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A cone beam CT evaluation of the maxillary dento skeletal complex after rapid palatal expansion

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A cone beam CT evaluation of the maxillary dento skeletal complex after rapid palatal expansion

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Content A CONE‐BEAM CT EVALUATION OF THE MAXILLARY
DENTO‐SKELETAL COMPLEX AFTER
RAPID PALATAL EXPANSION

by

Armine Kartalian

____________________________________________________________________

A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)

May 2008

Copyright 2008 Armine Kartalian

ii
DEDICATION
To my Family and Friends:
Takouhi Kartalian
Hrachya Kartalian
Tigran Kartalian
Alisa Konanyan
Rose Kistorian
Elizabeth Gohl

iii
ACKNOWLEDGEMENTS
A special thank you to:

Dr. Reyes Enciso

Dr. Elizabeth Gohl

Dr. Glenn Sameshima

Michelle Bailey

My Co-Residents

iv
TABLE OF CONTENTS

Dedication ii
Acknowledgements iii
List of Tables v
List of Figures vi
Abstract vii
Chapter 1: Introduction 1
Chapter 2: Review of Literature 2
Chapter 3: Hypotheses 26
Chapter 4: Subjects and Methods 27
Chapter 5: Results 46
Chapter 6: Discussion 59
Chapter 7: Assumptions 63
Chapter 8: Limitations 64
Chapter 9: Summary 65
Chapter 10: Conclusions 66
Bibliography 67

v
LIST OF TABLES
Table 1 - Age and gender descriptive statistics 46
Table 2 - Comparison of transverse dimension between
RPE and Controls at baseline 47
Table 3 - Comparison of angulations between RPE and Controls at baseline 48
Table 4 - Comparison of absolute transverse changes between RPE and 49
Control patients
Table 5 - Comparison of absolute angulation changes between RPE and 50
Control patients
Table 6 - Comparison of transverse percent changes between RPE and Controls 51
Table 7 - Comparison of angulation percent changes between RPE and Controls 52

Table 8 - Comparison of transverse dimension between RPE and Control 53
patients after treatment

Table 9 - Comparison of angular measurements between RPE and Control 54
patients after treatment

Table 10 - Reproducibility analysis of transverse measurements for RPE 55
and Control patients

Table 11 - Reproducibility analysis of angulation measurements for RPE 56
and Control patients

Table 12 - Absolute tip of the posterior dentition 58

Table 13 - Comparison of absolute tip between RPE and Control patients 58

vi
LIST OF FIGURES
Figure 1 - The three stages of sutural development 2
Figure 2 - Illustration of Angel's device 6
Figure 3 - Haas appliance 7
Figure 4 - Hyrax appliance 7
Figure 5 - Maxillary articulations 10
Figure 6 - Direction of movement of the pterygoid processes 11
and maxillary halves
Figure 7- Depiction of how alveolar ridges tip and bend 12
buccally and the teeth both move bodily and tip
Figure 8 - Pyramid-like configuration of sutural opening 13
Figure 9 - NF 29
Figure 10 - HP 30
Figure 11 - PA 31
Figure 12 - BAC 32
Figure 13 - DA.E 33
Figure 14 - DA.E’ 34
Figure 15 - DA.I 35
Figure 16 - DA.I’ 36
Figure 17 - LAC 37
Figure 18 - Alv 38
Figure 19 - Alv – Horizontal 39
Figure 20 - Alv – Vertical 40
Figure 21 - Dent – Horizontal 41
Figure 22 - Dent –Vertical 42
Figure 23 - Incl – Horizontal 43
Figure 24 - Incl – Vertical 44

vii
ABSTRACT

Introduction: Rapid Palatal Expanders (RPEs) have routinely been used to
correct transverse deficiencies in the maxilla but their effects on the dento-alveolus
are uncertain. Purpose: To compare the Cone-Beam Computerized Tomography
(CBCT) scan measurements between patients with RPE and controls to determine
transverse dimension increases and the amount of alveolar and dental tipping.
Methods: 25 patients who required RPE treatment and 25 gender-and-age matched
controls were orthodontically treated and received CBCT scans at the beginning and
progress of treatment. Transverse widths and several angulations were measured and
matched paired t-tests conducted. Results: RPE treatment produced a significant
increase in all measured transverse dimensions. Alveolar and absolute dental tipping
was significantly different between cases and controls (both with p< 0.001) while
relative dental tipping was not (p = 0.897).Conclusions: RPE treatment increases the
transverse dimensions of the maxilla, and causes significant amount of tip in the
alveolus and absolute tooth angulation.

1
Chapter 1: Introduction
Rapid Palatal Expanders (RPEs) have routinely been used to remedy
transverse deficiencies in the maxilla since their conception in the 1900s. The
effects of RPE on the dentoskeletal complex have been studied through the use of
dental casts and lateral and Postero-anterior cephalograms. While these studies
have provided insight into the mechanotherapy, a truly detailed and cohesive
depiction of the changes in the dento-alveolar complex is lacking. Recent advances
in Cone-Beam Computerized Tomography (CT) 3-D imaging enable the capture
and reproduction of a real maxillary section in all three planes and hence allow the
measurement of axial inclinations of the dentition, changes in the transverse
dimension and the magnitude of displacement of the maxillary halves free from
distortion, magnification and superimposition.
RPE treatment contributes to the increase in the maxillary arch by a
combination of orthodontic (tipping and translation) and orthopedic (bony separation
and remodeling at the suture) effects. Various degrees of dental tipping resulting
from RPE treatment have been noted by Wertz[1] and Hicks[2], but a thorough
examination of this topic remains largely unexplored.
The objective of this study is to compare the dimensional changes of skeletal
and dental structures in a group of growing patients treated for maxillary constriction
before and after RPE, with a matched control group, using CBCT 3-D imaging. The
study will quantify the increase in the transverse dimensions of the maxilla post
2
palatal expansion therapy at various levels of the maxilla. It will also attempt to
reveal the quantity and direction of alveolar and dental response to the therapy.

Chapter 2: Review of Literature
The Suture
Melsen’s[3] study recovered histological sections of palatal bone from the
autopsy of 27 females and 33 males varying in age from 0 to 21years. Examinations
of these slides shed light on the three distinct stages of transverse patterning of the
suture.
In the first stage, the infantile period, the suture presented as a broad, flat,
“Y” shape. The suture took on a more wavy morphology during the juvenile period
(about age 10years). During the adolescent period, the suture became more tortuous
with increasing digitations. The interdigitations became so heavy that separation of
the two halves of the maxilla was not possible without fracturing the segments.
Sharpey’s fibers were seen running across the suture uninterruptedly in the inactive
sutures of older people.
Figure 1-The three stages of sutural development

3
Until the ages of 14-15 years, the nasal surface of the hard palate showed
evidence of resorption and then consisted of resting lamellar bone. Conversely, until
the ages of 13-14 years, the oral surface of the palatal bone showed apposition. Up to
the ages of 16-18 years, the posterior border of the palate was seen to remodel,
indicating growth in length of the hard palate. In the adult period, the suture showed
varying degrees of synostoses and bony bridge formations[4].

Growth and Transverse Width Increase
The dental casts of 36 normal, untreated class I subjects between the ages of
7-26 years comprised the sample for Hesby’s[5] measurements of maxillary cross-
arch widths at the palatal mid-alveolar and palatal crest levels. The study revealed
that the mean cross-arch width change at the alveolar crest palatal (at the level of the
first molars) was less than 2.5mm between the ages of 7.6 and 16.5 years. The trans-
palatal width increase was only 0.67mm between the ages of 13 and 16.5 years (ages
at which most RPE treatment occurs). The greatest change was at the level of the
maxillary basilar width with a mean increase of 6mm. These age-related changes in
the maxillary basilar and alveolar arch width were correlated with maxillary molar
uprighting (buccal root torque) that occurs normally with molar eruption. The
authors suggested that these results followed the idea that lateral growth away from
the mid-saggital plane was greater at the first molar roots than at the alveolar crest.
Thus, as the suture widened, the erupting maxillary molars moved laterally, with the
mean transverse growth of the mid-palatal suture between the ages of four and
adulthood being 6.9mm[6]. The molars then encountered cheek pressure that forced
4
the crowns lingually and increased their torque. The normal uprighting process of
molars can be prevented by crossbites, which tend to lock them in position with
increased lingual root torque.

