Int. J. Oral Maxillofac. Surg. 2014; 43: 581–586 http://dx.doi.org/10.1016/j.ijom.2013.11.002, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Volumetric upper airway assessment in patients with transverse maxillary deficiency after surgically assisted rapid maxillary expansion
V. A. Pereira-Filho, M. S. Monnazzi, M. A. C. Gabrielli, R. Spin-Neto, E. R. Watanabe, C. M. M. Gimenez, A. Santos-Pinto, M. F. R. Gabrielli Department of Diagnosis and Oral Surgery, Dental School of Araraquara (UNESP), Araraquara, Sa˜o Paulo, Brazil
V.A. Pereira-Filho, M.S. Monnazzi, M.A.C. Gabrielli, R. Spin-Neto, E.R. Watanabe, C.M.M. Gimenez, A. Santos-Pinto, M.F.R. Gabrielli: Volumetric upper airway assessment in patients with transverse maxillary deficiency after surgically assisted rapid maxillary expansion. Int. J. Oral Maxillofac. Surg. 2014; 43: 581–586. # 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. Transverse maxillary deficiency is commonly found in patients with sleep apnea and is also related to abnormal breathing patterns. Maxillary expansion procedures promote widening of the nasal floor and reduce the resistance to airflow, and have a positive influence on nasopharynx function. In order to evaluate volume changes in the upper airway, 15 adult patients with transverse maxillary deficiency underwent surgically assisted rapid maxillary expansion (RME) until a slight overcorrection of the crossbite was obtained. Cone beam computed tomography (CBCT) volumetric images were obtained at three predefined time points. The mean age of the patients was 30.2 (7.4) years; nine were females and six were males. The area, volume, and the smallest transverse section area of the airway were assessed using Dolphin Imaging 3D software. Statistical comparisons were made of the changes between time periods. No statistically significant differences were found for volume or area. However a significant difference was found between the preoperative and immediate postoperative smallest transverse section area (P < 0.05). Maxillary expansion, as an isolated procedure, does not result in a statistically significant improvement in the airway dimensions and results in an inferior relocation of the smallest transverse section area.
Transverse maxillary deficiency is a pathological condition that may be associated with other types of dentoskeletal alterations, with esthetic1–3 and functional implications,4–7 including respiratory 0901-5027/050581 + 06 $36.00/0
problems. The incidence is around 3– 18% in orthodontic patients.1,8 Patients with this condition have a narrow nasal cavity,4,5 which increases the resistance to nasal airway flow.7–10
Key words: maxillary transverse deficiency; oropharynx; malocclusion; airway assessment. Accepted for publication 4 November 2013 Available online 20 December 2013
Recently, the relationship between transverse maxillary deficiency and obstructive sleep apnea (OSA) has received attention in the literature. It is a common finding in sleep apnea patients, as well as
# 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
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Pereira-Filho et al.
being related to abnormal breathing patterns. OSA syndrome is a condition that occurs secondary to the collapse of the upper airway. It results in mechanical obstruction of the airflow during sleep, producing hypoxia and/or tachycardia and bradycardia episodes, and increasing peripheral vasoconstriction and the risk for cardiovascular and cerebrovascular events. The obstruction can occur at the level of the nasal cavities, soft palate, tonsils, and retro-lingual area of the oral pharynx. Retrusion of the jaws is frequently associated with sleep apnea syndrome due to malpositioning of the soft tissue structures and a reduction in the volume of the upper airway.11,12 Maxillary expansion procedures,13 both orthodontic (patients with growth potential) and surgically assisted (adult patients), promote widening of the nasal floor and reduce resistance to airflow, with a positive influence on the function of the nasopharynx and correction of respiratory dysfunction. To define the modality of treatment, age, skeletal maturation, severity of the deformity, and functional implications have to be considered.14–17 Well planned and performed treatment can be executed, even in adult patients, without excessive inclination or extrusion of teeth, dental or periodontal damage, or pain.4,12,18 The surgical treatment of adult patients can be performed through a segmented Le Fort I osteotomy or by surgically assisted expansion.19 The first option can correct the maxillary position in three dimensions. Surgically assisted expansion will correct the transverse dimension and is followed by orthodontic treatment and/ or orthognathic surgery. It is a simpler technique than the Le Fort I osteotomy procedure, and is considered an efficient and stable method.1,5,8,20 Several studies have shown an improvement in nasal obstruction after maxillary expansion.3,7,13,21,22 It improves the distance between the nasal walls and the septum, promoting widening of the nasal cavity, mainly in its anterior portion.14,23 The vertical dimension of the nasal cavity is also improved due to inferior rotation of the palate and the associated correction to the nasal septum.24,25 Although the nasal cavity alterations are variable and depend on age and the procedure,14 some authors have recorded improvements in nasal patency,2,26 with a decrease in respiratory problems.11,14,27,28 Postoperative stability is very similar for surgical maxillary expansion and orthodontic expansion, if the indication is correct.6 Changes after maxillary
