Hyrax appliance opening and pattern of skeletal maxillary expansion after surgically assisted rapid palatal expansion: a computed tomography evaluation

Hyrax appliance opening and pattern of skeletal maxillary expansion after surgically assisted rapid palatal expansion: a computed tomography evaluation Dov C. Goldenberg, MD, PhD,a Fernanda C. Goldenberg, DDS, PhD,c Nivaldo Alonso, MD, PhD,a Eloisa S. Gebrin, MD, PhD,b Theresinha S. Amaral, DDS,b Marco A. Scanavini, DDS, PhD,c and Marcus C. Ferreira, MD, PhD,a Sao Paulo, Brazil UNIVERSITY OF SAO PAULO MEDICAL SCHOOL AND METHODIST UNIVERSITY OF SAO PAULO

Objective. The objective of this study was to evaluate, using computed tomography, correlations between Hyrax appliance opening and post-SARPE skeletal changes. Study design. Fifteen patients underwent SARPE according to a specific protocol and were followed. Linear and angular measurements of the anterior, intermediate, and posterior portions of the maxilla were evaluated. The correlation between maxillary expansion and appliance opening was investigated. Results. Significant overall expansion was observed. In the anterior and intermediate portions of the maxilla, the increase in maxillary width was greater than that observed in the posterior portion. The degree of appliance opening was significantly greater than that of the skeletal expansion. Also, no linear correlation between appliance opening and regional maxillary expansion was established. Conclusion. The transverse expansion of the maxilla was less than uniform. The lack of linear correlation between appliance opening and skeletal expansion is attributable to multiple factors, including those related to the device, the surgical technique, and the craniofacial deformity itself. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008; 106:812-819)

Transverse maxillary deficiency is a clinical problem with which the orthodontist is frequent confronted. In complex maxillofacial abnormalities, this condition complicates vertical and sagittal deformities, thereby posing a challenge to the craniofacial or maxillofacial surgeon.1-8 The preferred treatment for transverse maxillary deficiency is a procedure that expands the maxilla without causing segmental tilting, orthodontic/orthopedic relapse, or dental/periodontal damage.9 In recent years, surgically assisted rapid palatal expansion (SARPE) has become the procedure of choice for treating transverse maxillary deficiency in adult patients.6,10-13 Using a Hyrax appliance and performing maxillary osteotomies, the maxilla can be safely expanded. More recently, the use of computed tomography (CT) has come to be considered a reliable method

a

Division of Plastic Surgery, Hospital das Clinicas, University of Sao Paulo Medical School, Sao Paulo, Brazil. b Department of Radiology, Hospital das Clinicas, University of Sao Paulo Medical School, Sao Paulo, Brazil. c Department of Orthodontics, Methodist University of Sao Paulo, Sao Paulo, Brazil. Received for publication Jan 8, 2008; accepted for publication Feb 25, 2008. 1079-2104/$ - see front matter © 2008 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2008.02.034

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of evaluating the changes in maxillary dimensions after SARPE.14-16 In term of the skeletal effects of SARPE, many studies have shown that use of Hyrax appliances can increase the width of the maxilla, nasal cavity, and maxillary arch. For orthodontists and surgeons, it would be of interest and relevance to have objective knowledge of how the appliance opening relates to skeletal expansion, and to know whether or not there is a consistent relationship between the two. However, there are little data in the literature regarding the correlation between the degree of appliance opening and the pattern of transverse skeletal expansion, including the role of osteotomy sites and the mechanical forces transferred to the bone via the appliance. The goals of the present study were to assess maxillary skeletal changes after SARPE, using CT to evaluate those parameters, and to look for correlations between such changes and the degree of appliance opening. PATIENTS AND METHODS Between June 2004 and May 2005, 15 patients (10 females and 5 males) underwent SARPE according to a defined multidisciplinary protocol at the Hospital das Clínicas-University of São Paulo Medical

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Fig. 1. Maxillary osteotomies: transverse and sagittal osteotomies without pterygomaxillary separation.

