The "3-3-3 rule" — brushing three times a day, within three minutes after meals, for at least three minutes — has long been considered the gold standard of oral care. However, experts are increasingly warning that this conventional wisdom may actually damage teeth.
According to the "2025 Oral Health Survey" released by Hankook Research on Tuesday, 81% of respondents said they pay attention to managing their oral health, including teeth and gums. The figure is similar to those for physical health (81%) and mental health (75%).
In particular, among respondents who brush three times a day, 31% said they brush "within 30 minutes after breakfast, lunch, and dinner" — the highest share.
However, actual habits, including brushing frequency and duration, fall significantly short of expert recommendations. In other words, there is a wide gap between awareness and practice.
Dr. Kami Hoss, a U.S. dentist and orthodontist, said on CNN's podcast "Chasing Life" that "brushing right after waking up is effective in removing bacteria that have multiplied overnight and reducing bad breath," adding, "I recommend brushing before breakfast in the morning."
He also noted that for those who sleep with their mouths open, dry mouth becomes more severe, making morning brushing even more necessary.
In addition, the inside of the mouth becomes acidic right after eating. Brushing at this time can weaken "enamel," the hard layer that protects the surface of the teeth, leading to tooth damage. Enamel needs time to harden again.
Experts say that at least 30 to 60 minutes must pass after a meal before the tooth surface moves out of an acidic state and returns to a stable condition.
In particular, after consuming highly acidic foods such as orange juice or coffee, it is safer to wait about an hour before brushing.
According to research by the Academy of General Dentistry in the United States, a group that brushed within 20 minutes after drinking a carbonated beverage showed more severe damage to the tooth surface than a group that brushed 30 minutes to an hour later.
Experts recommend lowering oral acidity first instead of brushing immediately after meals. To do so, rinsing the mouth with warm water or green tea can help.
