Expansion Screws

Expansion Screws

Write short note on expansion screw.
Answer. An expansion screw is used for expansion of arch, e.g. in rapid maxillary expansion or in slow expansion or in patient of unilateral or bilateral crossbite.

• A typical expansion screw consists of a long body divided into two halves.
• Each half has a threaded inner side that receives one end of a double ended screw.
• Screw has a centered boxing with four holes.
• These holes receive a key which is used to turn the screw.
• Turning of the screw by 90 degree, (i.e. one turn bring about a linear movement of 0.18 mm).
• The pattern of threading on either side is of opposite direction.
• Thus, turning the screw withdraws it from both sides simultaneously.
• Various expansion screws which are used in removable and fixed appliances are jackscrews, coffin springs, quad helix, Isaacson, hyrax, Derichsweiler

Activation Schedule

For achieving the desirable results, different activation schedules are given by various authors, out of which the two are most popular i.e.

According to Timms

• Patients aged till 15 years: 90° rotation is given in morning and evening
• Patients aged over 15 years: 45° rotation is given four times a day.

According to Zimring and Isaacson

• In growing individuals: Two turns are given each day for 4 to 5 days and later one turn per day for next 5 to 7 days and one turn every alternate day till the desired expansion is achieved.
• In non – growing individuals: Two turns each day for fist two days and later one turn per day for next 5 to 7 days and one turn every alternate day till desired expansion is achieved.