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Rapid maxillary expansion with incisor intrusion: A study of vertical control
CONTINUING EDUCATION ARTICLE Rapid maxillary expansion with incisor intrusion: A study of vertical control Lloyd E. Pearson, DDS, MSD,a and Bradley L. Pearson, DDS, MSa Edina, Minn This is a prospective study of 20 consecutively treated patients needing maxillary expansion and incisor intrusion. The patients were treated with a bonded maxillary expansion appliance, intrusion of the incisors with either a one-piece or three-piece base arch and anchorage augmented by the use of vertical pull chincup therapy. Because rapid palatal expansion and intrusion of maxillary incisors both produce extrusion of posterior teeth, this study was undertaken to determine if a combination of controlled forces could prevent undesirable increases in vertical dimension. The maxillae were widened approximately 8 mm, the incisors were intruded 3 mm, the maxillary molars stayed the same or were intruded slightly, and the mandibular plane angle stayed essentially the same. In addition, A-point was retracted slightly and the occlusal plane was rotated in a counter-clockwise direction. (Am J Orthod Dentofacial Orthop 1999;115:576-82)
I
n contemporary orthodontics, Haas must be credited with making rapid palatal expansion (RPE) more popular and for stimulating significant interest with his publications in 19591 and again in 1961.2 He presented a tissue-borne banded expander that produced significant expansion with some opening of the mandibular plane and downward descent of the maxilla. Wertz3 published a similar article in which he presented 60 cases and reported significant skeletal change, some opening of the mandibular plane and descent of the maxilla. Isaacson et al4-6 published three articles about the forces involved and suggested the appliance be left in place until the forces were completely dissipated. Development of the bonded Herbst appliance7 led clinicians into the frequent use of the bonded maxillary expansion appliance. Cohen and Silverman,8,9 followed by Mondro and Litt,10 were early advocates of bonded expanders. McNamara and Brudon11 have presented a careful protocol for placement and removal of bonded expanders. In addition, they advocated uprighting of the mandibular posteriors when tipped lingually. This compensatory tipping is frequently found in cases with narrow maxillae, in which case he advocated both
aIn private practice. Reprint requests to: Lloyd Pearson, DDS, MSD, 6545 France Ave South, Edina, MN 55435. Copyright © 1999 by the American Association of Orthodontists. 0889-5406/99/$8.00 + 0 8/1/93965
576
uprighting of the mandibular posteriors as well as widening of the maxilla. In 1989, Sarver and Johnston12 reported on the effects of the bonded maxillary expander and compared their results to those of Wertz’s study. Sarver and Johnston found there to be less extrusion of the maxillary posteriors with the bonded maxillary expansion appliance and postulated that the thickness of the acrylic acts as a deterrent for extrusion. Sandstrom et al13 discussed expansion of the mandibular arch concomitant with rapid maxillary expansion. They reported spontaneous uprighting of the mandibular posteriors following palatal expansion. Intrusion of teeth has been advocated by several authors,14-16 and Burstone17 has presented an effective method of controlling forces to accomplish incisor intrusion. Many patients may require intrusion of the maxillary incisors and RPE where an increase in vertical dimension is not indicated. Because both procedures produce extrusion of posterior teeth, this study was undertaken to determine if a combination of (1) controlled intrusive forces to the incisors, (2) occlusal coverage on a bonded RPE, and (3) vertical pull chincup therapy could prevent undesirable increases in vertical dimension. METHOD
The protocol is a prospective study involving the first stage of 20 consecutively treated patients requiring palatal expansion and maxillary incisor intrusion. All
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patients exhibited narrow maxillae and relatively steep mandibular plane angles (36.2°; range, 29° to 42°). The sample comprised 12 females and 8 males, average age 11 years 2 months, (range, 7 years 11 months to 13 years 7 months). A bonded palatal expansion appliance with a soldered buccal tube with posterior occlusal acrylic 2 to 3 mm thick was bonded onto the maxillary posterior occlusal surfaces (Fig 1). A vertical pull chincup was added to enhance the anchorage.18,19 The bonded palatal appliance was activated by turning the screw one-quarter turn per day for 5 to 6 weeks. Some posterior overexpansion was sought to permit uprighting of the maxillary posterior teeth.2 Incisor intrusion was initiated after diastema closure, which was approximately 1 month after expansion was completed. A continuous intrusion arch was used in most of the patients (Fig 2). In patients with protruding incisors a 3-piece intrusion mechanism was used (Fig 3). Intrusion was completed in 4.2 months on average (range, 2 to 6 months). The average time between records was 9.7 months (range, 7 to 14 months). Immediately after removal of the bonded expander, progress records were taken that consisted of study models, a cephalometric radiograph, orthopantomograph, facial photographs, and intraoral slides. The following cephalometric measurements were made and are shown in Fig 4. 1. Sella-nasion to A-point (SNA) 2. Sella-nasion to B-point (SNB) 3. A-point-nasion to B-point (ANB) 4. Sella-nasion plane to palatal plane (SN-PP) 5. Sella-nasion plane to mandibular plane (SN-MP) 6. Perpendicular distance from sella-nasion plane to posterior nasal spine (SN-PNS) 7. Perpendicular distance from sella-nasion plane to anterior nasal spine (SN-ANS) 8. Horizontal distance of A-point to a perpendicular from the sella-nasion plane at sella (S-A) 9. Perpendicular distance from sella-nasion plane to the maxillary incisor tips (SN-1) 10. Sella-nasion plane to the maxillary central incisor (SN-1) 11. Horizontal distance of the most prominent maxillary incisor to a perpendicular from the sellanasion plane at sella (S-1) 12. Frankfort to mandibular plane (FMA) 13. Maxillary molar to palatal plane 14. Mandibular molar to mandibular plane 15. Anterior nasal spine to menton (ANS-M) 16. Maxillary central incisor to palatal plane 17. Occlusal plane to sella nasion
Fig 1. Bonded expander with buccal tube soldered to metal framework.
