Oral Surgery
The skeletal and dentoalveolar stability of the maxilla after LeFort I osteotomy for cant correction Seigo Ohba1, Noriko Nakao2, Yuya Nakatani3, Tokutarou Minamizato3, Takako Kawasaki3, Takamitsu Koga3, Takiko Matsuura1, Hitoshi Yoshimura1, Noriaki Yoshida4, Kazuo Sano1, Izumi Asahina3 1
Division of Dentistry and Oral Surgery, Department of Sensory and Locomotor Medicine, Faculty of Medical Sciences, University of Fukui, Japan, 2Department of Special Care Dentistry, Nagasaki University Graduate School of Biomedical Sciences, Japan, 3Department of Regenerative Oral Surgery, Nagasaki University Graduate School of Biomedical Sciences, Japan, 4Department of Orthodontics and Dentofacial Orthopedics, Nagasaki University Graduate School of Biomedical Sciences, Japan Objectives: The aim of this study was to assess the stability of the maxilla after LeFort I osteotomy for correction of maxillary canting caused by skeletal or dentoalveolar disorders. Methods: The patients underwent conventional LeFort I osteotomy for correction of maxillary canting. Frontal cephalograms were obtained before surgery (T1), immediately after surgery (T2) and more than 1 year after surgery (T3). The angles between the line connecting bilateral latero-orbitales (Lo–Lo9) and zygoma planes (ZPs) or occlusal planes (OPs) were measured, and the distances from the Lo–Lo9 or ZP to the left and right upper first molars were also measured to assess skeletal or dentoalveolar disorders at three time points (T1–T3). Results: In cases in which the Lo–ZP was more than 2u before surgery (T1), the Lo–ZP changed from 2.28u (T1) to 1.57u (T2) or 1.50u (T3). In cases in which the Lo–ZP changed less than two degrees and the Lo–OP changed more than 2u, the Lo–OP changed from 2.69u (T1) to 1.41u (T2) or 1.08u (T3), and these changes were significant. Lo–ZP was nearly stable across the time points. The distances from the Lo–Lo9 or ZP to left and right upper first molars were nearly stable from T2 to T3. Conclusion: Skeletal and dentoalveolar stabilities were obtained regardless of whether the canting was caused by skeletal or dentoalveolar disorder. Keywords: LeFort I osteotomy, Skeletal stability, Dentoalveolar stability, Canting
Introduction The appropriate diagnosis of the cause of maxillofacial asymmetry is important in the treatment of patients whose chief complaints are maxillofacial asymmetries. The treatment procedure varies widely, depending on the cause of asymmetry, maxilla, mandible, dentoalveolar, or temporomandibular joint.1,2 Moreover, etiology of the asymmetry is considered to be congenital, and requires factors such as tumors and traumas.1,2 When the asymmetry is caused only by the mandible, mandibular osteotomies, such as sagittal
Correspondence to: S. Ohba, Division of Dentistry and Oral Surgery, Department of Sensory and Locomotor Medicine, Faculty of Medical Sciences, University of Fukui, 23-3 Shimoaizuki, Matsuoka, Eiheiji-co, Yoshida-gun, Fukui 910-1193, Japan. Email: [email protected] ß W. S. Maney & Son Ltd 2014 DOI 10.1179/2151090314Y.0000000028
split ramus osteotomies or vertical ramus osteotomies, are commonly performed.3 If the asymmetry is caused by maxillary canting (tilting of maxilla), maxillo-mandibular osteotomy is performed to correct the asymmetry. Because the position of the mandible is greatly affected by the position of the maxilla, the postoperative stability of the maxilla is important to ensure good outcomes in these cases. Therefore, if maxillary canting causes maxillofacial asymmetry, the determination of whether the etiology is due to a skeletal or dentoalveolar disorder is quite important.4,5 It is also important to assess the postoperative stability of each case. When the cause of maxillary canting is attributable to a skeletal disorder, LeFort I osteotomy (L-1) is the
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Materials and Methods Thirty-four patients underwent conventional L-1 surgery on their maxillae due to jaw deformities at the Department of Oral and Maxillofacial Surgery at the Nagasaki University Hospital and the Division of Dentistry and Oral Surgery at the University of Fukui Hospital between 2006 and 2012. Fifteen of these 34 patients required correction of their cants with L-1, and these patients were included in this study. Patients who had previously undergone orthognathic surgery were excluded. No critical complications or difficulties associated with the osteotomies or osteosynthesis materials were observed during or after surgery. No temporomandibular joint disorder was observed in this study before or after surgeries, even though temporomandibular joint disorder sometimes occurs in patients with facial asymmetry.1,2
Surgical procedure
Figure 1 The frontal cephalometric analysis. Lo/Lo9: left (Lo) and right (Lo9) latero-orbitales. OP: the line connecting UR6 and UL6. UR6/UL6: the top of the right (UR6) and the left upper first molar (UL6). ZP: the line connecting the lowest points of the bilateral inferior border of the zygoma. x-axis: the line connecting Lo and Lo9. y-axis: the perpendicular line from the Lo–Lo9 (x-axis) through the center of the Lo-Lo9.
