SARME study compares transverse effects of Haas vs. Hyrax expanders

Copyright @ 200 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.8
Transverse Effects of Surgically Assisted
Rapid Maxillary Expansion: A Comparative
Study Using Haas and Hyrax
Claudia Toyama Hino, DDS, PhD, Max Domingues Pereira, MD, PhD,
Christiane Steponavicius Sobral, MD, PhD, Tessie Maria Kreniski, MD,
Lydia Masako Ferreira, MD, PhD
Saõ Paulo, Brazil
Background: Surgically assisted rapid maxillary
expansion is the treatment of choice for correcting
transverse maxillary deficiency in patients with
skeletal maturity, although the influence of the
expander type on these alterations has not been
elucidated yet.
Objective: Determine the skeletal and dental trans-
verse effects on the maxilla after completion of
surgically assisted rapid maxillary expansion, with
Haas and Hyrax expanders.
Methods: Thirty-eight patients (aged between 18
and 39 years) were submitted to subtotal Le Fort I
osteotomy and divided into Hass and Hyrax groups
(19 patients each). Measurements of maxillary
width, upper intermolar width, and its inclination
on the posteroanterior cephalometric radiographs
were obtained in the preoperatory period (T1), after
the completion of the expansion (T2), and 4 months
after the completion of the expansion (T3). The
intercusp and intergingival distances measured on
the plaster models were obtained from the first
premolars and molars, before expander cementation
(M1) and after the expander removal (M2).
Results: Both groups revealed statistically signifi-
cant increase in the maxillary width, upper inter-
molar width, and inclination of the molars in T2
(P G 0.001); T3 showed a statistically significant
decrease in the maxillary width and inclination of
the molars (P G 0.001). The expansion presented an
increment on the maxillary width of 71% from the
upper intermolar width (T1 j T3), and molars had
vestibular inclination (P G 0.05). The ratio of
width increase of maxilla by the amount of
device activation was of 69% for Haas and 74.5%
for Hyrax.
Conclusion: Clinically, the transversal effects were
similar for both groups.
Key Words: Palatal expansion technique, orthodontic
appliances, cephalometry
S
urgically assisted rapid maxillary expansion
(SARME) is a procedure of choice to obtain
the correction of the transverse maxillary
dimension, in treatment of skeletally mature
patients. It is indicated to individuals who have
transverse maxillary deficiency, skeletal maturity, and
maxillomandibular transverse differential index with
discrepancy of more than 5 mm.1
The expander appliance that will be used is of
basic importance to assist, obtain, and maintain the
required expansion. Two types of appliances for
SARME are most widely recognized in the literature:
tooth-tissueYborne expander (Haas expander) and
tooth-borne expander (Hyrax expander).
Haas2
has developed his appliance in 1961,
emphasizing the importance of the acrylic palatal
button to promote an efficient transmission of force
and, in this way, provide the adequate orthopedic
movement and more stability after rapid maxillary
expansion. Many studies over SARME3Y6 have used
Haas appliance and reported appropriated results of
expansion without adverse effects. However, Lehman
and Haas7
and Anttila et al8
have reported complica-
tions with Haas appliance during the expansion, as a
necrosis and a palate lesion caused by the pressure of
the acrylic on the palatal mucosa.
The Hyrax appliance (Hygienic Appliance for
Rapid Expansion), consisting of a metal framework,
was introduced by Biederman in 1968.9
The author
observed as an advantage of his appliance the fact that
it was more hygienic than Haas, once it avoids food
718
From the Division of Plastic Surgery, Federal University of Saõ
Paulo, Saõ Paulo, Brazil.
Address correspondence and reprint requests to Max Domingues
Pereira, MD, PhD, Division of Plastic Surgery, Federal University of
Saõ Paulo, Rua Napoleaõ de Barros, 715-4- andar, CEP 04024-002,
Saõ Paulo, Brazil; E-mail: maxdp@terra.com.br

impaction and soft tissue irritation. Some studies,9Y13
evaluating the SARME using Hyrax appliance,
revealed satisfactory expansion effects. However,
Glassman et al14
mentioned the extrusion of the teeth
support as a complication, and Braun et al15
empha-
sized that the Hyrax appliance did not present
sufficient rigidity because of its wire construction,
causing undesired inclination of the supporting teeth.
