Shocking Fact: One in Four Children Aged 5–7 May Have “Oral Hypofunction”? The Latest Research and What Moms Should Know and Do | 六本木の歯医者・歯科医院 | 東京国際歯科 六本木

Hypofunction

Have you noticed any of these “oral SOS” signs in your child during everyday life? “Their mouth is always slightly open,” “Meals take a very long time,” or conversely, “They swallow without chewing much.”

These are not just habits or picky eating. They may be signs that oral functions have not yet fully developed. According to the latest research published in 2026 (Kawamura et al.), ages 5–7 represent a critical turning point when “the oral functions used for life” are established. Notably, around the time of entering elementary school, both tongue strength (tongue pressure) and the ability to keep the lips closed develop dramatically.

From a specialist perspective, this article logically explains surprising findings from recent data and practical strategies you can start at home today.

A Striking Reality: “Functional Deficits” Hide Even Among Kids Who Don’t Visit the Dentist

An underdeveloped state of oral function is clinically called Developmental Insufficiency of Oral Functions (DIOF). It refers to insufficient development of functions such as eating and speaking.

What this study reveals is the sheer prevalence of this “invisible risk.”

– About 23% (roughly one in four) of community-dwelling children aged 5–7 meet the criteria for DIOF

– Some nursery/preschool surveys report rates approaching 40%

– Meanwhile, the diagnostic rate in dental clinics is as low as 2.4% to under 10%

This discrepancy indicates that many parents are unaware of problems in their child’s oral function, allowing latent risks to be overlooked. Because there is usually no pain, it is hard to notice—yet a significant number of children are missing appropriate support right around this “developmental turning point” before and after starting elementary school.

Key Warning Signs: Don’t Miss “Open-Mouth Posture” and “Eating Time”

According to the data, children diagnosed with DIOF share characteristic signs. Pay particular attention to the following two:

1. Lips don’t close (open-mouth posture): The mouth remains open at rest.

2. Chewing time is either excessively long or unusually short.

These are not merely “manners” issues. They suggest insufficient development of the perioral muscles (muscles around the mouth). Supporting this, the study reported:

“Over 60% of the DIOF group showed incomplete lip closure at rest and abnormal chewing time.” (Source: Kawamura+2026.pdf)

A Surprising Finding: “Liking Hard Foods” Matters More Than “How Often They’re Eaten”?

There’s no need to feel pressured to “force hard foods to train the mouth.” The latest research offers a slightly unexpected, parent-friendly message:

– Children who like hard foods (e.g., rice crackers, carrot sticks, walnuts) have a significantly lower risk of DIOF (aOR = 0.636).

– By contrast, the mere “frequency” of eating hard foods was not directly associated with reduced risk.

In other words, a child’s psychological preference is more important than sheer repetition. Rather than making them chew by force, nurture the mindset that “crunchy, chewy textures are tasty and fun,” and create opportunities to enjoy them. That intrinsic enjoyment becomes the shortcut to self-driven development of oral musculature.

The Overlooked Cost: Oral Function Is Directly Linked to Nutrition

“Won’t weak chewing just resolve as they grow?” It’s risky to be optimistic. Insufficient oral function can rob children of the very “nutrition” most needed during growth.

The data show that, compared to peers without DIOF, children with DIOF have significantly lower intake of the following key nutrients:

– Energy, carbohydrates, fats

– Protein

– Calcium, iron

– Vitamin A, vitamin D

– Vitamin B1, vitamin B2, vitamin C

There is a real risk of a negative spiral: “Chewing is hard, so they eat less. Because they eat less, the oral muscles are used less and don’t develop.” Early detection is essential to support healthy bodies in the years ahead.

Summary: What You Can Do Now for Future Smiles

Here are the three key takeaways the latest research offers for moms:

– One in four children aged 5–7 may have unrecognized “oral hypofunction (DIOF).”

– “Open-mouth posture” and “abnormal eating time” are SOS signals from the perioral muscles.

– Rather than forcing hard foods, nurturing a love for “chewy/crunchy textures” is the key to development.

The period around entering elementary school is the prime window when tongue strength and lip-closure ability develop significantly.

When you observe your child at mealtime today, are they enjoying each bite with a happy “Yummy”? That sense of enjoyment is the very first step in building lifelong oral health.

Reference

Kawamura, J., Kanno, S., Shintani, T., Matsui, M., Komagamine, Y., Soeda, H., … & Kanazawa, M. (2026). Evaluation of Oral Function Development and Eating Habits in Children Aged 5–7 Years. Journal of Oral Rehabilitation.