expansion can be evaluated by frontal and lateral cephalometry, tomography, and photography. Is also possible to evaluate the nasal airway resistance (NAR) and the nasopharyngeal space by rhinomanometry, acoustic rhinomanometry, and nasofibroscopy.14 There is a need for more studies to clarify the correlation between maxillary expansion and upper airway changes. The aim of this study was to perform a threedimensional (3D) evaluation of the upper airway in patients submitted to surgically assisted maxillary expansion. A prospective evaluation was done of the upper airway volume of 15 patients presenting with transverse maxillary deficiency treated with surgically assisted rapid maxillary expansion (RME). Patients and methods
This study included 15 patients with the diagnosis of transverse maxillary deficiency. Surgically assisted RME by the technique described by Kraut,16 with separation of the pterygoid plates, was performed in all patients. No individuals presenting with clefts or craniofacial syndromes were included in the study. All subjects received a Hyrax-type palatal expander banded to the maxillary first
premolars and first molars. Activation started after 7 days. The patients were monitored 3 times weekly for appropriate activation of the appliance. The activation consisted of one quarter turn (0.25 mm) performed 3 times a day (every 8 h), resulting in 0.75 mm every 24 h, until the required expansion with a slight overcorrection of the crossbite was obtained (mean 14.4 days); the appliance was the stabilized and maintained for an additional 4 months. Cone beam computed tomography (CBCT) volumetric images (I-Cat; Fa´brica KaVo do Brasil Ind. Com. Ltda, Joinville, SC, Brazil) were obtained in the immediate preoperative period (T1), immediately after the end of maxillary expansion (T2), and at 6 months after expansion (T3) (Figs. 1–3). Computed tomography (CT) images were obtained with the patients seated and in natural head position. All patients were instructed not to breathe or swallow during image capture to avoid motion artefacts. The imaging field-of-view included the region from the hard palate to the third cervical vertebra. Images were taken parallel to the intervertebral space C2–C3. All were recorded on DVD for later analysis using computer software. 3D reconstructions were obtained using Dolphin Imaging 3D software (Dolphin Imaging and
Fig. 1. Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software in the preoperative period (T1).
Volumetric upper airway assessment
Fig. 2. Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software immediately after the end of expansion (T2).
583
Management Solutions, Chatsworth, CA, USA). Airway volume was assessed using a specific tool of the software. The region of interest was defined with its upper limit corresponding to a plane defined from the posterior limit of the hard palate and parallel to the Frankfort horizontal plane, and the inferior limit corresponding to a plane built from the most anterior and inferior point of the second cervical vertebra and also parallel to the Frankfort plane. The volumetric analysis of the determined 3D area was done by the software using a grey-scale. The darkest zone on the image indicates the airway and the volume is given in cubic millimetres. Thus, it was possible to assess the total volume of the airway and the diameter of the region of the smallest transverse section or zone. The airway was then measured: (1) the area (mm2), using the predefined superior and inferior limits and a two-dimensional tool of the software, (2) the volume (mm3), and (3) the smallest transverse section area (mm2). The measurements were submitted to descriptive statistical analysis, and statistical comparisons of changes were made between periods using GraphPad statistical software package (GraphPad Software Inc., La Jolla, CA, USA). Results
The sample comprised adults of both genders; nine were female and six were male, and their mean age was 30.2 7.4 years. The average period of activation of the appliance was 14.4 1.8 days. The average expansion in the inter-molar region immediately at the end of the activation was 6.93 3.43 mm. Data were considered parametric and the Tukey test showed no significant statistical differences between the volumes and areas evaluated in the previously defined periods (Table 1). Variations in the area, volume, and smallest transverse section area in relation to the different time periods are shown in Figs. 4–6, respectively. The exception was the smallest transverse section area, which presented a significant difference between the preoperative and the immediate postoperative periods (P < 0.05). A tendency to relapse with a reduction in the volume was observed between T2 and T3. Discussion Fig. 3. Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software at 6 months after the end of maxillary expansion (T3).
