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Applying new knowledge to the correction of the
transverse dimension
Chapter · January 2017
2 authors, including:
Ignacio Blasi
University of Pennsylvania
Some of the authors of this publication are also working on these related projects:
Transverse dimension - Orthopedic expansion View project
Porphyromonas gingivalis View project
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Robert L. Vanarsdall Jr. and Ignacio Blasi Jr.
Rapid palatal expansion (RPE) has been used primarily to treat dental crossbites
or for space gaining to prevent extractions with little or no attempt made to
coordinate or normalize the transverse skeletal pattern. Traditionally, maxillary
orthopedics has been performed using the dental units only as anchorage
(e.g., Hyrax or Haas appliances). Dental anchorage not only has created limited
skeletal orthopedic change, but also can cause significant adverse periodontal
outcomes and unstable side effects. There is a clear correlation between buccal
tooth movement and gingival recession and bone dehiscences. These adverse
periodontal responses with RPE indicate the importance of early treatment.
The beneficial periodontal effects of transverse skeletal correction have been a
primary focus of our research for the past 35 to 40 years. We have emphasized
the importance of correcting transverse skeletal discrepancy to: 1) prevent
periodontal problems; 2) achieve greater dental and skeletal stability; 3) improve
dentofacial esthetics by eliminating or improving buccal corridors; and 4) improve
airway resistance. When it may be critical to save the natural dentition, we do
not want to introduce adverse dental/skeletal changes for adolescent patients
and/or patients with advanced periodontal disease. New advances in skeletal
anchorage should permit orthopedic change without adverse dental changes
by applying force directly to the maxillary bone; an innovative technique to
maximize the skeletal maxillary changes in the transverse dimension is explained
in this chapter. Furthermore, diagnosis of the transverse dimension—the use of
cone-beam computed tomography (CBCT) for 3D evaluation of skeletal changes,
the benefits of the skeletal transverse changes of the whole maxillofacial complex
and its periodontal response, the changes in airway and non-surgical RPE with
bone-anchored appliances utilizing temporary anchorage devices (TADs)—is
described and discussed.
key words: expansion, transverse dimension, TAD RPE, orthopedics, hyrax
Correction of the Transverse Dimension
Diagnosis in orthodontics must be performed with respect to all
three planes of space. These include the sagittal, vertical and transverse
planes in both the dental and skeletal dimensions. While our specialty
always has been focused on profile views and a diagnosis on the sagittal
plane, the vertical and transverse dimensions also are of critical importance. When Broadbent (1931) introduced cephalometric radiography
at Case Western, the frontal postero-anterior cephalometric radiograph
was included; however, its use in orthodontics was limited to asymmetric
types of cases.
It is essential to examine and quantify the degree of discrepancy
of the radiographic films to determine the skeletal pattern in these three
planes. It has been shown that clinical inspection of transverse maxillary
deficiency is inadequate for diagnostic value (Crosby et al., 1992; Flickinger et al., 1995) and can mislead the clinician. Likewise, a panoramic
film is not sufficient for a complete orthodontic diagnosis. At present,
the new technology, digital dentistry (Blasi et al., 2016) and three-dimensional (3D) radiographs (e.g., cone-beam computed tomography [CBCT])
allow the orthodontist to evaluate the patient in 1:1 proportions and
in three dimensions. However, visualizing these beautiful images is not
enough and there is a need to quantify the skeletal and dental components for a proper diagnosis. For example, two different cases could have
the same amount of dental overjet when measured and quantitated using a lateral cephalogram; however, one case could be a Class I skeletal
pattern and the other a Class II skeletal pattern. The same might occur
for two different cases with different dental overjets and the same Class
II skeletal relationship (Fig. 1). Therefore, a skeletal diagnosis must be
performed regardless of any dental compensation, since measuring teeth
is not diagnostic for the skeletal component. The purpose of this chapter
is to emphasize the importance of a 3D diagnosis and the impact of the
transverse dimension in our treatment outcomes.
Traditionally, the transverse dimension has been addressed in cases of dental crossbites, tapered arches and skeletal asymmetries without
an appropriate skeletal diagnosis. It is critically important to diferentiate
Vanarsdall and Blasi
Figure 1. Two different cases with the same Class II skeletal relationship and
different dental overjet. A-B: Patient with excessive overjet and a 7º ANB Class
II skeletal discrepancy. C-D: A different patient with no dental overjet and a 7º
ANB Class II skeletal pattern. Note that dental compensation hides a skeletal
discrepancy on the sagittal plane.
and quantitate between the width of the maxilla and the width of the
mandible, and it is essential that both jaws be measured to make a
skeletal diagnosis (Vanarsdall, 1999). Measuring only the upper jaw has no
value. Undiagnosed transverse discrepancy leads to adverse periodontal
response, improper occlusal function, unstable dental correction and
less-than-optimal dentofacial esthetics (Vanarsdall et al., 2017).