It is desirable that the transverse expansion
occurs with a minimum teeth inclination because
large inclinations denote that the teeth are being
moved against their cortical, and besides that, if the
expansion occurs without inclinations, the overcor-
rection will be dispensed, providing more stability
after the expansion.16Y18
There are some doubts about the appliance
anchorage influence (tooth tissue-borne or tooth-
borne) as well as the alterations provided in the
maxilla after the completion of SARME because, in
this situation, the bone resistance which interferes in
the expansion is eliminated by osteotomy. It is added
in this questioning the fact that SARME be the ideal
procedure to correct transverse maxillary deficiency,
frequently in adults screened at surgical-orthodontic
clinics (prevalence of 30% according Phillips et al).18
It
is important to evaluate whether the type of the
appliance interferes in the SARME results because the
expanders still present differences in the facility of
hygiene and in its costs. In vast literature searched, no
elucidations to the mentioned questions were found.
The main objectives of this study were to
evaluate and compare the skeletal and dental trans-
verse effects in the maxilla after the completion of
SARME, using the Haas and Hyrax expanders.
METHODS
This study was approved by the ethical committee
of Federal University of Sa˜o Paulo, and each
patient signed informed consent form. There were 38
adult patients evaluated from Division of Plastic
Surgery of Federal University of Sa˜o Paulo. The
inclusion criteria comprised patients older than 18
years with bilateral transverse maxillary deficiency
and maxillomandibular transverse differential index
with discrepancy higher than 6.5 mm. The exclusion
criteria comprised individuals who presented for
previous maxillary surgery or with maxillary trauma,
congenital anomalies, or third molars impacted. The
sample was sorted and divided into the following:
Hass group is composed of 19 patients aged 29 years
(range, 19Y39 years), 9 men and 10 women, who used
the Haas expander with 11-mm screw (Dentaurum,
Ispringen, Germany), fixed in teeth bands placed onto
the upper first premolars and first molars; and the
Hyrax group is composed of 19 patients aged 27.5
years (range, 18Y37 years) who used the Hyrax
expanders with 12-mm screw (Dentaurum), soldered
to the bands cemented onto the upper first premolars
and first molars.
In each band of upper first right and left molars,
for both Haas and Hyrax appliances, a stainless steel
wire of 1.0-mm diameter and 0.7-cm length was
soldered, in the vestibular surface, placed vertically,
forming metallic pins and used as reference17
(Fig 1).
In the absence of the first premolars or first molars, the
bands were cemented onto the second premolars and
the second molars, respectively. All the appliances
were built by the same technical professional in
laboratory prosthesis.
To predict the transverse maxillary dimension of
each patient and correct the deficiency, the maxillo-
mandibular transverse differential index was used,
calculated by the measurements in the posteroanter-
ior (PA) radiographs.
One week before the operation, the first work
plaster model was made (M1Vinitial model), and the
appliance was installed. After the placement of the
expander, the first PA radiographs were done
(T1Vpreoperative).
The surgery subtotal Le Fort I osteotomy was
carried out after the expander has been installed,
under general anesthesia, as proposed by Betts et al.1
Immediately after the operation, the expander was
activated in 1.6 mm by the surgeon. After 4 days of
latency period, the patients were intruded to start
activation of their appliance with 2 quarter turns per
day (twice a day), corresponding to 0.4 mm of daily
expansion, until the necessary amount of expansion
was achieved. The expander screw was locked with a
stainless steel wire. At this moment, the second PA
Fig 1 Vertical pin soldered to the bands cemented onto the
first molars.
TRANSVERSE EFFECTS OF SARME / Hino et al
719

radiograph was requested (T2Vcompletion of the
expansion).