RME is a commonly used procedure to correct posterior crossbite, maxillary constriction, atresia or overdevelopment, and
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Pereira-Filho et al.
Table 1. Area and volume measurements obtained preoperatively and after maxillary expansion. Results are given as the mean standard deviation value, with the 95% confidence interval in parenthesis. 2
Area (mm ) Volume (mm3) Smallest transverse section area (mm2)
Immediately preoperative
After maxillary expansion
After 6 months
601.6 93.9 (549.6–653.6) 13,060 3697 (11,012–15,107) 138.8 58.2 (106.5–171.0)
646.1 165.3 (554.5–737.6) 15,212 5721 (12,044–18,380) 181.7 92.8 (130.3–233.1)
646.9 98.45 (592.4–701.4) 13,949 4319 (11,557–16,341) 173.5 88.0 (124.7–222.2)
inter-arch transverse discrepancies. It is also recommended to increase the upper airway space.1,2 Therefore it is important to understand its effect on the upper airway.
Changes in the craniofacial structures resulting from RME are considered capable of increasing the nasal cavity volume and reducing nasal resistance to airflow
Fig. 4. Box plot of the area at T1, T2, and T3, with the respective standard deviations.
Fig. 5. Box plot of the volume at T1, T2, and T3, with the respective standard deviations.
Fig. 6. Box plot of the smallest transverse section area at T1, T2, and T3, with the respective standard deviations.
and the apnea/hypopnea index in OSA patients.20 Upper airway changes are presently considered when planning surgical correction of dentofacial deformities. Studies focus mainly on bimaxillary advancements, usually applied to the treatment of OSA. There is a paucity of information regarding the effect of isolated maxillary expansion. Zhao et al.29 evaluated the upper airway space in 24 growing patients presenting maxillary transverse deficiency submitted to RME and compared the measurements with those from 24 patients without transverse deficiency. They observed that the airway volume in patients with transverse deficiency was significantly smaller and that maxillary expansion did not increase the volume of the oropharyngeal airway. In contrast, Smith et al.22 evaluated the upper airway space in 20 young adults through CBCT 3 months after RME and noted increases in the volume of the nasal cavity and nasopharynx, anterior and posterior facial heights, and palatal and mandibular plane angles. Perhaps the difference found between the current study and that of Smith et al.22 regarding the volume increase has some relation to the length of follow-up, because at the first evaluation in our study, an increase in the volume was also found, but then relapse occurred and the gain was lost. Variations in results between these studies may be due to several factors, such as patient positioning, tongue position during image acquisition,15 software used,5 size of the transverse discrepancy, and the population studied, among others. The present study included a non-growing adult population as verified by wrist and hand radiographs. Image acquisition was done with the head in natural position and the patient was instructed not to swallow to reduce the effect of the tongue on the oropharynx. All these factors could influence the airway images and consequently the measurements acquired. Patient characteristics such as age and gender, the surgical procedure followed for all of the patients, and patient positioning at the time of the scan are all variables that should be as standard as possible.
