Dental Anatomy
What is actually going on inside your mouth. The parts of a tooth, the jobs each type of tooth does, and how problems start.
Dental anatomy is the study of how a tooth is built. Each tooth has a crown above the gum and one or more roots below it, layered from a hard enamel shell, through softer dentin, to a living pulp of nerves and blood vessels at the centre. Knowing those layers explains almost every symptom you can feel.
Most dental problems make more sense once you can picture the structure underneath. Sensitivity, a dull ache, a chip, a loose tooth: each one points to a particular layer. The cross-section below is labelled, and every part is explained underneath it.
Structure
The parts of a tooth
Ten structures, from the surface you brush to the bone that holds everything in place.
Crown
The part you can see above the gum line. Its shape does the work of biting, tearing, and grinding, and it is what shows when you smile.
Neck
The narrow zone where the crown meets the root at the gum line. Gum recession exposes this area first, which is why it is a common site for sensitivity.
Root
The portion below the gum that anchors the tooth in the jaw. Front teeth usually have one root; molars have two or three.
Enamel
The hard, glassy outer shell of the crown and the hardest substance in the body. It has no living cells, so once it wears away or decays it cannot grow back.
Dentin
The yellowish layer under the enamel that forms the bulk of the tooth. It is softer than enamel and threaded with microscopic tubules leading to the nerve, so exposed dentin feels sensitive.
Pulp
The soft core in the middle of the tooth, holding the nerves and blood vessels. When decay or a crack reaches the pulp, the result is usually a persistent, throbbing ache.
Nerves & blood vessels
They run from the jaw up through the root canals into the pulp. Nerves supply sensation, including pain; the blood vessels feed the tooth from the inside.
Cementum
A thin, bone-like layer covering the root. It is the anchor point for the periodontal ligament fibres that hold the tooth in its socket.
Gum
The soft tissue that seals around the neck of each tooth and shields the roots. Healthy gums are firm and do not bleed when you brush.
Bone
The jawbone surrounding each socket. It needs the stimulation of a tooth root to keep its volume, which is why bone recedes after a tooth is lost.
When one of these layers fails, the fix is usually named after it. Damage confined to enamel and dentin is repaired with fillings; a crown that has lost too much structure is rebuilt with a dental crown; and when the root and bone can no longer hold a tooth, a dental implant replaces both.
Types
The four types of teeth
Adults have 32 permanent teeth, in four shapes. Each shape does a different job, which is why losing one changes how you chew.
Incisors
8 total
The four flat, chisel-edged teeth at the front of each jaw. They cut food and shape most of what people see when you smile.
Canines
4 total
The pointed teeth at the corners of your smile, with the longest roots of any tooth. They tear food and guide the jaw as it closes.
Premolars
8 total
Also called bicuspids. They sit between the canines and molars with two cusps each, crushing food and handing it back to the molars.
Molars
12 total
The broad grinding teeth at the back, including the four wisdom teeth. Their wide chewing surfaces have grooves that trap food and often decay first.
Because each shape has a job, a gap is not only cosmetic: neighbouring teeth drift into the space and the bite shifts. That is the reasoning behind treating missing teeth and correcting alignment problems.
Eruption
When teeth do not come in straight
A tooth is impacted when it cannot fully break through the gum, usually because it is angled wrong or the jaw has run out of room. Wisdom teeth are the usual culprits, and the pattern determines what happens next.
Mesial impaction
The tooth tilts forward, toward the front of the mouth. This is the most common way a wisdom tooth becomes impacted.
Vertical impaction
The tooth is upright and correctly positioned but still trapped, held below the gum or pressed against the tooth in front of it.
Distal impaction
The tooth angles backward, toward the rear of the jaw, which can make it difficult to clean and difficult to remove.
Horizontal impaction
The tooth lies on its side, roughly at right angles, pushing into the roots of its neighbour. This is usually the most troublesome pattern.
Partial eruption
Part of the crown breaks through while the rest stays covered, leaving a flap of gum that traps food and bacteria and inflames easily.
Impaction is usually found on a routine X-ray long before it hurts, which is one of the quieter reasons to keep up with regular cleanings and exams. When a tooth does need to come out, that is oral surgery; crowding that stops short of impaction is often handled with Invisalign.
Decay
The five stages of tooth decay
Decay moves inward through the layers, and the treatment changes at every stage. Only the first one is reversible, which is the whole argument for catching it early.
- 1
Healthy tooth
Enamel is intact and sealed. Nothing hurts, and nothing needs treating. This is what regular cleanings and daily brushing are protecting.
- 2
Enamel decay
Acid from plaque starts dissolving minerals out of the enamel, first as a chalky white spot, then a genuine hole. There is usually no pain yet. Caught at the white-spot stage, this is the one point where decay can still be reversed.
- 3
Dentin decay
The cavity breaks through into the softer dentin underneath and spreads faster. Sweet, hot, or cold food starts to register. A filling is now needed; the tooth will not repair itself.
- 4
Pulp involvement
Bacteria reach the pulp and inflame the nerve, which typically means a constant, throbbing toothache. Saving the tooth at this point means root canal therapy or removing it.
- 5
Abscess
Infection passes out of the root tip into the surrounding bone, causing swelling, severe pain, and sometimes fever. This is urgent and needs to be seen promptly.
Read more about how cavities form and how they are treated, or about gum disease, which attacks the same tooth from the outside in. Grinding wears enamel down from above: see teeth grinding and the night guards made to stop it.
Dental anatomy FAQs
What are the layers of a tooth?+
A tooth has three main layers. Enamel is the hard outer shell covering the crown, dentin sits beneath it and makes up most of the tooth, and the pulp at the centre holds the nerves and blood vessels. Cementum covers the root.
Why are my teeth sensitive to hot and cold?+
Sensitivity usually means dentin is exposed, through worn enamel, a receding gum line, or decay. Dentin contains microscopic tubules that carry temperature straight to the nerve. A dentist can find the cause and seal or restore the affected surface.
What is an impacted tooth?+
An impacted tooth cannot fully erupt through the gum, usually because it is angled wrong or the jaw has too little room. Wisdom teeth are the most common. An X-ray shows the position long before it causes pain.
Can tooth decay be reversed?+
Only at the earliest stage. While decay is limited to enamel, fluoride and better daily hygiene can remineralise the surface. Once it reaches the dentin the damage is permanent and needs a filling. Decay does not heal on its own after that.
How many teeth do adults have?+
Most adults have 32 permanent teeth: eight incisors, four canines, eight premolars, and twelve molars including four wisdom teeth. Many people have their wisdom teeth removed, leaving 28. Children have 20 primary teeth that fall out from roughly age six.
Medical disclaimer
This page is general educational information about dental anatomy and the typical course of tooth decay and eruption. It is not a diagnosis, a treatment plan, or a substitute for being examined. Anatomy varies from person to person, and identical symptoms can have very different causes. Severe pain, facial swelling, fever, difficulty swallowing or breathing, or an injury that loosens or knocks out a tooth all need prompt in-person care. See a qualified dentist or physician for advice about your own symptoms.
Something in your mouth not feeling right?
An exam and an X-ray answer most of these questions in a single visit, and we will explain what we find in plain English.