Rapid maxillary expansion in the primary and mixed dentitions: A cephalometric evaluation Omar Gabriel da Silva Fo,* Maria Cecilia Villas Boas,** and Leopoldino Capelozza Fo*** Sdo Paulo, Brazil
The present study evaluated the skeletal alterations induced by rapid maxillary expansion procedures in 30 patients in the primary and mixed dentitions. The results were obtained with the use of lateral cephalometrics before and immediately after the active phase of expansion. The time span between these two cephalometric films ranged from 14 to 21 days; therefore the "growth factor" was not considered. Based off the differences in the cephalometric measurements studied on the first and second tracings, it seems that anterior displacement of the maxilla with significant changes in the SNA angle should not be expected, although point B was repositioned more posteriorly (SNB) because of the man~libular downward and backward rotation, with subsequent increase of the inclination of the mandibular plane. The alterations in the A-P position of the mandible was reflected in the increase of ANB and NAP angles. The maxilla always dislocates downward, displaying a downwarcl and backward rotation in the palatine plane, significantly altering the following measurements: N-ANS, PNS-PNS', A-A', SN.PP. The anchoring molars also follow the downward maxillary displacement (M-M') and, as a direct consequence of the vertical displacement of the maxilla and upper molars (N-ANS, A-A', ANS-Me, N-Me, PNS-PNS'), the facial heights increase. (AM J ORTHODDENTOFACORTHOP 1991;100:171-81.)
T h e present concepts concerning posterior crossbites are well defined in the literature and widely accepted by orthodontists. Among mixed dentition children displaying malocclusions in the region of Bauru (Silo Paulo, Brazil), we found an 18.2% incidence of posterior crossbitesY This entity may occur in the primary dentition and manifest itself as a constriction in the lateral dimensions of the upper arch and, as a rule, will not self-correct. On the basis of these concepts, it is necessary to correct this form of malocclusion as early as possible, preferably in the primary dentition stage. Modem orthodontics has a wide variety of mechanical appliances that will release forces to laterally expand upper constricted arches? The jackscrew has been applied in removable 3.4 or fixed appliances 2'59 as a source to generate forces against the palatine surfaces of the upper teeth. When the jackscrew is used in removable appliances, it produces only slow expansion, which is indicated for dentoalveolar constrictions. In
From the University of Sao Paulo. *Orthodontist. **Resident of the Department of Orthodontics. ***Head of the Department of Orthodontics; Assistant Professor at Faculdade de Odontologia de Bauru. 1811121630
our clinical+ practice, we do not use the jackscrew for the particular purpose aforementioned. For slow expansions we use mainly the quad-helix appliance, m In rapid maxillary expansion procedures (RME) indicated for the correction of skeletal constrictions, even in early occlusal developmental stages, we use the jackscrew in fixed appliances, following the basic standards proposed by Haas 7 with a few modifications (Fig. I). Rapid maxillary expansion procedures are indicated in the primary and mixed dentitions every time the crossbite is associated with a skeletal constriction, which might be clinically identified as: 1. Unilateral or bilateral posterior crossbite with normal inclination of the dentoalveolar processes 2. Unilateral or bilateral posterior crossbite with retrusion of the middle third of the face (Class III tendency) 3. Total crossbite REVIEW OF THE LITERATURE Rapid maxillary expansion procedures have been proposed since the past century by Angell" and consolidated clinically by Haas. 6-8 This procedure leads to an increase in the upper arch transverse dimensions by mainly skeletal alterations associated with dental alterations, which may manifest themselves distinctly, de171
"17'2 Sih'a, Boas, and Capelozza
Am. J. Orthod. Dentofac. Orthop. Aug,st 1991
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Fig. 1. A through C, Unilateral posterior crossbite in the patient's right side, associated with an anterior crossbite. D, A rapid maxillary expansion appliance of the Haas type has been used for a. simultaneous correction of the posterior and anterior crossbites.
pending on the sutural resistance, which increases as a person matures. ~2 Although slow expansion appliances do promote a slight opening in the median palatine suture in the primary and mixed dentition stages, 2"~°'~4"~5 cephalometrically and clinically the results cannot be compared with the orthopedic effects of the Haas type of appliance. :'~6 Rapid maxillary expansion increases the upper arch transverse dimensions mainly by separation of the two maxillary halves (orthopedic effect), followed by buccal movement of the posterior teeth and alveolar processes (orthodontic effect). The force delivered by activation of the jackscrew exceeds the sutural resistance limit and splits not only the intermaxillary suture but also all the other maxillary sutures. Through this sutural splitting, the maxilla is incited to displace itself downward and forward, with a rotation in the maxillary components in both the horizontal and frontal planes. 6.7.sA2.17-t9 In the horizontal plane, the behavior of the maxilla is easily determined by an occlusal x-ray film (Fig. 2).The maxillary halves split along the median palatine suture, creating a triangular radiolucent area with its base toward the anterior region in which the resistance of the facial structures is weaker. 2,7-9.'2,'7.]8
In the frontal plane, the separation of the two maxillary halves also follows a triangular pattern 6,8.~z,18,19 with its base downward and the center of rotation located near the frontonasal suture.~2 The magnitude of increments can be listed in decreasing order as follows: transversal diameter at the level of the crowns of the teeth, alveolar arch, maxillary base, and nasal cavity, tT.z8 It is important to emphasize that these skeletal changes tend to be less significant with skeletal maturity because of the increased rigidity of the articulations of the maxilla with the face, 9'12 which can be felt clinically by the patient as either discomfort or pain. 9 The downward displacement of the maxilla has a direct effect in the spatial positioning of the mandible when related to the anterior cranial base. The mandible rotates downward and backward. This mandibular rotation 6"7'8"t2induces other alterations such as opening of the bite, occlusal plane inclination, increase in the mandibular plane angle and the y axis, and a downward and backward displacement of menton. Although the use of RME procedures in the primary and mixed dentitions are mentioned in the literature,2"5'6'8"9'12"2°'21 nothing has been published concerning
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Fig. 1 (Cont'd). E through G, After 7 days the activations were interrupted and the expansion screw was stabilized with acrylic resin (H). The open diastema in the upper central incisors (G) suggests the maxillary separation at the level of the median palatine suture. I and J illustrate the occlusion and the dental arch immediately after the retention period.
the specific cephalometfic alterations induced by these procedures in these early occlusal developmental stages. To fill this gap, this article studies the cephalometric alterations induced by the Haas type appliance, when used in the primary and mixed dentitions.
