Growing class III malocclusions are often treated by extraoral forces to correct the developing skeletal Class III malocclusion. The results are often encouraging, but the problem of patient compliance is a major hurdle in achieving successful results [13, 14]. The other treatment modality for correction of class III malocclusion is reverse twin block (RTB) which is intraoral functional appliance. Studies have reported that RTB effects are primarily dental, characterized by upper incisor proclination and lower incisor retroclination with minimal skeletal change [6, 7, 16, 17].
Conventional RTB was modified in this study by the incorporation of HYRAX screw and upper lip pads with an objective to achieve maximum skeletal effects and minimal dental side effects. A study by Turley PK  showed that rapid expansion enhances the protraction effect which in turn reduces the treatment time and produces lesser dental effects. The flaring of the upper incisors is limited because of the space created by the expansion appliance. It also brings about transverse skeletal expansion thus overcoming the transverse maxillary deficiency and also overcomes the resistance of the circummaxillary sutures .
Upper lip pads hold the upper lip away, thus eliminating restrictive pressure on the underdeveloped maxilla and also exert tension on the tissues and periosteal attachment at the depth of maxillary sulcus to stimulate bone growth .
In present study, RTBLP-RME appliance was cemented to lessen the chance of relapse of expansion. The correction of class III was achieved in a short duration of 9 months in both the treatment groups.
Effects on cranial base angulation
Over a period of 9 months in the treatment and the control group, no significant changes were observed in cranial base angulations.
Antero-posterior skeletal measurements
The RTBLP-RME group had a greater impact on maxillary advancement with a mean change in SNA of 2.0 as compared to the FM-RME group (1.31) and control group (0.81).
Changes in angle SNB in RTBLP-RME group (− 1.08), FM-RME group (− 0.73), and control group (1.38) showed that RTBLP-RME has more posterior holding effect/rotational effect on mandibular position than the FM-RME and control groups.
Thus, the mean change in resultant angle ANB for RTBLP-RME group (3.08 ± 1.55) was increased as compared to FM-RME group (2.04 ± 1.08). In the control group, the angle ANB decreased (− 0.58 ± 0.49) indicating that class III worsens with growth.
These effects were in contrast to studies by Kidner et al.  and Seehra et al. [7, 16] who had reported minimal effect on SNA, SNB, and ANB. This difference could be attributed to the modification of the reverse twin block done in the present study. Similar positive findings were seen with removable mandibular retractor (RMR) by Saleh et al.  and Majanni et al.  But in the present study, the amount of sagittal changes seen are more as compared to that in removable mandibular retractor (RMR). This could be attributed to additional components added to reverse twin block in the present study.
Studies on the efficacy of protraction face mask [12,13,14,15,16,17,18] have reported similar findings.
Wits appraisal showed greatest mean change with the RTBLP-RME group (4.23) as compared to the FM-RME group (2.83) which was highly significant (< 0.01) again indicating that RTBLP-RME has more positive effect on anteroposterior maxillomandibular relationship in class III malocclusion.
Similar findings have been reported in studies with face mask therapy as compared to control group [13,14,15,16,17,18,19]. None of the reverse twin block studies has assessed this parameter.
Mean change in A-Vert T in RTBLP-RME group was (3.04) which was greater than that in the FM-RME group (2.50) and control group (1.73) thus showing that RTBLP-RME appliance is more effective in maxillary advancement. Similar improvement in maxillary advancement has also been noted with removable mandibular retractor (RMR) [8,9,10] appliance.
Baccetti et al.  studied the effect of expansion face mask combination in early and late mixed dentition and found mean change in A-Vert T of 3.58 and 1.89, respectively, thus showing both appliances had nearly the same positive effect on midfacial length as compared to the control group.
Similar findings were recorded by Tortop et al.  and Masucci et al.  with a mean difference of (2.1) and (8.3), respectively, with face mask treatment.
Mean change of Pr-Vert in RTB (2.54), PFM (2.92), and control group (1.54) indicated that dentoalveolar maxillary protrusion was slightly more with FM-RME group as compared with RTBLP-RME group and least in the control group. A study by Baccetti et al.  showed similar findings in early (4.14) and late (2.37) face mask-treated group.
During the treatment period, the changes in B-Vert T were significant for RTBLP-RME group (− 0.38), FM-RME group (0.23), and control group (2.85). Similarly, the changes in Co-Vert T were also significant with mean values of 1.27, 1.31, and 0.42, respectively. These findings support the fact that RTBLP-RME has more hold on the posterior positioning of the mandible.
