Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a novel coronavirus infection (COVID-19) which has spread globally. Since the World Health Organization (WHO) declared the pandemic on March 11, 2020, the infection has spread throughout Japan, causing the government to declare an emergency. SARS-CoV-2 is abundant in nasopharyngeal secretions and saliva. Its route of infection is via inhalation of droplets or aerosols, and by contact with places contaminated by the virus exhaled by an infected person; that is, it is considered to invade exposed persons through the mucous membranes of the nose, mouth, and eyes. Due to its characteristics, dental treatment has the risk of exposure to saliva, droplets, and aerosols containing the virus, and so it is desirable to take new infection prevention measures that are very different from those performed until last year. To deal with emerging infectious diseases that may occur even after this COVID-19, we will need to implement dental care considering new measures to prevent infection. In this paper, in addition to the standard precautions that have been generally taken to date, we propose to develop measures against this infectious disease that is mainly caused by aerosols. We also report on the measures taken at the Dental Hospital of Tokyo Medical and Dental University.

 Objective: The purpose of this study was to establish a treatment for allergic rhinitis by wearing a mouthguard (MG), by clarifying the correlation between salivary properties and allergic symptoms. In this study, a MG, which was found to have the effect of increasing saliva flow rate, was used for SAR patients and healthy subjects, and saliva properties were analyzed using saliva before and after wearing a MG.

 Method: From among patients who visited the Kanagawa Dental University Hospital, 24 SAR patients and 7 non-allergic healthy controls were enrolled. Allergic rhinitis symptoms (3TNSS), salivary flow rate, and biological properties of saliva before and after wearing a MG were examined. The biological salivary properties were analyzed based on seven items: cariogenic bacteria, pH value, acid buffer capacity, occult blood concentration, relative number of white blood cells, protein concentration, and ammonia production by multi-item saliva test.

 Results: The 3TNSS score was significantly decreased and the symptoms were improved in SAR patients with MG. The salivary flow of SAR patients was significantly lower than that in healthy subjects, whereas the salivary flow of SAR with MG was significantly increased. The multi-item saliva test of SAR patients showed a significant increase in cariogenic bacteria, acid buffering capacity, and ammonia production, but a significant decrease in pH, occult blood, leukocyte count, and protein concentration, compared with healthy subjects. In SAR patients, only occult blood decreased after wearing a MG; the other test items did not change.

 Conclusion: Allergic rhinitis was found to be improved in SAR patients by wearing a MG. Salivary secretion was involved in symptom improvement, and the effect of saliva properties was hardly observed.

 Purpose: Alveolar bone resorption due to chronic inflammation is the main symptom of periodontitis. Conventional mouse periodontitis models need to be improved as models of chronic inflammation, particularly with respect to the method of inducing inflammation during the observation period. In this study, alveolar bone resorption was induced by a method which caused little mechanical irritation, and the progression of periodontitis in young and old mice was compared.

 Methods: Lipopolysaccharide (LPS) from Porphyromonas gingivalis was administered 12 times (twice per week) on the palatal gingiva of 8- or 24-week-old C57BL/6J mice. The LPS was injected by a microsyringe (33 G), and the dose was 20 μg per shot. Maxilla samples were collected 1 week and 4 weeks after the final administration, and micro-CT scans and tissue slices were prepared.

 Results: Injection of LPS by the microsyringe did not require strong external force. Results from the micro-CT showed that bone resorption stimulated by LPS was greater in the older mice than in the young mice. In the comparison between 1 week and 4 weeks after the final administration, the aged mice demonstrated more bone resorption later than the young mice after 4 weeks.

 Conclusion: LPS administration with a microsyringe caused alveolar bone resorption in both young and old mice. In older mice, bone resorption was observed continuously during 4 weeks after LPS administration.

 Purpose: We evaluated the ability of optical coherent tomography (OCT) to detect remaining enamel thickness (RET).

 Methods: The labial surfaces of extracted bovine teeth were ground with wet silicon carbide papers ranging from #240-grit to #1,200-grit to create different RETs. A time-domain (TD)-OCT imaging system was projected onto the specimen surface, and scanning was performed across the areas of interest using a probe attached to a mounting device. A depth profile of backscattering along a line perpendicular to the object surface was generated (A-scan), and the RET was obtained. Following the OCT measurement, the specimens were sectioned along the tooth axis in the vertical direction (labial-lingual), and the thicknesses of the specimens were measured using scanning laser microscopy. The data obtained from the different measurements were subsequently compared. The Bland-Altman comparison and the paired t-test were used at a significance level of 0.05.

 Results: The agreement among the different measurement methods was analyzed to assess inter-methodology variation, with strong and positive correlations found for each group of measurements. The results indicated that the mean difference between the OCT measurement and the direct measurement was −16.333±7.997 μm, with the 95% Bland-Altman limits of agreement ranging from −32.001 to −0.659 μm.