MATERIALS AND METHODS The subjects in the sample comprised 30 children with ages ranging from 5 years to 10 years 11 months, with a mean age of 8 years. All children had posterior crossbites with skeletal involvement. All cases were satisfactorily cor-
rected by means of an RME appliance of the Haas type (Fig. 1). The activations of the jackscrew were started 24 hours after the appliance was cemented in place. The parents were instructed to activate a 1/z turn in the morning and a 1/2 turn in the evening, thus performing one complete turn of the screw per day. The active period of activations ranged from I to 2 weeks, depending primarily on the degree of maxillary constriction. The lateral expansion of the upper arch was deemed sufficient when the posterior crossbite was ovcrcorrected by 2 to 3 mm (Fig. 1). The alterations promoted by the RME procedures were
174
Sih'a, Boas, and Capelozza
Am. J. Orthod. Dentofac. Orthop. August 1991
At
(3
0
,,k PTt{ '--~
..
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Fig. 2. A, The typical triangular opening of the median palatine suture confirms the separation of the maxillary processes during the rapid r~axillary expansion. B, The median palatine suture area is repaired totally after 90 days of the active phase of expansion.
appraised by two cephalometric x-ray films taken according to the guidelines of Broadbent."-" The first cephalogram was taken before any activation was performed; the second was taken after the active phase of expansion. For didactic purposes in the interpretation of the results, the cephalometric measurements used in this study were divided into three major groups: 1. Anteroposterior alterations of the apical bases (Fig. 3) a. Angular measurements: NAP, SNAp SNB, ANB b. Linear measurements: S-A', S°ENP', PTM-A 2. Vertical alterations of the apical bases (Fig. 4) and facial height alterations (Fig. 5) a. Angular measurements: SN.ANS-PNS (SN.PP), SN.GoGn, SNGn, ANS-PNS.GoGn (PP.GoGn) b. Linear measurements: N-ANS, ANS-Me, N-Me, A-A', PNS-PNS' 3. Anchoring molars alterations (Fig. 5) a. Linear measurements: M-M', S-M' The means and standard deviations for all cephalometric measurements were calculated in both cephalograms and the alterations that occurred in the postexpansion cephalogram, when compared to the preexpansion cephalogram, were analyzed statistically 1Jy the paired t test.
Fig. 3. The angular and linear cephalometric measurements through points S, N, A, B, Pog, PNS, and P'IM made possible the evaluation of the anteroposterior alterations of the apical bases.
RESULTS The results are shown in Tables I through III, which contain the means and standard deviations of the cephalometric measurements of the initial and postexpansion cephalograms. In addition, we have calculated the difference between the cephalometric measurements of the initial and postexpansion cephalograms, and the paired t test has been applied to assess the statistical significance.
DISCUSSION Anteroposterior alterations of the apical bases Surprisingly, the maxilla did n o t show any statistically significant alterations in the anteroposterior position (Fig. 6), which contradicts the works of Haas, 6-8 Krebs, ~7''8 and W e r t z .12. 19 This finding is based on the angular and linear measurements used in this study to define the A-P position of the m a x i l l a - namely, SNA, S - A ' , S-PNS', and PTM-A. The slight anterior displacement of the maxilla, denoted by the 0.5 ° SNA small increment (Table I), was not significant according to the paired t test. With the orthopedic expansion of the maxilla, the individual SNA variation ranged from - 3 . 0 ° to + 2 . 0 ° . These findings differ
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N"
Gf
Fig. 4. The angular cephalometric measurements on the points S, N, PNS, ANS, Go and Gn made possible the evaluation of the vertical behavior of the apical bases.
from the results of Haas, 7 which ranged from 0.0 ° to + 3.5 °. In his work Haas 7 found an anterior displacement of the maxilla in all of the 10 cases studied. Based on our results, we can infer that if an advancement of the maxilla is necessary along with expansion for the success of the treatment, we will have to resort to auxiliary orthopedic appliances that stimulate anterior maxillary displacement immediately after the active phase of expansion with the Haas type of appliance. Though this significant forward displacement of the maxilla observed by Haas 6-8 may be related to the magnitude of the expansion achieved by the appliance, Haas always expands the maxilla more than we do. As previously stated, all the cases in this study were not overcorrectcd beyond 2,0 to 3.0 mm. Clinically, the occlusal inclines on the palatine cusps of the upper molars occlude with the occlusal inclines of the buccal cusps of the lower molars. In addition, we suggest another possibility related to the skeletal resistance. In this early developmental stage, the least resistance of the facial structures to the expanded maxilla hinders its forward displacement during expansion.
Haas6-8 appraised this forward displacement of the maxilla by Use of linear me~isurements. He registered a 1.0 to 4.0 mm forward displacement of point A, although he used the facial plane (N-Pog) as a reference line. Because of the mandibular spatial alterations that follow RME procedures, this line does not represent a reliable reference. This fact led us to choose other measurements that would truly represent the effective maxillary length. The two chosen measurements (S-A' and PTM-A) did not display any Significant alterations (Table I), thus corroborating the alteration of SNA angle. This altei'ation differed from the observations of Wertz ~2 who found an increase in the S-A distance that amounted to 1.5 mm in a few days, using RME procedures in patients aged 7 to 29 years. In the present study, we found a reduction in the S-A' distance in 11 children, which ranged from - 4 . 4 to - 0 . 8 mm. Regarding the PTM-A distance, we also found a reduction that ranged from - 3 . 3 to - 0 . 4 mm in 12 children. Although these two measurements represent maxillary length, they are defined as perpendicular to the SN line (Fig. 3). The decrease in these two
176
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Am. J. Orthod. Dentofac. Orthop.
Sih'a, Boas, and Capelozza
1991
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Fig. 6. During the rapid maxillary expansion, the SNA angle changes varied from a reduction of 3.5° to an increase of 2.0°. In the mean the SNA angle value has remained stable.
