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| Distribution of subject wise questions in NEET MDS examination. |
The harmful effects of the excessive dose of the ionizing radiation can be divided into two types. These are as follows:
We shall discuss them one by one in detail.
In earlier articles on radiography, you studied the effects of ionizing radiation on biological tissues. These effects can be divided into two types- Deterministic and Stochastic. Therefore, the radiation safety becomes of paramount importance white taking a radiograph.
In this article termed as radiation physics, we shall talk about the ways, the x-rays are produced, the events that occur at atomic level during their production and how can one save oneself and others.
Electrons that travel from the filament to the tungsten convert part of their kinetic energy into x-ray photons. This phenomenon occurs by the formation of bremsstrahlung and characteristic radiation.
Radiation biology is the study of effects of ionizing radiation on living systems. In this article we shall talk about the harmful effects of ionizing radiation on tissues, how does it occur, and how sensitive different types of cells are?
The effects of radiation on the tissues can be divided into 2 broad categories. The Deterministic and Stochastic effects.
Odontogenic Cysts
Nonodontogenic Cysts
Pseudocysts
A cyst is defined as “an epithelial lined pathologic cavity”. The periapical/radicular cyst is an odontogenic cyst. The classification of the cysts can be seen HERE. It is important to read for ADC Exams or NEET MDS purpose.
Periapical cysts are inflammatory cysts. Their epithelial lining originates from the odontogenic epithelium of the tooth buds that remains within periodontal ligaments (epithelial rests of Malassez) after completion of tooth maturation. Due to inflammatory response, the epithelial rests of Malassez start proliferating and provide cystic lining.
Dentigerous (Follicular) Cysts are the second most commonly occurring odontogenic cysts after periapical cyst and the most common developmental cysts of the jaws. By definition, a dentigerous cyst is attached to the tooth cervix (enamel-cementum junction) and encloses the crown of the unerupted tooth.
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| Photograph1: Dentigerous cyst surrounding the crown of right mandibular third molar and going upward in ascending ramus. [1] |
A dentigerous cyst originates from the enamel organ remnant or reduced enamel epithelium. The expansion of the dentigerous cyst is related to epithelial proliferation, release of bone-resorbing factors, and an increase in cyst fluid osmolality.
Dentigerous cysts are most commonly seen associated with third molars and maxillary Canines. The peak incidence of dentigerous cysts occurs between twenty to 40 years. Males have more predilection with a ratio of l.6 to 1.
Dentigerous cysts are generally symptomless. The delayed eruption is the most common indication of dentigerous cyst formation. This cyst can achieve significant size, occasionally causes cortical bone expansion but rarely reaches a size that predisposes the patient to a pathologic fracture.
Radiographically, a dentigerous cyst manifests as a well-defined, unilocular or sometimes multilocular radiolucency with corticated margins in attached with the crown of an unerupted tooth. The concerned unerupted tooth is mostly displaced. In the mandible the related radiolucency may extend superiorly from the third molar site into the ramus or anteriorly and inferiorly along the body of the mandible. In maxillary dentigerous cysts in the canine region, extension into the maxillary sinus or to the orbital floor may be seen.
The cyst is lined by stratified squamous epithelium. In a noninflamed dentigerous cyst the epithelial lining is nonkeratinized. It remains approximately four to six cell layers thick. Sometimes, numerous mucous cells, ciliated cells, and rarely, sebaceous cells may be found in the lining of the epithelium. The epithelium-connective tissue junction is generally flat. But when secondary inflammation established, epithelial hyperplasia may be noted.
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| Photomicrography 2: showed a thin non-keratinized epithelial lining composed of 2–3 layers of cuboidal epithelial cells and a fibrous connective-tissue wall loosely arranged. The arrow indicates an occasional mucous cell (bar = 0.2 mm) [1] |
When it is small, it is difficult to differentiate a dentigerous cyst from a large but normal dental follicle. When larger, the differential is essential that of lytic lesions of the jaw and includes:
Removal of the associated tooth and enucleation of the soft tissue part is definitive therapy in most cases. When cysts affect significant portions of the mandible, exteriorization or marsupialization of the cyst is done to allow for decompression and subsequent shrinkage of the lesion followed by surgical enucleation.
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Odontogenic keratocyst (OKC) is a parakeratin lined cyst like lesion within bone.
OKCs mostly occur in the 2nd and 3rd decades of life; although can occur over a wide age range with male predilection. Odontogenic keratocyst comprises of 4 to 12 percent of all odontogenic cysts. Ninety percent of odontogenic keratocysts are solitary. Multiple cysts are found in Nevoid Basal Cell Carcinoma Syndrome / Gorlin Syndrome[1].
The most commonly involved body part in mandible, 65-85%; mostly posterior mandible. Normally, they are associated with third molars but may be present without associating with third molars; rarely occur in soft tissues.
They are considered to arise from dental lamina.
Odontogenic keratocysts are often asymptomatic. They are incidentally discovered on radiographs. They can cause symptomatic swelling. They can cause parasthesia of lip and teeth. Symptoms of pain and drainage are found if secondarily infected. They can cause local bone and soft tissue destruction, but usually spare teeth and roots.
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| Swelling observed at the right buccal mucosa (dotted area) posterior to the orifice of Stensen’s duct-arrow head [3]. |
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| Odontogenic keratocyst-exposed anterior to the masseter muscle. |
Mostly, they are seen as small unilocular radiolucent lesions with variable sclerotic margins. Larger lesions are often seen multilocular with variable scalloped margins. Therefore, They may resemble radicular cyst, dentigerous cyst, lateral periodontal cyst, and ameloblastoma.
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| Keratocystic Odontogenic tumer in orthopantomograph being shown as multiple radiolucencies associated with mandibular anterior region, maxillary right and left as well as mandibular left impacted third molar tooth [5]. |
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| Classic look to a keratocyctic odontogenic tumor in the right mandible in the place of a former wisdom tooth. Unicystic lesion growing along the bone. Lesion was seen by oral surgeon on routine panoramic radiography without any symptoms [2]. |
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Histological findings in the above slides are a: The cyst wall is lined with parakeratinized squamous cells with a corrugated surface. b: Nuclei of the cells in the basal layer are palisaded. The rete ridge of the epithelium is not evident [3]. |
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