Posted at the Institutional Resources for Unique Collection and Academic Archives at Tokyo Dental College, Available from http://ir.tdc.ac.jp/
Title Morphologic Evaluation for Safe Le Fort I Osteotomy in Cleft Lip and Palate
Author(s) 渡邉, 美貴 Journal
URL http://hdl.handle.net/10130/6131 Right
Description 博士（歯学）・第２１８９号（甲 第１３９０号）・平
成２９年３月３１日
Morphological evaluation for Safe Le Fort I Osteotomy in Cleft Lip and Palate
Miki Watanabe
Department of Oral andMaxillofacial Surgery, Tokyo Dental College
1 [Abstract]
Objective: The present study aimed to determine the structure and morphology of the maxilla for safe Le Fort I osteotomy (LFI) in unilateral cleft lip and palate.
Patients: A total of 34 sides of 17 patients with unilateral cleft lip and palate without the syndrome were included in this study. The control group included 10 sides of 5 patients who had skeletal mandibular protrusion without malformation.
Interventions: Finite element analysis was performed to examine the distribution of occlusal force over the maxilla, and continually three-dimensional measurement was performed at the sites of stress concentration.
Results: In unilateral cleft lip and palate, bones at the lateral border of the piriform aperture and the anterior wall of the maxillary sinus were significantly thicker than in controls (p <
0.05). Furthermore, the attachment of the pterygomaxillary junction was wider and thicker (p < 0.05), and the anterior distance to the descending palatine artery was shorter (p < 0.01) than controls. Our results indicated that alveolar bone graft may significantly influence bone thickness and the attachment state of the pterygomaxillary junction.
Conclusions: It is possible that the complications of LFI in unilateral cleft lip and palate have been reduced by proper understanding of maxillary anatomy and bone thickness, as well as the location of the descending palatine artery and the attachment state of the pterygomaxillary
2 junction.
Key Words: cleft lip and palate, Le Fort I osteotomy, finite element analysis, 3D measurement
3 [Introduction]
Cleft lip and palate tend to exhibit maxillary hypoplasia due to multiple surgeries, often beginning immediately after birth. In addition, complex and varied morphology of the maxilla observed in such patients, depending on the width of the alveolar cleft and the degree of the bone bridge formation (Jiang et al., 2015; Abuhijleh et al., 2014). We must consider not only the complex morphology of the maxilla in cleft lip and palate but also the presence of scar tissue (Huang et al., 2002; Oberoi et al., 2008; Voshol et al., 2012) and velopharyngeal closure (Poole et al.,1986) . Although Le Fort I osteotomy (LFI) require to perform for patients with maxillofacial deformities, various complications have been reported (Pereira et al., 2010;
Lanigan et al., 1990; Cruz and dos Santos.2006; Chung et al., 2014). There are mainly two contents regarding LFI in cleft lip and palate. First, it is necessary to consider whether blood flow can be established in the descending palatine artery, which is often narrowed as a result of primary surgeries (Drommer, 1979). Second it is to evaluate whether complex maxilla can be caused an abnormal fracture.
Previous studies have investigated the development of complex maxilla over time in patients with cleft lip and palate via cephalometric analysis and three-dimensional (3D) measurement (Jiang et al., 2015). And surgical rapid maxillary expansion and implantation of orthodontic anchor screws have often evaluated using finite element analysis (FEA). However, no methods
4
utilizing FEA and 3D measurement to investigate the maxillary anatomy in cleft lip and palate exist.
The present study aims to determine the structure and morphology of the maxilla for safe LFI in unilateral cleft lip and palate exhibiting maxillary retrusion. FEA is performed to examine the distribution of occlusal force over the maxilla, and continually 3D measurement is performed for the site under the greatest degree of stress.
[Materials and Methods]
1. Patients
The patients had undergone orthognathic surgery in the department of Oral and Maxillofacial Surgery at Tokyo Dental College between 2002 and 2015. The present study included 17 patients (34 sides) with unilateral cleft lip and palate without the syndrome (CLP group). The mean age of patients in CLP group was 23.8 years old (Table 1). The control group included 5 patients (10 sides) with skeletal mandibular protrusion, none of whom exhibited malformation.
Cephalometric analysis was conducted for patients of the control group, and the following criteria was used: Sella-Nasion A point angle (SNA): ± 1 SD; McNamara line from -1 mm to +3 mm. In the control group, patients exhibiting asymmetry were excluded. The mean age of patients in the control group was 20 years old. DICOM data for images obtained immediately
5
prior to surgery were used for FEA and 3D measurement. A SOMATOM plus 4® or Definition AS® (Siemens, Erlangen, Germany) scanner was used for image acquisition. The imaging conditions were as follows: the slice thickness, 1 mm; tube voltage, 120 kV; tube current, 90mA.