Cessation of Normal Growth
Pubertal growth spurt is variable not just between individuals but between the
genders as well. On average, females experience their growth spurt about two years
earlier than males. While the average peak height velocity (PHV) is at 11.5 years in
females, the average for males is at 13.5 years. Termination of growth in females is
marked by menarche[7]. Males experience their PHV further into their puberty and
continue to grow with great variation of termination. Usually growth is complete at
around 17 years of age[8].

Maxillary Transverse Deficiency
The manifestation of maxillary transverse deficiency is in skeletal and or
dental upper arch constriction with the presentation of a unilateral or a bilateral
posterior crossbite. Crossbites appear early in age, are not self-correcting and are
consistently distributed within the malocclusions. Genetic, functional [9][10] and
environmental factors contribute to the discrepancy. Some of the factors include
crowding, premature loss of or prolonged retention of deciduous teeth, thumb-
sucking habits and palatal clefts[11]. The most important factor determining the
transverse dimension of the maxilla, however, is growth at the mid-palatal suture as
reported by the implant studies of Bjork[6]. A trans-palatal width of 36-39mm
5
measured from the closest points of the maxillary first molars can typically
accommodate a dentition of average size without the presence of much
crowding[12]. An arch narrower than 36mm is often too narrow to couple with a
lower arch and will manifest clinically as a crossbite. The prevalence of posterior
crossbites has been reported to be 7% in white American children, 1-2% in African
American children[13], 23% in European children[14], 9.4% in Danish males and
14.1% in Danish females[15]. A recent study of Turkish children reported posterior
crossbite incidence of 9.5%[16].

Rational for Treatment
Clinical problems such as altered dento-facial esthetics, maxillary hypoplasia,
asymmetrical facial growth, positional and functional deviations of the mandible,
adverse periodontal responses, unstable tipping, and other functional problems can
arise from untreated transverse maxillary deficiencies[17]. These reasons lend
maxillary constriction to treatment with orthopedic expansion.

History of RPE
Treatment of crossbites by maxillary expansion has been in use for nearly
150 years[18] but has only enjoyed wide popularity since the 1960s[19, 20]. Several
modalities of expansion have been in existence such as expansion with auxiliary or
overlay wires, slow palatal expansion with a quad helix, semi-rapid expansion,
surgically assisted rapid palatal expansion, and finally rapid palatal expansion[21].
6
The first description of rapid palatal expansion appeared in the 1860s by
Emerson Angel[18] where a jackscrew with contra-rotating heads was used[22].
Figure 2 - Illustration of Angel's device

Interest in the treatment modality waned in the early 1900s[23] only to be
revitalized in the middle of the century based on beliefs of its advantageous effects
for orthodontic and respiratory purposes[24-28]. It was thought that widening of the
palate increased the nasal width, flattened the palatal vault and straightened the nasal
septum, thus allowing improved respiration.
RPE treatment became the most popular means by which to correct maxillary
arch constriction[19] when Haas described his rigid appliance. This expander had
acrylic pads which contacted the soft tissues of the palate and transmitted the
expansion forces across the mid-palatal suture and directly to the skeletal structures
causing limited tipping of the molars. Although the Haas appliance is still used by a
substantial number of orthodontists today, the large acrylic framework makes it
difficult to clean the appliances, causes gingival irritation and has prompted the
modification of the appliance.
7
Figure 3 - Haas appliance

A more hygienic appliance, the Hyrax appliance, was conceived by
Biederman in 1968. The design includes bands on the premolars and molars and
lacks gingival coverage in order to facilitate oral hygiene and prevent gingival
irritation[29].
Figure 4 - Hyrax appliance

Since both the Haas and the Hyrax appliances are widely used throughout
orthodontic practices, recent studies by Garib[30, 31]attempted to uncover their
limitations, advantages and differences in their mode of action by comparing them.
8
Both the tooth-borne and the tooth-tissue-borne devices produced similar orthopedic
effects. The Haas appliance produced a greater change in the axial inclination of
supporting teeth, especially the first premolars compared to the Hyrax appliance[30].
The Hyrax appliance produced a greater reduction of buccal alveolar bone crest at
the first premolars than did the Haas[31]. Overall, consensus as to which appliance
is better has not yet been reached.

Arch Perimeter Increases
Aside from their use in correcting maxillary transverse deficiencies, RPEs
have more recently been used for alleviating other problems. A study in the 80’s
revealed that dental crowding in the maxillary arches of Caucasian patients were
more often related to arch perimeter deficiencies rather than to the large size of the
teeth[32]. The crowding can be successfully relieved by RPE’s provision of
additional space. According to Brust et al.[33], this space can range from 3-4mm.
This is consistent with the previous findings by Adkins et al.[34] where the average
arch perimeter gain was 4.3mm or approximately 0.7 times the change in first
premolar width.
Other popular indications for RPE use have been the improvement of airway
function[24, 35, 36], the spontaneous correction of class IIs [12][37, 38] or other
antero-posterior discrepancies[1, 9, 24][19][39, 40], correction of asymmetries of
condylar position[41], and more recently the reduction of the dark spaces in the
buccal corridors[42]. Because they are beyond the scope of this thesis, however, they
will not be further discussed.
9
RPE Forces
Orthopedic separation of the maxillary segments can occur when the applied
transverse forces of the RPE are sufficient in magnitude to overcome the bioelastic
strength of the sutural elements[41]. The magnitude must be sufficient to displace the
skeletal components without displacing the teeth. Multiple turns of the activation
screw can deliver forces of 100N or more (up to 20 lbs) [43][44]. Generally, if the
skeleton does not immediately respond to activation, the force is stored in the
appliance in the form of potential energy. Such energy can accumulate to reach
forces as high as 34.8lbs[45]. This energy must be allowed to dissipate prior to
removal of the appliance in order to prevent relapse of the bony segments[44].

How the RPE Works on the Suture
A combination of orthopedic and orthodontic effects is responsible for
increases in trans-palatal width after RPE treatment. To achieve orthopedic
expansion of the maxilla, the right and left halves need to be separated at the mid-
palatal suture. In an attempt to separate the suture, orthodontic effects result with the
maxillary teeth tipping buccally. The RPE framework is therefore designed to be
rigid in order to prevent this crown tipping by holding the alveolar segments firmly.
While the achieved expansion is mostly orthopedic and therefore stable, the
component of tipping is not entirely excluded.
Since the maxillary bones are connected to the palatine bones, which in turn
are connected to the pterygoid processes of the sphenoid bone, the entire complex
acts as a single bone in response to RPE treatment. As the expansion forces are
10
applied to the maxillary bones, they disarticulate at the suture and apply a separation
force to the palatine bones. The palatine bones separate and propagate the force to
the pterygoid processes.

Figure 5 - Maxillary articulations[46]

Since the pterygoid processes are part of the sphenoid bone (cranial bone)
they are not actually paired and cannot separate. In fact, they tend to splay outward
in an upward and outward motion while dropping the medial portions downward[26,
46, 47]. This physiologic bending has been though to be accountable for the
flattening of the palatal vault[24, 48, 49]. Essentially, the configuration of sutural
opening is non-parallel with the maxillary components arcing laterally with a
fulcrum of rotation at the maxillo-frontal suture[1, 24].

11

Figure 6 - Direction of movement of the pterygoid processes
and maxillary halves

The transverse arrows show the movement of the maxillary halves away from the
suture, while the rotational arrows show the lateral bending of the pterygoid
processes[50].

12
Figure 7- Depiction of how alveolar ridges tip and bend
buccally and the teeth both move bodily and tip[51]

The triangular pattern of expansion has been noted extensively throughout
orthodontic literature. The orthopedic behavior of the maxilla is the attainment of a
large width at the level of the dento-alveolus with a diminishing pyramid-like
attenuation of width gain at the maxillary base and nasal cavity.
In 1964, Krebs[26] evaluated the effects of RPE by using implants in the
infrazygomatic ridge and the alveolar process lingual to the maxillary canines. His
findings indicated that the width gain at the level of the basal maxillary segment
(3.7mm) was half that which was seen at the level of the molars (7.5mm)[26].
Similarly, Hicks[2] used implants to evaluate the tip of the maxillary halves to one
another and found them to be in the range of 1-8 degrees, showing ones again the
rotational quality of expansion with the fulcrum positioned superiorly. Many recent
studies by Chung[52] and Garib[30] have evaluated and concluded similar
observations regarding the configuration of sutural opening.