Volumetric upper airway assessment The gain in inter-molar distance was 6.93 3.43 mm. This is considerable, because the greatest increase occurs in the inter-canine region. However, there was no statistically significant increase in the airway space. This is in agreement with the results of Zhao et al.,29 who did not observe a significant volume increase in the oropharynx airway space. However, Zhao et al. did find a significant increase in the retropalatal space. The present results showed a modification of the area of greatest constriction (smallest transverse section area) that was statistically significant, and a dislocation or displacement of the smallest transverse section area point was also noted. This suggests that there was some change in the more superior regions of the nose and oropharynx; the smallest transverse section area that was at some high in the T1 dislocated for another high at the T2, it changed the position in some patients. It has been shown that RME increases the patency of the upper airway. However, as reported by de Freitas et al.,2 the causes of that effect are complex and involve several nasal structures. It can be demonstrated by means of acoustic rhinomanometry, computerized rhinomanometry, and cephalometric radiographs that a significant increase in the nasal cavity and reduction in the resistance to airflow occur. de Freitas et al. concluded that the effect of RME is more evident on bone than on the mucosa.2 The airway volume in the hard tissue parameters could be altered because of soft tissue hypertrophy. Nasal resistance could also be due to factors such as nasal polyps, large adenoids, and a deviated septum. The effects of surgically assisted maxillary expansion on the nasal airway and the nasal respiratory pattern in adult patients depend on the existence or not of nasal obstruction and on its cause, location, and severity. Wide variations in individual responses should be expected and this procedure does not necessarily result in an improvement in the airway dimensions. Maxillary expansion, as an isolated procedure, does not result in a statistically significant improvement in airway dimensions; RME results in inferior relocation of the smallest transverse section area.
Funding
Funded by FAPESP.
Competing interests
None declared. Ethical approval
Approved by the Ethics Committee of Araraquara Dental School. Patient consent
Patient consent was obtained. References 1. Betts NJ, Vanarsdall RL, Barber HD, Higgins-Barber K, Fonseca RJ. Diagnosis and treatment of transverse maxillary deficiency. Int J Adult Orthodon Orthognath Surg 1995;10:75–96. 2. de Freitas RR, Gonc¸alves AJ, Moniz NJ, Maciel FA. Surgically assisted maxillary expansion in adults: prospective study. Int J Oral Maxillofac Surg 2008;37:797–804. 3. Landes CA, Laudemann K, Petruchin O, Mack MG, Kopp S, Ludwig B, et al. Comparison of bipartite versus tripartite osteotomy for maxillary transversal expansion using 3-dimensional preoperative and postexpansion computed tomography data. J Oral Maxillofac Surg 2009;67: 2287–301. 4. Chiari S, Romsdorfer P, Swoboda H, Bantleon HP, Freudenthaler J. Effects of rapid maxillary expansion on the airways and ears—a pilot study. Eur J Orthod 2009;31: 135–41. 5. Kilic¸ N, Oktay H. Effects of rapid maxillary expansion on nasal breathing and some naso-respiratory and breathing problems in growing children: a literature review. Int J Pediatr Otorhinolaryngol 2008;72: 595–601. 6. Lobato HI, Machado SM, Ribeiro SM, Salgado PA, Pedreira EN. Airway flow and audiologic ability evaluation after rapid maxillary expansion—case report. Int J Pedriatr Otorhinolaryngol Extra 2010;5:89–90. 7. Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening the midpalatal suture. Angle Orthod 1961;31: 73–90. 8. Hartgerink DV, Vig PS, Abbott DW. The effect of rapid maxillary expansion on nasal airway resistance. Am J Orthod Dentofac Orthop 1987;92:381–9. 9. Wertz RA. Changes in nasal airflow incident to rapid maxillary expansion. Angle Orthod 1968;33:1–11. 10. Moss ML. The functional matrix. In: Kraus BS, Riedel RA, editors. Vistas of orthodontics. Philadelphia: Lea and Febiger; 1962. p. 88–9. 11. Byloff FK, Mossaz CF. Skeletal and dental changes following surgically assisted rapid palatal expansion. Eur J Orthod 2004;26: 403–9.