A
B Fig 2. A, Continuous intrusion arch illustrates activation before tying to anterior segment. B, Continuous intrusion arch tied to anterior segment.
In addition, one measurement was made on the models: 18. Palatal expansion (measured on models between mesial-lingual cusps of maxillary first molars) For measuring the maxillary incisor intrusion to the palatal plane, a separate template for the maxillary central was used. The distance from the apex to the incisal edge was measured and the midpoint was designated as the centroid. The template was then placed on the
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Fig 3. Three-piece intrusion arch designed to intrude maxillary centrals, maintaining a constant inclination.
American Journal of Orthodontics and Dentofacial Orthopedics May 1999
Fig 5. Maxillary 0.032 inch round horseshoe-shaped lingual arch to upright molars.
RESULTS
The results of 20 consecutively treated patients who had bonded RPE with maxillary incisor intrusion with anchorage supplemented with vertical pull chincup therapy are found in Table I. The upper incisors were intruded 2.9 mm relative to the palatal plane. Upper first molars were expanded 7.9 mm. Even with the large amount of incisor intrusion and molar expansion, no increase in vertical dimension or mandibular plane angle was observed. In addition, a small reduction (flattening) of occlusal plan occurred. As an example, the following case is presented. Fig 4. Cephalometric measurements of example patient.
Case Report
progress cephalometric radiograph and the intrusion was determined by measuring the distance between the markings. In two of the 20 patients treated, the maxillary molars had excessive buccal inclination. In these individuals with tipped maxillary molars, and particularly in the backward growth rotational patterns, it has been helpful to upright the maxillary posteriors before placing an RPE appliance. This can be accomplished with bands on the maxillary molars and a 0.032 inch horseshoe-shaped round wire that uprights and constricts (Fig 5). The precision adjusted lingual sheath has a 0.032 inch square slot, and when used with a 0.032 inch round wire in it, provides an effective lingual tipping force to the maxillary molars. Recently, a hinged cap lingual sheath has been developed that is helpful because it makes adjustment and replacement of the lingual arch much easier and more efficient.20
The patient was 10 years 11 months old and presented a narrow maxilla, elongated maxillary incisors (9 mm below the lip at rest and an 11 mm interlabial gap), a tall lower face, and significant profile problems. Her mandibular plane angle measured 41° to sella nasion, and her lower facial height was somewhat excessive. Her maxilla was widened from 32.5 mm to 40.2 mm, a 7.7 mm maxillary expansion. The palatal plane remained relatively constant and her maxillary incisors were intruded 4.65 mm. Her palatal expansion appliance was active for 6 weeks, and she had 4.5 months of maxillary incisor intrusion. The initial and progress records were 9 months apart. Cephalometric tracings illustrate these changes (Fig 6). The mandibular plane angle stayed the same. The maxillary molars were intruded 1 mm, the mandibular molars were intruded 1 mm, and her ANS Menton measurement was reduced 3 mm. Fixed appliances were then placed and the intrusion continued after expansion. She wore a vertical pull chincup and occipital headgear. She had intrusion with a continuous
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Fig 6. Cephalometric tracing illustrates maxillary incisor intrusion of 4.65 mm after maxillary expansion.
