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The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection
Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
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The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection Tong Xi a, *, 1, Magdalena Laskowska b, 1, Neeltje van de Voort a, Hossein Ghaeminia a, a, Thomas Maal a Wojciech Pawlak b, Stefaan Berge a b
Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6525 GA Nijmegen, The Netherlands Department of Oral and Maxillofacial Surgery, University Hospital of Wroclaw, Borowska 213, 50-556 Wroclaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Paper received 24 January 2017 Accepted 21 August 2017 Available online xxx
Objective: To quantify the postoperative changes of the dental show and chin projection following SARME using 3D CBCT imaging. Material and methods: 78 patients with transversal maxillary hypoplasia and mandibular hypoplasia who underwent SARME were enrolled into the study. A cone beam computed tomography (CBCT) scan was acquired preoperatively and at least 1 year postoperatively. 3D postoperative changes in the dental show and pogonion position were measured based on soft tissue and hard tissue landmarks. Results: 68 patients (87%) exhibited a postoperative increase in the dental show. The dental show was increased by a mean of 2.2 ± 2.0 mm (p < 0.01). The mean horizontal and vertical displacement of the chin (pogonion) following SARME was 1.6 ± 2.5 mm posteriorly and 1.6 ± 2.0 mm inferiorly (p < 0.01). An inferior displacement of the maxilla and maxillary tooth as well as a consequent clockwise pitch of the mandible seemed to play a role in inducing these postoperative changes. Conclusion: An increase in dental show and a posterior and inferior displacement of the chin should be considered prior to SARME to prevent undesirable postoperative changes of the facial esthetics. © 2017 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Keywords: 3D CBCT Chin Dental show Maxillary expansion SARME
1. Introduction Surgically assisted rapid maxillary expansion (SARME) is a commonly adopted surgical technique to expand the maxilla in skeletally mature patients with transversal maxillary hypoplasia and/or transverse occlusal problems (Mommaerts, 1999). Following the surgical separation of the maxillary segments the expansion can be performed by using either tooth-borne or bone-borne distractors (Koudstaal et al., 2005). Tooth-borne and bone-borne SARME were found to have comparable results in terms of maxillary expansion, segmental maxillary tipping, and relapse
* Corresponding author. Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, Postal Number 590, The Netherlands. Fax: þ31 24 354 11 65. E-mail addresses: [email protected] (T. Xi), magdakowalinska@gamil. com (M. Laskowska), [email protected] (N. van de Voort), [email protected] (H. Ghaeminia), wojciech.pawlak@umed. ), Thomas.Maal@ wroc.pl (W. Pawlak), [email protected] (S. Berge radboudumc.nl (T. Maal). 1 Both authors contributed equally.
(Koudstaal et al., 2009; Laudemann et al., 2010; Nada et al., 2012; Zandi et al., 2014). However, bone-borne distractors have been reported to result in slightly more anterior maxillary expansion compared with tooth-borne distractors (Pinto et al., 2001; Nada et al., 2012). Besides maxillary expansion, SARME also results in postoperative changes of the facial soft tissues. A widening of the nasal base and alar soft tissue is a frequently seen phenomenon following SARME (Ramieri et al., 2008; Metzler et al., 2014; Altindis et al., 2016). Several authors have reported a postoperative anterior and downward displacement of the maxilla, and a consequent downward and clockwise rotation of the mandible, resulting in an increase in the anterior facial height (Chung and Font, 2004; Farronato et al., 2011; Altindis et al., 2016). In addition to the findings described in earlier studies, an increase in dental show and a slight decrease in chin projection have been seen in many patients who underwent SARME in our clinic. In some patients, these effects may be clinically desirable. In other patients, however, these sideeffects can be unfavorable, and may even require additional osteotomies for secondary correction. So far, little is known with
http://dx.doi.org/10.1016/j.jcms.2017.08.023 1010-5182/© 2017 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
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T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
regard to the potentially relevant esthetic changes to the soft tissue facial profile following SARME. The use of cone-beam computed tomography (CBCT) and 3D cephalometry in the contemporary diagnosis, treatment planning, and follow-up of orthognathic patients provides accurate data on 3D changes of the jaws, facial soft tissue, and dentition (Swennen et al., 2009a,b; Schendel, 2015). With 3D image data, the dental, skeletal, and soft tissue changes after SARME can be quantified in an objective way, allowing dental show and chin projection to be analyzed systematically. The aims of this study were to quantify the postoperative changes to dental show and chin projection following SARME using 3D CBCT imaging, and to identify the contributing factors to these changes.
The mobility of the maxillary segments was checked by the activation of the distractor. In cases of asymmetric mobility, the maxilla was additionally mobilized using osteotomes at the level of the lateral nasal wall and pterygo-maxillary junction. Expansion was carried out following a latency period of 1 week. The distractors were activated at a rate of 1 mm per day until the palatal cusps of the upper teeth touched the buccal cusps of the lower teeth. When the amount of desired expansion was achieved, the TPD was locked by inserting a locking screw in the TPD appliance. The distractor was consequently replaced with a transpalatal arch on the first molars. A consolidation period of 8e10 weeks was taken into account before further orthodontic treatment using fixed appliances.
2. Material and methods
2.3. Data acquisition, 3D cephalometry, and measurements
2.1. Patients All consecutive patients treated with SARME at the Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, between 2006 and 2012, were enrolled in this retrospective cohort study. All data were anonymized prior to analysis. Approval from the regional institutional review board (CMO Arnhem-Nijmegen) was obtained for this study. This study was conducted in compliance with the World Medical Association Declaration of Helsinki on medical research ethics. Inclusion criteria were: non-syndromic patients with transversal maxillary hypoplasia and mandibular hypoplasia (class II skeletal relationship); clinically significant expansion of the maxillary dental arch following SARME; and the availability of a preoperative CBCT scan as well as a postoperative CBCT scan taken in centric occlusion prior to secondary corrective surgery (BSSO or bimaxillary osteotomy). Exclusion criteria were: incomplete CBCT scans; a previous history of orthognathic surgery; simultaneously performed orthognathic surgery other than SARME; and any form of facial surgery carried out in the period between the preoperative and postoperative CBCT scans. Two types of distractor for expanding the maxilla were used in this study e the tooth-borne Hyrax distractor, and the bone-borne TPD distractor (UNI-Smile distractor, Titamed, Kontich, Belgium). The choice of distractor was made by agreement between the orthodontist and surgeon, taking into account factors such as the amount of dental crowding and periodontal condition of the anchored teeth.
CBCT scans were acquired for each patient 1e4 weeks prior to surgery (Tpre) and after completion of the maxillary expansion following surgery (Tpost) using a standard CBCT scanning protocol (i-CAT, 3D Imaging System, Imaging Sciences International Inc, Hatfield, PA, USA) in ‘Extended Field’ modus (field of view: 16 cm in diameter; 22 cm in height; scan time: 2 20 s; voxel size: 0.4 mm). All patients were scanned while seated in a natural head position and in centric occlusion. They were asked to swallow, to relax their lips and facial muscles, and to keep their eyes open. The acquired CBCT data were saved in DICOM format and exported into Maxilim® software (Medicim NV, Mechelen, Belgium). In Maxilim, a 3D virtual head model was rendered (Swennen et al., 2009a,b). A 3D cephalometric reference frame was set up for the 3D model of a patient at Tpre according to the validated procedure described by Swennen et al. (2006). The 3D model at Tpost was superimposed on the Tpre 3D model using voxel-based registration on the unaltered subvolume of the anterior cranial base, forehead, and zygomatic arches (Nada et al., 2011). 3D cephalometric landmarks were identified for the 3D cephalometric hard tissue and soft tissue analysis to quantify the maxillary skeletal expansion, postoperative changes to dental show, and displacement of the mandible and chin (Table 1). Eight different linear and angular measurements were performed (Table 1). Dental show is defined as the distance between the landmark stomion superius and the upper incisor point along the vertical axis of the reference frame. Anterior and posterior maxillary expansions were measured, as well as the horizontal and vertical chin positions (Fig. 2).
