Ethical aspects and participants
This study was approved by the Ethic Committee of the School and Hospital of Stomatology, Wuhan University (Approval no. HGGC-035). Caregivers with preschool children aged 3–6 years living in China during Wuhan lockdown participated in the survey. The questionnaire is completed on a voluntary basis. Completing and submitting this questionnaire would be regarded as consent to participate. In this study, random sampling was used. Accordingly, the sample size was calculated by the Cochrane formula as following. However, for more accuracy in citing the research results, the sample was increased to over 4000.
$$\begin{aligned}& {\text{Sample}}\,{\text{size}} = \left[ {{\text{X}}^{2} {\text{NP}}\left( {1 - {\text{P}}} \right)} \right]/\left[ {{\text{d}}^{2} \left( {{\text{N}} - 1} \right) + {\text{X}}^{2} {\text{P}}\left( {1 - {\text{P}}} \right)} \right] \\ & = [1.96^{2} \times 60000000 \times 0.5(1 - 0.5)\left] / \right[0.05^{2} \times (60000000 - 1) \\ & \quad + \,1.96^{2} \times 0.5(1 - 0.5)] \approx 384 \\ \end{aligned}$$
N is the population size of 3–6 years old children in China.
Questionnaire
The questionnaire was designed by experts in preventive dentistry through discussion (Additional files 1 and 2). This cross-sectional survey was carried out from 1 to 7 May 2020, which was the week that marked 100 days after the beginning of Wuhan lockdown. Because a community-based national sampling survey was still not feasible to conduct in the present, the information was collected online. An electronic questionnaire was designed by using Questionnaire Star (http://www.wjx.cn) [10]. We conducted sampling using the snowball strategy [11]. Through the authors’ networks with people in China, a recruitment link or quick response (QR) code was distributed to groups in their WeChat accounts. Then the individuals in this group distributed to other people who can participate in the survey. This process continued until sample size met the requirements. No monetary rewards were given for the completion of the questionnaire.
The questionnaire consisted of two parts: demographics and variables. Demographics included gender (male and female), age (3, 4, 5, 6 years old), and place of residence (Wuhan, other cities of China) during Wuhan lockdown. Variables were developed according to the influences of COVID-19 on the oral health and its associated issues of preschool children. These variables addressed oral health status, attitudes and behaviour (oral hygiene and utilization of dental services behaviour).
To understand pre-schoolers’ oral health status, we listed options including dental caries, toothache, halitosis, gingival bleeding, gingival swelling, tooth trauma, fillings removal and others for them to multiply choose. It was a self-assessed question. Caregiver assessed the children whether they had these oral diseases.
Attitudes towards the oral healthcare of caregivers were also measured by questions, which were involving oral health attention and preventive measure during Wuhan lockdown and in the future when the epidemic was controlled.
In the aspect of oral health-care behaviour, there were sugar consumption behaviour, oral hygiene behaviour and utilization of dental services behaviour. For sugar consumption, three typical categories of sweet things were questioned, including sweet foods, sweet drinks, and sweetened milk/yogurt/tea/coffee. The frequencies were little or never/One to three times a month/once a week/two to six times a week/once a day/more than once a day. For oral hygiene behaviour, the questions contained: (1) brushing frequency, (2) caregiver helping brush, (3) toothpaste utilization. For utilization of dental services behaviour, the solutions of oral problems during Wuhan lockdown and in the future were compared, moreover, the worries about treatment were analyzed.
To ensure the quality of the questionnaire, a pilot survey was conducted. After the questionnaire was modified timely, the network survey was carried out on a voluntary basis. All questions were required to be completed as to ensure the response rate.
Statistical analysis
After the national cross-sectional survey, the data were exported, logically checked and statistically analysed by SPSS 19.0 (SPSS Inc., Chicago, IL, USA) software. The results were described by the composition ratio. The differences between variables and places of residence places were compared by the chi-square test. The inspection level was set at α = 0.05.
