Are Craze Lines on Teeth Harmful?

They're hairline cracks that sit only in the enamel, the hard outer shell of the tooth. They don't go through into the softer layer underneath or anywhere near the nerve. The Oral Health Foundation describes them the same way: tiny cracks in the enamel that cause no pain.

Think of the glaze on an old china mug. Over the years it picks up a network of fine lines, but the mug still holds your tea perfectly well. Craze lines are the dental version: a surface finish that's seen some life, not a structural problem.

They tend to run up and down the tooth rather than across it, and in my experience they're easiest to spot on front teeth, under a bright light or when the teeth are a little dry. Some people have several on every front tooth and have never noticed. Others spot one in a new mirror and assume the worst.

There's no single cause, and there's not much research on craze lines specifically. The general stresses the Oral Health Foundation lists for cracks in teeth include grinding or clenching, biting on hard things and sudden changes in temperature. Add up decades of chewing, a hot coffee followed by a cold drink, and the odd bite on an olive stone, and it's no surprise that enamel collects a few fine lines. That's why they're so common in adults.

If you grind or clench, particularly at night, it's worth knowing, because grinding is also on the list of causes for more serious cracks. That's one of the first things I'd ask about if I saw lots of wear alongside the lines.

On their own, no. I'll say that plainly because it's the question you came here for. The AAE classes them as the least serious of its five types of crack: craze lines, a fractured cusp, a cracked tooth, a split tooth and a vertical root fracture. Craze lines are the only one of the five that's described as purely cosmetic.

I think of diagnosing cracks as detective work. Cracks are the master criminals of dentistry: good at hiding, hard to catch on an X-ray, and the pain they cause comes and goes. Craze lines are the innocent bystanders who happen to look a bit like the suspect. They were at the scene, they fit the description, but they didn't do it.

The catch is that a tooth can have craze lines and a deeper crack, and you can't tell the difference with a bathroom mirror. That's why pain is the clue I care about most. If there's no pain on biting, no twinge as you let go, and no sensitivity that hangs around, a line you can see is very likely a craze line. I explain how to tell the two apart in craze lines vs a cracked tooth.

They don't need treatment for health reasons, so this is entirely about how they look to you. For minor cracks, the Oral Health Foundation lists smoothing and polishing the surface, bonding with tooth-coloured resin, or veneers where there's enough healthy tooth.

• Leave them alone. A perfectly good option, and the one I'd suggest for most people. Nobody else is looking at your enamel with a torch.
• Composite bonding. A thin layer of tooth-coloured material over the front of the tooth. Quick and conservative. Our composite bonding page explains more.
• Veneers. A thin facing over the front of the tooth, usually for people who want to change the look of several teeth anyway. See our veneers page.

Whether any of these suits you depends on the teeth, the bite and what you want, and that's a conversation to have in the chair, not on a blog. Prices vary, and I'll always confirm the fee in writing before any treatment.

This is the bit that matters. A hairline crack in a tooth that goes deeper than the enamel behaves differently. The classic cracked tooth symptoms are a sharp pain when you bite, often worst as you release your bite, sensitivity to hot or cold, and pain that comes and goes. The AAE and the Oral Health Foundation both say a cracked tooth can't heal itself, and I cover that properly in can a cracked tooth heal naturally?

Book a normal appointment if:

• a line looks new, darker or longer than it did
• it's on a back tooth, especially one with a big filling
• you know you grind or clench and your teeth look worn
• you're simply not sure and would like it checked

Call us today if:

• the tooth hurts when you bite or let go, and it's getting worse
• pain lingers after hot or cold, or the tooth aches on its own or kept you awake
• there's swelling of the gum or face, or a bad taste
• part of the tooth has broken off, or it feels like it's in two pieces

Call 999 or go to A&E, not a dentist, if:

• you're finding it hard to breathe, swallow or speak
• swelling is spreading towards your eye or down into your neck
• your eye is swollen or painful, or your eyesight has suddenly changed
• you can't open your mouth properly because of swelling

If you're near Harlow or Enfield and a line on your tooth is playing on your mind, I'd much rather take a look than have you spend another week inspecting it in the mirror. Ring your nearest Minti practice and book a check-up, and if there's pain, say so and we'll do our best to see you sooner. Anywhere else, or out of hours, call NHS 111.

This article is general information, not a diagnosis. A line or crack in a tooth needs examining in person to know what it is.