Abstract
Surgically assisted rapid palatal expansion (SARPE) is associated with postoperative cephalometric changes. In this study we analyse these changes in the sagittal plane in orthognathic patients undergoing SARPE followed by orthodontic treatment and Le Fort I, bilateral sagittal split osteotomy (BSSO), or bimaxillary surgery. This is a retrospective review of 50 patients (20 males, 30 females) undergoing orthognathic treatment with SARPE to correct transversal deficiency of the maxilla as part of a comprehensive treatment plan. PP-SN, SNA, and ANB angles were increased and U1-SN and U1-PP angles were decreased. All changes were statistically significant. Changes of SNB, PP-Mand plane angle, and SN-Mand. plane angle were not statistically significant. Surgically assisted rapid palatal expansion using a bone-borne appliance as a preparative step for later orthognathic surgery results in clockwise rotation of the maxilla.
In orthognathic surgery, correction of the maxillary transversal dimension via Le Fort I expansion osteotomy is one of the least stable movements . Relapse is most common during the first postoperative year. The authors’ approach to correct transverse maxillary deficiency in non-syndromic adolescent or adult orthognathic patients is to perform multisegmental Le Fort I osteotomy when an expansion of less than 5 mm in the molar area is needed in adults or when a dual-plane maxilla is present. In other cases, a preliminary surgically assisted rapid palatal expansion (SARPE) is preferred . This operation is performed at least 1 year before the planned Le Fort I procedure and allows for simultaneous extraction of premolars and/or third molars, because of the bone-borne nature of the transpalatal distractor.
Transverse maxillary hypoplasia is a frequent finding in non-syndromic adolescents and adults . Non-surgical treatment options to correct transverse maxillary hypoplasia in children and young adolescents are slow maxillary expansion (SME) for mild discrepancies or rapid maxillary expansion (RME) for more severe cases. Owing to the increased skeletal resistance, RME in adults is associated with alveolar bending, periodontal ligament compression, buccal root resorption of the anchor teeth, fenestration of the buccal cortical plate, and tipping and extrusion of the anchor teeth . The negative effects are presumably due to the tooth-borne anchorage of conventional appliances. Tooth-borne appliances deliver stress to the roots and periodontal ligament as well as the alveolar bone during expansion. Additionally, the bony movement is not retained during the consolidation period . This led to the introduction of the first bone-borne appliance (distractor) in 1999, which delivers the expansion force directly to the maxillary bone and avoids the negative orthodontic and periodontal effects .
After M ommaerts introduced the ‘Transpalatal Distractor’ (TPD) in 1999, researchers evaluated the dental and skeletal effects of this appliance. Most of these studies focused on the amount of transverse expansion after activating TPD or its dental and periodontal effects . In this study the authors analyse the lateral cephalometric changes associated with TPD.
Materials and methods
Of 280 patients treated by SARPE using TPD from July 2000 to February 2010 in Hasselt University, Belgium, 50 patients (20 male, 30 female) who also underwent orthognathic surgery after palatal expansion were selected.
Pretreatment records, including posteroanterior (PA) and lateral cephalograms, panoramic and periapical radiographs, intraoral and extraoral photographs, and study models were taken for all patients. The lateral cephalometric radiograph was taken using the Orthophos XG Plus (SIRONA Company). Using Onyx software, the SNA, SNB, ANB, PP-SN plane angle, PP-Mand. (angle between palatal plane and mandibular plane), SN-Mand. angle (angle between SN plane and mandibular plane), U1-palatal plane angle, and U1-SN plane angle were measured and recorded ( Fig. 1 ).