The presence or absence of clinical posterior dental crossbite
does not indicate the absence of a transverse skeletal discrepancy or
Correction of the Transverse Dimension
skeletal crossbite. In many clinical scenarios, a skeletal discrepancy is accompanied by dental compensation and lack of a dental crossbite (Fig.
2A). The upper posterior dentition is inclined buccally and the lower posterior inclined lingually, dentally compensating for a narrow maxilla. The
lower teeth may be collapsed leaning inward, thus creating a crowded
lower arch. These compensations may create an exaggerated curve of
Wilson and consequently, posterior interferences on the non-working
side as the patient goes into lateral excursions, which can predispose the
patient to TMD symptoms, tooth wear and periodontal problems.
Two of the most significant factors in determining the proper
treatment (orthodontics, orthopedics or surgery) of the transverse dimension and its prognosis are the severity of the skeletal discrepancy and
the skeletal maturation of the patients. Established skeletal landmarks
must be compared to diagnose the severity of the skeletal width of both
the maxilla and mandible. The differential between the width of the maxilla and mandible is a critical evaluation for the individual patient. The
posterior-anterior (PA) cephalogram, or a perfectly extracted PA cephalogram from a CBCT image (Fig. 2B-C), not only will show the existence of
a discrepancy between the maxilla and mandible, but also will show the
severity of such a discrepancy.
Most treatment modalities (e.g., fixed and functional appliances) are used to correct the transverse plane, where treatment potentials are limited much more than in other planes. Orthodontics used to
achieve unstable dental camouflage of the underlying skeletal discrepancy in the transverse dimension have been shown to lead to unsatisfactory treatment outcomes (Vanarsdall and White, 1994; Vanarsdall
et al., 2017). Rapid palatal expansion (RPE) produces an orthopedic
(skeletal) correction of the transverse dimension when used properly
(at the correct skeletal age and with the proper appliance selection).
Orthopedic maxillary expansion is the result of skeletal (sutural openings), dental (tipping) and alveolar (bending and remodeling) alterations.
As a child (7 to 9 years) grows and matures skeletally, more force may
be required to achieve proper expansion. The more mature the child,
the less skeletal expansion is achieved and the more dental tipping occurs. Krebs (1964) reported such changes using metal markers during
orthopedic expansion in children and adolescents. He demonstrated
that children had 50% skeletal and 50% dental expansion, while the
Vanarsdall and Blasi
Figure 2. A: A patient with absence of dental crossbite and a narrow maxilla. Note the upper posterior teeth are inclined buccally, creating an exaggerated curve of Wilson; the lower posterior dentition is inclined lingually,
dentally compensating the narrow maxilla. B-C: Posterior-anterior view of a
3D-rendered image of a CBCT and a perfectly extracted PA cephalogram (C)
from the same CBCT to evaluate the skeletal transverse dimension.
adolescent group exhibited 35% skeletal and 65% dental expansion. A
tendency of dental tipping and alveolar bending to relapse was observed
after appliance removal.
Correction of the Transverse Dimension
Diagnosing the transverse plane must be based on skeletal, not
dental, components. A dental diagnosis cannot provide information for
skeletal correction. Moreover, separation of the midpalatal suture does
not mean that the skeletal discrepancy has been corrected. There is a
need to calculate the amount of skeletal discrepancy and to know what
the appliance will provide in correction of such discrepancy. This will guide
the practitioner in setting up realistic goals and objectives to correct the
transverse dimension without estimating, guessing or eyeballing. Therefore, treatment planning for the transverse skeletal problem requires a
comprehensive diagnosis differentiates between the skeletal and dental
components, a determination of the severity of the skeletal discrepancy
and maturity of the facial skeleton (skeletal age), an understanding of the
patient’s periodontal susceptibility and biotype, and selection of the appropriate appliance for the orthopedic/orthodontic correction.
Orthodontics is the most conservative and predictable treatment to improve
many of the local etiologic factors that contribute to periodontal susceptibility
and breakdown (Vanarsdall et al., 2017).
It is important intrinsically as a clinician to identify the periodontally susceptible patient (Vanarsdall et al., 2017). When examining
the patient clinically, evaluation of the gingival tissues—specifically biotype—is critical to be able to provide optimal treatment. A patient with
thin biotype (thin periodontal tissues) should be evaluated carefully. The
biotype of both the soft and hard tissue has a crucial role in the outcome
of the treatment (Lindhe et al., 2008). Orthodontic movement of teeth
should be made carefully within the alveolar housing. Even though gingival recession has a multi-factorial etiology (Helm and Petersen, 1989;
Offenbacher, 1996; Kornman and Van Dyke, 2008), a failure to make a
correct diagnosis could cause orthodontics to be a contributing etiologic
factor to periodontal breakdown and gingival recession (Vanarsdall et
al., 2017).