2.2. Surgical procedure
2.4. Statistical analysis
All operations were performed or supervised by an experienced orthognathic surgeon. After nasotracheal intubation, the mucobuccal fold of the maxilla was infiltrated with local anesthetic (Ultracain DS Forte). In patients treated with Hyrax, the tooth-borne distractor was cemented with orthodontic bands on the first premolars and first molars several days prior to SARME by the orthodontist. In patients treated with TPD, the operative procedure started with the placement of the bone-borne distractor onto the hard palate. After local flap raising, the distractor was fixed to the palatal bone by means of two 7 mm self-drilling screws placed between the second premolars and first molars. The SARME procedure started with an incision in the gingivobuccal sulcus from canine to canine. After the elevation of mucoperiosteum and nasal mucosa, and detachment of soft tissue from the anterior nasal spine, the osteotomy was carried out at the level of Le Fort I using a reciprocal saw. The lateral nasal walls and nasal septum were osteotomized with nasal osteotomes. An additional midline osteotomy was performed using Epker chisels.
IBM SPSS software, version 23.0 (IBM corp., Armonk, NY, USA) was used to perform the statistical data analysis. Descriptive statistics were used to explore the results of cephalometric measurements. The normality of data distribution was assessed with the KolmogoroveSmirnov test. Covariance analysis was performed to assess changes in cephalometric measurements from Tpre to Tpost, as well as differences in patients' characteristics, and postoperative bony and soft tissue changes between the hyrax group and TPD group. Pearson's correlation coefficient was used to investigate correlations between scale variables. Multivariate linear regression analyses, with backward elimination, involving the variables age, gender, postoperative changes in occlusal plane angle, mandibular plane angle, chin height, chin advancement, vertical height between nasion and A-point, anterior and posterior maxillary expansion, and type of distractor, were carried out to identify prognostic factors for postoperative changes in dental show and chin projection. The level of significance was set at 0.05.
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
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Table 1 Definitions of the 3D cephalometric landmarks and measurements. Landmark
Definition
A-point (A) Anterior maxilla (ApN) Gonion (Go) Menton (Me) Nasion (N) Pogonion (Pog) Posterior maxilla (Zy) Sella (S) Stomion superius (lip) UI-point (UI)
The The The The The The The The The The
Bilateral
point of maximum concavity in the midline of the alveolar process of the maxilla most caudal and lateral point of the osseous nasal aperture most caudal and most posterior point of the mandibular angle most inferior midpoint of the chin on the outline of the mandibular symphysis midpoint of the frontonasal suture most anterior midpoint of the chin on the outline of the mandibular symphysis point on the posterior maxilla that is located cranially to the apex of the first upper molar center of the hypophyseal fossa (sella turcia) most inferior point of the upper lip in the midsagittal plane most inferior point on the junction between the upper central incisors
Measurement Dental show Mandibular plane angle Occlusal plane angle Vertical position of maxilla Vertical chin position Anterior maxillary width Posterior maxillary width Horizontal chin position
X X
X
Bilateral The distance from lip to UI along the vertical axis of reference frame The angle between the SN-line and the mandibular plane (a plane passing through Go and Me) The angle between the SN-line and the occlusal plane (a plane passing through UI and the mesiobuccal cusps of the first upper molars) The distance from N to A along the vertical axis of reference frame The distance from N to Pog along the vertical axis of reference frame The distance between the left and right ApN along the horizontal axis of reference frame The distance between the left and right Zy along the horizontal axis of reference frame The distance between S and Pog along the midsagittal plane of reference frame
3. Results A total of 106 patients underwent SARME between 2006 and 2012. 78 patients met the inclusion criteria and were enrolled into
the study, comprising 22 males and 56 females, with an average age of 27.2 ± 10.4 years (range 15e60) at the time of surgery (Fig. 1). The mean interval between the CBCT scan acquired prior to (Tpre) and after surgery (Tpost) was 20.3 ± 6.2 months. The cephalometric measurements of the patients' facial characteristics are presented in Table 2. All variables showed a normal distribution except for the variable dental show before surgery. 3.1. Maxilla expansion The mean anterior and posterior maxillary expansions following SARME were 1.9 ± 1.1 mm and 2.2 ± 1.6 mm, respectively (Fig. 3). No statistically significant correlation between the mean maxillary expansion and the type of palatal distractor used was detected (p ¼ 0.66; Table 3). A positive correlation between the magnitude of anterior maxilla expansion and the mandibular plane angle was found (Pearson's; r ¼ 0.24, p ¼ 0.03). However, posterior maxillary expansion was not correlated with the mandibular plane angle (Pearson's; r ¼ 0.12, p ¼ 0.31). A negative correlation between the magnitude of posterior maxillary expansion and age at surgery was seen (Pearson's; r ¼ 0.31, p < 0.05). Older patients tended to exhibit less posterior maxillary expansion than younger patients. 3.2. Dental show
Fig. 1. The inclusion and exclusion criteria for patients.
68 patients (87%) exhibited an increase in dental show (mean ¼ 2.7 mm, SD ¼ 1.8) whereas 10 patients (13%) demonstrated a decrease in dental show (mean ¼ 0.9 mm, SD ¼ 0.8). Overall, dental show increased by a mean of 2.2 mm (SD ¼ 2.0, p < 0.01) after SARME. No statistically significant correlations were found between the changes in dental show and the amount of anterior maxillary expansion (Pearson's; r ¼ 0.14, p ¼ 0.22), posterior maxillary expansion (Pearson's; r ¼ 0.14, p ¼ 0.21) or the type of palatal distractor used. Postoperative increase in dental show was also not correlated with downward displacement of the maxilla (Pearson's; r ¼ 0.11, p ¼ 0.32). Patients who exhibited a postoperative increase in dental show and those with a postoperative decrease in dental show were further analyzed for differences in postoperative soft tissue and skeletal changes (Table 4). It is worth noting that patients who had an increase in dental show after SARME exhibited a larger postoperative increase in the
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
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T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
Fig. 2. Illustrations of 3D cephalometric measurements: A measurement of dental show (lip-UI); B measurement of vertical chin position (N-Pog) and posterior maxillary width (Zyl-Zyr); C measurement of horizontal chin position (S-Pog).
Table 2 Mean postoperative changes following SARME. Variables
Mandibular plane angle ( ) Occlusal plane angle ( ) Dental show (mm) Vertical maxilla position (mm) Vertical chin position (mm) Anterior maxillary width (mm) Posterior maxillary width (mm) Horizontal chin position (mm)
Preoperative (T0)
(T1 T0)
Postoperative (T1)
Mean
SD
Mean
SD
Mean
SD
p-value
38.6 16.0 3.3 55.2 109.3 21.9 57.5 54.1
7.9 6.2 2.1 4.7 9.2 2.1 4.2 10.7
39.7 20.5 5.5 56.7 110.9 23.9 59.7 55.5
8.0 5.7 2.5 4.8 9.4 2.3 4.4 11.0
1.1 4.5 2.2 1.5 1.6 1.9 2.3 1.6
1.5 3.9 2.1 1.9 2.0 1.1 1.6 2.5
<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
SD ¼ standard deviation; p < 0.05 ¼ significant.
occlusal plane angle compared with patients whose dental show decreased postoperatively (mean difference ¼ 3.6 , p ¼ 0.01). A multivariate linear regression analysis was applied to identify prognostic factors for postoperative changes in dental show. The
regression analysis had an explained variance of 0.06 and identified the postoperative changes in the occlusal angle as a weak prognostic factor for postoperative changes in dental show (B ¼ 0.14, p ¼ 0.02). 3.3. Chin The average horizontal change in chin position (at pogonion) following SARME was 1.6 mm posteriorly (SD ¼ 2.5 mm, Table 3 Mean postoperative changes after SARME in the tooth-borne and the borne-borne appliance groups of patients.
