NEET MDS Shorts
25787
Dental Materials
Heat-activated resins typically have a higher degree of polymerization, resulting in less residual monomer and greater strength compared to chemically activated resins.
69190
Dental MaterialsFins or spines may be produced on a casting because of 1.cracks in the investment 2. too rapid heating of the mold 3. steam production which causes the walls of the mold to flake off
26641
Dental Materials
A luting agent's primary function is to bond the restoration to the tooth and enhance its retention.
89882
Dental Materials
The Vickers hardness test is the most suitable for materials that exhibit
elastic recovery. The Vickers hardness test involves the use of a diamond
indenter in the form of a pyramid with a square base. The test applies a
controlled load to the specimen and measures the depth of the resulting
indentation. It is a micro-indentation hardness test, meaning it is used for
small or thin sections or for precise measurements. This test is particularly
useful for brittle materials, such as ceramics, because it creates a very small
indentation and applies a relatively low load compared to the other methods.
The other options are not as suitable for materials with elastic recovery for
the following reasons:
2. Brinell hardness test: This test uses a spherical indenter, usually a hard
steel or tungsten carbide ball, to press into the material with a significant
load. It is typically used for softer materials and is not as precise for small
indentations or for materials that are prone to plastic deformation, which may
affect the accuracy of the elastic recovery measurement.
3. Knoop hardness test: Similar to the Vickers test, the Knoop test uses a
diamond indenter but in the shape of a rhombic pyramid. Although it is also a
micro-indentation test, the Knoop indenter has a more pointed tip compared to
the Vickers pyramid. This can make it less ideal for certain materials that
exhibit elastic recovery since the sharp tip can cause more plastic deformation
and potentially damage the material.
While all three tests can be used to measure the hardness of materials, the
Vickers test is generally considered the best for materials that exhibit elastic
recovery due to its ability to produce precise and reliable results with minimal
plastic deformation.
74037
Dental Materials
Conventional composites have a filler particle size of 8-12 µm. Microfilled composites have smaller particles (0.04-0.4 µm), small particle composites have intermediate sizes (1-5 µm), and hybrid composites have even smaller sizes (0.1-0.01 µm).
50814
Dental Materials
Occurence of carbon contamination from investment can easily be observed in case casting temp. are high as seen in melting of high noble alloys for metal ceramic (eg. AgPd or Pd-Ag alloys) or base metal alloys. Such contamination embrittles the alloy.
80434
Dental MaterialsThe working time for a polysulfide impression material can be safely and effectively increased by cooling the mixing slab to a temperature above the dew point
16344
Dental Materials
The frozen slab technique increases the working time of zinc phosphate cement by allowing more moisture to condense on the cool glass slab.
30817
Dental Materials
one ot the main adanhtges of GIC as a restoratie material was its ability to form chemical bonds with the tooth structure. Bonding in GIC primarily invokes chelation of carboxyl groups of the polyacids sith the calcium in the apatite of enamel and dentin. Bond rength of enamel is always greater than that of dentin due to higher mineral content. The bonding is improved by the removal of the debris layer called smear layer’ by a process called conditioning.
57640
Dental Materials
Platinized gold foil is a combination of gold and platinum where 15% of the content is platinum. It is produced by rolling layers of gold and platinum together to achieve the desired thickness and distribution of the platinum within the gold foil. This process creates a homogeneous mixture that enhances the hardness and wear resistance of the restoration, making it suitable for high-stress areas like incisal edges and cusp tips.