A typical expansion screw consists of an oblong body divided into two halves. Each half has a threaded inner side that receives one end of a double ended screw.
The screw has a central bossing with four holes.
These holes receive a key which is used to turn the screw.
The turning of the screw by 90 degree (i.e. one turn) brings about a linear movement of 0.18mm.
The pattern of threading on either side is of opposite direction. Thus turning the screw withdraws it from both sides simultaneously.
DURATION REQUIRED FROM LAB : 1 day
REQUIREMENT FOR LAB :Upper and lower( type 3) dental stone models without voids made from good alginate impression