A study at the University of Pennsylvania (Saacks and Vanarsdall, 1994) showed that buccal gingival recession is correlated directly
with maxillary transverse deficiency as measured in a group of untreated patients with a transverse discrepancy of 5 mm or greater (than the
Vanarsdall and Blasi
normal 19.6 mm maxillomandibular differential). Moreover, Anzilotti
(2002) compared a group of patients treated with orthopedics (Haas RPE)
and an edgewise appliance, a group treated only with an edgewise appliance and a control group of untreated subjects from the Center for
Human Growth and Development at The University of Michigan. The orthopedic group was evaluated at time point 1 (T1)-11.3y and time point
2 follow-up records (T2)-20.7y; the edgewise-only group at T1-12.3y and
T2-19.3y; and the control group records at T2-17.2y. All three groups revealed gingival recession when the differential between the maxilla and
mandible was greater than 5 mm of transverse discrepancy. A negative
transverse differential > 5 mm from the Rocky Mountain analysis norm
may be a risk marker for gingival recession (Anzilotti, 2002). This data may
help identify patients at greater risk of gingival recession (Figs. 3 and 4).
Garib and associates (2006) evaluated the periodontal outcomes of RPE with a tooth-tissue-borne (Haas RPE) and a tooth-borne
(Hyrax) appliance. Utilizing CBCT images, they observed that both RPEs
decreased the buccal plate thickness of the maxillary posterior teeth and
induced bone dehiscences on the buccal aspect. Furthermore, the Hyrax
appliance created a greater decrease of the buccal alveolar crest level
than did the Haas RPE expander.
Several other studies evaluating the Hyrax appliances demonstrated a decrease in thickness of the buccal bone on the anchorage teeth
area and dental tipping (Rinderer, 1966; Oliveira et al., 2004; Garrett et
al., 2008), thus indicating major recession with potential damage to the
buccal cortical plate. It can be concluded that the Hyrax appliance is a
“tooth tipper” and may predispose the patient to greater gingival recession (Fig. 5). Dental expansion and alveolar bending predispose the patient to recession and dental instability if treated beyond the limits of
the transverse envelope of discrepancy. Even when the gingiva is normal in thickness, recession can be present if the transverse dimension
is violated by tooth movement alone. Therefore, it is critical to make a
proper diagnosis and a proper selection of the type of appliance needed.
Gingival recession also may occur in cases of excessive lingual inclination of the lower teeth, leaving alveolar support in the apical third only
and/or excessive buccal inclination of the upper teeth that can result in
alveolar support limited to the apical third of the teeth. When the tissue
becomes inflamed, it recedes and the soft tissue and the roots become
Correction of the Transverse Dimension
Figure 3. Case 1. Patient treated without proper diagnosis of the skeletal transverse dimension. A: PA cephalometric analysis indicating a severe skeletal discrepancy on the transverse plane: transverse deficiency of > 9.3 mm between
the upper and lower jaws with a narrow maxilla and a wide mandible. B: Initial
cast of the patient before treatment. C: Final cast after two years of orthodontic treatment. The patient was treated with two expanders and four premolar
extractions. D: One year after treatment cast. Note evidence of recession that
starts to appear and relapse of the dental correction. E: Two years post-orthodontic treatment. The case was treated beyond dental camouflage which resulted in further dental relapse and gingival recession.
Vanarsdall and Blasi
Figure 4. Case 2. Patient seeking orthodontic treatment for a second time. A: PA
cephalometric analysis exhibited a transverse skeletal deficiency of > 6.4 mm.
B-C: Intra-oral pictures. The patient was treated orthodontically with four premolar extractions. Note severe gingival recessions with normal thickness architecture of the soft tissues.
Figure 5. A: Hyrax expander with a metal framework anchored to the dentition
only. B: CBCT coronal cut at the level of the first maxillary molar on a mix dentition patient after expansion with a Hyrax. Note the clear buccal angulation (dental tipping) of the anchored teeth, even in a skeletally immature patient.
