to each patient, endodontic diagnosis determined for the offending tooth and verbal numerical rating scale (VNRS) was used to record pain levels. Results: Of total patient visits during this period, 50.26% of visits were for endodontic treatment. No patients had fever (>37.2 ). One patient with a confirmed COVID-19 history was admitted after recovery. Three admitted patients had been exposed to confirmed or suspected COVID-19 patients. Twelve admitted patients (12.5%) with mean age of 62.42 ± 13.77 years had a history of systemic diseases.
The most common age group for endodontic emergencies was 45-64 years (30.21%) and patients of this group showed significantly higher mean VNRS score compared with that of the 6-19 years group and 20-34 years group (p<0.05). The majority of endodontic emergency diagnosis was diseases of symptomatic irreversible pulpitis (53.10%). Patients who were diagnosed with symptomatic irreversible pulpitis, symptomatic apical periodontitis and acute apical abscess showed significantly higher mean VNRS Score than that of other groups (p<0.05). Conclusion: Endodontic emergencies, with symptomatic irreversible pulpitis being the most common, consist of a much higher proportion of dental emergencies in a COVID-19 high risk area than normally. Vital pulp therapy can advantageously reduce treatment time resulting in reduced risk of infection for vital pulp cases. Rubber dam, personal protective equipment and patient screening are of great importance during the COVID-19 outbreak in protecting clinicians.
Cases of the novel severe acute respiratory syndrome coronavirus (SARS-CoV-2), the causative agent of the coronavirus disease 2019 (COVID-19) disease, were first reported in Wuhan, Hubei, China in December 2019 1 . Ever since the emergence of these first cases, COVID-19 has become a public health crisis globally. As of March 2, 2020, National Health Commission of China reported 49,426 cumulative cases and 2,251 deaths in the city of Wuhan 2 . To halt transmission, Hubei Province activated its Level 2 response to public health emergencies on January 23, 2020, and the city of Wuhan with a population exceeding 11 million was under lockdown and remains under lockdown at present 3-5 . In consideration of the risk dental treatment may pose during the outbreak, the Hubei Province government suspended regular dental treatments allowing only emergency treatments 4 . Endodontic infections can cause serious pain 6 , and endodontic emergencies are considered to be an important category of dental emergencies 7 . From January 24, 2020, all patients receiving emergency dental treatment were directed to the School and Hospital of Stomatology, Wuhan University's (WHUSS) General and Emergency Department, which remained the only hospital open within Wuhan for emergency dental treatments until March 2, 2020. Since February 22, 2020, the General and Emergency Department began administering a COVID-19 epidemiological investigation questionnaire, which was of particular interest for the purposes of this study. This study aimed to analyze the characteristics of endodontic emergency patients at WHUSS between February 22 and March 2, 2020 and is the first descriptive study that examines endodontic emergency dental patients at the epicenter of the COVID-19 outbreak. Here, we also provide suggestions for endodontic practice and infection control strategies based on these novel observations.
The study has been approved by the Ethics Committee of the School and Hospital of Stomatology at Wuhan University (project number: 2020B08). Patients who visited the General and Emergency Department at WHUSS due to endodontic emergencies from February 22 to March 2, 2020 were reviewed. Body temperature was acquired for each patient, and a COVID-19 epidemiological questionnaire was given before dental treatment.
The questionnaire consisted of the following four questions:
1. Are you a confirmed or suspected COVID-19 patient who has recovered after treatment?
2. Are you a confirmed or suspected COVID-19 patient with no symptoms?
3. Have you recently been showing COVID-19 symptoms? (optional) Such as: fever, cough, fatigue, vomiting, et cetera. 4 . Have you been in contact with confirmed or suspected COVID-19 patients recently?
Patients were asked to describe their level of pain using the verbal numerical rating scale (VNRS) 6 .
Only patients that had answered the questionnaire, described their level of pain, had their body temperature measured and received an endodontic diagnosis were included in this study.
