Abstract
There are few studies on maxillomandibular skeletal alterations. Twenty-one patients with unilateral coronal craniosynostosis were analysed and compared with controls. Landmarks analysed were: sella-nasion-point A and B angles, point A-nasion-point B angle, interincisal angle, angle of superior incisor axis on the sella-nasion plane, lower incisor to mandibular plane angle, Frankfort mandibular plane angle, zygomatic-frontal suture (Z), point on the most concave part of pyramidal apophysis of the upper maxilla (Mx), antegonial incisure (AG), upper (UMT) and lower (LMT) molar teeth. Differences were significant for class II dentoskeletal occlusion ( p < 0.0001), mandibular hyperdivergence ( p < 0.0001), lingualization of superior incisor ( p < 0.005), deviation of inferior interincisal contralateral line to the synostosis ( p < 0.0001) in the plagiocephalic population. Compared with contralateral counterpoints, Z ( p < 0.05), Mx ( p < 0.005) and UMT ( p < 0.0005) on the affected side were closer to the midline; AG ( p < 0.0005) and LMT ( p < 0.05) were further from it. On the frontal plane, Z, Mx, UMT, LMT and AG on the affected side were higher. Vertical and transversal contraction of the jaw of the synostotic side and laterodeviation of the mandibular interincisal line of the contralateral synostotic were clear. The altered position of the glenoid cavity, anteriorized in unilateral coronal craniosynostosis, could be the cause of mandibular dentoskeletal asymmetry.
‘Plagiocephaly’ is a generic term used to indicate the presence of a cranial asymmetry. This refers exclusively to the morphology of the cranium and not to the aetiology of the malformational condition. Various classifications of plagiocephaly have been proposed, although no consensus has been reached . C ohen and M acLean have outlined plagiocephalies in synostotic and deformational forms, each of which can be anterior or posterior. Deformational plagiocephaly is the consequence of external factors, such as pressure exerted on the cranium in the uterus or postnatally. Synostotic plagiocephalies are the result of altered cranial growth due to early closure of a cranial suture. In synostotic posterior plagiocephaly, the cranial suture involved is the lambdoid suture. In synostotic anterior plagiocephaly, the coronal hemi-suture, the fronto-sphenoidal suture, or the fronto-zygomatic suture unilaterally can be involved . Frontal sphenoid and fronto-zygomatic sutures are involved in only a few patients, but unilateral coronal craniosynotosis is the second most common non-syndromic craniosynostosis, with an estimated incidence of 0.4–1 in 1000 live births . It is considered the most common heritable form of single-suture fusion. A mutation of fibroblast growth factor receptor III (FGFR 3P250R ) is present in about 10% patients affected with unilateral coronal craniosynostosis . Unilateral coronal craniosynostosis is associated with altered facial growth. Cranio-orbital clinical characteristics of unilateral coronal craniosynostosis include displacement towards the superposterior of the ipsilateral superior orbital edge, compression of the ipsilateral frontal region, deviation of the nose root towards the affected side, and the ipsilateral ear positioned anterosuperiorly . Various authors have described the cranial and orbital characteristics of unilateral coronal craniosynostosis, but there are only a few studies on maxillomandibular skeletal alterations . The aim of this study is to determine if there are occlusion and maxillomandibular skeletal alterations in patients affected with unilateral coronal craniosynostosis.
