Dental Care: Keep Your Smile Strong!
Every time you bite a pineapple bun or chew a mouthful of rice, your teeth are hard at work. You only get two sets of teeth in your life, so look after them well!
In this chapter you will learn: (1) what is inside a tooth, (2) the types of teeth and their jobs, (3) how tooth decay and periodontal (gum) disease happen, and (4) how to protect your teeth and gums.
1. The Structure of a Tooth
Two main parts: crown and root
A tooth is a bit like an iceberg – you can only see part of it!
Crown – the part of the tooth you can see, above the gum.
Root – the hidden part below the gum, fixed in the jawbone.
The layers of a tooth
If you cut a tooth in half, you would see these layers, from outside to centre:
Enamel – the hard, white outer layer that covers the crown. It is the hardest substance in the human body and is made mainly of calcium compounds. Enamel has no nerves or blood vessels, so it is not living. Once a hole forms in it, it cannot grow back.
Dentine – the layer under the enamel that makes up most of the tooth. It is hard but softer than enamel. Dentine has tiny channels that lead to the pulp, so when it is exposed, hot, cold or sweet food can cause a sharp pain.
Pulp cavity – the space in the centre of the tooth. It contains soft pulp with nerves and blood vessels. The blood vessels bring food substances and oxygen to the living cells of the tooth. The nerves let you feel pain, heat and cold.
Cement – a thin, bone-like layer that covers the root. Tiny fibres join the cement to the jawbone, holding the tooth firmly in place.
What holds a tooth in place?
Gum – the soft pink tissue that covers the jawbone and fits tightly around each tooth, sealing the root off from bacteria.
Jawbone – the bone of the upper or lower jaw. Each root sits in a hole (socket) in the jawbone.
Memory aid: From outside to inside, think "Every Dog Plays" – Enamel, Dentine, Pulp cavity.
Did you know? Enamel is even harder than bone. But teeth are not bones: a broken bone can heal itself, while a hole in enamel cannot!
Key takeaway: A tooth has a crown and a root. Enamel, dentine and the pulp cavity are its layers; cement, gum and jawbone hold it in place.
2. Types of Teeth and Their Functions
Four types of teeth
Your teeth have different shapes, and each shape suits a different job – just like the tools in a kitchen.
Incisors – at the front of the mouth. They are flat and chisel-shaped with a sharp edge, for cutting and biting food, e.g. biting off a piece of apple. Each has one root.
Canines – next to the incisors, one on each side of each jaw. They are pointed, for tearing food, e.g. tearing a piece of beef jerky. Each has one long root.
Premolars – behind the canines. They have a broad surface with bumps (cusps), for grinding and crushing food. They have one or two roots.
Molars – at the back of the mouth. They are the largest teeth, with broad, bumpy surfaces for grinding and crushing food, e.g. chewing nuts. Their two or three roots stand the strong forces of chewing.
Memory aid: From front to back, "I Can Pretty Much eat anything" – Incisors, Canines, Premolars, Molars. Their jobs: cut, tear, grind, grind.
Chewing breaks food into smaller pieces that are easier to swallow and digest (see the "Digestion and absorption of food" chapter).
Two sets: milk teeth and permanent teeth
Milk teeth (baby teeth) – the first set. They start to appear when a baby is about 6 months old. There are 20 milk teeth: incisors, canines and molars, but no premolars. From about age 6, they fall out one by one.
Permanent teeth – the second set, which replaces the milk teeth. An adult has 32 permanent teeth, including 4 wisdom teeth (the last molars at the very back). Most permanent teeth are in place by about age 12 to 13. Wisdom teeth usually come later, and some people never get them.
Counting the teeth
Count the teeth in one quarter of the mouth (incisors, canines, premolars, molars), then multiply by 4:
\(\text{milk teeth} = (2 + 1 + 0 + 2) \times 4 = 20\)
\(\text{permanent teeth} = (2 + 1 + 2 + 3) \times 4 = 32\)
Common mistake: "Milk teeth will fall out anyway, so they don't need care." Wrong! Milk teeth help children chew and speak clearly, and they keep the space for the permanent teeth. Decayed milk teeth can be painful and get infected.
Key takeaway: Incisors cut and bite, canines tear, and premolars and molars grind and crush. We have 20 milk teeth (no premolars) and then 32 permanent teeth.
3. Tooth Decay: How Holes Form
Plaque: the sticky villain
Plaque is a soft, sticky, pale film full of bacteria that keeps forming on our teeth. That furry feeling on your teeth before brushing in the morning is plaque!
From sugar to a hole, step by step
\(\text{bacteria in plaque} + \text{sugar} \rightarrow \text{acid}\)
Step 1 – We eat or drink something sugary, e.g. sweets or sweet milk tea.
Step 2 – Bacteria in the plaque feed on the sugar and make acid.
Step 3 – The acid slowly dissolves the enamel. A white or brown spot may appear, and then a small hole (a cavity). This usually does not hurt yet.
