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Background To study the caries lesion activity response to topical 38% silver diamine fluoride (SDF) therapy with increasing treatment application time. Methods/design The design is a stratified-randomised, double-blind, active-controlled, parallel-group clinical trial with nine treatment arms. The trial will involve recruiting at least 414 3- to 5-year-old kindergarten children with caries, who will receive approximately 0.004 mL of 38% SDF (the typical amount applied per the manufacturer’s instructions) to treat each caries lesion. The children will be stratified by caries status, randomised by blocks, and allocated to nine groups of SDF application times: 3, 5, 10, 15, 30, 45, 60, 120, and 180 s. The outcome measure is caries lesion activity (active/arrest) at the tooth-surface level at 6 months post-initial treatment. A calibrated dentist will conduct the blinded clinical examinations at baseline and at the 6-month follow-up. In addition, the parents will be surveyed to examine the effects of the moderating variables, such as oral hygiene, on caries lesion activity. The hypothesis is that a monotonically increasing trend can be found between the SDF application time and the proportion of caries lesions that are arrested. The Cochran-Armitage test for trends in proportions, corrected for clustering within children, will be used to determine the relationship between the exposure to SDF (the SDF application time) and the response (proportion of lesions arrested) in children, taking into consideration the effect of the moderating variables as well as the nesting of multiple caries lesions within an individual child. An EC 80 analysis (an 80% maximal concentration) will be used to determine the exposure (the SDF application time) for 80% caries lesion arrest. Bootstrap methods will be used for clustered data and will be resampled by clustering to determine the 95% confidence interval. Discussion This study will help with determining the optimal application time for SDF treatment. It will provide an evidence-based protocol for the use of SDF to arrest tooth decay in the primary teeth of young children. The results will inform an evidence-based SDF protocol to arrest caries, which affects 573 million children with tooth decay worldwide. Trial registration ClinicalTrials.gov NCT04655430. Registered on 7th December 2020.

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This cross-sectional survey investigated untreated early childhood caries (ECC) and its associated factors among 5-year-old children in Hong Kong. Children were recruited using a multistage sampling method. One dentist examined the children in kindergarten to diagnose untreated ECC (dt) at the cavitation level. Each child’s demographic information, snacking behaviour, and oral health-related practice were collected using a parental questionnaire. The relationships between the untreated ECC and demographic information, snacking behaviours, and oral health-–related practice were analysed by zero-inflated negative binomial (ZINB) regression analysis. This survey recruited 404 children. Their dt score was 2.8 ± 3.8. The significant untreated ECC (SiUC) index, which was one-third of the children with the highest dt score, was 7.1 ± 3.6. Their untreated ECC prevalence was 57%, which was associated with the district the child lived in. Most children with untreated ECC (71%, 164/231) had never visited a dentist. Children who brushed without toothpaste had more untreated ECC. Children coming from low-income families and with a lower maternal education level had a higher risk of ECC. In conclusion, untreated ECC was prevalent and unevenly distributed among 5-year-old children in Hong Kong. Its prevalence was associated with toothpaste use, family income, maternal education level and the district they lived in.

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Background Silver diamine fluoride (SDF) and sodium fluoride (NaF) are widely used for caries management. The objectives of this study are (i) to compare the caries-arresting and caries-preventive effects of SDF and NaF in young children, (ii) to determine children’s and parents’ acceptance of these fluoride therapies and (iii) to investigate the short-term (1 day) and long-term (1 year) adverse effects of these fluoride therapies. Methods/design This is a randomised, double-blind, active-controlled clinical trial to be conducted in Hong Kong kindergartens. The study has received approval from the local institutional review board. Written consent will be obtained from the parents/guardians before the study. The study will recruit at least 688 healthy 3-year-old children. This sample size is sufficient for an appropriate statistical analysis. Stratified randomisation will be performed for intervention allocation. The two intervention groups are 38% SDF and 5% NaF varnish applied on six primary upper anterior teeth. At baseline, one trained examiner will perform clinical examinations of the children in the kindergartens. The caries experience and oral hygiene status of each child will be recorded using the decayed, missing (due to caries) and filled primary tooth index and visual plaque index, respectively. Then, an independent operator will apply the assigned fluoride after the dental examinations. The examiner, the children and their parents will be blinded to the intervention allocation. In addition, a research assistant will evaluate the child’s acceptance using interval rating scales for children’s uncooperative behaviour. The examiner will then visit the children the next day to study the short-term potential adverse effects of the fluoride therapies. The same examiner will perform a follow-up examination after 1 year to evaluate the children’s caries experiences, their oral hygiene statuses and the adverse effects of the fluoride. Parental questionnaires will be used to assess parental satisfaction and concerns about the fluoride therapies. Discussion This study provides essential information about using SDF in an outreach kindergarten service for caries management from different aspects, which include the caries-arresting and caries-preventive effects, the adverse effects and children’s and parents’ acceptance. The success of the service can help to increase the adoption of SDF to reduce the global burden of early childhood caries. Trial registration ClinicalTrials.gov NCT04399369. Registered on May 2020

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