Table I. Results
of study
Measurement SNA SNB ANB SN–PP SN–MP SN–PNS mm SN–ANS mm S–A mm SN–1 mm SN–1 S–1 mm Frankfort to mandibular plane Maxillary molar to palatal plane Mandibular molar to mandibular plane ANS to Menton Maxillary central to palatal plane Occlusal plane to SN Model measurements Upper first molar expansion
Mean differential
Standard deviation
–0.5 –0.3 –0.4 0.3 0.1 1.1 1.2 –0.6 –1.9 6.2 1.3 0.0 –0.4 0.8 0.0 –2.9 –2.3
1.34 1.03 1.12 1.30 1.79 1.30 1.16 1.74 1.25 7.82 1.97 1.97 1.30 1.07 1.79 0.98 2.01
–3.0 to +2.0 –2.0 to +2.0 –2.0 to +2.0 –1.0 to +3.0 –3.0 to +3.0 –1.0 to +4.0 –1.0 to +4.0 –3.0 to +3.0 –4.0 to 0 –16.0 to +16.0 –1.0 to +5.0 –3.0 to +3.0 –3.0 to +3.0 –1.0 to +2.0 –3.0 to +3.0 –1.8 to –5.1 –6.0 to +1.0
7.9
1.70
5.0 to 11.9
intrusion arch and her maxillary incisors were slightly vertical (Fig 2).17 The incisor root apices moved posteriorly as the incisors were intruded. Had a three-piece intrusion arch been used and the force directed in a gingival direction from a more posterior position, it would have been possible to intrude without changing the inclination (Fig 3).21 Care must be taken to evaluate the position of the unerupted maxillary canine crown as related to the maxillary lateral incisor root. As the lateral incisor is
Range
intruded, it is important that the maxillary canine has erupted far enough incisally to clear the lateral root. Occasionally, it is necessary to upright the maxillary incisors before beginning the intrusion. The patients in this study typically had the maxillary canines just beginning to erupt through the gingival tissue. It is easier to control the biomechanics necessary to intrude the maxillary four incisors than when the canines must be included. If the canines erupt as the incisors are intruding, it facilitates the next stage of treatment. The bonded
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American Journal of Orthodontics and Dentofacial Orthopedics May 1999
DISCUSSION
Fig 7. Maxillary molars illustrates excessive buccal inclination.
Fig 8. Maxillary molars after uprighting.
Fig 9. Maxillary molars after expansion are more vertical than initial record in Fig 7.
expansion appliance can be removed and fixed appliances placed. The maxillary posteriors can be controlled by the addition of a transpalatal arch and an occipital type of headgear. An example is shown of a patient who had buccally tipped maxillary molars. The measured width between the maxillary molars is 30 mm (Fig 7). These maxillary molars were uprighted to 27 mm (Fig 8). A bonded RPE appliance was placed, widening the maxilla to 39 mm (Fig 9). At 39 mm, the molars appear to be more vertical than they were at 30 mm.
With this therapeutic approach it is apparent that it is possible to widen the maxilla, intrude the maxillary centrals, and not increase the lower facial height or open the mandibular plane. In addition, the counterclockwise rotation tendency of the occlusal plane would generally be a benefit in many cases. To provide some comparison with other studies, we have reviewed and compared it first with Wertz’s study3 of 60 patients, and then with the study of 20 patients by Sarver and Johnston,12 using a t test. If the 11 measurements that Wertz used are compared with the first 11 measurements in the present study, 7 were significantly different than the Wertz study. In the Wertz’s study, A-point came forward, and in the present study, A-point was retracted. ANB was reduced, whereas it increased in Wertz’ study. The sella mandibular plane angle opened about 1° in the Wertz study, and essentially stayed the same in the present study; the maxillary incisor measurements were significantly different, which would be expected because of the intrusion in this study. When comparing the present study with Sarver’s study, there were six measurements that were significantly different. All the maxillary incisor measurements were different, which would be expected because intrusion was done in the present study and not in Sarver’s study. The SNB, ANB, and the sella to PNS measurements were all significantly different. So it would appear that this study, which differed from Sarver’s in that it had intrusion and vertical pull chincup therapy, showed differences in incisor response and also some mandibular plane and ANB benefits from the addition of the vertical pull chincup and the intrusion. The results of 20 patients in the present study of bonded palatal expansion, vertical pull chincup, and intrusion, were compared with Wertz’s banded palatal expansion study and Sarver’s bonded palatal expansion study. The results are listed in Table II. There are significant differences between these three studies. Wertz’s study used a banded appliance whereas Sarver’s study and the present study used bonded appliances. All these studies had a larger percentage of female patients than male patients. Wertz’s study had 62% females, Sarver’s study had 70% female patients, and the present study had 60% female patients. In the Wertz and Sarver studies, the appliance was activated twice a day, whereas in the present study the appliance was activated once each day. In the Wertz and Sarver studies, the appliance was left in place for 3 months after the activation; in the present study, the expansion was