Fig. 3. The CBCT at T0 (blue) and T1 (beige) were superimposed on the anterior cranial base, forehead, and zygomatic arches using voxel-based matching. Expansion of the anterior and posterior maxilla can be seen. Note the downward displacement of the upper incisors and the clockwise rotation of the mandible.
Variables
Tooth-borne appliance
Bone-borne appliance
p-value
Mean
SD
Mean
SD
Age (y) Dental show (mm) Mandibular plane angle ( ) Occlusal plane angle ( ) Vertical changes at A-point (mm) Vertical changes at pogonion (mm) Anterior maxillary expansion (mm) Posterior maxillary expansion (mm) Chin advancement (mm)
25.3 2.0 1.1 4.2 1.4
9.4 2.0 1.6 3.3 1.7
30.2 2.5 1.1 4.9 1.6
11.2 2.1 1.1 4.7 2.3
0.042 0.356 0.984 0.448 0.751
1.5
2.1
1.8
1.8
0.583
1.9
1.2
1.8
1.0
0.659
2.1
1.5
2.6
1.8
0.186
1.6
2.7
1.5
2.2
0.863
SD ¼ standard deviation; p < 0.05 ¼ significant.
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
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Table 4 Mean postoperative changes after SARME in the group of patients with and without postoperative increase in dental show. Variables
Postoperative increase in dental show Yes
Age (years) Dental show (mm) Mandibular plane angle ( ) Occlusal plane angle ( ) Vertical changes at A-point (mm) Vertical changes at pogonion (mm) Anterior maxillary expansion (mm) Posterior maxillary expansion (mm) Chin advancement (mm)
(n ¼ 68)
No
p-value
(n ¼ 10)
Mean
SD
Mean
SD
26.8 2.7 1.1 4.9 1.6
9.8 1.7 1.5 3.7 1.8
30.2 0.9 1.2 1.3 0.8
14.1 0.8 1.2 3.8 2.4
0.335 0.00 0.868 0.006 0.228
1.6
2.0
1.6
2.0
0.951
1.9
1.2
1.8
1.0
0.846
2.3
1.6
1.9
1.8
0.473
1.8
2.4
0.3
3.0
0.084
SD ¼ standard deviation; p < 0.05 ¼ significant.
Fig. 5. The correlation between the amount of vertical change in chin height and changes in the mandibular plane angle.
4. Discussion
Fig. 4. The correlation between the amount of postoperative chin advancement and changes in the mandibular plane angle.
range ¼ 3.4 to 8.0 mm, p < 0.01), Fig. 3. 52 patients (67%) demonstrated a posterior displacement of the chin with a mean of 2.9 mm (SD ¼ 1.9 mm), in contrast to the other 26 patients whose chin was displaced anteriorly (mean ¼ 1.1 mm, SD ¼ 0.9). Linear regression analysis identified the postoperative changes in dental show (B ¼ 0.28, p < 0.01) and mandibular plane angle (B ¼ 1.4, p < 0.001) as prognostic factors for postoperative horizontal changes of the chin (explained variance ¼ 0.69). Mandibular plane angle was well correlated to horizontal changes in the pogonion (Pearson's; r ¼ 0.81, p < 0.001 e Fig. 4). Considering postoperative vertical changes to the pogonion, 61 patients (78%) showed an inferiorly displaced chin (mean ¼ 2.4 mm, SD ¼ 1.6 mm), while in the remaining group (n ¼ 17) the chin was displaced slightly superiorly (mean ¼ 1.0 mm, SD ¼ 0.8 mm). Postoperative change in mandibular plane angle was identified as the best prognostic factor for postoperative vertical changes to the chin (explained variance ¼ 0.35, B ¼ 0.83, p < 0.001). A postoperative increase in mandibular plane angle was positively correlated to an inferior displacement of the chin (Pearson's; r ¼ 0.60, p < 0.001 e Fig. 5).
SARME with tooth-borne or bone-borne distractors is a widely used technique for correcting transverse maxillary discrepancies and has become an integral part of orthodontics and orthognathic surgery. Despite its proven effect on the skeletal widening of the maxilla, it certainly induces soft tissue and dental changes that may affect facial aesthetics (Berger et al., 1999; Ramieri et al., 2008). Respecting the 3D nature of the face, a 3D approach was used in our study to quantify parameters that are related to soft tissue, bony tissue, and dental changes. The major advantage of CBCT compared with conventional radiographs (orthopantomograph and lateral cephalogrammetry) is the possibility to render 3D head models, allowing measurements to be performed free of overprojection of anatomical structures and magnification errors. CBCT scans were acquired prior to SARME to register the pretreatment skeletal baseline values and, a minimum of 1 year after the completion of the maxillary expansion, for the 3D planning of consequent maxillary and/or mandibular osteotomies. Using voxelbased registration of the pre-SARME and post-SARME CBCT scans, soft tissue, dental, and skeletal changes could be measured without additional radiation exposure to the patients enrolled in this study. Previous studies have reported high accuracies for CBCT-based cephalometric measurements (Gribel et al., 2011; Pittayapat et al., 2015). The measurement error present in this study can be regarded as a sum of errors caused by the superimposition of CBCT scans and errors due to the manual identification of 3D cephalometric landmarks. The absolute mean distance error induced by the voxelbased registration ranged from 0.05 to 0.12 mm (Almukhtar et al., 2014). As only validated cephalometric landmarks were used by an experienced clinician, landmark identification errors were estimated to vary between the previously reported values of 0.88 mm and 1.26 mm (Swennen et al., 2006). A total measurement error of approximately 1 mm was not regarded to be clinically relevant considering the magnitude of facial morphology changes. The unique finding of this study was a mean postoperative increase in dental show of 2.2 mm; no previous data on this topic are present. There is little evidence that the postoperative increase in dental show was a result of peri-oral soft tissue changes. The effect of temporary swelling of soft tissues was eliminated in this study by
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
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T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
evaluating the patients at a minimum of 1 year after the surgical treatment. Berger et al. reported no enduring changes in the upper lip length following maxillary expansion with 1-year follow-up (Berger et al., 1999). Long-term changes of the peri-oral soft tissues were also not evident, as described by Ramieri et al. (2008). Clinical 3D facial analysis demonstrated a mean soft tissue variation of 0.38 mm in the peri-oral region when comparing two different 3D photographs that were acquired with an interval of 6 weeks. Thus, the effect of differences in the peri-oral muscle tonus and posture between the two moments of CBCT acquisition on the dental show seem to be limited. The question arises as to whether the postoperative increase in dental show was a result of the skeletal downward movement of maxilla, or an orthodontic side effect of closing the central diastema with an arch wire. Despite the mean overall postoperative increase of the distance between nasion and A-point of 1.5 mm, no significant differences in changes of the NA distance were found between patients who exhibited and those who did not exhibit a postoperative increase in dental show (Table 3). Results also showed that patients whose dental show was increased after SARME exhibited a significantly larger postoperative increase in the occlusal plane angle. An increase in the occlusal plane angle was a better predictor of the increase in dental show than the downward movement of the maxilla. These findings suggested that postSARME tooth movements certainly had played a significant role in inducing an increased dental show, alongside some skeletal displacement of the maxilla. The precise correlation between tooth movement and dental show changes is unknown because the orthodontic effect of SARME was not the focus of this study. Further clinical studies involving the analysis of post-SARME tooth movements are required to clarify the relationship between post-SARME orthodontics and changes in dental show. Besides a postoperative increase in dental show, the chin was displaced posteriorly and inferiorly by 1.6 mm and 1.6 mm respectively. These findings are