most frequently used surgical strategy for the maxilla to correct the canting.6 In contrast, when the cause of maxillary canting is a dentoalveolar disorder, corticotomy, L-1, or multisegmental osteotomy is applied, depending on the area of the disorder that induces the maxillary cant.7–9 It is important to assess changes in facial appearance after surgery because most patients who require correction of the cant during surgery believe that they have facial asymmetries.5,10,11 When the facial asymmetry is caused by maxillary canting, it is difficult to obtain mandibular and occlusal stabilities without maxillary stability after surgery. Despite this fact, there are no reports that refer to assessments of maxillary stability according to whether the causes of facial asymmetry are due to skeletal or dentoalveolar disorders of the maxillae. The aim of this study was to assess the stability of the maxilla after L-1 to correct maxillary canting caused by skeletal or dentoalveolar disorders. 2
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Conventional L-1 surgeries with down fractures were performed on all maxillae. The segments were rigidly fixed at the planned position with a splint after osteotomy using four titanium plates with five titanium screws in each plate at the bilateral paranasal aperture and the root of the zygoma.
Frontal cephalometric analysis (Fig. 1) Frontal cephalograms were obtained before surgery (T1), immediately after surgery (T2), and more than 1 year after surgery (T3). The line connecting the bilateral latero-orbitale (Lo-Lo9) was defined as xaxis. The perpendicular line from the x-axis through the center of the Lo-Lo9 was defined as the y-axis. The zygoma plane (ZP) was defined by the line that connected the bilateral lowest points of the inferior border of the zygoma. The occlusal plane (OP) was defined as the line that connected the bilateral upper first molar occlusal surfaces in accordance with a previous report.12 The angles between the x-axis and ZP (Lo–ZP) and the x-axis and OP (Lo–OP) were measured at three time points (T1, T2, and T3). A Lo–ZP represents a tilting of the body of the maxilla. A Lo–OP represents a tilting of the midface that includes the body of the maxilla, the alveolar bone, and the maxillary teeth. The differences in the distances from the Lo–Lo9 or ZP to the upper first molars of each side were also measured, and these differences are expressed as the absolute values of |UR6–UL6|(Lo) and |UR6– UL6|(ZP), respectively. |UR6–UL6|(Lo) represents the laterality of the summation of the maxillary body, the alveolar bone, and the teeth, while |UR6– UL6|(ZP) represents that of the maxillary alveolar bone and the teeth. VOL .
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Figure 2 Lo–OP .2u (n515) Lo–OP (u): the angle between the Lo-Lo9 and the OP. Lo–ZP (u): the angle between the Lo–Lo9 and the ZP. |UR6–UL6|(Lo) (mm): the discrepancy between the distances from the Lo–Lo9 to the UR6 and the UL6. |UR6–UL6|(ZP) (mm): the discrepancy between the distances from the ZP to the UR6 and the UL6.
Hwang et al.3 defined facial asymmetry as occlusion cants of greater than 2u. According to this report, if the Lo–OP is more than 2u, the patient is diagnosed with maxillary canting. Based on this definition, 15 patients were included in this study. Among these 15 patients, whose Lo–ZPs were less than 2u, were diagnosed with maxillary canting caused by dentoalveolar disorder. The patients whose Lo–ZPs were more than 2u were diagnosed with maxillary canting caused by skeletal disorder. The numbers of patients with dentoalveolar and skeletal disorders were 6 and 9, respectively. All measurements were carried out by one specialist on orthodontology. The orthodontist measured three times and the average was represented for each point.
Statistical analyses Student’s t-tests were used to compare average cephalometric measurements to evaluate changes in these measurements at the different time points. A Pvalue of ,0.05 was considered to be statistically significant.
Note This study evaluated only the stability of the maxilla, and does not include an evaluation of mandibular or occlusal stability.
