Undifferentiated mesenchymal cells around blood vessels are known as:

# Undifferentiated mesenchymal cells around blood vessels are known as:

A. Histiocytes

B. Pericytes

C. Fibroblast

D. Osteoblast

The correct answer is B. Pericytes.

Experimental studies have shown that a population of progenitor cells with the potential to differentiate into several distinct mesenchymal cell types can be isolated from the periodontal ligament. In cell culture, periodontal ligament stem cells can differentiate into cells that form bone, cementum, cartilage, fat, muscle, and neuron- and glial-like cells. Recent work indicates that perivascular cells (pericytes) associated with the microvasculature of alveolar bone and periodontal ligament of mice can differentiate into osteoblasts, cementoblasts, cementocytes, and periodontal ligament fibroblasts in

untreated animals, as well as after injury of the periodontium.

Reference: Fundamentals of Oral Histology and Physiology, Arthur R. Hand, 2014, Page no 128

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The protein content of a keratocyst is found to be:

# The protein content of a keratocyst is found to be:

A. less than 4 gm/dL

B. 6 mg/dL

C. Equal to serum protein

D. More than serum protein

The correct answer is A. less than 4 gm/dL.

Aspirational biopsy of odontogenic keratocysts contains a greasy fluid which is pale in colour and contains keratotic squames. Protein content of cyst fluid below 4g% is diagnostic of odontogenic keratocysts. Smaller and unilocular lesions resembling other types of cysts may require a biopsy to confirm the diagnosis. On a CT scan, the radiodensity of a keratocystic odontogenic tumour is about 30 Hounsfield units, which is about the same as ameloblastomas. However, ameloblastomas show more bone expansion and seldom show high density areas.

Reference: Wikipedia

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Familial multilocular cystic disease of the jaws

 # Which of the following is also known as familial multilocular cystic disease of the jaws?

A. Osteopetrosis

B. Cleidocranial dysostosis

C. Hemifacial microsomia

D. Cherubism

The correct answer is D. Cherubism.

Cherubism, a non-neoplastic hereditary bone lesion that is histologically similar to central giant cell granuloma, affects the jaws of children bilaterally and symmetrically, usually producing the so-called cherubic look (Fig. 17-13). The disease was first described in 1933 by Jones, who called it familial multilocular disease of the jaws. The term ‘cherubism’, was introduced by Jones and others to describe the clinical appearance of affected patients. According to the WHO classification, cherubism belongs to a group of non-neoplastic bone lesions affecting only the jaws. It is a rare, benign condition with autosomal dominant inheritance, and it is one of the very few genetically determined osteoclastic lesions in the human body. It appears to have 100% penetrance in males and only 50–70% penetrance in females. There is great variation in the clinical expression.

Reference: Shafer’s Textbook of ORAL PATHOLOGY, 7th Edition, Page No: 715

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Cause of osteogenesis imperfecta is:

# Cause of osteogenesis imperfecta is:

A. Defect in type I collagen

B. Defect in type II collagen

C. Defect in maturation process

D. Defect in calcification process

The correct answer is A. Defect in type I collagen.

Osteogenesis imperfecta (OI) is a serious disease, the molecular pathogenesis of which is being elucidated and it bears a superficial relatedness to dentinogenesis imperfecta, a milder condition affecting mesodermal tissues. It is a condition resulting from abnormality in the type I collagen, which most commonly manifests as fragility of bones. Although osteogenesis imperfecta is generally recognized as representing a hereditary autosomal dominant characteristic, autosomal recessive and nonhereditary types also occur.

Reference: Shafer’s Textbook of ORAL PATHOLOGY, 7th Edition, Page No: 699

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Dysplastic changes, carcinoma in situ or even early invasive cancer is seen in:

# Which of the following clinical lesions is most likely to harbor dysplastic changes, carcinoma in situ or even early invasive cancer?

A. Erythroplakia

B. Lichen planus

C. Leukoplakia

D. Stomatitis nicotiana

The correct answer is A. Erythroplakia.

Erythroplakia

(Erythroplasia of Queyrat)

Whilst leukoplakia is a relatively common condition, erythroplakia is rare. In contrast to leukoplakia, erythroplakia is almost always associated with premalignant changes histologically and is, therefore, the most important precancerous lesion.

The high rate of premalignant and malignant changes noticed in erythroplakia is true for all clinical varieties of this lesion and not solely a feature of speckled erythroplakia. Different studies have demonstrated that 80–90% of erythroplakias are histopathologically either severe epithelial dysplasia, carcinoma in situ, or invasive carcinoma.  

 Reference: Shafer’s Textbook of ORAL PATHOLOGY, 7th Edition, Page No: 95

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Most sensitive to radiation induced cancer?

 # Which of the following is the most sensitive to radiation induced cancer?

A. Nerves

B. Female breast

C. Thyroid

D. Skin

The correct answer is B. Female breast.

Susceptibility of Different Organs to Radiation-Induced Cancer

High: Colon, Stomach, Lung, Bone marrow (leukemia), female breast

Intermediate: Bladder, Liver, Thyroid

Low: Bone surface, Brain, Salivary glands, skin

Reference: Oral Radiology Principles and Interpretation, 7th Edition, Page no 26

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Tetanus is due to:

# Tetanus is due to:

A. Exotoxin fixed to motor end plate

B. Endotoxin fixed to motor end plate

C. Circulating exotoxin

D. Circulating endotoxin

The correct answer is A. Exotoxin fixed to motor end plate.

Clostridium tetani produces two types of toxins:

 1. Endotoxin-cardiotoxin- selective on hemopoetic cells and cardiac tissue 

2. exotoxin; Tetanospasmin acts on CNS.it acts at four sites

i). Motor end plate 

ii). Brain 

iii). spinal chord and 

iv) sympathetic nervous system. 

This Tetanospasmin inhibits cholinesterase at the motor end plate and as a result there is pooling of Acetyl choline resulting in sustained state of clonic muscle spasm, exotoxin travels to the CNS and it causes hyperexcitibity of the motor neurons at the Anterior horn cells there by evoking explosive spasms to sensory stimuli, once exotoxin is fixed in CNS, it cannot be neutralised by the antitoxin. 

C. tetani is an anaerobic， gram-positive， spore-forming rod whose spores are highly resilient and can survive readily in the environment throughout the world. Spores resist boiling and many disinfectants. In addition， C. tetani spores and bacilli survive in the intestinal systems of many animals， and fecal carriage is common. The spores or bacteria enter the body through abrasions， wounds， or (in the case of neonates) the umbilical stump. Once in a suitable anaerobic environment， the organisms grow， multiply， and release tetanus toxin， an exotoxin that enters the nervous system and causes disease. Very low concentrations of this highly potent toxin can result in tetanus (minimum lethal human dose， 2.5 ng/kg).

Genome sequencing of C. tetani has allowed identification of several exotoxins and virulence factors. Only those bacteria producing tetanus toxin ( tetanospasmin) can cause tetanus. Although closely related to the botulinum toxins in structure and mode of action， tetanus toxin undergoes retrograde transport into the central nervous system and thus produces clinical effects different from those caused by the botulinum toxins,  which remain at the neuromuscular junction.

Reference: S. Das Manual of Surgery and Harrison's Principles of Internal Medicine, 19th Edition, Page no: 984

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