The current study compared the skeletal and dental effects of two protocols in the correction of Class III malocclusion. The approaches differed significantly in the mode of force application used for maxillary protraction. The first approach (RME–FM) used a tooth-borne appliance with an extraoral face mask for part-time force application (14–16 h/day) while the HE-MP protocol relied on skeletal anchorage and the intraoral application of full-time elastic traction.
The skeletal changes shown in the RME–FM group in this study were similar to those reported by other studies using face mask therapy, with a 1.14° increase in the SNA angle, a 0.89° reduction in the SNB angle, an overall skeletal change of 2° in the ANB angle (Table 4). Other studies on the tooth-borne RME face mask have shown changes between 0.7°  and 1.8° for SNA [22,23,24,25]. The mandibular and overall skeletal changes as well as the significant dental changes observed in this study are also similar to others [2, 22,23,24,25,26,27].
The maxillary advancement was significantly higher in the HE-MP group, with more than threefold the increase in SNA angle than that observed in the RME–FM group. This was also reflected by the fact that the linear measurement in the HE-MP group displayed more than twice the advancement at A point that was observed in the RME–FM group. The effect on the mandible was similar in both groups, with a reduction in the SNB of approximately 1°. In addition, there was no significant change in the mandibular plane angle in the HE-MP group, while there was an increase in the mandibular plane angle in the RME–FM group. The greater skeletal changes seen in the HE-MP group can be attributed to the use of skeletal anchorage. A similar skeletal response was reported using the Hybrid Hyrax with a Mentoplate [13, 14] as well as with a face mask . Similar differences between skeletal anchorage and traditional tooth-borne expansion and face mask were also found by Cevidanes et al.  when comparing the BAMP protocol to the face mask with maxillary expansion. They reported a 5.9 mm improvement in the Wits measurement in the BAMP group as opposed to only 3.6 mm with RME–FM and, similar to the HE-MP in this study, the majority of the skeletal change was due to maxillary protraction with minimal vertical change. The reduced vertical side effect in the HH-MP is useful in patients with increased face heights.
Differences in dental effects
The use of skeletal anchorage significantly reduced the dental side effects in the maxillary dentition, with mild and non-significant uprighting of the upper incisors reported in the HE-MP group. These findings are consistent with those of other studies which have used hybrid expanders, where the use of palatal miniscrews to support expansion and protraction eliminated the maxillary dental side effects [14, 23]. It should be noted that the expansion protocols in the two groups were different. In the HH-MP group, since the maxillary expander was supported with palatal TADs, a slower rate of expansion was chosen, since the load of the appliance is mostly on the skeletal anchors, anchorage loss from dental movements is not expected . Whereas in the RME–FM group, since the appliance is tooth borne, a rapid expansion protocol is utilised to be able to build up the forces to be high enough for sutural disarticulation, before dental movements take place. Nevertheless, there was a small amount of maxillary molar tipping observed with the HE-MP, which was similar to observations in other studies [14, 23]. This maxillary mesial molar tipping can be attributed to some wire bending and flexure of the appliance.
As in previous studies [2, 22,23,24,25,26,27], the mandibular incisors retroclined with the RME–FM. On the other hand, the mandibular incisors advanced slightly (on average) with the HE-MP. The standard deviation, however, shows that the response varied greatly between patients (Table 4). This variability was also seen in other studies [6, 14]. Willmann et al.  for example found that, on average, there was no change in the mandibular incisor inclination with Hybrid Hyrax-Mentoplate treatment, while Cevidanes et al.  reported a slight advancement of the lower incisors, which was similar to results in this study. This seems to be a finding that is unique to the use of skeletal anchorage plates in the mandible and may be attributed to two causes. Firstly, when Class III elastics are attached to the anchorage plates in the presence of an anterior crossbite, there is no direct force transmission to the lower incisors from the elastics. At the same time, the upper incisors are moving forwards as part of the downward and forward movement of the maxilla, and they may in turn indirectly push the lower incisors forward. Secondly, once the crossbite or edge-to-edge relationship is corrected and there is a positive overjet, there is a change in the tongue position, where it can now freely put pressure on the lingual surface of the lower incisors and move them to the newly established neutral zone between the lips and tongue .
