ABSTRACT
Objective: To evaluate three-dimensional (3-D) soft tissue facial changes following rapid maxillary expansion (RME) and to compare these changes with an untreated control group.
Materials and Methods: Patients who need RME as a part of their orthodontic treatment were randomly divided into two groups of 17 patients each. Eligibility criteria included having maxillary transverse deficiency with crossbite, and to be in the normal range according to body mass index. In the first group (mean age = 13.4 ± 1.2 years), expansion was performed. The second group received no treatment initially and served as untreated control (mean age = 12.8 ± 1.3 years). Skeletal and soft tissue changes were evaluated using posteroanterior cephalograms and 3-D facial images. The primary outcome of this study was to assess the soft tissue changes. The secondary outcomes were evaluation hard tissue and soft tissue relations. Randomization was done with preprepared random number tables. Blinding was applicable for outcome assessment only. MANOVA, t-test, and correlation analyses were used (P = .05).
Results: In both groups, there was a general trend of increase for the transverse skeletal measurements, but these increases were more limited in the control group. Alar base width was greater in the treatment group (P = .002). Pogonion soft tissue point (P = .022) was located more posteriorly in the expansion group compared with the control group.
Conclusions: Soft tissue changes between groups were similar, except for the alar base, which became wider in the treatment group. Weak correlations were found between the skeletal and soft tissue changes.
INTRODUCTION
The goals of orthodontic treatment are to improve esthetics and correct the occlusion. The primary concern of patients has been improvement in facial appearance, which is considered an important factor of well-being and social success.1 Recently, a paradigm shift has occurred from hard tissue to soft tissue known as the soft tissue paradigm.1 According to this reverse approach, the key determinant is soft tissue positions, necessitating evaluating the effects of various orthodontic treatments and their effect on the face.
The maxilla is a large facial bone that articulates with 10 facial and cranial bones.2 The maxilla moves downward and forward after rapid maxillary expansion (RME) and, except for the sphenoid bone, all craniofacial bones articulating with the maxilla also displace.3 Nasal cavity width increases, particularly at the floor of the nose.4 Thus, treatment effects of RME are not only limited to oral structures but are also related to changes in the circummaxillary region. There has been copious literature about the skeletal and dental effects of RME, whereas only scarce information and nonconsensus exist about soft tissue changes.
According to the findings of cephalometric studies, nose tip and soft tissue A-point move forward5 and H angle and profile convexity increase after this treatment.3 Nasal width increase was reported in studies using serial frontal photographs6 and anthropometric measurements.7 Three-dimensional (3-D) evaluation of widths of the nasal base,8,9 mouth,8 and columella9 increased with flattening of the nose9 and upper lip elongation and thinning.10
3-D stereophotogrammetry is a method of acquiring images using one or more pairs of simultaneously taken photographs. Soft tissue records are easy to capture using optical scanners with short shutter speeds. Erratic movement of the patient is not a matter discussion with fast scanning speed.11 Inclusion of surface texture is another advantage of the system. The reproducibility and accuracy of the technique, has been stated to be “more than sufficient for clinical needs” and has greater accuracy compared with direct anthropometry and 2-D photography.12
The aim of this prospective clinical trial was to quantify the soft tissue facial changes following RME and to compare these changes with an untreated control group using 3-D facial images. To our knowledge, this study was the first to include a control group to distinguish the changes after RME treatment with those resulting from normal growth and development. The null hypothesis was that soft tissue changes are not significantly different between treatment and control group. Also, the soft tissue adaptability to the dento-skeletal changes associated with expansion of the maxilla will be evaluated. In this study, the following hypotheses were tested: (1) there is no difference between RME-treated and untreated subjects regarding soft tissue changes and (2) there is no relation between hard and soft tissue changes.
Specific Objectives or Hypotheses
In this study following hypotheses were tested (1) there is no difference between RME-treated and untreated subjects regarding the soft tissue changes (2); there is no relation between hard and soft tissue changes.
MATERIALS AND METHODS
This was a parallel-group, randomized, controlled trial with a 1:1 allocation ratio.
Sample Size Calculation
The optimal sample size determination prior to the statistical analyses was performed based on the effect size (Cohen’s d = 0.99) reported by Johnson et al.,7 which indicated that group sizes of 17 (total 34) would provide at least 80% statistical power.
Participants, Eligibility Criteria, and Settings
Ethical approval was obtained from the Izmir Katip Celebi University, Clinical Research Ethics Committee (No. 54). Informed consent for the study was obtained from all the parents.
Patients requiring RME as a part of their individual treatment plan in the initial examination were selected from the patient waiting list of the Orthodontic Department Clinics. Inclusion and exclusion criteria are given in Table 1. Among these patients, patients who fulfilled the inclusion criteria were informed about the study and invited to participate.
