Skeletal and dental effects of Herbst appliance have been routinely investigated by the conventional cephalometric radiographs, which were subjected to magnification, distortion, patient positioning errors, and obstruction of critical landmarks by overlapping anatomic structures. Therefore, the bottom line of the present study was to investigate the changes after Herbst appliance treatment and relate them to the pubertal status of the skeletal Class II patients using CBCT. The pubertal status was determined with respect to the CVMS by Bacetti et al.9
Skeletal and Dental Changes :
Previous reports on the maxillary restraining effect are controversial; in the present study, there were no statistically significant changes in any of the two variables used to evaluate the maxillary impact for both age groups. The insignificant effect on the maxilla is in agreement with those of previous studies12,13 However, this decrease is not of statistical significance, yet it could be of clinical importance, particularly in growing patients, because it suggests restriction of the maxillary growth that is expected to take place on this period for Class II patients. 14
However, other studies reported that Herbst had a significant restraining effect on maxillary growth.3,15 This controversy could be explained by variation in treatment age, different treatment mechanics, or treatment duration. The reported decrease in SNA could not be exclusively attributed to the limitation of maxillary growth; it could be due to the remodeling at A-point due to the distal tipping of the incisors.
According to the result of the present study, the Herbst IV appliance resulted in significant retroclination of the upper incisors and distalization of the upper molars, which could be the result of the distally directed force of the appliance (headgear effect) on the maxillary arch. This result is in agreement with previous studies that have reported similar findings.16–19
Since most Class II patients come from mandibular rather than maxillary origin 20, the question about those patients' ability to catch up mandibular growth in two different maturity stages using Herbst appliances is the cornerstone of the present study.
After Pancherz reintroduced the Herbst in 1979 21 broad debate was raised about the possible effect of the Herbst appliance on the mandible in patients with limited growth potential. He published a study in 1997 and reported a non-significant difference between 3.1mm sagittal advancement in the early treatment (defined by maturity stages MP3-E and F) and 2.4mm in the late treatment (defined maturity stages MP3-H and -I). Two years later, 22, he reported significant difference of 2.3mm for young adults (defined R-IJ and RJ) and 4.3mm for adolescents (defined byMP3-E to MP3-G). Later, 23, he compared the effect of Herbst appliance treatment and sagittal split osteotomy on mandibular base advancement and showed that the latter had a more significant impact than Herbst appliance. In the present study, the pre-pubertal group showed a significant increase in SNB as well as forward displacement of point B. On the contrary, mandibular sagittal position in Post-pubertal group exhibited a non-significant increase, indicating that the Herbst could not stimulate forward mandibular growth. This finding agrees with those of other studies that reported little or no effect on mandibular growth. 24–26 The results of the present study emphasize the importance of detection and treatment of Class II cases in the Pre-pubertal years to get more skeletal and stable results, while the results in the post-pubertal years are nearly dental.
Forward movement of the lower molars and proclination of the lower incisors were also evident. Weschler and Pancherz17 reported, "Mandibular anchorage loss in Herbst treatment is a reality with which the orthodontist has to live with" Lower incisor inclination changes in both groups demonstrated significant proclination, which was an inevitable side effect of Herbst with subsequent early correction of the overjet, thus limiting skeletal correction. 1–3, 6 Clinicians should be aware of that when planning Herbst treatment for Class II cases with initially proclined lower incisors by adding TADs to support the lower incisors. Also, selecting brackets with negative crown toque in the second stage of the treatment could be helpful.