Coronavirus disease 2019 (COVID- 19) was first reported in Wuhan (Hubei Province, China) in December, 2019. With stunning speed, now it is sweeping across the whole world, causing a global health emergency of international concern. On March 11, 2020, the World Health Organization declared COVID-19 a global pandemic. By May 28, 2020, the disease has been reported in over 210 countries and territories with increasing confirmed cases in Italy, the United States, Brazil, Russia, Spain, etc. With the ongoing outbreak, mental health of COVID-19 patients, health workers and the public has become great concern. 1 During the pandemic, all the provinces in China, as well as many cities in other countries like Italy, have raised highest health emergency level. Cities were locked down with residents staying at home to avoid disease transmission. Due to the prolonged lockdown, individuals are suffering from the feeling of isolation from society, which could further develop to depression and anxiety. 2 Among these individuals, a group of dental patients should be particularly focused on.
In a dental clinic setting, the patients, dentists and dental assistants are exposed to the aerosol mist of saliva or blood droplets generated from high-speed handpiece or ultrasonic instruments to the surroundings.
The delivery of orthodontic treatment involves close contact with patients. It was found that droplet and close contact transmission were the main transmission route for COVID-19. 3 It was previously reported that nine dental practitioners were infected by the coronavirus in the School and Hospital of Stomatology, Wuhan University. 4 As such, many dental hospitals and clinics were advised to provide treatment for dental emergencies only with the shutdown of all other dental departments especially in the Hubei province since the 23rd of January, 2020. Thus, routine follow-up visits of orthodontic treatment had been interrupted by the pandemic. Furthermore, some patients suffered from orthodontic emergencies, such as loose brackets, protruding wire, etc., but they were unable to get timely and effective help from the specialists. After the 25th of February, some hospitals and clinics were allowed to open with extra-protective measures like epidemiological record evaluation, temperature check and upgraded personal protective measures during the dental treatment. [4] [5] [6] All these factors might lead to an increase in mental stress of the patients.
The objectives of the present study were to evaluate the mental distress of orthodontic patients and to investigate the level of their anxiety on treatment duration and outcome during the early stage of the pandemic.
The study protocol was approved by the West China Hospital of Stomatology (Approval no.WCHSIRB-D-2020-218). Since the investigator could reach the participants only by telephone or internet, an online anonymous questionnaire consisting of 5 sections (Figures 1 and 2 ) was developed in Mandarin Chinese via www.wjx.cn.
A total of 48 orthodontists were invited to distribute the questionnaire to their patients, asking their patients to fill in this questionnaire. The inclusion criteria were as follows: (1) in the process of orthodontic treatment; 2) able to read Mandarin online; (3) had informed consent for the use of the data recorded; (4) completed all the items in the questionnaire within a reasonable time. The online questionnaire was available from February 20 to February 22, which was during the early stage of the pandemic. Section 1 is the demographic and COVID-19 related epidemical information, including gender, age, education level, residence, family income, marital status, profession and accompany status, and the history of COVID-19 related symptoms, close contact with individuals from Hubei province, close contact with confirmed or suspected patients.
Section 2 is about the perception of the epidemic, which includes the knowledge and severity of the epidemic, the risk of infection of themselves and people around them, and the main concerns about the epidemic.
Section 3 is focused on the orthodontic state of the patients, including the type of their dental institutions and orthodontic appliances, interval from their last dental visit, the duration since treatment began, the way they get the suspension notice, and the frequency of contacts from their orthodontist. Section 4 assesses the orthodontic related mental state. There are 15 items in this section with a five-point scale ranging from score 1 to 5 for each item. The 15 items aim to evaluate the patients' anxiety about treatment duration and outcome, their compliance, patience and independence. Specifically, compliance is defined as the ability to perform the home instructions such as elastics use, sequential change of aligners and oral hygiene maintenance. Independence refers to the ability to deal with orthodontic accidents and the initiative to communicate with the dentist. Patience is defined as the willing to wait for the appointment until the epidemic was under control. Section 1-4 are developed by a proficient orthodontist who has more than 20 years of experiences with the help of two junior orthodontists. All these items were validated preliminarily. Section 5 is the Kessler-10 Psychological Distress Scale. There are 10 items to evaluate the mental distress in the past 4 weeks. 7 A five-point scale of each item ranges from score 1 (none of the time) to score 5 (all of the time), summing up to a total score ranging from 10 to 50. The Chinese version (CK-10) had been proved with highly acceptable validity and reliability (Cronbach's α ranged from 0.80~0.87) in previous studies. [8] [9] [10] A total score of 10-19 is considered normal, 20-50 considered having mental distress.
After data collection, internal consistency of items in section 4 and 5 was evaluated by calculating Cronbach's alpha coefficients. 11 The items in section 4 were selected for subsequent principal component analysis (PCA). 12 Sampling adequacy was tested using Kaiser-Meyer-Olkin (KMO) test. 13 Then K-means cluster analysis was performed using each principal component (PC) to classify the study samples into two categories based on the characteristics of each PC. The mental distress and the classifications of PC, which were binary variables, were considered as dependent variables in bivariate logistic regression analysis, to assess the association with their independent variables. The strength of the relationship was interpreted using odds ratios (OR) with 95% confidence intervals (CI). The model adequacy in bivariate logistic regression was approved with Hosmer and Lemeshow goodness of fit test. All statistical tests were two-sided, and were (Table I) .
