Teething isn't a single bad week — it's a process that starts in the second half of the first year and continues until the second molars settle in around the age of two and a half. Once you have the timeline, it gets much easier to tell teething from everything else that happens during the same months. For a wider view, see our complete guide to child health.
The Active Discomfort Window
For any individual tooth, the period of noticeable irritability is short — roughly two to seven days around the moment the tooth breaks through the gum surface. Once the tooth has erupted through the mucosa, the soreness drops off quickly because the pressure on the gum has been relieved.
This means teething is not a continuous state of pain. Between teeth — which can be weeks or months apart — most babies aren't experiencing teething discomfort at all. When a baby seems uncomfortable for extended periods, the cause is usually something else: sleep regression, an ear infection, a viral illness, a developmental leap. Attributing weeks of unsettled sleep to teething is the most common parental misdiagnosis I see.
The Full Primary Teeth Timeline
The complete set of 20 primary teeth (10 upper, 10 lower) typically follows this sequence, give or take:
- Lower central incisors (bottom front two): 6–10 months — the usual first arrival
- Upper central incisors (top front two): 8–12 months
- Upper lateral incisors: 9–13 months
- Lower lateral incisors: 10–16 months
- First molars (upper and lower): 13–19 months — bigger teeth, often described by parents as the most disruptive phase
- Canines (upper and lower): 16–22 months — the awkwardly placed pointed teeth between the lateral incisors and first molars
- Second molars (upper and lower): 23–31 months — the last to come in. Their eruption often coincides with a noticeable uptick in night waking around age 2 to 2.5
By around 2.5 to 3 years, most children have all 20 primary teeth and are done with teething until the permanent dentition starts arriving around age 6.
What Counts as Normal Variation
The above is typical, not universal. The actual range is wide:
- A first tooth at 4 months is normal. So is a first tooth at 14 months.
- Some teeth arrive in clustered pairs, others appear one at a time over weeks.
- Some children sail through the whole process with barely noticeable fuss; others are clearly unsettled around each eruption — and the same child can vary tooth to tooth.
- Boys and girls follow the same overall pattern, with boys averaging slightly later eruption.
- Family pattern matters: late teethers tend to come from late-teether families.
A baby who reaches their first birthday with no teeth is not behind. By the 18-month mark, a dental review is reasonable if nothing has come through — sometimes the explanation is simply a constitutional pattern, occasionally there are missing teeth (hypodontia) or a problem with eruption that benefits from assessment.
A small number of babies are born with one or two teeth already present (natal teeth), or develop one in the first month (neonatal teeth). They occasionally need removal if they're loose enough to risk aspiration or cause feeding pain — otherwise they stay.
Multiple Teeth at Once
It is common — particularly in the molar phase — for more than one tooth to be working through the gum at the same time. This makes the disrupted phase last longer than it would for a single eruption. The first molars (13–19 months) are often described by parents as the worst stretch, partly because the teeth are larger than the incisors, partly because two molars can be erupting in close sequence, and partly because this overlap with separation anxiety, language frustrations, and the 18-month sleep regression amplifies the picture.
The second molars (23–31 months) are often easier than the first, even though they're similar-sized teeth — by then the child is older, more verbal, and better able to indicate discomfort.
When to Start Dental Care
Dental hygiene begins the day the first tooth appears, regardless of how early or late that is.
- A tiny smear of fluoride toothpaste (1000 ppm fluoride or more — check the tube; most baby toothpastes are this strength) on a soft brush or clean gauze
- Twice daily — morning and last thing before bed (the night brush is the more important of the two)
- Spit, don't rinse — the residual fluoride film on the teeth is what does the protective work
- The first dental visit is recommended around the time of the first tooth or by 12 months, whichever comes first. NHS dental care for children is free.
Once you have a few teeth, supervised brushing (you doing the brushing, not the toddler, until they're around seven) is the standard. Most toddlers will tolerate a brief brush if you do it consistently, even if they protest the first few times.
Key Takeaways
The active discomfort window for any one tooth is typically two to seven days around eruption — not a constant state of pain. The full set of 20 primary teeth completes by about 2.5–3 years. Lower central incisors usually arrive first at 6–10 months. The normal range is wide: a first tooth at 4 months or at 14 months is fine. No teeth by 12 months is common; if no teeth have appeared by 18 months, a dental review is reasonable. The first molars, around 13–19 months, are often the most disruptive. Brushing with fluoride toothpaste starts the day the first tooth comes through.