Correction of the Transverse Dimension
exposed. In cases of partial edentulism and implant rehabilitation treatment, the implant fixtures can be affected severely and even lost if there
is a significant transverse skeletal problem (Vanarsdall, 1999). Placing implants in a narrow maxilla could be a challenge. In many cases, there is a
need to augment the bone with guided bone regeneration (GBR) or sinus
lift augmentation. If not grafted, the lack of buccal bone could be a limitation and the implants may be at risk to be lost. Moreover, when implants
are placed in patients with a severe transverse skeletal discrepancy, even
if grafted, they have to be angulated excessively in order to meet the
occlusal requirements of correct dental buccal-lingual landmarks. When
angulated in such a manner, the occlusal forces may create additional
stress on the implant units. If the transverse dimension is not corrected
orthopedically/surgically, the implant units should be placed at the center of the alveolus and the posterior restorations in dental crossbite.
Currently, many adult patients are seeking orthodontic treatment
for the second or third time (Fig. 4). Many of them have been treated in
the past with extractions and present with normal tissue, but with gingival recession. Some cases will present with:
1. Only upper premolar extraction treatment decision
due to a narrow maxilla and consequently crowding
on the upper arch;
2. Lower premolar extraction treatment decision due
to a narrow maxilla and crowding on the lower arch
(crowding occasioned by lingually inclined teeth to
compensate dentally for a narrow upper jaw); or
3. A combination of both, upper and lower premolar extractions.
The majority of these cases lacks an orthopedic transverse skeletal correction and can result in partially exposed roots, with only soft tissue coverage around the remaining apical root and no buccal bone. Whether the
type of treatment is extraction or non-extraction, the patient is predisposed and more susceptible to gingival recession if there is a mismatch
on the transverse dimension.
We have reported that the transverse dimension may be the
most crucial risk marker for facial gingival recession (Vanarsdall et al.,
2017), yet there are other significant factors (e.g., gingival bleeding from
Vanarsdall and Blasi
probing, tooth mobility and thin, friable gingival tissue). These all are
critical reasons to make the skeletal correction in the transverse dimension based on skeletal landmarks and not on dental landmarks (e.g., the
lingual of the upper teeth contacting the buccal surfaces of the lower).
As stated earlier in this chapter, there are noticeable definitive
limits to dental expansion. If these boundaries are violated, there are
adverse consequences. Establishing the envelope of discrepancy and
delineating the limits of these boundaries is highly relevant and should
be made for each individual patient. Proffit and Ackerman (1982) first
introduced and developed the sagittal and vertical envelope of discrepancy concept. We later added the transverse envelope of discrepancy
(Vanarsdall and Musich, 2017). Figure 6 helps simplify and visualize the
limits of the three major treatment modalities for skeletal discrepancies.
The inner envelope illustrates the limits of camouflage with orthodontic
treatment alone; the middle envelope establishes the limits of orthodontic treatment combined with orthopedics and growth modification; and
the outer circle represents the limits of the correction with orthodontics
and orthognathic surgical procedures. The numbers on the diagram are
simple guidelines and may under-/overestimate the potentials for any
given patient; nevertheless, they help place the potential of the three
major treatment options in perspective.
It is important to note that the envelopes of discrepancy for the
transverse dimension are much smaller (Fig. 6); the premolar areas are
smaller considerably than those for incisors in the anterior-posterior (AP)
plane. When violating these limits, teeth are placed in a position where
they could be traumatized and possibly lost. Clinicians need to develop an
envelope of discrepancy concept for the transverse dimension, as well as
for the sagittal and vertical dimension for every case.
Orthopedic transverse correction, utilizing growth in children,
is the most desired approach to any skeletal discrepancy when growth
potential exists (DeGeorge, 2015). The envelope of discrepancy is increased greatly with orthopedics and may allow the clinician to provide
a non-extraction treatment if the transverse skeletal discrepancy is corrected. In adolescents and young adults, an orthopedic correction may
Correction of the Transverse Dimension
Figure 6. Envelopes of discrepancy for the transverse dimension of the maxilla
(A) and mandible (B). The inner circle establishes the limits of orthodontic treatment alone; the middle circle exhibits the limits of orthodontic treatment combined with growth modification; and the outer circle illustrates the limits with
orthodontics and surgical procedures.
be possible utilizing bone-anchored RPEs. In adults, when the sutures already are closed, the clinician may choose to correct the skeletal pattern
using surgically-assisted palatal expansion (SARPE) or to leave the patient
in a dental crossbite distal to the premolars (Betts et al., 1995).
Camouflaging the transverse skeletal deficiency by moving only
the teeth may cause periodontal problems and instability of the occlusal
scheme. Consideration of camouflage requires careful examination of the
patient’s ultimate periodontal status, occlusal function and stability, and
facial esthetics. If the clinical and radiographic analysis indicates less significant transverse maxillary deficiency in the mature patient, however,
sufficient buccal maxillary bone may remain to allow dental tipping and
camouflage of the transverse skeletal dimension.