Results Lo–OP .2u (n515) (Fig. 2) Lo-OP and |UR6–UL6|(Lo) imply total amounts of cant that require correction. The Lo–OPs significantly decreased from 3.10u (T1) to 1.63u (T2) and 1.19u (T3). The Lo–OPs only decreased by 0.44u from
T2 to T3. The |UR6–UL6|(Lo)s decreased significantly by 1.41 mm from T1 to T2 (P,0.0001) and by 1.65 mm from T1 to T3 (P,0.0001). A small change in |UR6–UL6|(Lo)s (0.24 mm) was observed from T2 to T3. These changes in |UR6–UL6|(Lo)s completely paralleled those of the Lo–OPs. In contrast, Lo–ZP implies that the cant is constructed by the body of the maxilla. The Lo– ZPs showed small changes across the time points. The |UR6–UL6|(ZP)s decreased 0.34 mm from T1 to T2 and 0.43 mm from T2 to T3.
Lo-ZP .2u (n56) (Fig. 3) The patients in this group were considered to have skeletal disorders underlying their maxillary canting. The Lo–OPs decreased 1.72u from T1 to T2 (P50.0467) and were nearly stable from T2 to T3. The |UR6–UL6|(Lo)s decreased 1.42 mm from T1 to T2. These changes were nearly identical to those in the cases in which the Lo–OPs changed by more than 2u. The Lo–ZPs changed from 2.28u (T1) to 1.57u (T2) and 1.50u (T3). The T2 to T3 change in the Lo–ZP was only 20.07u. The |UR6–UL6|(ZP) did not show a visible change from T1 to T2. The T2 to T3 change in |UR6–UL6|(ZP) was only 20.34 mm.
Lo-ZP ,2u and Lo-OP .2u (n59) (Fig. 4) When the Lo–ZP was less than 2u and the Lo–OP was more than 2u, the canting was determined to be caused by a dentoalveolar disorder. The Lo–OP changed from 2.69u (T1) to 1.41u (T2) and 1.08u (T3), and these changes were statistically significant. The |UR6–UL6|(Lo) changed from
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Figure 3 Lo–ZP .2u and Lo–OP .2u (n56). Lo–OP (u): the angle between the Lo-Lo9 and the OP. Lo–ZP (u): the angle between the Lo-Lo9 and the ZP. |UR6–UL6|(Lo) (mm): the discrepancy between the distances from the Lo–Lo9 to the UR6 and the UL6. |UR6–UL6|(ZP) (mm): the discrepancy between the distances from the ZP to the UR6 and the UL6.
2.30 mm (T1) to 0.97 mm (T2) and 0.91 mm (T3) (P,0.0001). The |UR6–UL6|(Lo) changed 0.06 mm from T2 to T3. These changes were nearly identical to those in the cases in which the Lo–OP or Lo–ZP changed more than 2u. In contrast, the Lo–ZPs were nearly stable across the time points. The |UR6–UL6|(ZP) changed from 2.00 mm (T1) to 1.59 mm (T2) and 1.11 mm (T3), and the |UR6–UL6|(ZP) changed 0.48 mm from T2 to T3.
Discussion The diagnosis of the cause of facial asymmetry is important. Such diagnoses can include maxillary
cant, mandibular deflection and maxillomandibular disharmony, and skeletal or dentoalveolar disorders in other aspects; and the determination of the diagnosis is important for the selection of the orthognathic surgical procedure.4 Hwang et al.10 introduced a method for classifying asymmetry using only frontal cephalograms. This method is simple and is considered useful in assessing asymmetries. However, these authors did not assess the outcomes of treatments for maxillary cants. In this study, the stabilities of the maxillae after L-1 surgery to correct cants caused by skeletal or dentoalveolar disorders were assessed using the Lo–Lo9, ZP, and OP as references.
Figure 4 Lo-ZP ,2u and Lo-OP .2u (n59). Lo–OP (u): the angle between the Lo–Lo9 and the OP. Lo–ZP (u): the angle between the Lo–Lo9 and the ZP. |UR6–UL6|(Lo) (mm): the discrepancy between the distances from the Lo–Lo9 to the UR6 and the UL6. |UR6–UL6|(ZP) (mm): the discrepancy between the distances from the ZP to the UR6 and the UL6.
