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Skeletal changes in vertical and anteriordisplacement of the maxilla with bonded rapidpalatal expansion appliances

David M. Sarver, DMD, MS, and Mark W. Johnston, DMDBirmingham, Ala.The purpose of this study was to determine whether anterior and inferior displacement of the maxillaseen with rapid palatal expansion when done with a banded rapid palatal expansion appliance issignificantly different from an occlusally bonded rapid palatal expansion appliance. It washypothesized that the bonded appliance would limit unwanted displacement of the maxil la byproducing vertical forces on both arches in a manner s imila r to a functional appliance. The studywas conducted using the bonded appliance on 20 adolescents and comparing the results with thoseof a banded appliance population-namely, 60 cases from Wertzs study. Lateral cephalometricradiographs were taken before treatment and again after the expansion appliances were removed.The resul ts of this study suggest that the downward and anterior displacement of the maxilla oftenassociated with the banded rapid palatal expansion appliance may be negated or minimized with themore versatile bonded appliance. (AM J ORTHOD DENTOFAC ORTHOP 1989;95:462-6.)

R apid palatal expansion has long been acommonly used means of correcting maxillary trans-verse deficiency. Although many articles have beenpublished concerning structural and histologic changesof sutures, alterations in maxillary airway resistance,and general skeletal and dental changes, few articleshave specifically addressed the basic problem of ante-rior and inferior displacement of the maxilla caused byskeletal changes. 2-4This movement is an obviously un-desirable characteristic for many dental and skeletaltypes of patients. For example, the patient with a ClassII dentition, long face, and open bite pattern could il lafford the extrusive characteristics of rapid palatal ex-pansion.

Rapid palatal expansion is performed in two phases.The first phase is an active expansion of the maxilla bysutural expansion; the second phase of retention allowsfor reorganization and calcification of the midpalatalsuture. Haas described the sequence of events that oc-curs during rapid palatal expansion with a bonded ap-pliance:-A parallel opening of the midpalatal suture in an anterior-

posterior direction and a triangular opening inferior-superiorly with the apex in the nasal cavity.

-Separation of the central incisors (coincidental as the sutureseparates) with convergence of the clinical crowns anddivergence of the roots due to transseptal f ibers

-A downward and lateral movem ent of the maxilla w ithcoincidental inferior movem ent of the palatal processes

-A downward and backward movem ent of the mandibleresulting in an increased v ertical dim ension

462

Wertz not only recorded data from his clinical studybut used dried skul ls to supplement his work concerningskeletal changes. The skulls showed changes to themaxillonasal, maxillofrontal, and maxilloethmoidal su-tures but litt le or no changes to the pterygopalatine andmaxillopalatine junctions. In the clinical part of hisstudy, the lateral cephalograms showed that the maxi llaconsistently moved inferiorly but rarely moved ante-riorly to a significant degree. Other authors had similarfindings for vertical movement, but also state that theirstudies showed various degrees of anterior movementof the maxilla.3-5 The inferior movement of the maxi llaaccounted for the consequential opening of the man-dibular angle while also promoting an anterior openbite.6.7 Although for some patients it is beneficial tohave an increase in vertical dimension, often it is anunwanted characteristic.

Other adverse features commonly seen with bandedrapid palatal expansion appliances are lack of rigid ityand tooth extrusion. Proper rigidity of the appliance isnecessary to prevent unwanted tipping of the dentition.Several authors point out that increasing the rigidity ofan appliance decreases the rotational component offorce along the long axis of the tooth., Extrusion ofabutment teeth should be limited to prevent further ver-tical opening.

Bonded rapid palatal expansion appliances were de-signed to cover the maxillary posterior occlusal-buccalsegments so that the appliance not only serves as anexpansion device but intrudes on the freeway spacethrough its vertical thickness. It acts as a functional

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Number 6

Z-3mm

Fig. 1. Maxillary expansion appliance bonded to upper posteriorarch. Approximately 2 to 3 mm of acrylic is bonded to maxillaryposterior teeth so that passive stretch of elevator and retractormusculature provides an apically directed force to mandib le andmaxilla.

appliance with a small range of clinical applications.Further explanation of this concept is described by Gra-ber and Neumann in regard to their open bite appliancewith its lateral bite-blocks. Theoretically, by infringingon the freeway space with the displacement of the man-dible 2 to 3 mm below the intercuspal position, a con-stant passive force is exerted on the maxilla and themandible. Ahlgren, suggests that the elevator mus-culature is stretched beyond its resting length with theappliance in place. Such tension by the muscles arecaused by a stretch reflex that continues as long as themuscle is maintained at greater than resting length..The appliance therefore i s transferring an apically d i-rected force to the maxil lary and mandibular teeth fromthe passive stretch of the musculature (Fig. I). Theappliance should not only promote expansion but limitchanges in vertical dimension while serving as a func-tional appliance with intrusive forces against the maxillaand the mandible.

