Introduction
The aims of this study were to evaluate the long-term skeletodental effects, the volume of maxillary tuberosity, and airway space changes after maxillary molar distalization using modified C-palatal plate (MCPP) in adolescents with Class II malocclusion.
Methods
The sample consisted of 20 adolescent patients (MCPP group; mean age, 12.9 ± 1.0 year) who underwent bilateral distalization of their maxillary dentition and 20 subjects as a control group. In the MCPP group, cone-beam computed tomography images were taken before distalization, at the end of the treatment, and during retention with a minimum of a 3-year posttreatment follow up period. Repeated measures ANOVA followed by post-hoc analysis with the Bonferroni test were used to identify significant differences between time points.
Results
After the long-term observation period, sagittal skeletal and dental relationships were maintained (there were no significant changes in ANB, occlusal plane angle, and overjet postretention). The vertical skeletal dimension did not change during treatment and was stable at the long-term follow-up (the mandibular plane angle and ANS-Me were relatively well maintained). The volume of the maxillary tuberosity showed no significant change during long-term retention. However, the volume was significantly smaller in the treatment group than in the control group ( P <0.0001). There were no significant airway space changes after distalization and the postretention period. In addition, there was no significant difference between the MCPP and control groups.
Conclusions
Improved sagittal skeletal and dental relationships because of treatment were maintained in the long-term evaluation. There was no negative long-term effect on airway space associated with the maxillary arch distalization. Therefore, these findings might be beneficial for clinicians in diagnosis and treatment planning for Class II malocclusion in adolescents.
Highlights
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Adolescents were treated with maxillary molar distalization and modified C-palatal plate.
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Improved sagittal skeletal and dental relationships were maintained at 6 years.
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No negative long-term effect on airway space was observed.
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Modified C-palatal plate is a viable treatment option for adolescents.
Distalization of maxillary dentition is a viable, nonextraction treatment option for patients with Class II malocclusion. Various methods have been successfully used for molar distalization; however, it is crucial for clinicians to achieve bodily movement without extrusion during molar distalization to achieve stable results in long-term retention.
Many studies have used 2-dimensional (2D) lateral cephalograms to evaluate long-term skeletodental effects after application of different mechanics for molar distalization. It was found that distalized molars generally relapsed during fixed appliance phase with pendulum appliances but there was no significant change during the postretention period. A cervical headgear study concluded that there was a strong tendency for molars to return to their original position, whereas with anteroposterior molar correction the posttreatment skeletal effects with high-pull headgear were stable in the long-term.
The maxillary tuberosity area has been used for molar distalization because it allows distal movement of maxillary dentition, and, thus, there might be volumetric changes of maxillary tuberosity. Recently, Lee et al concluded that maxillary total arch distalization in adolescents was effective with an insignificant increase in the volume of maxillary tuberosity posttreatment.
Regarding airway space, many investigators have demonstrated that the abnormal dental position and atypical growth pattern of craniofacial structures can affect airway space. , In addition, several researches have reported that extraction treatment may decrease the size of airway space., In contrast, Park et al concluded that there was no significant effect on the airway space with both extraction and nonextraction treatment of adults.
The modified C-palatal plate (MCPP) has been introduced as an efficient and easy approach to maxillary molar distalization with minimal tipping and without molar extrusion. , However, no long-term 3-dimensional (3D) evaluations of skeletodental effects and volume of maxillary tuberosity and airway space after maxillary arch distalization using MCPPs in adolescent patients with Class II malocclusion have been reported.
Therefore, the objectives of this study were to evaluate the long-term skeletodental effects after distalization with MCPPs in adolescent patients using cone-beam computed tomography (CBCT) images and to compare the changes in the volume of maxillary tuberosity and airway space in this group with a matched control group.
Material and methods
This study was approved by the institutional review board at The Catholic University of Korea (institutional review board approval number KC18RESI0593). Subjects were informed of the study design and purpose according to the Declaration of Helsinki.
The sample consisted of 20 patients who visited the Department of Orthodontics at Seoul St. Mary’s Hospital, The Catholic University of Korea. They were treated with maxillary molar distalization using MCPP appliances (MCPP group; mean age at initial treatment, 12.9 ± 1.0; 12 girls and 8 boys), and 20 dental Class II subjects who had no previous orthodontic treatment (control group; mean age, 19.3 ± 1.6; 9 girls and 11 boys). Both control and MCPP group during retention with a minimum of a 3-year posttreatment follow up period (T3) were matched in chronological age, gender, and skeletal age ( Table I ). CBCTs in control group were taken for reasons other than this study such as an impacted tooth or some pathology.
| Characteristics | MCPP (n = 20) | Control (n = 20) | ||
|---|---|---|---|---|
| T1 | T2 | T3 | ||
| Age, y (mean ± SD) | 12.9 ± 1.0 | 14.1 ± 1.3 | 19.8 ± 1.4 | 19.3 ± 1.6 |
| Sex | ||||
| Male | 8 | 11 | ||
| Female | 12 | 9 | ||
| CVMS | CS2 (n = 8) CS3 (n = 12) |
CS3 (n = 7) CS4 (n = 13) |
CS5 (n = 4) CS6 (n = 16) |
CS5 (n = 5) CS6 (n = 15) |
CBCT images in the MCPP group were taken before distalization (T1) for a pretreatment evaluation of the anatomy, after distalization (T2) for the posttreatment evaluation (mean duration; 13.9 ± 2.3 months), and then after long-term retention (at T3) to evaluate long-term changes (mean duration; 5.9 ± 2.7 years).