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|UR6–UL6|(Lo) represents the differences in the distances from the Lo–Lo9 to the right and left upper first molars, and the OP was determined by connecting the occlusal surfaces of the bilateral upper first molars in this study. Therefore, the changes in the |UR6–UL6|(Lo)s and Lo–OPs should always be synchronized. Otherwise, the assessment might not be correct, and reassessment would be necessary. According to the results of the present study, the changes in the Lo–OPs and |UR6–UL6|(Lo)s were completely synchronized regardless of whether the maxillary canting was caused by skeletal or dentoalveolar disorders. This finding indicates that the authors’ measurement was a reliable method for assessing maxillary cants. The T2 to T3 changes in the Lo–OPs and |UR6–UL6|(Lo)s were sufficiently small to indicate that postoperative stabilities of the maxillae, including skeletal and dentoalveolar factors, were obtained after L-1 to correct the maxillary cants. Proffit et al.13 also reported good stabilities after cant corrections, and their findings coincide with the authors’ results. In cases in which the tilting of the body of the maxilla caused the maxillary canting (Lo–ZP .2u), the Lo–ZPs changed from 2.28u (T1) to 1.57u (T2). This finding indicates that the osteotomies were performed superior to the ZP. The T2 to T3 change in Lo–ZP was 20.07u. This finding suggests that skeletal stability was obtained after L-1 in the cases of asymmetry that were caused by maxillary skeletal disorders. The Lo–OP was also stable from T2 to T3 (0.23u). Moreover, the T2 to T3 change in |UR6–UL6|(Lo) was 0.34 mm. These findings indicate that the cants were mostly corrected by the surgeries and that minimal modifications of the tooth alignments were required following surgery, when the maxillary canting was attributable to the tilting of the body of the maxilla. In contrast, in the cases of maxillary canting caused by dentoalveolar disorders (Lo–ZP ,2u, LO–OP .2u), the Lo–ZPs changed minimally and were completely stable. This finding suggests that the osteotomies were performed inferior to the ZP. Complete skeletal and dental stabilities were obtained. Skeletal and dentoalveolar stabilities were obtained regardless of whether the canting was caused by skeletal or dentoalveolar disorders. The authors believe that it is important to decide whether the canting is caused by the body of the maxilla or a dentoalveolar disorder by measuring the Lo–ZP, Lo– OP, and the distance from the Lo or the ZP to the upper first molars of both sides, when L-1 is performed to correct the maxillary canting. Thereupon, the position of L-1 should be decided. The surgical
Skeletal and dentoalveolar stability of maxilla
procedures that are appropriated based on suitable methods of assessing the maxillary may result in skeletal and dentoalveolar stability and reliable outcomes following L-1 surgery to correct the mild-to-moderate maxillary cants of patients with facial asymmetries. Of course, the sample number is too small to make this conclusion strongly. Therefore, further study is needed to confirm the authors’ opinions.
Disclaimer Statements Contributors All authors contributed to this clinical research. Funding None. Conflicts of interest The authors do not have any conflict of interest to declare. Ethics approval Not applicable.
References 1 Wolford LM. Facial asymmetry: diagnosis and treatment considerations. In: Fonseca BT, Marciani RD, Turvey TA, editors. Oral and maxillofacial surgery. 2nd edn. Vol. III. Orthognathic surgery, esthetic surgery, cleft and craniofacial surgery. St Louis, MO: Elsevier/Saunders; 2008. p. 272–315. 2 Wolford LM. Mandibular asymmetry: temporomandibular joint degeneration. In: Bagheri SC, Bell RB, Khan HA, editors. Current therapy in oral and maxillofacial surgery. St Louis, MO: Elsevier/Saunders; 2012. p. 696–725. 3 Hwang HS, Min YS, Lee SC, Sun MK, Lim HS. Change of lipline cant after 1-jaw orthognathic surgery in patients with mandibular asymmetry. Am J Orthod Dentofacial Orthop. 2009;136:564–9. 4 Baik UB, Han KH, Yoo SJ, Park JU, Kook YA. Combined multisegmental surgical-orthodontic treatment of bialveolar protrusion and chin retrusion with severe facial asymmetry. Am J Orthod Dentofacial Orthop. 2013;143:s148–60. 5 Bishara SE, Burkey PS, Kharouf JG. Dental and facial asymmetries: a review. Angle Orthod. 1994;64:89–98. 6 Ko EWC, Huang CS, Chen YR. Characteristics and corrective outcome of face asymmetry by orthognathic surgery. J Oral Maxillofac Surg. 2009;67:2201–9. 