The appliance was used as a retainer during 4
months, when the third PA radiograph was requested
(T3V4 months after the completion of the expansion).
After the removal of the appliance, the second work
plaster model (M2) was taken from the superior
dental arch.
Evaluation of the Expansion Quantity Obtained in
the Appliance
The quantity of transverse expansion obtained with
the appliance was verified, subtracting the value of
the measurement obtained after the fixation of the
expander screw from the value obtained at the
beginning (Fig 2).
Evaluation of PA Cephalographs
The PA radiograph was obtained in the same
odontological radiology center, where the machine
model X Mid Tome Ceph (Soradex) was used.
An anatomic drawing of interest to elaborate the
cephalogram19
was made over each PA radiograph19
(Fig 3). Three cephalograms were obtained in each
radiograph.
Fig 3 Posteroanterior tracing and analysis. Landmarks:
RMx, right maxillary; LMx, left maxillary; RO, right orbital;
LO, left orbital; RM, the most inferior point on pin of the
right molar; LM, the most inferior point on pin of the left
molar. Planes and lines: RO-LO, orbital plane OP; RMx-
LMx, maxillary width; RM-LM, upper intermolar width;
RM-OP, inclination of the right molar (angle between the
long axis of the right molar and orbital plane); LM-OP,
inclination of the left molar (angle between the long axis of
the left molar and orbital plane).
Fig 2 Method used for evaluation of the expansion quantity obtained with the appliance. Measurements obtained with
digital caliper. A, Hass after the completion of the expansion. B, Haas before operation. C, Hyrax after the completion of the
expansion. D, Hyrax before operation.
THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 19, NUMBER 3 May 2008
720

The linear measurements: orbital plane, maxillary
width, and upper intermolar width, were carried out
with a digital caliper (Mitutoyo) of 0.01-mm precision.
The angular measurements, inclination of the right
molar (angle between the long axis of the right molar
and orbital plane) and inclination of the left molar
(angle between the long axis of the left molar and
orbital plane), were obtained with a cephalometric
protractor with subdivision of 0.5 grade.
Evaluation of the Work Plaster Orthodontic Models
Transverse measurements between cusp tips (inter-
cusp distance) were obtained in 2 regions: molar
and premolar. The reference point in the molar
region was the mesiolingual cusp tips (ML) of the
first molars, and the reference point in the premolar
region was the lingual cusp tips (L) of the first
premolars. Other measurements were carried out
between gingival margins (intergingival distances).
The reference for the first molars and the first
premolars was the most-palatal point in the tooth
gingival margin. The points were marked with a
sharp 4H pencil in the models, which were erased
after the measurement, which were carried out with
a digital caliper.
The same investigator (C.T.H.) made all the measure-
ments (cephalograms and models) for 3 times with an
interval of 15 days and averaged.
Statistical Method
The Friedman test was applied to compare each
variable of the PA radiograph (maxillary width, upper
intermolar width, and inclinations of the right and left
molars) in each group, in the periods T1, T2, and T3.
The Wilcoxon test was applied to compare the
variables (maxillary width versus upper intermolar
width and inclinations of the right versus left molars)
in each group, in which relative measures were
calculated by the percentage of each variable. The
same test was applied to compare the intercusp and
intergingival distances, using absolute values. The
Mann-Whitney U test was applied to compare the
variables between the Haas and Hyrax groups. P e
0.05 established the significance for all statistical tests.
RESULTS
The measurements of the PA radiographs and the
study models showed that the maxillary expan-
sion was successful in all patients.
The quantity of expansion obtained in this study
did not differ significantly between the Haas (8.9 mm)
and Hyrax (8.6 mm) groups.