in line with most of the previous studies, which have associated SARME with a postoperative downward movement of the maxilla and a subsequent downward and backward rotation of the mandible (da Silva Filho et al., 1991; Chung and Font, 2004). The observed changes in chin position could be the result of the transverse cusp-to-cusp occlusion from overexpansion, and the downward displacement of the maxilla (Davis and Kronman, 1969). Linear regression analysis showed that a postoperative increase of the mandibular plane angle, and thus a clockwise rotation of the mandible, was the main contributing factor to the postoperative posterior and inferior chin displacement. Concerning the relationship between the bone and soft tissue changes, and the type of distractor used, no significant differences were found between the tooth-borne and bone-borne devices in our study, as in most of the previous studies (Koudstaal et al., 2005; Landes et al., 2009; Verstraaten et al., 2010; Zandi et al., 2014). In spite of bone-borne distractors being proposed as a method that reduces the side-effects of tooth-borne distractors (Lagravere et al., 2006; Verstraaten et al., 2010), their influence on dental show and chin position is similar. Each technique has its own advantages and disadvantages, and so selection of the distractor device for SARME should be based on each individual patient's requirements (Zandi et al., 2014). In an era in which an increasing attention is paid by patients and professionals to the esthetic aspects of orthodontic treatment and orthognathic surgery, a good understanding of the sideeffects of SARME on the smile line and facial profile is essential. For patients with a gummy smile and retrusive chin, SARME may lead to undesirable dental and facial esthetics, whereas in patients with too little dental show and a prominent chin, SARME can be
beneficial for the facial profile. In cases where a secondary surgical correction is planned, the undesired increase of gummy smile following SARME may require a bimaxillary osteotomy, instead of a BSSO. Professionals should be aware of these effects, adjust the treatment plan to deal with the anticipated effects of SARME, and communicate these considerations to patients carefully. To be able to quantify and predict the exact changes on dental show and chin position, future clinical studies involving a meticulous analysis of post-SARME tooth movements are recommended. 5. Conclusion CBCT-based evaluation of changes in dental show and chin projection following SARME demonstrated a mean postoperative increase in dental show of 2.2 mm and a mean inferior and posterior chin displacement of 1.6 mm. These esthetically relevant postoperative soft tissue changes should be considered during treatment planning, and communicated to patients accordingly prior to surgery. Funding None. Sources of support None. References Almukhtar A, Ju X, Khambay B, McDonald J, Ayoub A: Comparison of the accuracy of voxel based registration and surface based registration for 3D assessment of surgical change following orthognathic surgery. PLoS One 9: e93402, 2014 Altindis S, Toy E, Basciftci FA: Effects of different rapid maxillary expansion appliances on facial soft tissues using three-dimensional imaging. Angle Orthod 86: 590e598, 2016 Berger JL, Pangrazio-Kulbersh V, Thomas BW, Kaczynski R: Photographic analysis of facial changes associated with maxillary expansion. Am J Orthod Dentofacial Orthop 116: 563e571, 1999 Chung CH, Font B: Skeletal and dental changes in the sagittal, vertical, and transverse dimensions after rapid palatal expansion. Am J Orthod Dentofacial Orthop 126: 569e575, 2004 da Silva Filho OG, Boas MC, Capelozza Filho L: Rapid maxillary expansion in the primary and mixed dentitions: a cephalometric evaluation. Am J Orthod Dentofacial Orthop 100: 171e179, 1991 Davis WM, Kronman JH: Anatomical changes induced by splitting of the midpalatal suture. Angle Orthod 39: 126e132, 1969 Farronato G, Giannini L, Galbiati G, Maspero C: Sagittal and vertical effects of rapid maxillary expansion in Class I, II, and III occlusions. Angle Orthod 81: 298e303, 2011 Gribel BF, Gribel MN, Frazao DC, McNamara Jr JA, Manzi FR: Accuracy and reliability of craniometric measurements on lateral cephalometry and 3D measurements on CBCT scans. Angle Orthod 81: 26e35, 2011 Koudstaal MJ, Poort LJ, van der Wal KG, Wolvius EB, Prahl-Andersen B, Schulten AJ: Surgically assisted rapid maxillary expansion (SARME): a review of the literature. Int J Oral Maxillofac Surg 34: 709e714, 2005 Koudstaal MJ, Wolvius EB, Schulten AJ, Hop WC, van der Wal KG: Stability, tipping and relapse of bone-borne versus tooth-borne surgically assisted rapid maxillary expansion; a prospective randomized patient trial. Int J Oral Maxillofac Surg 38: 308e315, 2009 Lagravere MO, Major PW, Flores-Mir C: Dental and skeletal changes following surgically assisted rapid maxillary expansion. Int J Oral Maxillofac Surg 35: 481e487, 2006 Landes CA, Laudemann K, Schubel F, Petruchin O, Mack M, Kopp S, et al: Comparison of tooth- and bone-borne devices in surgically assisted rapid maxillary expansion by three-dimensional computed tomography monitoring: transverse dental and skeletal maxillary expansion, segmental inclination, dental tipping, and vestibular bone resorption. J Craniofac Surg 20: 1132e1141, 2009 Laudemann K, Petruchin O, Nafzger M, Ballon A, Kopp S, Sader RA, et al: Long-term 3D cast model study: bone-borne vs. tooth-borne surgically assisted rapid maxillary expansion due to secondary variables. Oral Maxillofac Surg 14: 105e114, 2010 Metzler P, Geiger EJ, Chang CC, Steinbacher DM: Surgically assisted maxillary expansion imparts three-dimensional nasal change. J Oral Maxillofac Surg 72: 2005e2014, 2014 Mommaerts MY: Transpalatal distraction as a method of maxillary expansion. Br J Oral Maxillofac Surg 37: 268e272, 1999
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7 Nada RM, Fudalej PS, Maal TJ, Berge SJ, Mostafa YA, Kuijpers-Jagtman AM: Threedimensional prospective evaluation of tooth-borne and bone-borne surgically assisted rapid maxillary expansion. J Craniomaxillofac Surg 40: 757e762, 2012 Nada RM, Maal TJJ, Breuning KH, Berge SJ, Mostafa YA, Kuijpers-Jagtman AM: Accuracy and reproducibility of voxel based superimposition of cone beam computed tomography models on the anterior cranial base and the zygomatic arches. Plos One 6, 2011 Pinto PX, Mommaerts MY, Wreakes G, Jacobs WV: Immediate postexpansion changes following the use of the transpalatal distractor. J Oral Maxillofac Surg 59: 994e1000, 2001 [discussion 1001] Pittayapat P, Bornstein MM, Imada TS, Coucke W, Lambrichts I, Jacobs R: Accuracy of linear measurements using three imaging modalities: two lateral cephalograms and one 3D model from CBCT data. Eur J Orthod 37: 202e208, 2015 Ramieri GA, Nasi A, Dell'acqua A, Verze L: Facial soft tissue changes after transverse palatal distraction in adult patients. Int J Oral Maxillofac Surg 37: 810e818, 2008 Schendel SA: Computer simulation in the daily practice of orthognathic surgery. Int J Oral Maxillofac Surg 44: 1451e1456, 2015
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Swennen GR, Mollemans W, De Clercq C, Abeloos J, Lamoral P, Lippens F, et al: A cone-beam computed tomography triple scan procedure to obtain a threedimensional augmented virtual skull model appropriate for orthognathic surgery planning. J Craniofac Surg 20: 297e307, 2009a Swennen GR, Mollemans W, Schutyser F: Three-dimensional treatment planning of orthognathic surgery in the era of virtual imaging. J Oral Maxillofac Surg 67: 2080e2092, 2009b Swennen GR, Schutyser F, Barth EL, De Groeve P, De Mey A: A new method of 3-D cephalometry part I: the anatomic Cartesian 3-D reference system. J Craniofac Surg 17: 314e325, 2006 Verstraaten J, Kuijpers-Jagtman AM, Mommaerts MY, Berge SJ, Nada RM, Schols JG: Eurocran Distraction Osteogenesis G: a systematic review of the effects of boneborne surgical assisted rapid maxillary expansion. J Craniomaxillofac Surg 38: 166e174, 2010 Zandi M, Miresmaeili A, Heidari A: Short-term skeletal and dental changes following bone-borne versus tooth-borne surgically assisted rapid maxillary expansion: a randomized clinical trial study. J Craniomaxillofac Surg 42: 1190e1195, 2014
