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Closer look at sarpe chamberland-proffit joms sept08
 

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Purpose: To assess the amount of dental and skeletal expansion and stability after surgically assisted ...

Purpose: To assess the amount of dental and skeletal expansion and stability after surgically assisted
rapid maxillary expansion (SARPE).
Patients and Methods: Data from 20 patients enrolled in this prospective study were collected before
treatment, at maximum expansion, at the removal of the expander 6 months later, before any second
surgical phase, and at the end of orthodontic treatment, using posteroanterior cephalograms and dental
casts.
Results: With SARPE, the mean maximum expansion at the first molar was 7.48  1.39 mm, and the
mean relapse during postsurgical orthodontics was 2.22  1.39 mm (30%). At maximum, a 3.49  1.37
mm skeletal expansion was obtained, and this expansion was stable, such that the average net expansion
was 67% skeletal.
Conclusion: Clinicians should anticipate a loss of about one third of the transverse dental expansion
obtained with SARPE, although the skeletal expansion is quite stable. The amount of postsurgical relapse
with SARPE appears quite similar to the changes in dental-arch dimensions after nonsurgical rapid palatal
expansion, and also quite similar to dental-arch changes after segmental maxillary osteotomy for
expansion.

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    Closer look at sarpe chamberland-proffit joms sept08 Closer look at sarpe chamberland-proffit joms sept08 Document Transcript

    • J Oral Maxillofac Surg 66:1895-1900, 2008 Closer Look at the Stability of Surgically Assisted Rapid Palatal Expansion Sylvain Chamberland, DMD, MSc,* and William R. Proffit, DDS, PhD† Purpose: To assess the amount of dental and skeletal expansion and stability after surgically assisted rapid maxillary expansion (SARPE). Patients and Methods: Data from 20 patients enrolled in this prospective study were collected before treatment, at maximum expansion, at the removal of the expander 6 months later, before any second surgical phase, and at the end of orthodontic treatment, using posteroanterior cephalograms and dental casts. Results: With SARPE, the mean maximum expansion at the first molar was 7.48 1.39 mm, and the mean relapse during postsurgical orthodontics was 2.22 1.39 mm (30%). At maximum, a 3.49 1.37 mm skeletal expansion was obtained, and this expansion was stable, such that the average net expansion was 67% skeletal. Conclusion: Clinicians should anticipate a loss of about one third of the transverse dental expansion obtained with SARPE, although the skeletal expansion is quite stable. The amount of postsurgical relapse with SARPE appears quite similar to the changes in dental-arch dimensions after nonsurgical rapid palatal expansion, and also quite similar to dental-arch changes after segmental maxillary osteotomy for expansion. © 2008 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 66:1895-1900, 2008 Although a number of reports on stability after surgi- More recent papers using pre-expansion and post- cally assisted rapid palatal expansion (SARPE) have expansion P-A cephs and dental casts have reported been published, surprisingly little detailed informa- more change than earlier papers. In a series of 14 tion exists to document postsurgical changes with cases, Byloff and Mossaz observed a mean 8.7-mm this procedure, and to differentiate between dental expansion at the first molar, and on average, 36% of and skeletal outcomes. This is the case for 2 reasons: this expansion (3.1 mm) had relapsed on debonding.6 most of the previous studies used only dental casts or The skeletal expansion involved 1.3 mm, or 24%, of direct measurements of dental-arch dimensions, with- the dental expansion. Berger et al reported an average out the use of posteroanterior cephalograms (P-A of 2.49 mm of skeletal expansion (52% of dental cephs) so that skeletal change could be differentiated expansion).7 Nevertheless, 2 recent systematic re- views concluded that no good evidence exists for the from tooth movement,1-5 and stability was often re- amount of relapse after SARPE.8,9 ported from the end of postexpansion orthodontic Our research project sought to provide detailed treatment, and not from the point of maximum data for both dental and skeletal stability after SARPE, expansion.1-4 and to put outcomes in the context of stability after nonsurgical orthopedic maxillary expansion and ex- *Part-time Clinical Teacher and Lecturer, Faculté de Médecine pansion with segmental Le Fort I osteotomy. Dentaire, Université Laval; and Private Practice, Quebec City, Que- bec, Canada. Patients and Methods †Professor, Department of Orthodontics, School of Dentistry, University of