Randomization
If the child and parent consented, initial records are taken and each patient was randomized to receive treatment or to have treatment delayed for at least 6 months. The randomization was made at the start of the study with preprepared random number tables. One researcher evaluated the patients and the other author did the enrolling. Thirty-four subjects were randomized into two groups of 17 patients each. Mean ages of the treatment and control subjects were 13.4 ± 1.2 years and 12.8 ± 1.3 years, respectively. A patient flowchart is shown in Figure 1.
Interventions
All patients were submitted to the RME protocol established by a bonded acrylic splint expander (Figure 2). The screw was activated a quarter turn twice per day (0.5 mm) for the first week, then a quarter turn per day (0.25 mm), until the palatal cusps of the maxillary molar contacted the buccal cusps of the mandibular molar.13 Mean maxillary expansion achieved was 6.25 ± 2.9 mm, with a mean number of activations of 25 ± 11.6 turns. After the expansion completed, the appliance was kept in the mouth passively for the first month. The mean active expansion period was 0.7 ± 0.4 month in the treatment group. A Hawley retainer was delivered to all patients for the rest of the retention period. After 6 months, T1 records were taken of the participants. Mean observation time was 6.1 ± 0.6 months. Three-dimensional facial surface images and posteroanterior cephalograms (PACs) were taken before treatment (T0) and immediately after the retention/observation period (T1).
Soft tissue changes were evaluated using 3-D facial images, which were captured in the natural head position using the 3dMD imaging system (3dMD, Atlanta, Ga) in less than 1.5 milliseconds. Each patient was positioned on an adjustable stool and instructed to look into his or her eyes in a mirror placed between the cameras with eyes open and facial musculature relaxed.14 All images were saved as TSB files and manipulated using the 3dMD Vultus software (3dMD). Each 3-D facial image was cleaned to exclude confounding regions by removing the extraneous surface data from the neck, ears, and scalp hair.
PACs were used to assess transverse changes on the skeletal, dental, and nasal structures. The standard scan takes only 10 seconds with 2.3 seconds exposure time and optimized patient dose (Orthopantomograph OP300, Instrumentarium, Tuusula, Finland).
Individual changes of the soft tissue landmarks were recorded using superimposed images. In order to accurately superimpose the two 3-D facial images, the registration protocol was performed on the forehead, upper nasal dorsum, and zygoma. These were defined as the most stable regions over time.15 The 3-D facial images were then landmarked by a single trained investigator. The software was designed to automatically calculate the Euclidean distance of the landmark positions (Figure 5). Positive values indicated forward movement of the specific landmark in three planes of space according to Euclidean distance matrix analysis,16 while negative values indicated posterior movement.
Superimposition and soft tissue point measurement using the software.
Interim Analyses and Stopping Guidelines
Not applicable.
Outcomes and Changes After Trial Commencement
The primary outcome of this study was to assess soft tissue changes. Secondary outcomes were to evaluate hard and soft tissue relations. No changes in methodology or outcome changes occurred after trial commencement. Blinding of neither patient nor operator was possible but was feasible during evaluation and outcome assessment.
Statistical Analysis
Statistical analysis was performed using the Statistical Package for Social Sciences, Version 20.0 (SPSS Inc, Chicago, III). The normality test of Shapiro-Wilks and Levene’s variance homogeneity tests were applied to the data. Intragroup comparisons were determined with paired-samples t-tests (Bonferroni correction) and intergroup comparisons were determined with MANOVA. Pearson correlation analyses were used to assess the degree of correlation between soft and hard tissue changes.
RESULTS
Method Error
The same author repeated the measurements 1 month after the first measurements on 20 3-D images and 20 PACs randomly selected from 10 patients. Intraclass correlation coefficients (r) ranged from 0.94 (6A-6B) to 1.00 (AG-GA). No significant errors were found when repeat measurements were evaluated with paired t-tests.
Baseline demographic and clinical characteristics of the patients are given in Table 2. Patient treatment and observation were completed without dropouts from either group. The follow-up period for both groups was 6 months.
Transverse Measurements
A comparison of starting forms of treated and control subjects is given in Table 5. Only face widths (ZA-AZ, P = .042) and maxillary intermolar distances (P = .008) were different between groups. Initial soft tissue cephalometric values were comparable between groups.
Table 6 shows the intra-and intergroup comparisons of the mean changes between T0 and T1. In both groups, there was a general trend of increase for the transverse skeletal measurements, especially in the expansion group, but these increases were not as great in the control group. Maxillary and mandibular midlines, mandibular intercanine width, ZL-ZR, AG-GA, and occlusal difference changes were not statistically significant between groups. Average molar relation was increased and average maxillomandibular relation was decreased in the expansion group; these changes were the opposite in the control group.
Similar to transverse skeletal measurements, increases in soft tissue measurements were found. Except for alar base width (P = .002), soft tissue differences were comparable between groups.
Soft Tissue Point Measurements
To determine soft tissue point changes, the distance between locations of the same point was calculated after superimposition of pre-and posttreatment stereophotogrammetric images (Table 7). No statistically significant differences were found between groups, except for pogonion (P = .022), which was found to be posteriorly located in the expansion group (−1.33 mm), but forward movement (0.11 mm) was recorded in the control group.
