Lower teeth look darker than upper teeth mostly because of how they are seen and what builds up on them, not because they are a different colour, and they whiten less because the gel has a harder job reaching them and staying there. It surprises many patients I see that when researchers measured tooth colour with three shade guides, the lower front teeth were recorded as lighter than the uppers in roughly 87 to 89.5 percent of people. If your lower teeth look darker and whiten less, the cause is usually shadow, tartar, thin enamel, naturally darker canines or a tray that does not sit well on the lower arch. Each has a fix.
Written by Dr James Tran, BDent (University of Sydney), MICOI, GradDip (Oral Implants), general dentist at Lumi Dental in Melrose Park.
The short version
- Lower front teeth sit behind the uppers and in the shadow of the lower lip, so the same shade reads darker.
- Tartar forms fastest on the inside of the lower front teeth, beside the openings of the salivary glands under the tongue; tartar and plaque block whitening gel. Our guide to plaque versus tartar explains the difference.
- Canines are naturally more yellow than incisors in both arches, and the lower canines are the ones you see most when you talk.
- Enamel is thinner near the gum line and thins with age, so the yellow dentine shows through more on small lower teeth.
- Saliva pools in a lower tray and dilutes the gel, and crowded lower teeth stop a tray sealing evenly.
- The single rule: whiten both arches, give the lower arch the same number of nights, and judge the result at two weeks, not on night one.
Measured colour versus what you see in the mirror
The mouth is a poor light box. The lower front teeth are smaller, sit a step behind the uppers in a normal bite and spend much of the day under the lower lip, so even when an instrument says the two sets are the same shade, the lower set looks darker.
The research backs this up. A study of 400 people using three shade guides reported that the lower incisors were lighter than the uppers in most participants, and that teeth darken appreciably with age. Separate spectrophotometer work found that incisors are the lightest teeth, canines are darker and more yellow, and molars are the most chromatic of all. In my experience the darkest-looking tooth in a lower arch is nearly always a canine, and a canine one shade behind its neighbours is normal, not a whitening failure.
Why lower front teeth collect tartar first
Run your tongue behind your lower front teeth and you will often feel a rough ledge. That is calculus, or tartar: plaque hardened by minerals from saliva. It forms there before anywhere else because the ducts of the submandibular and sublingual salivary glands open on the floor of the mouth right beside those teeth. A paper in the Journal of the Canadian Dental Association describes a fast-moving film of saliva across the inside of the six lower front teeth that clears sugar quickly and keeps the pH high, exactly the conditions in which plaque mineralises.
Tartar is yellow to brown, sits where the lower teeth are seen from the side, and whitening gel cannot pass through it. The Australian Dental Association's teeth.org.au is clear that whitening gel only lightens natural enamel, so anything sitting on top of the enamel stays the colour it was. That is why the hygiene team removes tartar before whitening starts; our article on whitening before or after a scale and clean covers the timing.
Thin enamel, canines and the gum line
Enamel is translucent. Where it is thin, more of the warm dentine underneath shows and the tooth reads yellower. Enamel is thinnest near the gum line on every tooth, and lower incisors are the smallest teeth in the mouth with the least enamel to begin with. Teeth.org.au notes that as you get older the enamel layer becomes thinner and lets the dentine show through, which is why the gum-line third of a lower tooth is usually the last part to respond to whitening. Our guide to why teeth look yellower with age goes through this in more detail.
Whitening works on enamel and the stain within it, not on dentine, so a tooth that is yellow because its enamel is thin will lighten but not to the brightness of a thick-enamelled upper incisor. Canines have more dentine for their size and are usually the last teeth to catch up.
| Reason lower teeth look darker | What you notice | What usually helps |
|---|---|---|
| Tartar on the inside surfaces | Rough ledge behind the lower front teeth, brown line near the gum | Scale and clean before whitening; angle the brush upward behind the lower teeth |
| Thin enamel near the gum line | Yellow band along the gum third that lightens slowly | More nights of take-home gel; accept a gentle gradient as natural |
| Canines | One tooth each side a shade darker than the incisors | Extra wear time on those teeth; expect them to lag |
| Saliva diluting a lower tray | Lower arch moves fewer shades than the upper on the same gel | Dry the teeth before loading the tray; wear the full time |
| Fillings or crowns | A tooth that stays the same shade | Restorations do not whiten; they may need replacing to match |
Why lower teeth whiten less: four practical reasons
Saliva pools in the lower tray
Gravity works against the lower arch. Saliva collects on the floor of the mouth, seeps under the tray edge and thins the gel, and the salivary ducts behind the lower front teeth pump fresh saliva into exactly that spot. Drying the teeth before the tray goes in, using the amount of gel you were shown and not talking while it is in all help.
