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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