7 Baik UB, Han KH, Yoo SJ, Park JU, Kook YA. Combined multisegmental surgical-orthodontic treatment of bialveolar protrusion and chin retrusion with severe facial asymmetry. Am J Orthod Dentofacial Orthop. 2013;143:s148–60. 8 Kretchmer WB, Baciut G, Bacuit M, Zoder W, Wangerin K. Intrarative blood loss in bimaxillary orthognathic surgery with multisegmental Le Fort I osteotomies and assitional procedures. Br J Oral Maxillofac Surg. 2010;48:276–80. 9 Ohba S, Tobita T, Matsuo K, Tajima N, Shiraishi T, Yoshida N, et al. Correction of an asymmetric maxillary dental arch by alveolar bone distraction osteogenes. Am J Orthod Dentofacial Orthop. 2013;143:266–73. 10 Hwang HS, Youn IS, Lee KH, Lim HJ. Classification of facial asymmetry by cluster analysis. Am J Orthod Dentofacial Orthop. 2007;132:279.e1–6. 11 Severt TR, Proffit WR. The prevalence of facial asymmetry in the dentofacial deformities population at the University of North Carolina. Int J Adult Orthod Orthognath Surg. 1997;12:171–6. 12 Kim YH, Jeon J, Rhee JT, Hong J. Change of lip cant after bimaxillary orthognathic surgery. J Oral Maxillofac Surg. 2010;68:1106–11. 13 Proffit WR, Turvey TA, Phillips C. The hierarchy of stability and predictability in orthognathic surgery with rigid fixation: an update extension. Head Face Med. 2007;3:21–31.
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The skeletal and dentoalveolar stability of the maxilla after LeFort I osteotomy for cant correction Seigo Ohba1, Noriko Nakao2, Yuya Nakatani3, Tokutarou Minamizato3, Takako Kawasaki3, Takamitsu Koga3, Takiko Matsuura1, Hitoshi Yoshimura1, Noriaki Yoshida4, Kazuo Sano1, Izumi Asahina3 1
Division of Dentistry and Oral Surgery, Department of Sensory and Locomotor Medicine, Faculty of Medical Sciences, University of Fukui, Japan, 2Department of Special Care Dentistry, Nagasaki University Graduate School of Biomedical Sciences, Japan, 3Department of Regenerative Oral Surgery, Nagasaki University Graduate School of Biomedical Sciences, Japan, 4Department of Orthodontics and Dentofacial Orthopedics, Nagasaki University Graduate School of Biomedical Sciences, Japan Objectives: The aim of this study was to assess the stability of the maxilla after LeFort I osteotomy for correction of maxillary canting caused by skeletal or dentoalveolar disorders. Methods: The patients underwent conventional LeFort I osteotomy for correction of maxillary canting. Frontal cephalograms were obtained before surgery (T1), immediately after surgery (T2) and more than 1 year after surgery (T3). The angles between the line connecting bilateral latero-orbitales (Lo–Lo9) and zygoma planes (ZPs) or occlusal planes (OPs) were measured, and the distances from the Lo–Lo9 or ZP to the left and right upper first molars were also measured to assess skeletal or dentoalveolar disorders at three time points (T1–T3). Results: In cases in which the Lo–ZP was more than 2u before surgery (T1), the Lo–ZP changed from 2.28u (T1) to 1.57u (T2) or 1.50u (T3). In cases in which the Lo–ZP changed less than two degrees and the Lo–OP changed more than 2u, the Lo–OP changed from 2.69u (T1) to 1.41u (T2) or 1.08u (T3), and these changes were significant. Lo–ZP was nearly stable across the time points. The distances from the Lo–Lo9 or ZP to left and right upper first molars were nearly stable from T2 to T3. Conclusion: Skeletal and dentoalveolar stabilities were obtained regardless of whether the canting was caused by skeletal or dentoalveolar disorder. Keywords: LeFort I osteotomy, Skeletal stability, Dentoalveolar stability, Canting
Introduction The appropriate diagnosis of the cause of maxillofacial asymmetry is important in the treatment of patients whose chief complaints are maxillofacial asymmetries. The treatment procedure varies widely, depending on the cause of asymmetry, maxilla, mandible, dentoalveolar, or temporomandibular joint.1,2 Moreover, etiology of the asymmetry is considered to be congenital, and requires factors such as tumors and traumas.1,2 When the asymmetry is caused only by the mandible, mandibular osteotomies, such as sagittal
Correspondence to: S. Ohba, Division of Dentistry and Oral Surgery, Department of Sensory and Locomotor Medicine, Faculty of Medical Sciences, University of Fukui, 23-3 Shimoaizuki, Matsuoka, Eiheiji-co, Yoshida-gun, Fukui 910-1193, Japan. Email: [email protected] ß W. S. Maney & Son Ltd 2014 DOI 10.1179/2151090314Y.0000000028