School (HC-FMUSP) and at the Department of Orthodontics, Methodist University of São Paulo. This project was approved by the Ethical Committee at Hospital das Clinicas, University of Sao Paulo Medical School, and informed consent was obtained from every patient. All patients were skeletally mature. Ages ranged from 18 to 37 years old (mean 24.47 years, SD 5.79 years). All patients presented a total transverse maxillary deficiency of more than 5 mm, a maxillomandibular transverse differential index (according to Betts et al.6) greater than 5 mm, and a crossbite (anterior or posterior). None had any history of orthodontic treatment or presented any craniofacial syndromes. Preoperative evaluation The preoperative protocol included orthodontic photographic documentation (frontal and lateral photographs using the natural head position as guideline), dental casting, frontal and lateral cephalograms, and multislice CT scans (collimation of 1 mm at 0.5-mm intervals) in the axial plane. Preoperative appliance placement One week before the surgery, an expansion Hyrax appliance (Dental Morelli, São Paulo, Brazil) with a 13-mm expansion screw was bonded to the 2 maxillary

first premolars and first molars, and fixed with 1.2-mm orthodontic wires. When first molars or first premolar teeth were absent, the adjacent molar or premolar was used. Surgical technique SARPE was performed under general anesthesia and nasotracheal intubation. A modified Le Fort I maxillary osteotomy was performed, not including the separation of the pterygomaxillary suture. In conjunction, a sagittal palatal osteotomy was carried out, running from the midline of the alveolar bone, between the central incisors, to the posterior nasal spine (Fig. 1). After the osteotomies the Hyrax appliance was activated to obtain maximum aperture and diastema formation. This was followed by immediate regression, leaving a 1-mm gap. All patients received prophylactic antibiotics (cefazolin 2 g, intravenous) during the first 24 hours. A single dose of hydrocortisone (300 mg) was administered intraoperatively. Expansion protocol On the third postoperative day, SARPE was initiated by the orthodontic team by effecting a 0.25-mm expansion (one-fourth turn). The patient was instructed to perform additional 0.25-mm expansions, one every 12

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Fig. 2. Coronal reconstruction evaluation. Maxillary width was measured at the level of the nasal floor (L1), at the level of the palatine process of the maxilla (L2), and at the level of the inferior palatine margin of the alveolar process of the maxilla (L3). The angle between the anterior nasal spine and the palatine alveolar bone (A-Ns-A) was also measured on both sides.

Fig. 3. Axial plane CT evaluation. The anatomical landmarks used in measurements were the greater palatine foramina (points A and C, left and right), the anterior nasal spine (point B), and the medial wall of the maxillary sinus (points D and E). A linear segment, designated AC, connected the greater left and right palatine foramina and reflects the width of the posterior portion of the maxilla. The angle between the anterior nasal spine and the palatine foramina (ABC) also was used to evaluate the posterior portion of the maxilla. The projection of the midpoints of segments AB and BC into the medial maxillary sinus walls were designated points D and E, respectively. The measurement of segment DE reflects the width of the intermediate portion of the maxilla.

hours. Weekly evaluations were performed. The expansion was finalized when an overcorrection of 2.5 mm had been achieved on each side or when the lingual canines of maxillary teeth met the buccal canines of the mandibular teeth. After the expansion had been com-

pleted, the appliance was stabilized with an orthodontic wire to lock the expander and was left in place for 3 months, at which point it was removed and replaced with a retention appliance, which was left in place for at least 3 additional months.

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Fig. 4. Patient with transverse maxillary deficiency presenting bilateral crossbite. Occlusal and palatine views. Upper row, preoperative aspect. Second row, after 28 days, at completion of maxillary expansion. Third row, after 3 months of expansion and screw-locking. Lower row, 6 months after surgery and immediately after replacing the expander with a retention appliance.

The duration of the expansion phase, the number of activations, and the expansion obtained (in millimeters) were noted for each patient. After appliance removal, the opening was confirmed by direct measurement and by counting the number of turns required to place the screw back into its initial position. Tomography study An established study protocol, using multislice CT (Philips MX8000, IDT10 and IDT16; Philips Medical Systems, Eindhoven, The Netherlands), was defined. Axial slices parallel to the palatine plane were obtained for each patient before and 6 months after the SARPE. Computed coronal reconstruction derived from the original axial image acquisition was performed. In the preoperative scans, head position was adjusted and standardized in order to obtain comparable images in the postoperative period. Linear and angular measurements of the anterior, intermediate, and posterior portions of the maxilla were evaluated to determine the pattern of transversal maxillary expansion. The cross-sectional area of the maxilla was calculated to obtain general information about maxillary expansion. All measurements were taken in duplicate by 2 professionals, the senior surgeon (D.C.G.) and the radiologist in charge of the protocol (T.S.A.).

