Why do children still get cavities if they brush twice a day and floss?

Why Children Continue to Get Cavities Despite Brushing and Flossing

Brushing and flossing alone are insufficient to prevent cavities if other critical risk factors remain unaddressed—specifically dietary sugar frequency, inadequate fluoride exposure, improper brushing technique, and lack of parental supervision in young children.

The Core Problem: Caries Requires Multiple Factors

The cariogenic process requires three elements working together: bacterial colonization (particularly Streptococcus mutans), substrate availability (fermentable carbohydrates), and frequency/duration of exposure 1. Simply removing plaque twice daily does not eliminate these other critical factors 2.

• Dietary sugar frequency matters more than total amount: The number of eating occasions and duration of sugar contact with teeth directly correlate with caries risk 1. Even with good brushing, constant snacking or more than 4 eating occasions daily creates repeated acid attacks that overwhelm protective mechanisms 1.

• Sugar intake threshold: Dental caries is lower when free-sugars intake is less than 10% of total energy intake, with optimal protection at less than 5% 1. The relationship between sugar consumption and dental caries is supported by consistent moderate-quality evidence 3.

Fluoride Exposure: The Missing Link

• Fluoride toothpaste concentration matters: Standard fluoride toothpaste (1,000-1,100 ppm) reduces caries by only 15-30% 4. Many children use lower-concentration "child-strength" toothpaste (250-550 ppm), which is significantly less effective 3.

• Inadequate fluoride retention: Children who rinse vigorously with water after brushing wash away protective fluoride 3. Persons aged >6 years should rinse briefly with minimal water or not at all to retain fluoride 3.

• Suboptimal water fluoridation: If drinking water contains insufficient fluoride, brushing alone may not provide adequate systemic and topical fluoride exposure 1, 5.

Brushing Technique and Supervision Failures

• Inadequate brushing duration: While 40% of parents report brushing for 30 seconds to 1 minute, most patients cannot achieve sufficient plaque removal with home oral hygiene measures 6, 7. Observed brushing duration of 1-2 minutes was recorded in only 51% of preschoolers 7.

• Insufficient parental supervision: Only 11% of preschool children brush under parental supervision 7. Mothers place dentifrice on the toothbrush 85% of the time at 9 months but only 31% at 60 months 8, leaving young children to manage their own oral hygiene prematurely.

• Excessive toothpaste use without supervision: The percentage of children using more than the recommended pea-sized amount increased from 12% at 9 months to 64% at 60 months 8. While this doesn't cause cavities directly, it indicates lack of parental oversight in oral hygiene practices.

• Inadequate brushing frequency: By age 5, less than half of children brush twice daily 8, despite this being the basic recommendation for caries prevention 3.

Specific High-Risk Behaviors Often Overlooked

• Prolonged bottle feeding: This well-established risk factor for early childhood caries provides fermentable carbohydrates that create an acidogenic environment 1. Breastfeeding beyond 24 months, especially at-will nighttime feeding, increases caries risk 2.4-fold 1.

• Bacterial transmission: Children acquire cavity-causing bacteria primarily from their mothers during the critical "window of infectivity" between 19-31 months 1. Poor oral hygiene in caregivers directly correlates with infant caries development 1.

Common Pitfalls in "Good" Oral Hygiene

• Timing misconception: Brushing twice daily is effective, but whether increasing from two to three times daily reduces caries is unclear 3. The critical factor is eliminating food impaction and shortening sucrose impact duration 6.

• Flossing alone is insufficient: While flossing removes interproximal plaque, it does not deliver fluoride or address dietary factors that drive the cariogenic process 2.

• Brushing effectiveness varies: Toothbrushing behaviour including technique, duration, pattern, frequency, toothbrush type, toothpaste type and amount, and parental involvement contributed significantly to plaque score change (86%), dental caries status (73%), and gingival index (66%) 7.

Actionable Algorithm for Prevention

1. Restrict eating occasions to ≤4 per day and limit free sugars to <5% of energy intake 3, 1

2. Verify fluoride exposure: Test drinking water fluoride concentration and ensure use of 1,000-1,100 ppm fluoride toothpaste (not child-strength formulations) 4, 5

3. Supervise brushing until age 6-8 years: Parents must place pea-sized toothpaste amount and ensure 2-minute brushing duration twice daily 1, 8

4. Minimize post-brushing rinsing: Rinse briefly with small amounts of water or not at all in children >6 years 3

5. Discontinue bottles by 12-24 months and wipe gums/teeth after nighttime breastfeeding beyond 12 months 1

6. Consider professional fluoride application: Semiannual fluoride varnish for high-risk children provides additional 26% caries reduction 4

The evidence clearly demonstrates that mechanical plaque removal through brushing and flossing addresses only one component of a multifactorial disease process—without controlling dietary sugar frequency, optimizing fluoride exposure, and ensuring proper technique under supervision, cavities will continue to develop despite apparent compliance with oral hygiene recommendations.