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119
0886-9634/2302-
119$05.00/0, THE
JOURNAL OF
CRANIOMANDIBULAR
PRACTICE,
Copyright © 2005
by CHROMA, Inc.
ABSTRACT: There is a growing interest in the relationship between occlusion and posture because of
a greater incidence of neck and trunk pain in patients with occlusal dysfunction. The study was designed
to verify whether an alteration of the spinal column alignment may be experimentally induced in rats as
a consequence of altering dental occlusion and also to investigate whether the spinal column underwent
any further changes when normal occlusion was then restored. Thirty rats were divided into two groups.
Fifteen (15) rats (test group) wore an occlusal bite pad made of composite resin on the maxillary right
first molar for a week (T1). The same rats wore a second composite bite pad for another week on the left
first molar in order to rebalance dental occlusion (T2). Fifteen rats were included in an untreated control
group. All the rats underwent total body radiographs at T0 (before the occlusal pad was placed), at T1
(one week after application of a resin occlusal bite pad on the maxillary left first molar) and at T2 (one
week after application of a second resin occlusal bite pad on the maxillary right first molar). A scoliotic
curve developed in all the test rats at T1. There were no alterations of spinal position observed in any of
the control rats. Additionally, the spinal column returned to normal condition in 83% of the test rats when
the balance in occlusal function was restored. The alignment of the spinal column seemed to be influ-
enced by the dental occlusion.
Dr. Michele DÕAttilio received his D.D.S.
degree in 1987 from the Faculty of
Dentistry, University of L’Aquila, Italy.
He has been a researcher in the
Department of Orthodontics at the
University of Chieti, Italy, since 2000 and
is chairman of orthodontics at the same
faculty. Dr. D’Attilio has written many
clinical and research articles.
Investigators have sought to produce scoliotic curves
in several animal species using a variety of tech-
niques.1-15 These experiments on various animal
models suggest possible anatomic or functional influence
for each of these elements (spinal, neuromuscular, meta-
bolic, endocrine) in the etiology of idiopathic scoliosis. In
dentistry, the study of the relationship between occlusal
problems and the spine are of increasing interest. This is
the result of a greater incidence of pain in the muscles of
the neck, trunk, the upper and lower limbs, and in the
temporomandibular joints (TMJ) of patients with occlusal
dysfunction.16
There are several conditions that impede normal trunk
alignment in the frontal plane, and it should be interesting
to investigate whether such conditions also affect dental
occlusion.
Previously, Muller-Wachendorff17 investigated 420
children with various postural disorders. Among the 164
children diagnosed as scoliotic, 60 (37%) were observed
to have crossbites. Later, a noticeable prevalence of uni-
lateral crossbite (11-15%) was shown in a group of
Swedish children.18-19 Finally, Huggare, et al.20 investi-
The Influence of an Experimentally-Induced
Malocclusion On Vertebral Alignment in Rats: A
Controlled Pilot Study
Michele DÕAttilio, D.D.S.; Maria R. Filippi, M.D.; Beatrice Femminella, D.D.S.;
Felice Festa, M.D., M.S., D.D.S., Ph.D.; Simona Tecco, D.D.S.
OCCLUSION
Manuscript received
August 19, 2003; revised
manuscript received
October 13, 2004;
accepted
October 18, 2004
Address for reprint
requests:
Dr. Michele D’Attilio
c/o Dr. Simona Tecco
Via Le Mainarde 26
65121 Pescara
Italy
E-mail: simtecc@tin.it
gated 22 young adults who had been previously treated
for scoliosis and were using a Boston-brace and were
diagnosed or had a history of treatment for lateral cross-
bite in 55% of the subjects, compared with 18% in the
control group.
Since these studies were based on a cross-sectional
study method, no conclusion could be drawn with regard
to the mechanism used or Òwhat caused whatÓ. For that
reason, the purpose of this study was to evaluate any
changes occurring in the position of the spinal column on
the frontal plane in a group of rats, both when the occlu-
sion was experimentally altered and then following reha-
bilitation of the condition. Previous studies17-2l have
underlined a notable prevalence of cross-bite malocclu-
sion in patients diagnosed with, or recently treated for,
scoliosis. In the current study, the occlusion was altered
in such a way as to induce the rat into a crossbite occlusal
relationship.
