Tooth Preparation for metal crown

 # The amount of reduction required for a tooth for all metal crown restoration is:

a) So that there is proper clearance between the teeth

b) So that the tooth architecture interferes with the arch of rotation

c) So that the tooth architecture doesn't interfere with the arch of rotation

d) At least 2mm on all the surfaces

The correct answer is: B. So that the tooth architecture interferes with the arch of rotation

The longer the occlusogingival length of the preparation, the greater is the retention. This is because longer preparations interfere with the arc of the casting pivoting about a point than shorter preparations.

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Finish lines of a complete coverage crown should lie:

 # Finish lines of a complete coverage crown should lie?

a) Supragingivally 

b) Subgingivally

c) Subgingival if required

d) Gingival margin

The correct answer is C. Subgingival if required. 

Whenever possible the finish lines of crowns should terminate supragingivally. Subgingival margins are required in the following situations.

• Esthetics.

• Cervical erosion and caries.

• Insufficient crown length for retention.

• Elimination of persistent root hyper sensitivity.

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Paired cartilages of larynx

 # Which of the following is a paired cartilage of larynx?

A. Thyroid

B. Cricoid

C. Epiglottis

D. Arytenoid

The correct answer is D. Arytenoid.

The laryngeal skeleton is made of nine cartilages: the thyroid cartilage, cricoid cartilage, epiglottis, arytenoid cartilages, corniculate cartilages, and cuneiform cartilages. The first three are unpaired cartilages, and the latter three are paired cartilages.

Paired = Arytenoid, Corniculate, Cuneiform

Unpaired= Thyroid, Cricoid, Epiglottis

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Extension of Larynx

 # Larynx extends from:

A. C2-C7

B. C1-C4

C. C5-C6

D. C3-C6

The correct answer is D. C3-C6

Larynx is the organ of voice (Phonation), an air passage sphincter at the inlet of the lower respiratory passage.

In adult male, it lies opposite to third, fourth, fifth, sixth cervical vertebrae, but in children, and in adult female, it lies at a higher level.

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The arterial supply of trachea is by the:

 # The arterial supply of trachea is by the:

A. Bronchial artery

B. Tracheal artery

C. Inferior thyroid artery

D. Superior thyroid artery

The correct answer is C. Inferior thyroid artery.

Inferior thyroid artery is a branch of thyrocervical trunk, which arises from the subclavian artery. Its terminal part is related to recurrent laryngeal nerve. Apart from trachea, it also supplies lower two thirds of thyroid lobe and lower half of the isthmus, parathyroid, thymus, larynx, pharynx, and the surrounding muscles. 

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Trachea bifurcates at the level of:

 # Trachea bifurcates at the level of:

A. C7

B. Lower border of T3

C. Upper border of T4

D. Upper border of T5

The correct answer is D. Upper border of T5.

Trachea begins at C6 and bifurcates at the level of T5. Trachea bifurcates at the level of sternal angle.

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Carotid Sinus vs Carotid body

 # Select the incorrect statement about the carotid sinus:

A. It is a dilatation near the beginning of the internal carotid artery

B. It is innervated by the glossopharyngeal nerve

C. It acts as a chemoreceptor

D. Its wall has thick tunica adventitia

The correct answer is C. It acts as a chemoreceptor; which is incorrect because carotid sinus is a baroreceptor. 

Carotid Sinus : The termination of the common carotid artery, or the beginning of the internal carotid artery shows a slight dilatation, known as the carotid sinus which receives a rich innervation from the glossopharyngeal and sympathetic nerves. The carotid sinus acts as a baroreceptor or pressure receptor and regulates blood pressure.

Carotid Body: Carotid body is a small, oval reddish-brown structure situated behind the bifurcation of the common carotid artery. It receives a rich nerve supply mainly from the glossopharyngeal nerve, but also from the vagus and sympathetic nerves. It acts as a chemoreceptor and responds to changes in the oxygen and carbon dioxide and pH content of the blood.

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