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The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection Tong Xi a, *, 1, Magdalena Laskowska b, 1, Neeltje van de Voort a, Hossein Ghaeminia a, a, Thomas Maal a Wojciech Pawlak b, Stefaan Berge a b
Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6525 GA Nijmegen, The Netherlands Department of Oral and Maxillofacial Surgery, University Hospital of Wroclaw, Borowska 213, 50-556 Wroclaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Paper received 24 January 2017 Accepted 21 August 2017 Available online xxx
Objective: To quantify the postoperative changes of the dental show and chin projection following SARME using 3D CBCT imaging. Material and methods: 78 patients with transversal maxillary hypoplasia and mandibular hypoplasia who underwent SARME were enrolled into the study. A cone beam computed tomography (CBCT) scan was acquired preoperatively and at least 1 year postoperatively. 3D postoperative changes in the dental show and pogonion position were measured based on soft tissue and hard tissue landmarks. Results: 68 patients (87%) exhibited a postoperative increase in the dental show. The dental show was increased by a mean of 2.2 ± 2.0 mm (p < 0.01). The mean horizontal and vertical displacement of the chin (pogonion) following SARME was 1.6 ± 2.5 mm posteriorly and 1.6 ± 2.0 mm inferiorly (p < 0.01). An inferior displacement of the maxilla and maxillary tooth as well as a consequent clockwise pitch of the mandible seemed to play a role in inducing these postoperative changes. Conclusion: An increase in dental show and a posterior and inferior displacement of the chin should be considered prior to SARME to prevent undesirable postoperative changes of the facial esthetics. © 2017 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Keywords: 3D CBCT Chin Dental show Maxillary expansion SARME
1. Introduction Surgically assisted rapid maxillary expansion (SARME) is a commonly adopted surgical technique to expand the maxilla in skeletally mature patients with transversal maxillary hypoplasia and/or transverse occlusal problems (Mommaerts, 1999). Following the surgical separation of the maxillary segments the expansion can be performed by using either tooth-borne or bone-borne distractors (Koudstaal et al., 2005). Tooth-borne and bone-borne SARME were found to have comparable results in terms of maxillary expansion, segmental maxillary tipping, and relapse
* Corresponding author. Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, Postal Number 590, The Netherlands. Fax: þ31 24 354 11 65. E-mail addresses: [email protected] (T. Xi), magdakowalinska@gamil. com (M. Laskowska), [email protected] (N. van de Voort), [email protected] (H. Ghaeminia), wojciech.pawlak@umed. ), Thomas.Maal@ wroc.pl (W. Pawlak), [email protected] (S. Berge radboudumc.nl (T. Maal). 1 Both authors contributed equally.
(Koudstaal et al., 2009; Laudemann et al., 2010; Nada et al., 2012; Zandi et al., 2014). However, bone-borne distractors have been reported to result in slightly more anterior maxillary expansion compared with tooth-borne distractors (Pinto et al., 2001; Nada et al., 2012). Besides maxillary expansion, SARME also results in postoperative changes of the facial soft tissues. A widening of the nasal base and alar soft tissue is a frequently seen phenomenon following SARME (Ramieri et al., 2008; Metzler et al., 2014; Altindis et al., 2016). Several authors have reported a postoperative anterior and downward displacement of the maxilla, and a consequent downward and clockwise rotation of the mandible, resulting in an increase in the anterior facial height (Chung and Font, 2004; Farronato et al., 2011; Altindis et al., 2016). In addition to the findings described in earlier studies, an increase in dental show and a slight decrease in chin projection have been seen in many patients who underwent SARME in our clinic. In some patients, these effects may be clinically desirable. In other patients, however, these sideeffects can be unfavorable, and may even require additional osteotomies for secondary correction. So far, little is known with
http://dx.doi.org/10.1016/j.jcms.2017.08.023 1010-5182/© 2017 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
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T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
regard to the potentially relevant esthetic changes to the soft tissue facial profile following SARME. The use of cone-beam computed tomography (CBCT) and 3D cephalometry in the contemporary diagnosis, treatment planning, and follow-up of orthognathic patients provides accurate data on 3D changes of the jaws, facial soft tissue, and dentition (Swennen et al., 2009a,b; Schendel, 2015). With 3D image data, the dental, skeletal, and soft tissue changes after SARME can be quantified in an objective way, allowing dental show and chin projection to be analyzed systematically. The aims of this study were to quantify the postoperative changes to dental show and chin projection following SARME using 3D CBCT imaging, and to identify the contributing factors to these changes.
The mobility of the maxillary segments was checked by the activation of the distractor. In cases of asymmetric mobility, the maxilla was additionally mobilized using osteotomes at the level of the lateral nasal wall and pterygo-maxillary junction. Expansion was carried out following a latency period of 1 week. The distractors were activated at a rate of 1 mm per day until the palatal cusps of the upper teeth touched the buccal cusps of the lower teeth. When the amount of desired expansion was achieved, the TPD was locked by inserting a locking screw in the TPD appliance. The distractor was consequently replaced with a transpalatal arch on the first molars. A consolidation period of 8e10 weeks was taken into account before further orthodontic treatment using fixed appliances.
2. Material and methods
2.3. Data acquisition, 3D cephalometry, and measurements
2.1. Patients All consecutive patients treated with SARME at the Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, between 2006 and 2012, were enrolled in this retrospective cohort study. All data were anonymized prior to analysis. Approval from the regional institutional review board (CMO Arnhem-Nijmegen) was obtained for this study. This study was conducted in compliance with the World Medical Association Declaration of Helsinki on medical research ethics. Inclusion criteria were: non-syndromic patients with transversal maxillary hypoplasia and mandibular hypoplasia (class II skeletal relationship); clinically significant expansion of the maxillary dental arch following SARME; and the availability of a preoperative CBCT scan as well as a postoperative CBCT scan taken in centric occlusion prior to secondary corrective surgery (BSSO or bimaxillary osteotomy). Exclusion criteria were: incomplete CBCT scans; a previous history of orthognathic surgery; simultaneously performed orthognathic surgery other than SARME; and any form of facial surgery carried out in the period between the preoperative and postoperative CBCT scans. Two types of distractor for expanding the maxilla were used in this study e the tooth-borne Hyrax distractor, and the bone-borne TPD distractor (UNI-Smile distractor, Titamed, Kontich, Belgium). The choice of distractor was made by agreement between the orthodontist and surgeon, taking into account factors such as the amount of dental crowding and periodontal condition of the anchored teeth.
