Most mouth habits in children do no lasting harm; the ones that matter press on the front teeth for hours a day and are still going once the adult front teeth come through. Lip biting, pencil chewing, nail biting and cheek biting look alarming to a parent, yet they behave very differently in the mouth. A pooled analysis covering more than 53,000 children aged 3 to 18 has reported that around 29% have at least one oral habit, with lip biting the least common at around 9%.
Written by Dr James Tran, BDent (University of Sydney), MICOI, GradDip (Oral Implants), general dentist at Lumi Dental in Melrose Park.
The short version
- A habit changes teeth through duration (hours a day), frequency and intensity. Duration matters most.
- Lower lip sucking or biting behind the upper front teeth is the habit most likely to push the top teeth forward.
- Pencil and pen chewing rarely moves teeth but can chip the edges of new adult front teeth.
- Nail biting, cheek biting and hair chewing are mostly a problem for nails, cheeks and stomach, not the bite; see our article on nail biting and teeth.
- Most sucking habits stop between two and four; one still present at six or seven, when the adult front teeth arrive, is the one to act on.
- Praise, awareness and a substitute beat punishment.
Duration, frequency and intensity: why some habits move teeth
Teeth sit in a balance between the tongue pushing out and the lips and cheeks pushing in. A habit upsets that balance only when it applies force for long enough, often enough. Orthodontic reviews describe sucking habits in terms of duration, frequency and intensity, and note that the severity of any change depends more on the hours a day the habit is practised than on how hard the child pushes.
Age matters as much. While the baby teeth are in place, the same reviews report that if a sucking habit stops by about three to four, cheek and lip pressure often bring the front teeth back towards their natural alignment. Once the adult front teeth are through, from about six, a persistent habit shapes where those teeth settle. In my experience, parents worry most about the habits they can see, such as a pencil at homework time, and least about a lower lip tucked behind the upper teeth while a child concentrates.
Habit by habit: what each one can do
The right-hand column gives the point at which a dentist would usually want to see the child rather than keep watching.
| Habit | What it can do to teeth or the bite | When to act |
|---|---|---|
| Lower lip sucking or biting | Pushes upper front teeth forward and lower front teeth back, widening the overjet; chaps the lip | Still present once adult front teeth are through, or top teeth already prominent |
| Pencil, pen or object chewing | Chips or notches biting edges; can tip a single tooth; graphite stains | Any chip in an adult tooth; a daily habit past age seven |
| Nail biting | Wears front edges over years; little evidence it changes the bite | Worn edges, or anxiety driving it |
| Cheek biting | White ridged line and ulcers inside the cheek; does not move teeth | Ulcers keep returning in the same spot |
| Hair chewing | Rarely affects teeth; swallowed hair is the concern | Child is swallowing hair |
| Thumb or finger sucking | Open bite, increased overjet and a narrow upper jaw with long daily duration | Still going at four, certainly by six |
Thumb sucking and grinding have their own guides: thumb sucking and teeth and teeth grinding in children.
Lip biting and lip sucking: the habit to watch most closely
Lip sucking usually means the lower lip is drawn up and held behind the upper front teeth while a child concentrates, watches a screen or feels anxious. Lip biting is the same posture with the teeth gripping the lip. Both put a steady forward pressure on the upper incisors and a backward pressure on the lower ones, and over months that can increase the overjet, the horizontal gap between the upper and lower front teeth; our guide to overbite versus overjet explains the difference. A chapped or cracked lower lip is often the clue.
Children whose upper front teeth already sit forward find it easier to tuck the lip behind them, so the habit and the bite feed each other. The pooled review found habits most common at 6 to 12, so I treat lip sucking in a seven year old differently from the same habit in a three year old. A study of preschoolers has also reported that an incompetent lip seal, where the lips do not meet comfortably at rest, was significantly associated with malocclusion; our article on mouth breathing in children covers what that can mean.
Pencil, pen and object chewing
Chewing on a pencil, a pen lid or a shirt collar is common from the early primary years, and the Raising Children Network lists it among the ordinary habits of childhood. The main cost is to the biting edges: a hard pencil ground against a new adult front tooth can chip a corner or wear a notch, and graphite can lodge in a groove and leave a grey mark that looks like a filling.