13
Figure 8 - Pyramid-like configuration of sutural opening[1]

When viewed occlusally, we see yet another non-parallel pattern of opening.
Wertz’ 1968-70[1, 53] studies showed that in most cases, the midpalatal opening is
wider in the anterior segment of the palate than the posterior with a ratio of 3 to
2[53]. Kudlick’s[54] investigation of the effects of RPE on the skeletal structures
reinforced these observations and can be summarized with the following:
1. all craniofacial bones directly articulating with the maxilla, except the
sphenoid bone, displace;
2. displacement of the maxillary halves occurs asymmetrically;
3. the sphenoid bone acts as the main buttress against maxillary expansion.
14
Treatment Affected by Growth
Recalling Melsen’s descriptions of the various stages of sutural development
in the palate, it is easy to see that the amount of interdigitations found across the
sutures of younger patients is far less than those of adults. Therefore, the bioelastic
strength at the younger suture must be far easier to overcome than that of the adult
suture. Some previously reported results showed that expansion in non-growing
patients can achieve similar width gains as those seen in growing patients while
others refuted these findings and stated that the orthopedic effects of RPE are largely
influenced by treatment timing[55-57]. One must take into account that individual
variation can permit flexibility of the suture in some non-growing patients, and RPE
treatment in those patients can be an effective means to gain width; however, implant
studies conducted by Bjork[58, 59] indicated that the transverse growth pattern of the
maxilla closely followed the velocity of and completion time of the adolescent
growth spurt and skeletal maturation. According to Bishara[51], the optimal age for
expansion is before the ages of 13 to 15 years. Wertz and Dreskin reported that the
greatest and most stable orthopedic changes were achieved when RPE was done
prior to the age of 12 years[55]. Patients treated with RPE at an older age displayed
loss of their initial width increases.
In 2001, Baccetti et al.[56] delved into an investigation of RPE therapy and
treatment timing. Their aim was to compare the short-term and long term effects of
RPE in 2 groups, one before and one after the peak in skeletal maturation, assessed
by the cervical vertebral maturation (CVM) method. 10.5mm of activation of the
appliance produced 9mm of transverse increase in both groups, however, more
15
pronounced and more effective long-term transverse changes at the skeletal level
were seen in the early-treated group. The late-treated group had 0.9mm width
increase at the skeletal level, whereas the early-treated group had a 3mm gain.
Pioneer investigations of the effects of RPE in the mixed dentition by
McNamara et al.[33, 60, 61] showed that an average trans-palatal width increase of
5-6mm was attainable with 80% width retention 2.4 years post-treatment. Sari et
al.[62] compared the long-term effects of RPE in a group with mixed dentition
patients and a group with permanent dentition and found that there was a greater
tendency for relapse in the mixed dentition group. Furthermore, their results showed
that the expansion forces on the immature suture forced the 2 maxillary halves to
bend more than in the permanent dentition group. The authors advocated delaying
the therapy to early permanent dentition.
By using bone scintigraphy to look at metabolic activity in the craniofacial
region, Baydas[63] studied a sample of non-growing females between the ages of 16-
18 years who had RPE treatment. The study revealed that there was a substantial
amount of metabolic activity, meaning new bone formation, at the midpalatal suture
and some metabolic activity around the zygomatic, sphenoid, and nasal bones.
While RPE treatment can produce width gains at the level of the dento-
alveolus at any age, the gain is not attributed to any skeletal changes when the
treatment is done post the peak in pubertal growth. Expansion during the peak
propagates the forces to the fulcrum of separation located near the fronto-maxillary
suture[1]. The increase in calcifications at the midpalatal suture and the increase in
the rigidity of the skeleton with advancing age would limit the movement of the
16
pterygoid hamulus[46] and force the fulcrum more inferiorly towards the appliance,
hence producing more dental tipping. The amount of expansion is further limited
with increasing age when considering that the palatal suture closes from posterior to
anterior, thus restricting transverse gains in the posterior[20]. Conventional
orthodontic wisdom dictates that if a patient has ceased growing, then their suture
has fused and RPE treatment should be carried out with surgery (SARPE) in order to
preclude adverse effects such as instability of the denture, severe dental tipping and
the accompanying gingival recession[64].

Changes in the Palatal Vault
Due to the pyramid-like configuration of the expanding suture, the maxillary
halves move laterally as well as rotate or splay outwards while dropping the medial
aspects of the halves downward. This observation led to the belief that the lowering
of the alveolar processes led to the subsequent lowering of the palatal vault[24, 48,
49, 65, 66].
Pre and post treatment cast measurements by Davis and Kronman (1969)[67]
challenged these beliefs. The palatal vault tracings of models (sectioned through the
mesiobuccal cusps of the first molars) were recorded for twenty-six children. Their
study revealed that RPE treatment does not cause lowering of the palatal vault. In
fact, the vault remained relatively constant. Similar conclusions were made by
Linder-Aronson and Lindgren[68] after examining plaster casts and lateral
cephalometric x-rays of 16 females and 23 males. They further concluded that there
is no relationship between inter-molar width and palatal vault height[68, 69].
17
The height and volume of the palate are significant parameters when
considering their relevance to the tongue. According to Brodie[70, 71], patients with
maxillary constriction tend to carry their tongues in a lower position. An increase in
either the height or the volume of the palate provides the tongue with enough room
to stay in a more favorable position. An investigation into the palatal height and
volume changes due to RPE treatment by Gohl[72] revealed that when comparing 16
RPE treated patient to 16 control patients, the difference in volume change between
the two groups before and after treatment was 13.4%. The palatal vault height
change between the two groups before and after treatment was non-significant.
Therefore, while RPE effectively increases the volume of the palate, it does not have
an effect on the height of the palatal vault.

Previous Orthodontic Measurements
The body of orthodontic findings on the effects of RPEs prior to the advent of
computed tomography has previously been obtained by studies primarily through
either dental casts using soft tissue landmarks, or PA cephalograms. Since most
measurements used the molar crowns as landmarks, it should be noted that buccal
tipping was a large component of the reported widths.

18
1) Transverse width measurements on dental casts
a) Timms[46] found an average increase in inter-molar width of 6.5 –
9.5mm measured from the lingual cervical margins of the permanent first
molars in a sample of 32 patients (20 female, 12 male) with an age range of
8.2-24 years (average age 11-14 years).
b) Adkins et al.[34] reported an average increase in inter-molar width
of 6.5mm measure from the most lingual points at the gingival margins of the
first molars in a sample of 21 patients (14 female, 7 male) with an age range
of 11.6-17 years.
c) Chung et al.[52] found an average increase in inter-molar width of
7.92mm measured from the cusp tips of the first molars in a sample of 20
patients (14 female, 6 male) with a mean age of 11.7 years. 0.34mm of the
expansion was attributed to buccal crown tipping since the mean expansion
of the Haas appliance was 7.58mm.
d) McNamara[73] found an average increase in trans-molar width of
3.7mm measured from the junction of the lingual groove with the palatal
mucosa in a sample of 112 patients and controls.
e) Handleman[74] surveyed the pre-treatment and post-treatment (in
retention for at least 1 year) cast of 47 adult patients (28 female, 19 male)
with an age range of 29.9 ± 8 years and their controls. A 4.8mm molar trans-
arch width net gain was found in the RPE patients with all the measurements
taken at the lingual cervical margins.

19
2) Transverse width measurements on PA cephalograms
a)Baccetti et al.[56] reported an average increase in inter-molar width
of 3.5mm measured from the lateral aspect of the first molars in a sample of
42 patients (25 female, 7 male) at various ages, and their controls.
b) Cross et al.[20] found an average increase in inter-molar width of
5.5mm measured from the lateral aspect of the first molars in a sample of 20
patients (15 female, 5 male) with the average age of 13.4 years.
c) Garib et al.[30] used computed tomography and found an average
increase in inter-molar width of 4.3mm measured from the lingual alveolar
crests of the first molars in a sample of 4 patients (all female) with an average
age of 12.6 years.

