Do changes in spheno-occipital synchondrosis after rapid maxillary expansion affect the maxillomandibular complex?

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1 A. Silvestrini-Biavati, F. Angiero*, A. Gambino, A. Ugolini University of Genoa, Italy Department of Surgical Sciences, Orthodontics Unit *Department of Surgical Sciences, the University of Genoa, Italy Conclusion After RME there were statisticallysignificant effects on spheno-occipital synchondrosis length and cranial base angle; however, these changes in the mid-term did not affect the vertical or sagittal parameters of the skeletal maxillomandibular complex. Keywords Cranial base angle; Rapid maxillary expansion; Spheno-occipital synchondrosis. Do changes in spheno-occipital synchondrosis after rapid maxillary expansion affect the maxillomandibular complex? abstract Aim This was to evaluate changes in spheno-occipital synchondrosis one year after rapid maxillary expansion (RME), in order to assess the influence that any change might have on sagittal and vertical skeletal cephalometric variables. Materials and methods Patients were selected consecutively and grouped into: Group 1 comprised 30 Caucasian patients (13 m; 17 f) undergoing RME therapy; after active expansion therapy, the Haas expander was worn as passive retainer for an average of 7 months. Group 2 as control included 14 untreated subjects (6 m, 8 f), matched by age, sex and vertebral skeletal maturity (CVM method, stages 1-3). Six cephalometric variables concerning spheno-occipital synchondrosis were studied: N-S-Ba ; SOS-Ba; SOS-S; S-Ba; Ba-N; S-N; nine skeletal variables for sagittal and vertical evaluation were also checked. T-test was used for comparing the 2 groups data. Results A statistically-significant opening of the spheno-occipital synchondrosis and increase of the posterior cranial base length (Ba-SOS) were found between group 1 and 2. After 1 year, these modifications in spheno-occipital syncondrosis produced no change in the anteroposterior or vertical skeletal parameters examined. Introduction Rapid maxillary expansion (RME) is indicated in the treatment of maxillary transverse deficiency and unilateral or bilateral crossbite. RME is used in order to widen the midpalatal suture and to correct maxillary and dental transverse discrepancies. The maxilla is connected with several bones in the head through sutures: frontomaxillary, frontonasal, frontozygomatic, nasomaxillary, zygomaticomaxillary, temporozygomatic, pterygomaxillary, internasal. When orthopedic forces are applied from RME activation to the maxillary basal bone, they may be transmitted on closed facial bones. Therefore RME may affect structures directly or indirectly related to the maxilla [Ballanti et al., 2010; Christie et al., 2010; Sun et al., 2011; Martina et al., 2012; Farronato et al., 2012]. Baydas et al. [2006], Cordasco et al. [2012], Leonardi et al. [2012] included the nasal cavity, the pharyngeal structures, the temporomandibular joints and the pterygoid process of the sphenoid bone; Leonardi et al. [2010], reported indirect effects of RME even on the spheno-occipital synchondrosis. The effect of orthopedic forces on the craniomaxillary sutures have been studied [Ghoneima et al., 2011]: animal-based research found histologic changes in suture tissue after orthopedic forces were applied, such as stretching of sutural connective tissue fibers and new bone deposition along the stretched fibers. Not all studies agree about the suture and bones involved during RME therapy. Gardner and Kronman [1971] found changes in lambdoid, parietal, and midsagittal sutures in rhesus monkeys; Kudlick [1973] postulated the involvement of all craniofacial bones adjacent to the maxilla, except the sphenoid bones. Wertz and Dreskin [1977] found that the maxilla moved downward and forward during midpalatal suture opening; conversely, Timms [1980] showed that the maxilla and palatine bones moved apart, along with the pterygoid processes of the sphenoid bone. Leonardi et al. [2010] reported the opening of zygomaticomaxillary, frontomaxillary and internasal sutures. Suture changes after RME therapy have been suggested to induce changes in the craniofacial complex growth. In particular, it has been hypothesised that the cranial base is a guide for the development of the maxilla, midface, and lower facial complex, and its modification 63 European Journal of Paediatric Dentistry vol. 14/ art_sincondrosi.indd 63 19/02/13 17:16