Patients and methods
From February 1993 to September 2007, 21 patients affected with unilateral coronal craniosynostosis were enrolled in this study; patients with syndromic craniosynostosis were excluded. The clinical, photographic and radiographic documentation of all patients was analysed. Data were collected on the age of the patients, the sutures involved, the primary affected side, the surgical operation and the age of the patient when it was performed. Data were also collected from cephalometric investigations conducted from chalk models of dental arcades and from intra and extra oral photographs of the patients before starting orthodontic therapy and clinical files and entered into a spreadsheet. The clinical occlusion parameters investigated were: presence of overjet, overbite, crossbite, intermolar and intercanine mandibular diameter, deviation from the superior and inferior interincisal line, molar and canine class. Cephalometric analyses were performed for every patient on cranial teleradiographies on posteroanterior and laterolateral projections. The following were sought on normal lateral cephalometry: sella-nasion-point A angle (SNA), sella-nasion-point B angle (SNB), point A-nasion-point B angle (ANB), interincisal angle, the angle of the superior incisor axis on the sella-nasion plane (1/SN), lower incisor to mandibular plane angle (IMPA), Frankfort mandibular plane angle (FMA). Two groups of parameters were evaluated in the posteroanterior cephalometry. The first group included the distances on the transversal plane of zygomatic-frontal suture (Z), the point on the most concave part of pyramidal apophysis of the upper maxilla (Mx), antegonial incisure (AG), upper molar teeth (UMT) and lower molar teeth (LMT) landmarks of the midline. The second group of values was obtained by projecting the same cephalometric landmarks as the first group on the midline and calculating the vertical difference between them. By convention, the authors have attributed a positive value to this difference when the landmark on the synostotic side was higher than its counterpoint on the opposite site. It was impossible to consider the line that passes by the crista galli, the anterior nasal spine, and the chin nor the perpendicular to the line that joins the two frontal zygomatic sutures nor the perpendicular at the bipupillar or the bimastoid as midline, because each of the structures mentioned could have been involved and distorted by unilateral coronal craniosynostosis. It was decided to use the line passing by the superior margin of the foramen magnum and perpendicular to the two occipital condyles, anatomical structures that have a low likelihood of being altered by unilateral coronal craniosynostosis, in accordance with G iannì .
Since patients had different ages and physical parameters (weight and height) when they started orthodontic management, it was decided not to consider absolute values, but the ratio between the right and left linear cephalometric measurements, in order to allow comparison to achieve homogeneity in the study population. The side involved with the synostosis was defined for simplicity as the ‘affected’ side, even though the contralateral side may be involved by the compensatory and rotary effects of plagiocephaly. The cephalometric values found in patients affected with unilateral coronal craniosynostosis were compared with values obtained from a control group of 20 patients from 7 to 10 years of age, randomly selected from those who visited the orthodontics centre. Two-tailed t tests were performed to find statistically significant differences amongst cephalometric parameters in patients affected by unilateral coronal craniosynostosis and the control population.
Results
The preoperative computed tomography (CT) scans of patients revealed that in 20 cases an exclusive synostotic involvement of the ipsilateral coronal hemi-suture was present, whilst in 1 case the involvement of a frontal sphenoid suture was also found. The unilateral coronal craniosynostosis involved the right side in 10 patients (48%) and the left in 11 (52%). All patients underwent cranio-orbital remodelling surgery between 6 and 12 months of age. The patients were sent to the orthodontics centre by the maxillofacial team that had performed the operation. The mean age of the patients at the time of the first visit was 8.6 years (range 6.2–10.2 years).
Analysis of the clinical occlusional parameters investigated in patients affected with unilateral coronal craniosynostosis revealed: mean overjet of 3.9 mm (range 1.5–7 mm); average overbite of 2.3 mm (range 1.5–5 mm); lateroposterior crossbite of the synostotic side in 14 patients (67%); mean mandibular intercanine diameter of 29.0 mm (range 24–36 mm); and mandibular intermolar of 46.0 mm (range 41–60 mm); presence of dental crowding in 17 patients (81%); no deviation of the superior interincisal line, with the exception of a patient who had a deviation of 2 mm from the plagiocephaly side (left); in 10 patients with right plagiocephaly, the inferior interincisal line deviated, compared with the midline, in 8 cases to the left (average 2.1 mm; range 1.5–3.1 mm), in 1 case to the right (3.0 mm), and in one case was central; in the 11 patients with left plagiocephaly, the inferior interincisal line deviated, in 8 cases to the right (average 2.5 mm; range 2.1–4.2 mm), in 2 patients to the left (3.2 mm and 4.1 mm) and in one was central. The interincisal line was found deviated contralaterally on the affected side in 16 of 21 patients (76%). 16 patients (76%) showed canine and molar dental class II according to the angle classification, 4 patients (19%) were in dental class I, and 1 patient (5%) in class III.
