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प्रश्न
Write down the explanation.
Explain the structure of tooth.
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उत्तर
Structure of tooth:
Tooth Anatomy
- A tooth consists of the portion that projects above the gum called crown and the root that is made up of two or three projections which are embedded in gum.
- A short neck connects the crown with the root.
- The crown is covered by the hardest substance of the body called enamel, which is made up of calcium phosphate and calcium carbonate.
- Basic shape of tooth is derived from dentin which is a calcified connective tissue.
- The dentin encloses the pulp cavity. It is filled with connective tissue pulp. It contains blood vessels and nerves.
- Pulp cavity has extension in the root of the tooth called root canal.
- The dentin of the root of tooth is covered by cementum, which is a bone like substance that attaches the root to the surrounding socket in the gum.
- We have four different types of teeth hence, we are heterodont. Types of teeth are incisors (I), canines (C), premolars (PM) and molars (M). Each half of each jaw has two incisors, one canine, two premolars and three molars.
- Thus, the dental formula of adult human can be represented as.
`I2/2, C1/1, PM2/2, M3/3 = (2, 1, 2, 3)/(2, 1, 2, 3)`
i.e. 8 × 2 = 16 teeth in each jaw = 32 teeths
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संबंधित प्रश्न
| If the teeth are not cleaned regularly, they become covered with a sticky yellowish layer W of food particles and bacteria. Since layer W covers the teeth, the alkaline liquid X secreted by glands Y inside the mouth cannot reach the teeth surface to neutralise the acid formed by the action of organisms Z on sugary food, and hence tooth decay sets in. |
- What is W known as?
- What are (i) X and (ii) Y?
- What are organisms Z?
- State one way of removing layer W from the teeth.
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| Across | Down | ||
| 1. | Cream-coloured digestive gland | 2. | Feeds with the help of pseudopodia |
| 3. | Undigested excretory solid residues | 6. | Total number of molars in one jaw of an adult |
| 4. | Organ that mixes saliva with the food | 8. | Largest gland |
| 5. | Point of defecation | 9. | Watery secretion in the mouth |
| 7. | Stored in gall bladder | 11. | A ruminant |
| 10. | Finger-like outgrowth in the small intestine | 12. | Form of food chewed by ruminants |
| 13. | Kind of taste buds | ||
| 14. | Kills bacteria in the stomach | ||
