This clinical trial had two objectives. The first was to compare the effectiveness of 950 ppm fluoride toothpaste versus probiotic toothpaste in preventing dental caries in 4- to 5-year-old children. The second was to understand how children's oral hygiene habits and dietary habits influence the development of dental caries.

The main questions it aimed to answer are:

• Does fluoride toothpaste reduce new caries more than control toothpaste?
• Does probiotic toothpaste reduce new caries more than control toothpaste?
• Which oral hygiene and dietary habits are risk factors for dental caries?

Researchers compared fluoride toothpaste and probiotic toothpaste to a control toothpaste (without active ingredients).

Participants were asked to complete the following tasks:

• Complete a questionnaire about their oral hygiene and dietary habits at baseline
• Undergo oral health examinations at baseline and after 12 months
• Brush their teeth twice daily (morning and before bedtime) with their assigned toothpaste for 12 months
• Use a pea-sized amount of toothpaste each time
• Brush under the supervision of parents to ensure brushing quality

Study design and setting This was a cross-sectional survey combined with a prospective, randomized, single-blind, controlled trial conducted in Pingdu City, China. Five kindergartens (two urban, three rural) were randomly selected.

Cross-sectional survey phase A total of 540 children aged 4-5 years underwent oral examinations performed by two trained and calibrated dentists. Parents completed a questionnaire on children's oral hygiene behaviors and dietary habits.

Randomized controlled trial phase

After baseline assessment, 508 children were randomly assigned to three groups (1:1:1):

• Fluoride toothpaste group: 950 ppm fluoride toothpaste
• Probiotic toothpaste group: Toothpaste containing Lactobacillus paracasei
• Control group: Toothpaste without active ingredients

Participants brushed twice daily (morning and before bedtime) with a pea-sized amount of assigned toothpaste for 12 months under parental supervision. Kindergarten teachers supervised lunchtime brushing. All participants received standardized oral health education at baseline and each semester.

Compliance monitoring Compliance was assessed using daily toothbrushing record cards and collected toothpaste tubes. Only children with moderate or good compliance were included in final analysis.

Ethical approval The study was approved by the Human Research Ethics Committee of The Affiliated Hospital of Qingdao University (Approval No.: QYFYWZLL29924). Written informed consent was obtained from parents or legal guardians, and verbal assent from each child.

Inclusion Criteria:

• Age 4-5 years (48-59 months)
• Informed consent obtained from parents or guardians, with permanent residence in Pingdu City and willingness to actively cooperate throughout the study
• No long-term medication use
• Absence of systemic diseases and mental health disorders

Exclusion Criteria:

• Not meeting any of the inclusion criteria
• Children whose parents or guardians did not provide informed consent
• Presence of systemic diseases or mental health disorders
• Long-term medication use