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Table II. Mean
difference before and after treatment Study 1 (Wertz, n = 60)
OBS SNA SNB ANB SN–PP SN–MP SN–PNS mm SN–ANS mm S–A mm SN–1 mm SN–1 S–1 mm
Study 2 (Sarver and Johnston, n = 20)
Study 3 (present study, n = 20)
P value
P value
Mean
SE
Mean
SE
Mean
SE
Study 1 + study 3
Study 2 + study 3
0.51 –0.18 0.37 0.20 0.96 0.89 1.01 0.41 1.36 –0.66 0.15
0.11 0.13 0.14 0.16 0.16 0.13 0.14 0.11 0.14 0.31 0.13
–0.75 –1.00 0.50 0.50 0.75 0.35 1.25 –0.30 1.65 –3.00 –1.00
0.32 0.25 0.28 0.30 0.39 0.18 0.19 0.18 0.26 1.06 0.41
–0.50 –0.25 –0.35 0.25 0.10 1.10 1.20 –0.60 –1.85 6.15 1.30
0.30 0.23 0.25 0.29 0.40 0.29 0.26 0.39 0.28 1.75 0.44
0.0002* 0.7896 0.0127** 0.8776 0.0192** 0.4557 0.5115 0.0009* 0.0000* 0.0000* 0.0011*
0.5721 0.0334** 0.0293** 0.5526 0.2519 0.0342** 0.8804 0.4892 0.0000* 0.0001* 0.0005*
SE, Standard error. *P value < .005. **P value < .05.
retained somewhat longer because of the intrusion phase of treatment (a mean of 4.15 months). Because of the differences in sample age, malefemale distribution, and length of treatment, it is difficult to make comparisons of the efficacy of the therapy used among the three studies. Nevertheless, Table II suggests the procedures described in this article are very effective for vertical control when both RPE and incisor intrusion are indicated. Eleven of 20 patients in the present study had mandibular posterior uprighting, and two had maxillary molars uprighted before placement of the palatal expansion appliance. Joe Lavin has developed a technique of expanding the maxillary arch, using the Haas-type expander with some modification (personal communication). The modification consists of uprighting the upper posterior teeth that are to be included in the expander. This is done before the expander is placed. Typically, these maxillary posterior teeth are originally inclined to the buccal. The uprighting is accomplished by use of a palatal bar. Lavin reports of having four sets of records on some 1500 cases. He postulates that there is less maxillary posterior extrusion and better bone movement with this procedure. There may be two factors to consider that support this hypothesis. When the maxillary posteriors are uprighted and narrowed, new bone is formed buccal to the roots of these teeth. This osteoid is likely to be more resistant to tooth movement. In addition, the roots of the maxillary molars with the buccal crown inclination may be more prone to extrude and tip when a lateral force is applied. When the expander is placed, it is left in
place for 3 months before activation to allow the tissues to stabilize. After the activation, he leaves the palatal expansion appliance in place for 3 months. Then, after 3 months of stabilizing, he no longer retains the expansion, and he reports and shows excellent stability. In cases where the mandibular posteriors exhibit significant lingual tipping, these teeth can be uprighted over the mandibular bone by simple tipping forces. Thus, the amount of maxillary expansion is determined by the amount desired to upright the lower posterior teeth. CONCLUSION
In conclusion, it was found with the use of a bonded RPE appliance, together with maxillary incisor intrusion, and augmenting the anchorage with a vertical pull chincup, that it was possible to widen the maxilla approximately 8 mm, intrude the maxillary incisors approximately 3 mm (keeping the mandibular plane and the lower facial height the same), hold the maxillary molars in essentially the same position or intrude slightly, and rotate the occlusal plane in a counterclockwise direction. We would like to thank Dr Michael Riolo and Dr Charles Burstone for their assistance and advice, and Mr Bruce Lindgren, MS, at the University of Minnesota, for the statistical analysis.
REFERENCES 1. Haas AJ. Gross reactions to the widening of the maxillary dental arch of the pig by splitting the hard palate. Am J Orthod 1959;45:868. 2. Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening the midpalatal suture. Angle Orthod 1961;31:73-90.
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3. Wertz RA. Skeletal and dental changes accompanying rapid midpalatal suture opening. Am J Orthod 1970;58:41-66. 4. Isaacson RJ, Wood JL, Ingram AH. Angle Orthod 1964;34:256-60. 5. Isaacson RJ, Wood JL, Ingram AH. Angle Orthod 1964;34:261-70. 6. Zimring JF, Isaacson RJ. Angle Orthod 1965;35:178-86. 7. McNamara JA Jr. Components of Class II malocclusion in children 8-10 years of age. Angle Orthod 1981;51:177. 8. Cohen M, Silverman E. A new and simple palate splitting device. J Clin Orthod 1973;7:368-9. 9. Cohen M, Silverman E. Removing the bonded palate splitting device. J Clin Orthod 1973;7:523. 10. Mondro J, Litt R. J Clin Orthod 1977;11:203-6. 11. McNamara JA Jr, Brudon WL. Orthodontic and orthopedic treatment in the mixed dentition, Ann Arbor, MI: Needham Press; 1993. 12. Sarver DM, Johnston MW. Skeletal changes in vertical and anterior displacement of the maxilla with bonded rapid palatal expansion appliances. Am J Orthod Dentofacial Orthop 1989;95:462-6.