For the patients' perception of the epidemic, 292(63.76%) respondents thought they knew COVID-19 much and 107 (23.36%) thought they knew very much. 304 respondents reckoned this disease as very severe ( were concerned about the isolation from the family or society (Table III) .
For the patients' orthodontic status, 264 (57.64%) patients were registered in orthodontic departments in dental hospitals. Fixed labial appliances were worn by 309 (67.47%) patients, 94 (20.52%) clear aligners and 35 (7.64%) patients wore fixed lingual appliances. Only 9.61% (44/458) of the patients had visited the orthodontist within a month. For the way to get the suspension notice, 242 (52.84%) were informed by the doctor. For the frequency of contact from dentist, 283(61.79%) had contacted the dentist 0-1 time while 70 (15.28%) had 3 times or more (Table IV) .
Cronbach's alpha value for the total 15 items in section 4 was 0.700. The PCA derived 5 components with 66.26% of cumulative explanation (Table V , Ⅱ). The KMO value was 0.787. PC1 and PC2 depicted the anxiety about treatment duration and treatment outcome. The compliance, independence and patience of the patients were described in the PC3, PC4 and PC5, respectively ( Table Ⅱ) . The classifications of K-means cluster analysis based on each PC were shown in Table Ⅱ .
Cronbach's alpha value (internal consistency) for the 10 items in section 5 was 0.938. The mean value (±SD) of CK-10 scale in this study was 18.38(±7.21). The prevalence of mental distress among the participants was 38.00% (174/458) with 95% CI (33.50, 42.50). Table VII , the results of multi-variable regression showed that female patients (OR 1.77, 95% Cl 1.07-2.93), concern about isolation from the family or society (OR 1.54, 95% Cl 1.04-2.30), time interval of more than 6 months since last visit (OR 5.023, 95% Cl 1.45-17.38) and Hubei residence (OR 5.69, 95% Cl 2.30-14.12) revealed higher odds of mental distress. were found less associated with high anxiety about treatment duration (PC1) compared with fixed labial appliance. In addition, 1-2 months since last visit (OR 2.18, 95% Cl 1.12-4.22) and 2-6 months since last visit (OR 2.89, 95% Cl 1.20-6.95) were more associated with high anxiety about treatment duration compared with within 1 month since last visit. Knowing about suspension from official accounts (OR 1.72, 95% Cl 1.14-2.59) and told by other patients (OR 3.96, 95% Cl 1.14-13.76) were more associated with high anxiety about treatment duration compared with informed by their doctors (Table VIII) .
Residing in urban area (OR 0.53, 95% Cl 0.33-0.86), concern about isolation (OR 2.02, 95% Cl 1.37-2.97) and more than 6 months since last visit (OR 7.44, 95% Cl 1.97-28.11) were more associated with high anxiety about treatment outcome (PC2 , Table VIII ). No independent variable was found to be associated with high compliance (PC3, P>0.05).
General dental departments (OR 2.61, 95% Cl 1.97-28.11, compared with dental clinic) and clear aligners (OR 2.25, 95% Cl 1.34-3.80) showed higher association with high independence (PC4).
Non-medical related occupation showed less association with high independence. Two times of dentist contact (OR 2.21, 95% Cl 1.35-3.62) and 3 times and more (OR 2.06, 95% Cl 1.15-3.69) were more associated with high independence compared with 0-1 time ( Table Ⅷ) .
Receiving treatment in dental clinics (OR 1.88, 95% Cl 1.01-3.48), general dental departments (OR 1.75, 95% Cl 1.11-2.76) were more associated with high patience (PC5). Patients with non-medical related occupation (OR 0.57, 95% Cl 0.34-0.96) revealed lower odds of high patience (Table ) Ⅷ .
Our study revealed that 38% (174/458) of the participants had mental distress, which was relatively worse compared with previous studies. 7, 14 The mean value (18.38) was relatively higher than the mean value The number of female patients was three times more than that of male patients, which was consistent with the trend that females are more likely to seek orthodontic treatment. 16, 17 Half of the patients were undergraduates and 61 (13.32%) patients had a higher education level than undergraduate. The reason might be that patients with higher educational level were familiar with the online technology and were more willing to fill the online questionnaires. 18 Another reason might be that some patients in primary or high schools were not allowed to use the smartphones by their parents.
The results of the questionnaires showed that the majority of the respondents took COVID-19 as a serious disease and showed great concerns, though this study was conducted at a relatively early stage of the pandemic. Majority of the patients (90.39%) were unable to visit the orthodontists for over 1 month amid the outbreak, and the interval tends to extend as some hospitals and clinics remain closed. Over half of the patients seldom got contact with the orthodontist, since some orthodontists might not share their contact details with the patients.