Since these different studies had variations in the landmarks used for the
measurements, the variations in the width gains reported can be accounted for.
A meta-analysis of the orthodontic literature on the subject of immediate changes
cause by rapid maxillary expansion conducted by Lagravere et al.[21] using stringent
inclusion criteria applied to 337 articles, pooled measurement of 14 qualifying
studies and analyzed their findings. For the purpose of not being redundant, none of
the studies included in the meta-analysis have been discussed in the above
paragraphs. The findings showed average maxillary inter-molar width increases of
6.04mm off of PA cephalograms and 6.74mm off of dental casts. 4.44mm of inter-
molar mesioapex root width increase was also noted along with statistically
significant changes in the nasal cavity width of 2.14mm and inter-alveolar width of
20
2.73mm. The authors concluded that the majority of width gain was attributable to
dental rather than true skeletal expansion.

Buccal Tipping
Lagravere’s[21] meta-analysis reported a maxillary inter-molar angulation
increase of 3.1 degrees, though this increase was not statistically significant in the
model casts. One must consider however, that when there is a net inter-molar width
increase of 6.04mm but only 4.4mm of mesioapex root width increase, that RPE
therapy does provide expansion in part through dental tipping, albeit non-
significantly. Wertz and Dreskin[55] stated that “as buccal teeth are moved laterally,
they become inclined to the buccal as a result of the arcing of the bones themselves,
some alveolar bending, and tipping of teeth. It must be realized that without any
tipping, the buccal teeth would assume a more flared axial inclination from the
arcing in a buccal direction of the bone segments.” Uprighting of the molars after
expansion may account for some of the measured loss in width seen post-treatment.
Previous efforts to quantify the amount of dental tipping contributions to expansion
remain inconclusive. A review of the available measurements in the literature is
included.
a) Hicks[2] studied a sample of 5 patients (2 female, 3 male) with an age
range of 10-15 years. Bilateral maxillary implants were used to measure linear and
angular changes in the maxilla during slow maxillary expansion and PA
cephalograms taken each week to evaluate the response. The angular measurements
of the first molars were taken relative to each other using the cranial base for
21
reference. Though the results of the angular changes were not averaged, a range of
1degree change to a 24 degree change was observed. The author also observed that
when comparing the ratio of net angular change to linear change, the angular change
drastically dominated the first week or so of the activation, but then leveled off with
the linear change. This phenomenon was attributed to the initial compression of the
periodontal ligament. In the end, the transverse gains observed were due to bodily
translation of the teeth rather than tipping. Hicks also observed that the two
maxillary halves not only rotated laterally from the fulcrum, but also underwent
“bending” or elastic deformation in response to the forces.
b) Adkins et al.[34] sectioned the casts of a sample of 21 patients (14 female,
7 male) with an age range of 11.6-17 years. By tracing the pre and post treatment
angulations of the first molars with tangent lines to the cusp tips, they reported
seeing great variation in the amount of angulation change ranging from none in some
patients to as much as 15 degrees (on average 7.3 ± 5.8 degrees). Regression
analyses revealed no relationships between the amount of tipping and variables such
as patients’ age, initial palatal width, and the amount of expansion. The authors did
note, however, that there were greater degrees of tipping in patients who had bilateral
crossbites versus those who had unilateral crossbites. They theorized that in patients
with posterior crossbites, the palatal inclines of the palatal cusps occluded with the
buccal inclines of the lingual cusps of the mandibular teeth and the consequent
occlusal forces enhanced the tipping.

22
c) Garib et al.[30] studied a sample of 4 patients (all females) with an average
age of 12.6 years using computed tomography to evaluate pre and post expansion
inclination changes in the posterior teeth. A comparison between 2 patients treated
with a Hyrax-type RPE and 2 patients treated with a Haas-type RPE revealed
significant amount of tipping in all the posterior teeth in the Haas group and non-
significant tipping in the Hyrax group. When pooling the groups together, there
were significant inclination changes in the anchorage teeth (teeth that were banded)
averaging at 2.3 degrees of change at the first premolar and 2.5 degrees of change at
the first molar (degree changes are on one side only). An average inclination change
of 6.7 degrees was observed for the second premolar. Since this tooth was not
banded, the authors suggested that a greater amount of tipping was produced due to
the lack of rigidity to move the tooth bodily. In explanation for the differences
between the two groups, the authors suggested that the rigid framework of the
Hyrax-type RPE was able to produce more bodily translation and hence less tipping
than the Haas-type RPE.
d)McNamara et al.[73] studied the casts of 112 patients (61 female, 51 male)
with an average age of 12.2 years. 6 degrees of maxillary molar tipping was
observed when tracing the pre and post treatment angulations of the first molars with
tangent lines to the cusp tips.
e) Handleman[74] surveyed the pre-treatment and post-treatment (in retention
for at least 1 year) cast of 47 adult patients (28 female, 19 male) with an age range of
29.9 ± 8 years and their controls. After tracing the tangent lines to the cusps of the
first molars, 6.2 degrees of buccal tipping was observed.
23

Various other studies observing the effects of RPE make note of some extent
of buccal tipping of the molars, however, a conclusive understanding of the degree of
tipping to be expected can not be reached when the orthodontic literature is rife with
studies that show very broad ranges from 0 degrees of tipping[75] to 24 degrees[2].
This investigation will attempt to quantify the amount of tipping one can expect by
using the same protocol of measurement as the one used by Garib et al.

Relapse
Stabilization of the expanded suture serves to allow the tissues to reorganize
and for the residual forces to dissipate. Otherwise, these residual forces may cause
the tissues to rebound, thus causing the loss of the width gained through the RPE
treatment. The retention protocol is key in the amount of relapse experienced[2].
Immediate removal of the device without retention could result in as much as 45 %
lose of the initial expansion. A 3 – 6 month retention period is recommended after
RPE treatment to allow for bony infill at the separated suture[76][51].

Cone-Beam Computed Tomography
Since the introduction of computerized axial transverse scanning by Sir
Godfrey Hounsfield over 30 years age, the medical and dental community has
experienced a revolution in imaging. The reconstruction of 3 dimensional images by
using computers to analyze analog signals enabled the visualization of structures in
their true form without the hindrance of superimpositions. Furthermore, it enabled
24
clinicians to extract images in any plane of space by reformatting the scan[77]. In the
recent years, computed tomography has been evolving rapidly offering clinicians
faster scanning speeds and improved quality of images.
Cone‐beam CTs have been enjoying great popularity in the dental realm
due to their cost, access, ability to visualize pathology in multiple
dimensions[78], and decreased overall effective absorbed dose of radiation (E)
for the same diagnostic yield of information. The NewTom® 9000 and
NewTom® 3G CBCT have specifically been designed for imaging of the
maxillofacial complex. Its scanning times are between 36‐66 seconds, slightly
longer than traditional radiographs. Within that time, the machine acquires 360
pictures (1 picture per degree of rotation) which will be used to reconstruct a 3‐
dimensional volume. The overall absorbed dose from this scan (57uSv) is
roughly equivalent to a full mouth periapical series of x‐rays (33‐84uSv)[79].
This technology is quickly replacing traditional two‐dimensional
radiography in orthodontics. Several recent studies have looked into the
accuracy of measurements derived from NewTom® 9000 CBCT scans and have
concluded that with regard to linear measurements in the maxillo‐dental
complex, the values are accurate though slightly underestimated[80]. It should
be noted that measurements obtained from NewTom® scans are limited by the
resolution. For this study, 9 and 12 inch sensors were used which yielded voxel
sizes of 0.25mm and 0.36mm, respectively.

25

Significance:
The age range of the patient population enlisted in this study allows the
assumptions that the patients are still growing and that their palatal sutures have not
fully calcified[51]. Rapid palatal expansion increases maxillary arch width with a
combination of both orthodontic (tipping and bodily translation) and orthopedic
(bony separation and remodeling at the suture) effects. The effects of arch wire
treatment alone are orthodontic only. Therefore, we can evaluate the RPE effects of
orthopedic change as well as orthodontic change in the experimental patients and
evaluate whether these changes increase the transverse dimensions and alveolar and
dental inclinations over that which would be normally seen with regular orthodontic
treatment.