The inclusion criteria for the MCPP group were (1) age range from 11 to 14 years, (2) dental Class II relationship more than 1/4 cusp, (3) mild to moderate maxillary crowding up to 5 mm, and (4) the presence of CBCT images taken immediately before distalization (at T1); at the end of orthodontic fixed appliance therapy (at T2); and during retention with a minimum of a 3-year posttreatment follow up period (at T3). The inclusion criteria for the control group (patients who visited the hospital to start orthodontic treatment or to evaluate some other pathology such as an impacted third molar) were (1) the age of 19.3 ± 1.6 years, (2) dental Class II relationship, (3) no previous orthodontic treatment, (4) CBCT images taken at 1 time point to compare with the changes in maxillary tuberosity and airway of the MCPP group, and (5) no craniofacial syndromes.
CBCT images were obtained using an i-CAT scanner (Imaging Sciences International, Hatfield, Pa). The scanning parameters were adjusted to these settings: 120 kV, 47.7 mAs, 20 seconds per revolution, field of view of no more than 17 cm in height × 23 cm in depth, and a voxel size of 0.4 mm. Each participant was seated with their head oriented in a natural head position so that the Frankfort plane was parallel to the floor and the images were taken at the intercuspal position.
The CBCT data were exported in a digital imaging and communications in medicine multifile format and imported into Invivo software (version 5.2; Anatomage, San Jose, Calif) for 3D volume rendering.
Reorientation of the head position of each scan was performed as follows; the horizontal plane (x) was defined through the right and left orbitales and the left porion, and the midsagittal plane (y) was defined as the perpendicular plane passing through nasion and anterior nasal spine. The vertical plane (z) was perpendicular to both x and y. Then, using the super-ceph module in the Invivo software, a lateral cephalometric image was created for each right and left side independently and saved in a JPG format. Each image was then superimposed on the sella-nasion line and traced using V-Ceph software (version 5.5; Cybermed, Seoul, South Korea) with the manual geometric method. , The horizontal reference line was the Frankfort horizontal plane (FH), and the vertical reference line was the perpendicular at sella (SVL).
All tracings and digitizations were made by 1 examiner (A.M.S) to minimize operator-generated variation in the measurements. A single operator (Y.A.K) inserted the MCPPs with three 2.0-mm-diameter, 8-mm-length miniscrews (Jeil Corporation, Seoul, Korea) in the paramedian area of the palate ( Fig 1 ). A palatal bar with 2 hooks was banded on the maxillary first molars. Elastics were connected from the MCPPs to the hooks of the palatal bar to apply approximately 300 g of force per side.
MCPP appliances come with 2 extended lever arms that have 3 notches on each of them. The notches are designed to provide a more secure engagement during intrusion mechanics. If the most apical hook of the plate is engaged, the force vector passes close to the center of resistance of the first molar; therefore, it results in a minimal amount of distal tipping combined with a larger amount of distalization and intrusion of the molars. When the most coronal hook is engaged, there is more distal tipping and less bodily movement, and almost no intrusion should be expected. ,
The software calculated the linear and angular dimensions between certain landmarks according to the definitions given in Figures 2 and 3 .
The bone volume of the maxillary tuberosity was measured using CBCT with Invivo5 (Anatomage). Using this software, the volume of bone under the palatal plane (ANS-PNS) and posterior to the maxillary second molar was measured mesially from the distal side of the second molar to the pterygopalatine fissure distally and pyramidal process of the palatine bone regardless of the position of the third molar ( Fig 4 , A ).
During CBCT imaging, all subjects were asked to hold their breath after the end of expiration, without swallowing, because the pharyngeal airway caliber is smallest under these conditions when subjects are awake. The scanning process was done at this time. By having the subjects hold their breath during imaging, the static pharyngeal airway size can be recorded consistently in all CBCT scans, thereby reducing variations caused by changes in pharyngeal airway caliber during the respiratory cycle ( Fig 4 , B ). This position is stable and has high reproducibility for measurement. ,
The oropharynx was divided into the following 2 areas: velopharynx and glossopharynx. The velopharynx was defined as the area from the horizontal level of the palatal plane to the horizontal level of the end of the uvula, while the glossopharynx was defined as the area from the horizontal level of the end of the uvula to the horizontal level of the C3 (the most anterior and inferior point of the third cervical vertebra). The volume of the airway space and the minimum cross-sectional area (MCA) were computed automatically by the software ( Fig 4 , B ). The amounts of change between predistalization, postdistalization, and posttreatment observation period variables were calculated. Records of 10 randomly selected patients were retraced and analyzed 2 weeks later by the same examiner. A Bland-Altman test was performed, and the result showed that no significant deviation was present outside the upper and lower limits in the maxillary tuberosity volume. Intraexaminer reliability was assessed for all variables by intraclass correlation coefficient, which showed that the measurements were reliable (ICC > 0.90).
