Enamel

• Enamel forms the outer layer of the crowns of all teeth and is the

hardest substance in the body

• Microscopically enamel is composed of prisms of inorganic crystals in an organic matrix arranged to run at right angles to the underlying dentine

• Bacteria within plaque(sticky mix of food debris and bacteria formed within two hours of eatin) adhere to the enamel surface

• Acid production reduces the pH level within the mouth from neutral, and once it reaches below 5.5 the enamel is attacked or demineralised by the acids

• Weak organic acids (lactic or citric acid) produced by oral bacteria cause dimineralisation of the enamel structure, but the enamel may remineralise if the attacks are infrequent, the salivary minerals can neutralise the acid and if treated with topical fluoride at this stage

• If the acid attack continues the dimineralisation progress along the prism structure towards the dentine and the enamel becomes undermined and eventually collapses into a cavity

• An excess of fluoride present in the diet causes flourosis . with the result that the enamel gas an unsightly mottle appearance

• Chronic childhood illness can cause hypominerilisation of the enamel with discolouration and pitting being present

• Its inorganic crystals are called hydroxyapatite

• Enamel contains no nerve fibres or blood vessels

• Flouride can be incorporated into the hydroxyapatite structure thorugh ingestion during the period of enamel formation to give a more acid resistant mineral called flourapatite

• This is the basis of the use of fluoride to prevent dental caries

Dentine

• Dentine is made up of hollow tubes running from the pulp to the

• enamel layer above

• The dentine tubules contain nerve endings called dentinal fibrils which run from the pulpal tissues and allow the dentine layer of tooth to experience sensation

• The tubular structure of the dentine allows for rapid progression of caries than it does in enamel and the patient is only made aware of the sensitivity in the affected tooth as the nerve endings are stimulated

• The rapid progression of caries in tooth produces a `mushrooming' of decay within the dentine layer. Once sufficient enamel has been undermined, the overlying tooth structure collapses in on itself and a cavity is formed

• This in itself will open a wider surface area of the dentine to the carious attack so the tooth decays further and rapidly

• The odontoblast cells which form the dentine try to protect the the pulpal tissues from the caries and prevent pulp death by laying down a layer of secondary dentine

• Without dental intervention the caries will inevitably reach the pulpal tissues once the dentine layer becomes involved

• This is because unlike enamel, dentine cannot repair itself

Periodontal ligament

• is arranged as groups of fibres holding each tooth within its socket

• they act as shock absorbers so that normal masticatory forces allow the tooth to `bounce' in its socket, thus preventing damage to the tooth

• the fibres run obliquely from cementum to lamina dura of the alveolar bone and also into the gingival tissues at the gingival margins of the teeth

• chronic periodontitis involves the gradual destruction of the fibres so that the tooth becomes mobile in its socket

• with no dental intervention and treatment this will eventually will lead to tooth loss

• loss of the ligament allows the formation of periodontal pockets, these can be measured with pocket measuring probes

• acute infection of the pocket with pus formation is called a lateral periodontal abscess

• the periodontal ligament contains many nerve fibres and blood vessels; pressure sensation is not lost even after local anaesthesia

Upper first molar teeth

• these are charted as 6's

• they have 3 roots: palatal, mesio-buccal and disto-buccal

• their nerve supply is posterior superior and middle superior dental nerves

• they have four large cusps and a fifth cusp unique to the upper first molars called `cusp of Carabelli'

• They each have a wide occusal surface for chewing food

• They usually erupt between the 6 and 7 years of age, distal to the deciduous molars

• They are often fissure sealed to prevent occlusal carious attacks while the child develops a good oral hygiene technique

• The position of the mesiobuccal cusp in relation to the buccal groove of the lower first molars determine Angle's classification of occlusion used in orthodontotics

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