The coronal reconstruction was used to evaluate changes in the most anterior portion of the maxilla. Coronal reconstruction was performed perpendicular to the palatine plane. Maxillary width was measured at the level of the nasal floor, the palatine process of the maxilla, and the inferior margin of the maxillary alveolar process. The angle between the anterior nasal spine and the inferior margin of the alveolar bone was also measured (Fig. 2). The intermediate and posterior portions of the maxilla were evaluated in the axial images. Axial acquisition was performed with slices parallel to the palatine plane. The angle formed by anterior nasal spine and greater palatine foramina, as well the distance between the greater palatine foramina were measured in order to evaluate posterior expansion. The intermediate portion of the maxilla was evaluated by measuring the distance between the medial maxillary sinus walls at the midpoint between the greater palatine foramina and the anterior nasal spine (Fig. 3). The cross-sectional area of the maxilla was calculated. Measurement was obtained in the axial plane, at the level of the most cranial slice after the end of maxillary sinus. Screen capture software (SnagIt, version 5.0; TechSmith Corporation, East Lansing, MI) was used to store preoperative and postoperative images in TIFF format

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for future measurements, as well as for the identification and evaluation of measurement errors.

Table I. Mean absolute and relative differences between preoperative and postoperative measurements

Correlation between Hyrax appliance opening and skeletal maxillary expansion The opening of the Hyrax appliance (in millimeters) was compared to the degree of maxillary skeletal expansion in the three portions of the maxilla evaluated. The ratio between skeletal expansion and appliance opening (designated the S/A ratio) was calculated as follows: S/A ⫽ Skeletal Maxillary Expansion (POST– PRE)(mm)/Appliance opening (mm)

L1

Measurement

Measurement evaluation and statistics The linear and angular measurements were evaluated statistically. Normal distribution of data was determined using normal probability plots, the ShapiroWilks test, and the Kolmogorov-Smirnov test. All preoperative and postoperative measurements taken in each axial and coronal slice were compared using the Student t test. Values of P less than .05 were considered statistically significant. Absolute differences and relative differences before and after expansion were analyzed. The relative differences were calculated using the formula: 100 ⫻ (post–pre)/pre. The results are expressed in percentages. The relationship between the Hyrax appliance opening and skeletal maxillary expansion was evaluated using Pearson’s correlation coefficient (r). RESULTS Mean duration of the procedure was 80 minutes. All patients were discharged at 24 hours after surgery. Follow-up evaluations continued for 6 months, and all of the patients were monitored for at least 1 year. Mean appliance opening was 11.47 ⫹ 1.65 mm. The desired transverse expansion was clinically obtained in all cases (Fig. 4). Descriptive measurements The cross-sectional area of the maxilla was significantly increased. Transverse expansion of the maxilla as a consequence of opening of the Hyrax appliance occurred in all cases, with differences among the 3 portions analyzed in terms of the patterns of expansion. Measurements of the anterior portion of the maxilla obtained from the coronal reconstruction revealed a statistically significant transverse increase. A statistically significant increase in maxillary width was also observed in the intermediate portion of the maxilla. In the evaluation of the posterior portion of the maxilla, no statistically significant differences were found (Table I). The appliance opening was significantly greater than

L2 L3 A-Ns-A

DE AC ABC

AREA

Difference

Mean ⫾ SD

Absolute (mm) Relative (%) Absolute (mm) Relative (%) Absolute (mm) Relative (%) Absolute (degrees) Relative (%) Absolute (mm) Relative (%) Absolute (mm) Relative (%) Absolute (degrees) Relative (%) Absolute (mm) Relative (%)

2.45 ⫾ 1.56 11.52 ⫾ 8.97 5.16 ⫾ 1.4 28.28 ⫾ 8.72 5.41 ⫾ 2.23 19.10 ⫾ 8.35 9.67 ⫾ 4.53

P ⬍ .0001 (s) .0002 (s) ⬍ .00001 (s) ⬍ .0001 (s) ⬍ .0001 (s) ⬍ .0001 (s) ⬍ .0001 (s)

13.54 ⫾ 6.48 4.05 ⫾ 1.97 16.08 ⫾ 9.38 0.34 ⫾ 0.96 1.10 ⫾ 2.82 0.13 ⫾ 2.10

⬍ .0001 (s) ⬍ .0001 (s) ⬍ .0001 (s) .1898 (s) .1522 (s) .8093 (ns)