This study was conducted after obtaining the approval of the ethical committee of Tokyo Dental College (No.628).
2. FEA
A TRI-3D/FEM® system (RATOC System Engineering, Tokyo, Japan) was used for finite element analysis. For the FEA model, 3D image construction from the parietal bone to the maxilla was performed using the DICOM data of the control group (Yang et al., 2012). Three types of models were created: a control model (FEA-c); a model of the CLP group without alveolar bone graft (FEA-nBG); and a model of the CLP group with alveolar bone graft (FEA- BG) (Fig.1 a-c). The FEA-nBG was created from the FEA-c based on a method previously described by Yang et al (Yang et al., 2012). The FEA-nBG was defined as complete cleft lip and palate on the left side, including defects of the left cuspid, alveolar bone and palatine bone.
For the FEA-BG, the bone bridge was placed at the site of the alveolar cleft in the FEA-nBG.
The parietal region was completely restricted, following which a load of 300 N was applied to the occlusal surface of molar tooth in order to reproduce occlusion associated with cleft lip and
6
palate (Garcia et al., 2016). Material properties are shown in Table 2 (Benazzi et al., 2011). The results were obtained to use the von Mises stress.
3. 3D measurement (1) Instruments
3D image analysis software Mimics® and 3-Matic® (Materialise, Leuven, Belgium) were used for measurement. Measurements were obtained by creating 3D models similar to the process used for FEA.
(2) Reference plane and measurement plane
Three reference planes were set as follows: The horizontal reference plane was defined as the plane passing through the bilateral porion (Po) and left infraorbital foramen (I-Or) . For the CLP group, this plane was defined as that passing through the bilateral Po and the I-Or of the large segment(non cleft side). The midsagittal reference plane was defined as the plane passing through the middle point of the bilateral Po, perpendicular to the horizontal reference plane.
The coronal reference plane was defined as the plane perpendicular to both the horizontal reference plane and the midsagittal reference plane.
For the measurement plane, the vertical distance was measured from the I-Or to the anterior
7
nasal spine (ANS), and the one-fifth (1/5Cut) of the plane closest to the ANS was regarded as the osteotomy line for LFI (Fig. 2) (Drommer, 1986; Epker and Wolford, 1980).
(3) Measurement items
A total of 15 measurement items were set to the site including the landmark for LFI (Fig.3).
Ten items were associated with bone thickness: lateral border of the piriform aperture(i);
zygomaticoalveolar crest(ii); thickness of the pterygomaxillary junction(iii); width of the pterygomaxillary junction(iv); outside of the anterior wall of the maxillary sinus(v); central anterior wall of the maxillary sinus(vi); anterior sidewall of the nasal cavity(vii); central sidewall of the nasal cavity(viii); posterior maxilla(ix); and cross-sectional area of the coronal section(x)(Green is x). Four items were associated with the control of blood flow:
anteroposterior diameter of the greater palatine canal(xi); anterior distance to the greater palatine canal(xii); posterior distance to the greater palatine canal(xiii); and lateral distance to the greater palatine canal(xiv). Finally, the volume of the maxillary sinus(xv) was used as an indicator of maxillary growth.
8 4. Statistical analysis
SPSS® Version23(IBM, US) was used for all statistical analysis. The significance level was set at p < 0.05. The Kruskal-Wallis test was conducted to evaluate the cleft type among the following three groups: large segment in the CLP group (LS); small segment(cleft side) in the CLP group (SS); and control group (C). The Kruskal-Wallis test was also used to evaluate the influence of alveolar bone graft among the following five groups: large segment of the CLP group with alveolar bone graft (LS-BG); small segment of the CLP group with alveolar bone graft (SS-BG); large segment of the CLP group without alveolar bone graft (LS-nBG); small segment of the CLP group without alveolar bone graft (SS-nBG); and control group (C).
The Peason product moment coefficient (r) was used to determine the relation of the anterior wall of the maxillary sinus and the volume of the maxillary sinus.
[Results]
1. FEA
In each of the three models, stress concentration was observed at the lateral border of the piriform aperture and the outside of the anterior wall of the maxillary sinus ( Red is the site of stress concentration.) (Fig.4a-c). Among the FEA-c, FEA-BG, and FEA-nBG, a greater concentration of stress was observed at SS in the FEA-nBG, while approximately equal stress
9
distribution was observed at the lateral border of the piriform aperture and the anterior wall of the maxillary sinus in the FEA-BG.
