i. The posterior region of mandible is more commonly affected than the maxilla due to the microanatomy and reduced vasculature of the mandible.

ii. Intermittent swelling and drainage extraorally.

iii. Intense pain may occur; pain is of severe, boring type, which may continue for weeks or months.

iv. Swelling of face results from secondary infection.

v. Trismus, fetid odour and pyrexia can be noted.

vi. Soft tissue abscesses.

vii. Persistently draining sinuses.

viii. Exposure of bone is the hallmark of osteoradionecrosis.

ix. The exposed bone becomes necrotic as a result of loss of vascularity from periosteum and subsequently it sequestrates.

x. Pathological fractures of bone is common.

xi. Osteoradionecrosis is treated by hyperbaric oxygen therapy.

• Protective measures are employed for the operator of the X-ray equipment, patients and any associated personnel including individuals in adjacent office and occupants of doctor’s reception.

• Despite the low risk to the patient from dental radiography, it is always best to keep exposure to ionizing radiation to a minimum. Hence, the ALARA concept should be kept in mind when exposing dental films. This can be achieved by:

i. The operator should not:

ii. The operator should:

iii. There are exposure limits for occupationally exposed radiation workers. The maximum permissible dose (MPD) is the dose of radiation to the whole body that produces very little chance of somatic or genetic injury. The MPD for whole body exposure per year for occupationally exposed personnel is 0.05 Sv(5 rem).

i. Only people whose presence is required should stay in room.

ii. Plan and design maxillofacial radiology department. Conch shell design of the operatory area is recommended to protect people in surrounding areas from radiation.

iii. An X-ray tube should be away from doorways to avoid accidental exposure.

iv. Radiation exposure to the room and to adjacent office premises should be monitored.

v. The walls of the room should be reinforced with barium plaster or the thickness of the walls should be increased by using an additional layer of bricks.

vi. Caution or warning signs should be displayed.

a. Stochastic effect: It includes increase in probability of occurrence of biological effect with increasing absorbed dose rather than its severity. They occur as direct effect of dose.

b. Non-stochastic effects or Deterministic effect: It is one in which severity increases with increase in absorbed dose in affected individual.

• Acute or immediate effect: The effect appearing shortly after the exposure as a result of large dose.

• Chronic or long-term effect: The changes become evident after long period of time.

a. Somatic Stochastic Effects

b. Somatic Deterministic Effects or Non-stochastic Effects

• Genetic effects are not seen in the person irradiated but are transferred to future generation.

• Generic cells are germ cells of the reproductive organs. Reproductive cells are prone to damage with comparatively much smaller dose than amount needed to produce radiation effect in somatic cells of the body.

• Radiations cause fragmentation of chromosomes and mutation of genes of sex cells and these mutant genes with altered characteristics pass on to next generation.

• Mutations are the changes in the information carried by the chromosomes within the germ cells, i.e. sperm and egg cells. It is indicative of change in the DNA of the cells.

• It may result in congenital abnormality in the offspring of the person irradiated. There may be retardation of growth rate.

• Doubling dose: This is the dose that causes complete doubling of all gene mutations.

• Damage can be caused to either dominant or recessive genes. The dominant variety effect is seen in next generation, whereas recessive variety effect may be seen after several generations.

• Genetic damage follows non-threshold type of response, i.e. small amount of radiation has the potential to produce lesser number of mutations in chromosomes.

• Genetic damage is cumulative and it cannot be repaired.

• Human embryo is said to be most sensitive especially during 15–42 days of its life, so radiation is avoided during pregnancy.

• Sterility in human beings has been reported on exposure to heavy doses.

• No genetic effect is seen in individuals beyond the age of reproduction.

• Acute somatic effects will be manifested within few hours to few days of acute irradiation and the severity of the effect will depend upon dose and dose rate.

• Following the latent period, effects are seen within minutes, days or weeks.

• Acute radiation effect is short-term effect. It occurs when large dose of radiation given in short period of time as in atomic bomb explosion and in nuclear accidents.

• Short-term effect is not applicable to the dentistry as dental diagnostic radiographs use less than 5 rads.

• Sensitivity: It is determined by the sensitivity of parenchymal cells. If continuously proliferating tissues are irradiated with a moderate dose, cells are lost primarily by mitosis-linked death.