Application of this theory could possibly counteractsome of the disadvantages of the orthodontically bandedappliance. The bonded rapid palatal expansion appli-ance would increase rigid ity by limiting unwanted tip-ping and rotation of teeth due to the increased surfaceof acrylic bonded to the teeth. Furthermore tooth su-pereruption would be limited because of the bondingof the entire posterior arch.MATERIALS AND METHODS

The subjects of the study were 20 adolescents withbonded appliances-6 boys and 14 girls with a meanage of 10.8 years (range, 7.5 to 16 years). Al l patientsneeded posterior transverse expansion and all weretreated with the bonded appliance (Fig. 2). Our samplewas compared against Wertz s data. The subjects inWertzs sample were 37 girls, aged 7 to 29 years, and23 boys, aged 8 to 14 years. H is study involved allbanded appliances. Although there is a difference in

Fig. 2. Bonded rapid palatal expansion appliance.

sample size of 60 patients (banded) to 20 patients(bonded), statis tically this is not a problem. If a dif-ference between maxilla ry parameters is detected (inthis case to a p value of 0.0.5), then the samples aresufficient. Increasing the sample size would only detecta smaller difference in means. Lateral cephalometricradiographs were taken and comparisons were calcu-lated before and after palatal expansion for both groups.An example of comparative points is shown in Fig. 3.

Except for appliance design, both groups had sim-ilar treatment parameters. Both groups used a similarscrew mechanism and with both groups activation timewas dependent on the individual case. Activation ofappliances for both groups was twice daily, morningand evening. Both samples were retained for stabili-zation for approximately 3 months.

Frontal cephalometric radiographs of the bondedgroup were not taken. Although Wertz had data con-cerning posteroanterior cephalograms. his data showedonly horizontal changes in the nasal cavity and in the

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464 Sarver and Johnston Am J. Orthod. Dentofac. Orthop.June 1989

A. Angular measwements ,n deqrees1 Sella-naslon-point A CSNAI2 Sella-naslon-pant 6 ISNBl3 Point A-Nas~on-point B (ANBI4 Sella-nas~on plane lo palatal plane (SN-PPI5 Sella-nas~on pla ne to mandibular plane

(SN-MP)

B Linear measurements in mllltmeters1 Perpendicular dlslance lrom sella-naslon

plane to posterior nasal spine E N-PNSI2 Perpendicular distance lrom sella-naslon

olane to anterior nasal SDI~ EN-AN 33 berpend,clar distance i;om sella-nas~onplane lo the maxillary mc~sor tips (SN-1)

4 Hor~zorltal distance 01 pant A to a perpedlcular from the sella-aslon plane at sella(S-Al5 Howontal drstance of the most prommentmaxillary nc~sor to a perpendicular fromthe sella-naslon plane al sell8 IS 11

Flg. 3. Comparative measurem ents used for bonded and banded populations. (From Wertz RA. A M JORTHOD1970;58:41-85.)

Table I. Mean value (M) of comparable measurements, standard error (SE), and range with number ofapplicable patients in parenthesis-Italicized values statis tical ly significant to a p value of 0.05using a t test

M 2 SESNA () 0.51 f 0.11SNB () -0.18 4 0.13ANB () 0.37 + 0.14SN-PP () 0.20 k 0.16SN-MP () 0.96 f 0.16SN-PNS (mm) 0.89 k 0.13SN-ANS (mm) 1.01 0.14S-A (mm) 0.41 2 0.11S-1 (mm) 1.36 - 0.14SN-1 () -0.66 +- 0.31S-1 (mm) 0.15 & 0.13

*Or less than; **or greater than.