Table 2. Comparison of the Mean Increase of Maxillary Width and of Upper Intermolar Width in the Haas
and Hyrax Groups
(T2 j T1) / T1 Â 100 Maxilla Â molar (T3 j T1) / T1 Â 100 Maxilla Â molar
Maxilla, (T2 j T1) /
T1 Â 100
Molar, (T2 j T1) /
T1 Â 100 Z calc P
Maxilla, (T3 j T1) /
T1 Â 100
Molar, T3 j T1) /
T1 Â 100 Z calc P
Haas 12.4 16.3 j3.823* G0.001* 11.1 16.3 j3.824* G0.001*
Hyrax 12.1 14.6 j3.421* G0.001* 9.9 14.4 j3.726* G0.001*
Differences % = (T2 j T1) / T1 Â 100 and (T3 j T1) / T1 Â 100.
* indicates statistically significant.
Table 3. Proportion of the Increase of Maxillary Width
by the Increase of Upper Intermolar Width, 4 Months
After the Completion of the Expansion in the Haas and
Hyrax Groups
Haas Hyrax
(Maxilla T3 j T1) /
(molar T3 j T1) Â 100
(Maxilla T3 j T1) /
(molar T3 j T1) Â 100
71.3 71.6
Z calc = j0.512 (NS); P = 0.609 (NS)
Medium measurements % = (maxilla T3 j T1) / (molar T3 j T1) Â 100.
NS indicates not statistically significant.
Table 1. Maxillary Width and Upper Intermolar Width
(Mean Values in Millimeters) in Preoperative (T1), in the
Completion of the Expansion (T2), and 4 Months After
the Completion of the Expansion (T3) in the Haas and
Hyrax Groups
Haas (n = 19) Hyrax (n = 19)
Maxilla T1 Maxilla T2 Maxilla T3 Maxilla T1 Maxilla T2 Maxilla T3
62.6 70.3 69.5 64.1 71.8 70.4
x2
calc = 38.000*, P G 0.001* x2
calc = 38.000*, P G 0.001*
T1 G T2 and T3 T1 G T2 and T3
T2 9 T3 T2 9 T3
Molar T1 Molar T2 Molar T3 Molar T1 Molar T2 Molar T3
60.0 69.6 69.6 61.6 70.5 70.4
x2
calc = 38.000*, P G 0.001* x2
calc = 38.000*, P G 0.001*
721

PA Cephalometric Analysis
The measurements obtained from the analysis of the
alterations in the maxillary width among the periods
T1, T2, and T3 showed a statistically significant
transverse increase, as well a decrease in the maxillary
width from T2 to T3, for the Haas and Hyrax groups
(Table 1). The alteration of upper intermolar width
between T2 and T1 made evident a transverse
increase statistically significant, which continues in
T3 in the 2 groups (Table 1). The percentage difference
was used to compare the increase between the
maxillary width and upper intermolar width. A
statistically significant transverse increase was
observed in the upper intermolar width in relation
to the maxillary increase in both groups (Table 2). The
proportion increase of the maxillary width in relation
to the upper intermolar width (T1 j T3) appeared
similar in the Haas and Hyrax groups (Table 3).
Between the Haas and Hyrax groups, comparing the
maxillary width and the upper intermolar width, a
similar increase in the maxillary was verified between
T2 and T1, showing no statistically significant
difference. A statistically significant transverse
decrease occurred between T3 and T2, in the max-
illary width in the Hyrax group. In the Haas group, a
statistically significant transverse increase in the
intermolar width was revealed in both periods
analyzed (T2 j T1 and T3 j T2) (Table 4). The ratio
between the increases of the width of maxilla by the
amount of activation of the screw expander did not
show statistically significant difference (Table 5). The
angle measurements obtained in the evaluation of
molar inclination between T2 and T1 demonstrated a
statistically significant increase in both groups
(Table 6). Comparing the inclination of the molars
between groups showed a statistically significant
angular increase in the Haas group, except in the
left molar angle difference % = (T3 j T1) / T1 Â 100
(Table 7).
Orthodontic Plaster Models Analysis
In relation to the Haas and Hyrax groups, the
intercusp distances of the first molars showed a
statistically significant increase in the intergingival
distance (Table 8). The intercusp and intergingival
distances did not show statistically significant differ-
ences between the Haas and Hyrax groups (Table 9).
