Matrix vesicles are derived from:

 # Matrix vesicles are derived from:

A. Elastin fibres

B. Collagen

C. Osteoblast

D. Inflammatory cells

The correct answer is C. Osteoblast.

The term matrix vesicles (MV) refers to small (20-200 nm) spherical bodies observed in the pre-mineralized matrix of dentin, cartilage and bone. They appear to be bounded by a lipid bilayer, and are often found associated with small crystals of calcium phosphate mineral. They are derived from the plasma membrane of mineral forming cells i.e. chondrocytes, osteoblasts, odontoblasts. The matrix vesicles promotes the formation of apatite by increasing the concentration of alkaline phosphatase that play a role in calcification. 

Reference: Orban's

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Discoloration of a denture constructed from cold cure acrylic resin is due to:

 # Discoloration of a denture constructed from cold cure acrylic resin is due to: 

A. Absorption of oral fluids 

B. PH changes in saliva 

C. Leaching out of tertiary amines 

D. Leaching out of excess monomer 

The correct answer is C. Leaching out of tertiary amines.

The color stability of chemically activated resins is generally inferior to the color stability of heat activated resins. This property is related to the presence of tertiary amines with in the cold cure resins, which are highly susceptible to oxidation. 

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Most common reason for failure of rest seat in RPD is :

 # Most common reason for failure of rest seat in RPD is : 

A. Improper rest seat preparation 

B. Contaminated metal 

C. Distorted occlusal rest 

D. Excessive occlusal forces 

The correct answer is A. Improper rest seat preparation.

The most common reason for failure of rest seat in RPD is improper rest seat preparation. Inadequate preparation will result in either occlusal interference or perforation of the metal due to lack of clearance. Failure of rest seat due to contaminated metal or distortion is very rare. 

Reference: McCracken's

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The function of reciprocal clasp arm is:

 # The function of reciprocal clasp arm is:

A. To balance the denture 

B. To act as a direct retainer 

C. To counteract the movement of denture which is caused during engagement of retentive arm  

D. None of the above 

The correct answer is C.  To counteract the movement of denture which is caused during engagement of retentive arm 

The rigid reciprocal arm helps in reciprocating stress generated against the tooth by the retentive arm. It also stabilizes the denture against horizontal movement and is always situated above the height of contour. 

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