 Conclusion: While this preliminary study involved several limitations, the OCT method is a promising non-destructive method for evaluating RET under the conditions applied in this in vitro study.

 Purpose: This study aimed to evaluate the canal-centering ability, working time and frequency of procedural errors of nickel-titanium (NiTi) rotary and hand stainless-steel root canal instrumentation performed by undergraduate students who were inexperienced in NiTi rotary instrumentation.

 Methods: Fifty-nine undergraduate students with no experience of NiTi rotary instrumentation participated in this study. Simulated J-shaped resin canals that had been preflared with ProTaper SX were instrumented by the students using either ProTaper NEXT (NiTi-file Group) or K files (K-file Group) (n=1, each). In the NiTi-file Group, after glide path preparation with #10-20 K files, the canals were instrumented with ProTaper NEXT X1, X2 and X3 to the full working length using an endodontic motor (X-Smart Plus). In the K-file Group, the canals were instrumented manually to the full working length with #15-30 K files and then step-back prepared in 1-mm increments up to #55. The working time was measured with a stopwatch by the instructor. The frequency of instrument fracture and ledge formation was recorded. Pre- and post-instrumentation images were superimposed with image processing software (Photoshop 7.0) and the centering ratio was calculated at 0, 0.5, 1, 2 and 3 mm from the apex by the following formula: [(amount of resin removed from outer side) − (amount of resin removed from inner side)] / (post-instrumentation canal diameter). Data were statistically analyzed with the paired t-test for the centering ratio and working time and with the McNemer test for the frequency of ledge formation (σ=0.05).

 Results: At 0, 0.5, 1, and 2 mm from the apex, the NiTi-file Group showed significantly lower canal-centering ratio (i.e., less deviation) than the K-file Group (p<0.05). The working time of the NiTi-file Group was shorter than that of the K-file Group (p<0.05). Ledge formation occurred in 5 and 43 canals in the NiTi-file Group and K-file Group, respectively (p<0.05). No instrument fracture occurred in either group.

 Conclusion: Within the limitations of this study, instrumentation with ProTaper NEXT showed better canal centering ability, shortened working time and decreased frequency of ledge formation compared with manual K-file instrumentation, when curved canals were instrumented by operators who had no experience of NiTi rotary instrumentation.

 Purpose: A cemental tear is a type of root fracture in which part of the cementum exfoliates along the cemento-dentinal junction or the cementum growth line, resulting in local destruction of periodontal tissue. Because the symptoms are similar to those of periodontal disease and apical periodontitis, it is important to perform an accurate differential diagnosis. This report describes two cases in which different treatments were performed depending on the location of the cemental tear. We compare the degree of difficulty in imaging diagnosis and treatment planning using periapical radiography and cone-beam computed tomography (CBCT), and the related clinical considerations.

 Case: In case 1, a 71-year-old male patient was found to have a deep periodontal pocket at the mesial and palatal sides of the maxillary left central incisor. Periapical radiography and CBCT examinations were performed, and a diagnosis of cemental tear was established from these findings. During flap surgery, the fragment of cementum was removed and debridement was performed, and the periodontal pocket depth was subsequently reduced. In case 2, a 76-year-old female patient was found to have a sinus tract in the gingiva between the maxillary right central incisor and the lateral incisor. The central incisor was slightly painful, and the periodontal pocket depths around the central and lateral incisors were 2-3 mm. A diagnosis of chronic apical periodontitis of the central incisor was established by periapical radiography, and root canal treatment was performed as usual, but the sinus tract did not disappear. Because abnormal findings in the root canal such as root fractures were not detected using a microscope, CBCT examination was performed taking into consideration the possibility of performing an apicoectomy. The CBCT images showed a low density area extending at the palatal and distal sides of the maxillary right central incisor, and there was no contact between the lesion and the apical foramen. Therefore, it was unlikely to be apical periodontitis in this case, but no diagnosis was reached. Although endodontic surgery was considered, the patient requested prompt and reliable healing, so the tooth was extracted and the lesion was removed. Examination of the extracted tooth revealed signs of a cemental tear on the palatal surface at the midpoint of the root, so a diagnosis was made of an inflammatory lesion associated with a cemental tear.

 Conclusion: To determine the optimal treatment strategy for a cemental tear, it is important to choose a treatment option based on an understanding of the location and situation of the cemental tear, as well as the three-dimensional progression of the lesion.

 Purpose: In this case report, we describe the application of behavior change in a patient who had generalized severe chronic periodontitis and was unconcerned about her oral health. After the behavior change, the patient agreed to periodontal therapy including autogenous bone graft and enamel matrix protein (Emdogain) applied to experimental periodontal bone defects.

