“Is it really necessary to brush your teeth three times a day?”

Faced with this question he often received from patients in the clinic, Professor Seokmo Heo of the Department of Periodontology, College of Dentistry, Jeonbuk National University (JBNU) long hesitated to give a straightforward answer. He found it difficult to disclose that, as a dentist, he had for many years brushed his teeth only once a day, before going to bed.

Having been taught from childhood the so‑called "3‑3‑3 rule" — three times a day, for three minutes, within three minutes after eating — he had repeatedly experienced bleeding gums when brushing more often. The answer to this long‑standing question came from a lecture by a professor during his dental school years.

“The claim that you must brush three times a day actually lacks scientific evidence. It is far more important to brush thoroughly and properly even if only once a day.”

However, he too went through trial and error. Even when he followed the textbook methods taught in dental school diligently, his gums receded and his teeth developed wear, and one day he even discovered hidden cavities in the mirror. After re‑examining his brushing habits from a scientific standpoint, he has maintained such healthy gums in his 50s that a fellow periodontology professor told him his alveolar bone resembled that of someone in their mid‑30s.

Based on this experience and 26 years of clinical practice and research, Professor Heo has published a popular science book, Brushing for a Century: One Proper Brushing a Day — A Scientific Routine to Protect Your Teeth for Life (Sorinae). Drawing on the clinical evidence and studies summarized in his earlier professional work, Plaque Control Clinical Guide: Evidence‑Based Oral Hygiene Education, the book explains those findings in a way general readers can immediately understand and apply in daily life.

Since its release on September 20, the book rose to No. 2 on the weekly bestseller list (Health Information — Other) at the online bookstore Aladin within about a week (4th week of September). An author interview posted on the YouTube channel "Retirement School" has also attracted attention, surpassing 510,000 views (as of September 28).

The book's message is clear. The goal of brushing is not to eliminate all oral bacteria but to consistently control the plaque that accumulates on tooth surfaces. Therefore, technique matters more than frequency. Rather than brushing frequently, for a long time, or forcefully, it is better to thoroughly clean every tooth surface, the spaces between teeth, and the gumline even if only once a day.

To that end, the author proposes a three‑step routine: "tooth brushing" to clean tooth surfaces meticulously; "interdental brushing" to manage areas that are hard for the toothbrush to reach; and "periodontal brushing" to gently care for the gumline. He introduces a method of rinsing with water immediately after meals and then waiting 30 minutes to an hour before brushing, because the mouth becomes acidic right after eating. Brushing before sleep, when saliva secretion decreases, is identified as an essential time to perform oral hygiene.

Professor Heo emphasizes, however, that this does not mean one can neglect brushing. Even when brushing only once a day, one must thoroughly clean between the teeth and along the gums, and combine daily care with regular dental checkups and professional periodontal treatment when needed.

“Preserving your teeth for a long time is fundamental to living well: eating well, speaking well, and smiling comfortably,” Professor Heo said. “I hope people reconsider brushing not as a thoughtless repetitive habit but as a scientific routine for caring for their bodies.”

The book addresses readers’ frequently asked questions in everyday life, including the origin and limitations of the "3‑3‑3 rule," how to choose a toothbrush and toothpaste, the differences between electric and manual toothbrushes, correct use of dental floss and interdental brushes, misconceptions about fluoride, and the connections between gum health and systemic conditions such as diabetes and cardiovascular disease. Rather than listing complex dental knowledge, the book first explains "why" and then provides step‑by‑step guidance on "how" to implement it. Full‑color photographs and diagrams, along with a two‑week routine checklist for each part, help readers put the guidance into practice.

Seeing patients in the university hospital clinic who continue to eat with their own teeth into their 80s and 90s convinced him that lifelong preservation of teeth stems from consistent daily oral hygiene care, Professor Heo said. The "Brushing for a Century" he advocates is not merely a brushing technique but the most basic daily habit for preserving one’s natural teeth before considering implants and for preparing for healthy longevity in the centenarian era.

Professor Seokmo Heo graduated from Seoul National University College of Dentistry, completed his periodontology specialty training at the University at Buffalo School of Dental Medicine, State University of New York, and earned a Ph.D. in Oral Biology from the same graduate school. He is currently a professor in the Department of Periodontology, College of Dentistry, JBNU, and a periodontology specialist at the JBNU Dental Hospital. He has served as head of the Department of Periodontology at JBNU Dental Hospital, an item writer for the Korean National Dental Licensing Examination and the periodontology specialty exam, and a director of the Korean Academy of Periodontology and the Korean Academy of Gerodontology. He continues research and education in plaque control, periodontal disease prevention, and evidence‑based oral hygiene education.

[Book Information] Brushing for a Century, by Seokmo Heo | Sorinae | September 20, 2026 | KRW 20,000 | ISBN 979-11-6372-270-0