image based Q. 137 - Clast act

Q.   Marble bone disease has problem with which of these compound at cellular level?

a. Phosphate
b. Calcium sulphate
c. Hydrochloric acid
d. Bicarbonates
e. Phosphoric acid
f. Anhydrase

Answer -
c

Marble bone disease is also called osteoporosis and presents as hard sclerotic bones on radiographs.

Osteopetrosis or Albert Schoenberg disease presents as bones with thick, disorganised and incomplete remodelling.  Osteoblastic activity is intact while osteoclastic activity is hampered.

Lack of hydrochloric acid leading to abnormal dissolution of hydroxyapatite leads to improper remodeling.

Osteoclasts are not able to acidify Howship lacunae.

image based Q. 136 - Screw screwed

Q.    Which site of below implant is prone for failure/ breakage or weakest region ?

a. Head shaft junction ( red line)
b. Shaft of screw. (green line)
c. Shaft thread junction (yellow line)
d. Thread area (orange line)
e. Tip (blue line)

Answer -
c

In a partially threaded screw the area where shaft ends and thread begins is weakest.

This area is also called 'Run Out' of the screw.