Moving teeth is less likely. A pencil is held for seconds rather than hours, so the duration is low even when the frequency is high. The exception is a child who holds something between the same two teeth for long stretches, which can tip a tooth. A chip in an adult front tooth is worth a visit even if it does not hurt; our article on a chipped permanent front tooth explains what can be done.
Nail biting, cheek biting, hair chewing and chin resting
Nail biting is the most common biting habit, reported in around 16% of children in the pooled review. Over years it can wear or chip a thin front edge, but there is little evidence it changes the bite, and the preschool study above found no link between nail biting and malocclusion. The review noted that anxiety was the most common trigger and that raising a child's awareness was the most effective way to stop it.
Cheek biting leaves a pale, ridged line inside the cheek and can cause ulcers in the same spot. It does not move teeth, though it can be hard to break, as our article on chronic cheek biting describes. Hair chewing is rarely a dental problem; swallowed hair is a question for your GP. Chin resting is debated: the forces are light and children shift position constantly.
The single rule: if the habit is still there when the adult front teeth arrive, book a check
Up to about four, most habits can be watched. Better Health Channel notes that children usually stop thumb and finger sucking between two and four, and that the younger a child stops, the more likely the teeth and jaws correct any changes on their own. Once the adult front teeth come through, from around six to seven, a habit that is still daily is the one to act on. Book a check at any age for a chip, a widening gap between the front teeth, lips that no longer meet at rest, or a new lisp; our article on the right age for a first orthodontic check covers that assessment.
Helping a child stop without a battle
Most habits fade on their own, and attention can make them worse. The Raising Children Network suggests involving the child in finding a solution, gentle reminders, distraction such as a fidget toy during television, tackling one habit at a time, and praise when the child remembers.
- Ignore the habit and praise the times it is absent.
- Build awareness with a private signal and offer a substitute: a chewable pencil topper, or lip balm for a lip biter.
- Where worry drives the habit, Raising Children suggests talking to your GP about a referral.
- Habit reminder appliances are a last step; I usually reserve them for children over about seven who want to stop and cannot catch themselves.
How we approach this at Lumi Dental
A children's check at Lumi Dental includes the habits as well as the teeth. The dentist examines the biting edges, measures the overjet, checks whether the lips meet at rest, and the hygiene team of oral health therapists reinforces the plan at cleans. Where a bite change needs more than watching, the team refers to a registered orthodontist or a paediatric dentist. The whole practice accepts the Child Dental Benefits Schedule, so eligible children can have these checks bulk billed; our guide to how the CDBS works explains eligibility.
Questions patients ask
Can lip biting cause an overbite?
It can increase the overjet, the horizontal gap between the top and bottom front teeth, which is what most people mean by overbite, if the lip is held there for hours a day.
Is chewing on pencils bad for your teeth?
It is more of a chipping risk than a bite risk. A silicone pencil topper gives the same feedback without the hard edge.
At what age should I worry about my child's habit?
Most habits can be watched until about four. The age that matters most is six to seven, when the adult front teeth come through. A daily habit at that point is worth a check.
Does nail biting move teeth?
Rarely. It can wear the front edges over years, but studies have not found a consistent link with bite problems.
Will my child need an appliance to stop?
Usually not. Praise, awareness and substitutes work for most children. You can ask us at your child's next check.
Noticed a habit you are not sure about? Book a children's check at Lumi Dental in Melrose Park
If you have noticed a habit, a check lets us look at the front teeth and the bite and tell you whether to keep watching or act now. Families come to Lumi Dental at Melrose Central from Melrose Park, Ryde, Parramatta, Ermington and Rydalmere. See our current offers, read about children's dentistry at Lumi Dental, or check eligibility under the Child Dental Benefits Schedule.
Sources
- National Library of Medicine (PMC): Prevalence of oral deleterious habits among children, a systematic review and meta-analysis
- National Library of Medicine (PMC): Influence of oral habits on pediatric malocclusion, etiology and preventive approaches
- Better Health Channel: Thumb sucking
- Raising Children Network: Children's habits and how to handle them
About the author
Dr James Tran is a general dentist at Lumi Dental in Melrose Park. He holds a BDent from the University of Sydney and a Graduate Diploma in Oral Implants, and is a Member of the International Congress of Oral Implantologists (MICOI).
This article is general information only and is not a substitute for an examination and individual advice from a registered dental practitioner. Suitability for any treatment varies from person to person.