Material and Methods
Thirty female Sprangue Dawley rats weighing 350 g
(average age, 309 days) were used in the study: 15 in the
study group and 15 in an untreated control group. All the
rats in the two groups underwent spinal radiographs at
baseline (T0) before any change in occlusion had occurred.
In the rats in the study group, an occlusal bite pad made
of composite and measuring 0.5 mm in height, was
applied to the upper right molar, (Figure 1).
To apply the bite pad, the following procedures were
used. The rats were anesthetized in a bell-shaped glass
chamber, which contained ether-soaked cotton balls. The
rats were also injected intra-peritoneally with benzodi-
azepine (5-10 mg/Kg body weight) and ketamine (20-40
mg/Kg body weight). The occlusal pad was made from a
controlled measure of composite resin (Figure 1). A
hollow plastic cylinder, 0.5 mm in height, was used to
measure the composite which was then spread over the
whole occlusal surface of the molar. The unilateral pad
created a dysfunction in the bite position as an induced
premature occlusal contact. The occlusion on a single
premature contact was not stable so the rats adjusted their
bite to a more stable position. They deviated the way they
closed their jaw, either to the right or the left side. This
deviation in closing movement caused a crossbite occlu-
sion on the side to which the mandible deviated. The
altered bite position is evident when looking at the
ratÕs occlusal midline which deviated to the left side
(Figure 2).
The rats in the study group wore the occlusal pad for
one week (T1) then underwent another total body radi-
ograph of the spinal column to evaluate any changes as a
result of the experimental premature contact. At this time
(T1), the rats in the control group also underwent another
total body radiograph. After the radiographs were taken,
a second occlusal pad was applied to the left upper molar
in order to rebalance the occlusion. The new contact on
the opposite side induced the rats to straighten their clos-
ing movement. The rats in the study group wore the
second occlusal pad for one week (T2), then both groups
underwent the last total body radiographs of the spinal
column.
Radiographs
At T0, T1, and T2, each rat had undergone two total
body radiographs, the first one on the frontal plane and
the second on the sagittal plane. In order to perform
EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS D’ATTILIO ET AL.
120 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE APRIL 2005, VOL. 23, NO. 2
Figure 1
In the rats in the study/therapy group, a composite bite pad (less
than 0.5 mm in height) was applied to the upper right molar. One
week later, the same was applied to the opposite side to balance the
occlusion.
Figure 2
The lower incisal midline deviated to the left side after the first
occlusal bite pad was applied to the maxillary right first molar.
spinal radiographs in a reproducible and standardized
way and according to the canons of veterinary medicine,
the rats were placed on the table as follows: on their
backs with the spinal column resting on the surface; and
in muscle traction via their fore- and hind-limbs.
Radiographs were taken using ALEM 100KW, 100ma.
Radiographic specifications were 40Kw and 50mA for
0.2 seconds. The distance between the focus and the film
was fixed to 90 cm. Three-M (Minnesota Mining and
Manufacturing Co., St. Paul, MN) photographic films
(24x30) were used. The method used for the procedure
was as follows:
1. A bottomless and lidless metal box (Figure 3A) was
built to an appropriate size to be placed on the radi-
ographic table. The box was equipped with two run-
ners with two metal rods each, parallel to each other
on the horizontal and sagittal planes (Figure 3B).
These rods were used to anchor the fore- and hind-
limbs of the rats and were long enough to nearly
touch the table in order to guarantee traction of the
animals as close as possible to the table.
2. For each rat, the four limbs was anchored in the
metal box by using four bandage-type adhesive
strips of the same length, one for each limb. Before
each of the four limbs were anchored, two reference
lines were drawn on every adhesive strip, each one
perpendicular to the long axis of the strip and a dis-
tance of two cm from each contour of the strips
(Figure 4). These reference lines were necessary to
allow for wrapping the strip around the rods (on the
metal base) and around the limbs the same number of
millimeters. Additionally, the adhesive strips were
always attached by the same operator and at the same
points on the wrists and ankles of the rats and near
the head of the metal rods (Figure 5).