 Case: A 58-year-old female visited our clinic complaining of mobility of the maxillary left lateral incisor. The patient did not expect tooth extraction. At this visit, pus from buccal apical gingiva was detected. There was no supragingival calculus, but redness was detected on marginal gingiva. The probing depth (PD) was>4 mm in 39.8% of sites and PD>6 mm in 22 sites, and the rate of bleeding on probing (BOP) was 27.6%. Radiographic examinations disclosed the presence of moderate horizontal bone loss, and the presence of angular bone defects with vertical bone loss in the maxillary right first molar, maxillary left first molar and mandibula left second premolar. Especially, PD was>10 mm on the maxillary left lateral incisor.

 The patient was unconcerned about periodontitis, but we applied behavior change therapy. After re-evaluation, she was concerned about her oral health and requested treatment. We subsequently performed flap surgery with an autogenous graft and enamel matrix protein for periodontal tissue regenerative therapy on the remaining deep periodontal pockets. After surgery, fixed bridges were fabricated at edentulous areas and supportive periodontal therapy (SPT) was initiated.

 Results: After 4 years, the patient had PD<3 mm in 98.7% of sites and PD=4 mm in two sites, and the rate of BOP was 0%. Radiographic examinations showed increased radiodensity. We performed SPT every 3 months, which appeared to be sufficient for effective periodontal tissue maintenance.

 Conclusion: This case report indicates that behavior change is beneficial to improve patient compliance with periodontal therapy. After the behavior change, the patient was motivated to undergo periodontal treatment, and SPT was necessary for long-term stabilization.

 Purpose: In severe cases of erosive tooth wear. the tooth form and color are altered, leading to the need for functional and esthetic enhancement. Conventionally, indirect crown or onlay restorations requiring tooth preparation have been applied as suitable restorative methods for such cases. However, the development of adhesive systems and resin composite has expanded the treatment modalities and enabled the concept of minimal intervention dentistry. This case report describes a minimally invasive full-mouth reconstruction of eroded teeth using direct resin composite restorations.

 Case: The patient was a 48-year-old male experiencing decreased vertical dimension of occlusion (VDO) and non-esthetic appearance in the anterior region. After diagnostic waxing, it was decided to increase the VDO by 1 mm in both the maxillary and mandibular dentition (2 mm in total), creating an appropriate space for direct resin composite build-ups. To enhance the esthetic appearance, anterior teeth were also labially veneered. Subsequently, a protective night guard was delivered. As part of a periodical maintenance program, slight occlusal adjustments were performed if necessary and the restorations were repolished to maintain high gloss. After 1 year and 11 months, the restoration of the mandibular right second molar partially fractured, but it was directly repaired according to the manufacturer’s instructions. The outcome at the 3-year follow-up was excellent both functionally and esthetically. No apparent wear of the placed restorations was observed, suggesting that this minimally invasive approach could be a valid treatment option for severely eroded teeth. The advantage of the presented restorative procedure is that it does not require large-scale tooth preparation, preserving the sound dental tissues. Further clinical research is necessary to verify the long-term effectiveness of full-mouth reconstructions with direct resin composite restorations.

 Conclusion: Decreased VDO due to severe erosive tooth wear was successfully restored using direct resin composite build-ups and veneers. The reconstruction enhanced the esthetics and function, and the outcome remained excellent after 3 years.

 Introduction: Apical periodontitis adjacent to the maxillary sinus may induce the formation of a thin hard tissue dome on the sinus floor. This reactive bone formation can be detected as a halo-like radiopaque lesion and is termed periapical osteoperiostitis (PAO). We herein report the successful surgical endodontic treatment of a radicular cyst accompanied with PAO in a maxillary first molar.

 Case: A 47-year-old female was referred for endodontic treatment of her right maxillary first molar. Panoramic and periapical radiographs revealed a diffuse periapical radiolucency around the mesiobuccal and distobuccal roots and elevation of the floor of the right maxillary sinus with a radiopaque lesion. Cone-beam computed tomography (CBCT) demonstrated a well-defined radiolucency of about 8×8×10 mm encompassing the apices of the mesiobuccal and distobuccal roots of the right maxillary first molar, and elevation of the maxillary sinus floor adjacent to the radiolucent lesion with a dome-shaped radiopacity. A diagnosis of previously-treated root canals with symptomatic apical periodontitis accompanied with PAO was made, and root canal treatment was instituted according to the standard procedure. However, the mesiobuccal and second mesiobuccal canals presented persistent exudation, and thus apicoectomy and retrograde filling were performed on the buccal roots under a dental operating microscope. The removed tissue was histopathologically diagnosed as radicular cyst. One-year follow-up showed an increase of radiopacity in the periapical area of the buccal roots and a reduction of the mesiodistal width of the radiopacity on the floor of the maxillary sinus.

 Conclusions: A case of radicular cyst accompanied with PAO in the maxillary first molar was successfully treated with surgical endodontic treatment. CBCT was useful for the diagnosis and treatment planning of this case.