2. 3D measurement (1) The cleft type
Among the three groups (LS, SS, and C), the range of the measured value was extended, and no characteristic findings were observed (data not to show). Because the maxillary morphology varied, it was difficult to obtain the average values. The volume of the maxillary sinus was used to determine the thickness of each patient's maxilla according to the following formula:
Value of the measurement item/the volume of the maxillary sinus × 100.
A significant difference was observed for seven of 13 items (Fig.5). Areas with significantly greater thickness in the LS and SS groups relative to the C group included the width of the pterygomaxillary junction (iv), central anterior wall of the maxillary sinus (vi), lateral distance to the descending palatine artery (xiv)(p < 0.05), central sidewall of the nasal cavity (viii) and posterior maxilla (ix)(p < 0.01). The lateral border of the piriform aperture (i) was significantly thicker in the SS group than in the C group (p < 0.05), while the posterior distance to the descending palatine artery (xiii) was significantly longer in the LS group than in the C group (p < 0.05).
10 (2) The influence of alveolar bone graft
Comparisons of alveolar bone grafting were made among five groups (LS –BG, SS –BG, LS –nBG, SS -nBG, and C) (Fig.6). The measurement items were evaluated based on the volume of the maxillary sinus at each segment, following which a significant difference was observed for nine of 13 items (Fig.6). For the LS-nBG and SS-nBG groups, areas of significantly greater thickness included the width of the pterygomaxillary junction (iv)(p < 0.01), outside of the anterior wall of the maxillary sinus (v) and the posterior maxilla (ix)(p < 0.05). For the LS-nBG, SS-nBG, and LS-BG groups, items with significantly greater thickness relative to the C group included the central sidewall of the nasal cavity (viii)(p < 0.05) and anterior distance to the descending palatine artery (xii)(p < 0.01). For the LS-nBG group, items with significantly greater thickness relative to the C group included the lateral border of the piriform aperture (i), thickness of the pterygomaxillary junction (iii)(p < 0.05), central anterior wall of the maxillary sinus (vi) and the lateral distance to the descending palatine artery (xiv)(p < 0.01).
(3) The relation of the anterior wall of the maxillary sinus and the volume of the maxillary sinus.
Significant differences were observed a correlation between the volume of the maxillary sinus and the thickness of the central anterior wall of the maxillary sinus in the SS-BG group
11
(r = -0. 67), and a correlation between the volume of the maxillary sinus and the thickness of the outside of the anterior wall of the maxillary sinus in the SS-nBG group (r = -0. 88) and in the SS-BG (r = -0. 68)(data not shown).
【Discussion】
Since the first successful tumorectomy of the rhinopharynx by Von Langenbeck in 1859, LFI has been established as an appropriate surgical treatment for maxillofacial deformities, allowing for both functional and esthetic correction via various modifications (Pingarron et al., 2013).
The incidence of complications following LFI is approximately 6.4%, including post-operative hemorrhage, necrosis of the maxilla and abnormal fracture of the pterygomaxillary junction (Pereira et al., 2010; Lanigan et al., 1990; Robinson and Hendy, 1986). Thus, LFI is difficult surgery. For patients with abnormal maxillary structure—such as those with cleft lip and palate—the incidence of complications increases to 25.2% (Kramer et al., 2004). The complexity of the surgery also increases. We observed the range of the measured value was extended in unilateral cleft lip and palate, reflecting variations in maxillary morphology. Such variations were thought to be the difference of the patient’s background such as the number of surgeries prior to LFI, age at surgery, degree of cleft, segment position, and occlusal status.
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Thus, it is important to know proper understanding of each patient’s maxillary anatomy for sefe LFI.
1. Distribution of occlusal force to the maxilla
These results of the FEA are consistent with those of a previous study, which reported that the alveolar bone graft is important to distribute the stress (Yang et al., 2012). Since it has been reported that bone formation progresses at the site of mechanical stress concentration (Cortese et al., 2014), we speculated that the bone at the lateral border of the piriform aperture and the anterior wall of the maxillary sinus would thicken. In addition, as we observed that stress distribution differed between the FEA-BG and FEA-nBG, our results suggest that the alveolar bone graft significantly influences bone thickness.