2 Silvestrini-Biavati A. et al. could affect the maxillomandibular complex [Proff et al., 2008]. To asses this hypothesis, the effects of RME on the cranial base and the spheno-occipital synchondrosis have been investigated [Iseri et al., 1998; Jafari et al., 2003; Baydas et al., 2006; Holberg and Rudzki-Janson, 2006; Rukkulchon and Wong, 2008; Cendekiawan et al., 2008; Leonardi et al.,2010]. Some of these studies have hypothesised that opening of the synchondrosis could account for the forward and downward displacement of the maxilla. Some studies report a downward and forward movement of the maxilla when the midpalatal suture opens, due to displacement of the maxillocranial sutures [Garib et al., 2005]. Some of these studies are limited to short-term evaluation; some lack control groups, and others are based on animal or experimental models, such as finite element analyses. The aim of this controlled study is to evaluate changes in cranial base features one year after RPE therapy, in order to assess the influence such changes may have on sagittal and vertical skeletal cephalometric variables. Materials and methods Subjects were treated from 2008 to 2011 at the Department of Orthodontics, Faculty of Dentistry, Genoa University; they were selected consecutively, according to skeletal maturity as evaluated by means of the CVM method [Baccetti et al., 2006]. All subjects presented cervical vertebral stages 1-3 (CVS 1 3) evaluated on lateral cephalograms, at T1. Exclusion criteria were: previous orthodontic treatment, hypodontia in any quadrant (excluding third molars), hormonal imbalance, temporomandibular joint symptoms, craniofacial abnormalities, arthritis, inadequate radiographs (poor quality at the cranial base area or unknown magnification factor). Thirty patients matched with inclusion criteria (13 m, 17 f; mean age 8.0±1.5 years, at T1). Subjects characteristics were: Class I or Class II division 1 malocclusion (18 and 12 patients, respectively) with transverse maxillary deficiency and posterior unilateral crossbite at treatment onset (T1). The records available included dental casts, panoramic radiographs and lateral cephalometric head films at pretreatment stage (T1) and one year after the end of active expansion (T2). The study group (group 1) underwent tooth-tissue supported (Haas type) RME, expanded by 2 turns a day (0.20 mm per turn). When the desired overcorrection for each patient had been achieved, the appliance was stabilised. Expansion was considered adequate when the occlusal aspect of the maxillary lingual cusp of maxillary first molars contacted the occlusal aspect of the facial cusp of the mandibular lower first molars. The Haas expander remained on the teeth as passive retainer for an average of 7 (SD ±2) months, after which a removable palatal plate, with Adams clasp on the first maxillary molars, was worn full-time. T2 was after a minimum of 6 months of removable palatal plate wear (1.1±0.4 years, at T2). For all patients, crossbite was corrected at the end of active expansion. The control group (group 2) comprised 14 subjects (6 m, 8 f; mean age 7.6±1.7 years, at T1) with untreated cross-bite, matched by age, sex and skeletal maturity. Control subjects presented Angle Class I (n=8) or Class II, division 1 (n=6) malocclusions and transverse maxillary deficiency with posterior unilateral crossbite; they had postponed orthodontic treatment for economic reasons. Cephalometric analysis Cephalograms were traced digitally, by a single examiner, using Ceph Basic v software (Image Instruments GmbH, Chemnitz Germany). Landmark location and accuracy of the anatomic outlines was verified by a second senior clinician (ASB). Cephalometric points selected are showed in figures 1 and 2. Six cranial base measurements [N-S-Ba ; SOS-Ba(mm); SOS-S(mm); S-Ba(mm), S-N(mm) and Ba-N(mm)] and eight skeletal variables (SNA ; SNB, AFH/PFH(mm), Jarabak s Sum S, S-N/Go-Me, N-S-Ar, S-Go(mm) and Ar-Go-Me ) were determined. To analyse method error, five randomlyselected lateral cephalometric radiographs were digitally retraced. A combined error of landmark location, tracing, and measurement was determined. Intraclass correlation coefficients (ICC) were used to determine intra- and inter-rater agreement for each cephalometric variable. Correlation coefficients for the skeletal measures were greater than Linear measurement errors averaged 0.4 mm (SD 0.6 mm), and angular measurement errors averaged 0.5 (SD 0.5 ). Statistical analysis Descriptive statistics were calculated for each variable. The Shapiro-Wilks test demonstrated the normal distribution