DISCUSSION
Comparing the Haas and Hyrax groups (Table 4),
an increase in the upper intermolar width in the
Haas group was observed in T2 and T3. This fact may
be related to the larger quantity of the expansion in
the Haas group, which was necessary to correct the
transverse maxillary deficiency (Haas 8.9 mm and
Hyrax 8.6 mm). In relation to maxillary width, a
similar increase in both groups was verified in T2,
which means that the appliances performed in a
similar manner. These findings could not be con-
fronted because no identical experiments and corre-
sponding results were encountered in the literature
available in this study. However, a decrease in the
maxillary width in the Hyrax group was observed in
T3, which can be related to the absence of anchorage
acrylic palatal button.20
In T2, the increase of the ratio of the maxilla
width by the amount of the screw expander activation
(Table 5) was of 69% for the Haas group and 74.5% for
the Hyrax group. Statistically significant difference
was not observed.
Analyzing the modifications in the maxilla width
in the 3 periods (Table 1), an increase in T2, followed
by a decrease in T3, in both groups was verified.
Table 4. Comparison of Maxillary Width and of Upper Intermolar Width in the Haas and Hyrax Groups
Maxilla (T2 j T1) / T1 Â 100 Maxilla (T3 j T1) / T1 Â 100 Molar (T2 j T1) / T1 Â 100 Molar (T3 j T1) / T1 Â 100
Haas Hyrax Haas Hyrax Haas Hyrax Haas Hyrax
12.4 12.1 11.1 9.9 16.3 14.6 16.3 14.4
Z calc = j0.102, NS Z calc = j2.192* Z calc = j2.059* Z calc = j2.059*
P = 0.919, NS P G 0.05* P G 0.05* P G 0.05*
Differences % = (T2 j T1) / T1 Â 100 and (T3 j T1) / T1 Â 100. Medium measurements.
NS, not statistically significant.
Table 5. Average Ratio of the Increase of the Maxilla
Width in T2 (After the Completion of the Expansion) by
the Amount of Srew Activation in the Haas and Hyrax
Groups
Haas Hyrax
(Maxilla T2 j T1) / quantity of
activation Â 100
(Maxilla T2 j T1) / quantity of
activation Â 100
69 74.5
Z calc = j1.474, NS P = 0.140, NS
722

Similar results were obtained by Northway and
Meade,5
Bays and Greco,10
and Pogrel et al.21
However, this decrease was low: 0.8 mm for the
Haas group and 1.4 mm for the Hyrax group.
This research revealed an increase in the width of
the maxilla of 7.7 mm in both groups (T1 j T2) and of
6.9 mm in the Haas group and 6.3 mm in the Hyrax
group (T1 Y T3), although all the other studies had
demonstrated lower results: 3.8 mm.17
More discoura-
ging results was obtained by Byloff and Mossaz,22
with
an increase of 1.31 mm in the maxillary width, in
relation to 5.6 mm of molar expansion.
The differences in the results could be attributed
to the used operative technique. Whereas this study
made use of subtotal Le Fort I osteotomy, removing
the resistance of the maxillary articulations, others
applied wall maxillary osteotomy. Berger et al23
used
the technique described by Epker et al,24
subtotal Le
Fort I osteotomy, in which they obtained the increase
of only 3.13 mm in the maxillary width.
The expansion did not occur in parallel, being
smaller in the maxilla (Table 2). Betts et al1
mentioned
that an outward rotation of the maxillary halves,
around an axis of rotation located near the frontonasal
suture, occurred during the expansion because of
small articulation of the palatine bone within the
posterior orbit, as well as the fact that the posterior
portion of the palatine was not sectioned during the
procedure and was subjected to lateral forces during
expansion. Pinto et al,25
using the transpalatal
distractors, also described this rotation movement of
hemimaxillas by means of measurements in digitizing
models, revealing an increase in the inclination of the
first molars and the first premolars, that is, in the same
teeth used as anchorage in SARME.