Fig. 5. The linear cephalometric measurements on points N, ANS, Me, A, PNS, and M made possible the evaluation of the facial alterations and the changes of the anchoring molars.
measurements observed in the second cephalogram might be explained by the maxillary rotational effect on the positioning of points PTM and A'. This rotational effect also explains the reduction in the SNA angle in 11 children. Contrasting with the maxillary behavior, we found significant cepha!ometric alterations in the A-P position of the mandible (F!g. 7). A mean reduction of 1.5 ° in the SNB angle, reflected by a reduction in the mandibular projection, has a direct effect on the ANB and NAP angles, increasing their values. This decrease in the SNB angle and increase in the ANB and NAP angles are positive assets for the patients displaying straight or concave profiles since these alterations improve the AP maxillomandibular relation. Haas 8 observed these same results in his work, but with higher proportions when compared with our findings. Of the 30 patients who submitted to RME procedures, six showed an increase in the SNB angle that ranged from 0.2 ° to 1.4°. This can be explained by an anterior postural repositioning of the mandible resulting from the occlusal interferences induced by the expansion procedures.
The vertical alterations of apical bases and facial height alterations The RME procedures induced statistically significant alterations in all horizontal lines and planes of the face used in the present study (SN.PP, SN.GoGn, SN.Gn, PP.GoGn) (Table II). The maxilla displayed a tendency to rotate downward and backward increasing the SN.PP angle value (Fig. 8) with a variation that ranged from - 3.7 ° to 3.9 °. However, only seven cases displayed an upward and forward rotation of the palatal plane, displacing PNS downward. The mean increase in the SN.PP measure was 0.5°; this value is compatible with the Wertz '2 findings. The mandible also displayed postural alterations (Fig. 9) denoted by downward and backward rotation, just like the maxilla. This is probably a result of the maxillary rotation (Fig. 8) and molar extrusion caused by their buccoversion. The downward and backward rotation was significant in relation to the anterior cranial base (Sn.GoGn, SN.Gn) and the palatal plane (PP.GoGn). We interpret the molar extrusion as the reason for the mandibular rotation being more accentuated than the maxillary rotation. These data agree with those of Haas. s These facts led us to the conclusion that RME procedures induce downward and backward apical base rotations. Mandibular rotation has a direct effect in the
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'.-.
177
Nt
79°
~-~0.5° ~~
-3
Fig. 8. Rotation of the palatine plane during the rapid expansion. The mean value of the SN.PP angle shows a downward and backward rotation of this plane in relation to the cranial base.
Fig. 7. With the expansion the SNB angle showed a statistically significant mean reduction of 1.15°; although with variations this ranged from a reduction of 3.3 ° to a forward movement of 1.4°.
A-P position of point B, reducing the SNB angle and increasing the reading of ANB and NAP angles. Rapid maxillary expansion incited an increase in the vertical dimensions of the face (Table I[) because of the maxillary and mandibular downward and backward rotation. This increase was noticed in the (1) upper facial height (N-ANS) as a result of the downward displacement of the maxilla, (2) in the lower facial height (ANS-Me) as a result of the mandibular rotation, and (3) in the total anterior facial height (N-Me) because of the rotation of both the maxilla and the mandible. The increase in the lower facial height is caused by the downward displacement of both the maxilla and upper teeth. This increase was mentioned in the works of Wertz ~2 and Byrom. '~ Maxillary posterior height also showed an increase (PNS-PNS'), denoting a downward displacement of PNS point, although the PNS point came down to a lesser extent than ANS point (N-ANS), which obviously was responsible for the downward and backward palatine plane rotation (SN.PP).
Go
Fig. 9. The Sn-GoGn angle reduced 0.5° after the rapid expansion in only one patient. This angle increased up to 4.6 °. The mandibular backward and downward rotation (mean value of 1.9 °) influenced the anteroposterior positioning of the point B.
178 Sih'a, Boas, attd Capelozza
Am. J. Orthod. Dentofac. Orthop. August 1991
Table I. Anteroposterior alterations of apical bases
Mean
SD
Mean
SD
5.473 81.736 79.018 2.721 58.54 13.293 44.116
6.449 3.631 3.014 2.936 4.975 2.460 3.415
8.99 82.063 77.863 4.216 58.493 13.113 44.536
5.818 3.631 2.993 2.547 4.877 2.356 3.290
3.517 0.327 - 1.155 1.495 -0.050 -0.180 0.420
7.132" 1.039 4.834* 6.139" 0.185 0.185 1.645
Paired t test-postexpansion and initial cephalograms (N = 30; 29 df," 2.045 T critic)
2.561" 8.610' 8.014" 4.020* 9.211" 5.460* 8.842* 6.928* 3.371"
In#ial cephalogram
NAP SNA SNB ANB S-A' S-ENP' PTM-A
Paired t test-postexpansion and hdtial cephalograms (N = 30; 29 df," 2.045 T critic)
Difference-poste.tpansion and initial cephalograms
Post~rpansion cephalogranz
*Statistical significance.
Table
II. Vertical alterations of apical bases and facial alterations
Mean
SD
Mean
SD
Difference-postexpansion and hzitial cephalograms
8.063 35.706 67.154 27.642 47.0 62.975 107.860 51.975 39.539
3.462 3.810 3.581 3.686 3.718 4.261 6.708 3.577 2.887
8.636 37.613 68.986 28.983 48.136 63.943 109.326 52.746 40.073
3.281 4.302 3.782 4.282 3.882 3.300 6.'179 3.748 2.580
0.573 1.907 1.832 1.341 1.136 0.968 1.466 0.771 0.534
Initial cephalogrant
SN.PP SN.GoGn SN.Gn PP.GoGn N-ENA ENA-Me N-Me A-A' PNS-PNS'
Postexpansion cephalogram
*Statistical significance.
Table
IlL Alterations of anchoring molars
Mean
SD
Mean
SD
Difference-postexpansion and initial cephalograms
56.318 22.051
3.152 5.823
56.833 21.99
2.896 6.198
0.515 -0.061
Initial cephalogram
M-M' S-M'
Postexpansion ceplmlogram
Paired t test-postexpansion attd hfftial cephalograms (N = 30; 29 df," 2.045 T critic)
2.896* 1.428
*Statistical significance.