of data, thus parametric statistics could be applied. Patients data were compared with data from the control group using parametric t-tests. Probabilities of <0.05 were accepted as significant in all statistical analyses. The power of the study was adequate (>0.83), calculated a priori using the mean values and standard deviations of N-S-Ba reported by Maestripieri et al. [(2002] at an alpha of Results There were no significant differences between the two groups regarding age and skeletal maturity. No significant differences in any of the variables used in the study were found between genders, thus data concerning the two genders were pooled for analysis. Baseline (T1) and followup (T2) cephalometric measurements are summarised in Table 1. During the treatment period (T1 to T2), study and control groups showed significant changes in all cranial base variables, except for N-S-Ba ( ) and BA-SOS (mm) 64 European Journal of Paediatric Dentistry vol. 14/ art_sincondrosi.indd 64 19/02/13 17:16

3 Relationship between synchondrosis and the maxillomandibular complex fig. 1 Cephalometric analysis: Gonion (Go), Menton (Me), Nasion (N), Articulare (Ar), Sella turcica (S), A point (A), B point (B), Basion (Ba), Sphenoccipital Synchondrosis (SOS), the most posterior point of the spheno-occipital synchondrosis on the sphenoid bone. in the control group. A statistical comparison of changes from T1 to T2 in RME group versus control group showed significant differences in three cranial base variables (N-S- Ba, Ba-SOS, S-Ba). There was no statistical difference between the two groups regarding sagittal and vertical changes (Table 1). Discussion fig. 2 Sphenooccipital synchondrosis area: SOS-S (mm); SOS-Ba (mm); S-Ba (mm). A recent CT scan study on patients with transverse maxillary deficiency showed that intermaxillary, internasal, nasomaxillary, frontomaxillary, and frontonasal sutures were affected by the mechanical forces generated by RME [Ghoneima et al., 2001]. After RME therapy, another study found significant opening in zygomaticomaxillary, frontomaxillary and internasal sutures [Leonardi et al., 2011]. Unfortunately, neither of these studies analyses changes in the spheno-occipital synchondrosis. Although various studies have demonstrated that the posterior cranial base and spheno-occipital synchondrosis are involved during RME therapy, only recently a clinical CBCT study showed that RME leads to a significant immediate widening of the spheno-occipital synchondrosis in young subjects [Leonardi et al., 2010]. Opening of the spheno-occipital synchondrosis and stresses acting upon the cranial base during RME therapy have also been demonstrated in finite element studies [Iseri et al., 1998; Jafari et al., 2003; Holberg and Rudzki-Janson, 2006], and animal model research [Rukkulchon and Wong, 2008; Cendekiawan et al., 2008]. Although the radiation dose of a CBCT scan is lower than that of a CT scan, CBCT is not suitable for regular monitoring of orthodontic patients and it is questionable whether it is appropriate to perform more than one CBCT scan per year. Moreover, Kokich [2010] suggested that ethical implications should be examined about CBCT, since it is not known which orthodontic cases benefit from 3D imaging, and what risks might be entailed in a CBCT scan, especially in growing patients. For these reasons, in order to avoid any X-ray damage to the patients involved in this study, we analysed changes occurring to the cranial base region after RME therapy on traditional cephalograms. The group of patients who underwent RME treatment was compared to a group of untreated control subjects, matched by age, sex and skeletal maturity. All subjects were selected before the pubertal peak (CVM 1 3), since it has been shown that, at these three stages, RME patients undergo significant and more effective long-term changes at the skeletal level, in both maxillary and circummaxillary structures [Baccetti et al., 2001]. The control group of untreated subjects was also used to identify confounding factors, such as the expression of craniofacial growth and development during the study period. The untreated group showed craniofacial growth with significant changes in the same variables, except for N-S-Ba and Ba-SOS. The statistical comparison of the changes between T1 and T2 in the two groups demonstrated significant differences in the three cranial base variables (N-S-Ba, Ba-SOS, S-Ba) (Table 2). These results support the hypothesis of a potential involvement of the cranial base structures