North Carolina, Chapel Hill, NC. Twenty patients aged between 15 and 54 years, Address correspondence and reprint requests to Dr Chamber- participating in a prospective, observational study of land: 10345 Boulevard de l’Ormiere, Quebec City, Quebec G2B SARPE outcomes approved by the Laval University 3L2, Canada; e-mail: drsylchamberland@biz.videotron.ca Ethics Committee, received dental casts and P-A © 2008 American Association of Oral and Maxillofacial Surgeons cephalograms before SARPE (time-point [T] 1), at the 0278-2391/08/6609-0016$34.00/0 completion of expansion (T2), at the removal of the doi:10.1016/j.joms.2008.04.020 expander approximately 6 months later (T3), before any second surgical phase (T4), and at the end of 1895
    • 1896 CLOSER LOOK AT SARPE changes in distance between the jugula (left and right), and changes in the width of the nasal cavity (Fig 1). Measurements of dental casts to evaluate changes in tooth positions were performed at each time point, using a digital caliper. Intercanine widths were measured at the cusp tip. The inter-premolar (first and second) widths were measured in the mesial fossa, and the intermolar (first and second) widths were measured in the central fossa. The width of the expansion screw was measured before cementation (T1). After removal of the ex- pander (T3), the appliance was poured into labora- tory stone, and the screw width was measured again. The screw width was also measured on the P-A ceph at T1 and T2. These measurements were used to calculate the true enlargement factor of the cephalo- gram, which was 4%. FIGURE 1. Width measurements on P-A cephalometric radio- The method error was tested on dental casts and P-A graphs used in this study. Maxillary (MX) width was measured cephs. Every measurement of the dental casts at T5 was between jugula left (JL) and right (JR), with jugula defined as the point on the jugal process at the intersection of the outline of the repeated, and every P-A ceph at T5 was retraced. Pear- maxillary tuberosity and the zygomatic process. Nasal-cavity (NC) son correlations indicated a coefficient of fidelity of width was measured between the left and right points at the max- 99.94% for the measurements of dental casts, and of imum concavity of the piriform rim. Mandibular width was mea- sured between antegonion (AG) left and right. 99.90% for the P-A cephs. Statistical significance be- Chamberland and Proffit. Closer Look at SARPE. J Oral Maxillo- tween baseline and post treatment data collection was fac Surg 2008. assessed using Student t tests, Wilcoxon rank tests, paired t tests, 1-way analysis of variance, and repeated- measures analysis of variance. orthodontic treatment (T5). All had a transverse dis- crepancy of 5 mm or more, and were beyond the level Results of maturity at which palatal expansion without sur- gery would be possible (age range, 15 to 54 years). Changes during expansion (T1 to T3), changes after The surgical technique involved essentially all bone expansion (T3 to T5), and net expansion (T1 to T5) cuts required for a Le Fort I osteotomy, and included the are shown in Figure 2. All changes were significantly separation of the pterygoid junction and the separation different from zero (P .001), except those for the of the midpalatal suture between the incisor roots with a thin osteotome.10-13 During surgery, the expansion device (Superscrew; Superscrew Superspring Co, High- Canine wood, IL) was activated sufficiently to achieve a 1- to 1.5-mm separation of the maxillary central incisors. All 1st premolar surgery was performed by the same surgeon. A latency period of 7 days was observed, and then 2nd premolar patients were instructed to activate the screw by 0.25 mm twice a day. Patients were monitored twice a 1st molar week until the planned expansion was achieved, 12 to 20 days later. Brackets were bonded on the maxil- 2nd molar lary teeth 2 months after the expansion had stopped. Active orthodontic treatment was usually initiated be- 1st lower molar fore SARPE in the mandibular arch, and 2 months after expansion had stopped in the maxillary arch. The ex- -6 -4 -2 0 2 4 6 8 pansion device was kept in place for approximately 6 months. Following the removal of the expansion device, FIGURE 2. Changes in arch width with SARPE. All maxillary no other retention except the main arch wire was used changes were statistically significantly different from zero; the man- dibular first molar change was not. Blue, changes during expan- until the end of orthodontic treatment. sion (T1 to T3). Red, postexpansion changes (T3 to T5). Yellow, net Standardized P-A cephs14 were digitized using expansion (T1 to T5). Quick Ceph 2000 (Quick Ceph Systems, San Diego, Chamberland and Proffit. Closer Look at SARPE. J Oral Maxillo- CA), and maxillary width changes were evaluated as fac Surg 2008.