In the individual analysis of point "A" alterations, we observed a downward displacement (A-A') but no alteration in the anteroposterior position (S-A'). The behavior of these linear measurements agrees with the alterations observed in the angular measurements of the maxilla (SNA and SN.PP). These alterations led us to the conclusion that the maxilla always displaces itself downward as a result of RME procedures in the primary and mixed dentitions. Byrom 2j also observed this behavior in patients in the mixed and permanent dentitions.
Alterations of the anchoring molars The alterations of the anchoring molars were identified in the anteroposterior position by the S-M' dist a n c e and in the vertical dimension by the M - M ' distance. These data can be seen in Table III. In the anteroposterior dimension, the distance S-M' did not show any molar displacement, indicating that the Haas-type appliance does not induce any modification in the anteroposterior position of the anchorage molars. In the vertical dimension, it was seen as a downward displacement of the rnolars with an increase in the
Volume tO0 Number 2
M-M' distance. The method used to evaluate this downward movement of the molars relied on a point on the largest posterior convexity of the upper molar crowns as a reference point. The molar downward displacement was measured from the SN line by a perpendicular line to the largest distal molar crown convexity. Therefore this distance indicates only that the upper molars followed the downward displacement of the maxilla as suggested by Byrom. 2' This measurement is not sensitive enough to evaluate molar extrusion relative to its own basal bone. As it is widely known, even in these early developmenfal stages, the orthopedic expansion (osseous displacement) is followed by buccal movement of the dentoalveolar process (orthodontic effect). This molar inclination, whose long axis can be deflected up to 24 ° in the permanent dentition (Hicks23), places the palatine cusps in an extrusive relation with the lower molars. SUMMARY AND CONCLUSIONS
Based on the interpretation of the cephalometric alterations observed after rapid maxillary expansion procedures during mixed denture, we conclude the following: 1. Anterior displacement of the maxilla with significant changes in the SNA angle should not be expected. 2. The maxilla always dislocates downward, displaying a downward and backward rotation in the palatine plane, significantly altering the following measurements: N-ANS, PNS-PNS', A-A', SN.PP. 3. The upper anchoring molars follow the downward maxillary displacement (M-M'). 4. The facial heights increase as a direct effect of the vertical displacement of the maxilla and upper molars (N-ANS, A-A', ANS-Me, N-Me, PNS-PNS'). 5. The subsequent mandibular rotation increases the inclination of the mandibular plane (SN.GoGn, SN.Gn, PP.GoGn) and repositions point B more posteriorly (SNB). REFERENCES 1. Silva Filho OG da, Freitas SF de, Cavassan A de O. Prevalrncia de oclusSo normal e m5 oclusSo em escolares da cidade de Baum ($5o Paulo). Part I. Rela~,5osagittal. Rev Fac Odontol [In press]. 2. Silva Filho OG da, Valladares Neto J, Almeida RR de. Early correction of posterior crossbite: biomechanieal characteristics of the appliances. J Pedodont 1989;13:195-221. 3. BadcockJH. The screw expansion plate. DentRec 1911;31:58890, 596-9.
R M E in p r h n a r 3, a n d m i x e d dentitions
179
4. Wick Wire NA. A simple technique for correction of bilateral maxillary dental constriction in the primary and mixed dentitions. Dent Clin North Am 1973;17:!51-9. 5. Berlocher WC, Mueller BH, Tinaoff N. The effect of maxillary palatal expansion on the primary dental arch circumference. Pediatr Dent 1980;2:27-30. 6. Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. AM J ORTHOD 1970;57:219-55. 7. Haas AJ. Rapid expansionofthe maxillary dental archand nasal cavity by opening the mid-palate suture, Angle Orthod 1961; 31:73-90. 8. Haas AJ. The treatment of maxillary deficiency by opening the midpalatal suture. Angle Orthod 1965;16:200-17. 9. Silva Filho OG da, Capellozza Filho L. Expans~o r~ipida da maxila: preceitos clfnicos. Ortodontia 1988;21:49-69. 10. Silva Filho OG da, Oliveira EA de, Capelozza Filho L. Avalia~fio das altera~6es dent{trias e esquelr-ticas ocorridas na dentadura mista ap6s o uso de expansor fixo tipo quadrihrlice. Ortodontia 1985; 18:23-35. 11. Angell EH. Treatment of irregularity of the permanent or adult teeth. Dent Cosmos 1860;1:540-4. 12. Wertz RA, Skeletal and dental changes accompanying rapid midpalatal suture opening. AM J OR'rnoD 1970;58:41.66. 13. Bell RA, Lecompte FA. The effects of maxillary expansion using a quad-helix appliance during the deciduous and mixed dentitions. AM J ORTttOD 1981;79:152-61. 14. Harberson VA, Myers DR. Midpalatal suture opening during functional crossbite correction. AM J ORTHOD1978;74:310-3. 15. Lindner A, Henrikson CO, Odenrick L, Modrer T. Maxillary expansion of unilateral cross-bite in preschool children. Scand J Dent Res 1986;94:411-8. 16. Silva Filho OG da, Alves RM, Capelozza Filho L. Altera~6es cefalomrtricas ocorridas na dentadura mista ap6s o uso de um expansor fixo tipo quadrihrlice. Ortodontia 1986;19:22-3. 17. Krebs A. Expansion of the midpalatal suture studied by means of metallic implants. Acta Odontol Scand 1959;17:491-501. 18. Krebs A. Midpalatal suture expansion studied by the implant method over a seven-year period. Eur Orthod Soc Rep Congr 1964;40:131-42. 19. Wertz RA. Changes in nasal airflow incident to rapid maxillary expansion. Angle Orthod 1968;38:1-% 20. Brogan WF. The stability of maxillary expansion. Aust Dent J 1977;22:92-9. 21. Byrom AG. Evaluation of antero-posterior and vertical skeletal change versus dental charge in rapid palatal expansion cases as studied by lateral cephalograms. AM J ORTItOD 1971;60:419. 22. Broadbent BH. A new x-ray technique and its application to orthodontia. Angle Orthod 1931;1:45-66. 23. Hicks EP. Slow maxillary expansion: a clinical study of the skeletal versus dental response to low-magnitude force. AM J ORTIIOD 1978;73:121-41. Reprhzt requests to: Omar Gabriel da Silva Filho Hospital de Pesquisa e Reabilita~.~o de LesBes L~bio-Palatais da Universidade de S~o Paulo Rua Silvio Marchione, 3-20 C. Postal: 620 17.043-Bauru-SP-Brazil
The present study evaluated the skeletal alterations induced by rapid maxillary expansion procedures in 30 patients in the primary and mixed dentitions. The results were obtained with the use of lateral cephalometrics before and immediately after the active phase of expansion. The time span between these two cephalometric films ranged from 14 to 21 days; therefore the "growth factor" was not considered. Based off the differences in the cephalometric measurements studied on the first and second tracings, it seems that anterior displacement of the maxilla with significant changes in the SNA angle should not be expected, although point B was repositioned more posteriorly (SNB) because of the man~libular downward and backward rotation, with subsequent increase of the inclination of the mandibular plane. The alterations in the A-P position of the mandible was reflected in the increase of ANB and NAP angles. The maxilla always dislocates downward, displaying a downwarcl and backward rotation in the palatine plane, significantly altering the following measurements: N-ANS, PNS-PNS', A-A', SN.PP. The anchoring molars also follow the downward maxillary displacement (M-M') and, as a direct consequence of the vertical displacement of the maxilla and upper molars (N-ANS, A-A', ANS-Me, N-Me, PNS-PNS'), the facial heights increase. (AM J ORTHODDENTOFACORTHOP 1991;100:171-81.)
