MDS PREP
What are the main components of a typical dental composite resin?
1) Monomers, fillers, initiators, and accelerators.
2) Resins, fillers, catalysts, and diluents.
3) Polymers, pigments, and plasticizers.
4) Monomers, fillers, and cross-linking agents.
Dental composite resins typically consist of a resin matrix (monomers), filler particles (such as silica or glass), initiators (like camphorquinone), and accelerators (such as amines) to control the setting process.
What happens to acrylic resin when it absorbs water?
1) It expands linearly
2) It contracts linearly
3) It remains the same dimensionally
4) It swells in volume
When acrylic resin absorbs water, it expands linearly by approximately 0.23%, which can affect the fit and function of the denture.
What is the typical pH of a resin cement immediately after mixing?
1) Less than 2
2) Between 2 and 4
3) Between 4 and 7
4) Greater than 7
The pH of resin cements is usually slightly acidic after mixing, subject to variation in formulation.
Epoxy resins are compatible with which of the following impression material :
1) Polysulphide impression material
2) Polyether impression material
3) Agar
4) Alginate
Dental Materials Answer: 2
Epoxy resins
· Abrasion resistance is many times greater than gypsum
· More expensive
· Undergoes 0.1 – 0.2% shrinkage, thus their shrinkage is approximately equal to gypsum. This is less of problem with newer formulations & polyurethane resin.
· Their detail reproduction is better.
· Hydrocolloids, polysulfides are not compatible with them.
Which of the following is not a type of temporary cementing material?
1) Zinc oxide-eugenol (type III)
2) Calcium hydroxide
3) Glass ionomer cement (type 1)
4) Resin-modified glass ionomer cement
Resin-modified glass ionomer cement is not listed as a type of temporary cementing material in the text.
What is the purpose of zinc in amalgam alloys?
1) It acts as a reinforcing agent.
2) It improves the castability of the alloy.
3) It is a primary reactant with mercury.
4) It has no significant role in the properties of amalgam.
Zinc is included in amalgam alloys as an aid in manufacturing to produce clean, sound castings of the ingots used for cut-particle alloys.
What is the effect of temperature on the setting time of gypsum products?
1) Increased temperature accelerates the setting reaction.
2) Increased temperature has no effect on the setting reaction.
3) Increased temperature retards the setting reaction.
4) Temperature has an inconsistent effect on the setting reaction.
Higher temperatures generally speed up the chemical reactions involved in the setting of gypsum products, leading to a shorter setting time.
What is the purpose of adding barium sulfate to Gutta Percha?
1) To make it more radio-opaque
2) To improve thermal conductivity
3) To enhance the setting reaction
4) To act as a plasticizer
Barium sulfate is added to Gutta Percha to enhance its radiographic visibility.