NEET MDS Shorts
18571
Dental Materials
Main causes of the porosity of alloy castings are:
1) Solidification defects
2) Trapped gases
3) Residual air
1. Solidification defects
Solidification defects cold lead to two different manifestations of porosity;
localised shrinkage porosity and Microporosity.
Localised shrinkage porosity is caused by insufficient feeding of the alloy
during solidification.
Microporosity is also caused by solidification shrinkage, but generally happens
in fine grain alloys when the solidification is too rapid for the microvoids to
segregate. This in turn is caused the mould or casting temperature being too
low.
2. Trapped gases
Many metals dissolve or occlude gases when they are molten. On solidification,
these gases are forced out of the casting causing what is usually called pinhole
porosity. These voids are rather small.
3. Incomplete casting
If the molten alloy is prevented from fully or partially filling the mould and
incomplete or even no casting at all can result.
92920
Dental Materials
Ormocers offer several advantages over conventional composites. They have excellent biocompatibility, minimal shrinkage, and their chemical structure allows for high resistance to masticatory forces. Additionally, they are aesthetically pleasing and can be polished to resemble natural teeth.
40347
Dental Materials
The compressive strength of hardened zinc oxide eugenol (ZnOE) impression paste is generally about 7 MPa, indicating its ability to withstand compressive forces without deformation or failure.
83593
Dental MaterialsCobalt in a cast chromium-cobalt-nickel alloy contribute to strength, rigidity, and hardness
36631
Dental Materials
While it has good mechanical properties, poorly placed zinc phosphate cement can cause pulpal irritation.
20682
Dental Materials
The material is derived from the structural formula of anhydro-?-d-mannuronic acid, which is extracted from certain types of brown seaweed.
58279
Dental Materials
Giomers are a combination of fluoraluminosilicate glass and silica-filled urethane resin. This unique composition allows for the release of fluoride and improved physical properties compared to traditional composites.
30178
Dental Materials
Resin cements are known for their excellent adhesion, providing a strong bond to tooth structure and restorative materials.
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
61285
Dental Materials
In orthodontics, wires with a low load deflection rate are typically preferred for areas requiring large tooth movements because they provide a more constant force as the tooth moves and the appliance is deactivated. This constant force is beneficial for controlling the rate of tooth movement.