T h e present concepts concerning posterior crossbites are well defined in the literature and widely accepted by orthodontists. Among mixed dentition children displaying malocclusions in the region of Bauru (Silo Paulo, Brazil), we found an 18.2% incidence of posterior crossbitesY This entity may occur in the primary dentition and manifest itself as a constriction in the lateral dimensions of the upper arch and, as a rule, will not self-correct. On the basis of these concepts, it is necessary to correct this form of malocclusion as early as possible, preferably in the primary dentition stage. Modem orthodontics has a wide variety of mechanical appliances that will release forces to laterally expand upper constricted arches? The jackscrew has been applied in removable 3.4 or fixed appliances 2'59 as a source to generate forces against the palatine surfaces of the upper teeth. When the jackscrew is used in removable appliances, it produces only slow expansion, which is indicated for dentoalveolar constrictions. In
From the University of Sao Paulo. *Orthodontist. **Resident of the Department of Orthodontics. ***Head of the Department of Orthodontics; Assistant Professor at Faculdade de Odontologia de Bauru. 1811121630
our clinical+ practice, we do not use the jackscrew for the particular purpose aforementioned. For slow expansions we use mainly the quad-helix appliance, m In rapid maxillary expansion procedures (RME) indicated for the correction of skeletal constrictions, even in early occlusal developmental stages, we use the jackscrew in fixed appliances, following the basic standards proposed by Haas 7 with a few modifications (Fig. I). Rapid maxillary expansion procedures are indicated in the primary and mixed dentitions every time the crossbite is associated with a skeletal constriction, which might be clinically identified as: 1. Unilateral or bilateral posterior crossbite with normal inclination of the dentoalveolar processes 2. Unilateral or bilateral posterior crossbite with retrusion of the middle third of the face (Class III tendency) 3. Total crossbite REVIEW OF THE LITERATURE Rapid maxillary expansion procedures have been proposed since the past century by Angell" and consolidated clinically by Haas. 6-8 This procedure leads to an increase in the upper arch transverse dimensions by mainly skeletal alterations associated with dental alterations, which may manifest themselves distinctly, de171
"17'2 Sih'a, Boas, and Capelozza
Am. J. Orthod. Dentofac. Orthop. Aug,st 1991
#
"j
~',
)"
b"
L
I
r"A
/,
_2_~ .,f,
Fig. 1. A through C, Unilateral posterior crossbite in the patient's right side, associated with an anterior crossbite. D, A rapid maxillary expansion appliance of the Haas type has been used for a. simultaneous correction of the posterior and anterior crossbites.
pending on the sutural resistance, which increases as a person matures. ~2 Although slow expansion appliances do promote a slight opening in the median palatine suture in the primary and mixed dentition stages, 2"~°'~4"~5 cephalometrically and clinically the results cannot be compared with the orthopedic effects of the Haas type of appliance. :'~6 Rapid maxillary expansion increases the upper arch transverse dimensions mainly by separation of the two maxillary halves (orthopedic effect), followed by buccal movement of the posterior teeth and alveolar processes (orthodontic effect). The force delivered by activation of the jackscrew exceeds the sutural resistance limit and splits not only the intermaxillary suture but also all the other maxillary sutures. Through this sutural splitting, the maxilla is incited to displace itself downward and forward, with a rotation in the maxillary components in both the horizontal and frontal planes. 6.7.sA2.17-t9 In the horizontal plane, the behavior of the maxilla is easily determined by an occlusal x-ray film (Fig. 2).The maxillary halves split along the median palatine suture, creating a triangular radiolucent area with its base toward the anterior region in which the resistance of the facial structures is weaker. 2,7-9.'2,'7.]8
In the frontal plane, the separation of the two maxillary halves also follows a triangular pattern 6,8.~z,18,19 with its base downward and the center of rotation located near the frontonasal suture.~2 The magnitude of increments can be listed in decreasing order as follows: transversal diameter at the level of the crowns of the teeth, alveolar arch, maxillary base, and nasal cavity, tT.z8 It is important to emphasize that these skeletal changes tend to be less significant with skeletal maturity because of the increased rigidity of the articulations of the maxilla with the face, 9'12 which can be felt clinically by the patient as either discomfort or pain. 9 The downward displacement of the maxilla has a direct effect in the spatial positioning of the mandible when related to the anterior cranial base. The mandible rotates downward and backward. This mandibular rotation 6"7'8"t2induces other alterations such as opening of the bite, occlusal plane inclination, increase in the mandibular plane angle and the y axis, and a downward and backward displacement of menton. Although the use of RME procedures in the primary and mixed dentitions are mentioned in the literature,2"5'6'8"9'12"2°'21 nothing has been published concerning
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Fig. 1 (Cont'd). E through G, After 7 days the activations were interrupted and the expansion screw was stabilized with acrylic resin (H). The open diastema in the upper central incisors (G) suggests the maxillary separation at the level of the median palatine suture. I and J illustrate the occlusion and the dental arch immediately after the retention period.
the specific cephalometfic alterations induced by these procedures in these early occlusal developmental stages. To fill this gap, this article studies the cephalometric alterations induced by the Haas type appliance, when used in the primary and mixed dentitions.