Additionally, this envelope of discrepancy may be expanded
with periodontally-accelerated osteogenic orthodontics (PAOO), alveolar decortication and augmentation bone grafting. In selected cases, the
procedure will help expand the boundaries of dental movement with
reduced loss of attachment. This novel approach changes only the alveolar bone and not the basal structures. It also does not substitute for
Vanarsdall and Blasi
orthopedic expansion; however, it may be indicated for mild transverse
discrepancies with dental camouflage for changes of arch form
(Vanarsdall et al., 2017; Blasi and Pavlin, 2017).
It is important to initiate early treatment, since the transverse
growth of the maxilla is completed sooner than in most of the other
maxillofacial structures and its growth slows first (Korn and Baumrind,
1990; Edwards et al., 2007). This growth is differential, with the mandible outgrowing the maxilla. The Burlington template for the transverse
demonstrates that from ages 4 to 20, the normal maxillary (Mx) growth is
down, following a continuous pattern with minimal increase in width and
the normal mandible (Ag) growth is down and out transversally (Popovich and Thompson, 1977). For example, a case that is two standard deviations (SD) narrow in the maxilla and 5 mm wide in the mandible is a
difficult combination and worsens because of the differential transverse
growth. In this case, the objective would be to make a wide maxilla to
match a wide mandible (wide-wide).
Males usually are approximately 1.5 to 2 years younger skeletally
than their calendar age; females are usually older skeletally than their
calendar age. After sutural closure or significant slowing in maxillary
transverse growth (15 years for females and 16 years of age for males),
skeletal expansion mostly has been ineffective. At this age, the expansion is primarily alveolar or dental tipping with little or no basal skeletal
change (Vanarsdall, 1999), unless a bone-anchored RPE is used.
DeGeorge (2015) reported that with lip bumper (LB) therapy, the
growth of the transverse dimension of the mandible can be changed and
increased significantly if the LB is used between 20 and 25 months. We
evaluated the changes at the level of the mucogingival junction (MGJ),
of 26 consecutive patients with pre-treatment age of 9.2 +/- 0.8 and
the post-treatment of 12.3 +/- 0.8, treated with a bonded RPE (occlusal and palatal coverage) and LB. The control group consisted of 15 untreated individuals. A significant increase in the left to right MGJ distance
(P < 0.001) was found. The mean change at the level of the first molar
was 4.9 mm, second premolar 4.1 mm, first premolar 4.9 mm and canine 3.1 mm. The control group had little to no change. Therefore, the
Correction of the Tranverse Dimension
younger the patient is and the longer the LB is used, the better the response to treatment.
Vanarsdall and associates (2004) reported a skeletal result of
the LB on the basal bone as well. The transverse dimension of the basal
structure of the mandible measured at the antegonial notch (Ag-Ag) increased relative to double the control. The jaws are more responsive
to modification at an early phase of growth and development than at
future stages. Proper management of growth and development and control of habits (tongue thrust, low tongue posture) that will worsen as the
patient grows are important to avoid secondary effects (e.g., developing
an adenoid face). Furthermore, it is possible to redirect the growth in
the transverse dimension and create a better occlusal and periodontal
environment (Fig. 7).
Beginning early treatment with orthopedic appliances (e.g., RPE
and LB) permits the clinician to take advantage of muscles, eruption
and growth, coordinate the skeletal pattern and develop a broader arch
form. Early skeletal correction of the transverse dimension is valuable
for managing growth and development, long-term periodontal health,
proper occlusal function and stability (Secchi and Wadenya, 2009; De
George, 2015).
Changes of the basal form cannot be accomplished with wires
or brackets (Lundstrom, 1925). Orthodontics alone will move teeth only
within the basal structure of the jaws. If a skeletal discrepancy needs
to be corrected, orthopedics and/or surgery may be the treatment of
choice. Orthopedic maxillary expansion is accomplished by placing transversally directed forces in the orthopedic range on the maxilla to accomplish transverse maxillary expansion. There is increased facial resistance
to skeletal expansion with increasing maturity and age. The higher site
of resistance is not the midpalatal suture, but the remaining maxillary
articulations (Zimring and Isaacson, 1965) increased rigidity of the facial bones (e.g., the zygomatic buttress) and other circummaxillary sutures. As the sutures mature, the majority of rapid orthopedic palatal
expansion occurs via dental tipping and alveolar bone bending, rather
than skeletal movement. RPE may affect structures directly or indirectly
Vanarsdall and Blasi
Figure 7. Early treatment case. The patient was treated with phase I for 20 months
with bonded tooth-tissue-borne expander (occlusal and palatal coverage) and lip
bumper (LB). A: Initial coronal CBCT cut shows buccal inclination of upper molars. B: After early phase I treatment. CBCT coronal cut reveals properly inclined
molars creating a better periodontal environment. The teeth are centered on the
alveolar process, where occlusal forces of mastication are received over the long
axis of the dentition.
related to the maxilla, mandible, nasal cavity, pharyngeal structures, zygomatic bone and the pterygoid process of the sphenoid bone (Brodie,
1950). The maxilla is associated with ten bones in the face and head. For
this reason, when purely skeletal expansion occurs, these anatomical
structures are affected (Fig. 8).