split ramus osteotomies or vertical ramus osteotomies, are commonly performed.3 If the asymmetry is caused by maxillary canting (tilting of maxilla), maxillo-mandibular osteotomy is performed to correct the asymmetry. Because the position of the mandible is greatly affected by the position of the maxilla, the postoperative stability of the maxilla is important to ensure good outcomes in these cases. Therefore, if maxillary canting causes maxillofacial asymmetry, the determination of whether the etiology is due to a skeletal or dentoalveolar disorder is quite important.4,5 It is also important to assess the postoperative stability of each case. When the cause of maxillary canting is attributable to a skeletal disorder, LeFort I osteotomy (L-1) is the
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Skeletal and dentoalveolar stability of maxilla
Materials and Methods Thirty-four patients underwent conventional L-1 surgery on their maxillae due to jaw deformities at the Department of Oral and Maxillofacial Surgery at the Nagasaki University Hospital and the Division of Dentistry and Oral Surgery at the University of Fukui Hospital between 2006 and 2012. Fifteen of these 34 patients required correction of their cants with L-1, and these patients were included in this study. Patients who had previously undergone orthognathic surgery were excluded. No critical complications or difficulties associated with the osteotomies or osteosynthesis materials were observed during or after surgery. No temporomandibular joint disorder was observed in this study before or after surgeries, even though temporomandibular joint disorder sometimes occurs in patients with facial asymmetry.1,2
Surgical procedure
Figure 1 The frontal cephalometric analysis. Lo/Lo9: left (Lo) and right (Lo9) latero-orbitales. OP: the line connecting UR6 and UL6. UR6/UL6: the top of the right (UR6) and the left upper first molar (UL6). ZP: the line connecting the lowest points of the bilateral inferior border of the zygoma. x-axis: the line connecting Lo and Lo9. y-axis: the perpendicular line from the Lo–Lo9 (x-axis) through the center of the Lo-Lo9.
most frequently used surgical strategy for the maxilla to correct the canting.6 In contrast, when the cause of maxillary canting is a dentoalveolar disorder, corticotomy, L-1, or multisegmental osteotomy is applied, depending on the area of the disorder that induces the maxillary cant.7–9 It is important to assess changes in facial appearance after surgery because most patients who require correction of the cant during surgery believe that they have facial asymmetries.5,10,11 When the facial asymmetry is caused by maxillary canting, it is difficult to obtain mandibular and occlusal stabilities without maxillary stability after surgery. Despite this fact, there are no reports that refer to assessments of maxillary stability according to whether the causes of facial asymmetry are due to skeletal or dentoalveolar disorders of the maxillae. The aim of this study was to assess the stability of the maxilla after L-1 to correct maxillary canting caused by skeletal or dentoalveolar disorders. 2
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Conventional L-1 surgeries with down fractures were performed on all maxillae. The segments were rigidly fixed at the planned position with a splint after osteotomy using four titanium plates with five titanium screws in each plate at the bilateral paranasal aperture and the root of the zygoma.
Frontal cephalometric analysis (Fig. 1) Frontal cephalograms were obtained before surgery (T1), immediately after surgery (T2), and more than 1 year after surgery (T3). The line connecting the bilateral latero-orbitale (Lo-Lo9) was defined as xaxis. The perpendicular line from the x-axis through the center of the Lo-Lo9 was defined as the y-axis. The zygoma plane (ZP) was defined by the line that connected the bilateral lowest points of the inferior border of the zygoma. The occlusal plane (OP) was defined as the line that connected the bilateral upper first molar occlusal surfaces in accordance with a previous report.12 The angles between the x-axis and ZP (Lo–ZP) and the x-axis and OP (Lo–OP) were measured at three time points (T1, T2, and T3). A Lo–ZP represents a tilting of the body of the maxilla. A Lo–OP represents a tilting of the midface that includes the body of the maxilla, the alveolar bone, and the maxillary teeth. The differences in the distances from the Lo–Lo9 or ZP to the upper first molars of each side were also measured, and these differences are expressed as the absolute values of |UR6–UL6|(Lo) and |UR6– UL6|(ZP), respectively. |UR6–UL6|(Lo) represents the laterality of the summation of the maxillary body, the alveolar bone, and the teeth, while |UR6– UL6|(ZP) represents that of the maxillary alveolar bone and the teeth. VOL .