Step 4 – The decay reaches the dentine. Dentine is softer, so decay spreads faster. The tooth may hurt when you eat sweet, hot or cold food.
Step 5 – If nothing is done, the decay reaches the pulp cavity. The nerves are affected, causing a bad toothache, and the pulp may become infected. A dentist may need to clean out and fill the tooth, or even remove it.
Why "how often" matters more than "how much"
After each sugary snack or drink, plaque makes acid for a while – an acid attack. Saliva slowly washes away food and makes the mouth less acidic again.
So sipping a sweet drink all afternoon is worse than having the same amount of sugar in one go with a meal – the teeth face many more acid attacks.
Common mistake: "Sugar dissolves our teeth." Not exactly! Sugar itself does not dissolve teeth. Bacteria in plaque change sugar into acid, and it is the acid that dissolves the enamel.
Did you know? Tooth decay is one of the most common diseases in the world, yet it can largely be prevented with good habits!
Key takeaway: Bacteria in plaque turn sugar into acid, which dissolves enamel, then dentine, and may reach the pulp cavity.
4. Periodontal (Gum) Disease
Periodontal disease is disease of the gums and the tissues that support the teeth. It is also caused by plaque.
From plaque to tartar
Plaque left along the gum line (where the teeth meet the gums) hardens into yellow or brown tartar within a few days. It cannot be removed by brushing – a dentist must scrape it off (this is called scaling). Its rough surface also traps even more plaque.
Stage 1: Gingivitis (inflamed gums)
Bacteria in plaque and tartar irritate the gums, which become red, swollen and bleed easily, e.g. when you brush. This early stage is called gingivitis. Good news: it can be reversed by cleaning the teeth well every day and visiting a dentist.
Stage 2: Periodontitis (serious gum disease)
If gingivitis is not treated, the infection spreads deeper. The gums pull away from the teeth, and the tissues and jawbone that hold the teeth are slowly destroyed. The teeth become loose and may even fall out.
Warning signs: bleeding gums, red or swollen gums, bad breath that does not go away, gums shrinking from the teeth, and loose teeth.
Common mistake: "My gums bleed when I brush, so I should stop brushing there." Wrong! Bleeding is often a sign of gingivitis. Keep brushing gently but thoroughly along the gum line, and see a dentist if the bleeding does not stop.
Did you know? Smoking raises the risk of gum disease. (You will learn more in the "Effects of smoking" chapter.)
Key takeaway: Plaque and tartar at the gum line inflame the gums (gingivitis); without treatment, periodontitis damages the jawbone and loosens teeth.
5. Protecting Our Teeth and Gums
Both tooth decay and gum disease can largely be prevented. The main idea is simple: remove plaque and cut down on sugar.
Daily habits
1. Brush at least twice a day with fluoride toothpaste – e.g. after breakfast and before bed, for about two minutes. Clean every surface of every tooth and brush gently along the gum line. Change your soft toothbrush about every three months.
2. Floss every day – a toothbrush cannot reach the narrow gaps between teeth. Dental floss removes plaque and food from these gaps and from just under the gum line.
3. Limit sugary snacks and drinks – choose water instead of soft drinks or sweet lemon tea, have sweet foods with meals rather than between meals, and rinse your mouth with water after eating. Acidic drinks such as soft drinks can also wear away enamel directly.
How does fluoride help?
Fluoride makes enamel stronger and more able to resist acid. It also helps repair very early damage before a hole forms. Hong Kong also adds a small, safe amount of fluoride to its drinking water to help protect teeth.
Help from the dentist
4. Have regular dental check-ups – usually once or twice a year, as your dentist advises. The dentist can find decay early, fill small holes, remove tartar by scaling and show you how to brush and floss correctly.
In Hong Kong, the Department of Health runs the School Dental Care Service, which gives primary school pupils who join it a dental check-up every year.
Other healthy habits
Eat a balanced diet with enough calcium and vitamin C for healthy teeth and gums (see the "Nutrition and health" chapter). Do not smoke. Never use your teeth to open bottles or packets, and wear a mouthguard when playing contact sports.
Key takeaway: Brush twice a day with fluoride toothpaste, floss daily, limit sugary snacks and drinks, and have regular dental check-ups.
Quick Review
1. A tooth has a crown (above the gum) and a root (in the jawbone).
2. Outside to inside: enamel, dentine, pulp cavity (nerves and blood vessels). Cement, gum and jawbone hold the tooth.
3. Incisors cut and bite; canines tear; premolars and molars grind and crush.
4. 20 milk teeth (no premolars), then 32 permanent teeth (including 4 wisdom teeth).
5. Tooth decay: bacteria in plaque make acid from sugar; acid dissolves enamel, then dentine.
6. Periodontal disease: plaque and tartar at the gum line inflame the gums and can loosen teeth.
7. Protection: fluoride toothpaste twice a day, floss, less sugar, regular check-ups.
Well done! A few minutes of care each day can keep your permanent teeth strong for life. Keep smiling!