Under general anaesthesia, M ommaerts ’ TPD appliance was mounted onto the molar region of the palate. Mid-palatal osteotomy with Le Fort I osteotomy and nasal and pterygopalatal disjunction was performed in all patients ( Fig. 2 ). Adequate mobilization of the maxillary halves was checked both with the osteotome and with activation of the TPD, until a central diastema of a few millimetres was reached. The TPD screw was then turned until a central diastema of 1 mm was reached and the lock screw was placed. In patients requiring only minimal expansion in the anterior region and wide expansion in the posterior region, an anterior blockage was applied from the left to the right upper incisor. Between the fifth and seventh postoperative days, patients were evaluated for removal of the lock screw and to begin activation of the TPD at 120° (0.33 mm) a day. During the activation period, patients were seen each week until the desired expansion was achieved. No overcorrection was done. 12 weeks after surgery, the patient’s orthodontist started orthodontic treatment. The distractor was kept in place for a maximum of 9 months to minimize the risk of relapse. After completion of orthodontic treatment, standard imaging (panoramic radiograph, PA, lateral cephalograms and occlusal view) were taken. Postoperatively, the SNA, SNB, ANB, PP-SN plane, PP-Mand. angle, SN-Mand. angle, U1-palatal plane, and U1-SN plane angle changes were evaluated.
Statistical methods
To evaluate patterns within the data, EDA was performed. Descriptive statistics including means and standard deviations (SD) for each measurement of each angle were calculated.
Student’s paired t -test was used to compare preoperative and postoperative data for each patient. The paired t -test provides a hypothetical evaluation of the difference between population means for a pair of random samples whose differences are approximately normally distributed.
Regression analysis was performed to investigate the ability to predict postoperative PP-SN angle based on patient characteristics.
The Institute for Biostatistics at Hasselt University performed all statistical analyses.
Results
The patient group consisted of 50 patients, 35 (70%) had class II occlusion and 15 (30%) had class III occlusion. The average age of the participants was 26 years (range 15–49 years); none were younger than 15 years. Follow-up measurements were performed after completion of orthodontic alignment of the upper and lower jaw before orthognathic surgery (Le Fort I, bilateral sagittal split osteotomy (BSSO), bimaxillary surgery) (20 ± 9 months).
EDA
Table 1 shows that angles did not change in a minority of patients. Most patients had decreased UI-SN and UI-PP angles and increased SNA, PP-SN, and ANB angles after surgery. For PP-Mand., SN-Mand., and SNB, the number of patients with increasing versus decreasing angles were similar. This is confirmed by paired t -test analysis ( Table 2 ).
| Angle (°) | Direction of change | ||
|---|---|---|---|
| Increase (+) | Decrease (−) | No change (difference = 0) | |
| UI-SN | 13 | 35 | 2 |
| UI-PP | 13 | 36 | 1 |
| PP-SN | 29 | 11 | 10 |
| PP-Mand. | 23 | 22 | 5 |
| SNA | 35 | 9 | 6 |
| SNB | 22 | 21 | 7 |
| ANB | 30 | 7 | 13 |
| SN-Mand. | 29 | 16 | 5 |
| Angle (°) | Pre surgery | Post surgery | Change | 95% CI Change | Prob. | ||||
|---|---|---|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | Mean | SD | Lower | Upper | ||
| U1-SN | 102.6 | 9.39 | 97.78 | 8.32 | −4.82 | 8.94 | −7.36 | −2.28 | 0.000 * |
| U1-PP | 108.22 | 9.33 | 104.36 | 8.33 | −3.86 | 8.56 | −6.29 | −1.43 | 0.002 |
| PP-SN | 5.62 | 3.66 | 6.56 | 3.89 | 0.94 | 2.13 | 0.33 | 1.55 | 0.003 * |
| PP-Mand. | 34.88 | 7.78 | 34.66 | 8.47 | −0.22 | 3.38 | −1.18 | 0.74 | 0.648 |
| SNA | 80.3 | 4.08 | 81.9 | 3.74 | 1.60 | 2.57 | 0.87 | 2.33 | 0.000 * |
| SNB | 76.46 | 5.54 | 76.92 | 5.80 | 0.46 | 2.61 | −0.28 | 1.20 | 0.219 |
| ANB | 3.94 | 4.38 | 5 | 4.30 | 1.06 | 2.00 | 0.49 | 1.63 | 0.000 * |
| SN-Mand. | 40.5 | 7.67 | 41.16 | 8.19 | 0.66 | 3.03 | −0.20 | 1.52 | 0.131 |
* Changes statistically significant with α = 5%. The null hypothesis is that there is no change after SRPE in the sagittal planes or angles (two sided Student’s paired t -test). For abbreviations see Table 1 .