2. 3D measurement of sites at which stress concentration was observed
The range of the measured values was extended in cleft lip and palate and it suggested that maxillary morphology varies each patients. We observed no significant difference in cross- sectional area between the CLP group and the C group, although sinus volume was significantly lower in the CLP group. This result suggested maxilla is thick in cleft lip and palate. As the sinus volume influence maxillary growth, we use it as the indicator. So we determined to use
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the ratio of the volume of the maxillary sinus per measurement item and segment.
1) Items associated with bone thickness
Cho have reported no correlation between the volume of the maxillary sinus and the thickness of the anterior wall of the maxillary sinus. However, we observed a correlation between them in unilateral cleft lip and palate. These results suggest that the thickness of the bones at the anterior wall of the maxillary sinus can be predicted by measuring the volume of the maxillary sinus in unilateral cleft lip and palate.
Stress concentration was observed at the lateral border of the piriform aperture in the SS for the FEA-nBG (Fig. 4-b), and consistent with the results of 3D measurements (Fig.5). These findings suggest that stress distribution significantly influenced bone thickness. However, since the data of the LS in the FEA-nBG was not consistent with the results of stress concentration and 3D measurement, we speculated that factors influence bone thickness such as oral environmental factors (segment state, width of the alveolar cleft, state of the bone bridge, occlusal contact area, tooth arrangement, and residual teeth), the living environment factors (customs) and the physiological factors such as bone density.
The thickness of the pterygomaxillary junction (iii), the width of the pterygomaxillary junction (iv) and the posterior maxilla (ix) indicate the attachment state of the pterygomaxillary
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junction. We observed that the attachment of the pterygomaxillary junction was significantly wider and thicker in the nBG group (Fig.6). These findings suggest that the alveolar bone graft significantly influences the attachment state of the pterygomaxillary junction. The bones of the pterygomaxillary junction are thickened in cleft lip and palate (Lee et al., 2011) and isolation is difficult, further complicating LFI in these patients. As various complications associated with the isolation of pterygomaxillary junction have been reported (Pereira et al., 2010; Lanigan et al., 1990; Cruz and dos Santos.2006; Chung et al., 2014), LFI should be performed by experienced surgeons. Precious et al have reported the potential to avoid such complications via solation of the pterygomaxillary junction without the use of an osteotome. However, isolation without an osteotome is impossible in cleft lip and palate due to the increased thickness of the pterygomaxillary junction, which renders manual isolation difficult and increases the risk of complications, such as fracture of the pterygomaxillary junction and relapse (Robinson and Hendy, 1986; Lanigan and Guest, 1993).
Cortese has reported that bones at the sidewall of the nasal cavity in controls are thin and exhibit low resistance to chiseling. We observed the sidewall of the nasal cavity significantly thicker in the BG group (Fig.6).
15 2) Items associated with the control of blood flow
As the descending palatine artery is an important nutrient vessel supplying blood to the postoperative maxilla, careful attention should be paid. And this artery may narrow following palatoplasty in cleft lip and palate (Pereira et al., 2010) or develop vascular anomalies due to the presence of scar tissue (Cortese, 2012). The anterior distance to the greater palatine canal in Japanese is approximately 36.6 mm (Kawahara et al., 2004). We observed significant differences in cleft lip and palate (LS 31.6 mm; SS 29.6 mm). The anterior distance to the greater palatine canal in the nBG group was longer than that in the BG group. These results suggested that the alveolar bone graft influenced inhibition of anterior segment growth (Fig.6).
The posterior and the lateral distance to the greater palatine canal was greater in cleft lip and palate (Fig.5). There is adequate distance from the deepest site of the pterygomaxillary junction for positioning of the osteotome to the descending palatine artery . However, surgical separation of this region remains difficult, as the attachment state of the pterygomaxillary junction is wider and thicker in cleft lip and palate. Since the anterior distance to the greater palatine canal varies depending on the segment and the influence of alveolar bone grafts, we must change the insertion distance for the bone saw during osteotomy. And the positioning of the osteotome is also important to prevention the injury of the descending palatine artery.
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Cruz AA, dos Santos AC. Blindness after Le Fort I osteotomy: a possible complication associated with pterygomaxillary separation. J Craniomaxillofac Surg. 2006;34:210–216.
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Drommer R. Selective angiographic studies prior to Le Fort I osteotomy in patients with cleft lip and palate. J Maxillofac Surg. 1979;7:264-270.
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cheiloplasty on maxillary dental arch development in infants with unilateral complete cleft lip and palate. Cleft Palate Craniofac J. 2002;39:513– 516.