The expansion achieved with RPE is in a vertical, triangular
shape. The structures at the level of the expansion jackscrew are affected
Figure 8. A 16-year-old female patient treated with a bone-borne expander. A:
Superimposition of rendered CBCTs before and after expansion on the cranial
base. Note the midfacial skeletal expansion of bony structures surrounding the
maxilla. B-C: Comparison of nasal cavity 3D volume increased from before (84.0
cc) to after expansion (99.4 cc).
Correction of the Transverse Dimension
most and as it progresses vertically, the expansion diminishes. Due to the
correlation of anatomical structures with the maxillary bone, a midface
skeletal expansion occurs as well (Fig. 8A). The zymogatic bone and the
nasal width are expanded among others. The nasal cavity increases in
volume as nasal width is expanded, which reduces nasal resistance and
improves nasal respiration (Fig. 8B). There have been multiple reports on
airways and RPE demonstrating that RPE improves the posterior airway
spaces and other skeletal characteristics (Wriedt et al., 2001; Kiliç and
Oktay, 2008; Haralambidis et al., 2009; Villa et al., 2011).
With bone-anchored RPE, skeletal expansion can be achieved in
mature patients. However, the benefits of changing the skeletal characteristics associated with maxillary expansion while growing and skeletally
developing at an early age patient are irreplaceable.
The midpalatal suture opening by orthopedic expansion was described first by Angell (1860) and the concept was reintroduced by Haas
(1961, 1965). Orthopedic expansion was successful mainly in children prior to suture closure. The most effective skeletal expansion was achieved
with a Haas-type bonded appliance (Christie et al., 2010). The Haas-type
RPE is a tooth-tissue-borne expander that has acrylic palatal flanges integrated into the appliance and has been shown to result favorably in skeletal expansion with less dental tipping. The Hyrax RPE is a tooth-borne
appliance similar in design, but without acrylic palatal coverage and with
only the expansion screw and a metal framework. It has been shown to
result in more dental tipping and less skeletal expansion (Fig. 5). The occlusal-coverage Haas-type bonded appliance (bonded tooth-tissue-borne
RPE) is essentially a hybrid of the Haas appliance and a flat-plane occlusal
coverage splint. It is bonded to the maxillary teeth and its use is recommended in growing patients for a significant skeletal correction. Additionally, rapid—as opposed to slow—maxillary expansion is used to maximize
skeletal expansion over dental expansion (Hicks, 1978).
Oliveira and colleagues (2004) evaluated the morphologic
changes of the maxilla, comparing two different types of RPE designs.
They evaluated data from a previous prospective, randomized clinical
study using PA cephalometric and cast analysis, and compared the Haas
Vanarsdall and Blasi
appliance to the Hyrax RPE. Both appliances showed maxillary expansion.
However, the Haas appliance had a higher component of true orthopedic
movement and the Hyrax appliance had expansion by means of dentoalveolar tipping.
As a result of the dental tipping side effect and the popular use of
temporary anchorage devices (TADs), more than a decade ago we started
evaluating the skeletal anchorage supported appliances in surgically assisted rapid palatal expansion (SARPE) cases that had no posterior dentition and/or periodontally compromised teeth (Fig. 9A). An evident lack of
dental tipping was noted in the upper posterior teeth, as the maxilla was
changed with a skeletal anchorage type of expander; bone-borne RPE
design was modified to avoid including the dentition into the appliance
and its use was expanded to the mature patient. It includes four TADs
inserted on the palatal slopes of the maxilla with acrylic palatal coverage,
similar to a Haas-type design (Fig. 9B); two TADs per side give a better
distribution of forces. This design has been shown to be the choice for efficient treatment of maxillary transverse deficiency (Lee et al., 2014). We
reported the difference between a bone-borne and bonded tooth-tissueborne RPEs used in twin patients with the same skeletal severity, age and
gender (Vanarsdall et al., 2012). There was a significant increase in width
of the basal bone as a result of the palatal expanders as measured on
CBCT imaging. Both appliances demonstrated significant skeletal change;
however, the bone-borne RPE achieved significantly more skeletal basal
change without dental compensation that did the bonded tooth-tissueborne appliance (Vanarsdall et al., 2012). Moreover, the bone-borne RPE
twin completed orthodontic treatment six months earlier than did the
bonded tooth-tissue-borne RPE twin, even with teeth in a better position.
