). No significant differences in the presence of accessory canals were found by either age or sex. Conclusions: The results of this study show that the rate of occurrence of accessory canals in the mandibular canines of Japanese people is 38.0%. Accessory canals in the mandibular canine were shown to be significantly more likely to be absent than present.

A patient was first seen in 2012 and recently came back because the root canal had failed. Upon radiographic examination however, the original lesion had healed. PA radiographs and CBCT examination revealed an inter-radicular lesion. Recommendations were made and micro-surgical treatment was rendered accordingly.

This article reported a case of severe peri-implantitis that was successfully managed with Er,Cr:YSGG laser. The patient was seen at 2 and 7 months for post-operative follow-up. The symptoms of inflammation around the implant were improved and the patient felt satisfied with this outcome. The application of Er,Cr:YSGG laser played a critical role in the stabilization and survival of the implant.

Objective: As a reference for the safe use of nickel-titanium rotary files (Ni-Ti files), the limit number of root canals for consecutive cutting with the Hyflex CM (Coltene Whaledent, Altstätten, Switzerland) and the JIZAI (MANI, Tochigi, Japan) R-phase Ni-Ti files with repeated heat treatments for phase transformation was evaluated, and their courses of transition to fracture occurrence were compared. Materials and methods: A simulated root canal (Endo Training Block J-shaped simulated root canal) was subjected to root canal enlarging and shaping with Hyflex CM (25 mm, #25, .06 taper) or JIZAI (25 mm, #25, .06 taper). As a low-speed engine, the Tri Auto ZX2 (Morita, Kyoto, Japan) was used in the OTR mode. After root canal enlargement, the file was submerged for 5 s in heated water at 60-70℃ to induce phase transformation, and file deformation was observed microscopically before and after heating. Fracture surfaces were also observed by a scanning electron microscope (SEM). Results: The mean number of root canals to file fracture was 16.4 (±5.4) with Hyflex CM and 90.2 (±12.0) with JIZAI, significantly higher with JIZAI. The mean number of root canals to onset of deformation was also found to be markedly higher with JIZAI, at 15.5, than with Hyflex CM, at 1.8. In terms of permanent deformation before and after heating, moreover, permanent deformation was found for Hyflex CM after a mean of 9 root canals, but JIZAI, in contrast, was found to return to its initial file form after a mean of ≥20. In both files, the point of fracture was located approximately 3 mm from the tip, and observation of the fracture surfaces by SEM showed a dimpled structure in both files, with many dimples located in the center of the Hyflex CM cross-section, but near the radial land in the JIZAI cross-section. Conclusion: It was found that, in root canal shaping with an R-phase Ni-Ti file, elimination of file deformation by heat treatment can effectively increase the number of times the file can be used for root canal enlarging and shaping. If recovery from deformation fails to occur, however, the probability of file fracture increases, and replacement of the file is therefore recommended.