MATERIALS AND METHODS The subjects in the sample comprised 30 children with ages ranging from 5 years to 10 years 11 months, with a mean age of 8 years. All children had posterior crossbites with skeletal involvement. All cases were satisfactorily cor-
rected by means of an RME appliance of the Haas type (Fig. 1). The activations of the jackscrew were started 24 hours after the appliance was cemented in place. The parents were instructed to activate a 1/z turn in the morning and a 1/2 turn in the evening, thus performing one complete turn of the screw per day. The active period of activations ranged from I to 2 weeks, depending primarily on the degree of maxillary constriction. The lateral expansion of the upper arch was deemed sufficient when the posterior crossbite was ovcrcorrected by 2 to 3 mm (Fig. 1). The alterations promoted by the RME procedures were
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Am. J. Orthod. Dentofac. Orthop. August 1991
At
(3
0
,,k PTt{ '--~
..
[ ,%.
Fig. 2. A, The typical triangular opening of the median palatine suture confirms the separation of the maxillary processes during the rapid r~axillary expansion. B, The median palatine suture area is repaired totally after 90 days of the active phase of expansion.
appraised by two cephalometric x-ray films taken according to the guidelines of Broadbent."-" The first cephalogram was taken before any activation was performed; the second was taken after the active phase of expansion. For didactic purposes in the interpretation of the results, the cephalometric measurements used in this study were divided into three major groups: 1. Anteroposterior alterations of the apical bases (Fig. 3) a. Angular measurements: NAP, SNAp SNB, ANB b. Linear measurements: S-A', S°ENP', PTM-A 2. Vertical alterations of the apical bases (Fig. 4) and facial height alterations (Fig. 5) a. Angular measurements: SN.ANS-PNS (SN.PP), SN.GoGn, SNGn, ANS-PNS.GoGn (PP.GoGn) b. Linear measurements: N-ANS, ANS-Me, N-Me, A-A', PNS-PNS' 3. Anchoring molars alterations (Fig. 5) a. Linear measurements: M-M', S-M' The means and standard deviations for all cephalometric measurements were calculated in both cephalograms and the alterations that occurred in the postexpansion cephalogram, when compared to the preexpansion cephalogram, were analyzed statistically 1Jy the paired t test.
Fig. 3. The angular and linear cephalometric measurements through points S, N, A, B, Pog, PNS, and P'IM made possible the evaluation of the anteroposterior alterations of the apical bases.
RESULTS The results are shown in Tables I through III, which contain the means and standard deviations of the cephalometric measurements of the initial and postexpansion cephalograms. In addition, we have calculated the difference between the cephalometric measurements of the initial and postexpansion cephalograms, and the paired t test has been applied to assess the statistical significance.
DISCUSSION Anteroposterior alterations of the apical bases Surprisingly, the maxilla did n o t show any statistically significant alterations in the anteroposterior position (Fig. 6), which contradicts the works of Haas, 6-8 Krebs, ~7''8 and W e r t z .12. 19 This finding is based on the angular and linear measurements used in this study to define the A-P position of the m a x i l l a - namely, SNA, S - A ' , S-PNS', and PTM-A. The slight anterior displacement of the maxilla, denoted by the 0.5 ° SNA small increment (Table I), was not significant according to the paired t test. With the orthopedic expansion of the maxilla, the individual SNA variation ranged from - 3 . 0 ° to + 2 . 0 ° . These findings differ
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N"
Gf
Fig. 4. The angular cephalometric measurements on the points S, N, PNS, ANS, Go and Gn made possible the evaluation of the vertical behavior of the apical bases.
from the results of Haas, 7 which ranged from 0.0 ° to + 3.5 °. In his work Haas 7 found an anterior displacement of the maxilla in all of the 10 cases studied. Based on our results, we can infer that if an advancement of the maxilla is necessary along with expansion for the success of the treatment, we will have to resort to auxiliary orthopedic appliances that stimulate anterior maxillary displacement immediately after the active phase of expansion with the Haas type of appliance. Though this significant forward displacement of the maxilla observed by Haas 6-8 may be related to the magnitude of the expansion achieved by the appliance, Haas always expands the maxilla more than we do. As previously stated, all the cases in this study were not overcorrectcd beyond 2,0 to 3.0 mm. Clinically, the occlusal inclines on the palatine cusps of the upper molars occlude with the occlusal inclines of the buccal cusps of the lower molars. In addition, we suggest another possibility related to the skeletal resistance. In this early developmental stage, the least resistance of the facial structures to the expanded maxilla hinders its forward displacement during expansion.
Haas6-8 appraised this forward displacement of the maxilla by Use of linear me~isurements. He registered a 1.0 to 4.0 mm forward displacement of point A, although he used the facial plane (N-Pog) as a reference line. Because of the mandibular spatial alterations that follow RME procedures, this line does not represent a reliable reference. This fact led us to choose other measurements that would truly represent the effective maxillary length. The two chosen measurements (S-A' and PTM-A) did not display any Significant alterations (Table I), thus corroborating the alteration of SNA angle. This altei'ation differed from the observations of Wertz ~2 who found an increase in the S-A distance that amounted to 1.5 mm in a few days, using RME procedures in patients aged 7 to 29 years. In the present study, we found a reduction in the S-A' distance in 11 children, which ranged from - 4 . 4 to - 0 . 8 mm. Regarding the PTM-A distance, we also found a reduction that ranged from - 3 . 3 to - 0 . 4 mm in 12 children. Although these two measurements represent maxillary length, they are defined as perpendicular to the SN line (Fig. 3). The decrease in these two
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A" N.~
~.,~
Fig. 6. During the rapid maxillary expansion, the SNA angle changes varied from a reduction of 3.5° to an increase of 2.0°. In the mean the SNA angle value has remained stable.
