BACKGROUND

Protraction facemask has been advocated for treatment of class III malocclusion with maxillary deficiency. Studies using tooth-borne rapid palatal expansion (RPE) appliance as anchorage have experienced side effects such as forward movement of the maxillary molars, excessive proclination of the maxillary incisors, and an increase in lower face height. A new Hybrid Hyrax bone-anchored RPE appliance claimed to minimize the side effects of maxillary expansion and protraction. A retrospective study was conducted to compare the skeletal and dentoalveolar changes in patients treated with these two protocols.

METHODS

Twenty class III patients (8 males, 12 females, mean age 9.8 ± 1.6 years) who were treated consecutively with the tooth-borne maxillary RPE and protraction device were compared with 20 class III patients (8 males, 12 females, mean age 9.6 ± 1.2 years) who were treated consecutively with the bone-anchored maxillary RPE and protraction appliances. Lateral cephalograms were taken at the start of treatment and at the end of maxillary protraction. A control group of class III patients with no treatment was included to subtract changes due to growth to obtain the true appliance effect. A custom cephalometric analysis based on measurements described by Bjork and Pancherz, McNamara, Tweed, and Steiner analyses was used to determine skeletal and dental changes. Data were analyzed using a one-way analysis of variance.

RESULTS

Significant differences between the two groups were found in 8 out of 29 cephalometric variables (p < .05). Subjects in the tooth-borne facemask group had more proclination of maxillary incisors (OLp-Is, Is-SNL), increase in overjet correction, and correction in molar relationship. Subjects in the bone-anchored facemask group had less downward movement of the "A" point, less opening of the mandibular plane (SNL-ML and FH-ML), and more vertical eruption of the maxillary incisors.

CONCLUSIONS

The Hybrid Hyrax bone-anchored RPE appliance minimized the side effect encounter by tooth-borne RPE appliance for maxillary expansion and protraction and may serve as an alternative treatment appliance for correcting class III patients with a hyperdivergent growth pattern.