CBCT scans were acquired for each patient 1e4 weeks prior to surgery (Tpre) and after completion of the maxillary expansion following surgery (Tpost) using a standard CBCT scanning protocol (i-CAT, 3D Imaging System, Imaging Sciences International Inc, Hatfield, PA, USA) in ‘Extended Field’ modus (field of view: 16 cm in diameter; 22 cm in height; scan time: 2 20 s; voxel size: 0.4 mm). All patients were scanned while seated in a natural head position and in centric occlusion. They were asked to swallow, to relax their lips and facial muscles, and to keep their eyes open. The acquired CBCT data were saved in DICOM format and exported into Maxilim® software (Medicim NV, Mechelen, Belgium). In Maxilim, a 3D virtual head model was rendered (Swennen et al., 2009a,b). A 3D cephalometric reference frame was set up for the 3D model of a patient at Tpre according to the validated procedure described by Swennen et al. (2006). The 3D model at Tpost was superimposed on the Tpre 3D model using voxel-based registration on the unaltered subvolume of the anterior cranial base, forehead, and zygomatic arches (Nada et al., 2011). 3D cephalometric landmarks were identified for the 3D cephalometric hard tissue and soft tissue analysis to quantify the maxillary skeletal expansion, postoperative changes to dental show, and displacement of the mandible and chin (Table 1). Eight different linear and angular measurements were performed (Table 1). Dental show is defined as the distance between the landmark stomion superius and the upper incisor point along the vertical axis of the reference frame. Anterior and posterior maxillary expansions were measured, as well as the horizontal and vertical chin positions (Fig. 2).
2.2. Surgical procedure
2.4. Statistical analysis
All operations were performed or supervised by an experienced orthognathic surgeon. After nasotracheal intubation, the mucobuccal fold of the maxilla was infiltrated with local anesthetic (Ultracain DS Forte). In patients treated with Hyrax, the tooth-borne distractor was cemented with orthodontic bands on the first premolars and first molars several days prior to SARME by the orthodontist. In patients treated with TPD, the operative procedure started with the placement of the bone-borne distractor onto the hard palate. After local flap raising, the distractor was fixed to the palatal bone by means of two 7 mm self-drilling screws placed between the second premolars and first molars. The SARME procedure started with an incision in the gingivobuccal sulcus from canine to canine. After the elevation of mucoperiosteum and nasal mucosa, and detachment of soft tissue from the anterior nasal spine, the osteotomy was carried out at the level of Le Fort I using a reciprocal saw. The lateral nasal walls and nasal septum were osteotomized with nasal osteotomes. An additional midline osteotomy was performed using Epker chisels.
IBM SPSS software, version 23.0 (IBM corp., Armonk, NY, USA) was used to perform the statistical data analysis. Descriptive statistics were used to explore the results of cephalometric measurements. The normality of data distribution was assessed with the KolmogoroveSmirnov test. Covariance analysis was performed to assess changes in cephalometric measurements from Tpre to Tpost, as well as differences in patients' characteristics, and postoperative bony and soft tissue changes between the hyrax group and TPD group. Pearson's correlation coefficient was used to investigate correlations between scale variables. Multivariate linear regression analyses, with backward elimination, involving the variables age, gender, postoperative changes in occlusal plane angle, mandibular plane angle, chin height, chin advancement, vertical height between nasion and A-point, anterior and posterior maxillary expansion, and type of distractor, were carried out to identify prognostic factors for postoperative changes in dental show and chin projection. The level of significance was set at 0.05.
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
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Table 1 Definitions of the 3D cephalometric landmarks and measurements. Landmark
Definition
A-point (A) Anterior maxilla (ApN) Gonion (Go) Menton (Me) Nasion (N) Pogonion (Pog) Posterior maxilla (Zy) Sella (S) Stomion superius (lip) UI-point (UI)
The The The The The The The The The The
Bilateral
point of maximum concavity in the midline of the alveolar process of the maxilla most caudal and lateral point of the osseous nasal aperture most caudal and most posterior point of the mandibular angle most inferior midpoint of the chin on the outline of the mandibular symphysis midpoint of the frontonasal suture most anterior midpoint of the chin on the outline of the mandibular symphysis point on the posterior maxilla that is located cranially to the apex of the first upper molar center of the hypophyseal fossa (sella turcia) most inferior point of the upper lip in the midsagittal plane most inferior point on the junction between the upper central incisors
Measurement Dental show Mandibular plane angle Occlusal plane angle Vertical position of maxilla Vertical chin position Anterior maxillary width Posterior maxillary width Horizontal chin position
X X
X
Bilateral The distance from lip to UI along the vertical axis of reference frame The angle between the SN-line and the mandibular plane (a plane passing through Go and Me) The angle between the SN-line and the occlusal plane (a plane passing through UI and the mesiobuccal cusps of the first upper molars) The distance from N to A along the vertical axis of reference frame The distance from N to Pog along the vertical axis of reference frame The distance between the left and right ApN along the horizontal axis of reference frame The distance between the left and right Zy along the horizontal axis of reference frame The distance between S and Pog along the midsagittal plane of reference frame
3. Results A total of 106 patients underwent SARME between 2006 and 2012. 78 patients met the inclusion criteria and were enrolled into
the study, comprising 22 males and 56 females, with an average age of 27.2 ± 10.4 years (range 15e60) at the time of surgery (Fig. 1). The mean interval between the CBCT scan acquired prior to (Tpre) and after surgery (Tpost) was 20.3 ± 6.2 months. The cephalometric measurements of the patients' facial characteristics are presented in Table 2. All variables showed a normal distribution except for the variable dental show before surgery. 3.1. Maxilla expansion The mean anterior and posterior maxillary expansions following SARME were 1.9 ± 1.1 mm and 2.2 ± 1.6 mm, respectively (Fig. 3). No statistically significant correlation between the mean maxillary expansion and the type of palatal distractor used was detected (p ¼ 0.66; Table 3). A positive correlation between the magnitude of anterior maxilla expansion and the mandibular plane angle was found (Pearson's; r ¼ 0.24, p ¼ 0.03). However, posterior maxillary expansion was not correlated with the mandibular plane angle (Pearson's; r ¼ 0.12, p ¼ 0.31). A negative correlation between the magnitude of posterior maxillary expansion and age at surgery was seen (Pearson's; r ¼ 0.31, p < 0.05). Older patients tended to exhibit less posterior maxillary expansion than younger patients. 3.2. Dental show
Fig. 1. The inclusion and exclusion criteria for patients.
68 patients (87%) exhibited an increase in dental show (mean ¼ 2.7 mm, SD ¼ 1.8) whereas 10 patients (13%) demonstrated a decrease in dental show (mean ¼ 0.9 mm, SD ¼ 0.8). Overall, dental show increased by a mean of 2.2 mm (SD ¼ 2.0, p < 0.01) after SARME. No statistically significant correlations were found between the changes in dental show and the amount of anterior maxillary expansion (Pearson's; r ¼ 0.14, p ¼ 0.22), posterior maxillary expansion (Pearson's; r ¼ 0.14, p ¼ 0.21) or the type of palatal distractor used. Postoperative increase in dental show was also not correlated with downward displacement of the maxilla (Pearson's; r ¼ 0.11, p ¼ 0.32). Patients who exhibited a postoperative increase in dental show and those with a postoperative decrease in dental show were further analyzed for differences in postoperative soft tissue and skeletal changes (Table 4). It is worth noting that patients who had an increase in dental show after SARME exhibited a larger postoperative increase in the
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
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T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
Fig. 2. Illustrations of 3D cephalometric measurements: A measurement of dental show (lip-UI); B measurement of vertical chin position (N-Pog) and posterior maxillary width (Zyl-Zyr); C measurement of horizontal chin position (S-Pog).