With the knowledge that the expansion in the
maxilla was smaller, the definition of the efficacy in
the maxillary expansion proportioned by SARME
became important, so that the proportion between the
quantity of the maxillary expansion and the quantity
of dental expansion was calculated (Table 3). The
maxillary expansion was similar in both groups,
71.3% (Haas) and 71.6% (Hyrax). Kuo and Will16
reported superior efficacy in the maxillary expansion
of 83% that could be related to the lower quantity of
the needed expansion (4.5 mm), when compared with
8.9 mm (Haas) and 8.6 mm (Hyrax) in this study, once
it is supposed that the higher the quantity of the
appliance expansion, the higher the rotation of the
maxillary halves will be.
The image of the metallic pins in the PA radio-
graph allowed the evaluation of the teeth inclination
with a higher precision, due to many superpositions of
images in the molars region. Mossaz et al17 included
one reference line 3 median line 4 extended from the
medium point of the orbital plane to the anterior nasal
spine that allowed to take measurements of the in-
ferior angle, formed between the median line passed
Table 7. Comparison of the Inclination of Right and Left Molars (Angle RM and Angle LM) Between the Haas
and Hyrax Groups
Angle RM (T2 j T1) /
T1 Â 100
Angle RM (T3 j T1) /
T1 Â 100
Angle LM (T2 j T1) /
T1 Â 100
Angle LM (T3 j T1) /
T1 Â 100
Haas Hyrax Haas Hyrax Haas Hyrax Haas Hyrax
5.3 2.5 1.9 0.1 4.2 2.5 1.3 0.8
Z calc = j3.257* Z calc = j2.059* Z calc = j2.600* Z calc = j1.198, NS
P G 0.001* P G 0.05* P G 0.05* P = 0.231, NS
Differences % = (T2 j T1) / T1 Â 100 and (T3 j T1) / T1 Â 100. Medium measurements.
Table 6. Inclination of the Right and Left Molars (Angle RM and Angle LM; in Degrees) in Preoperative (T1),
Completion of the Expansion (T2), and 4 Months After the End of the Expansion (T3) in the Haas and Hyrax Groups
Angle RM T1 Angle RM T2 Angle RM T3
Angle
LM T1
Angle
LM T2 Angle 88 LM T3
Haas 87.2 91.7 88.7 87.9 91.5 89.1
x2
calc = 29.368* P G 0.001* x2
calc = 30.658* P G 0.001*
Hyrax 86.8 88.9 86.9 88.4 90.6 89.0
x2
calc = 21.971* P G 0.001* x2
calc = 22.622* P G 0.001*
Medium measurements.
723

over the axis of the metallic pin of each side and the
median line. In this study, the measurement of the
internal angle was used, formed between the orbital
plane and the line, which passed on the long axis of the
metallic pins, on the right and on the left, which
variations had indicated alterations in the inclination
of the molars. The median line was not used, as
described by the authors, once the anterior nasal spine
was judged inadequate as reference point because of
the dislocation during the expansion.
There was an inclination of the molars to the
vestibular after the completion of the expansion on the
right side (4.5 degrees [Haas]; 2.1 degrees [Hyrax]) and
on the left side (3.6 degrees [Haas] and 2.2 degrees
[Hyrax]) (Table 6). The same was observed by Mossaz
et al,17
which was evidenced the increase of 5 to 20
degrees for each side. Byloff and Mossaz22
reported
medium increase of 9.6 degrees in the inclination of
molars and explained that these changes in the inclina-
tion of the molars did not occur because of the dental
inclination only, exactly because if this occurred, the
gingival resection, as well as the dental mobility, should
be observed clinically. They suggested that the changes
had resulted in a dental inclination and the lateral
rotation of hemimaxillas.17,22
However, it was evidenced
that this angular change was not stable and relapsed
during the retention period.17,22
Similar fact was proved
in this research (Table 6). This tendency of the maxillary
teeth and skeletal segments returning to their original
positions was attributed to the following factors:
accumulated forces in the circummaxillary articulations,
occlusal forces, the surrounding buccal musculature, and
the stretched fibers of the palatal mucosa.26
The increase in the molar inclination in the Haas
group (Table 7) could be related to a higher quantity
of necessary expansion to correct the transverse
maxillary deficiency in this group, requiring posterior
studies to explain this fact better.