26

Chapter 3: Hypotheses
• RPE therapy significantly increases the transverse dimensions of the
maxillary base and the dentition
• RPE therapy produces a significant amount of tipping of the alveolus
• There is a significant difference in the amount of absolute dental tip produced
by RPE therapy

Null-hypotheses
• RPE therapy does not significantly increase the transverse dimensions of the
maxillary base and the dentition
• RPE therapy does not produce a significant amount of tipping of the alveolus
• There is no significant difference in the amount of absolute dental tip
produced by RPE therapy

27
Chapter 4: Subjects and Methods
Clinical treatment was rendered at the Advanced Orthodontic Clinic at the
University of Southern California. Twenty five healthy patients (18 female, mean
age12.6 years, range 8.8-15 years; 7 male, mean age 13.2, range 9.1- 15.8) who
required RPE due to a unilateral or bilateral crossbite and orthodontic treatment and
had cone-beam CT imaging, were selected for the study. Twenty five controls were
selected for similar age and gender (18 female, mean age 12.7 years, range 8.6-14.7
years; 7 male, mean age 13.2, range 9.2 – 15.7 years), had orthodontic treatment only
(no RPE), and also had a cone-beam CT scan.
All scans were retrieved from the archives of the department’s NewTom®
(DVT9000) Volume Scanner QRsr1 Verona CBCT unit. Clinical judgment and the
patients’ age were key factors in determining that all patients were still growing and
that the treatment preceded the fusion of their midpalatal sutures. All the patients
were in the late transitional or early permanent dentition stage. Patients did not have
any craniofacial abnormalities, surgical treatment or extraction treatment.
Patients treated with the RPE had a Hyrax palatal expander banded on the
maxillary first premolars and first molars. Patients were monitored weekly for
appropriate activation of the appliance. Expanders were turned 1-2 times per day
until the required expansion, i.e. slight overcorrection of the crossbite was achieved
(average time 4-6 weeks) after which they were stabilized. The RPE (or a TPA) was
used for retention for at least 3 months post-expansion. Most patients with RPE did
not have any orthodontic treatment until after the fixed retention period, but several
28
did have some appliances placed (such as a 2x4) during the fixed retention period.
Control patients started orthodontic treatment at approximately the same time as the
experimental group started expansion therapy. NewTom® scans on all patients were
taken as part of beginning and progress records at the midpoint in treatment which
ranged from 8 months to 2 years (average 15 months). The patients were asked to
put their head in Frankfort horizontal for the NewTom® scan; however, there were
variations in their head position between scans (difference in angulation).
Scans were imported and cross-sectional slices were made in the InVivo™
dental software (Anatomage, San Jose, CA). The slices were coronal bisections
through the buccal grooves and the palatal roots of the maxillary first molars. The
following measurements were recorded for each scan:
Transverse measurements: NF, HP, PA, BAC, DA.E, DA.E’, DA.I, DA.I’, LAC
Angular measurements: Alv, Alv – Horizontal, Alv – Vertical,
Dent – Horizontal, Dent – Vertical, Incl – Horizontal, Incl – Vertical
Identification of the dentoskeletal landmarks and subsequent measurements
were manually performed by a single investigator for both groups. Twenty patients
(10 RPE treated, 10 controls) were randomly selected and their images re-sliced and
re-measured by the same examiner after a 60-day interval. All data was stored on
the Resident Computer 1 located in the Redmond Imaging Center at the USC School
of Dentistry.

29
External Maxillary Width Measurements

Figure 9 - NF - transverse width of the nasal floor tangent to the most superior levels of the
right and left sides to the outermost limit of the alveolar cortices.

30

Figure10 - HP- transverse width of the hard palate between the right and left alveolar cortices

31

Figure 11 - PA - transverse width of maxilla between the palatal apices of the maxillary
molars

32

Figure 12 - BAC - transverse maxillary width at the level of the buccal alveolar crests

33
Figure 13 - DA.E - maxillary widths at the level of the buccal cusp tips of the maxillary first
molars

34
Figure 14 - DA.E' - maxillary width at the level of the most prominent area of the buccal aspects
of the maxillary first molars

35
Internal Maxillary Widths

Figure 15 - DA.I - transverse width of the maxilla at the level of the palatal cusp tips of the
maxillary first molars

36
Figure 16 - DA.I' - transverse width of maxilla between the most prominent areas of the lingual
aspects of the maxillary first molars

37

Figure 17 – LAC - transverse width of the maxilla between the lingual alveolar crests

38
Angular Measurements

Figure 18 - Alv - angle the alveolar bone makes to the soft tissue of the palate

39

Figure 19 - Alv – Horizontal - angle between the alveolar bone and a horizontal reference line
parallel to the palatal plane

40

Figure 20 - Alv – Vertical - angle between the alveolar bone and a vertical reference line parallel
to the patient's skeletal midline

41

Figure 21 - Dent – Horizontal - angle between the most lingual aspect of the palatal root and a
horizontal reference line parallel to the hard palate

42

Figure 22 - Dent – Vertical - angle between the most lingual aspect of the palatal root and a
vertical reference line parallel to the patient's skeletal midline

43

Figure 23 – Incl – Horizontal – angle between the long axis of the palatal root to a horizontal
reference line parallel to the patient’s hard palate

44

Figure 24 - Incl – Vertical - angle between the long axis of the palatal root to a vertical reference
line parallel to the patient's skeletal midline

45
Statistical Analyses
Descriptive statistics (means and standard deviations) were obtained for each
measurement for before and after treatment. To assess differences among the
matched pairs between means of continuous variables, we used the paired t-test with
significance level set at 5%, and Wilcoxon Rank Signed Test for non-parametric
paired samples. Histograms and Kolmorogov‐Smirnov tests were used to check
for normality of the variables.
To test the reliability of the measurements, 20 patients were randomly
selected and their images re-measured by the same examiner after a 60-day interval.
Statistical analysis of the difference between the duplicate measurements was
conducted by deriving the absolute and percent difference (Table10). Aung[81]
reported that a mean difference less than 1.0 mm was considered a highly reliable
measurement and less than 1.5 mm was considered a reliable measurement; however
orthodontic literature has considered errors of less than 0.5mm to be the standard of
reliability. No measurement in this study showed an error greater than 0.5mm or
1.5%, therefore, it can be assumed that the data obtained are highly reliable. As it
relates to angular measurements, Hicks[2] reported error measurements of 2 degrees
to be reliable. All of the measurements here showed an error less than 1.4 degrees
(Table 11). Theoretically, however, a 2 degree difference can be quite
substantial depending on the acuteness of the angle being measured. Instead of
relying on the 2 degree standard, a percent difference has been used as the
guideline to test reliability. As expected, the measurements displaying great
variability were very acute angles.
46
Chapter 5: Results
Table 1-Age and gender descriptive statistics for RPE and control groups
Experimental group (RPE) Control group
Age (yrs) 12.8 ± 1.84 12.8 ± 1.83
Gender 18M : 7F 18M : 7F

Baseline Characteristics
Transverse measurements -A comparison of anatomic form at baseline
(Table 2) revealed that the RPE group significantly differed (p< = 0.05) from the
control group in almost all of the parameters. All but three of the transverse lengths
were significantly greater for the control group before treatment, as would be
expected. While the lengths of the nasal floor (NF) and the trans-palatal lengths of
the palatal cusps were not significantly different, they were substantially smaller in
the RPE group.
At the level of the hard palate, a little over 3.75mm of width difference was
observed between the two groups, indicating the extent of transverse deficiency in
the RPE group before treatment. As we moved away from the palate towards the
dentition, the width differences ranged in the 2 – 2.5mm. Though these widths were
still statistically significantly different, the magnitude of the deficiency in the RPE
group diminished from the palate down to the dentition.

47
Table 2 - Comparison of transverse dimension between RPE and Controls at baseline
Before
treatment

Parameter
In mm
Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED
T-TEST
P-value
NF 64.85 ± 9.11 68.53 ± 5.08 0.118
HP 60.98 ± 6.96 64.82 ± 3.91 0.0295
PA 30.06 ± 3.63 32.80 ± 4.72 0.0211
BAC 57.21 ± 4.24 59.80 ± 3.76 0.0041
DA.E 51.13 ± 4.28 53.49 ± 3.43 0.013
DA.E’ 54.87 ± 4.14 57.46 ± 3.40 0.0064
DA.I 38.65 ± 4.03 40.28 ± 3.55 0.0868
DA.I’ 31.63 ± 3.67 33.26 ± 3.25 0.067
LAC 28.70 ± 3.29 32.49 ± 2.95 <0.001

48
Angulation measurements - No significant differences between the two
groups in degrees of dental angulation from horizontal or vertical references were
seen at baseline (Table 3). Significant differences were seen between the groups in
the angulations between the alveolar bone and the horizontal and vertical reference
lines (P < 0.0002, P < 0.0005, respectively). The angles measured between the
alveolus to either horizontal or vertical references were about 8.5degrees more acute
in the RPE group than those measured in the control group.