Patient information such as date of visit, gender, age, systemic disease history and VNRS score were included in the study. Acquired body temperature and the COVID-19 epidemiological investigation questionnaires were reviewed. Diagnoses were based on the recommended consensus by the American Board of Endodontics and American Association of Endodontics 8 . The number of total patient visits and type of visits at the General and Emergency Department, WHUSS during the dates studied were compared to past statistics corresponding to these same dates in 2018 and 2019.
The characteristics of patients with endodontic emergency were stratified by subgroups including sex, age group and diagnosis by multivariate Poisson regression. Independent sample t-test or one-way analysis of variance (ANOVA) was performed to compare mean VNRS score. VNRS scores with p set to < 0.05 for statistical significance. All statistical analyses were performed with the SPSS 20.0 software (IBM Corp, Armonk, NY).
Demographic patient information is shown in Fig. 1 VNRS scores by gender, age, and endodontic emergencies are summarized in Table 2 .
Patients in the 45-64 years group accounted for 30.02% of total endodontic emergency patients and showed significantly higher VNRS scores compared to those of patients in the 6-19 years group and 20-34 years group (p<0.05). Among the patient population in this study, 97.90% were first-visit patients and the most common endodontic emergency diagnosis was symptomatic irreversible pulpitis (53.1% or 51/96 patients). In addition, patients with symptomatic irreversible pulpitis, symptomatic apical periodontitis and acute apical abscess had significantly higher reported VNRS scores than any other diagnosis (p<0.05).
The total number of patients attending General and Emergency Department at WHUSS during the COVID-19 outbreak (n=191) in our study was 18.24% of that of corresponding periods in 2019 (n=1047) and 19 .27% of that in 2018 (n=991). These results are consistent with that of a previous study 9 In this study, there was nearly the same ratio of male to female patients for both endodontic emergency patients (1.1:1) and all dental emergency patients (1.2:1), in contrast to other studies 11-15 that have shown a greater percentage of male patients presenting with dental emergencies. However, this discrepancy may be due to the higher proportion of endodontic emergency patients in our patient population. The largest age group for endodontic emergencies was 45-64 years (30.21%, 29/96) in our study. Importantly, older age and the existence of underlying comorbidities are associated with poorer COVID-19 prognosis 4, 16, 17 .
Since patients older than 65 years represented approximately 15% of all patients, care should be exercised to avoid cross contamination.
Patient screening was crucial during the SARS epidemic in 2002 and 2003 18 . An important tool in patient screening is the use of disease-specific questionnaires, which can differ depending on the location at which they are employed, for example, epicenter versus other sites. In this study, four patients with a previous COVID-19 history or possible COVID-19 cases were identified using the questionnaire. Fever was reported to be the most common clinical symptom (98%) for 41 patients diagnosed with COVID-19 in a previous study 19 . No patient with fever presented to the WHUSS due to endodontic emergencies".
Conversely, a patient with pyogenic osteomyelitis of the jaw was found to have fever (>37.2℃), but tested negative for COVID-19 by a series of diagnostic tests. Notably, several infections of the oral cavity could present with fever that could confound the diagnosis of COVID-19; thus fever alone should not be the only sign and symptom of COVID-19 to be evaluated and oral disease needs to be accurately diagnosed. The diagnosis of COVID-19 is currently based on a combination of epidemiologic information, clinical symptoms, chest CT imaging findings, and laboratory tests such as on RT-PCR respiratory tract specimens 4 .
Sabino-Silva et al. 20 has raised important questions about the role saliva plays in the human-to-human transmission of diseases, in particular respiratory coronaviruses 21, 22 .
The incubation period of COVID-19 has been estimated to be between 2 to 14 days 5 . It has been shown that patients with no symptoms or during incubation periods may have the potential to infect others 5 . Positive RT-PCR test results have been reported in recovered patients 23 . Endodontists should take appropriate measures to stay safe. During the COVID-19 outbreak, dentists in WUHSS were equipped with disposable N95 masks, gloves, cap, shoe cover, face shield, and gowns 4 . From February 22, 2020, patients with fever, or who had answered "yes" to any of four questions on the questionnaire, or needing dental procedures producing droplets and/or aerosols were required to undergo examination and treatment in an isolated clinic room with dentists equipped with protective suit instead of gowns 4 . To date, no cases of COVID-19 were reported among the twenty-six working staff of the General and Emergency Department at WHUSS working during the COVID-19 outbreak. RT-PCR findings for all working staff came back negative on March 24, 2020. Before the beginning of the study, nine working staff at the hospital level have been confirmed to have COVID-19, including three doctors, three nurses, two administrative staff, and one postgraduate student 4 .
