ABSTRACT
To evaluate the skeletal, soft tissue, and airway effects of the alternate maxillary expansions and constrictions (Alt-RAMEC) protocol in prepubertal patients.
The appliance containing a double-hinged expansion screw was applied to 20 patients with Class III skeletal malocclusion characterized by maxillary retrognathia. The mean age of the study group was 9 years and 8 months. The patients' parents were instructed to open the screw by 1 mm per day during the first week and to close it by 1 mm per day the week after. This alternate opening and closing was repeated for 9 consecutive weeks. Cone beam computed tomography records and three-dimensional photographs were taken before treatment and after 9 week of the Alt-RAMEC protocol.
Point A moved slightly forward (0.89 mm) and downward (0.92 mm) (P < .05). The average amount of expansion achieved at the level of point A was 5.54 mm (P < .05). Besides the maxilla, the expansive forces also affected the nasal bone, the zygomaticomaxillary and zygomaticotemporal sutures (P < .05). The soft tissue nasal width increased significantly. The airway volume of the anterior nasal compartment and the nasal cavity also increased (P < .05).
Slight forward movement of point A occurred with the Alt-RAMEC protocol. The expansion affected not only the maxilla but also other structures of the face. Significant cutaneous changes occurred in the paranasal area. Some significant increase in the upper airway volume was obtained.
INTRODUCTION
Class III skeletal malocclusion is among the most challenging problems to treat in orthodontics. Maxillary retrognathia is an important component of Class III malocclusion. For adults, camouflage or surgical interventions are treatment options, whereas for younger patients maxillary retrognathia can be successfully corrected with early treatment. Rapid maxillary expansion (RME) combined with face mask therapy is a routine clinical procedure as it is assumed that RME disarticulates the circummaxillary sutures.1–3 Liou4 introduced a different method called “alternate rapid maxillary expansions and constrictions” (Alt-RAMEC). This protocol is performed with a special double-hinged expansion screw that is alternately opened and closed for 7 to 9 consecutive weeks.4–6 Liou7 stated that this special screw has an advantage in that the center of rotation can be located near the maxillary tuberosity, thereby enhancing the forward movement of maxilla. Liou and Tsai5 reported a 3-mm advancement of point A with the Alt-RAMEC protocol and 5.8 mm of total advancement after protraction. This result is dramatic, as conventional RME+protraction procedures achieve an average advancement of only 1.5–3 mm.8,9
In the literature some articles report successful clinical results with this protocol, but because the second records are taken after protraction, the amount of advancement related solely to Alt-RAMEC protocol cannot be isolated.10,11 Other than Liou and Tsai's study,5 no other study has evaluated the pure effects of the Alt-RAMEC protocol.
In this study, we decided to test whether the Alt-RAMEC protocol can be an alternative treatment modality for mild skeletal discrepancies in preadolescent patients using three-dimensional (3D) imaging.
MATERIALS AND METHODS
The study group comprised 10 girls (∼9 years 2 months old) and 10 boys (∼10 years 3 months old) with maxillary retrognathia. The mean age of the group was 9 years 8 months.
The screw (US Patent No 6334771B1) was positioned parallel to the midline and the arms were bent to the buccal side to form the hooks for face mask application after expansion (Figure 1).
The parents were instructed to open the screw by 1 mm per day during the first week (two turns in the morning and two turns in the evening) and to close it by 1 mm per day the following week. This alternating opening and closing was repeated for 9 consecutive weeks.
Cone beam computed tomography (CBCT) images were taken before and after 9 weeks with an Iluma Imtec Imaging machine (3M, Ardmore, OK, USA), while patients were sitting in an upright position (x-ray tube, 120kV; x-ray tube current, 1–4 mA; scanning time, 40 seconds maximum and 7.8 seconds minimum; field of view, 14.2 × 21.1 cm; voxel size, 0.0936 mm; grey scale, 14 bit). In addition, ear-to-ear 3D photographs were shot using the 3dMDface system (3dMD LLC, Atlanta, GA, USA). The data was analyzed using MIMICS version 14.0 (Materialize Interactive Medical Image Control Systems, Leuven, Belgium). The study was approved by the Bezmialem University Ethical Committee.
Skeletal Evaluation
After the DICOM (digital imaging and communications in medicine) data were uploaded to the software, a full-head mask was created by calibrating the bone tissue. The mask containing the nasomaxillary complex and the head bones was obtained by subtracting the mandibular and vertebral masks from the main mask.
Masks before and after the protocol were first superimposed, and the horizontal reference plane (HRP) was formed between the right and left porion and the right infraorbital point. The vertical reference plane (VRP) was formed by the plane passing through the porions, perpendicular to the HRP (Figure 2). The measurements were made to the same reference planes for the superimposed masks. Ten skeletal landmarks were defined and distances to HRP and VRP were measured together with five bilateral measurements (Figure 3a,b; Table 1).
(a) Skeletal reference points. (b) Bilateral distance measurements.