Statistical analysis
Data analysis was performed using SPSS statistical software (version 23; IBM, Armonk, NY). Distribution of the data was examined using the Kolmogorov-Smirnov test of normality and was found to be parametric distribution. Repeated measures ANOVA followed by post-hoc analysis using the Bonferroni test were applied for comparisons. The confidence interval was set to 95% and the acceptable margin of error was set to 5%. Results were considered significant as P <0.05.
Results
The mean and standard deviation of the changes in skeletal, dental and soft tissue measurements relative to T1-T2, T1-T3 and T2-T3 are summarized in Tables II and III , respectively. Tables IV and V show changes in volume of tuberosity, airway space, and maxillary arch width measurements at T1-T2 and T2-T3.
| Variables | T1 | T2 | T3 |
|---|---|---|---|
| SNA (°) | 78.85 ± 2.41 | 77.62 ± 2.74 | 78.99 ± 3.01 |
| SNB (°) | 74.73 ± 2.65 | 75.12 ± 2.77 | 76.27 ± 3.15 |
| ANB (°) | 4.11 ± 1.05 | 2.50 ± 1.19 | 2.73 ± 1.24 |
| Palatal plane angle (°) | −2.33 ± 3.17 | −1.92 ± 3.09 | −0.66 ± 2.59 |
| Mandibular plane angle (°) | 28.58 ± 4.05 | 29.89 ± 4.72 | 29.85 ± 5.31 |
| A point-SVL (mm) | 61.72 ± 3.89 | 60.77 ± 3.56 | 61.79 ± 3.59 |
| A point-FH (mm) | 27.61 ± 2.09 | 28.92 ± 2.96 | 30.62 ± 3.47 |
| ANS-Me (mm) | 67.16 ± 5.21 | 68.59 ± 3.79 | 70.07 ± 4.91 |
| Co-Gn length (mm) | 106.66 ± 7.40 | 107.95 ± 5.56 | 110.77 ± 7.52 |
| U6-SVL (mm) | 28.68 ± 3.86 | 24.02 ± 4.39 | 26.95 ± 4.20 |
| U6r-SVL (mm) | 36.05 ± 3.66 | 31.66 ± 4.03 | 32.35 ± 4.11 |
| U6-FH (mm) | 39.07 ± 3.04 | 39.32 ± 2.81 | 42.99 ± 3.95 |
| U6r-FH (mm) | 24.57 ± 2.48 | 24.89 ± 2.91 | 28.52 ± 3.79 |
| U6 axis-FH (°) | 64.47 ± 6.57 | 62.99 ± 5.06 | 66.61 ± 4.99 |
| U1-SVL (mm) | 67.84 ± 4.92 | 64.22 ± 5.02 | 65.50 ± 4.50 |
| U1r-SVL (mm) | 58.20 ± 4.07 | 57.83 ± 3.33 | 58.92 ± 3.41 |
| U1-FH (mm) | 52.14 ± 4.00 | 54.14 ± 3.46 | 56.02 ± 4.15 |
| U1r-FH (mm) | 30.93 ± 3.16 | 31.64 ± 3.21 | 34.34 ± 3.99 |
| U1axis-FH (°) | 114.53 ± 6.47 | 105.98 ± 8.14 | 106.90 ± 5.59 |
| Occlusal plane angle (°) | 6.91 ± 3.94 | 10.68 ± 4.49 | 10.01 ± 3.33 |
| IMPA (°) | 93.70 ± 7.14 | 91.39 ± 5.87 | 93.28 ± 5.36 |
| Overjet (mm) | 4.80 ± 1.37 | 2.89 ± 0.83 | 3.16 ± 0.97 |
| Overbite (mm) | 3.99 ± 1.52 | 4.12 ± 1.15 | 3.88 ± 1.11 |
| Ls-TVL (mm) | 5.32 ± 1.91 | 3.64 ± 1.16 | 3.56 ± 1.55 |
| Li-TVL (mm) | 2.73 ± 2.79 | 1.77 ± 1.48 | 1.93 ± 1.44 |
| Soft Pog-TVL (mm) | −6.08 ± 5.41 | −8.35 ± 4.77 | −8.89 ± 5.78 |
| Nasolabial angle (°) | 94.01 ± 8.39 | 96.92 ± 9.60 | 96.03 ± 8.99 |
| Mentolabial fold (°) | 131.21 ± 9.22 | 134.20 ± 7.41 | 132.07 ± 12.64 |
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