A study by Baccetti et al.  showed a more significant change in B-Vert T in early (− 1.13) and late (− 1.92) treated groups with face mask.
Mean change Id-Vert T in the RTBLP-RME group (− 0.23), FM-RME group (0.77), and control group (3.08) showed more dentoalveolar remodeling with RTBLP-RME. A study by Baccetti et al.  showed significant change in early treated (− 0.29) group and late-treated group (− 1.41) with face mask treatment.
Total mandibular length Co-Gn in the overall comparison between the three groups was significant, similar to Baccetti et al. , Tortop et al. , and Masucci et al. .with face mask therapy.
A highly significant change was seen in ramus length Co-Go with mean change in RMELP-RTB group (3.0), FM-RME group (3.92), and control group (1.38). However, within the treated groups, no significant change was observed.
These findings are in contrast to studies by Saleh et al.  and Majanni et al.  which were with removable mandibular retractor (RMR), and there was no significant difference as compared to control group. Baccetti et al.  also found no difference in early versus late treated face mask groups.
Mandibular body length Go-Gn showed mean change with RTBLP-RME group (1.69), FM-RME group (3.38), and control group (1.54). Thus, comparing the effect of RTBLP-RME and FM-RME on mandible, RTBLP-RME showed a significant control on mandibular skeletal base.
Measurements for vertical relationship
The mandibular plane rotation (ML-SBL) was almost similar in both the treated groups with mean change (0.77°) where as in the control group (− 0.31°), closure of this plane was observed.
Palatal plane inclination (NL-SBL) remained unchanged in FM-RME group (0.00), but in the RTBLP-RME group (− 0.54) it tipped upward anteriorly.
Angulation between the palatal plane and mandibular plane (NL-ML) was more with the RTBLP-RME (1.31) than with the FM-RME (0.77). Though the mandibular plane remained unchanged in the RTBLP-RME group, the divergence in the base plane could be a result of mild anteriorly upward tip of the palatal plane.
Ar-Go-Me showed mean change in RTBLP-RME (0.62), FM-RME (− 0.77), and control group (1.54). Opening in gonial angle was more with RTBLP-RME appliance than that with FM-RME appliance.
Changes in lower anterior face height (ANS-Me) were significant in overall comparison with mean change of RTBLP-RME group (4.08), FM-RME group (3.46), and control group (1.54).
Study by Baccetti et al.  recorded no significant change in the early treated group but a significant increase in lower anterior face height in the late treated face mask group.
Measurements for assessment of condyle inclination
For angle Cond-AX-SBL, Cond-Ax-ML and Ar-Go-Vert T overall change was significant. Baccetti et al.  study with face mask .similar changes.
For condylar inclination, the findings are homogenous within both the treated groups showing posterior positioning of the condyle in the RTBLP-RME group and forward positioning of condyle with FM-RME group.
In RTBLP-RME bite was registered in the most retruded position which may be the cause of posterior position of condyle in glenoid fossa.
Inclination of upper incisors (UI-SN) showed proclination in the RTBLP-RME group (3.08°), FM-RME group (5.46°), and control group (2.38°). A study by Masucci et al.  showed mean change of (2.4°) with face mask therapy.
Thus, with FM-RME, there was an increase dental compensation by upper incisor proclination along with alveolar bone remodeling. In the RTBLP-RME-treated group, the effect was more skeletal on the maxilla with significant maxillary advancement and minimal incisor proclination.
The findings of Seehra et al.  differ from the present study as maxillary incisor proclination was more in their study with reverse twin block compared to face mask. Kidner et al.  also found increase upper incisor proclination with reverse twin block.
Angle IMPA showed retroclination of lower incisors with FM-RME (− 0.62°) as compared to RTBLP-RME (0.23°).
Increased maxillary incisors proclination with decrease in mandibular incisor inclination with RTB therapy was reported by Kidner et al.  and Seehra et al. , suggesting primarily a dental effect with RTB in their study. With other removable functional appliance like removable mandibular retractor (RMR), similar findings have been reported [8,9,10].
In the present study, the overall evaluation period was short with no follow-up data. In fact, this is a limitation that should be further evaluated with larger sample size. Similarly, although in the present study we did not find any drop outs, the effect of compliance of patients in using these appliances is an area of future research.
Another limitation of the study was regarding the large age range. But because of some limitations (single center with low prevalence and time for study), we tried to take the average age range between early and late mixed dentition. This could have affected the clinical outcome of the appliances used and thereby the conclusion of the study.