American Journal of Orthodontics and Dentofacial Orthopedics May 1999
13. Sandstrom RA, Klapper L, Papaconstantinou S. Expansion of the lower arch concurrent with rapid maxillary expansion. Am J Orthod 1988;94:296-301. 14. Dellinger EL. A histologic and cephalometric investigation of premolar intrusion in the ‘Macaca speciosa’ monkey. Am J Orthod 1967;53:325-55. 15. Marcotte ML. Biomechanics in orthodontics. Philadelphia: BC Decker; 1990. 16. Schroff B, Lindauer SJ, Burstone EJ, Leiss BJ. Segmented approach to simultaneous intrusion and space closure: biomechanics of the three-piece base arch appliance. Am J Orthod Dentofacial Orthop 1995;107:136-43. 17. Burstone CJ. Deep overbite correction by intrusion. Am J Orthod 1977;72:1-22. 18. Pearson LE. Vertical control in fully-banded orthodontic treatment. Angle Orthod 1986;56:205-24. 19. Pearson LE. Case report KP: treatment of a severe open bite, excessive vertical pattern with an eclectic nonsurgical approach. Angle Orthod 1991;61:71-6. 20. Burstone CJ. The precision lingual arch hinge cap attachment. J Clin Orthod 1994;28:139. 21. Wertz RA. Changes in nasal airflow incident to rapid maxillary expansion. Angle Orthod 1968;38:1-11.
I
n contemporary orthodontics, Haas must be credited with making rapid palatal expansion (RPE) more popular and for stimulating significant interest with his publications in 19591 and again in 1961.2 He presented a tissue-borne banded expander that produced significant expansion with some opening of the mandibular plane and downward descent of the maxilla. Wertz3 published a similar article in which he presented 60 cases and reported significant skeletal change, some opening of the mandibular plane and descent of the maxilla. Isaacson et al4-6 published three articles about the forces involved and suggested the appliance be left in place until the forces were completely dissipated. Development of the bonded Herbst appliance7 led clinicians into the frequent use of the bonded maxillary expansion appliance. Cohen and Silverman,8,9 followed by Mondro and Litt,10 were early advocates of bonded expanders. McNamara and Brudon11 have presented a careful protocol for placement and removal of bonded expanders. In addition, they advocated uprighting of the mandibular posteriors when tipped lingually. This compensatory tipping is frequently found in cases with narrow maxillae, in which case he advocated both
aIn private practice. Reprint requests to: Lloyd Pearson, DDS, MSD, 6545 France Ave South, Edina, MN 55435. Copyright © 1999 by the American Association of Orthodontists. 0889-5406/99/$8.00 + 0 8/1/93965
576
uprighting of the mandibular posteriors as well as widening of the maxilla. In 1989, Sarver and Johnston12 reported on the effects of the bonded maxillary expander and compared their results to those of Wertz’s study. Sarver and Johnston found there to be less extrusion of the maxillary posteriors with the bonded maxillary expansion appliance and postulated that the thickness of the acrylic acts as a deterrent for extrusion. Sandstrom et al13 discussed expansion of the mandibular arch concomitant with rapid maxillary expansion. They reported spontaneous uprighting of the mandibular posteriors following palatal expansion. Intrusion of teeth has been advocated by several authors,14-16 and Burstone17 has presented an effective method of controlling forces to accomplish incisor intrusion. Many patients may require intrusion of the maxillary incisors and RPE where an increase in vertical dimension is not indicated. Because both procedures produce extrusion of posterior teeth, this study was undertaken to determine if a combination of (1) controlled intrusive forces to the incisors, (2) occlusal coverage on a bonded RPE, and (3) vertical pull chincup therapy could prevent undesirable increases in vertical dimension. METHOD
The protocol is a prospective study involving the first stage of 20 consecutively treated patients requiring palatal expansion and maxillary incisor intrusion. All
Pearson and Pearson 577
American Journal of Orthodontics and Dentofacial Orthopedics Volume 115, Number 5
patients exhibited narrow maxillae and relatively steep mandibular plane angles (36.2°; range, 29° to 42°). The sample comprised 12 females and 8 males, average age 11 years 2 months, (range, 7 years 11 months to 13 years 7 months). A bonded palatal expansion appliance with a soldered buccal tube with posterior occlusal acrylic 2 to 3 mm thick was bonded onto the maxillary posterior occlusal surfaces (Fig 1). A vertical pull chincup was added to enhance the anchorage.18,19 The bonded palatal appliance was activated by turning the screw one-quarter turn per day for 5 to 6 weeks. Some posterior overexpansion was sought to permit uprighting of the maxillary posterior teeth.2 Incisor intrusion was initiated after diastema closure, which was approximately 1 month after expansion was completed. A continuous intrusion arch was used in most of the patients (Fig 2). In patients with protruding incisors a 3-piece intrusion mechanism was used (Fig 3). Intrusion was completed in 4.2 months on average (range, 2 to 6 months). The average time between records was 9.7 months (range, 7 to 14 months). Immediately after removal of the bonded expander, progress records were taken that consisted of study models, a cephalometric radiograph, orthopantomograph, facial photographs, and intraoral slides. The following cephalometric measurements were made and are shown in Fig 4. 