Table 2 Mean postoperative changes following SARME. Variables
Mandibular plane angle ( ) Occlusal plane angle ( ) Dental show (mm) Vertical maxilla position (mm) Vertical chin position (mm) Anterior maxillary width (mm) Posterior maxillary width (mm) Horizontal chin position (mm)
Preoperative (T0)
(T1 T0)
Postoperative (T1)
Mean
SD
Mean
SD
Mean
SD
p-value
38.6 16.0 3.3 55.2 109.3 21.9 57.5 54.1
7.9 6.2 2.1 4.7 9.2 2.1 4.2 10.7
39.7 20.5 5.5 56.7 110.9 23.9 59.7 55.5
8.0 5.7 2.5 4.8 9.4 2.3 4.4 11.0
1.1 4.5 2.2 1.5 1.6 1.9 2.3 1.6
1.5 3.9 2.1 1.9 2.0 1.1 1.6 2.5
<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
SD ¼ standard deviation; p < 0.05 ¼ significant.
occlusal plane angle compared with patients whose dental show decreased postoperatively (mean difference ¼ 3.6 , p ¼ 0.01). A multivariate linear regression analysis was applied to identify prognostic factors for postoperative changes in dental show. The
regression analysis had an explained variance of 0.06 and identified the postoperative changes in the occlusal angle as a weak prognostic factor for postoperative changes in dental show (B ¼ 0.14, p ¼ 0.02). 3.3. Chin The average horizontal change in chin position (at pogonion) following SARME was 1.6 mm posteriorly (SD ¼ 2.5 mm, Table 3 Mean postoperative changes after SARME in the tooth-borne and the borne-borne appliance groups of patients.
Fig. 3. The CBCT at T0 (blue) and T1 (beige) were superimposed on the anterior cranial base, forehead, and zygomatic arches using voxel-based matching. Expansion of the anterior and posterior maxilla can be seen. Note the downward displacement of the upper incisors and the clockwise rotation of the mandible.
Variables
Tooth-borne appliance
Bone-borne appliance
p-value
Mean
SD
Mean
SD
Age (y) Dental show (mm) Mandibular plane angle ( ) Occlusal plane angle ( ) Vertical changes at A-point (mm) Vertical changes at pogonion (mm) Anterior maxillary expansion (mm) Posterior maxillary expansion (mm) Chin advancement (mm)
25.3 2.0 1.1 4.2 1.4
9.4 2.0 1.6 3.3 1.7
30.2 2.5 1.1 4.9 1.6
11.2 2.1 1.1 4.7 2.3
0.042 0.356 0.984 0.448 0.751
1.5
2.1
1.8
1.8
0.583
1.9
1.2
1.8
1.0
0.659
2.1
1.5
2.6
1.8
0.186
1.6
2.7
1.5
2.2
0.863
SD ¼ standard deviation; p < 0.05 ¼ significant.
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
T. Xi et al. / Journal of Cranio-Maxillo-Facial Surgery xxx (2017) 1e7
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Table 4 Mean postoperative changes after SARME in the group of patients with and without postoperative increase in dental show. Variables
Postoperative increase in dental show Yes
Age (years) Dental show (mm) Mandibular plane angle ( ) Occlusal plane angle ( ) Vertical changes at A-point (mm) Vertical changes at pogonion (mm) Anterior maxillary expansion (mm) Posterior maxillary expansion (mm) Chin advancement (mm)
(n ¼ 68)
No
p-value
(n ¼ 10)
Mean
SD
Mean
SD
26.8 2.7 1.1 4.9 1.6
9.8 1.7 1.5 3.7 1.8
30.2 0.9 1.2 1.3 0.8
14.1 0.8 1.2 3.8 2.4
0.335 0.00 0.868 0.006 0.228
1.6
2.0
1.6
2.0
0.951
1.9
1.2
1.8
1.0
0.846
2.3
1.6
1.9
1.8
0.473
1.8
2.4
0.3
3.0
0.084
SD ¼ standard deviation; p < 0.05 ¼ significant.
Fig. 5. The correlation between the amount of vertical change in chin height and changes in the mandibular plane angle.
4. Discussion
Fig. 4. The correlation between the amount of postoperative chin advancement and changes in the mandibular plane angle.
range ¼ 3.4 to 8.0 mm, p < 0.01), Fig. 3. 52 patients (67%) demonstrated a posterior displacement of the chin with a mean of 2.9 mm (SD ¼ 1.9 mm), in contrast to the other 26 patients whose chin was displaced anteriorly (mean ¼ 1.1 mm, SD ¼ 0.9). Linear regression analysis identified the postoperative changes in dental show (B ¼ 0.28, p < 0.01) and mandibular plane angle (B ¼ 1.4, p < 0.001) as prognostic factors for postoperative horizontal changes of the chin (explained variance ¼ 0.69). Mandibular plane angle was well correlated to horizontal changes in the pogonion (Pearson's; r ¼ 0.81, p < 0.001 e Fig. 4). Considering postoperative vertical changes to the pogonion, 61 patients (78%) showed an inferiorly displaced chin (mean ¼ 2.4 mm, SD ¼ 1.6 mm), while in the remaining group (n ¼ 17) the chin was displaced slightly superiorly (mean ¼ 1.0 mm, SD ¼ 0.8 mm). Postoperative change in mandibular plane angle was identified as the best prognostic factor for postoperative vertical changes to the chin (explained variance ¼ 0.35, B ¼ 0.83, p < 0.001). A postoperative increase in mandibular plane angle was positively correlated to an inferior displacement of the chin (Pearson's; r ¼ 0.60, p < 0.001 e Fig. 5).
