To evaluate and compare the intensity of pain caused by rapid maxillary expansion (RME) with two expanders: Hyrax and Haas type, in growing patients.

Materials and Methods

Thirty-nine patients (23 girls and 16 boys) with an average age of 9.3 years (SD = 1.39 years) were randomized into two groups and treated with Hyrax- and Haas-type expanders. In both groups, initial activation of the expander screw was one full turn on the first day followed by 2/4 of a turn two times a day (morning and night) for 7 days. Inclusion criteria were patients presenting with a posterior crossbite or maxillary atresia between 7 and 12 years old. To evaluate the intensity of pain during the active phase of the treatment, a combination of the Numerical Rating Scale and Wong-Baker Faces Pain Scale was used. Mann-Whitney test was used to compare the two treatment groups.


There was significant inverse correlation between days following insertion and pain. During the expansion period, 100% of the children reported some pain. Hyrax expander subjects reported greater pain than those treated with the Haas-type expander only on the first day. The level of pain remained greater in girls throughout treatment.


Pain was reported regardless of the type of expander and was higher in the Hyrax group only on the first day of activation.

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Author notes


PhD student, Department of Dentistry, University of Northern Parana (UNOPAR), Brazil.


Professor, Department of Dentistry, University of Northern Parana (UNOPAR), Brazil.