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Kramer FJ, Baethge C, Swennen G, Teltzrow T, Schulze A, Breten J, Brachvogel P. Intra and perioperative complications of the Le Fort I osteotomy: a prospective evaluation of 1,000 patients. J Craniofac Surg. 2004;15:971–977.
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hemorrhage associated with Le Fort I osteotomies. J Oral Maxillofac Surg. 1990;48:561–573.
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20 [Figure legends]
Fig.1 FEA-model. a: FEA-c, b: FEA-nBG, c: FEA-BG.
a. FEA-c: A control model.
b. FEA-nBG: A model of the CLP group without bone graft. It defined as complete cleft lip and palate on the left.
c. FEA-BG: A model of the CLP group with bone graft. The bone bridge was placed at the site of the alveolar cleft in the FEA-nBG model.
Green is Maxilla; red is tooth in FEA-c, tooth of non-cleft side in FEA-nBG and FEA-BG; blue is tooth of cleft side in FEA-nBG and FEA-BG.
Fig. 2 Measurement plane (one-fifth cutting plane)
The vertical dimension from I-Or to ANS was measured and the plane that passing through ANS was defined as 0 Cut. The measurement plane was defined as the plane that was cut in the one-fifth from ANS.
Fig.3 Measurement items are 15.
Ten items were associated with bone thickness: lateral border of the piriform aperture(i);
zygomaticoalveolar crest(ii); thickness of the pterygomaxillary junction(iii); width of the
21
pterygomaxillary junction(iv); outside of the anterior wall of the maxillary sinus(v); central anterior wall of the maxillary sinus(vi); anterior sidewall of the nasal cavity(vii); central sidewall of the nasal cavity(viii); posterior maxilla(ix); and cross-sectional area of the coronal section(x) (Green is x). Four items were associated with the control of blood flow:
anteroposterior diameter of the greater palatine canal(xi); anterior distance to the greater palatine canal(xii); posterior distance to the greater palatine canal(xiii); and lateral distance to the greater palatine canal(xiv). Finally, the volume of the maxillary sinus(xv) was used as an indicator of maxillary growth.
Fig.4 Stress distribution in three models.
Red is the site of stress concentration.
a. FEA-c: Stress is bilaterally distributed the lateral border of the piriform aperture and the anterior wall of the maxillary sinus.
b. FEA-nBG: Stress concentration is found the lateral border of the piriform aperture in LS and especially in SS, the zygomaticoalveolar crest in LS.
c. FEA-BG: Stress is distributed over bilaterally and equally.
22
Fig.5 Results of three-dimensional measurement: the cleft typet; Value of the measurement item/the volume of the maxillary sinus × 100
LS, large segment in the CLP group; SS, small segment in the CLP group; C, Control group
*: The significant difference.
Fig. 6 Results of three-dimensional measurement: the influence of bone graft; Value of the measurement item/the volume of the maxillary sinus × 100
LS –BG, bone graft at large segment in the CLP group; SS –BG, bone graft at small segment in the CLP group; LS –nBG, without bone graft at large segment in the CLP group; SS –nBG, without bone graft at small segment in the CLP group; C, Control group
*: The significant difference.
23 [Tables and Figures]
Table. 1 The characteristics in the CLP group
Case
Sex
Female 10
Male 7
Bone graft
Yes 11
No 6
Cleft type
Right 6
Left 11
24
Fig.1 FEA-model. a: FEA-c, b: FEA-nBG, c: FEA-BG
25 Table.2 Material properties
Material Young’s Modulus(MPa) Poisson’s ratio
Maxilla 13.7×10
30.3
Tooth 75×10
30.3
26 Fig.2 Measurement plane (one-fifth cutting plane)
27 Fig.3 Measurement items are 15.
Measurement item i Lateral border of the piriform aperture ii Zygomaticoalveolar crest
iii Thickness of the pterygomaxillary junction iv Width of the pterygomaxillary junction
v Outside of the anterior wall of the maxillary sinus vi Central anterior wall of the maxillary sinus vii Anterior sidewall of the nasal cavity viii Central sidewall of the nasal cavity
ix Posterior maxilla
x Cross-sectional area of the coronal section
xi Anteroposterior diameter of the greater palatine canal xii Anterior distance to the greater palatine canal
xiii Posterior distance to the greater palatine canal xiv Lateral distance to the greater palatine canal
xv Volume of the maxillary sinus
28 Fig.4 Stress distribution in three models.
29
Fig.5 Results of three-dimensional measurement: the cleft type
30
Fig. 6 Results of three-dimensional measurement: the influence of bone graft