0.53 ⫾ 5.07 287.07 ⫾ 119.96 13.18 ⫾ 5.54

.6907 (ns) ⬍ .0001 (s) ⬍ .0001 (s)

Absolute, mean absolute difference between preoperative and postoperative measurement; Relative, mean relative difference (100 ⫻ [post–pre]/pre) between preoperative and postoperative measurement; s, statistically significant (P ⬍ .05); ns, not statistically significant. Measurements of the anterior portion of the maxilla: L1, width at the level of the nasal floor; L2, width at the level of the hard palate; L3, width at the level of the inferior margin of the palatine alveolar bone; A-Ns-A, angle between the anterior nasal spine and the inferior margin of the alveolar bone. Measurement of the intermediate portion of the maxilla: DE, distance between the medial walls of the maxillary sinus. Measurements of the posterior portion of the maxilla: AC, distance between the left and right greater palatine foramina; ABC, angle formed by the greater palatine foramina and anterior nasal spine; AREA, cross-sectional area of the maxilla.

the skeletal expansion for all variables evaluated (Fig. 5). Comparison of S/A ratios between maxillary portions revealed that the greatest expansion occurred in the most inferior and anterior region of the maxilla, where it was nearly 50% that of the appliance opening (Figs. 6 and 7). Even with a consistent and predictable pattern of maxillary skeletal expansion such as that observed in this group of patients, no linear correlation between appliance opening and regional maxillary expansion was found (Table II). Overall complication rates and outcome No complications (such as significant bleeding, infection, or compromised tooth vitality) were observed during the 6 months of follow-up evaluation. Transient dental mobility was observed in 2 cases (13.3%). Mild pain was reported by 12 (80%) of the patients, all of whom responded satisfactorily to oral

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Fig. 5. Graphic illustration of relative skeletal maxillary expansion (S/A ratio), comparing appliance expansion and skeletal expansion in the anterior (L1, L2, and L3), intermediate (DE), and posterior (AC) portions of the maxilla.

Fig. 7. Relative skeletal maxillary expansion (S/A ratio) of the anterior, intermediate, and posterior portions of the maxilla secondary to the appliance opening. The greatest expansion occurred in the most anterior region of the maxilla.

Fig. 6. Relative skeletal maxillary expansion (S/A ratio) of the anterior portion of the maxilla secondary to the appliance opening. The greatest expansion occurred in the most inferior region of the maxilla.

analgesics. In all cases, edema regressed after 1 to 2 weeks, and food intake returned to normal within 2 weeks. All patients spontaneously reported a clinically significant improvement in nasal airflow and breathing.

DISCUSSION In skeletally full-grown individuals, SARPE has been advocated in order to overcome the fusion of the sutures and the resulting resistance to expansion.6,7,11,13,17-29 As a means of correcting severe transverse maxillary deficiencies, it is a procedure that is simple, highly effective, and stable.1,2,5-7,13,14,17-19 To date, there is no consensus regarding the minimum number of osteotomies required to allow a uniform and parallel maxillary expansion.1-3,5,6,8,10,11,22,23,30 It seems reasonable to assume that combining all transverse and midpalatal osteotomies provides the desired maxillary expan-

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Table II. Pearson’s correlation coefficient (r) between appliance opening and absolute and relative differences of skeletal maxillary expansion Absolute

Relative

Variable

r

P

r

P

AC DE L1 L2 L3

0.55 0.15 ⫺0.06 0.52 ⫺0.36

.0352 .5912 .8367 .0486 .1927

0.58 0.14 ⫺0.14 0.43 ⫺0.42

.0234 .6268 .6299 .1091 .1165

Absolute, mean absolute difference between preoperative and postoperative measurement; Relative, mean relative difference (100 ⫻ [post–pre]/pre) between preoperative and postoperative measurement. Measurements of the anterior portion of the maxilla: AC, distance between left and right greater palatine foramina; DE, distance between medial walls of maxillary sinus; L1, width at level of nasal floor; L2, width at level of hard palate; L3, width at level of inferior margin of palatine alveolar bone.

