The purpose of this prospective study was to determine whether dental intrusion is effective in treating growing retrognathic hyperdivergent patients without negatively affecting the roots and periodontal structures. The sample consisted of 17 (7 males and 10 females) consecutively treated patients who were 13.2 ?1.1 years old at the start of treatment (T1) and treated for 25.3 ? 9.3 months (T2). The maxillary posterior teeth (premolars and molars) were all intruded using a rigid segmental appliance. Two maxillary and two mandibular MSIs (immediately loaded with 150gr coil springs) were used for the intrusion mechanics and vertical control. A matched control group was used to evaluate the skeletal changes that occurred during treatment. CBCT records, taken at T1 and at the end of the orthopedic phase (T2) were used to evaluate the treatment effects. The results showed significant (p<.05) intrusion (2.5 ? 1.7 mm) of the maxillary dentition in the treated group. The mandibular plane angle closed 2? ?1.7? and the SNB angle increased 1.5? ?1.5?. True forward rotation of the treated sample was significantly (p<.05) greater (1.8?) than in the controls. The treated group showed greater superior and less posterior condylar growth than the controls, but the difference was not statistically significant. All of the maxillary roots showed statistically significant amounts of external apical root resorption (EARR), ranging from 0.67 mm to 1.21 mm. Pointed roots showed the greatest amounts of resorption, followed by bent roots, normal shaped roots, and roots with open apices, which showed the least EARR. Alveolar crest heights between first molar and second premolar decreased significantly (0.38 ? 0.6 mm) over time, and the distance between the bone and the CEJ increased significantly (0.52 ? 0.9 mm) only on the distal aspect of the maxillary second premolar. The overall MSI failure rate was 4.6%. It can be concluded that segmental intrusion of the posterior teeth with light forces and skeletal anchorage is effective for treating growing retrognathic hyperdivergent patients. The mechanics produced a significant true forward mandibular rotation, with minimal loss of crestal bone height and clinically acceptable EARR of the teeth that were intruded.
