The coronavirus disease 2019 (COVID-19) pandemic started in Wuhan, China, put all dentists in a difficult situation as modern dentistry had never experienced nor expected before. Even though the higher nosocomial infectious risk of COVID-19 in dental practice was pointed out at an early stage of the epidemic, there was no reliable method of controlling infection at that time. This article reviews the literature related to the crisis in Wuhan to figure out how Chinese dentists managed the world’s first epidemic of COVID-19.

 Wuhan city, the capital of Hubei province of the People’s Republic of China, has a population of about 11.2 million. As the School and Hospital of Stomatology of Wuhan University (WHUSHS) ranks 32nd among the world’s dental schools, and second in Mainland China, WHUSHS plays a dominant role in the dentistry of this megalopolis. The outbreak of COVID-19 was made public on December 31, 2019 by the Wuhan Municipal Health Commission. On January 23, 2020, due to a rapid increase of COVID-19 cases, Wuhan plunged into a citywide lockdown, the largest quarantine in history. The government banned non-emergency dental treatment in Hubei province, and all emergency dental patients in Wuhan were directed to WHUSHS. WHUSHS immediately prepared an emergency dental treatment method tailored to the epidemic, including an online consultation system on social media for proper screening of emergency patients. Infection control methods were devised to combat the urgent problem. Their experiences and ideas were promptly compiled and used to publish accurate guidelines for COVID-19 infection control in dental practice. While a total of 2,025 emergency cases were treated at WHUSHS during the lockdown period, only nine hospital staffs were confirmed with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Among them, no cluster of disease nor cross infection case was identified. During that time, a greater proportion of endo related patients was found, whilst the total number of emergency patients considerably decreased. Because all emergency dental cases in quarantine were gathered at one dental hospital, their epidemiological data are valuable for analyzing the impact of COVID-19 on dentistry. To resume general dental treatment after lifting of the lockdown, a cautious and systematic procedure was prepared at WHUSHS.

 Our review of publications from WHUSHS and related organizations revealed that dentists in Wuhan tactically and safely dealt with the world’s first COVID-19 epidemic.

 Purpose: While incremental filling is recommended for deep cavities when a light-cured composite resin (CR) is used, because of issues such as polymerization contraction stress and irradiation depth, bulk-fill CRs, which can be filled in large cavities at once, have been developed and used in clinical application. This study examined the effects of the polymerization contraction stress of bulk-fill CRs in high C-factor cavities by conducting visual evaluation using polycrystallized glass blocks, shear bond strength tests on bovine dentin, and measurement of the residual volume after curing.

 Materials and methods: Bulk Base Hard (BH) and Beautifil Bulk Flow (BF) were used as bulk-fill CRs, and Gracefil Flow (GF) as a conventional CR. As bonding systems, Clearfil Mega Bond2 (MB) and Clearfil Universal Bond Quick ER (ER) were used. Bioram-M was used as the polycrystallized glass block. The groups filled with each CR after bonding treatment with MB were designated as the MBH Group, MBF Group, and MGF Group, and the groups filled with each CR after bonding treatment with ER as the EBH Group, EBF Group, and EGF Group. A cylindrical cavity of 4.5 mm diameter and 4.0 mm depth in Bioram-M was formed, the cavity was repaired, and the state of gap and crack generation was classified and scored. Furthermore, a flat dentin surface on a bovine front tooth was prepared, repaired, and then the tensile-shearing strength was measured immediately after bonding.

 A rubber ring jig with 4.5 mm diameter and 4.0 mm height was prepared and each CR was filled in a darkroom to prepare cylindrical samples. The specimen was soaked in acetone immediately after curing, and the unpolymerized parts of the CR were removed. The residual volume of each specimen was measured after removing the unpolymerized CR.

 Results: As a result of visual evaluation, a significant difference in the state of gap and crack generation was observed in the MBH and MBF Groups compared to the MGF Group, and in the EBH and EBF Groups compared to the EGF Group (p<0.05). The MGF and EGF Groups showed gaps at the cavity floor. In addition, the bond strength of the MBF Group was significantly higher than those of the MBH and MGF Groups (p<0.05). The bond strengths of the EBF Group and EGF Group were significantly higher than that of the EBH Group (p<0.05). Although the residual volume of BH and BF were significantly larger than those of GF, there was no significant difference between BH and BF (p<0.05).

 Conclusion: The results indicated that care is needed during the filling operation of bulk filling with bulk-fill CRs, as the problems caused by polymerization contraction stress are not completely eliminated in high C-factor cavities, even though it is effective for the bonding of deep cavities.