Fig. 5. The linear cephalometric measurements on points N, ANS, Me, A, PNS, and M made possible the evaluation of the facial alterations and the changes of the anchoring molars.
measurements observed in the second cephalogram might be explained by the maxillary rotational effect on the positioning of points PTM and A'. This rotational effect also explains the reduction in the SNA angle in 11 children. Contrasting with the maxillary behavior, we found significant cepha!ometric alterations in the A-P position of the mandible (F!g. 7). A mean reduction of 1.5 ° in the SNB angle, reflected by a reduction in the mandibular projection, has a direct effect on the ANB and NAP angles, increasing their values. This decrease in the SNB angle and increase in the ANB and NAP angles are positive assets for the patients displaying straight or concave profiles since these alterations improve the AP maxillomandibular relation. Haas 8 observed these same results in his work, but with higher proportions when compared with our findings. Of the 30 patients who submitted to RME procedures, six showed an increase in the SNB angle that ranged from 0.2 ° to 1.4°. This can be explained by an anterior postural repositioning of the mandible resulting from the occlusal interferences induced by the expansion procedures.
The vertical alterations of apical bases and facial height alterations The RME procedures induced statistically significant alterations in all horizontal lines and planes of the face used in the present study (SN.PP, SN.GoGn, SN.Gn, PP.GoGn) (Table II). The maxilla displayed a tendency to rotate downward and backward increasing the SN.PP angle value (Fig. 8) with a variation that ranged from - 3.7 ° to 3.9 °. However, only seven cases displayed an upward and forward rotation of the palatal plane, displacing PNS downward. The mean increase in the SN.PP measure was 0.5°; this value is compatible with the Wertz '2 findings. The mandible also displayed postural alterations (Fig. 9) denoted by downward and backward rotation, just like the maxilla. This is probably a result of the maxillary rotation (Fig. 8) and molar extrusion caused by their buccoversion. The downward and backward rotation was significant in relation to the anterior cranial base (Sn.GoGn, SN.Gn) and the palatal plane (PP.GoGn). We interpret the molar extrusion as the reason for the mandibular rotation being more accentuated than the maxillary rotation. These data agree with those of Haas. s These facts led us to the conclusion that RME procedures induce downward and backward apical base rotations. Mandibular rotation has a direct effect in the
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Nt
79°
~-~0.5° ~~
-3
Fig. 8. Rotation of the palatine plane during the rapid expansion. The mean value of the SN.PP angle shows a downward and backward rotation of this plane in relation to the cranial base.
Fig. 7. With the expansion the SNB angle showed a statistically significant mean reduction of 1.15°; although with variations this ranged from a reduction of 3.3 ° to a forward movement of 1.4°.
A-P position of point B, reducing the SNB angle and increasing the reading of ANB and NAP angles. Rapid maxillary expansion incited an increase in the vertical dimensions of the face (Table I[) because of the maxillary and mandibular downward and backward rotation. This increase was noticed in the (1) upper facial height (N-ANS) as a result of the downward displacement of the maxilla, (2) in the lower facial height (ANS-Me) as a result of the mandibular rotation, and (3) in the total anterior facial height (N-Me) because of the rotation of both the maxilla and the mandible. The increase in the lower facial height is caused by the downward displacement of both the maxilla and upper teeth. This increase was mentioned in the works of Wertz ~2 and Byrom. '~ Maxillary posterior height also showed an increase (PNS-PNS'), denoting a downward displacement of PNS point, although the PNS point came down to a lesser extent than ANS point (N-ANS), which obviously was responsible for the downward and backward palatine plane rotation (SN.PP).
Go
Fig. 9. The Sn-GoGn angle reduced 0.5° after the rapid expansion in only one patient. This angle increased up to 4.6 °. The mandibular backward and downward rotation (mean value of 1.9 °) influenced the anteroposterior positioning of the point B.
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Table I. Anteroposterior alterations of apical bases
Mean
SD
Mean
SD
5.473 81.736 79.018 2.721 58.54 13.293 44.116
6.449 3.631 3.014 2.936 4.975 2.460 3.415
8.99 82.063 77.863 4.216 58.493 13.113 44.536
5.818 3.631 2.993 2.547 4.877 2.356 3.290
3.517 0.327 - 1.155 1.495 -0.050 -0.180 0.420
7.132" 1.039 4.834* 6.139" 0.185 0.185 1.645
Paired t test-postexpansion and initial cephalograms (N = 30; 29 df," 2.045 T critic)
2.561" 8.610' 8.014" 4.020* 9.211" 5.460* 8.842* 6.928* 3.371"
In#ial cephalogram
NAP SNA SNB ANB S-A' S-ENP' PTM-A
Paired t test-postexpansion and hdtial cephalograms (N = 30; 29 df," 2.045 T critic)
Difference-poste.tpansion and initial cephalograms
Post~rpansion cephalogranz
*Statistical significance.
Table
II. Vertical alterations of apical bases and facial alterations
Mean
SD
Mean
SD
Difference-postexpansion and hzitial cephalograms
8.063 35.706 67.154 27.642 47.0 62.975 107.860 51.975 39.539
3.462 3.810 3.581 3.686 3.718 4.261 6.708 3.577 2.887
8.636 37.613 68.986 28.983 48.136 63.943 109.326 52.746 40.073
3.281 4.302 3.782 4.282 3.882 3.300 6.'179 3.748 2.580
0.573 1.907 1.832 1.341 1.136 0.968 1.466 0.771 0.534
Initial cephalogrant
SN.PP SN.GoGn SN.Gn PP.GoGn N-ENA ENA-Me N-Me A-A' PNS-PNS'
Postexpansion cephalogram
*Statistical significance.
Table
IlL Alterations of anchoring molars
Mean
SD
Mean
SD
Difference-postexpansion and initial cephalograms
56.318 22.051
3.152 5.823
56.833 21.99
2.896 6.198
0.515 -0.061
Initial cephalogram
M-M' S-M'
Postexpansion ceplmlogram
Paired t test-postexpansion attd hfftial cephalograms (N = 30; 29 df," 2.045 T critic)
2.896* 1.428
*Statistical significance.