    • CHAMBERLAND AND PROFFIT 1897 ies using a comparable research design. The 30% relapse is less than the 36% relapse reported by Byloff 7.00 68 70 and Mossaz.6 Post-treatment retention is likely to be an important factor in any study of stability.15 In our 6.00 60 study, the expander was left in place for 6 months 52 (standard deviation, 5.98 0.72 months) after the 5.00 50 47 expansion had stopped, whereas Byloff and Mossaz6 46 left the distractor in for 3 months, and then used a 4.00 40 removable retainer for 3 months. The 30% relapse is higher than that reported by Berger et al7 and Pogrel 3.00 30 et al.5 Both of those studies used 12 months of follow- up, rather than the end of orthodontic treatment, as 2.00 20 their endpoint. The relapse we found is considerably higher than in reports from earlier studies that re- 1.00 10 ported changes from the end of treatment, and not from the point of maximal expansion.1-4 0.00 0 0.42 7.87 14.4 20.7 The amount of dental versus skeletal expansion observed in our SARPE patients, and in other stud- FIGURE 3. Changes over time after SARPE in dental and skeletal ies6,7,16 using P-A cephs, is larger than clinicians often dimensions, and in percentage of expansion that was skeletal. expect. Immediately after maximum expansion, Note that almost all relapse was dental, rather than skeletal. Re- about half the expansion (47%) was skeletal, as shown peated-measures analysis of variance confirmed a significant rela- tionship between amount of relapse and time elapsed after surgery. by a widening of the maxilla and nasal cavity, and Blue line with squares indicates expansion at first molar. Red line with about half the expansion (53%) was dental. The skel- diamonds indicates percentage of expansion that was skeletal at each etal expansion with SARPE was quite stable: the re- time point. Green line with Xs indicates maxillary skeletal expansion at jugula. Magenta line with triangles indicates expansion across lapse was almost totally attributable to lingual move- nasal cavity. ment of the posterior teeth. It was recommended Chamberland and Proffit. Closer Look at SARPE. J Oral Maxillo- previously that a 2-mm expansion beyond the desired fac Surg 2008. result should be performed. Because a mean relapse of about 30% at the first molars can be expected, we lower molar (not significant). Note that the amount of concur that a 2-mm excess expansion is indicated in expansion at the molars was very similar to the ex- SARPE patients with a typical expansion of 7 to 8 mm pansion at the first premolar (P .95). This shows at the first molar. This is needed to compensate for the parallelism of the expansion of the posterior buccal tipping of the entire posterior segment during teeth. expansion. Interestingly, there is no correlation be- The amount of skeletal expansion with SARPE and tween the amount of expansion and the amount of its stability are shown in Figure 3. Almost all the relapse at the first molar (r 0.01). relapse was dental, rather than skeletal. The skeletal The width of the midline diastema at the maximum expansion measured at both the jugula and the nasal expansion point (T2) is highly correlated with the cavity was quite stable, and the percentage of expan- first molar expansion (r 0.69). This indicates that sion because of skeletal change increased from 47% to the development of a diastema is a predictor that 68% as dental relapse occurred. At time of expansion, adequate molar expansion is occurring. all patients were expanded 2 mm beyond the ex- Even when skeletal expansion is obtained, the low pected final position, and despite the dental relapse, correlation between skeletal changes and dental none of the patients showed posterior crossbite at the changes (r 0.36) confirms that the maxillary seg- end of treatment. ments often do not expand symmetrically. Instead, Of 20 subjects, 8 underwent second-stage maxillary some rotation occurs, with the teeth expanding more surgery for anteroposterior or vertical repositioning, widely than the bone above, as explained by Byloff and 5 underwent mandibular advancement only. and Mossaz,6 and as demonstrated by Chung and There was no significant effect of phase 2 surgery on Goldman.17 This rotation of the maxillary segments or transverse relapses. alveolar bending explains why the skeletal change at the maximal expansion point is only 47% of the dental Discussion expansion (Fig 3). Hence, the horizontal portion of the screw should be more than 3 mm away from the COMPARISON TO OTHER STUDIES OF SARPE palatal mucosa, to avoid impingement. The mean expansion at the first molar observed in Interestingly, this study did not confirm previous the SARPE group was similar to that in previous stud- reports of a hinge-type expansion with SARPE, with