sion of the anterior, intermediate, and posterior portions of the maxilla. Since there is a risk of intraoperative bleeding during pterygoid plate separation, we agree to reserve pterygoid plate separation for situations in which the posterior portion of the maxilla is significantly affected,1,11,13,22,26,31 and in which there are posterior crossbites that must be addressed and corrected. In a recent report using CT to evaluate skeletal parameters, we observed that transverse expansion of the maxilla achieved through SARPE without pterygoid plate separation was less than uniform.14This fact could be related to the proposed surgical protocol, since the pterygomaxillary suture was not osteotomized. According to many studies, the patterns of maxillary expansion are more closely related to the maxillary osteotomies than to the appliance properties, and the posterior maxillary portion is typically considered the fulcrum, especially when the pterygomaxillary junction is left intact.31-33 However, the influence that the degree of appliance opening has on the pattern of maxillary expansion has been less explored. As observed in the present study, gradual appliance opening during the expansion phase does not reflect the true skeletal expansion. The appliance opening was always greater than the skeletal expansion for all variables evaluated. The greatest expansion occurred in the most inferior and anterior region of the maxilla, and achieved only 50% that of the appliance opening. Although the pattern of maxillary expansion obtained through this protocol was consistent and predictable, it was not possible to establish a correlation between the degree of appliance opening and the degree

of expansion. These findings can be attributed to a number of factors that must be considered in conjunction: the Hyrax appliance and its tension/resistance properties5,7,12,16,29; dentoalveolar movements and the effect of the appliance on support dental elements1,26,34; number of osteotomies and maxillary compliance3,5,9,14,15,24,29,33; and type of craniofacial deformity.11,14,18,28,30 In summary, although it is important to obtain a predictable pattern of 3-dimensional changes after maxillary expansion achieved through surgical procedures, clinical follow-up evaluation is still of great relevance. CONCLUSIONS In the present study, the transverse expansion of the maxilla achieved through SARPE without pterygoid plate separation was less than uniform. It is unlikely that the lack of a linear correlation between the degree of appliance opening and that of skeletal expansion is attributable to a single factor. The device itself, the surgical technique, and the type of craniofacial deformity are all potential contributing factors. REFERENCES 1. Byloff FK, Mossaz CF. Skeletal and dental changes following surgically assisted rapid palatal expansion Eur J Orthod 2004;26:403-9. 2. Anttila A, Finne K, Keski-Nisula K, Somppi M, Panula K, Peltomäki T. Feasibility and long-term stability of surgically assisted rapid maxillary expansion with lateral osteotomy. Eur J Orthod 2004;26:391-5. 3. Chung CH, Woo A, Zagarinsky J, Vanarsdall RL, Fonseca RJ. Maxillary sagittal and vertical displacement induced by surgically assisted rapid palatal expansion. Am J Orthod Dentofac Orthop 2001;120:144-8. 4. Cameron CG, Franchi L, Baccetti T, McNamara JA, Jr. Longterm effects of rapid maxillary expansion: a posteroanterior cephalometric evaluation. Am J Orthod Dentofac Orthop 2002;121:129-35. 5. Northway WM, Meade JB Jr. Surgically assisted rapid palatal expansion: a comparison of technique, response and stability. Angle Orthod 1997;67:309-20. 6. Betts NJ, Vanarsdall RL, Barbes HD, Higgins-Barber K, Fanseca RJ. Diagnosis and treatment of transverse maxillary deficiency. Int J Adult Orthod 1995;10:75-96. 7. Berger JL, Pangrazio-Kulbersh V, Borgula T, Kaczynski R. Stability of orthopedic and surgically assisted rapid palatal expansion over time. Am J Orthod Dentofac Orthop 1998;114:638-45. 8. Basdra EK, Zoller JE, Komposch G. Surgically assisted rapid palatal expansion. JCO 1995;29:762-6. 9. Matteini C, Mommaerts MY. Posterior transpalatal distraction with pterygoid disjunction: a short-term model study. Am J Orthod Dentofac Orthop 2001;120:498-502. 10. Lehman JA, Haas AJ, Haas DG. Surgical orthodontic correction of transverse maxillary deficiency: a simplified approach. Plast Reconstr Surg 1984;73:62-6. 11. Stromberg C, Holm J. Surgically assisted, rapid maxillary expansion in adults. A retrospective long-term follow-up study. J Craniomaxillofac Surg 1995;23:222-7.