1. Sella-nasion to A-point (SNA) 2. Sella-nasion to B-point (SNB) 3. A-point-nasion to B-point (ANB) 4. Sella-nasion plane to palatal plane (SN-PP) 5. Sella-nasion plane to mandibular plane (SN-MP) 6. Perpendicular distance from sella-nasion plane to posterior nasal spine (SN-PNS) 7. Perpendicular distance from sella-nasion plane to anterior nasal spine (SN-ANS) 8. Horizontal distance of A-point to a perpendicular from the sella-nasion plane at sella (S-A) 9. Perpendicular distance from sella-nasion plane to the maxillary incisor tips (SN-1) 10. Sella-nasion plane to the maxillary central incisor (SN-1) 11. Horizontal distance of the most prominent maxillary incisor to a perpendicular from the sellanasion plane at sella (S-1) 12. Frankfort to mandibular plane (FMA) 13. Maxillary molar to palatal plane 14. Mandibular molar to mandibular plane 15. Anterior nasal spine to menton (ANS-M) 16. Maxillary central incisor to palatal plane 17. Occlusal plane to sella nasion
Fig 1. Bonded expander with buccal tube soldered to metal framework.
A
B Fig 2. A, Continuous intrusion arch illustrates activation before tying to anterior segment. B, Continuous intrusion arch tied to anterior segment.
In addition, one measurement was made on the models: 18. Palatal expansion (measured on models between mesial-lingual cusps of maxillary first molars) For measuring the maxillary incisor intrusion to the palatal plane, a separate template for the maxillary central was used. The distance from the apex to the incisal edge was measured and the midpoint was designated as the centroid. The template was then placed on the
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Fig 3. Three-piece intrusion arch designed to intrude maxillary centrals, maintaining a constant inclination.
American Journal of Orthodontics and Dentofacial Orthopedics May 1999
Fig 5. Maxillary 0.032 inch round horseshoe-shaped lingual arch to upright molars.
RESULTS
The results of 20 consecutively treated patients who had bonded RPE with maxillary incisor intrusion with anchorage supplemented with vertical pull chincup therapy are found in Table I. The upper incisors were intruded 2.9 mm relative to the palatal plane. Upper first molars were expanded 7.9 mm. Even with the large amount of incisor intrusion and molar expansion, no increase in vertical dimension or mandibular plane angle was observed. In addition, a small reduction (flattening) of occlusal plan occurred. As an example, the following case is presented. Fig 4. Cephalometric measurements of example patient.
Case Report
progress cephalometric radiograph and the intrusion was determined by measuring the distance between the markings. In two of the 20 patients treated, the maxillary molars had excessive buccal inclination. In these individuals with tipped maxillary molars, and particularly in the backward growth rotational patterns, it has been helpful to upright the maxillary posteriors before placing an RPE appliance. This can be accomplished with bands on the maxillary molars and a 0.032 inch horseshoe-shaped round wire that uprights and constricts (Fig 5). The precision adjusted lingual sheath has a 0.032 inch square slot, and when used with a 0.032 inch round wire in it, provides an effective lingual tipping force to the maxillary molars. Recently, a hinged cap lingual sheath has been developed that is helpful because it makes adjustment and replacement of the lingual arch much easier and more efficient.20
The patient was 10 years 11 months old and presented a narrow maxilla, elongated maxillary incisors (9 mm below the lip at rest and an 11 mm interlabial gap), a tall lower face, and significant profile problems. Her mandibular plane angle measured 41° to sella nasion, and her lower facial height was somewhat excessive. Her maxilla was widened from 32.5 mm to 40.2 mm, a 7.7 mm maxillary expansion. The palatal plane remained relatively constant and her maxillary incisors were intruded 4.65 mm. Her palatal expansion appliance was active for 6 weeks, and she had 4.5 months of maxillary incisor intrusion. The initial and progress records were 9 months apart. Cephalometric tracings illustrate these changes (Fig 6). The mandibular plane angle stayed the same. The maxillary molars were intruded 1 mm, the mandibular molars were intruded 1 mm, and her ANS Menton measurement was reduced 3 mm. Fixed appliances were then placed and the intrusion continued after expansion. She wore a vertical pull chincup and occipital headgear. She had intrusion with a continuous
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Fig 6. Cephalometric tracing illustrates maxillary incisor intrusion of 4.65 mm after maxillary expansion.
