Teeth and digestion
Biology · Key Stage 2 · The School
Four shapes, four jobs
INCISORS at the front are chisels for cutting. CANINES beside them are points for gripping and tearing. PREMOLARS and MOLARS at the back are millstones for grinding. Run your tongue along your teeth and you can feel the change from flat to pointed to bumpy. A carnivore has huge canines; a cow has almost none and enormous molars — the teeth tell you the diet.
The journey
MOUTH: teeth grind and saliva starts breaking starch down. OESOPHAGUS: a muscular tube that squeezes food downward, which is why an astronaut can swallow upside down. STOMACH: acid and churning turn it to a paste. SMALL INTESTINE: nutrients pass into the blood through the wall. LARGE INTESTINE: water is absorbed and the rest is waste.
Why teeth decay
Bacteria in your mouth feed on sugar and produce acid as waste. That acid dissolves the enamel — the hardest substance in your body, and one that does not grow back. That is why it is how OFTEN you eat sugar that matters more than how much: every sugary snack starts another acid attack, and brushing removes the bacteria before they build up.
Both eat six sweets. Ali eats all six at once after lunch: one acid attack, and saliva neutralises the mouth over the next hour. Sara eats one every hour through the afternoon: six separate attacks, and the mouth never gets back to normal in between. Same sugar, very different risk. That is why dentists talk about how OFTEN, not how much — the bacteria need time you keep giving them.