Lagravère and associates (2010) reported that bone-anchored
maxillary expanders and traditional rapid maxillary expanders (Hyrax)
present similar results, though the Hyrax appliance resulted in greater
first premolar expansion than the bone-anchored appliance. Both treatment modalities showed an increase in crown inclinations and that
dental expansion was greater than skeletal expansion. Yet, this study
evaluated only dental objectives and focused on dental correction of
posterior crossbites. There were no skeletal objectives nor evaluation of
the skeletal transverse dimension changes at the basal bone level. Furthermore, the design of the bone-borne RPE included only two TADs
Correction of the Transverse Dimension
Figure 9. A: One of the first bone-borne expanders used on a periodontally compromised patient with missing teeth on the upper right segment. Two TADs were
used to support the appliance on the right side (arrows). Note the red patch of
atherton mesial to the right center incisor as the expansion increased. B-C: Boneborne expander modified to avoid including the dental units on the design. Note
opening of the suture in a parallel fashion from anterior to posterior. D-E: Hybrid
expander anchored on TADs and first molars. The occlusal radiograph shows a
triangular shape opening of the suture. From Garib et al., 2008. Reprinted with
permission of the Journal of Clinical Orthodontics.
when four TADs usually are recommended for a better anchorage and
appliance design (Lee et al., 2014).
We have reported and compared the treatment response of patients with similar transverse skeletal severity, gender and age with the
most effective orthopedic tooth-tissue-borne expander versus boneanchored maxillary expander on changes of the basal bone and molar
teeth of consecutively treated patients (Vanarsdall et al., 2017). Two
groups were evaluated after expansion and compared with CBCT data: a
group of eleven patients (11.3 to 17 years) treated by one clinician only
with bone-anchored expander (TAD type); and a group of 24 patients
(7.8 to 12.8 years; Christie et al., 2010) treated with a bonded toothtissue-born expander (bonded type). T-test statistical analysis demonstrated a statistically significant difference (p < 0.05) between the mean
of maxillary basal bone change at the first molars of both groups. The
percentage of the mean screw expansion associated with the width of
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the palatal expansion at the first molar was calculated as follows: 40.65%
on the bonded RPE group and 65.04% on the TAD RPE. The large difference in the efficiency of the expansion was due to the direct effects of the
expansion upon the palate itself and not the surrounding molars of the
maxillary arch where the bonded tooth-tissue-borne RPE device generally retains. This analysis also is supported strongly by the large inter-molar
tipping angle effect of the bonded RPE compared with the TAD group
before and after expansion. The bonded RPE group resulted in a mean
of 11.7 SD +/- 3.05° difference versus the near absence of any mean effect 0.2 SD +/- 3.47° difference in the case of the TAD treatment group. A
T-test exhibited a highly significant difference (p < 0.00001) between the
two groups. Furthermore, both groups exhibited midline suture opening
in a parallel fashion (Fig. 9C). This was different from the earlier type of
expanders, which have been reported to cause openings of the midpalatal suture in a triangular shape with extended opening on the anterior
maxilla area (Garib et al., 2008; Woller et al., 2014; Figs. 9D-E and 10AB). Expansion efficacy was exhibited in both significant skeletal changes.
However, the bone-anchored devices obtained 25% more skeletal basal change (Mx-Mx) without dental compensation than did the bonded
tooth-tissue-borne RPE. Greater maxillary orthopedic expansion was
seen with the bone-anchored versus the bonded tooth-tissue-borne expander and a highly statistically significant difference in molar tipping angulation. With the Hass appliance, therefore, 20% of basal bone change
from the jack screw activation can be achieved, 41% with the bonded RPE
and 65% with the TAD RPE (Fig. 10C-E; Vanarsdall et al., 2017). It is important to know what an appliance will provide for the skeletal correction.
Lin and coworkers (2015) reported similar results. They evaluated and compared the effects of a Hyrax expander and a bone-borne
expander (similar to our design). The Hyrax group had more buccal tipping of the dentition and alveolar process with significant adverse buccal dehiscence in the first premolar area. They also concluded that the
bone-borne expanders produced greater orthopedic changes and fewer
dentoalveolar tipping compared to the Hyrax expander group.