Table 3 - Comparison of angulations between RPE and Control patients at baseline
Before
treatment

Parameter
In degrees
Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED
T-TEST
P-value
Alv 118.0 ± 7.00 120.7± 9.15 0.276
Alv – Horizontal 108.13 ± 5.93 116.78 ± 6.54 0.0002
Alv – Vertical 18.48 ± 5.69 26.82 ± 6.04 0.0005*
Dent – Horizontal 103.43 ± 6.26 101.55 ± 7.18 0.379
Dent – Vertical 14.59 ± 5.04 11.96 ±7.11 0.349*
Inclination –
Horizontal
107.78 ± 6.11 105.69 ± 7.47 0.298
Inclination –
Vertical
18.12 ± 4.87 15.77 ± 7.32 0.538*

49
After Treatment Characteristics
Absolute Transverse Changes - The control group showed a non-significant
absolute change of less than 0.4mm in all parameters except for NF (0.85mm, non-
significant). The RPE group showed a substantial increase in all parameters, with all
differing significantly from control group absolute changes. Increases of
approximately 5mm were seen at the dental level, whereas 2mm were seen at the
skeletal level (Table 4).

Table 4 - Comparison of absolute transverse changes between RPE and Control patients

Absolute
changes

Parameter
In mm
Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED
T-TEST
P-value
NF 2.08 ± 5.66 -0.85 ± 2.38 0.0155
HP 2.25 ± 3.57 -0.12 ± 2.12 0.0023
PA 4.40 ± 2.69 0.03 ± 1.71 <0.001
BAC 3.00 ± 2.35 0.09 ± 1.00 <0.001
DA.E 5.35 ± 3.79 0.40 ± 1.69 <0.001
DA.E’ 5.42 ± 3.02 0.29 ± 0.88 <0.001
DA.I 4.56 ± 3.80 -0.08 ± 2.26 <0.001
DA.I’ 4.00 ± 2.77 -0.19 ± 1.69 <0.001
LAC 5.09 ± 3.04 0.02 ± 1.71 <0.001

50
Absolute Angulation Changes – No significant absolute changes were
observed in the angulations of the dentition. However, the angle of the alveolus
significantly increased on average approximately 5 degrees in the RPE group when
measured from all reference lines. These increases were statistically significant when
compared to the controls’. While the RPE group angles increased, the control group
angles decreased by an average of 2.7 degrees (Table 5).

Table 5 - Comparison of absolute angulation changes between RPE and Control patients
Absolute
changes

Parameter
In degrees
Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED
T-TEST
P-value
Alv 4.33 ± 8.28 -3.06 ± 8.48 0.0017
Alv – Horizontal 5.61 ± 6.94 -2.84 ± 7.09 <.0001*
Alv – Vertical 6.26 ± 7.24 -2.41 ± 6.69 <.0001*
Dent – Horizontal -0.95 ± 4.98 -0.88 ± 6.06 0.964
Dent – Vertical -1.08 ± 5.69 -0.95 ± 6.5 0.936
Inclination –
Horizontal
-0.81 ± 6.47 0.32 ± 5.63 0.454
Inclination –
Vertical
-0.55 ± 5.75 0.12 ± 5.59 0.968*

51
Transverse Percent Changes - There were significant transverse increase
percent changes between the control and RPE treated groups in all parameters. The
changes in the control group averaged less than 0.5 %. The greatest % changes were
seen in the RPE group at the level of the dentition, averaging at 11.75% (Table 6).

Table 6 - Comparison of transverse percent changes between RPE and Control patients
Percent change
Parameter
In %

Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED
T-TEST
P-value
NF 3.68 ± 9.6 -1.18 ± 3.62 0.0116*
HP 4.08 ± 7.08 -0.13 ± 3.35 0.0051
PA 14.87 ± 8.82 0.09 ± 5.04 <0.001
BAC 5.41 ± 4.39 0.21 ± 1.66 <0.001
DA.E 10.81 ± 8.24 0.77 ± 3.29 <0.001
DA.E’ 10.07 ± 6.10 0.53 ± 1.55 <0.001
DA.I 12.33 ± 10.40 0.06 ± 5.49 <0.001
DA.I’ 13.12 ± 9.9 -0.37 ± 4.94 <0.001*
LAC 18.41 ±13.05 0.15 ± 5.27 <0.001

52
Angulation Percent Changes – Only the alveolar structures showed
significant differences between the two groups. One angle, Alveolar – Vertical,
showed a 43% change. In general, measurements taken from the vertical reference
line exhibited very large standard deviations (Table 7).

Table 7 - Comparison of angulation percent changes between RPE and Control patients
Percent change
Parameter
In degrees
Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED
T-TEST
P-value
Alv 3.86 ± 7.2 -2.35 ± 6.95 0.0015
Alv – Horizontal 5.33 ± 6.54 -2.33 ± 5.99 <.0001
Alv – Vertical 43.72 ± 55.84 -7.23 ± 25.87 <.0001*
Dent – Horizontal -0.80 ± 4.9 -0.59 ± 6.46 0.897
Dent – Vertical -1.0 ± 54.18 7.97 ± 108.99 0.804*
Inclination –
Horizontal
-0.63 ± 6.01 0.56 ± 5.86 0.422
Inclination –
Vertical
-0.49 ± 32.81 1.77 ± 73.27 0.666*

53
Comparison of Transverse measurements - After treatment, the base of the
maxilla (NF, HP) showed no significant difference between the RPE and control
groups; however, though the widths of the RPE group appeared to approach those of
the controls, they were still smaller (Table 8). No differences were seen in the
alveolar structural measurements. Statistically significant differences were seen
between the two groups in the widths of the dental structures (DA.E, DA.E’, DA.I,
DA.I’). The dental crown widths of the RPE group were on average 2.5 mm larger
than those of the control group.

Table 8 - Comparison of transverse dimension between RPE and Control patients after
treatment
After treatment
Parameter
In mm
Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED T-
TEST
P-value
NF 66.94 ± 9.58 67.68 ± 5.1 0.7489
HP 63.23 ± 6.27 64.7 ± 3.98 0.3396
PA 34.46 ± 4.37 32.80 ± 5.05 0.1739
BAC 60.21 ± 3.74 59.90 ± 3.38 0.7040
DA.E 56.48 ± 4.3 53.89 ± 3.64 0.0077
DA.E’ 60.29 ± 4.17 57.75 ± 3.32 0.0058
DA.I 43.21 ± 4.28 40.20 ± 3.03 0.0029
DA.I’ 35.62 ± 3.92 33.07 ± 2.95 0.0062
LAC 33.80 ± 3.90 32.51 ± 3.05 0.1445

54
Comparison of Angulation measurements - Post- treatment angular
measurements revealed no significant differences between the groups, indicating that
the angulations of the RPE treatment group had caught up to the angulations of the
control group (Table 9).