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Figure 2 Lo–OP .2u (n515) Lo–OP (u): the angle between the Lo-Lo9 and the OP. Lo–ZP (u): the angle between the Lo–Lo9 and the ZP. |UR6–UL6|(Lo) (mm): the discrepancy between the distances from the Lo–Lo9 to the UR6 and the UL6. |UR6–UL6|(ZP) (mm): the discrepancy between the distances from the ZP to the UR6 and the UL6.
Hwang et al.3 defined facial asymmetry as occlusion cants of greater than 2u. According to this report, if the Lo–OP is more than 2u, the patient is diagnosed with maxillary canting. Based on this definition, 15 patients were included in this study. Among these 15 patients, whose Lo–ZPs were less than 2u, were diagnosed with maxillary canting caused by dentoalveolar disorder. The patients whose Lo–ZPs were more than 2u were diagnosed with maxillary canting caused by skeletal disorder. The numbers of patients with dentoalveolar and skeletal disorders were 6 and 9, respectively. All measurements were carried out by one specialist on orthodontology. The orthodontist measured three times and the average was represented for each point.
Statistical analyses Student’s t-tests were used to compare average cephalometric measurements to evaluate changes in these measurements at the different time points. A Pvalue of ,0.05 was considered to be statistically significant.
Note This study evaluated only the stability of the maxilla, and does not include an evaluation of mandibular or occlusal stability.
Results Lo–OP .2u (n515) (Fig. 2) Lo-OP and |UR6–UL6|(Lo) imply total amounts of cant that require correction. The Lo–OPs significantly decreased from 3.10u (T1) to 1.63u (T2) and 1.19u (T3). The Lo–OPs only decreased by 0.44u from
T2 to T3. The |UR6–UL6|(Lo)s decreased significantly by 1.41 mm from T1 to T2 (P,0.0001) and by 1.65 mm from T1 to T3 (P,0.0001). A small change in |UR6–UL6|(Lo)s (0.24 mm) was observed from T2 to T3. These changes in |UR6–UL6|(Lo)s completely paralleled those of the Lo–OPs. In contrast, Lo–ZP implies that the cant is constructed by the body of the maxilla. The Lo– ZPs showed small changes across the time points. The |UR6–UL6|(ZP)s decreased 0.34 mm from T1 to T2 and 0.43 mm from T2 to T3.
Lo-ZP .2u (n56) (Fig. 3) The patients in this group were considered to have skeletal disorders underlying their maxillary canting. The Lo–OPs decreased 1.72u from T1 to T2 (P50.0467) and were nearly stable from T2 to T3. The |UR6–UL6|(Lo)s decreased 1.42 mm from T1 to T2. These changes were nearly identical to those in the cases in which the Lo–OPs changed by more than 2u. The Lo–ZPs changed from 2.28u (T1) to 1.57u (T2) and 1.50u (T3). The T2 to T3 change in the Lo–ZP was only 20.07u. The |UR6–UL6|(ZP) did not show a visible change from T1 to T2. The T2 to T3 change in |UR6–UL6|(ZP) was only 20.34 mm.
Lo-ZP ,2u and Lo-OP .2u (n59) (Fig. 4) When the Lo–ZP was less than 2u and the Lo–OP was more than 2u, the canting was determined to be caused by a dentoalveolar disorder. The Lo–OP changed from 2.69u (T1) to 1.41u (T2) and 1.08u (T3), and these changes were statistically significant. The |UR6–UL6|(Lo) changed from
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Figure 3 Lo–ZP .2u and Lo–OP .2u (n56). Lo–OP (u): the angle between the Lo-Lo9 and the OP. Lo–ZP (u): the angle between the Lo-Lo9 and the ZP. |UR6–UL6|(Lo) (mm): the discrepancy between the distances from the Lo–Lo9 to the UR6 and the UL6. |UR6–UL6|(ZP) (mm): the discrepancy between the distances from the ZP to the UR6 and the UL6.