Table I. Results
of study
Measurement SNA SNB ANB SN–PP SN–MP SN–PNS mm SN–ANS mm S–A mm SN–1 mm SN–1 S–1 mm Frankfort to mandibular plane Maxillary molar to palatal plane Mandibular molar to mandibular plane ANS to Menton Maxillary central to palatal plane Occlusal plane to SN Model measurements Upper first molar expansion
Mean differential
Standard deviation
–0.5 –0.3 –0.4 0.3 0.1 1.1 1.2 –0.6 –1.9 6.2 1.3 0.0 –0.4 0.8 0.0 –2.9 –2.3
1.34 1.03 1.12 1.30 1.79 1.30 1.16 1.74 1.25 7.82 1.97 1.97 1.30 1.07 1.79 0.98 2.01
–3.0 to +2.0 –2.0 to +2.0 –2.0 to +2.0 –1.0 to +3.0 –3.0 to +3.0 –1.0 to +4.0 –1.0 to +4.0 –3.0 to +3.0 –4.0 to 0 –16.0 to +16.0 –1.0 to +5.0 –3.0 to +3.0 –3.0 to +3.0 –1.0 to +2.0 –3.0 to +3.0 –1.8 to –5.1 –6.0 to +1.0
7.9
1.70
5.0 to 11.9
intrusion arch and her maxillary incisors were slightly vertical (Fig 2).17 The incisor root apices moved posteriorly as the incisors were intruded. Had a three-piece intrusion arch been used and the force directed in a gingival direction from a more posterior position, it would have been possible to intrude without changing the inclination (Fig 3).21 Care must be taken to evaluate the position of the unerupted maxillary canine crown as related to the maxillary lateral incisor root. As the lateral incisor is
Range
intruded, it is important that the maxillary canine has erupted far enough incisally to clear the lateral root. Occasionally, it is necessary to upright the maxillary incisors before beginning the intrusion. The patients in this study typically had the maxillary canines just beginning to erupt through the gingival tissue. It is easier to control the biomechanics necessary to intrude the maxillary four incisors than when the canines must be included. If the canines erupt as the incisors are intruding, it facilitates the next stage of treatment. The bonded
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DISCUSSION
Fig 7. Maxillary molars illustrates excessive buccal inclination.
Fig 8. Maxillary molars after uprighting.
Fig 9. Maxillary molars after expansion are more vertical than initial record in Fig 7.
expansion appliance can be removed and fixed appliances placed. The maxillary posteriors can be controlled by the addition of a transpalatal arch and an occipital type of headgear. An example is shown of a patient who had buccally tipped maxillary molars. The measured width between the maxillary molars is 30 mm (Fig 7). These maxillary molars were uprighted to 27 mm (Fig 8). A bonded RPE appliance was placed, widening the maxilla to 39 mm (Fig 9). At 39 mm, the molars appear to be more vertical than they were at 30 mm.