during RME therapy. Specifically, we found a small but statistically significant opening of the cranial base angle (N-S-Ba ) in the RME group, with an increase in the posterior cranial base length (BA-SOS). The cranial base angle and spheno-occipital synchondrosis are interesting due to the relationship between the degree of cranial base flexion and type of malocclusion that has been suggested [Dhopatkar et al., 2002]. The spheno-occipital synchondrosis is also involved because growth of this structure causes the anterior cranial base with its attached maxillary complex to displace upward and forward, away from the foramen magnum. The mandible, maintaining a constant sagittal relationship with the foramen magnum, grows downward and forwards, away from the cranial base [Coben, 1998]. In our study, we found that all sagittal variables in the European Journal of Paediatric Dentistry vol. 14/ art_sincondrosi.indd 65 19/02/13 17:16

4 Silvestrini-Biavati A. et al. RME Group (n=30) Control Group (n=14) T1 T2 p T1 T2 p Age (y) Mean SD AFP/PFH (%) Mean NS NS SD SNA Mean NS ,3 NS SD SNB Mean NS NS SD S/N-Go/Me Mean NS NS SD N-S-Ba Mean < NS SD Ba-SOS (mm) Mean < NS SD S-SOS (mm) Mean < SD S-Ba (mm) Mean < SD Ba-N (mm) Mean < SD Σ ( ) Mean NS NS SD N-S-Ar ( ) Mean NS NS SD Ar-Go-Me ( ) Mean NS NS SD S-Go (mm) Mean NS NS SD S-N (mm) Mean < SD table 1 Statistical Comparison of T1 T2 Changes. SD: standard deviation; NS: not significant. Net Difference T2-T1 RME Group Control Group p Age (y) NS AFP/PFH (%) NS SNA NS SNB NS N-S-Ba Ba-SOS (mm) S-SOS (mm) NS S-Ba (mm) <0.01 Ba-N (mm) NS Σ ( ) NS S-N/Go-Me( ) NS N-S-Ar ( ) NS Ar-Go-Me ( ) NS S-Go (mm) NS S-N (mm) NS table 2 Statistical Comparison of T1 T2 net differences. NS: not significant. RME group were similar in value to those of the control group, throughout the study period (Table 1) and that they did not show any significant correlation with cranial base modifications. It is widely reported that, immediately after expansion, there is a downward maxillary displacement and an extrusion of the supporting teeth, leading to 66 European Journal of Paediatric Dentistry vol. 14/ art_sincondrosi.indd 66 19/02/13 17:16

5 Relationship between synchondrosis and the maxillomandibular complex downward and backward mandibular rotation; however, this is thought to be an ephemeral phenomenon [Garib et al., 2005; Lagravere et al., 2005; Lagravere et al., 2006]. We found no significant differences in the vertical skeletal variables one year after expansion therapy. As several studies have shown, although RME causes vertical maxillary displacement, this vertical alteration is not significant in the mid- or long-term [Garib et al., 2005; Lagravere et al., 2005; Lagravere et al. 2006]. Involvement of the spheno-occipital synchondrosis might have important clinical implications, such as the beneficial effect of RME in young Class III patients, because the suture opening might displace the maxilla forward and downward [Leonardi et al., 2010], but there is no general agreement [Garib et al., 2005] that, when the midpalatal suture opens, the maxilla moves downward and forward, because of the placement of the maxillocranial sutures. We obtained results similar to those of reports [Velasquez et al, 1996; Chang et al, 1997; Garib et al., 2005; Lagravere et al., 2005; Lagravere et al. 2006], showing that the skeletal changes in patients treated with RME were non clinically relevant, after taking into consideration the natural alterations resulting from individual facial growth. However we foud that maxillary expansion therapy did produce significant changes in the spheno-occipital syncondrosis area, but that these changes had not modified the craniofacial complex one year after the active expansion phase, neither in the sagittal nor in the vertical planes. Conclusions This mid-term controlled study showed that RME therapy leads to immediate significant effects on the spheno-occipital synchondrosis: an opening of the cranial base angle and an increase of the posterior cranial base length (Ba-SOS). One year after RME therapy, these changes had not modified the craniofacial complex in either the sagittal or the vertical skeletal patterns. References Baccetti T, Franchi L, Cameron CG, McNamara JA, Jr. Treatment timing for rapid maxillary expansion. Angle Orthodontist. 2001;71: Baccetti T, Franchi L, De Toffol L, Ghiozzi B, Cozza P. The diagnostic performance of chronologic age in the assessment of skeletal maturity. 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