The bulk of a tooth is formed of dentine, which is sensitive to ternperature change and other stimuli. In the centre of the tooth crown, and down the root.

The bulk of a tooth is formed of dentine, which is sensitive to ternperaturechange and other stimuli. In the centre of the tooth crown,and down the root to the tooth apex, is a hollow space occupied bythe pulp, which is soft tissue containing nerves and vessels. Thecrown projects from the gingiva and is protected by a layer ofenamel i n the form of a thimble or cap . Enamel is insensitiveand hard, like ivory (= elephant enamel) but is susceptible tocaries. Beyond the crown there is a thin layer of cementum coveringthe dentine of the root, and this layer forms the anchorage for theDental eruption is .Infection;Caries is a bacterial invasion of the tooth which first liquefies anarrow track through the enamel and then causes more extensive softeningand staining of the adjacent dentine.Once the pulp has died, infection may spread to theperiapical region. When infection has spread beyond the apex, the effect dependson the severity of the inflammation. An acute abscess i s the mostmarked reaction,Chronic apical infection may be present without clinical signs. cause the formation of a radicular cyst.The X-ray changes then are those of a discrete peripheral lucency.

Radiation changes in the jaw Radiation and chemotherapy cause damage to developing teeth. the fetus or infant is irradiated, damage to the developing toothgerm can cause either absence of the tooth or gross hypoplasia,both of primary and secondary dentition. In addition, mandibulargrowth is retarded and hypoplasia results . Irradiation of the oral tissues (e.g. for soft-tissue sarcoma) affects the salivary glands and the nature of their secretions, which diminishand become more acid. Caries is potentiated in a dry mouth andRadionecrosis Initially, osteoporosis is seen, but the end-stage is a pattern ofmixed sclerosis and lysis. Pathological fractures and bone resorptionas well as sequestra are seen. Periosteal new bone is not prominentin the mandible.

DDX OF sclerosing lesion of the jaw s;1-hypercementosis2-cementoma.3-post inflammatory sclerosing osteitis.4-odontomes(complex &compouind).5-localized fibrous dysplasia.6-pagets dissease.

generalized dissease effecting teeth&jaws; Hypopituitarism Hypoplasia of the jaws and teeth and delayeddental age arc found, as would be expected. Hyperparathyroidism Subperiosteal bone resorption is thepathognomonic bony change in this disease. Gigantism Dental separation again results from jaw enlargement,they are difficult teeth to radiograph.

Cyst of jaws;Cysts of the jaws may conveniently be classified into:I. Cysts of denial origin, developmental or post inflammatory2. Non-dental, developmental or fissural cysts3. Non-epitheliated cysts .

Post inflammatory Radicular (apical) cysts Most cysts of thejaws are radicular. They lie directly upon the apex of a tooth.which is usually diseased. They follow inflammation of thepulp and apical bone, when a local apical area of chronicinflammation, the granuloma. may result. This is seen radiologicallyas a poorly defined para-apical area of boneloss rather like a Brodie's abscess. The well-defined radicularcyst results. Its dense opaque margin is continuous with thelamina dura at the periphery of the cyst, but within the cyst thelamina dura is destroyed. These cysts are generally less than1.5 cnm in diameter and in grossly carious mouths may hemultiple .Treatment is by removal of the tooth and curettage. This shouldresult in bony healing with gradual obliteration of the cavity.Should the cyst persist after dental extraction, it is known as aresidual cyst and its origin cannot be interred from a radiograph

(i) Odontogenic keratocyst (primordial cyst) These mayfollow cystic degeneration of the enamel organ before the toothis formed, so that the cyst replaces the tooth, but they may alsoarise from cctopic odontogenic epithelium. Should a normalcomplement of teeth be present, the cyst is assumed to havereplaced a supernumerary tooth. Primordial cysts are morecommon in young men, but may be seen at all ages. They areslow-growing but may reach a very large size and may occupythe entire ascending ramus . The cortex becomesthinned and an axial view also demonstrates expansion in thebuccal-lingual plane. They are most commonly seen in the posteriormandible and arc usually monolocular. These cases presenteither because a critical size is reached and the patient feels afluctuant swelling of the mandible, or because of secondaryi nfection and purulent discharge.Because of their growth potential, they may abut against an initiallyunrelated and uneruptcd tooth. A dentigerous cyst is then simulated,although the size and location may help in differentiation.The diagnosis is in any case confirmed by enucleation and histological examination.These cysts are almost inevitably ke atinised and are very likelyto recur unless removed completely. Long-tern follow-up is thereforeadvisahle.

(ii) Dentigerous cyst (follicular cyst) Cystic degeneration ofthe enamel organ may occur after the tooth has been formed butbefore it has erupted. This results in a cyst related to the crown ofan uneruptcd tooth. Cysts enlarge in part because of local hydrostaticimbalance. if the pressure within the cyst exceeds the eruplivepressure of the tooth, that tooth is prevented from erupting. Itbecomes displaced, often for some distance. Part of the crownalways remains in contact with the cyst

2. Developmental (fissural) cystsThese presumably occur at sites of fusion of embryonic processes.Such cysts are:a. Medial mandibular .b. Medial rnaxillarvr c. Nasopalatine.The nasopalaline ducts connect the nasal cavitywith the palate behind the central incisors. Four ducts are present inutero, two on either side of the midline. Failure of normal ductalobliteration may result in local epithelial remnants undergoingcystic degeneration.d. Globulomaxillar_y. These cysts look like an inverted pear andlie between the upper lateral incisor and canine, the roots of whichare diverged. There is some doubt as to whether these are fissural ori nflammatory. The majority are odontogenic keratocysts.

Non epithelialised bone cyst;Simple bone cyst. These may follow trauma and are thus alsoknown as traumatic cysts. They appear in young patients, usuallyboys, in the posterior aspect of the body of the mandible. Like othertypes of cyst, they are vaguely spherical, well-defined, and surroundedby a thin dense zone of reactive sclerosis.Aneurysrnal bone cyst. These present as a well-defined expansileradiolucency, displacing teeth. Again, the lesion is not commoni n the jaws. and histology is usually needed to confirm its identity.They may be secondary to other tumours