In the individual analysis of point "A" alterations, we observed a downward displacement (A-A') but no alteration in the anteroposterior position (S-A'). The behavior of these linear measurements agrees with the alterations observed in the angular measurements of the maxilla (SNA and SN.PP). These alterations led us to the conclusion that the maxilla always displaces itself downward as a result of RME procedures in the primary and mixed dentitions. Byrom 2j also observed this behavior in patients in the mixed and permanent dentitions.
Alterations of the anchoring molars The alterations of the anchoring molars were identified in the anteroposterior position by the S-M' dist a n c e and in the vertical dimension by the M - M ' distance. These data can be seen in Table III. In the anteroposterior dimension, the distance S-M' did not show any molar displacement, indicating that the Haas-type appliance does not induce any modification in the anteroposterior position of the anchorage molars. In the vertical dimension, it was seen as a downward displacement of the rnolars with an increase in the
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M-M' distance. The method used to evaluate this downward movement of the molars relied on a point on the largest posterior convexity of the upper molar crowns as a reference point. The molar downward displacement was measured from the SN line by a perpendicular line to the largest distal molar crown convexity. Therefore this distance indicates only that the upper molars followed the downward displacement of the maxilla as suggested by Byrom. 2' This measurement is not sensitive enough to evaluate molar extrusion relative to its own basal bone. As it is widely known, even in these early developmenfal stages, the orthopedic expansion (osseous displacement) is followed by buccal movement of the dentoalveolar process (orthodontic effect). This molar inclination, whose long axis can be deflected up to 24 ° in the permanent dentition (Hicks23), places the palatine cusps in an extrusive relation with the lower molars. SUMMARY AND CONCLUSIONS
Based on the interpretation of the cephalometric alterations observed after rapid maxillary expansion procedures during mixed denture, we conclude the following: 1. Anterior displacement of the maxilla with significant changes in the SNA angle should not be expected. 2. The maxilla always dislocates downward, displaying a downward and backward rotation in the palatine plane, significantly altering the following measurements: N-ANS, PNS-PNS', A-A', SN.PP. 3. The upper anchoring molars follow the downward maxillary displacement (M-M'). 4. The facial heights increase as a direct effect of the vertical displacement of the maxilla and upper molars (N-ANS, A-A', ANS-Me, N-Me, PNS-PNS'). 5. The subsequent mandibular rotation increases the inclination of the mandibular plane (SN.GoGn, SN.Gn, PP.GoGn) and repositions point B more posteriorly (SNB). REFERENCES 1. Silva Filho OG da, Freitas SF de, Cavassan A de O. Prevalrncia de oclusSo normal e m5 oclusSo em escolares da cidade de Baum ($5o Paulo). Part I. Rela~,5osagittal. Rev Fac Odontol [In press]. 2. Silva Filho OG da, Valladares Neto J, Almeida RR de. Early correction of posterior crossbite: biomechanieal characteristics of the appliances. J Pedodont 1989;13:195-221. 3. BadcockJH. The screw expansion plate. DentRec 1911;31:58890, 596-9.
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4. Wick Wire NA. A simple technique for correction of bilateral maxillary dental constriction in the primary and mixed dentitions. Dent Clin North Am 1973;17:!51-9. 5. Berlocher WC, Mueller BH, Tinaoff N. The effect of maxillary palatal expansion on the primary dental arch circumference. Pediatr Dent 1980;2:27-30. 6. Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. AM J ORTHOD 1970;57:219-55. 7. Haas AJ. Rapid expansionofthe maxillary dental archand nasal cavity by opening the mid-palate suture, Angle Orthod 1961; 31:73-90. 8. Haas AJ. The treatment of maxillary deficiency by opening the midpalatal suture. Angle Orthod 1965;16:200-17. 9. Silva Filho OG da, Capellozza Filho L. Expans~o r~ipida da maxila: preceitos clfnicos. Ortodontia 1988;21:49-69. 10. Silva Filho OG da, Oliveira EA de, Capelozza Filho L. Avalia~fio das altera~6es dent{trias e esquelr-ticas ocorridas na dentadura mista ap6s o uso de expansor fixo tipo quadrihrlice. Ortodontia 1985; 18:23-35. 11. Angell EH. Treatment of irregularity of the permanent or adult teeth. Dent Cosmos 1860;1:540-4. 12. Wertz RA, Skeletal and dental changes accompanying rapid midpalatal suture opening. AM J OR'rnoD 1970;58:41.66. 13. Bell RA, Lecompte FA. The effects of maxillary expansion using a quad-helix appliance during the deciduous and mixed dentitions. AM J ORTttOD 1981;79:152-61. 14. Harberson VA, Myers DR. Midpalatal suture opening during functional crossbite correction. AM J ORTHOD1978;74:310-3. 15. Lindner A, Henrikson CO, Odenrick L, Modrer T. Maxillary expansion of unilateral cross-bite in preschool children. Scand J Dent Res 1986;94:411-8. 16. Silva Filho OG da, Alves RM, Capelozza Filho L. Altera~6es cefalomrtricas ocorridas na dentadura mista ap6s o uso de um expansor fixo tipo quadrihrlice. Ortodontia 1986;19:22-3. 17. Krebs A. Expansion of the midpalatal suture studied by means of metallic implants. Acta Odontol Scand 1959;17:491-501. 18. Krebs A. Midpalatal suture expansion studied by the implant method over a seven-year period. Eur Orthod Soc Rep Congr 1964;40:131-42. 19. Wertz RA. Changes in nasal airflow incident to rapid maxillary expansion. Angle Orthod 1968;38:1-% 20. Brogan WF. The stability of maxillary expansion. Aust Dent J 1977;22:92-9. 21. Byrom AG. Evaluation of antero-posterior and vertical skeletal change versus dental charge in rapid palatal expansion cases as studied by lateral cephalograms. AM J ORTItOD 1971;60:419. 22. Broadbent BH. A new x-ray technique and its application to orthodontia. Angle Orthod 1931;1:45-66. 23. Hicks EP. Slow maxillary expansion: a clinical study of the skeletal versus dental response to low-magnitude force. AM J ORTIIOD 1978;73:121-41. Reprhzt requests to: Omar Gabriel da Silva Filho Hospital de Pesquisa e Reabilita~.~o de LesBes L~bio-Palatais da Universidade de S~o Paulo Rua Silvio Marchione, 3-20 C. Postal: 620 17.043-Bauru-SP-Brazil
