www.BioTopics.co.uk
Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.


../nextblue.gif ../contentsblue.gif

TEETH

Structure of a tooth

Use terms from the list below to label this diagram of a tooth, using the correct technique.

Do not write over the diagram. Write the words horizontally in ink alongside the diagram, and rule labelling lines (no arrowheads) in pencil. Do not cross labelling lines.

crown
- exposed part of tooth

root
- part embedded in jaw

enamel
- outer biting surface
- hardest substance in body

dentine
- main section of the tooth
- living tissue like bone
- not as hard or resistant to decay as enamel

pulp cavity
- nerve endings connect to brain
- blood vessels carry oxygen
and nutrients in for cells, and remove waste products

cement
- rough covering, to which periodontal fibres are attached, holding tooth in place

jaw bone
- with sockets for teeth

gum
- protects jaw bone and roots of teeth
Tooth structure

Different types of teeth

In the human mouth there are 4 different types of teeth, each specialised for different functions. There are also 2 sets of teeth: the first - also called milk or deciduous teeth - usually "erupt" over a period from the age of about 6 months to 3 years.

From the age of about 5 to 14 these are gradually replaced from below by the permanent set, with the final "wisdom" teeth appearing in the late teens or early twenties.

Complete the table below about the different types of human teeth.

Teeth
type
> incisors > canines > premolars > molars






FRONT OF
MOUTH
incisor canine premolar molar





BACK OF
MOUTH
Number in 1st set 8 4 0 8 Total >20
Number in 2nd set 8 4 8 12 Total >32
Function

> cutting >stabbing
/piercing
>chewing > mastication
Notes on structure > chisel shaped > single,prominent cusp >2 cusps >4 or 5 cusps
>single roots >single deep roots >1 or 2 roots >3 roots - upper2 roots - lower

Whereabouts in the mouth are the extra teeth added in the second set?

> back of jaw

Why do you think humans need 2 sets of teeth?

> to accommodate the growth of the jaw

NOT because of decay/different diet/damage

What sort of tooth is illustrated overleaf?

> molar

The arrangement of teeth in various mammals may vary due to specialisation for different diets.

What type of teeth will be specially developed in meat-eaters?

> canines

What adaptations to the teeth are shown by animals that eat grass?

> incisors for cutting - only in bottom jaw

> (wear-away) molars for chewing - sideways action

Problems with the teeth


Tooth decay - also called caries - is usually started by the action on the outside of the teeth of acid produced by bacteria feeding mostly on sugary foods and sweets we eat. This has several stages.

Plaque consists of a sticky film of bacteria and other micro-organisms, together with materials from the saliva and foods we eat. This is relatively easy to remove by brushing, and can be felt by the tongue.

If this is allowed to build up over a period of time, inaccessible parts of the teeth become encrusted with a layer of "tartar" - also called calculus, formed from plaque together with calcium secretions from the saliva. This is difficult to remove, and it provides sites for bacterial growth.

The acid produced by the bacteria will weaken the enamel and dentine of the tooth, but when the decay reaches the nerve endings in the pulp cavity, then considerable pain may result.

If plaque gets between the gum and teeth (perhaps due to incorrect brushing), then a condition called periodontal disease may take hold. This affects the gum and bone structure, and may result in bad breath, bleeding gums and loose teeth. Filled tooth

If tooth decay proceeds too far, then the decayed area will have to be drilled out and replaced by a filling - many materials are available. Otherwise the tooth may be removed (the socket eventually healing), and partly replaced by a crown or completely by false teeth.

Prevention of tooth decay


Regular brushing with toothpaste should remove plaque, preventing decay and the buildup of calculus.

It is important to brush the teeth efficiently. This can be checked using disclosing tablets and liquids (food colourings which strongly stain plaque which has been missed).

However, it is important not to overdo brushing, or else the gums may recede, so that the cement of the roots is exposed. Toothpaste contains mildly abrasive compounds and the surface may be damaged. Mouthwashes are claimed to kill bacteria in the mouth, and therefore to freshen the breath and preserve the teeth.

Nowadays, most toothpastes also contain fluoride, which strengthens the enamel of the teeth, especially if it is used from an early age.
The almost universal introduction of fluoride is probably the most significant advance in dental care.

In some areas, fluoride is added to drinking water supplies (about 1 part per million).

Regular dental checkups - every 6 months - should detect any problems before they can progress too far. However the pattern of dentistry has recently altered dramatically from extractions and fillings to preventive and more cosmetic work.

Experiment to show the interaction between dental plaque and sugar

N.b. You must observe basic hygiene precautions in the course of this work.

Use only new untouched cotton wool buds, and do not put them down on the surface of the laboratory bench.

Materials

cotton wool buds

icing sugar

universal indicator solution + colour scale

Procedure

1) Moisten the teeth by passing the tongue over them.

2) Take a cotton wool bud and rub it firmly over the surface of the teeth. Holding it by the middle, start at the centre of the mouth and use one end to do the left side, and do the right side with the other end.

3) Dip only one end in the icing sugar, and roll it round to coat it evenly.

4) Leave the cotton wool buds on the mat provided, according to your position on the bench.

5) It is advisable to have a control experiment, which replicates the experiment with the exception of one factor. Think about the best way to do this.

oOo

6) After some time, add 2 drops of universal indicator solution to each end of the cotton wool buds.

Note the colour and match this to the scale provided (greenish means neutral to slightly acidic, orange and red mean more acidic).

7) Place the cotton wool buds in the container of disinfectant.

Results

( note also results from other members of the class)

Your experiment teeth scrapings alone teeth scrapings + sugar
indicator colour .. ..
pH .. ..
Control Treatment? Treatment?
indicator colour .. ..
pH .. ..

What did you learn from this experiment?

> combination of sugar and plaque causes acidity, neither is acidic on its own

Teeth models available online

Chart


Many other anatomical models and charts available by following this link.



Return to the previous unit? Return to the contents page? Another look? Back to the BioTopics index page? Next Unit?



www.BioTopics.co.ukHome Contents Contact via form Contact via email Howlers Books WWWlinks Terms of use Privacy