Crowded lower teeth stop the tray sealing
A tray made on a 3D scan can follow most of the overlap in crowded lower incisors, but where one tooth sits behind another the gel cannot reach the hidden surface, so that strip stays darker. Our guide to crowded lower front teeth in adults explains the options; whitening after alignment is usually more even.
In-chair whitening is harder to isolate on the lower arch
In the chair the gums are protected with a barrier and the teeth are kept dry. On the lower arch the tongue, the floor of the mouth and the salivary ducts all work against that, so the lower teeth often get slightly less effective contact time. Take-home trays afterwards let the lower arch catch up.
The lower arch is judged too early
The NHS describes take-home whitening as a course worn for around two to six weeks. The upper incisors lighten first, so after three nights the uppers look brighter and the lowers unchanged; the lower incisors, canines and gum-line thirds come later. Our article on uneven or blotchy teeth after whitening explains why patchiness in the first week usually evens out.
The single rule: whiten both arches and judge at two weeks
Whiten both arches, give the lower arch at least the same number of nights as the upper, and judge the result at two weeks rather than on night one. If the lower teeth are still a step behind at that point, I usually suggest a few extra nights on the lower tray only, with a dab of gel on the canines. The aim is a lower arch that sits a half shade behind the upper and looks natural. The NHS notes that whitening may not produce a complete colour change and that the effect, with care, may last around three years, so a sensible target matters more than a dramatic one.
How we approach this at Lumi Dental
At Lumi Dental in Melrose Park, the dentist works out why the lower arch looks darker before anyone talks about gel, because shadow, tartar, thin enamel, crowding and an old filling each call for a different answer. The hygiene team, our oral health therapists, removes plaque and tartar first, and that clean alone often lifts the lower teeth noticeably. Trays are made from a digital scan so they follow crowded lower incisors closely, and the whitening options, named Home, Refresh and Radiance, are matched to how far the lower arch has to travel. A written quote follows the examination; current offers are listed on our current deals page.
Questions patients ask
Why are bottom teeth more yellow than top teeth?
Usually because of shadow, tartar and canines rather than a true colour difference. Measured with a shade guide, lower incisors are often as light as the uppers, but they sit under the lower lip, collect tartar on their inside surfaces and are flanked by canines that are naturally more yellow.
Can you whiten just your top teeth?
You can, but it is rarely a good idea. The lower teeth show whenever you talk or laugh, and whitening only the uppers makes the contrast larger. Our guide to how many shades whiter teeth can go sets realistic expectations for both arches.
Why will the bottom teeth not whiten?
Nearly always tartar or plaque blocking the gel, saliva diluting the lower tray, a tray that does not touch crowded teeth, a filling or crown that cannot change colour, or fewer nights of wear. A dentist can tell which within a few minutes, and each has a fix.
Do you need a clean before whitening the lower teeth?
Yes, and it matters more on the lower arch. Tartar forms fastest behind the lower front teeth and gel cannot pass through it. A clean also lets the dentist check for gum recession and exposed roots, which whiten differently and can be sensitive.
Will the lower canines ever match the front teeth?
They will lighten, but they typically stay a touch deeper than the incisors, as they do in most natural smiles. Extra wear time narrows the gap. A canine that is dramatically darker points to an old filling, a past injury or a root-filled tooth, which call for different treatment.
Lower teeth letting your smile down? Complimentary cosmetic consult in Melrose Park
If your lower teeth look darker than the uppers, or a previous course left the bottom arch behind, the team at Lumi Dental in Melrose Park can examine both arches, clean away the tartar and plan whitening that treats the lower teeth properly. Book a complimentary cosmetic consult or read more about teeth whitening at Lumi Dental. Patients visit from Ryde, Parramatta, Ermington, Rydalmere and nearby suburbs.
Sources
- Australian Dental Association (teeth.org.au): Teeth whitening
- Australian Dental Association (teeth.org.au): Teeth staining
- NHS: Teeth whitening
- PubMed Central: An Evaluation of Shade Differences Between Natural Anterior Teeth in Different Age Groups and Gender Using Commercially Available Shade Guides
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.