The following average values were found from the normal lateral cephalometry in plagiocephaly patients: SNA 82.3° (range 78–89°); SNB 75.9° (range 72–81°); ANB 6.4° (range −2 to 13°); interincisal angle 135.4° (range 120–154°); 1/SN 97.8° (range 83–116°); IMPA 89.7° (range 82–99°); FMA 28.2 (range 22–39°). Comparison of this data with the corresponding values obtained in the control group revealed that in patients affected with unilateral coronal craniosynostosis there were statistically significant differences with class II dentoskeletal occlusion ( p < 0.0001), mandibular hyperdivergence ( p < 0.0001), lingualization of the superior incisor ( p < 0.005), deviation of the inferior interincisal contralateral line to the synostosis ( p < 0.0001) ( Table 1 ). From posteroanterior cephalometry the authors obtained the mean values of the ratios of the linear distances between the Z, Mx, AG, UMT and LMT landmarks and the midlines of the affected and the contralateral sides. Values were: Z 0.94 (range 0.81–1.06; p < 0.05); Mx 0.91 (range 0.75–1.06; p < 0.005); AG 1.10 (range 0.94–1.30; p < 0.0005); UMT 0.90 (range 0.75–1.04; p < 0.0005); LMT 1.14 (range 0.95–1.48; p < 0.05) ( Fig. 1 ). These values indicate that Z, Mx and UMT were closer to the midline compared with their contralateral counterpoints, whilst AG and LMT were further from it.
| Control group, mean | Plagiocephalic patients, mean | p value | Statistical significance | |
|---|---|---|---|---|
| Overjet | 1.816 | 3.976 | <0.0001 | Extremely significant |
| Overbite | 1.605 | 2.333 | 0.0173 | Significant |
| Maxillar intercanine diameter | 31.289 | 29.143 | 0.0133 | Significant |
| Maxillar intermolar diameter | 44.32 | 46.05 | 0.2449 | Not significant |
| Superior interincisal line deviation | 0.118 | 0.125 | 0.4047 | Not significant |
| Inferior interincisal line deviation | 0.263 | 2.238 | <0.0001 | Extremely significant |
| ANB | 4.042 | 6.429 | <0.0001 | Extremely significant |
| SNA | 80.153 | 82.31 | 0.0054 | Very significant |
| SNB | 76.984 | 75.929 | 0.1799 | Not significant |
| 1/SN | 104.684 | 97.833 | 0.0046 | Very significant |
| Interincisal angle | 128.16 | 135.48 | 0.0194 | Significant |
| IMPA | 90.11 | 87.11 | 0.8024 | Not significant |
| FMA | 22.79 | 28.24 | <0.0001 | Extremely significant |
| Ratio AG | 1.0032 | 1.1362 | 0.0002 | Extremely significant |
| Ratio Z | 0.9953 | 0.949 | 0.0343 | Significant |
| Ratio Mx | 0.9889 | 0.91 | 0.0009 | Extremely significant |
| Ratio UM | 1.0016 | 0.9057 | <0.0001 | Extremely significant |
| Ratio LM | 1.0079 | 1.0967 | 0.0015 | Very significant |
| Z | 0.056 | −0.119 | 0.8256 | Not significant |
| MX | 0.344 | 2.119 | 0.0025 | Very significant |
| UM | 0.184 | 1.69 | 0.0011 | Very significant |
| LM | 0.132 | 1.31 | 0.0060 | Very significant |
| AG | 0.211 | 3.048 | 0.0018 | Very significant |
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