MDS PREP
Before restoring a tooth with composite, the area is etched. Accidental contamination occurs with saliva, Therefore
1) the area is re-etched before restoration
2) the area is air-dried using an air spray and continue with restoring
3) wipe the saliva with cotton and continue to restore.
4) add excess composie material and cure it
Dental Materials Answer: 1
Etching of tooth surface with 37% phosphoric acid creates microporosities in the enamel and dentin. This is the main method of adhesion of composite resin to tooth surface.
After etching the surface energy of the enamel will increase. This will make it very sticky to any kind of contaminants. If salivary contamination will occur, the salivary proteins will precipitate in the microporosities. This will prevent the adequate penetration of the bonding agent, therby reducing the micotag formation. Hence, complete isolation is essential.
Brinnel hardness number of a dental gold alloy is directly proportional to its:
1) Tensile strength
2) Elongation
3) Modulus of elasticity
4) Modulus of resiLience
Dental Materials Answer: 1
Brinnel and Rockwell tests are cLassified as macrohardness tests and they aie not suitable for brittle materials.
The Knoop and Vickers tests are classified as microhardness tests. Both of these tests employ toads less than 9.8N.
The Shore and the Barcot tests are used for measuring the hardness of rubbers and plastics.
The Bnnnel test is the one of oldest tests used for determining the hardness of materials and is directly related to proportional limit and the ultimate tensile strength of dental gold alloys.
The convenience of the Rockwell test, with direct reading of the depth of the indentation, has lead to its wide usage.
The Knoop hardness test is used to obtain the values for both exceedingly hard and soft materials. The hardness value is independent of the ductility of the material.
The Vickers test is employed for dental costing gold alloys. It is suitable for determining the hardness of brittle materials.
What is the elastic limit of a wire?
1) The point at which the wire returns to its original shape.
2) The point at which the wire starts to weaken.
3) The point at which the wire yields permanently.
4) The point at which the wire breaks.
The elastic limit of a wire is the point at which it yields permanently, meaning any greater force applied will result in irreversible deformation.
What is the primary function of 2-hydroxyethyl methacrylate (HEMA) in dentinal bonding?
1) To act as an initiator for the polymerization reaction
2) To create a hydrophobic barrier between dentin and resin
3) To dissolve the dentin surface
4) To create a hydrophilic bridge between the dentin and resin
HEMA is a hydrophilic monomer that is applied to the conditioned dentin. It fills the dentinal tubules and adheres to the exposed collagen fibers, creating a wetting layer that allows subsequent hydrophobic resins to infiltrate and bond to the dentin. This bridging action is crucial for the adhesion of resin to the hydrophilic dentin surface, which is essential for the longevity and durability of the restoration.
What is the typical bond strength of etched enamel with restorative materials?
1) 5-10 MPa.
2) 15-25 MPa.
3) 5-10 MPa.
4) 30-50 MPa.
Properly etched enamel surfaces can achieve bond strengths of approximately 15 to 25 MPa when using suitable restorative materials.
What is the dough-forming time for denture base resin according to ANSI/ADA Specification No. 12?
1) Less than 10 minutes
2) Less than 5 minutes
3) Less than 20 minutes
4) Less than 30 minutes
ANSI/ADA Specification No. 12 requires that the material should reach a doughlike consistency in less than 10 minutes from the start of the mixing process.
What is the modified form of zinc oxide-eugenol used for temporary cementation?
1) Type I
2) Type II
3) Type III
4) Type IV
The modified form of zinc oxide-eugenol used for temporary cementation is commonly known as Type II due to its lower compressive strength and ease of removal.
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.