Table 9 - Comparison of angular measurements between RPE and Control patients after
treatment
After treatment
Parameter
In degrees
Experimental group (RPE)
Mean ± 1Std. dev.
Control group
Mean ± 1 Std. dev.
PAIRED
T-TEST
P-value
Alv 122.35 ± 8.18 117.68 ± 9.86 0.074
Alv – Horizontal 113.74 ± 7.19 113.94 ± 7.87 0.924
Alv – Vertical 24.74 ± 6.94 24.40 ± 7.18 0.868
Dent – Horizontal 102.48 ± 6.19 100.68 ± 6.13 0.270
Dent – Vertical 13.51 ± 6.37 11.01 ± 5.61 0.067
Inclination –
Horizontal
106.97 ± 7.15 106.01 ± 6.01 0.587
Inclination –
Vertical
17.57 ± 6.5 15.88 ± 5.18 0.574*

55
Error Analysis
Transverse measurements all proved highly reliable with all differences being
0.5mm or less. All but 2 measurements (PA in RPE group and DA-I in RPE group)
had differences of less than 1% (Table 10).
Table 10 - Reproducibility analysis of transverse measurements for RPE and Control patients
RPE patients

(N=25)
Control patients
(N=25)
Parameter

difference
Mean ± std. dev.
In mm
% difference
Mean ± std.
dev.
difference
Mean ± std. dev.
In mm
% difference
Mean ± std.
dev.
Before treatment parameters
NF 0.81 ± 0.32 0.15 ± 0.58 0.00 ± 0.36 0.02 ± 0.54
HP 0.18 ± 0.68 0.37 ± 1.18 0.35 ± 0.69 0.51 ± 1.03
PA 0.22 ± 0.63 0.67 ± 2.20 0.14 ± 0.40 0.45 ± 1.29
BAC 0.51 ± 0.69 0.87 ± 1.26 0.19 ± 0.59 0.32 ± 0.99
DA.E 0.34 ± 0.62 0.70 ± 1.21 0.27 ± 0.63 0.53 ± 1.19
DA.E’ 0.11 ± 0.41 0.18 ± 0.73 0.03 ± 0.49 0.04 ± 0.89
DA.I 0.01 ± 0.47 0.09 ± 1.11 0.24 ± 1.03 0.54 ± 2.48
DA.I’ 0.01 ± 1.13 0.26 ± 3.25 0.06 ± 0.46 0.17 ± 1.44
LAC 0.19 ± 0.70 0.83 ± 2.55 0.20 ± 0.34 0.60 ± 1.07
After treatment parameters
NF 0.11 ± 0.29 0.19 ± 0.44 0.07 ± 0.48 0.10 ± 0.75
HP 0.20 ± 0.64 0.26 ± 0.95 0.14 ± 0.65 0.21 ± 0.99
PA 0.50 ± 0.90 1.50 ± 2.89 0.28 ± 0.63 0.89 ± 1.92
BAC 0.07 ± 0.66 0.09 ± 1.12 0.14 ± 0.46 0.22 ± 0.78
DA.E 0.06 ± 0.73 0.13 ± 1.31 0.14 ± 0.38 0.27 ± 0.69
DA.E’ 0.04 ± 0.72 0.06 ± 1.22 0.27± 0.54 0.49 ± 0.95
DA.I 0.54 ± 0.72 1.26 ± 1.72 0.04 ± 0.52 0.09 ± 1.33
DA.I’ 0.03 ± 0.82 0.08 ± 2.11 0.02 ± 0.47 0.01 ± 1.42
LAC 0.07 ± 0.53 0.25 ± 1.61 0.26 ± 0.33 0.85 ± 1.07

56
Angulation measurements all proved reliable if we applied the “within 2
degree” standard; however, when applying the percent difference standard, a few
measurements showed large deviations (Table 11). Large percent differences were
found among the angles measured from a vertical reference line, suggesting that data
obtained from the vertical reference is not as reliable as data obtained from the
horizontal reference.

Table 11 - Reproducibility analysis of angulation measurements for RPE and Control patients
RPE patients

(N=25)
Control patients
(N=25)
Parameter
In degrees
difference
Mean ± std. dev.
In mm
% difference
Mean ± std.
dev.
difference
Mean ± std. dev.
In mm
% difference
Mean ± std.
dev.
Before treatment parameters
Alv 0.05 ± 1.31 0.06 ± 1.07 0.56 ± 1.15 0.43 ± 0.99
Alv – Horizontal 0.48 ± 1.64 0.45 ± 1.49 0.74 ± 2.01 0.62 ± 1.76
Alv – Vertical 1.40 ± 2.81 8.38 ± 15.54 1.22 ± 2.16 3.55 ± 9.16
Dent – Horizontal 0.08 ± 1.60 0.11 ± 1.49 0.39 ± 1.82 0.38 ± 1.78
Dent – Vertical 0.22 ± 4.49 0.70 ± 3.09 0.16 ± 0.47 0.14 ± 6.75
Inc – Horizontal 0.55 ± 1.20 0.52 ± 1.15 0.01 ± 1.69 0.04 ± 1.57
Inc – Vertical 0.10 ± 0.66 0.48 ± 3.40 0.22 ± 0.94 1.09 ± 7.73
After treatment parameters
Alv 0.06 ± 1.00 0.03 ± 0.80 0.83 ± 1.21 0.68 ± 1.06
Alv – Horizontal 0.71 ± 1.75 0.62 ± 1.51 0.38 ± 1.64 0.36 ± 1.46
Alv – Vertical 1.32 ± 1.67 6.23 ± 7.10 0.44 ± 2.09 3.22 ± 11.64
Dent – Horizontal 1.13 ± 1.71 1.03 ± 1.70 0.25 ± 1.64 0.21 ± 1.60
Dent – Vertical 0.04 ± 1.20 3.20 ± 16.0 0.11 ± 0.55 1.17 ± 4.67
Inc – Horizontal 0.69 ± 1.69 0.56 ± 1.59 0.01 ± 1.47 0.02 ± 1.36
Inc – Vertical 0.35 ± 0.89 3.81 ± 7.84 0.03 ± 0.78 0.28 ± 4.10

57
Relative versus Absolute Dental Tip – Since RPE produces bending and
tipping of the alveolar structures, it also moves the teeth they house with the same
magnitude and direction. Thus a relative tip of the posterior teeth is observed. Very
few efforts have previously been made to quantify the degree of relative tip in the
dentition and no efforts have been made at quantifying the degree of absolute tip –
the tip of the teeth independent of alveolar bending. It has been stated that the
amount of dental tip produced by the RPE is negligible and non-significant. If this is
so, then the difference between the absolute change in dental angulation and the
absolute change in alveolar angulation should be similar. To determine the validity
of this theory, the following equation was applied:

Absolute Change in Alveolar Angulation (Alv – Horizontal or Alv – Vertical)
minus
Absolute Change in Dental Angulation (Dent – Horizontal or Dent –Vertical)
= Absolute Dental Tip

The results (Table 12) indicated that in the RPE group there was a large
degree of difference between the amount of tip in the alveolus and the tip in the
dentition (6.56 degrees from horizontal reference and 7.34 degrees from vertical
reference). Therefore, the difference can be assumed to be the amount of absolute tip
of the dentition. Both quantities were statistically significant (P < 0.0002). No
difference was observed in the control group, as expected.
58
Table 12 - Absolute tip of the posterior dentition calculated by subtracting the absolute dental
angulation change from the absolute alveolar change

Alv-Absolute
Change
Mean ± std. dev.
Dent-Absolute
Change
Mean ± std. dev.
Absolute Tip
Mean ± std. dev.

PAIRED T-
TEST P-
value
Horizontal tip in
RPE group
5.61 ± 6.94 - 0.95 ± 4.92 6.56 ± 7.07 0.0001
Vertical tip in
RPE group
6.26 ± 7.24 -1.08 ± 5.69 7.34 ± 8.34 0.0002
Horizontal tip in
control group
-2.84 ± 7.09 -0.88 ± 6.06 -1.96 ± 10.17 0.35
Vertical tip in
control group
-2.41 ± 6.67 -0.95 ± 6.50 -1.46 ± 8.53 0.40

When comparing the absolute tip values of the 2 groups in both horizontal
and vertical planes, statistically significant differences were seen (P< 0.0017, P<
0.0004, respectively, Table 13).

Table 13 - Comparison of absolute tip between RPE and Control patients
Tip difference in
RPE
Mean ± std. dev.

Tip Difference in
control
Mean ± std. dev.

Difference

Mean ± std. dev
T – Test
P – value
Horizontal 6.56 ± 7.07 -1.96 ± 10.17 -8.52 ± 12.03 0.0017
Vertical 7.34 ± 8.34 -1.46 ± 8.53 -8.8 ± 10.57 0.0004

59
Chapter 6: Discussion
Understanding the effects of RPE treatment on the skeletal and dental
components is paramount for every orthodontist. While orthodontic literature is rife
with reports on the effects of RPE on the craniofacial complex and the transverse
changes in the dentition, very few have addressed the matter of dental tipping. A
recent meta-analysis of RPE induced changes conducted by Lagravere[21] evaluated
the entire RPE library only to find that very few of the studies have used stringent
scientific protocol. The vast body of experimentations on the effects of RPEs has
been conducted without the inclusion of controls, precise identification of the
landmarks used for measurements, or measurement reliability analyses.
An analysis of the qualifying experiments showed that on average about
6.04mm of molar crown to molar crown expansion was produced by the RPE along
with 4.4mm of expansion measured at the root apex. The study also averaged 3
degrees of molar tip though it was non-significant. Nasal cavity width and inter-
alveolar (measured from the buccal plates) width increases were around 2.14mm and
2.73mm, respectively. The purpose of our study was to further explore and reveal the
behavior of the alveolus and the teeth that it houses under the forces of an RPE
appliance. Since this study has used a control group, has identified the landmarks
used for each measurement and has conducted an error analysis, it is safe to assume
that the findings of this study can be corroborated with the measurements reported by
the meta-analysis.