 Purpose: The aim of this study was to evaluate the reading accuracy of an electronic apex locator connected to an endodontic motor with various nickel titanium rotary instruments and root canal irrigating solutions using plastic straight root canal models with apical constriction.

 Methods: Plastic blocks with 14.5 mm root canal length, φ0.2 mm apical foramen, φ0.15 mm apical constriction at 1 mm closer to the crown from the apical foramen, and 0.02 tapered straight root canal were used for preparation. The blocks were placed on the stand, establishing an electric circuit. Root canal preparation was performed using an X-Smart IQ endodontic motor connected to a Propex IQ apex locator in the state of filling with one of three types of root canal irrigating solution: ①saline, ②3% sodium hypochlorite solution (NaClO), and ③18% EDTA solution. All canals were randomly prepared to size 25 by three types of root canal preparation method: ①WaveOne Gold (WOG), ②ProTaper Gold (PTG), and ③stainless steel K-file (SSK) (n=6). The rubber stop on the file was fixed at the position where the tip of the master apical file of each group reached the reference point on the apex locator. The distance from the tip of the file to the rubber stop was established as the length that the file reached. The value obtained by subtracting the reached file length from the root canal length was taken as the distance between the tip of the file and the bottom of the root canal block.

 Results: Among the measured values in each file group, the WOG group was stable with the least fluctuation. In the PTG and SSK groups, the file tip position was about 0.5 mm closer to the bottom of the root canal block than the apical constriction when using saline and 18% EDTA. The measured values between the root canal irrigating solutions showed no difference between the files when using 3% NaClO, and the file tip position was close to the apical constriction. Under all conditions, the file tip position was within the allowable range of measurement error.

 Conclusion: The reading accuracy of Propex IQ connected to X-Smart IQ was not significantly affected by the file type, system or root canal irrigating solution.

 Purpose: The purpose of this study was to evaluate the effect of irradiation of low-power Er: YAG laser and chemical pretreatment after irradiation of high-power Er: YAG laser to promote the tensile bond strength (TBS) of the resin-lased dentin interface.

 Methods: Extracted human molars were prepared with flat dentin surfaces, and ground with wet 800-grit silicon carbide paper. The specimens were set on an X-Y-Z moving stage and mechanically irradiated at an energy setting of 150 mJ (C400F)/10 pps and/or 30 mJ (C800F)/10 pps while being sprayed with cooling water. We chose 6% sodium hypochlorite (NaClO), p-toluenesulfinate (Accel) and 10% citric acid/3% ferric chloride (FeCl₃/citric acid) as chemical pretreatment agents. Then, the Clearfil Mega Bond System and resin composite (Beautifil Flow F00) were placed. The TBS was measured after storage for 24 hours in an environment with 99% humidity at 37°C. The irradiated specimens were divided into six groups (A1, A2, A3, B1, B2, B3, n=10), and a control group (Cont1, 2, n=10) that did not receive any laser irradiation. Each group was follows: {Cont1: No irradiation, Cont2: No irradiation→Accel→FeCl₃/citric acid, A1: Irradiation with C400F, A2: Irradiation with C400F→Accel→FeCl₃/citric acid, A3: Irradiation with C400F→NaClO→Accel→FeCl₃/citric acid, B1: Irradiation with C400F and C800F, B2: Irradiation with C400F and C800F→Accel→FeCl₃/citric acid, B3: Irradiation with C400F and C800F→NaClO→Accel→FeCl₃/citric acid}. After the TBS testing, the type of failure was inspected by a stereomicroscope. The pretreatment conditioning patterns of the lased dentin were evaluated under SEM.

 Results: The order of the TBS (mean value±SD, MPa) for each group was follows: A1 (10.5±3.5)<B1 (11.2±3.3)<A3 (13.1±2.4)<B3 (15.0±4.6)<A2 (16.7±5.5)<Cont1 (17.6±5.6)<B2 (19.2±5.9)<Cont2 (22.4±6.7). The TBS of groups Cont1, Cont2, A2 and B2 were significantly higher than those of groups A1 and B1. Moreover, there was no significant difference among groups A1, B1, A3 and B3 (Fisher’s PLSD test, p<0.05). The predominant mode of failure of groups B2 and Cont2 exhibited cohesive failure of adhesive or tooth substrate. There was a clear tendency that more cohesive failures occurred in the groups with higher TBS. From SEM observation of the chemical pretreated dentin surface, groups A2 and B2 produced a more homogeneous smooth inter-tubular dentin surface, however, micro-cracks were clearly detectable on the peritubular and inter-tubular dentin surface. Groups A3 and B3 showed roughening of the inter-tubular dentin surface.