Soft Tissue Evaluation
After cleaning all the artifacts, 3D photographs were superimposed using 3dMD patient software. The superimposed masks were transferred to MIMICS software in STL file format.
A vertical plane was created passing through the right and left inner cantus and the right alar curvature point. The junction point between the earlobe and the face skin was defined; a second plane parallel to the first plane passing through this point formed the soft tissue reference plane (STRP) (Figure 4).
The landmarks shown in Figure 5a,b and described in Table 1 (defined by Farkas12) were selected. The distances were measured from these points to STRP. The distances between right and left alar curvature (ac) and subalare (sbal) points were also registered.
Airway Evaluation
The airway mask was created by thresholding the DICOM data between −1024 and −400 HU. The plane passing through the right and left anterior clinoid processes and nasion formed the upper limit of the analyzed airway. The plane passing through the most anterior and the lowest bound of the second cervical vertebrae and parallel to the upper plane formed the lower limit. The outer air was separated with the plane passing through the nasal tip and the most convex points of the alar curvature.
The airway was divided into three parts; pharyngeal, nasal, and anterior nasal compartments (Figure 6). A plane was formed passing through the lowest and most anterior bound of the first vertebrae and parallel to the upper limit. This plane determined the upper limit of the pharyngeal compartment. The nasal and anterior nasal compartments were separated with the plane passing through the sellion and bilateral ac points.
Three-dimensional mask of the airway divided into three compartments.
Statistical Analysis
Statistical Package for Social Sciences for Windows 15.0 software (SPSS Inc, Chicago, IL, USA) was used for the statistical analysis. The conformity of the parameters to the normal distribution was assessed by the Kolmogorov-Smirnov test and the parameters conformed to the normal distribution. A paired samples t-test was used for in-group comparisons of the parameters. The intraclass correlation coefficient (ICC) was calculated for the analysis of the method error. Significance was evaluated at a level of P < .05.
RESULTS
All patients followed the protocol well, although a few patients reported discomfort over the nasal bone and the zygomatic ridges during constriction. Clinically, maxillary expansion and slight improvement of the overjet was recorded in all patients (Figures 7a,b, 8a through c, and 9a,b).
Extraoral photographs taken (a) before treatment and (b) after the Alt-RAMEC protocol.
Extraoral photographs taken (a) before treatment and (b) after the Alt-RAMEC protocol.
(a) Pretreatment intraoral view. (b) After bonding the device. (c) After the Alt-RAMEC protocol.
(a) Pretreatment intraoral view. (b) After bonding the device. (c) After the Alt-RAMEC protocol.
Intraoral occlusal view (a) before and (b) after the Alt-RAMEC protocol.
The skeletal, soft tissue, and airway measurements were repeated by the same operator 3 weeks after the first measurement. Tables 2 through 4 present the ICC. The method is shown to be reliable and reproducible for all the analysis.
All the results presented in Tables 5 through 7 are mean change ± standard deviation. Point A moved slightly forward (0.89 ± 0.93 mm) and downward (0.92 ± 1.62 mm). The ANS moved slightly forward (0.76 ± 1.28 mm). The INC landmarks moved downward bilaterally (right, 0.83 ± 1.09 mm; left, 0.74 ± 1.24 mm). The INC-l point moved slightly upward (0.38 ± 0.78 mm) but no significant vertical change occurred for the right side. The ZTL right and left borders moved slightly upward (right, −0.31 ± 0.42 mm; left, −0.59 ± 0.57 mm) and the upper borders moved slightly downward (right, 0.26 ± 0.59 mm; left, 0.38 ± 0.45 mm). The right and left ZM landmarks moved backward (right, −0.60 ± 0.70 mm; left, −0.63 ± 0.79 mm). The amount of expansion achieved was 5.54 ± 1.48 mm at point A; 3.00 ± 1.4 mm at the nasal level; 1.61 ± 1.65 mm at the ZM level; and 0.75 ± 0.98 mm and 0.45 ± 0.82 mm at the ZTU and ZTL levels, respectively (Table 5).
The distance between the ac points and the sbal points increased significantly (1.69 ± 1.08 mm and 1.16 ± 1.38 mm, respectively). The ac-r (1.20 ± 1.50 mm), sbal-r (0.71 ± 1.54 mm), and mlr-r (1.03 ± 1.78 mm) points moved forward. This forward movement also occurred for the left side, but the changes were not statistically significant (Table 6).
The volume of the anterior nasal compartment (376.42 ± 276.20 mm3), volume of the nasal compartment (4632.28 ± 8165.95 mm3), and total airway volume (5320.91 ± 8305.92 mm3) increased significantly (Table 7).
DISCUSSION
The Alt-RAMEC duration varies from 4 to 9 weeks in different studies.10,13 Liou4,6,7 and Liou and Tsai5 advise following the protocol for at least 7 weeks to obtain enough release of maxilla. We decided to follow the protocol for 9 weeks to ensure maxillary mobility and standardization of the method.
