MDS PREP
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.
The impression for a diagnostic cast of a partial edentulous mouth should be taken in:
1) Impression wax
2) Modelling compound
3) Hydro-colloid
4) Hydro cal
Dental Materials Answer: 3
For making impressions of edentulous ridges, impression plaster and impression compound are considered to be useful. For partial edentulous mouth impressions, hydrocolloids are useful.
What is the primary difference between the setting mechanism of light-cured and chemically cured composite resins?
1) Light-cured resins shrink towards the external surface, while chemically cured resins shrink towards the center.
2) Chemically cured resins require light activation.
3) Light-cured resins require a chemical catalyst.
4) There is no significant difference in the setting mechanism.
The setting mechanism of light-cured resins involves free radical polymerization initiated by light, which causes the material to contract away from the light source (typically the external surface).
What is the purpose of using a temporary cement?
1) To provide a permanent seal
2) To allow for temporary fixation before the final restoration is placed
3) To strengthen the tooth structure
4) To fill gaps caused by caries
Temporary cements are used to hold a temporary restoration in place until the final restoration can be placed, and they should have a lower compressive strength to allow for easy removal.
What happens if the water temperature exceeds 50°C during the mixing of gypsum products?
1) The setting reaction is accelerated.
2) The setting reaction is retarded.
3) No reaction occurs.
4) The material becomes less soluble.
If the temperature of the water used to mix gypsum products exceeds 50°C, it can slow down the setting reaction due to the reversible nature of the gypsum crystal formation at higher temperatures.
What is the primary reason for using zinc polycarboxylate cement as a luting agent?
1) Its high compressive strength
2) Its ability to bond chemically to tooth structure
3) Its ease of manipulation
4) Its insolubility in oral fluids
Zinc polycarboxylate cement is favored as a luting agent for its chemical bonding capability with tooth structure.
What is the maximum allowable dimensional change for amalgams according to ANSI/ADA Specification No. 1?
1) Not more than 10 µm/cm.
2) Not more than 20 µm/cm.
3) Not more than 30 µm/cm.
4) Not more than 40 µm/cm.
The specification requires that amalgam neither contract nor expand more than 20 µm/cm.
What is the role of the silane-coupling agent in the bonding between the filler and matrix in a dental composite material?
1) It acts as a binder to physically hold the filler and matrix together
2) It creates a chemical bond between the filler and the matrix
3) It enhances the mechanical strength of the composite
4) It provides a smooth surface for the filler to be evenly distributed in the matrix
Silane-coupling agents are used to improve the bonding between filler particles and the matrix in dental composite materials. They contain a methacrylic group that can co-polymerize with the dimethacrylate monomers present in the matrix, while also having functional groups that can interact with the filler material, typically silica or glass particles. This dual interaction creates a chemical bond, which enhances the overall stability and strength of the composite material.