WHAT IS A TOOTH ?
A tooth is a part of digestive system which breaks the food into tiny fragments before swallowing. There are about 32 teeth in an adult human. It is ectodermal in origin ( other ectodermal organs include - hair , nails, skin etc ). The first tooth appear in the oral cavity at about 6 months of age. Tooth is anatomically divided into two parts - CROWN AND ROOT. Crown is the white portion of the tooth visible in the oral cavity while the roots are embedded in the alveolar socket.
parts OF A TOOTH
A tooth is mainly composed of -
ENAMEL It is the outer most layer of the tooth , white in colour and the hardest substance in the human body. It is mainly composed of 96% inorganic substance and 4 % organic substance.
DENTINE It is present just beneath the enamel and is slightly yellowish in colour. It contains 70% inorganic substance while the remaining 30% constitute for organic and water components.
PULP Pulp is present in the inner core of a tooth . It is soft , vascular and rich in nerve supply . The vitality of the tooth depends upon the pulpal condition.
CEMENTUM It is the substance that lines the root of the tooth and provides fibrous attachment. Cementum also aids in the eruption of tooth in the oral cavity.
PERIODONTAL LIGAMENTS It is composed mainly of TYPE 1 collagen fibres , divided into 5 groups and they mainly function to bear the masticatory forces and provides attachment of tooth in the alveolar socket.
Types of teeth
1. on the baSIS OF FUNCTION
INCISORS- These are front teeth that help in biting and cutting food.
CANINES- These teeth are placed at the corners of the mouth; they are sharp and help tear food.
PREMOLAR -These are present behind the canines; these teeth help grind the food.
MOLAR - These are located behind the premolars; these help grind and chew food properly.
2. ON THE BASIS OF SETS OF DENTITION
MONOPHYODONT- Presence of only one set of teeth for entire life.
DIPHYODONT- Presence of two sets of dentition. Example - HUMAN BEINGS.
POLYPHYODONT- Presence of more than two sets of dentition.
3. BASED ON THE SHAPE OF THE TOOTH
HOMODONT- All teeth have same shape without distinction.
HETERODONT- Presence of different group of teeth. E.g- INCISOR , CANINE, PREMOLAR, MOLARS
4. BASED ON THE SHAPE OF THE CUSPS
BUNODONT- Primitive type of teeth with simple conical cusps . E.g - cats , dogs
HAPLODONT- Simplest cone form of teeth with single root. Only simple hinge movements of jaw are seen. E.g- reptiles ( crocodile)
TRICONODONT- Three cusps arranged in line with largest cusp in the centre. E.g - EARLY MAMMALS.
TRITUBERCULAR STAGE- Three cusps arranged in a triangle form.
QUADRITUBERCULAR STAGE- Fourth cusp is formedamd an occlusal contact relationship between the upper and lower jaw is established.
HUMAN DENTITION
Presence of two sets of dentition viz. DECIDUOUS DENTITION AND PERMANENT DENTITION.
1. DECIDUOUS DENTITION -
Deciduous dentition is also known as MILK TEETH due to its resemblance to the colour and refractive index of milk. It consists of INCISORS , CANINES AND MOLARS.
ERUPTION TIME- 6 months - 5.5 years
TOOTH FORMULA- 2 1 0 2/2 1 0 2
2. PERMANENT DENTITION
It is slightly yellowish in colour. The colour of permanent dentition depends on the translucency of the enamel. It consists of - INCISORS, CANINES, PREMOLAR AND MOLAR .
ERUPTION TIME - 6 years onwards
TOOTH FORMULA - 2 1 2 3 / 2 1 2 3
DIFFERENCES BETWEEN DECIDUOUS DENTITION AND PERMANENT DENTITION
FEATURES | DECIDUOUS DENTITION | PERMANENT DENTITION |
NUMBER | 20 | 32 |
COLOUR | Yellow | White |
ENAMEL | Thinner (about 1mm) | Thicker (about 2-3 mm) |
MAMMELEONS | Absent | Present |
SHAPE OF ROOT | Longer, more slender | Shorter, bulbous |
FLARING OF ROOTS | Prominent flare | Less flaring |
PULP CHAMBER | Larger | Smaller |
ROOT CANALS | More ribbon-like | Well defined |