    • 1898 CLOSER LOOK AT SARPE Table 1. RELAPSE BETWEEN MAXIMUM EXPANSION AND (T3) END OF TREATMENT (T5) SARPE Le Fort I Control Group Variable n Mean SD % Relapse n Mean SD % Relapse Significance Canine 19 2.65 1.95 48 12 0.74 1.84 32 P .05 First premolar 16 1.85 2.04 25 9 1.32 1.67 33 NS Second premolar 20 2.14 2.48 27 11 2.06 1.45 39 NS First molar 20 2.22 1.69 30 12 3.06 1.31 42 NS Second molar 18 4.42 1.80 59 8 3.69 1.08 40 NS NOTE. Variation of n is explained by the fact that some patients underwent extraction of teeth, so that number of measurements is reduced for those teeth. Abbreviations: NS, no significance; SARPE, surgically assisted rapid palatal expansion; SD, standard deviation. Chamberland and Proffit. Closer Look at SARPE. J Oral Maxillofac Surg 2008. more expansion anteriorly than posteriorly (Fig 2). STABILITY COMPARED WITH This suggests that changes in recent years in the SEGMENTAL OSTEOTOMY surgical procedure for SARPE, which now includes The best data for stability after transverse expan- surgical release of the pterygoid junction, may allow a sion with segmental Le Fort I osteotomy were re- similar anterior and posterior expansion. The in- ported for 42 patients by Phillips et al27 in 1992. creased rigidity of the Superscrew, and its placement Comparisons of earlier studies of SARPE stability with more in line with the first molars, may also have this data set have provided the basis for recommend- contributed to the more parallel expansion.18 ing SARPE as a first stage of treatment, when reposi- tioning of the maxilla in all three dimensions is STABILITY COMPARED WITH NONSURGICAL RAPID planned. PALATAL EXPANSION Stability data for the 12 subjects in Phillips et al27 In prepubertal children and adolescents, loss of who showed expansion equivalent to that of our about one third of the maximum expansion across the SARPE patients are shown in Table 1 and Figure 4. first molars occurs after nonsurgical rapid palatal ex- The mean relapse across the first molars was greater pansion.15,19-23 The P-A cephs in patients with palatal for the Le Fort I group, but the difference was not implants who underwent maxillary expansion demon- statistically significant, whereas the mean relapse strated that approximately 50% of the expansion across the canines was greater for the SARPE group, achieved by rapid palatal expansion (RPE) in children and was significant. The greater change at the canines was skeletal, and the remainder was dentoalveolar.24,25 for the SARPE group almost surely reflects tooth Handelman et al22 compared expansion with non- movement generated by the finishing arch wires. surgical RPE in younger versus older patients, and Rather than mean changes, Figure 4 shows the num- estimated that skeletal expansion was only 18% in ber of patients with SARPE and Le Fort I expansion, their adult group, compared with 56% for younger with changes of specific magnitudes across the first patients. Baccetti et al19 showed that only 0.9 mm of molars and first premolars. The similarity of distribu- skeletal expansion is achieved in RPE patients treated tions is apparent. during or after their peak in skeletal maturation, whereas 3 mm of skeletal expansion was obtained in CLINICAL IMPLICATIONS a group treated before the peak of skeletal matura- These data do not support the conclusion of earlier tion. It is clear that with RPE, the nature of expan- studies of SARPE that this procedure produces more sion shifts from skeletal to dentoalveolar in mature stable expansion than do segmental osteotomies. Our individuals who are candidates for SARPE. When data are quite compatible, however, with data from changes largely involve tooth movement through other studies of SARPE that used both P-A cephs and the alveolar housing, it has been shown to be det- measurements of dental casts, and found significant rimental periodontally.1,26 postsurgical changes. Our data show a mean 3.47 mm of skeletal expan- It seems clear at this point that relapse in the sion, which is 68% of the mean dental expansion amount of arch-width increase produced by SARPE is (5.12 mm). Although the amount of relapse in dental comparable to the relapse with other expansion pro- arch widths with SARPE is about the same as with cedures. Our data show that with SARPE, the relapse nonsurgical RPE in younger patients, there is a differ- is almost entirely dental, so that at the end of treat- ence: with SARPE, the skeletal change is much more ment, there is a net skeletal expansion of 67% of the stable than with RPE. total change. With nonsurgical expansion in growing