Hard and Soft Tissue Relations
Correlation coefficients were calculated; the only statistically significant correlation was found between the amount of expansion and maxillary intermolar distance (r = 1.000, P = .001). The regression model was not used, as weak or no correlation existed between soft and hard tissue changes.
No serious harm was observed in the treatment group other than gingivitis associated with the difficulty of plaque removal.
DISCUSSION
The aim of orthodontic treatment is to achieve facial harmony as well as ideal occlusion. From this point of view, orthodontic procedures should be evaluated to clarify whether—and how—these procedures affect the appearance of soft tissues. In the present study, the soft tissue effects of RME were examined using 3-D stereophotogrammetric images.
The only statistically significant difference in soft tissue linear changes between groups was found for alar base width. In the treatment group, the difference was 1.41 ± 0.95 mm, which was approximately 1 mm greater than in the control group. Widening of the alar base is a common finding that does not exceed 2 mm.6–10 Also, statistically significant differences were reported, whose clinical significance is open to question.
An increase in hard tissue nasal width (2.42 ± 1.28 mm) was also found. Widening of the alar base after RME has been shown in studies using metallic markers.17 Berger et al.6 advocated that the soft tissue findings correlated well with the skeletal effects (1 to 1 ratio) and even the expansion was 4-5 mm, this amount lead to significant soft tissue changes. But weak correlation was found in our study.
Kim et al.10 found that the nose apex and the distance between zygion points increased immediately after RME. Berger et al.6 reported statistically significant increases in eye width (0.2 mm) and intercanthal distance (0.3 mm). In the current study, statistically significant increases were also found between the intercanthal distance and zygoma points in both groups. But the difference did not reach a statistically significant level, thus the increases were thought to be the result of normal growth and development.
Elongation of the upper lip,6,10 thinning of both lips,10 and increase in lower vermilion height8 were reported after RME. In this study, no statistically significant change was found for the lips in either group.
Records were taken after appliance removal and retention to eliminate the immediate positional changes of the lips, cheeks, chin, and mandible caused by adapting to the bulk of the expander.6 Changes in occlusion could also be a confounding factor that leads to soft tissue changes not related to expansion.10 The postretention records were therefore taken to account for occlusal settling and to obtain a stable mandibular position.
Soft tissue pogonion was positioned backward in the treatment group. The difference was approximately 1.5 mm; this change may be assumed to be clinically important. One explanation is rotation of the mandible, which has been stated to be the result of either extrusion of posterior teeth or downward displacement of the maxilla.18 We used bonded expanders to prevent the bite opening effect8,19 but found an approximately 1-mm increase in both groups. The other factor might be the result of a decrease in soft tissue chin thickness. Unfortunately, as stereophotogrammetric images do not provide information about subsurface structures, assessment of soft tissue chin thickness was not possible. Kilic et al.2 found no change in the soft tissue chin thickness after rapid maxillary expansion.
The change in the nasal prominence was non-significant. Similar2,9 and contrary5 results were reported.
The relation between the dentoskeletal changes and accompanying soft tissue changes was evaluated using correlation analysis. Weak correlation was found between the hard and soft tissues. These results bring us to conclude that the soft tissue effects of RME is hard predict before treatments just taking into account the dentoskeletal changes.
Advances in computer technology have enabled us to capture and superimpose 3-D images in order to evaluate soft tissue changes and prevent the information loss inherent in the use of 2-D imaging. In a recent study,12 reliability of the system was reported to be high, with a mean error of only 0.2 mm. Weinberg et al.20 compared two digital photogrammetry systems with direct physical measurements and found high intraobserver precision across the three methods. Similarly, we found no significant errors when repeat measurements were evaluated, showing high reliability of the measurements.
The best approach to evaluate treatment changes is to compare the treated samples with an untreated control group. To our knowledge, this is the first study to include a control group to distinguish the changes accompanying normal growth and development. The patients in the control group were called from the waiting list of the clinic. During the 6-month observation period, they underwent interceptive procedures (fissure sealants, space maintainers, fillings, extractions) if necessary. Immediately after 6 months of observation, all patients in the control group received orthodontic treatment including RME and fixed appliance therapy.
Within the limitations of this study, it can be concluded that alar base enlargement and backward movement of pogonion is a consequence of RME. But these minor changes were not clinically significant and their importance is questionable. Generalizability is limited because it was a single-center study with limited sample size.
CONCLUSIONS
After RME therapy, statistically significant hard tissue changes were observed compared with the untreated control group.
Soft tissue changes were similar in both groups, except the alar base, which became wider in the RME treatment group.
Soft tissue pogonion point was positioned backward in the treatment group.
Weak correlations were found between skeletal and soft tissue changes after RME therapy.
ACKNOWLEDGMENTS
This work was supported by a research grants from The Scientific and Technological Research Council of Turkey (Project 112R033) and Izmir Katip Celebi University, Scientific Research Projects Unit (Project 2013-3-TSBP-32).