Which bone reaches its adult size at birth?

 # Which bone reaches its adult size at birth?

A. Ear ossicles

B. Parietal bone

C. Mastoid process

D. Maxilla

The correct answer is A. Ear ossicles.

The bone that reaches its adult size at birth are ear ossicles. The tympanic cavity, mastoid antrum, auditory ossicles and structures of the internal ear are almost fully developed at birth and undergo little change after birth.

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Metopic suture fuses at:

 # Metopic suture fuses at:

A. 2.5 years

B. 6 years

C. 18 months

D. 9 months

The correct answer is D. 9 months.

The two frontal bones tend to fuse in the midline via the metopic or frontal suture. The timing of its closure is controversial. Fusion of metopic suture begins anteriorly at the bridge of the nose and progresses posteriorly. One-third of metopic sutures close at 3 months, and nearly 100% by 9 months. Although some may persist into 6 years and may not close until adulthood in up to 10% of patients. A premature fusion of the suture is termed metopic synostosis. This can result in trigonocephaly. It usually disappears by the age of 2 years but may even persist in a few individuals. 

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If access is made in gold crown for endodontic procedure and after completion of procedure

 # If access is made in gold crown for endodontic procedure and after completion of procedure hole is filled with amalgam, which is correct about subsequent possible event?

A.  Amalgam will act as anode to gold  

B. Amalgam will act as cathode to gold

C. Circuit will not be formed

D. All of the above

The correct answer is A. Amalgam will act as anode to gold.

If an amalgam is in direct contact with an adjacent metallic restoration such as a gold crown, the amalgam is the anode in the circuit. This type of electrochemical corrosion is called galvanic corrosion and is associated with the presence of macroscopically different electrode sites.

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What happens if gypsum is heated above 700 degree celsius?

 # What happens if gypsum is heated above 700 degree celsius?

A. No by-product

B. Breakdown of CaSO4 which affect gold alloy

C. Breakdown of Na2SO4 which affect gold alloy

D. Gas inclusion porosities

The correct answer is B. Breakdown of CaSO4 which affect gold alloy.

Gypsum-bonded investments are used for casting gold alloys. These can withstand a temperature of 700°C. If gypsum investment is heated about 700°C, decomposition of CaSO4 occurs with emission of SO2 gas. This not only causes shrinkage of the investment but also contaminates the gold castings with the sulphides of the non-noble elements such as silver and copper. So gypsum investments should not be heated above 700°C. 

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