    • CHAMBERLAND AND PROFFIT 1899 alignment of crowded maxillary incisors can be pro- A SARPE: Post-Tx changes vided by maxillary expansion rather than premolar 60 extraction. Thus decisions about extraction should be First Molar postponed until after the expander is removed. 50 First Premolar The similar stabilities of transverse expansion of the 40 dental arches with SARPE and segmental Le Fort I osteotomies provide some insight into the choice between procedures. In our view, when only a trans- 30 verse change is needed, SARPE would be the treat- ment of choice. When a second phase of maxillary 20 surgery to reposition the maxilla vertically or antero- posteriorly is required, the routine performance of a 10 preliminary SARPE procedure to obtain better trans- verse stability does not appear to be warranted.28 An 0 >-3 -3 to -1 -1 to 1 1 to 3 exceptionally narrow maxilla that requires major ex- Relapse (mm) pansion across the posterior teeth may be an excep- tion.29 Perhaps a current consensus view would state LeFort 1:Post-Tx Changes B 70 that the decision for a 2-stage versus 1-stage Le Fort I surgery should be based not on the stability of trans- First Molar verse expansion, but on the risk and morbidity of 2 60 First Premolar surgeries versus the risk and morbidity of 1-stage, multisegmented Le Fort I for large expansion along 50 with vertical or anteroposterior changes. 40 In conclusion, our findings are that: 30 1) Skeletal expansion with SARPE involves about half the total intermolar expansion at the maxi- 20 mum expansion point. From that point, dental relapse occurs, but the skeletal expansion is 10 stable, so that at the end of treatment, about two thirds of the net expansion is skeletal. 0 2) The transverse stability of SARPE is not signifi- >-3 -3 to -1 -1 to 1 1 to 3 cantly greater than that of segmental Le Fort I Relapse (mm) osteotomy, bringing into question the routine use FIGURE 4. Percentage of patients with major relapse ( 3 mm), of 2-stage surgery as a way to improve transverse moderate relapse (1 to 3 mm), minimal change (–1 to 1 mm), and stability in patients who require widening and post-treatment expansion. A, After SARPE (first molars, n 20; first premolars, n 16). B, After Le Fort I segmental osteotomy (first anteroposterior or vertical repositioning of the molars, n 12; first premolars, n 9). Variation of n is explained maxilla. by the fact that some patients underwent extraction of teeth, so that the number of measurements is reduced for those teeth. Acknowledgments Chamberland and Proffit. Closer Look at SARPE. J Oral Maxillo- We thank Jean-Paul Goulet, DDS, MSD, FRCD(C), and André fac Surg 2008. Fournier, DMD, for their direction and co-direction of this Master’s Degree project, Dany Morais, DMD, FRCD(C), Oral and Maxillofa- cial Surgeon, for careful surgical treatment, and Gaetan Daigle, patients, the expectation is that 50% of the total PStat, for statistical consultation and statistical analysis. This project change will be skeletal. No data from sequential P-A was supported in part by grant DE-05221 from the National Insti- tute of Dental and Craniofacial Research of the National Institutes cephs exist for Le Fort I expansion. of Health (Bethesda, MD). The clinical results involving our SARPE patients, none of whom showed posterior crossbite at the end of treatment despite their dental relapse, support the References routine use of a 2-mm overexpansion during treat- 1. Northway WM, Meade JB Jr: Surgically assisted rapid maxillary ment. In the Le Fort I patients reported by Philips expansion: A comparison of technique, response, and stability. Angle Orthod 67:309, 1997 et al,27 overexpansion was not performed. Given the 2. Bays RA, Greco JM: Surgically assisted rapid palatal expansion: similarity of relapse in intermolar width between the An outpatient technique with long-term stability. J Oral Maxil- SARPE and Le Fort I patients, it appears that routine lofac Surg 50:110, 1992 3. Stromberg C, Holm J: Surgically assisted, rapid maxillary ex- overexpansion should also be part of the protocol for pansion in adults. A retrospective long-term follow-up study. J expansion with osteotomy. With SARPE, space for the Craniomaxillofac Surg 23:222, 1995