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12. Babacan H, Sokucu O, Doruk C, Ay S. Rapid maxillary expansion and surgically assisted rapid maxillary expansion effects on nasal volume. Angle Orthod 2006;76: 66–71. 13. Charezinski M, Balon-Perin A, Deroux E, De Maertelaer V, Glineur R. Transverse maxillary stability assisted by a transpalatal device. A retrospective pilot study of 9 cases. Int J Oral Maxillofac Surg 2009; 38:937–41. 14. Wriedt S, Kunkel M, Zentner A, Wahlmann UW. Surgically assisted rapid palatal expansion: an acoustic rhinometric, morphometric and sonographic investigation. J Orofac Orthop 2001;62:107–15. 15. Sokucu O, Kosger HH, Bicakci AA, Babacan H. Stability in dental changes in RME and SARME: a 2-year follow-up. Angle Orthod 2009;79:207–13. 16. Kraut RA. Surgically assisted rapid maxillary expansion by opening the midpalatal suture. J Oral Maxillofac Surg 1984;42: 651–5. 17. Hershey HG, Stewart BL, Warren DW. Changes in nasal airway resistance associated with rapid maxillary expansion. Am J Orthod 1976;69:274–84. 18. Mitsuda ST, Pereira MD, Passos AP, Hino CT, Ferreira LM. Effects of surgically assisted rapid maxillary expansion on nasal dimensions using acoustic rhinometry. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:191–6. 19. Bicakci AA, Agar U, Sokucu O, Babacan H, Doruk C. Nasal airway changes due to rapid maxillary expansion timing. Angle Orthod 2005;75:1–6. 20. Korkhaus G. Discussion of report: a review of orthodontic research (1945–1950). Int Dent J 1953;3:356. 21. Haralambidis A, Ari-Demirkaya A, Acar A, Ku¨c¸u¨kkeles N, Ates M, Ozaya S. Morphologic changes of the nasal cavity induced by rapid maxillary expansion: a study on 3dimensional computed tomography models. Am J Orthod Dentofac Orthop 2009;136: 815–21. 22. Smith T, Ghoneima A, Stewart K, Liu S, Eckbert G, Halum S, et al. Three-dimensional computed tomography analysis of airway volume changes after rapid maxillary expansion. Am J Orthod Dentofac Orthop 2012;141:618–26. 23. Griffin CJ. The treatment of chronic nasal obstruction by subluxation of the vomeromaxillary articulation. Aust Dent J 1958;3: 107–17. 24. Northway WM, Meade Jr JB. Surgically assisted rapid maxillary expansion: a comparison of technique, response and stability. Angle Orthod 1997;67:309–20. 25. Capelozza Filho L, Cardoso Neto J, da Silva Filho OG, Ursi WJ. Non-surgically assisted rapid maxillary expansion in adults. Int J Adult Orthodon Orthognath Surg 1996;11: 57–66.
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26. Gurel HG, Memil B, Erkan M, Sukurica Y. Long-term effects of rapid maxillary expansion followed by fixed appliances. Angle Orthod 2010;80:5–9. 27. Bell WH, Epker BN. Surgical-orthodontic expansion of the maxilla. Am J Orthod 1976;70:517–28. 28. Basciftci FA, Mutlu N, Karaman AI, Malkoc S, Ku¨c¸u¨kkolbasi H. Does the timing and
method of rapid maxillary expansion have an effect on the changes in nasal dimensions? Angle Orthod 2002;72:118–23. 29. Zhao Y, Nguyen M, Gold E, Mah JK, Sameshima G, Enciso R. Oropharyngeal airway changes after rapid palatal expansion evaluated with cone-beam computed tomography. Am J Orthod Dentofac Orthop 2010; 137:S71–8.
Address: Marcelo S. Monnazzi Rua Volunta´rios da Pa´tria 2777 AP 1001 – Centro Araraquara – Sa˜o Paulo CEP 14801-320 Brazil Tel: +55 1633845822 E-mails: [email protected], [email protected]
Clinical Paper Orthognathic Surgery
Volumetric upper airway assessment in patients with transverse maxillary deficiency after surgically assisted rapid maxillary expansion
V. A. Pereira-Filho, M. S. Monnazzi, M. A. C. Gabrielli, R. Spin-Neto, E. R. Watanabe, C. M. M. Gimenez, A. Santos-Pinto, M. F. R. Gabrielli Department of Diagnosis and Oral Surgery, Dental School of Araraquara (UNESP), Araraquara, Sa˜o Paulo, Brazil
V.A. Pereira-Filho, M.S. Monnazzi, M.A.C. Gabrielli, R. Spin-Neto, E.R. Watanabe, C.M.M. Gimenez, A. Santos-Pinto, M.F.R. Gabrielli: Volumetric upper airway assessment in patients with transverse maxillary deficiency after surgically assisted rapid maxillary expansion. Int. J. Oral Maxillofac. Surg. 2014; 43: 581–586. # 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. Transverse maxillary deficiency is commonly found in patients with sleep apnea and is also related to abnormal breathing patterns. Maxillary expansion procedures promote widening of the nasal floor and reduce the resistance to airflow, and have a positive influence on nasopharynx function. In order to evaluate volume changes in the upper airway, 15 adult patients with transverse maxillary deficiency underwent surgically assisted rapid maxillary expansion (RME) until a slight overcorrection of the crossbite was obtained. Cone beam computed tomography (CBCT) volumetric images were obtained at three predefined time points. The mean age of the patients was 30.2 (7.4) years; nine were females and six were males. The area, volume, and the smallest transverse section area of the airway were assessed using Dolphin Imaging 3D software. Statistical comparisons were made of the changes between time periods. No statistically significant differences were found for volume or area. However a significant difference was found between the preoperative and immediate postoperative smallest transverse section area (P < 0.05). Maxillary expansion, as an isolated procedure, does not result in a statistically significant improvement in the airway dimensions and results in an inferior relocation of the smallest transverse section area.