OOOOE Volume 106, Number 6 12. Capelozza L, Cardoso Neto J, Silva OG, Ursi WJ. Non-surgically assisted rapid maxillary expansion in adults. Int J Adult Orthod Orthognath Surg 1996;11:57-66. 13. Cureton SL, Cuenin M. Surgically assisted rapid palatal expansion: orthodontic preparation for clinical success. Am J Orthod 1999;116:46-59. 14. Goldenberg DC, Alonso N, Goldenberg FC, Gebrin ES, Amaarl TS, Scanavini MA, et al. Using computed tomography to evaluate maxillary changes after surgically assisted rapid palatal expansion. J Craniofac Surg 2007;18:302-11. 15. Podesser B, Williams S, Bantleon H, Imhof H. Quantitation of transverse maxillary dimensions using computed tomography: a methodological and reproducibility study. Eur J Orthod 2004;26(2):209-15. 16. Garib DG, Henriques JF, Janson G, Freitas MR, Coelho RA. Rapid maxillary expansion—Tooth tissue-borne versus toothborne expanders. A computed tomography evaluation of dentoskeletal effects. Angle Orthod 2005;75:548-57. 17. Bays RA, Greco JM. Surgically assisted rapid palatal expansion. An outpatient technique with long-erm stability. J Oral Maxillofac Surg 1992;50:110-3. 18. Bell WH, Epker BN. Surgical-orthodontic expansion of the maxilla. Am J Orthod 1976;70:517-28. 19. Pogrel MA, Kaban LB, Vargervik K, Baumrind S. Surgically assisted rapid maxillary expansion in adults. Int J Adult Orthod Orthognath Surg 1992;7:37-41. 20. Gilon Y, Heymans O, Limme M, Brandt L, Raskin S. Indications et implications de la disjunction chirurgicale du maxillaire supérieur dans les traitements orthodonticochirurgicaux. Rev Stomatol Chir Maxillofac 2000;101:252-8. 21. Timms DJ. The dawn of rapid maxillary expansion. Angle Orthod 1999;69:247-50. 22. Woods M, Wiesenfeld D, Probert T. Surgically-assisted maxillary expansion. Austral Dental J 1997;42:38-42. 23. Banninig LM, Gerard N, Steinberg BJ, et al. Treatment of transverse maxillary deficiency with emphasis on surgically assisted-rapid maxillary expansion. Compendium 1996;17:170-8. 24. Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening the midpalatal suture. Angle Orthod 1961:31:73-90.

Goldenberg et al. 819 25. Toroglu MS, Uzel E, Kayalioglu M, Uzel I. Asymmetric maxillary expansion (AMEX) appliance for treatment of true unilateral posterior crossbite. Am J Orthod Dentofac Orthop 2002;122: 164-73. 26. Handelman CS, Wang L, BeGole EA, Haas AJ. Nonsurgical rapid maxillary expansion in adults: report on 47 cases using the Haas expander. Angle Orthod 2000;70(2):129-44. 27. Kennedy J, Bell WH, Kimbrough OL, James WB. Osteotomy as an adjunct to rapid maxillary expansion. Am J Orthod 1976; 70:123-37. 28. Bell R. A review of maxillary expansion in relation to rate of expansion and patient’s age. Am J Orthod 1982;81:32-7. 29. Braun S, Bottrel JA, Lee KG, Lunazzi JJ, Legan HL. The biomechanics of rapid maxillary sutural expansion. Am J Orthod Dentofac Orthop 2000;118:257-61. 30. Epker BN, Fish LC. Dentofacial deformities. Integrated orthodontic and surgical correction. Vol 5. St Louis (MO): Mosby; 1986. p. 818-75. 31. Silverstein K, Quinn PD. Surgically-assisted rapid palatal expansion for management of transverse maxillary deficiency. J Oral Maxillofac Surg 1997;55:725-7. 32. Phillips C, Medland WH, Fields HW, Proffit WR, White RP. Stability of surgical maxillary expansion. Int J Adult Orthod Orthognath Surg 1992;7:139-46. 33. Bailey LJ, White RP, Proffit WR, Turvey TA. Segmental LeFort I osteotomy for management of transverse maxillary deficiency. J Oral Maxillofac Surgery 1997;55:728-31. 34. Chung CH, Font B. Skeletal and dental changes in the sagittal, vertical, and transverse dimensions after rapid palatal expansion. Am J Orthod Dentofac Orthop 2004;126(5):569-75.

Reprint requests: Dov Charles Goldenberg, MD, PhD Rua Pedro de Toledo 980 cj. 124 Vila Clementino CEP 04039002 São Paulo, SP, Brazil [email protected]