In PCA, items with larger factor loadings (>0.60, Table V) were considered to be more critical in the meaning of the PCs. 19 Thus, the meaning of each PC was interpreted based on the content of the items. The results of K-means cluster analysis indicated that the majority of the patients hold relatively positive attitudes towards the pandemic. Over half of them had low level of anxiety about the treatment duration and outcome, but the anxiety might increase as the suspension goes on.
Many factors were found to be associated with orthodontic patients' mental health. In this study, we found that female patients were more likely to have mental distress, which might be attributed to the biological nature of their responses to stressors and risk factors, 20 as well as their lower quality of life in orthodontic treatment. 21 In addition, patients currently in Hubei had significantly higher odds of mental distress as they might suffer more from the fear of the virus and endure longer isolation from the society.
Patients living in rural areas were more prone to develop anxiety about treatment outcome. The reasons might be that they had lower incomes than urban residents (P <0.001, supplementary Table ) and might be Ⅰ more vulnerable to the economic impact brought by the pandemic. In addition, they might endure more transportation difficulties when revisiting their orthodontists as most dental clinics and hospitals were located in cities. Patients worried about isolation from the family or society might feel hopeless and being cut off from the society. Therefore, they were apt to have mental distress and anxiety about treatment outcome. Additional attention could be given to these patients.
Time interval from the last dental visit was shown to be an associated factor. Disruption of routine appointment led to higher odds of mental distress, anxiety about treatment duration and outcome, Beckwith FR et al. 22 reported that each missed appointment added 1.09 months to treatment time, and 64.63% of the patients held the view that the pandemic would extend the entire treatment. It could infer that a prolonged delay during a lockdown could potentially lead to a further increase in the severity and number of patients who developed anxiety and mental distress, although the delivery of orthodontic treatment is considered to be elective and regarded as non-essential dental service when compared with dental emergencies.
Orthodontists should work on relieving patients' anxiety, since two-month-delay does not affect that much in an overall 2 years of treatment. In addition, the prolonged delay might have impact on the gingival health and white spot lesion development when the lockdown period is extensive, since not every orthodontic patient develops good home care oral hygiene practices during treatment. This factor has implication on treatment outcome. Future researches could investigate the longer-term impact.
Type of appliances was associated with anxiety about treatment duration. Treatment duration of both labial and lingual fixed appliances could be affected by replaced brackets/bands and missed appointments. 23 The treatment duration of lingual appliances is similar with buccal appliances, 24 but with the invisible characteristics of lingual appliances, patients seems to be less worried about the treatment duration. Another consideration is that lingual appliance wearer had higher incomes than buccal appliance wearers (P <0.001,
supplementary Table Ⅱ) , and patients with better financial condition might be less anxious amid this pandemic. However, the explanations to substantiate this finding would require future investigation. The aesthetics of clear aligners is better than labial appliances as well, 25 and clear aligners are less affected by orthodontic emergencies and missed appointments if the patients have got enough sets of aligners from the orthodontist. Therefore, patients with clear aligners also tends to be less anxious about the treatment duration.
Type of dental institution was shown to play an important role in the mental behavior of orthodontic patients. Patients registered in dental clinics showed the lowest independence to deal with orthodontic accidents while patients receiving treatment orthodontic departments in dental hospitals wanted to revisit their dentists more urgently after the pandemic. These findings might be related with the differences of dental institutions, both in practitioners and infrastructures. In mainland of China, practitioners in public hospitals might provide patients with more official instructions, 26 contributing to their high independence.
The infrastructures in general dental departments and dental clinics might not be as comprehensive as the orthodontic departments in dental hospitals, 27 and that would increase patients' concern with nosocomial infection causing further delay in their revisit.
In this particular period, "teledentistry" is of great value. 28 The manner of communication with patients was associated with anxiety about treatment duration. Patients who got the suspension notice directly from the doctor showed less anxiety compared with patients who got the notices from official accounts, websites or other patients, suggesting effective contact was important for patients whose appointments have been interrupted. As the pandemic is not totally under control, orthodontists should contact the patients regularly and personally, especially patients from the "hotspot" areas, and give them instructions about oral health maintenance and emergency handling. In this way the patients might express less mental distress and could maintain better orthodontic condition by themselves.
Based on the results, we want to provide the following recommendations to the practitioners: (1) Routinely and directly communicate with the patients during a lockdown; (2) 29 it could be improved by implementing response scales with more points. In addition, no independent variable was found to be associated with PC3
(compliance) while personal characteristics, pain, inconvenience and specific dental knowledge were reported to be correlated with compliance in previous studies. 30 Items related to the associated factors about compliance could be added into section 1 in future questionnaires.
Over one third of the orthodontic patients experienced mental distress during the early stage of the COVID-19 pandemic. Multiple factors affected the level of mental distress of orthodontic patients, such as the type of orthodontic appliance, interval from the last dental visit, manner of communication with the orthodontist, and the localities of the pandemic progression. 