SARME with tooth-borne or bone-borne distractors is a widely used technique for correcting transverse maxillary discrepancies and has become an integral part of orthodontics and orthognathic surgery. Despite its proven effect on the skeletal widening of the maxilla, it certainly induces soft tissue and dental changes that may affect facial aesthetics (Berger et al., 1999; Ramieri et al., 2008). Respecting the 3D nature of the face, a 3D approach was used in our study to quantify parameters that are related to soft tissue, bony tissue, and dental changes. The major advantage of CBCT compared with conventional radiographs (orthopantomograph and lateral cephalogrammetry) is the possibility to render 3D head models, allowing measurements to be performed free of overprojection of anatomical structures and magnification errors. CBCT scans were acquired prior to SARME to register the pretreatment skeletal baseline values and, a minimum of 1 year after the completion of the maxillary expansion, for the 3D planning of consequent maxillary and/or mandibular osteotomies. Using voxelbased registration of the pre-SARME and post-SARME CBCT scans, soft tissue, dental, and skeletal changes could be measured without additional radiation exposure to the patients enrolled in this study. Previous studies have reported high accuracies for CBCT-based cephalometric measurements (Gribel et al., 2011; Pittayapat et al., 2015). The measurement error present in this study can be regarded as a sum of errors caused by the superimposition of CBCT scans and errors due to the manual identification of 3D cephalometric landmarks. The absolute mean distance error induced by the voxelbased registration ranged from 0.05 to 0.12 mm (Almukhtar et al., 2014). As only validated cephalometric landmarks were used by an experienced clinician, landmark identification errors were estimated to vary between the previously reported values of 0.88 mm and 1.26 mm (Swennen et al., 2006). A total measurement error of approximately 1 mm was not regarded to be clinically relevant considering the magnitude of facial morphology changes. The unique finding of this study was a mean postoperative increase in dental show of 2.2 mm; no previous data on this topic are present. There is little evidence that the postoperative increase in dental show was a result of peri-oral soft tissue changes. The effect of temporary swelling of soft tissues was eliminated in this study by
Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023
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evaluating the patients at a minimum of 1 year after the surgical treatment. Berger et al. reported no enduring changes in the upper lip length following maxillary expansion with 1-year follow-up (Berger et al., 1999). Long-term changes of the peri-oral soft tissues were also not evident, as described by Ramieri et al. (2008). Clinical 3D facial analysis demonstrated a mean soft tissue variation of 0.38 mm in the peri-oral region when comparing two different 3D photographs that were acquired with an interval of 6 weeks. Thus, the effect of differences in the peri-oral muscle tonus and posture between the two moments of CBCT acquisition on the dental show seem to be limited. The question arises as to whether the postoperative increase in dental show was a result of the skeletal downward movement of maxilla, or an orthodontic side effect of closing the central diastema with an arch wire. Despite the mean overall postoperative increase of the distance between nasion and A-point of 1.5 mm, no significant differences in changes of the NA distance were found between patients who exhibited and those who did not exhibit a postoperative increase in dental show (Table 3). Results also showed that patients whose dental show was increased after SARME exhibited a significantly larger postoperative increase in the occlusal plane angle. An increase in the occlusal plane angle was a better predictor of the increase in dental show than the downward movement of the maxilla. These findings suggested that postSARME tooth movements certainly had played a significant role in inducing an increased dental show, alongside some skeletal displacement of the maxilla. The precise correlation between tooth movement and dental show changes is unknown because the orthodontic effect of SARME was not the focus of this study. Further clinical studies involving the analysis of post-SARME tooth movements are required to clarify the relationship between post-SARME orthodontics and changes in dental show. Besides a postoperative increase in dental show, the chin was displaced posteriorly and inferiorly by 1.6 mm and 1.6 mm respectively. These findings are in line with most of the previous studies, which have associated SARME with a postoperative downward movement of the maxilla and a subsequent downward and backward rotation of the mandible (da Silva Filho et al., 1991; Chung and Font, 2004). The observed changes in chin position could be the result of the transverse cusp-to-cusp occlusion from overexpansion, and the downward displacement of the maxilla (Davis and Kronman, 1969). Linear regression analysis showed that a postoperative increase of the mandibular plane angle, and thus a clockwise rotation of the mandible, was the main contributing factor to the postoperative posterior and inferior chin displacement. Concerning the relationship between the bone and soft tissue changes, and the type of distractor used, no significant differences were found between the tooth-borne and bone-borne devices in our study, as in most of the previous studies (Koudstaal et al., 2005; Landes et al., 2009; Verstraaten et al., 2010; Zandi et al., 2014). In spite of bone-borne distractors being proposed as a method that reduces the side-effects of tooth-borne distractors (Lagravere et al., 2006; Verstraaten et al., 2010), their influence on dental show and chin position is similar. Each technique has its own advantages and disadvantages, and so selection of the distractor device for SARME should be based on each individual patient's requirements (Zandi et al., 2014). In an era in which an increasing attention is paid by patients and professionals to the esthetic aspects of orthodontic treatment and orthognathic surgery, a good understanding of the sideeffects of SARME on the smile line and facial profile is essential. For patients with a gummy smile and retrusive chin, SARME may lead to undesirable dental and facial esthetics, whereas in patients with too little dental show and a prominent chin, SARME can be
beneficial for the facial profile. In cases where a secondary surgical correction is planned, the undesired increase of gummy smile following SARME may require a bimaxillary osteotomy, instead of a BSSO. Professionals should be aware of these effects, adjust the treatment plan to deal with the anticipated effects of SARME, and communicate these considerations to patients carefully. To be able to quantify and predict the exact changes on dental show and chin position, future clinical studies involving a meticulous analysis of post-SARME tooth movements are recommended. 5. Conclusion CBCT-based evaluation of changes in dental show and chin projection following SARME demonstrated a mean postoperative increase in dental show of 2.2 mm and a mean inferior and posterior chin displacement of 1.6 mm. These esthetically relevant postoperative soft tissue changes should be considered during treatment planning, and communicated to patients accordingly prior to surgery. Funding None. Sources of support None. References Almukhtar A, Ju X, Khambay B, McDonald J, Ayoub A: Comparison of the accuracy of voxel based registration and surface based registration for 3D assessment of surgical change following orthognathic surgery. PLoS One 9: e93402, 2014 Altindis S, Toy E, Basciftci FA: Effects of different rapid maxillary expansion appliances on facial soft tissues using three-dimensional imaging. Angle Orthod 86: 590e598, 2016 Berger JL, Pangrazio-Kulbersh V, Thomas BW, Kaczynski R: Photographic analysis of facial changes associated with maxillary expansion. Am J Orthod Dentofacial Orthop 116: 563e571, 1999 Chung CH, Font B: Skeletal and dental changes in the sagittal, vertical, and transverse dimensions after rapid palatal expansion. Am J Orthod Dentofacial Orthop 126: 569e575, 2004 da Silva Filho OG, Boas MC, Capelozza Filho L: Rapid maxillary expansion in the primary and mixed dentitions: a cephalometric evaluation. Am J Orthod Dentofacial Orthop 100: 171e179, 1991 Davis WM, Kronman JH: Anatomical changes induced by splitting of the midpalatal suture. Angle Orthod 39: 126e132, 1969 Farronato G, Giannini L, Galbiati G, Maspero C: Sagittal and vertical effects of rapid maxillary expansion in Class I, II, and III occlusions. Angle Orthod 81: 298e303, 2011 Gribel BF, Gribel MN, Frazao DC, McNamara Jr JA, Manzi FR: Accuracy and reliability of craniometric measurements on lateral cephalometry and 3D measurements on CBCT scans. Angle Orthod 81: 26e35, 2011 Koudstaal MJ, Poort LJ, van der Wal KG, Wolvius EB, Prahl-Andersen B, Schulten AJ: Surgically assisted rapid maxillary expansion (SARME): a review of the literature. Int J Oral Maxillofac Surg 34: 709e714, 2005 Koudstaal MJ, Wolvius EB, Schulten AJ, Hop WC, van der Wal KG: Stability, tipping and relapse of bone-borne versus tooth-borne surgically assisted rapid maxillary expansion; a prospective randomized patient trial. Int J Oral Maxillofac Surg 38: 308e315, 2009 Lagravere MO, Major PW, Flores-Mir C: Dental and skeletal changes following surgically assisted rapid maxillary expansion. Int J Oral Maxillofac Surg 35: 481e487, 2006 Landes CA, Laudemann K, Schubel F, Petruchin O, Mack M, Kopp S, et al: Comparison of tooth- and bone-borne devices in surgically assisted rapid maxillary expansion by three-dimensional computed tomography monitoring: transverse dental and skeletal maxillary expansion, segmental inclination, dental tipping, and vestibular bone resorption. J Craniofac Surg 20: 1132e1141, 2009 Laudemann K, Petruchin O, Nafzger M, Ballon A, Kopp S, Sader RA, et al: Long-term 3D cast model study: bone-borne vs. tooth-borne surgically assisted rapid maxillary expansion due to secondary variables. Oral Maxillofac Surg 14: 105e114, 2010 Metzler P, Geiger EJ, Chang CC, Steinbacher DM: Surgically assisted maxillary expansion imparts three-dimensional nasal change. J Oral Maxillofac Surg 72: 2005e2014, 2014 Mommaerts MY: Transpalatal distraction as a method of maxillary expansion. Br J Oral Maxillofac Surg 37: 268e272, 1999
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Please cite this article in press as: Xi T, et al., The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection, Journal of Cranio-Maxillo-Facial Surgery (2017), http://dx.doi.org/10.1016/j.jcms.2017.08.023