The overjet reduction with the HE-MP was slightly less (1.07 mm; SD = 0.56) than what was seen with the RME–FM, despite the skeletal correction being greater in the HE-MP group. It was also noted that the treatment was, on average, 3 months longer with the HE-MP. This is likely due to the greater dental compensation associated with the RME–FM, which is achieved through upper incisor proclination and lower incisor retroclination, and which would lead to a faster development of a positive overjet. On the other hand, in the absence of dental compensation and even some mandibular dental decompensation, and with the correction almost exclusively stemming from skeletal changes, the overjet correction may take longer and show a smaller increase overall with the HE-MP. Similar results have also been shown with the BAMP protocol, where treatment has been recorded at an average of 2 months longer than with the face mask, with a smaller total correction in overjet . It may be argued that for the long-term stability of the treatment result, this is a positive finding, as Class III patients tend to resume the original growth pattern when treatment is completed . This lack of dental compensation may allow some room for future dental camouflage, should there be some relapse.
Advantages of using HH-MP
Willman et al. found that when the Hybrid Hyrax-Mentoplate protocol was compared with the Hybrid Hyrax-face mask protocol, the results were very similar, except for more backward rotation of the mandible when the face mask was used. The face mask, however, has the significant limitation of reduced patient acceptance due to the obtrusive extraoral nature of the appliance .
Furthermore, even though the HE-MP protocol shares similar skeletal and dental effects with the BAMP protocol , there are several differences between the two. Firstly, there are four fewer surgical procedures involved with the HE-MP protocol, as the elimination of the zygomatic plates for maxillary anchorage using the hybrid expander halves the number of flap procedures. This also reduces the chances of miniplate failure, which has been reported to be six times higher in the maxilla than in the mandible [24, 25]. The higher failure rate of the maxillary zygomatic miniplates may be due to the difficulty in placing them in younger patients, due to reduced bone density [24,25,26,27]. On the other hand, the use of palatal miniscrews in the anterior palate to support the hybrid expander for the maxillary anchorage ensures the miniscrews are in an area of good bone quality [28, 29] where the success rate is high (more than 96%) and predictable, even in young patients . Secondly, treatment with the HE-MP protocol can start earlier than with the BAMP protocol, which requires the mandibular canines to erupt prior to the placement of the miniplate. It is well documented that the maxilla is more responsive to protraction in younger patients, particularly those younger than 10 years old [31, 32]. The use of L-plates allows the miniplates to be placed before the eruption of the mandibular canines, thus allowing treatment in younger patients, much like what was reported with the use of Mentoplates . Lastly, the HE-MP allows the incorporation of bone-borne maxillary expansion, which allows the concomitant management of any transverse maxillary deficiency (often present in maxillary hypoplasia  during Class III correction.
L-plates offer an advantage over the Mentoplate as well, since the right and left plates are independent of each other, this allows the surgeon more freedom to vary the position of the plates and find the best cortical bone. Furthermore, the use of traditional trauma plates, as opposed to proprietary plates such as the Mentoplates (PSM Medical Solutions, Gunningen, Germany) or the Bollard plates (Bollard; Tita-Link, Brussels, Belgium), may make the protocol more accessible to patients and potentially reduces the cost, as most surgical theatres will be equipped with traditional orthognathic trauma plates.
It is important to mention that the results of this study are limited to a short-term evaluation after treatment in two different centres. Long-term evaluation will be required to assess the stability of this treatment once the patients have completed postpubertal growth. It has been shown that face mask therapy is stable in 75–80% of cases in the long term [4, 21]. It remains to be seen if the greater skeletal response in the active treatment phase with this skeletal anchorage protocol results in better long-term stability.
The starting forms of the two groups were similar in all parameters except for Ar-Go-Me and LOP-MP angles. Whether or not this affected the treatment outcomes is unclear; however, an increased gonial angle is one of the predictors of failure in the long term for Class III patients and this should be investigated . There was 1 patient in the HH-MP group, in whom compliance was poorer compared to others. However, since compliance of patients was not assessed for any of the patients, this patient’s data were still included in the results. It should again be noted that, in HH-MP patients, the dental effects are the opposite to RME–FM patients, which makes obtaining a positive overjet much more difficult.
It was also not possible to blind the T2 radiographs as images were collected with the skeletal anchors still in situ. Furthermore, the two groups were treated in different centres, so it can be argued that the outcomes may have differed; however, both treatment regimens followed universally used and accepted protocols. Another limitation of our study was the retrospective nature of the study; however, all patients fulfilling the inclusion criteria at the time of data collection were included.