MCQs on Dental Materials - Metallurgy

# All of the following statements about cast cobalt alloys are true EXCEPT:
A. They have a modulus of elasticity twice that of gold alloys
B. They are more rigid than gold alloys
C. They have higher ductility than gold alloys
D. They have a lower proportional limit than gold alloys

# The contraction of gold alloys on solidifying is approximately:
A. 0.4%
B. 1.4%
C. 2.4%
D. 3.4%

# Addition of large amounts of platinum to a casting gold alloy will:
A. Decrease its strength and ability to be hardened
B. Decrease its tarnish resistance
C. Increase its fusion temperature
D. Redden the alloy

# The pattern for the metallic framework of a removable partial denture is fabricated from:
A. Inlay wax type-II
B. Boxing wax
C. Modelling wax
D. Casting wax

Which of the following drugs is likely to damage the eighth cranial nerve when administered for a long period of time ?

 # Which of the following drugs is likely to damage the eighth cranial nerve when administered for a long period of time ?

 A. Ethambutol

 B. Isoniazide

 C. Rifampicin

 D. Streptomycin

The correct answer is D. Streptomycin.

Nephrotoxicity, ototoxicity, and contact sensitization (due to this, topical application is not indicated) are common side effects of Streptomycin. 8th nerve is usually affected. Vestibular involvement is more common and cochlear involvement is less common. 

Which of the following structures is not of ectodermal origin?

 # Which of the following structures is not of ectodermal origin?

A. Hunter Schreger bands

B. Enamel spindles

C. Enamel tufts

D. Enamel lamellae

The correct answer is B. Enamel spindles.

Enamel spindles are odontoblastic processes, which extend into enamel. Enamel spindles are mesenchymal in origin.

Malocclusion representing a transverse deficiency is often referred to as:

 # Malocclusion representing a transverse deficiency is often referred to as:

A. Open bite

B. Closed bite

C. Cross bite

D. Deep bite

The correct answer is C. Cross bite.

Patients with maxillary transverse deficiency usually have a narrow palate and a posterior crossbite. If the maxilla is narrow relative to the rest of the face, a diagnosis of transverse maxillary deficiency is justified. Occlusal relationships must be considered in all three planes of space. Lingual posterior crossbite (i.e., upper teeth lingual to lower teeth) is the major deviation from the normal transverse dental relationship and reflects deviations from ideal occlusion in the transverse plane of space.

Ref: Contemporary Orthodontics, William R. Proffit, 6th Edition.