This suggests that the safety precautions and screening measures enforced since February 22, 2020, were effective in protecting working staff.
Symptomatic irreversible pulpitis was the most common endodontic emergency, with significant high VNRS score in our study. Treatments for endodontic emergency were challenging during the COVID-19 outbreak, since inhalation of airborne particles and aerosols produced during dental procedures on patients with COVID-19 could potentially expose dentists to the virus 20 , thus making them high-risk procedures. Reducing treatment time and exposure control are two ways the risk of infection for endodontic treatment could be reduced. For vital pulp cases such as pulpitis, vital pulp therapy including pulpotomy or pulp capping might be helpful in terms of shortening treatment time. Pulpotomy has been reported to reduce pain symptoms in nearly 90% of dental emergency patients 1 day after treatment 24 . Partial pulpotomy using mineral trioxide aggregate (MTA) sustained a good success rate (85%) over 3-year follow-ups in mature permanent teeth clinically diagnosed with irreversible pulpitis 25 and full pulpotomy using MTA demonstrated 92.7% success rate at 3-year follow-up for caries exposed pulps in mature permanent molar teeth 26 . Direct pulp capping with MTA showed a cumulative survival rate of 85% in adult molars with carious pulpal exposure at 36 months 27 . For cases that required root canal treatments, cone-beam computed tomography (CBCT) and single file systems should be considered. Besides the advantages of detecting root canal location and configuration 28 , CBCT examination could avoid nausea or vomiting for patients that may occur during intraoral x-ray examination and prevent exposure to patients' oral cavity 4 . During root canal preparation, single file nickel-titanium systems could be used to save working time 29 , as well as prevent the risk of re-sterilization. For any treatment that produces droplets and/or aerosols, Dr. Hargreaves' group 30 suggested a number of preventative measures, such as the use of rubber dams. It has been reported that up to 70% airborne particles could be reduced around a 3-foot diameter of the operational field when a rubber dam was used 31 . In addition, rubber dam is not only able to limit the diffusion of the aerosol, but is also likely to dramatically reduce or even eliminate the presence of salivary components in the aerosol.
Only five cases of traumatic dental injury including two cases of "complicated crown fracture" and three cases of "dislocation of tooth," respectively, were diagnosed in our study.
Two patients made a subsequent visit for the completion of their root canal treatments. An online platform for patient consultations by the WHUSS was made available starting February 3, 2020 4 . It was reported that more than 1,600 patients had used this consultation platform, and only dental emergency cases were suggested for treatment at the hospital 4 .
In addition to providing endodontic treatment, endodontists should pay attention to patients' psychological health during the COVID-19 outbreak 32 . Public health emergencies may negatively impact individuals' mental health 33 . For instance, one patient in our study had a diagnosis of reversible pulpitis with dentin hypersensitivity had a high VNRS score of 8.
She demonstrated extreme anxiety and fear toward gaining a fever as a result of oral disease inflammation. During COVID-19 outbreak period, patients may suffer from psychological stress, endodontists should not only focus on the treatments of patients' endodontic diseases, but also their psychological state at times of emergency.
In conclusion, endodontic emergencies consist of a much higher portion of dental emergencies in a COVID-19 high risk area than normally. Reducing treatment time and exposure control are two ways to significantly reduce the risk of SARS-CoV-2 virus spreading during endodontic treatment. Vital pulp therapy has the advantage of shortening the treatment time. Rubber dam, personal protective equipment and patient screening are of great importance during the COVID-19 outbreak in protecting clinicians. Dentists should focus not only on the dental treatment but also patients' psychological status during public health emergencies. 