With this therapeutic approach it is apparent that it is possible to widen the maxilla, intrude the maxillary centrals, and not increase the lower facial height or open the mandibular plane. In addition, the counterclockwise rotation tendency of the occlusal plane would generally be a benefit in many cases. To provide some comparison with other studies, we have reviewed and compared it first with Wertz’s study3 of 60 patients, and then with the study of 20 patients by Sarver and Johnston,12 using a t test. If the 11 measurements that Wertz used are compared with the first 11 measurements in the present study, 7 were significantly different than the Wertz study. In the Wertz’s study, A-point came forward, and in the present study, A-point was retracted. ANB was reduced, whereas it increased in Wertz’ study. The sella mandibular plane angle opened about 1° in the Wertz study, and essentially stayed the same in the present study; the maxillary incisor measurements were significantly different, which would be expected because of the intrusion in this study. When comparing the present study with Sarver’s study, there were six measurements that were significantly different. All the maxillary incisor measurements were different, which would be expected because intrusion was done in the present study and not in Sarver’s study. The SNB, ANB, and the sella to PNS measurements were all significantly different. So it would appear that this study, which differed from Sarver’s in that it had intrusion and vertical pull chincup therapy, showed differences in incisor response and also some mandibular plane and ANB benefits from the addition of the vertical pull chincup and the intrusion. The results of 20 patients in the present study of bonded palatal expansion, vertical pull chincup, and intrusion, were compared with Wertz’s banded palatal expansion study and Sarver’s bonded palatal expansion study. The results are listed in Table II. There are significant differences between these three studies. Wertz’s study used a banded appliance whereas Sarver’s study and the present study used bonded appliances. All these studies had a larger percentage of female patients than male patients. Wertz’s study had 62% females, Sarver’s study had 70% female patients, and the present study had 60% female patients. In the Wertz and Sarver studies, the appliance was activated twice a day, whereas in the present study the appliance was activated once each day. In the Wertz and Sarver studies, the appliance was left in place for 3 months after the activation; in the present study, the expansion was
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Table II. Mean
difference before and after treatment Study 1 (Wertz, n = 60)
OBS SNA SNB ANB SN–PP SN–MP SN–PNS mm SN–ANS mm S–A mm SN–1 mm SN–1 S–1 mm
Study 2 (Sarver and Johnston, n = 20)
Study 3 (present study, n = 20)
P value
P value
Mean
SE
Mean
SE
Mean
SE
Study 1 + study 3
Study 2 + study 3
0.51 –0.18 0.37 0.20 0.96 0.89 1.01 0.41 1.36 –0.66 0.15
0.11 0.13 0.14 0.16 0.16 0.13 0.14 0.11 0.14 0.31 0.13
–0.75 –1.00 0.50 0.50 0.75 0.35 1.25 –0.30 1.65 –3.00 –1.00
0.32 0.25 0.28 0.30 0.39 0.18 0.19 0.18 0.26 1.06 0.41
–0.50 –0.25 –0.35 0.25 0.10 1.10 1.20 –0.60 –1.85 6.15 1.30
0.30 0.23 0.25 0.29 0.40 0.29 0.26 0.39 0.28 1.75 0.44
0.0002* 0.7896 0.0127** 0.8776 0.0192** 0.4557 0.5115 0.0009* 0.0000* 0.0000* 0.0011*
0.5721 0.0334** 0.0293** 0.5526 0.2519 0.0342** 0.8804 0.4892 0.0000* 0.0001* 0.0005*
SE, Standard error. *P value < .005. **P value < .05.
retained somewhat longer because of the intrusion phase of treatment (a mean of 4.15 months). Because of the differences in sample age, malefemale distribution, and length of treatment, it is difficult to make comparisons of the efficacy of the therapy used among the three studies. Nevertheless, Table II suggests the procedures described in this article are very effective for vertical control when both RPE and incisor intrusion are indicated. Eleven of 20 patients in the present study had mandibular posterior uprighting, and two had maxillary molars uprighted before placement of the palatal expansion appliance. Joe Lavin has developed a technique of expanding the maxillary arch, using the Haas-type expander with some modification (personal communication). The modification consists of uprighting the upper posterior teeth that are to be included in the expander. This is done before the expander is placed. Typically, these maxillary posterior teeth are originally inclined to the buccal. The uprighting is accomplished by use of a palatal bar. Lavin reports of having four sets of records on some 1500 cases. He postulates that there is less maxillary posterior extrusion and better bone movement with this procedure. There may be two factors to consider that support this hypothesis. When the maxillary posteriors are uprighted and narrowed, new bone is formed buccal to the roots of these teeth. This osteoid is likely to be more resistant to tooth movement. In addition, the roots of the maxillary molars with the buccal crown inclination may be more prone to extrude and tip when a lateral force is applied. When the expander is placed, it is left in
place for 3 months before activation to allow the tissues to stabilize. After the activation, he leaves the palatal expansion appliance in place for 3 months. Then, after 3 months of stabilizing, he no longer retains the expansion, and he reports and shows excellent stability. In cases where the mandibular posteriors exhibit significant lingual tipping, these teeth can be uprighted over the mandibular bone by simple tipping forces. Thus, the amount of maxillary expansion is determined by the amount desired to upright the lower posterior teeth. CONCLUSION
In conclusion, it was found with the use of a bonded RPE appliance, together with maxillary incisor intrusion, and augmenting the anchorage with a vertical pull chincup, that it was possible to widen the maxilla approximately 8 mm, intrude the maxillary incisors approximately 3 mm (keeping the mandibular plane and the lower facial height the same), hold the maxillary molars in essentially the same position or intrude slightly, and rotate the occlusal plane in a counterclockwise direction. We would like to thank Dr Michael Riolo and Dr Charles Burstone for their assistance and advice, and Mr Bruce Lindgren, MS, at the University of Minnesota, for the statistical analysis.
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