60
The baseline measurements of this study showed that the RPE group
presented with a statistically significant transverse insufficiency in all measured
parameters (Table 2) as would be expected. At the skeletal level, patients with
unilateral or bilateral crossbites showed approximately a 3.75mm deficiency when
compared to controls. At the dental level, the deficit was around 2-2.5mm. The
diminishing magnitude of width insufficiency observed from the base of the maxilla
down to the dental cusps in the RPE group prior to treatment can be explained by the
fact that the alveolar segments are bent inwards (relative to controls, p = 0.0002).
The manifestation is indicative of true skeletal deficiency with slight dental
compensation. The angulation measurements supported this observation with
significant differences seen in the alveolar angulations of nearly 8.5degrees of
acuteness and no significant differences in the angulations of the dentition between
the groups (Table 3).
After treatment, there were no significant transverse increases noted for any
parameters in the control group (Table 4), while all of the measured parameters for
the RPE group were significant. The midpalatal suture was opened in all patients
treated with RPE. The treatment augmented the base of the maxilla with 2.08 mm of
width of the nasal floor (NF) and 2.25mm of width of the hard palate. These values
are comparable with those reported by Lagravere. The width increase at the level of
first molar root apices was found to be 4.4mm, an exact match with Lagravere’s
average.
At the level of the buccal alveolar crests, our study observed a gain of 3mm, a
0.26 mm difference between the averaged 2.74mm by Lagravere. Measured at the
61
level of the lingual alveolar crests, we observed a 5mm width increase which is
consistent with Handleman’s[74] value. The transverse increases at the levels of the
buccal dental cusps reported by Lagravere averaged at 6.04mm. In comparison, ours
measured at 5.4mm. This value is slightly less than previous reports by Timms[46]
and Chung[52] who measured off of dental casts, but is in agreement with values
measured off of radiographs by Baccetti[56] and Cross[20]. In general more
expansion was achieved at the dental level than at the skeletal level. The ascending
pattern of width increases from maxillary base down to dental cups is consistent with
the pyramid-like configuration of expansion described by Wertz[1] and numerous
others.
When we compared the changes in the transverse dimension between the 2
groups at the skeletal level, we found that the post treatment widths of the maxilla
were similar (no significant differences, Table 8); however, the RPE group still
showed a slight narrowness of about 1 mm. At the dental level, significant
differences were seen with the widths of the RPE group being larger than the
controls by about 2.5mm.
Analysis of post-treatment angulation changes revealed that the alveolus does
substantially tip buccally by nearly 5.6 degrees (as measured from a horizontal
reference, Table 5). The angulations of the dentition, however, remained constant
between pre and post-treatment. In other words, our study showed no statistically
significant amount of relative dental tipping resulting from RPE treatment. While
previous studies also support that the amount of dental tipping is non-significant,
Adkins, McNamara, Handleman all estimated a net change of 6.2 degrees of inter
62
molar tip (right and left sides combined). Garib’s value of 2.5 degrees for 1 side lies
in agreement with their findings along with Lagrevere’s average of 3 degrees. Upon
a closer examination of angulation changes, we were able to derive the amount of
resultant dental tipping independent of alveolar tipping.
As was previously described, when the suture is subject to expansion forces,
it separates in a non-parallel fashion. Because the maxilla articulates with bones
which are not paired, the amount of separation is limited. Instead, what is seen is a
pyramid-like splaying of the maxillary components with fulcruming. The alveolar
halves splay buccally and carry the teeth with them. What should be observed after
expansion is that the inclination change of the teeth should be similar to the
inclination change of the alveolus; however this is not the case. Table 12 shows that
while the alveolar half inclined buccally, the tooth stayed relatively constant in its
angulation. In fact, it moved in a slightly lingual direction with the net difference
between the angles constituting an absolute tip of 6.5 degrees from the horizontal
reference. This amount of absolute tip can be attributed to denture uprighting after
expansion. This finding challenges the theory that when a vector of force is applied
across the palate in a buccal direction, then the teeth will also tip in that direction.
As we have shown, the opposite tends to happen with the teeth preserving their
original angulation to the palate and the opposing dentition.

63
Chapter 7: Assumptions

1. The patient pool at USC was representative of the general population of
Southern California
2. The distortion and magnification of NewTom® images was statistically
insignificant.
3. All patients were growing based on age and clinical judgment.
4. The determination of the vertical reference line used the patient’s skeletal
midline using nasion superiorly and the patient’s central incisors.
5. All angulations could correct for head position differences.
6. Required expansion was achieved by ‘slight overcorrection of the crossbite,’
which was based on clinical judgment
7. Measurements were accurate and reproducible.

64
Chapter 8: Limitations

1. There were a limited number of NewTom® records in department
archives that met study inclusion criteria.
2. The study only used orthodontic patients as opposed to the general
population.
3. Measurements were subjected to human error.

65
Chapter 9: Summary
1. In patients with transverse maxillary deficiency, the base of the maxilla
suffers from a 3.75mm of width deficit.
2. In patients with transverse maxillary deficiency, the alveolar segments are
approximately 8.5 degrees more acute than the controls.
3. RPE treatment can augment the base of the maxilla with 2.08 mm of width of
the nasal floor and 2.25mm of width of the hard palate.
4. At the dental level, a 5.4m width increase can be achieved through RPE
treatment.
5. In general, more expansion is achieved at the dental level than at the skeletal
level. The ascending pattern of width increases from maxillary base down to
dental cups is consistent with the pyramid-like configuration of sutural
opening described in the literature.
6. After treatment, the base of the maxilla in the RPE patients approached the
transverse dimensions of the controls.
7. The dental widths of the RPE group are larger than the controls by a2.5mm.
8. After RPE treatment, the alveolar angulations of the RPE group approach
those of the controls.
9. After RPE treatment, the alveolus substantially tips buccally by nearly 5.6
degrees, while the posterior teeth show consistency in their inclination.
10. After RPE treatment, the posterior teeth show an absolute tip of 6.5 degrees
from the horizontal reference.
66
Chapter 10: Conclusions
Correction of transverse maxillary deficiency with Rapid Palatal Expansion
(RPE) is very effective. While this mechanotherapy addresses and resolves the
insufficiencies in the maxilla, it also leaves it with effects which have not been
thoroughly explained in the literature. This study has shown that RPE therapy
effectively and adequately increases the transverse dimensions of the maxillary base
and the dento-alveolus in patients with crossbites. While it has been previously
thought that expansion is achieved through a combination of orthopedic and
orthodontic movements, this study has shown that the contribution of the orthodontic
effects is negligible. As the suture is opened, the base of the maxilla is spread apart
and the two halves rotate buccally. The posterior teeth upright to try to maintain their
original inclination to the palate. The majority of expansion is achieved through
tipping of the alveolus. Although the amount of relative dental tipping is non-
significant and provides no contribution to overall expansion, it should be
appreciated that there is a substantial amount of absolute tipping in the lingual
direction that occurs. This study is the first of its kind to differentiate between and
quantify the amount of relative and absolute tipping as a result of expansion and the
first to refute the popular opinion that RPE forces tend to tip the posterior dentition
buccally.

67
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Asset Metadata

Creator Kartalian, Armine (author)

Core Title A cone beam CT evaluation of the maxillary dento skeletal complex after rapid palatal expansion

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 03/13/2008

Defense Date 02/27/2008

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag alveolar tipping,cone-beam CT,dental tipping,maxilla,OAI-PMH Harvest,RPE

Language English

Advisor Reyes, Enciso (committee chair), Keim, Robert G. (committee member), Moon, Holly (committee member), Paine, Michael L. (committee member)

Creator Email kartalia@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m1049

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