Although there have been demonstrated benefits of skeletally anchored RPE, potential adverse effects may exist. These include reversible
microfractures at the level of the nasal bone or cracked nose that could
be seen clinically as a bump on the nose; damage to the surrounding
Correction of the Transverse Dimension
Figure 10. A-B: Hyrax appliance used on a mixed dentition case. The CBCT axial
cut reveals a triangular shape expansion more prominent on the anterior part
of the maxilla. From Woller et al., 2014. Reprinted with permission of Dental
Press Publishing. C-E: There is a need to select the proper rapid palatal expander
(RPE) that will provide the skeletal correction needed for the skeletal age of the
patient. C: Haas-type appliance provides 20% of basal change. D: Bonded toothtissue-borne expander, 41% of basal change. E: Bone-borne, 65% basal change
of the mean jackscrew opening at the level of the first permanent molars. From
Vanarsdall et al., 2017. Reprinted with permission of Elsevier.
tissues due to a failed TAD and/or pain if the RPE impinges on palatal
Skeletal anchorage should permit orthopedic change without
the adverse dental changes by applying force directly to the maxillary
bone. Its use is indicated for moderate to severe skeletal discrepancies,
skeletal mature individuals and patients with missing teeth and/or periodontal involved cases (Vanarsdall et al., 2017). Orthopedic expansion
can be accomplished in adolescents, even in young adults, with skeletally
anchored devices (Fig. 11). Future research is needed to determine the
skeletal age limitation of bone-borne RPEs; nevertheless, it is clear that
the envelope of treatment has evolved to include older patients (Fig. 12).
Figure 12. Treatment envelope of the transverse skeletal dimension. Although there is a need of future research to determine the skeletal age limits
of the bone-anchored expander, the envelope of treatment has been changed
to include adult patients without SARPE. From Vanarsdall et al., 2017. Reprinted
with permission of Elsevier.
Vanarsdall and Blasi
Figure 11. A 25-year-old female with history of orthodontic treatment. The patient was treated with upper premolar extractions only to relieve crowding due
to a narrow maxilla. A: Three TADs used per side to maximize the skeletal change
of the maxillary expansion. B: Rapid palatal expander bone-borne Haas type with
acrylic for better support and distribution of forces of expansion. C-D: 3D CBCT
confirms purely skeletal expansion with separation of the palatal suture in a parallel fashion in an adult patient.
Correction of the Transverse Dimension
In our view, RPE has less to do with gaining arch perimeter and
extraction/non-extraction treatment and more to do with the skeletal
correction of the transverse dimension.
It generally is accepted by orthodontists that mechanically
pushing or pulling the teeth to expand the dental arches is not a stable
correction. One of the biggest problems in orthodontics is arch form.
Clinicians want to keep that arch form because if it is modified, it can
relapse to the original configuration; however, it is important to realize
that if it is corrected orthopedically, it does not relapse.
Stability of RPE depends partially on the histological activity at
the site of the separated suture. Ten Cate and colleagues (1977) described
a single layer of active osteoblasts that continued to lay down new bone
at the bony margins of the suture. The uniting layers consisted of a large
fiber bundle running across the borders of the suture. The response to
expansion was osteogenesis and fibrillogenesis, followed by the sutural
connective tissue fibroblasts to remodel, which led to regeneration of the
suture (Revelo and Fishman, 1994).
With growth, the skeletal transverse correction with RPE and
LB do not reverse (Vanarsdall et al., 2004; DeGeorge, 2015). In a young
patient, when inducing tooth movement (orthopedics, LB) by muscles,
eruption and growth, the dentoaveolar widening that occurs provides
a broad arch form that is not determined mechanically by the brackets
and arch wires. Before any bracket system is used, the wider, natural or
broader arch form is established. Other treatment options that do not
influence the growth and change of the apical skeletal base (orthopedics/
surgery) are limited to maintain the original arch form of the malocclusion.
In these treated cases, satisfactory mandibular alignment may exist in
less than 30% of the cases long term (Little et al., 1981).
Relapse tendencies after RPE have been reported in the past, but
many of the studies are based on intermolar width dental measurements
(Mew, 1983). Much of the relapse may be due to expansion achieved
with means of dentoalveolar tipping, rather than palatal suture opening.
Therefore, it is important to maximize skeletal expansion and minimize
dental tipping for long-term stability of the correction.
Vanarsdall and Blasi
The benefits of correcting a transverse skeletal deficiency include:
1. Improved periodontal health;
2. Dental and skeletal stability of the correction;
3. Dentofacial esthetics—improving buccal corridors;
4. Improved airway resistance.
Its diagnosis must be based on skeletal and not dental components. The
earlier the patient is treated, the better the response to treatment. It is
important to assure skeletal expansion regarding the appliance selection.
With the new skeletally-anchored expanders, the envelope of treatment
definitely has changed to include mature patients and avoid certain surgical procedures (e.g., SARPE). Further research is needed to delineate the
limits of such expanders.
The authors would like to thank Dr. Normand S. Boucher for supporting the research with CBCT data.
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