For U1-SN and U1-PP angles, the majority of patients had a decreased measurement following surgery. For the PP-SN, SNA, and ANB angles more patients had increased rather than decreased values. Student’s paired t -test was used to determine the statistical significance of these changes.
Student’s paired t -test
Changes in U1-SN and U1-PP angles (retroclination of upper incisors towards SN or PP, respectively) and PP-SN, SNA, and ANB angles (clockwise rotation of palatal plane and increase of SNA and ANB) were statistically significant ( Fig. 3 ). Changes in PP-Mand., SNB, and SN-Mand. were not statistically different.
PP-SN plane angle
As shown in Fig. 3 , the PP-SN plane angle increased after surgery. On regression analysis, only a few response variables were available for analysis (PP-SN post jaw surgery with the covariates PP-SN pre surgery, gender, age, and occlusion). Table 3 shows that after TPD, male patients had a higher tendency towards a clockwise rotation of PP than female patients. This is indicated in the boxplot diagram in Fig. 4 . Table 4 shows descriptive statistics for PP-SN by occlusion. Class II patients tend to have smaller PP-SN values than Class III patients both pre- and post-SARPE ( Fig. 5 ).
| Gender | N | Minimum | Maximum | Mean | SD | |
|---|---|---|---|---|---|---|
| Female | PP-SN(pre) | 30 | −1 | 15 | 5.20 | 3.458 |
| PP-SN(post) | 30 | 0 | 16 | 5.77 | 3.839 | |
| Male | PP-SN(pre) | 20 | 1 | 15 | 6.25 | 3.945 |
| PP-SN(post) | 20 | 1 | 16 | 7.75 | 3.740 | |
| Occlusion | N | Minimum | Maximum | Mean | SD | |
|---|---|---|---|---|---|---|
| Class III | PP-SN(pre) | 15 | 1 | 15 | 6.67 | 4.100 |
| PP-SN(post) | 15 | 1 | 16 | 7.13 | 3.662 | |
| Class II | PP-SN(pre) | 35 | −1 | 13 | 5.17 | 3.417 |
| PP-SN(post) | 35 | 0 | 16 | 6.31 | 4.006 | |
To determine if age affects PP-SN angle after surgery, the authors created a scatter plot ( Fig. 6 ). As Fig. 6 shows, there is no relationship between age and PP-SN plane angle.
The correlation between PP-SN angle before (PP-SN pre) and after (PP-SN post) SARPE was established and is shown with the scatter plot presented in Fig. 7 . Patients with a lower PP-SN before surgery tend to have a lower PP-SN postoperatively. A higher preoperative PP-SN was associated with a higher postoperative PP-SN (post). The correlation between PP-SN before and after surgery is 0.84.
Regression analysis
Both the available covariates and their possible interactions were included to find the best statistical model. Confirmation of the assumption of regression analysis is also needed. The following model was reached:
y ˆ = − 1.331 + 0.897 PPSNpre + 1.483 GENDER + 0.063 AGE + 0.768 OCCLUSION
The significance of each covariate can be seen in Table 5 . The presurgical PP-SN angle has a significant effect on postoperative PP-SN angle. A unit increase in PP-SN before surgery leads to an increase in the post surgery PP-SN angle of 0.897 when other variables are held constant. Gender also affects PP-SN angle. Male patients tend to have an increased angle post surgery compared with female patients. The covariates, age and occlusion, had no significant effect on postoperative PP-SN. In the regression analysis, no assumption is violated.
| Model | Coefficients | t | Sig. | |
|---|---|---|---|---|
| B | SE | |||
| (Constant) | −1.331 | 1.296 | −1.027 | .310 |
| PPSN(pre) | .897 | .081 | 11.133 | .000 * |
| Gender | 1.483 | .619 | 2.396 | .021 * |
| Age | .063 | .036 | 1.740 | .089 |
| Occlusion | .768 | .656 | 1.170 | .248 |
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