Transverse maxillary deficiency is a pathological condition that may be associated with other types of dentoskeletal alterations, with esthetic1–3 and functional implications,4–7 including respiratory 0901-5027/050581 + 06 $36.00/0
problems. The incidence is around 3– 18% in orthodontic patients.1,8 Patients with this condition have a narrow nasal cavity,4,5 which increases the resistance to nasal airway flow.7–10
Key words: maxillary transverse deficiency; oropharynx; malocclusion; airway assessment. Accepted for publication 4 November 2013 Available online 20 December 2013
Recently, the relationship between transverse maxillary deficiency and obstructive sleep apnea (OSA) has received attention in the literature. It is a common finding in sleep apnea patients, as well as
# 2013 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
582
Pereira-Filho et al.
being related to abnormal breathing patterns. OSA syndrome is a condition that occurs secondary to the collapse of the upper airway. It results in mechanical obstruction of the airflow during sleep, producing hypoxia and/or tachycardia and bradycardia episodes, and increasing peripheral vasoconstriction and the risk for cardiovascular and cerebrovascular events. The obstruction can occur at the level of the nasal cavities, soft palate, tonsils, and retro-lingual area of the oral pharynx. Retrusion of the jaws is frequently associated with sleep apnea syndrome due to malpositioning of the soft tissue structures and a reduction in the volume of the upper airway.11,12 Maxillary expansion procedures,13 both orthodontic (patients with growth potential) and surgically assisted (adult patients), promote widening of the nasal floor and reduce resistance to airflow, with a positive influence on the function of the nasopharynx and correction of respiratory dysfunction. To define the modality of treatment, age, skeletal maturation, severity of the deformity, and functional implications have to be considered.14–17 Well planned and performed treatment can be executed, even in adult patients, without excessive inclination or extrusion of teeth, dental or periodontal damage, or pain.4,12,18 The surgical treatment of adult patients can be performed through a segmented Le Fort I osteotomy or by surgically assisted expansion.19 The first option can correct the maxillary position in three dimensions. Surgically assisted expansion will correct the transverse dimension and is followed by orthodontic treatment and/ or orthognathic surgery. It is a simpler technique than the Le Fort I osteotomy procedure, and is considered an efficient and stable method.1,5,8,20 Several studies have shown an improvement in nasal obstruction after maxillary expansion.3,7,13,21,22 It improves the distance between the nasal walls and the septum, promoting widening of the nasal cavity, mainly in its anterior portion.14,23 The vertical dimension of the nasal cavity is also improved due to inferior rotation of the palate and the associated correction to the nasal septum.24,25 Although the nasal cavity alterations are variable and depend on age and the procedure,14 some authors have recorded improvements in nasal patency,2,26 with a decrease in respiratory problems.11,14,27,28 Postoperative stability is very similar for surgical maxillary expansion and orthodontic expansion, if the indication is correct.6 Changes after maxillary
expansion can be evaluated by frontal and lateral cephalometry, tomography, and photography. Is also possible to evaluate the nasal airway resistance (NAR) and the nasopharyngeal space by rhinomanometry, acoustic rhinomanometry, and nasofibroscopy.14 There is a need for more studies to clarify the correlation between maxillary expansion and upper airway changes. The aim of this study was to perform a threedimensional (3D) evaluation of the upper airway in patients submitted to surgically assisted maxillary expansion. A prospective evaluation was done of the upper airway volume of 15 patients presenting with transverse maxillary deficiency treated with surgically assisted rapid maxillary expansion (RME). Patients and methods
This study included 15 patients with the diagnosis of transverse maxillary deficiency. Surgically assisted RME by the technique described by Kraut,16 with separation of the pterygoid plates, was performed in all patients. No individuals presenting with clefts or craniofacial syndromes were included in the study. All subjects received a Hyrax-type palatal expander banded to the maxillary first
