Oral Health: Teeth development

Oral health is achieved when the teeth and oral environment are not only healthy but also:

• Comfortable and functional, that is food can be chewed thoroughly and without pain or discomfort and the teeth are not sensitive to different stimuli such as cold

• Social acceptability is also of importance and the mouth must not give rise to bad breath, the appearance of the teeth and gums should be acceptable and not give rise to embarrassment

• There should be an absence of sources of infection which may affect general health

This state of oral health should persist for life, which given a healthy lifestyle, is achievable for the majority of the population.

Development of Teeth

Before Birth

By the third week after conception the primitive mouth has formed. Over the next few weeks the tongue, jaws and palate develop. During the sixth week formation of the teeth commences, and by eight weeks all of the primary (deciduous) incisors, canines and molars are discernable. The permanent teeth begin to develop shortly afterwards.

After Birth

The development of the teeth within the jaw continues after birth. Normally the primary teeth start to appear in the mouth around six months after birth. The primary central incisors, lateral incisors, first molars, canines and second molars appear in this order at intervals from 6-24 months. For each tooth type, lower teeth tend to appear about two months before the uppers.  By two years most children have their full compliment of 20 primary teeth, that is five on each side of the midline of the top and bottom jaws.

As the child grows the jaws grow and spaces may begin to appear between the primary teeth. This growth makes spaces for the larger permanent teeth. The growth in jaw length also accommodates the permanent molar teeth, which appear behind the primary teeth.

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The first permanent teeth to appear in the mouth are normally the four first permanent molars. These erupt at around age six years behind the primary teeth. At the same time the two lower central primary incisors begin to loosen and then fall out and are replaced by the lower central permanent incisors. Over the following six years (6-12) the remaining 18 primary teeth fall out and are replaced by permanent teeth. At about age 12 the four second permanent molars appear behind the first permanent molars. The last teeth to appear are the 3rd molars or wisdom teeth. Not everybody has 3rd molars and there is considerable variation in the age at which they erupt.

Teething

During the first two years of life many symptoms have been attributed to teething. The most common side effect of teething is drooling. Symptoms of teething may include disturbed sleep, feeding irritability and swollen tender gums. The response to tooth eruption is very varied however; other more severe symptoms such as diarrhoea, fever and convulsions should not be attributed to teething and require medical attention.

Tooth Types

There are four different tooth types in the mouth.

Mouth

The incisors at the front of the mouth have a sharp biting surface and are used for cutting or shearing food into small chewable pieces. There are eight incisors in both primary and permanent dentitions.

The canines are situated at the ‘corners’ of the dental arches. They have a sharp, pointed biting surface. Their function is to grip and tear food. There are four canine teeth in both primary and permanent dentitions.

The premolars, unlike the incisors and canines, have a flat biting surface. Their function is to tear and crush food. They are unique to the permanent dentition which has eight premolars.

The molars are the largest of the teeth. They have a large flat biting surface. The function of the molars is to chew, crush and grind food. There are eight molars in the primary dentition and twelve in the permanent dentition.

The Structure of a Tooth

The tooth has two anatomical parts. The crown of a tooth is that part of the tooth which is covered with enamel and this is the part usually visible in the mouth

The root is the part embedded in the jaw. It anchors the tooth in its bony socket and is normally not visible.

ENAMEL: The hard outer layer of the crown. Enamel is the hardest substance in the body.

DENTINE: Not as hard as enamel, forms the bulk of the tooth and can be sensitive if the protection of the enamel is lost.

PULP: Soft tissue containing the blood and nerve supply to the tooth. The pulp extends from the crown to the tip of the root.

CEMENTUM: The layer of bone-like tissue covering the root. It is not as hard as enamel.

Teeth

Structures around the tooth

Periodontal ligament: Made up of thousands of fibres which fasten the cementum to the bony socket. These fibres anchor the tooth to the jaw bone and act as shock absorbers for the tooth which is subjected to heavy forces during chewing.

Gingivae (gums): Soft tissue that immediately surrounds the teeth and bone. It protects the bone and the roots of the teeth and provides an easily lubricated surface.

Bone: Provides a socket to surround and support the roots of the teeth.

Nerves and blood supply: Each tooth and periodontal ligament has a nerve supply and the teeth are sensitive to a wide variety of stimuli. The blood supply is necessary to maintain the vitality of the tooth.

The Importance of Primary Teeth

Parents sometimes wonder why there is growing importance being placed on keeping a toddler’s primary teeth in good condition until they are replaced by their permanent successors. Many parents still feel that the primary teeth are not important because they are going to fall out anyway. Besides the obvious importance of healthy primary teeth for eating, appearance and speech, they are also essential for guiding permanent teeth, which develop underneath, into their correct positions. Early neglect or loss can result in a number of problems.

If a child’s primary molar tooth has to be extracted early due to severe tooth decay, then the guide for the permanent successor is lost. The space available for the permanent tooth can be reduced resulting in a crooked permanent tooth. The possible complications caused by crooked permanent teeth are enough motivation for most parents to take proper care of their child’s first set of teeth.

Saliva

The teeth and oral tissues are constantly bathed in saliva. Saliva is secreted by the salivary glands. The production of saliva increases when food or drinks are consumed. It’s presence is vital to the maintenance of healthy oral tissue. Saliva has many functions including the following:

Fluid/Lubricant: Coats mucosa and helps to protect against mechanical, thermal and chemical irritation. Assists smooth airflow, speech and swallowing.

Ion Reservoir: Holds ions needed for maintenance of enamel near the tooth. Helps prevent decay.

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Buffer: Helps to neutralise plaque acids after eating, thus helps prevent decay.

Cleansing: Clears food and aids swallowing.

Antimicrobial actions: Anti-microbial mechanisms in saliva help control the bacteria in the mouth.

Pellicle formation: Protective coating formed on enamel from salivary proteins.

Taste: Saliva acts as a solvent thus allowing interaction of foodstuff with taste buds to facilitate taste.

Plaque

Dental plaque is a common causative factor for caries and periodontal disease.

Dental plaque is an almost colourless sticky bacterial film, which adheres to the tooth surface. It is not removed by rinsing with water.

The accumulation of dental plaque around the gum margin leads to the development of gingivitis in most people. The longer the plaque is left, the greater the risk of gingivitis. Gingivitis is characterised by inflamed, reddened gums which bleed easily during normal tooth brushing. Daily careful plaque removal is required to prevent gingivitis.

Plaque is also involved in causing dental decay. When foods containing sugars are eaten the bacteria in plaque break down the sugars and acid is produced. This acid then dissolves the surface of the enamel under the plaque causing dental decay (caries).

Plaque is difficult to see and therefore can be difficult to remove. A special dye in the form of a disclosing tablet can be used to stain the plaque making it easier to see. These tablets are available in most chemists.

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