BandedRange

-2.0 (1) to +2..5 (I)-3.0 (1) to +2.0 (1)-3.0 (1) to +2.0 (6)-3.5 (1) to +3.5 (1)- 1.0 (I) to +4.5 (1)- 1.5 (1) to +4.0(l)-2.5 (1) to +4.5 (1)- 1.5 (3) to +2.5 (1)- 1.0 (1) to +3.5 (I)-5.5* (3)to +5.5** (2)-2.5 (1) to +2.0 (5)

BondedM k SE Range p value

-0.75 t 0.32 -5 (1) to +1 (2) 0.0001- 1.00 r 0.25 -4 (1) to + 1 (1) 0.004

0.50 2 0.28 -2 (1) to +3 (1) 0.650.50 0.30 -2 (1) to +3 (1) 0.360.75 2 0.39 -3 (1) to +5 (1) 0.560.35 k 0.18 - 1 (3) to +2 (1) 0.031.25 2 0.19 -1 (1) to +3 (1) 0.38

-0.30 t 0.18 - 1 (1) to +3 (1) 0.00181.65 ? 0.26 -2 (1) to +4 (1) 0.31

-3.00 t 1.06 -9 (2) to +8 (1) 0.005- 1.00 f 0.41 -5 (1) to +2 (2) 0.0007

width of the maxi llary molars. Our focus of comparisonis the vertical displacement of the maxilla with twotypes of expansion appliances.

The bonded appliance differs from the banded ap-pliance in its attachment to the teeth. Approximately 2to 3 mm in thickness of methylmethacrylate is con-structed on the occlusal-buccal surface and bonded di-rectly to the enamel, The acry lic is equilibrated so thatthe bite is equal bilaterally.CASE REPORT

The patient, a 13-year-old girl, was referred fo r correctionof her crossb ite and an anterior open bite. Along with herClass II skeletal pattern, she exhibited a moderately highmandibular plane angle with maxilla ry and mandibular pro-clination (ANB, 5; Wits, + 5 mm ). Rapid palatal expansion

was init iated as the f irst phase of treatment for maxillarytransverseexpansion and crossbitecorrection. The appliancewas bonded to the maxillary arch (second molar to f irst pre-molar) and was approximately 3 mm in thickness on theocclusal surface. The appliance was expanded on turn twotimes a day, producing 0.5 mm of expansion per day for I1days, achieving 5.5 mm of expansion. It was then left ce-mented in place for 3 months to allow calcif ication and sta-bilization of the midpalatal suture. A lateral head fi lm wastaken immediately after removal of the bonded appliance andsuperimposed; the init ial f i lm showed no inferior movem entof the maxilla and an extrusive and uprighting of the maxillaryincisors (Fig. 4). In this case the anterior open bite actuallydecreased from 3 mm to 2 mm (Fig. 5).

This case illustrates how the bonded rapid palatal e xpan-sion appliance is valuable in patients in who m th e undesirablemovem ent of rapid palatal expansion needs to be limited or

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Vo lume 95Number 6 Skeletal changes in vertical and anterior displacement of maxilla 465

Inmid 10 -17 - 85 -Pmgnrs03-16-.3fl-----

Fig. 4 . Patient at age 13 years , before and after rapid palatalexpansion with bonded appliance.

eliminated. Certain ly in this case, any inferior movement ofthe maxilla would have produced an anterior open bite. Inaddition any inferior positioning of the maxilla would worsenthe Class II skeleta l and dental relationships and the profile.The bonded appliance appeared to have been very helpful inovercoming these undesirable side effects of a banded rapidpalatal expansion appliance.RESULTS

Significant difference in data was noted (Table I).In both samples a ll cases were considered successfulin that the crossb ites were corrected. Although onechild with the bonded appliance had the applianceremoved because of poor compliance and subsequentlywas not included in the study, no other subject in eithergroup had reason for ear ly removal. Values of p lessthan 0.05 in the study were considered statis tical lysignificant.

Noted values were as follows:1. SNA. This angle value, an indicator of the hor-

izontal position of the maxilla to the cranial base,showed a significan t difference from Wertzs data. Theanterior movement of the maxil la in the bonded samplewas less than in the banded sample. Several patients inthe bonded group actually had posterior movement, onein the amount of 3 mm.

2. SNB. This value was significant (p = 0.03) andwould appear to indicate a downward and backwardmovement of the mandible by means of a clockwiserotation. An inferior movement of the maxil la wouldbe a like ly cause of this rotation; however, inferiormovements of the maxilla tended not to occur in oursample. A possible explanation is that the rotation ofthe mandible was caused by either posterior maxi llarypalatal cuspal interference after expansion with over-

Fig. 5, A and B. Intraoral photographs showing decrease inanterior open bite from 3 mm to 2 mm .

correction or occlusal interference from remnants of thebonding material on the occlusal surfaces.3. SN-PNS. This linear measurement i s an indi-

cation of the amount of movement the posterior nasalspine travels in an inferior or superior direction. Thisis important since the posterior reference point of thepalatal plane would be expected to move inferiorly withexpansion of the palate. The bonded group (range,- 1 .O to + 2.0 mm) had less inferior movement of PNSthan the banded group (range, - 1.5 to +4.0 mm).