premolars and first molars. Activation started after 7 days. The patients were monitored 3 times weekly for appropriate activation of the appliance. The activation consisted of one quarter turn (0.25 mm) performed 3 times a day (every 8 h), resulting in 0.75 mm every 24 h, until the required expansion with a slight overcorrection of the crossbite was obtained (mean 14.4 days); the appliance was the stabilized and maintained for an additional 4 months. Cone beam computed tomography (CBCT) volumetric images (I-Cat; Fa´brica KaVo do Brasil Ind. Com. Ltda, Joinville, SC, Brazil) were obtained in the immediate preoperative period (T1), immediately after the end of maxillary expansion (T2), and at 6 months after expansion (T3) (Figs. 1–3). Computed tomography (CT) images were obtained with the patients seated and in natural head position. All patients were instructed not to breathe or swallow during image capture to avoid motion artefacts. The imaging field-of-view included the region from the hard palate to the third cervical vertebra. Images were taken parallel to the intervertebral space C2–C3. All were recorded on DVD for later analysis using computer software. 3D reconstructions were obtained using Dolphin Imaging 3D software (Dolphin Imaging and
Fig. 1. Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software in the preoperative period (T1).
Volumetric upper airway assessment
Fig. 2. Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software immediately after the end of expansion (T2).
583
Management Solutions, Chatsworth, CA, USA). Airway volume was assessed using a specific tool of the software. The region of interest was defined with its upper limit corresponding to a plane defined from the posterior limit of the hard palate and parallel to the Frankfort horizontal plane, and the inferior limit corresponding to a plane built from the most anterior and inferior point of the second cervical vertebra and also parallel to the Frankfort plane. The volumetric analysis of the determined 3D area was done by the software using a grey-scale. The darkest zone on the image indicates the airway and the volume is given in cubic millimetres. Thus, it was possible to assess the total volume of the airway and the diameter of the region of the smallest transverse section or zone. The airway was then measured: (1) the area (mm2), using the predefined superior and inferior limits and a two-dimensional tool of the software, (2) the volume (mm3), and (3) the smallest transverse section area (mm2). The measurements were submitted to descriptive statistical analysis, and statistical comparisons of changes were made between periods using GraphPad statistical software package (GraphPad Software Inc., La Jolla, CA, USA). Results
The sample comprised adults of both genders; nine were female and six were male, and their mean age was 30.2 7.4 years. The average period of activation of the appliance was 14.4 1.8 days. The average expansion in the inter-molar region immediately at the end of the activation was 6.93 3.43 mm. Data were considered parametric and the Tukey test showed no significant statistical differences between the volumes and areas evaluated in the previously defined periods (Table 1). Variations in the area, volume, and smallest transverse section area in relation to the different time periods are shown in Figs. 4–6, respectively. The exception was the smallest transverse section area, which presented a significant difference between the preoperative and the immediate postoperative periods (P < 0.05). A tendency to relapse with a reduction in the volume was observed between T2 and T3. Discussion Fig. 3. Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software at 6 months after the end of maxillary expansion (T3).
RME is a commonly used procedure to correct posterior crossbite, maxillary constriction, atresia or overdevelopment, and
584
Pereira-Filho et al.
Table 1. Area and volume measurements obtained preoperatively and after maxillary expansion. Results are given as the mean standard deviation value, with the 95% confidence interval in parenthesis. 2
Area (mm ) Volume (mm3) Smallest transverse section area (mm2)
Immediately preoperative
After maxillary expansion
After 6 months
601.6 93.9 (549.6–653.6) 13,060 3697 (11,012–15,107) 138.8 58.2 (106.5–171.0)
646.1 165.3 (554.5–737.6) 15,212 5721 (12,044–18,380) 181.7 92.8 (130.3–233.1)
646.9 98.45 (592.4–701.4) 13,949 4319 (11,557–16,341) 173.5 88.0 (124.7–222.2)
inter-arch transverse discrepancies. It is also recommended to increase the upper airway space.1,2 Therefore it is important to understand its effect on the upper airway.
