# For maxillary expansion, HYRAX uses a force of:
A. 2 to 3 pounds
B. 10 to 20 pounds
C. >25 pounds
D. >50 pounds
The correct answer is B. 10 to 20 pounds.
Hyrax (Hygienic Rapid Expander):
• It is a fixed tooth borne rapid maxillary expansion appliance.
• The Hyrax Expander is essentially a non-spring-loaded jackscrew with an all wire frame. The main advantage of this expander is that it does not irritate the palatal mucosa and is easy to keep clean.
• It is capable of providing sutural separation of 11 mm within a very short period of wear and a maximum of 13 mm can also be achieved. Each activation of the screw produces approximately 0.2 mm of lateral expansion and it is activated from front to back.
• Fixed appliances like Hyrax or Haas, apply forces about 3 to 10 pounds, which can reach up to 20 pounds in daily activation
• Rapid maxillary expansion appliances uses 10-20 pounds force, whereas slow arch expansion uses 2-4 pounds.