2.30 mm (T1) to 0.97 mm (T2) and 0.91 mm (T3) (P,0.0001). The |UR6–UL6|(Lo) changed 0.06 mm from T2 to T3. These changes were nearly identical to those in the cases in which the Lo–OP or Lo–ZP changed more than 2u. In contrast, the Lo–ZPs were nearly stable across the time points. The |UR6–UL6|(ZP) changed from 2.00 mm (T1) to 1.59 mm (T2) and 1.11 mm (T3), and the |UR6–UL6|(ZP) changed 0.48 mm from T2 to T3.
Discussion The diagnosis of the cause of facial asymmetry is important. Such diagnoses can include maxillary
cant, mandibular deflection and maxillomandibular disharmony, and skeletal or dentoalveolar disorders in other aspects; and the determination of the diagnosis is important for the selection of the orthognathic surgical procedure.4 Hwang et al.10 introduced a method for classifying asymmetry using only frontal cephalograms. This method is simple and is considered useful in assessing asymmetries. However, these authors did not assess the outcomes of treatments for maxillary cants. In this study, the stabilities of the maxillae after L-1 surgery to correct cants caused by skeletal or dentoalveolar disorders were assessed using the Lo–Lo9, ZP, and OP as references.
Figure 4 Lo-ZP ,2u and Lo-OP .2u (n59). Lo–OP (u): the angle between the Lo–Lo9 and the OP. Lo–ZP (u): the angle between the Lo–Lo9 and the ZP. |UR6–UL6|(Lo) (mm): the discrepancy between the distances from the Lo–Lo9 to the UR6 and the UL6. |UR6–UL6|(ZP) (mm): the discrepancy between the distances from the ZP to the UR6 and the UL6.
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|UR6–UL6|(Lo) represents the differences in the distances from the Lo–Lo9 to the right and left upper first molars, and the OP was determined by connecting the occlusal surfaces of the bilateral upper first molars in this study. Therefore, the changes in the |UR6–UL6|(Lo)s and Lo–OPs should always be synchronized. Otherwise, the assessment might not be correct, and reassessment would be necessary. According to the results of the present study, the changes in the Lo–OPs and |UR6–UL6|(Lo)s were completely synchronized regardless of whether the maxillary canting was caused by skeletal or dentoalveolar disorders. This finding indicates that the authors’ measurement was a reliable method for assessing maxillary cants. The T2 to T3 changes in the Lo–OPs and |UR6–UL6|(Lo)s were sufficiently small to indicate that postoperative stabilities of the maxillae, including skeletal and dentoalveolar factors, were obtained after L-1 to correct the maxillary cants. Proffit et al.13 also reported good stabilities after cant corrections, and their findings coincide with the authors’ results. In cases in which the tilting of the body of the maxilla caused the maxillary canting (Lo–ZP .2u), the Lo–ZPs changed from 2.28u (T1) to 1.57u (T2). This finding indicates that the osteotomies were performed superior to the ZP. The T2 to T3 change in Lo–ZP was 20.07u. This finding suggests that skeletal stability was obtained after L-1 in the cases of asymmetry that were caused by maxillary skeletal disorders. The Lo–OP was also stable from T2 to T3 (0.23u). Moreover, the T2 to T3 change in |UR6–UL6|(Lo) was 0.34 mm. These findings indicate that the cants were mostly corrected by the surgeries and that minimal modifications of the tooth alignments were required following surgery, when the maxillary canting was attributable to the tilting of the body of the maxilla. In contrast, in the cases of maxillary canting caused by dentoalveolar disorders (Lo–ZP ,2u, LO–OP .2u), the Lo–ZPs changed minimally and were completely stable. This finding suggests that the osteotomies were performed inferior to the ZP. Complete skeletal and dental stabilities were obtained. Skeletal and dentoalveolar stabilities were obtained regardless of whether the canting was caused by skeletal or dentoalveolar disorders. The authors believe that it is important to decide whether the canting is caused by the body of the maxilla or a dentoalveolar disorder by measuring the Lo–ZP, Lo– OP, and the distance from the Lo or the ZP to the upper first molars of both sides, when L-1 is performed to correct the maxillary canting. Thereupon, the position of L-1 should be decided. The surgical
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procedures that are appropriated based on suitable methods of assessing the maxillary may result in skeletal and dentoalveolar stability and reliable outcomes following L-1 surgery to correct the mild-to-moderate maxillary cants of patients with facial asymmetries. Of course, the sample number is too small to make this conclusion strongly. Therefore, further study is needed to confirm the authors’ opinions.
Disclaimer Statements Contributors All authors contributed to this clinical research. Funding None. Conflicts of interest The authors do not have any conflict of interest to declare. Ethics approval Not applicable.
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