    • 1900 CLOSER LOOK AT SARPE 4. Anttila A, Finne K, Keski-Nisula K, et al: Feasibility and long- 16. Kuo PC, Will LA: Surgical-orthodontic treatment of maxillary term stability of surgically assisted rapid maxillary expansion constriction. Oral Maxillofac Surg Clin North Am 2:751, 1990 with lateral osteotomy. Eur J Orthod 26:391, 2004 17. Chung CH, Goldman AM: Dental tipping and rotation immedi- 5. Pogrel MA, Kaban LB, Vargervik K, et al: Surgically assisted ately after surgically assisted rapid palatal expansion. Eur rapid maxillary expansion in adults. Int J Adult Orthod Orthog- J Orthod 25:353, 2003 nath Surg 7:37, 1992 18. Klapper L, George R: A new telescopic maxillary expander. 6. Byloff FK, Mossaz CF: Skeletal and dental changes following J Clin Orthod 29:114, 1995 surgically assisted rapid palatal expansion. Eur J Orthod 26:403, 19. Baccetti T, Franchi L, Cameron CG, et al: Treatment timing for 2004 rapid maxillary expansion. Angle Orthod 71:343, 2001 7. Berger JL, Pangrazio-Kulbersh V, Borgula T, et al: Stability of 20. Lagravere MO, Heo G, Major PW, et al: Meta-analysis of imme- orthopedic and surgically assisted rapid palatal expansion over diate changes with rapid maxillary expansion treatment. J Am time. Am J Orthod Dentofacial Orthop 114:638, 1998 Dent Assoc 137:44, 2006 8. Koudstaal MJ, Poort LJ, van der Wal KG, et al: Surgically 21. Lagravere MO, Major PW, Flores-Mir C: Long-term dental arch assisted rapid maxillary expansion (SARME): A review of the changes after rapid maxillary expansion treatment: A system- literature. Int J Oral Maxillofac Surg 34:709, 2005 atic review. Angle Orthod 75:155, 2005 9. Lagravere MO, Major PW, Flores-Mir C: Dental and skeletal 22. Handelman CS, Wang L, BeGole EA, et al: Nonsurgical rapid changes following surgically assisted rapid maxillary expan- maxillary expansion in adults: Report on 47 cases using the Haas expander. Angle Orthod 70:129, 2000 sion. Int J Oral Maxillofac Surg 35:481, 2006 23. Spillane LM, McNamara JA Jr: Maxillary adaptation to expan- 10. Betts NJ, Vanarsdall RL, Barber HD, et al: Diagnosis and treat- sion in the mixed dentition. Semin Orthod 1:176, 1995 ment of transverse maxillary deficiency. Int J Adult Orthod 24. Krebs A: Midpalatal suture expansion studies by the implant Orthognath Surg 10:75, 1995 method over a seven-year period. Rep Congr Eur Orthod Soc 11. Chung CH, Woo A, Zagarinsky J, et al: Maxillary sagittal and 40:131, 1964 vertical displacement induced by surgically assisted rapid pal- 25. Lagravere MO, Major PW, Flores-Mir C: Long-term skeletal atal expansion. Am J Orthod Dentofacial Orthop 120:144, 2001 changes with rapid maxillary expansion: A systematic review. 12. Conley RS, Legan HL: Correction of severe vertical maxillary Angle Orthod 75:1046, 2005 excess with anterior open bite and transverse maxillary defi- 26. Vanarsdall RL: Periodontal/orthodontic interrelationships, in ciency. Angle Orthod 72:265, 2002 Graber TM, Vanarsdall RL (eds): Orthodontics, Current Princi- 13. Epker BN: Dentofacial Deformities: Integrated Orthodontics ples and Techniques. St. Louis, Mosby, 1994, pp 715-721. and Surgical Correction, Volume 2. St Louis, Mosby, 1986, pp 27. Phillips C, Medland WH, Fields HW Jr, et al: Stability of surgical 818-875 maxillary expansion. Int J Adult Orthod Orthognath Surg 14. Ghafari J, Cater P, Shofer F: Effect of film-object distance on 7:139, 1992 posteroanterior cephalometric measurements: Suggestions for 28. Bailey LJ, White RP Jr, Proffit WR, et al: Segmental Le Fort I standardized cephalometric methods. Am J Orthod Dentofacial osteotomy for management of transverse maxillary deficiency. Orthop 108:30, 1995 J Oral Maxillofac Surg 55:728, 1997 15. Zimring JF, Isaacson RJ: Forces produced by rapid maxillary 29. Silverstein K, Quinn PD: Surgically-assisted rapid palatal expan- expansion. 3. Forces present during retention. Angle Orthod sion for management of transverse maxillary deficiency. J Oral 35:178, 1965 Maxillofac Surg 55:725, 1997