Which of the following alloys exhibit superelasticity and shape memory

 # Which of the following alloys exhibit superelasticity and shape memory?

A. Nitinol

B. Beta titanium

C. Optiflex

D. Stainless steel

The correct answer is A. Nitinol.

The nickel-titanium alloys used in dentistry are based upon the equiatomic intermetallic compound NiTi, which contains 55% nickel and 45% titanium by weight. Orthodontic wire alloys contain small amounts of other elements, such as cobalt, copper, and chromium.

The alloy name “Nitinol” originally came from the two elements nickel (Ni) and titanium (Ti) and the Naval Ordnance Laboratory (NOL) where these alloys were developed. Superelasticity and shape memory are the properties exhibited by Nitinol.

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Which die material has a hazardous (lethal) potential during fabrication?

 # Which die material has a hazardous (lethal) potential during fabrication?

A. Improved stone

B. Silver amalgam

C. Electrodeposited silver

D. Epoxy resin

The correct answer is C. Electrodeposited silver.

• Has a lethal potential due to the Electro usage of silver cyanide plated silver 

• Polysulphide impressions can be easily electro plated

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The coefficient of thermal expansion of which of the following dental materials is the highest?

 # The coefficient of thermal expansion of which of the following dental materials is the highest?

A. Amalgam

B. Gold inlay

C. Silicate cement

D. Acrylic resins

The correct answer is D. Acrylic resins.

Linear coefficient of thermal expansion (α = coefficient of linear expansion (°C−1))

Tooth 9 - 11

Silicate 8

Unfilled acrylate 81

Composites 28 - 45

Amalgam 25

Direct gold 18

Aluminous porcelain 6 - 7

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The glass ionomer cement is not recommended for:

 # The glass ionomer cement is not recommended for:

A. Class V restoration

B. Class III restoration

C. Class IV restoration

D. None of the above

The correct answer is C. Class IV restoration 

INDICATIONS OF GIC

- The restoration of caries lesions on the roots of patients with active caries is the primary indication for the use of a glass ionomer as a restorative material.

- Because of their limited strength and wear resistance, glass ionomers are indicated generally for the restoration of low-stress areas (not for typical Class I, II or IV restorations), where caries activity potential is of significant concern.

- In addition to being indicated for root-surface caries lesions in Class V locations, slot-like preparations in Class II or III cervical locations (not involving the proximal contact) may be restored with glass ionomers, if access permits.

- Cervical defects of idiopathic erosion or abrasion origin (or any combination) also may be indications for restoration with glass ionomers, if esthetic demands are not critical.

 Reference: Sturdevant’s Art and Science of Operative Dentistry Second South Asia Edition 2019, Page No: 540

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