Changes in the craniofacial structures resulting from RME are considered capable of increasing the nasal cavity volume and reducing nasal resistance to airflow
Fig. 4. Box plot of the area at T1, T2, and T3, with the respective standard deviations.
Fig. 5. Box plot of the volume at T1, T2, and T3, with the respective standard deviations.
Fig. 6. Box plot of the smallest transverse section area at T1, T2, and T3, with the respective standard deviations.
and the apnea/hypopnea index in OSA patients.20 Upper airway changes are presently considered when planning surgical correction of dentofacial deformities. Studies focus mainly on bimaxillary advancements, usually applied to the treatment of OSA. There is a paucity of information regarding the effect of isolated maxillary expansion. Zhao et al.29 evaluated the upper airway space in 24 growing patients presenting maxillary transverse deficiency submitted to RME and compared the measurements with those from 24 patients without transverse deficiency. They observed that the airway volume in patients with transverse deficiency was significantly smaller and that maxillary expansion did not increase the volume of the oropharyngeal airway. In contrast, Smith et al.22 evaluated the upper airway space in 20 young adults through CBCT 3 months after RME and noted increases in the volume of the nasal cavity and nasopharynx, anterior and posterior facial heights, and palatal and mandibular plane angles. Perhaps the difference found between the current study and that of Smith et al.22 regarding the volume increase has some relation to the length of follow-up, because at the first evaluation in our study, an increase in the volume was also found, but then relapse occurred and the gain was lost. Variations in results between these studies may be due to several factors, such as patient positioning, tongue position during image acquisition,15 software used,5 size of the transverse discrepancy, and the population studied, among others. The present study included a non-growing adult population as verified by wrist and hand radiographs. Image acquisition was done with the head in natural position and the patient was instructed not to swallow to reduce the effect of the tongue on the oropharynx. All these factors could influence the airway images and consequently the measurements acquired. Patient characteristics such as age and gender, the surgical procedure followed for all of the patients, and patient positioning at the time of the scan are all variables that should be as standard as possible.
Volumetric upper airway assessment The gain in inter-molar distance was 6.93 3.43 mm. This is considerable, because the greatest increase occurs in the inter-canine region. However, there was no statistically significant increase in the airway space. This is in agreement with the results of Zhao et al.,29 who did not observe a significant volume increase in the oropharynx airway space. However, Zhao et al. did find a significant increase in the retropalatal space. The present results showed a modification of the area of greatest constriction (smallest transverse section area) that was statistically significant, and a dislocation or displacement of the smallest transverse section area point was also noted. This suggests that there was some change in the more superior regions of the nose and oropharynx; the smallest transverse section area that was at some high in the T1 dislocated for another high at the T2, it changed the position in some patients. It has been shown that RME increases the patency of the upper airway. However, as reported by de Freitas et al.,2 the causes of that effect are complex and involve several nasal structures. It can be demonstrated by means of acoustic rhinomanometry, computerized rhinomanometry, and cephalometric radiographs that a significant increase in the nasal cavity and reduction in the resistance to airflow occur. de Freitas et al. concluded that the effect of RME is more evident on bone than on the mucosa.2 The airway volume in the hard tissue parameters could be altered because of soft tissue hypertrophy. Nasal resistance could also be due to factors such as nasal polyps, large adenoids, and a deviated septum. The effects of surgically assisted maxillary expansion on the nasal airway and the nasal respiratory pattern in adult patients depend on the existence or not of nasal obstruction and on its cause, location, and severity. Wide variations in individual responses should be expected and this procedure does not necessarily result in an improvement in the airway dimensions. Maxillary expansion, as an isolated procedure, does not result in a statistically significant improvement in airway dimensions; RME results in inferior relocation of the smallest transverse section area.
Funding
Funded by FAPESP.
Competing interests
None declared. Ethical approval
Approved by the Ethics Committee of Araraquara Dental School. Patient consent
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