 Conclusion: Within the limitations of this study, it is concluded that p-toluenesulfinate and FeCl₃/citric acid conditioning have the effect of promoting resin bonding to irradiated dentin.

 Purpose: Resin-based sealers are difficult to remove at the time of root canal retreatment due to their adhesion to the root canal dentin. This study investigated the working time taken to remove the filling material and the remaining percentage in the root canal for MetaSEAL Soft (MSS), MetaSEAL Soft Paste (MSSP) with increased bismuth content for improved X-ray contrast, and two other usual standard sealers.

 Materials and Methods: For the root canal filling, 48 transparent simulated resin models with a 30-degree curved root canal were used. The working length was set to 12.5 mm. The root canals were enlarged up to 30/06 NiTi rotary file with TriAutoZX2. After root canal preparation, four root canal filling sealers, CANALS (CA), MSS, MSSP and AH Plus jet (AP), were used. The blocks were divided into the single-point root canal filling group and the sealer filling group (n=24). After the sealer had set, the filling material was removed until the file reached the working length and the time of sealer removal was measured as the removal time. In addition, Micro-CT was taken, and the volume of the remaining root canal filling material at the 3-mm apical area was measured and calculated with 3-dimensional analysis software. The obtained data were analyzed statistically with PC software.

 Results: The removal time of the single-point filling group was shorter in the order of MSS<MSSP<CA<AP. The removal time of MSS was significantly shorter statistically between MSS and MSSP, and between MSS and CA (p<0.05). In the sealer filling group, the removal time was shorter significantly in the order of MSS<CA<MSSP, and all three groups finished in less time than the single-point filling group. On the other hand, the file did not reach the working length after more than 10 minutes in the AP. The amount of remaining filling material was lower in MSS than in MSSP, in the order of MSS<MSSP<CA. There were significant differences between CA and MSSP, and between MSS and MSSP.

 Conclusion: MSS and MSSP were not affected by bismuth carbonate oxide and showed equal or superior removal to CA.

 Purpose: Gingival hyperplasia is induced by inflammation, drugs, heredity, tumors, etc., but cases that are frequently encountered in the clinic have gingival hyperplasia and are taking drugs for hypertension. In addition, diabetes and periodontal disease have been shown to have an interactive relationship, even considering the high frequency of onset. In this paper, we report a case of chronic periodontitis with drug-induced gingival hyperplasia in a diabetic patient who received initial periodontal therapy, for whom a good prognosis was obtained.

 Case: A 44-year-old man was referred by a local doctor with the chief complaint of swollen gums. From the results of periodontal pocket examination, the average probing pocket depth (PPD) was 4.9 mm, and pockets of 4 mm or more were found in 80.4% of the sites. The patient was diagnosed with generalized moderate chronic periodontitis (new classification: stage Ⅲ grade C) and drug-induced gingival hyperplasia. By thoroughly controlling inflammation with initial periodontal therapy, the periodontal pockets were significantly reduced (PPD average, from 4.9 mm to 2.5 mm). In addition, gingival hyperplasia, which was suspected to be affected by the drug, disappeared with the control of inflammation, so no drug change consultation was given to the medical department. After the swelling of the marginal gingiva disappeared, caries treatment and prosthetic treatment were performed to remove the plaque retention factor.

 Results: The periodontal inflamed surface area (PISA) value decreased from 2,291.0 mm² at the initial visit to 91.4 mm² at the latest SPT. The HbA1c level decreased from 7.9% at the initial visit to 6.9% at the latest SPT. It is considered that the remarkable decrease in the inflammatory surface area of the periodontal pockets may have helped to improve the control status of diabetes.

 Conclusion: We were able to obtain a good prognosis for this diabetic patient with chronic periodontitis accompanied by drug-induced gingival hyperplasia with only initial periodontal therapy without changing the drug. The control of risk factors such as drugs, diabetes, and smoking that could greatly contribute to the progression of periodontitis depends largely on the patient’s environment and personality; in actual control, cooperation with the medical department is important. When collaborating, it is necessary to avoid requests that affect the underlying disease control in hospitals and clinics as much as possible. At the same time, intensive periodontitis control in dentistry is good for systemic disease control and it is important to perform dental treatment while recognizing its strong influence.