The reference points used to evaluate the models
followed those described by Moorrees,27
who men-
tioned that the measurements in the gingival were
slightly influenced by the inclination of the teeth,
different from the cusp measurements, because of the
enlargement of the distance between cusps and the
fulcrum. This fact is proven in the present study, as
the averages of increases of the intergingival distances
of the molars for both groups were similar to the
quantity of expansion obtained (Table 9).
The measures in relation to the increment in the
intercuspidal distance with the increment in the
intergingival distance showed that the molar has
inclined to vestibular. The increases in intergingival
distances in the molars and premolars were practi-
cally parallel, lower in the premolars (Table 8). Similar
fact was observed by Bays and Greco,10
who verified
expansion of 5.76 T 2.56 mm in the premolars and of
5.78 T 2.68 mm in the molars.
This study reached promissory results in relation
to the maxillary skeletal expansion a ratio of 71%
between the increment in the maxillary width and the
increase of upper intermolar width. Small dental
expansion was observed, with a mean increase of
2.1 to 4.5 mm in the molar inclination and also
corroborated by the mean difference between the
intercusp and intergingival distances of 0.1 mm to 0.4
mm, which might be associated with the surgical
technique used, subtotal Le Fort I osteotomy, as
Table 8. Comparison of the Increase of Intercusp and
Intergingival Distances of the First Molars and First
Premolars (in Millimeters) in the Haas and Hyrax Groups
First molar First PM
Haas Cusp molar
M2 j M1 Â gingival
molar M2 j M1
Cusp PM
M2 j M1 Â gingival
PM M2 j M1
9.3 8.9 8.7 8.7
Z calc = j3.634* Z calc = j1.251, NS
P G 0.001* P = 0.211, NS
Hyrax Cusp molar
M2 j M1 Â gingival
molar M2 j M1
Cusp PM M2 j
M1 Â gingival PM
M2 j M1
8.7 8.6 8.4 8.4
Z calc = j2.410* Z calc = j0.35, NS
P G 0.05* P = 0.752, NS
PM, premolar; NS, not statistically significant.
Table 9. Comparison of the Increase of Intercusp and Intergingival Distances (in Millimeters) of the First Molars and
the First Premolars Between the Haas and Hyrax Groups
First Molar Cusp First Molar Gingival First PM Cusp First PM Gingival
Haas Â Hyrax Haas Â Hyrax Haas Â Hyrax Haas Â Hyrax
9.3 8.7 8.9 8.6 8.7 8.4 8.7 8.7
Z calc = j1.242, NS Z calc = j0.745, NS Z calc = j0.921, NS Z calc = j0.269, NS
P = 0.214, NS P = 0.456, NS P = 0.357, NS P = 0.530, NS
PM, premolar; NS, not statistically significant.
724

described by Shetty et al,28
who mentioned that the
choice of maxillary osteotomy is the critical point that
determines if the effects of the expander will have
orthopedic or orthodontic predominance.
CONCLUSIONS
1. Clinically, the skeletal and dental effects were
similar in both groups.
2. Skeletal and dental expansion occurred with a
maxillary increment of 71% of the transversal
distance increase of the molars in both groups.
3. The maxillary width decreases in the Hyrax group
for the period of 4 months after the completion of
the expansion and did not change in the Haas
group.
4. The molars transverse distance remained for 4
months after the completion of the expansion in
both groups.
5. There was inclination (of the molars or of the
maxillary) in the Haas and Hyrax groups.
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