The 3D measurements have been shown to be more reliable than two-dimensional (2D) tracings.14 The use of 3D imaging is crucial, especially for airway evaluation, because only surface measurements can be performed with 2D airway analysis.15,16 Thus, we prefer to use 3D imaging systems to obtain more accurate data.
CBCT was selected instead of conventional computed tomography because the radiation dose is lower, the procedure is cheaper, and the image quality is still good.17,18 According to the US Nuclear Regulatory Commission, the amount of annual artificial radiation dose exposure limit is 1 mSv (Code of Federal Regulations, Title 10, §20.1301, Subpart D). The radiation dose of one CBCT scan is 0.058 mSv. Because we take two records in approximately 3 months, the dose exposure is still far below the annual limit (0.116 mSv).
In the literature little data have been published related to the pure effects of the Alt-RAMEC protocol. Thus, we have to compare our results with studies evaluating the conventional RME. We found that the maxilla moved slightly forward (0.8 mm) and downward (0.92 mm). Liou and Tsai5 reported that the maxilla moved forward (3 mm) following the Alt-RAMEC protocol. The smaller amount of movement in our study might be explained by the skeletal differences in the cleft patients and the smaller sample size in their study. Moreover, it has been shown that measurements performed with 3D tomography are more reliable than tracings made on 2D cephalograms.14
Some studies evaluating the effects of the Alt-RAMEC protocol followed by face mask application reported 2–5 mm forward movement of point A.10,11 However, in such studies the amount of forward movement related to the Alt-RAMEC protocol cannot be isolated as the cephalometric records were taken after protraction.
In studies published by Podesser et al.19 and Ballanti et al.,20 1.4 mm and 1.2 mm of increase were reported for the nasal cavity width measured at the level of the first molars; Christie et al.21 reported 2.73 mm of widening. In our study, the expansion related to the nose is 3 mm, which seems to be larger than those reported, probably because our measuring points were located in the anterior part of the maxilla, where the largest expansion occurs. Moreover, those studies were performed with a conventional screw, whereas our study was performed with a double-hinged screw, which might have a different effect.
Besides the expansion of the maxillary bones, small but significant increases were found between the right and left upper/lower zygomaticotemporal (0.45–0.65 mm) and zygomaticomaxillary (1.61mm) points (Figure 3b). In the literature, several studies have reported that the circummaxillary sutures were affected by the RME protocol.22–24 In a study performed by Leonardi et al.,25 it is found that the RME also increased the bilateral distances of the zygomaticotemporal, zygomaticomaxillary, and other neighboring sutures.
On the other hand, the zygomaticomaxillary point presented backward movement. The upper borders of the zygomaticotemporal suture moved slightly downward, while the lower borders moved slightly upward. We can explain this with the triangular pattern of lateral movement of bone compartments during expansion. In the finite element morphometry study by Jafari et al.,22 they found that expansive forces are not restricted to the intermaxillary suture alone but are also distributed to the circummaxillary sutures.22 It is reported that the anterior part of the maxilla was displaced downward but the zygomatic bone moved upward. In the anteroposterior plane, the maxilla was slightly displaced forward but the zygomatic bone showed backward displacement (0.75 mm).
In terms of soft tissue changes, the only significant change was related to the nasal width. Berger et al.26 also showed that there was significant and stable change only for nasal width after RME (mean = 2 mm). Similarly, Johnson et al.27 reported 1.1 mm of significant and stable increase in nasal width after RME. Pangrazio-Kulbersh et al.28 performed a study to evaluate changes after RME with bonded and banded expanders. They reported that both appliances increased the skeletal and soft tissue dimensions of the nasal cavity, which supports our results. Nada et al.29 reported slight lip and cheek changes. We also recorded similar changes, but our findings were not statistically significant.
It is assumed that widening the nasal passages and the nasal cavity with RME will result in improved breathing.30–33 Haralambidis et al.34 evaluated airway volume changes after RME and reported an 11.3% increase for the anterior nasal compartment. Our value was 9.67% for the same anatomic area (P < .05), but we did not record any significant change for the pharyngeal airway. Zhao et al.35 and Pangrazio-Kulbersh et al.28 had similar findings concerning the posterior airway.
It is reported in the literature that there are changes in airway dimensions related to the respiration phase and the tongue position.36,37 No attempt was made during CBCT acquisition for our subjects to control respiratory movements and tongue posture. This problem can be minimized by training patients before scanning in future studies.
CONCLUSIONS
The protocol caused expansion in the maxilla of prepubertal patients and also affected the neighboring sutures.
The maxilla moved slightly forward and downward, but such a small change may have limited clinical utility.
The Alt-RAMEC protocol cannot be a treatment option alone without the use of a protraction modality for patients with retrognathic maxilla.
The soft tissue nasal width, anterior nasal volume, and nasal airway volume increased.
ACKNOWLEDGMENT
This study was supported by Marmara University Scientific Research Projects Commission (Project number SAG-C-DRP-101012-0318).