AGD Dental Materials and Biomaterials Questions and Answers

Question 1

A dentist is taking a final impression for a crown on a maxillary molar. The gingival margins are slightly subgingival, and maintaining a completely dry field is proving difficult despite best efforts. Which impression material would be the most suitable choice in this situation due to its inherent properties?

Accepted Answer

Polyether

Answer

Polyether is the most hydrophilic of the elastomeric impression materials. This property gives it a greater tolerance for residual moisture, allowing it to displace moisture and capture accurate marginal detail more reliably in a damp environment compared to the more hydrophobic silicone materials.

Question 2

The primary difference that accounts for the superior strength and abrasion resistance of a Type IV dental stone (die stone) compared to a Type III dental stone (model stone) is the:

Accepted Answer

Shape, size, and porosity of the hemihydrate particles.

Answer

The manufacturing process for Type IV stone creates dense, cuboidal, and less porous hemihydrate particles. This regular particle morphology allows for a lower water-to-powder ratio, which results in a set gypsum product that is significantly denser, stronger, and more resistant to abrasion than the more porous, irregular particles found in Type III stone.

Question 3

In the formulation of modern high-copper dental amalgams, what is the primary function of the increased copper content compared to traditional low-copper alloys?

Accepted Answer

To eliminate the weak and corrosion-prone Gamma-2 (Sn-Hg) phase.

Answer

High-copper amalgams contain sufficient copper (typically 12% or more) to react preferentially with the tin (Sn). This reaction prevents the formation of the Gamma-2 (Sn-Hg) phase, which is the weakest and most corrosion-susceptible component of low-copper amalgams. Eliminating this phase significantly improves the amalgam's marginal integrity, strength, and clinical longevity.

Question 4

A 55-year-old patient with a history of severe bruxism requires a three-unit fixed partial denture to replace tooth #19. Strength and fracture resistance are the highest priority. Which all-ceramic material would be the most appropriate choice for the framework of this prosthesis?

Accepted Answer

Zirconia

Answer

Zirconia (specifically, yttria-stabilized tetragonal zirconia polycrystal) possesses the highest flexural strength and fracture toughness of all currently available dental ceramics. This makes it the ideal choice for multi-unit posterior bridges, especially in high-stress situations such as in patients with parafunctional habits like bruxism.

Question 5

Which of the following dental cements is unique in its ability to form a true chemical bond to tooth structure via an ionic interaction between its polyacid component and calcium in the hydroxyapatite?

Accepted Answer

Glass ionomer cement

Answer

Glass ionomer and resin-modified glass ionomer cements contain polyacrylic acid. This acid component is able to chelate with calcium ions in the enamel and dentin, forming a true, continuous ionic bond. This chemical adhesion is a distinct advantage of this class of cements, in addition to their fluoride release.

(AGD) Academy of General Dentistry Certification Practice Test

(AGD) Academy of General Dentistry Certification Practice Test

AGD Dental Materials and Biomaterials Questions and Answers