4. S-A. This is a linear measurement to determinethe horizontal displacement of the anterior aspect of themaxilla . The data showed the bonded group actuallyhad a posterior displacement.

5. SN-I-. An angular measurement to show dis-placement of the axis of the central incisor . Both sam-ples showed a posterior tipping of the incisor with thebonded group being more severe.

6. S-1. A linear measurement to show anteropos-terior displacement of the tip of the central incisor. Thebonded group showed more posterior movement of theincisor tip than the banded group.DISCUSSION

The most significant finding of this study is that theinferior displacement of the maxil la i s lessened with

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466 Sarver and Johnston Am. J. Orrhad. Dentofac. Orthop.June 1989Before Expansion -After Expansion - - --

Fig. 6. Hypothetic skeletal changes associated with banded rapid palatal expansion appliance and (A)bonded palatal expansion appliance (8).

the use of the bonded rapid palatal expansion appliancewhen maxillary expansion is necessary. The downwardand forward movement of the maxilla associated withthe banded appliance is not necessary to achieve pos-terior expansion. The skeletal movement of the maxi llaseen with the bonded appliance is to a smal l degreesuperior (at PNS) and posterior with a clockwise ro-tation (Fig. 6). This infers that the inferior displacementof the maxilla may be limited by the forces placed onthe dentition by the elevator musculature and soft-tissuestretch. Wertz noted in his study that occasionally distaldisplacement of the maxilla also was seen in his sample.Other authors infer that the anterior movement of themaxilla is significant. 3,4 The dynamics of the skeletalmovement seen with the bonded appliance are sum-marized as follows:

1.

2.3.

A slight superior movement of the posterior as-pect of the palatal plane relative to the bandedapplianceA downward and posterior movement of the an-terior aspect of the maxilla (ANS)As the anterior maxilla moves posteriorly, in-ferior and posterior movement of the central in-cisors

The clinical significance of these characteristics ofthe bonded rapid palatal expansion i s important. Forexample, in the treatment of a patient with a long face,high mandibular plane angle, and open bite tendency,extrusion of the maxilla or maxillary dentition wouldworsen the open bite situation and create a more di fficultvertical pattern to treat. In addition Class II patientswho require rapid palatal expansion often can ill affordmore anterior movement of the maxil la. Limited an-

terior movement of the maxi lla with the bonded appli -ance would be an indication for use in Class II patients.

Further studies would be of benefit to compare allparameters of the bonded rapid palatal expansion ap-pliance. For the present the orthodontist should be cog-nizant of the possible options concerning treatment ofbilateral maxillary posterior deficiency.REFERENCES

4.

5.6.

I.

8.

9.10.

Wertz RA. Skeletal and dental changes accompanying rapid mid-palatal suture opening. AM J ORTHOD 1970;58:41-65.Timms DJ. Rapid maxillary expansion. Chicago: QuintessencePublishing, 1981:91-4.Haas AJ. Rapid expansion of the maxillary dental arch and nasalcavity by opening the midpalatal suture. Angle Orthod 1961;31:73-90.Haas AJ. Palatal expansion: just the beginning of dentofacialorthopedics. AM J ORTHOD 1970;57:219-55.Wertz RA. Midpalatal suture opening: a normative study. AM JORTHOD 1977;71:367-81.Davis WM , Kronman JH. Anatomical changes induced by split-t ing of the midpalatal suture. Angle Orthod 1969;39:126-32.Haas AJ. The treatment of maxillary defic iency by opening themidpalatal suture. Angle Orthod 1965;35:200-17.Spolyar JL. The design, fabrication, and use of a full coveragebonded rapid maxillary expansion appliance. AM J ORTHOD1984;86:136-45.Graber TM, Neumann B. Removable orthodontic appliances.Philadelphia: WB Saunders, 1977: 140.Ahlgren J. The neurophysiolog ical principles of the Andresenmethod of functional jaw orthopedics. a cr it ical analysis and newhypothesis. Svensk Tandlak Tidskr 1970;63:1-9.

Reprint requests to:Dr. David M. Sarver1705 Vestavia ParkwayBirmingham, AL 35216