• Proliferative rate: The extent of cell loss depends upon the damage to the stem cell pools, and the proliferative rate of cell population.

i. Skin: Excessive exposure causes dermatitis. Repeated exposures have a cumulative effect. Dryness, erythema, thickening, desquamation and cracking of hands may also occur.

ii. Finger nails: Fingernails may become brittle, develop longitudinal fissures and ridges, and finally crumbled.

iii. Hair: Radiation causes epilation. It is often seen in association with dermatitis. Hair loss can be permanent.

iv. Blood-forming tissue: The bone marrow and lymph nodes are susceptible to excessive exposure, and it can manifest itself as change in blood count. The usual blood picture is leukopenia.

v. Eyes: Radiation dose can cause cataract and larger doses can cause detached retina.

• Effect that appears after years, decades or generation is known as long-term effect.

• It depends upon the extent of damage to the fine vasculature.

• Irradiation of capillaries causes swelling, degeneration and necrosis.

• It increases the capillary permeability and initiates a slow progressive fibrosis around the vessels.

• Due to this, deposition of fibrous scar tissue increases around the vessels, leading to premature narrowing and eventual obliteration of vascular lumen.

• This impairs the transportation of oxygen, nutrients and waste products, and results in death of all cells.

• This leads to loss of function and reduced resistance to infection and trauma.

• Carcinoma: The cancer of skin is the earliest form of radiation-induced malignant tumour.

• Leukaemia: It is one of the late effects and can be due to primary and secondary radiation. A higher incidence of leukaemia is observed in radiologists as compared to others.

• Necrosis: Due to heavy radiations, destruction of tissue can occur. Necrosis can be seen in extraction socket after radiation exposure.

• Retardation of growth: Irradiation of developing teeth results in disorganization of the odontoblasts. With larger doses retardation of bone and tooth development is more obvious.

• Effect on the taste buds: Taste buds are very sensitive to radiation and soon degenerative changes begin. Loss of taste is very common.

• Effect on the salivary glands: The parenchymal component of salivary gland is more radiosensitive. Exposure to radiation leads to injury of these parenchymal cells leading to following conditions:

• After exposure of 1.5 Gy within the first few minute to few hours, symptoms characteristic of gastrointestinal tract disturbance occur, such as anorexia, nausea, vomiting, diarrhoea, weakness and fatigue.

• They are dose-dependent; higher the dose, the more rapid onset and greater is the severity of symptoms.

• After the prodromal period, latent period occurs, during which no signs and symptoms are present.

• This latent period is also dose-related. It varies from hours or days at supralethal exposure (>5Gy) to few weeks at sublethal exposures (<2 Gy).

• Whole body exposure of 2 to 7 Gy causes injury to the haematopoietic stem cells of the bone marrow and spleen. It causes rapid and profound fall in the number of circulating granulocytes, platelets and erythrocytes.

• Common signs: Infection, haemorrhage and anaemia. Death can result from this syndrome usually 10 to 30 days after irradiation.

• Exposure of whole body in the range of 7 to 15 Gy causes extensive damage to the gastrointestinal system.

• It causes considerable injury to the rapidly proliferating basal epithelial cells of the intestinal villi and leads to loss of the epithelial layer of the intestinal mucosa. Due to this denuded mucosal surface, plasma and electrolytes are lost, and efficient intestinal absorption is impaired.

• Signs and symptoms include ulceration following haemorrhage of the intestine. All these changes lead to diarrhoea, dehydration and loss of weight.

• Exposure in excess of 50 Gy can cause death in 1 to 2 days. Human beings show collapse of the circulatory system with precipitous fall in blood pressure in the hours preceding death.

• Victims may show intermittent stupor, incoordination, disorientation and convulsion suggestive of extensive damage to the nervous system.

• This syndrome is irreversible and clinical course may run from only few minutes to about 48 h before death commences.

• Antibiotics: Antibiotics should be started when infection threatens life or the granulocyte count falls.

• Fluid supplements: It is necessary to replace fluid and electrolytes.

• Blood transfusion: Whole blood transfusion is given to treat anaemia.

• Platelet: Administration of platelet to arrest thrombocytopenia.

• Bone marrow grafts: Bone marrow grafts are indicated for identical twins because there is no risk of graft-versus-host response.

i.