3. A series of lines, perpendicular to the long axis of
the radiographic table, were drawn with a glass
marking pencil by the operator. These lines were
important to allow reroducible radiographs each
time. In fact, for every radiograph, the joints of the
fore- and hind-limbs were positioned using the same
lines (Figure 6). Reference points were thus constant
and unchangeable.
4. Each rat was anesthetized and affixed to the rods of
the runners on the metal box after carefully checking
the alignment of the four limbs using the reference
lines (Figure 6). After the rat was anchored to the
runners, it was then put in traction (Figure 7). The
force was measured using a force gauge and the mea-
surement noted on the chart for each rat (Figure 8).
During successive radiographs (at T1 and T2), the
same force as in the first examination was applied.
The first radiograph (on the frontal plane) was taken
with the rat on its back
with the spinal column
resting on the surface.
The second radiograph
(the lateral body radi-
ograph) was taken soon
after the radiograph on
the frontal plane. The
rats were positioned in
profile while keeping
the four legs affixed to
the rods of the runners
on the metal box and
checking the alignment
of all four limbs care-
fully with regard to the
reference lines.
Variables considered on
radiographs: Rats normally
D’ATTILIO ET AL. EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS
APRIL 2005, VOL. 23, NO. 2 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE 121
Figure 3 (Aand B)
Bottomless, lidless metal box (A) used to position rats to be
radiographed. The box has two runners and two metal rods
parallel to each other on the horizontal and saggital planes (B).
AB
Figure 4
Measured adhesive strips applied two cm from each end of the box.
have 30 vertebrae: seven cervical, twelve thoracic, seven
lumbosacral and four caudal spine vertebrae. Spontaneous
fusion often occurs in the lumbosacral block.
Variables on the frontal radiographs: The C4, T1, T6,
T10, and L4 vertebrae were chosen as reference vertebrae
for the evaluation of the alteration of column posture. A
true vertical was traced on the radiographs parallel to the
margin of the radiograph and intersecting at the center of
the body of the fifth vertebra (which corresponds to the
center of the pelvis) (Figure 9). The centers of C4, T1,
T6, T10, and L4 vertebrae were marked on the radi-
ographs by the same operator (blinded as to the group
identity) and used as reference points. Five variables
were evaluated, respectively: distance (measured in mm)
between the reference points (the centers of the C4, T1,
EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS D’ATTILIO ET AL.
122 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE APRIL 2005, VOL. 23, NO. 2
Figure 5
The rat is anchored into the box for radiographing using the rods and
adhesive strips.
Figure 6
Using perpendicular lines drawn in the box, the ratÕs joints are kept in
alignment.
Figure 7
The rat shown in traction
in preparation for radi-
ographing.
Figure 8
The force used to suspend the rat is measured using a force gauge.
Figure 9
Reference points and lines:
C4 is the center of the fourth
cervical vertebra; T1 is the
center of the first thoracic
vertebra; T6 is the center of
the sixth thoracic vertebra;
T10 is the center of the tenth
thoracic vertebra; L4 is the
center of the fourth
lumbosacral vertebra. The line
representing true vertical was
traced parallel to the margin of
the radiograph and was cen-
tered on a point that was the
same for all radiographs: the
center of the last fifth vertebra.
T6, T10, and L4 vertebrae) and the true vertical. The five
radiographic variables indicated the alignment of the
spinal column, since the greater the distance, the more
inclined that segment of spinal column. The distance was
considered positive if the body of the vertebra was posi-
tioned on the right of the true vertical. Otherwise, it was
considered negative. The overlap between a reference
point and true vertical was considered as 0 value. All
measurements were taken by the same operator, blinded
to the group identity.
Variables on lateral radiographs: The outline of all
vertebrae was traced onto the radiographs by the same
operator (blinded to the group identify) and used as refer-
ence points. The alignment of the spinal column was cal-
culated by using a geometrical construction. The angle
between the tangent line to the upper contour of the upper
vertebra involved in the curvature and the tangent line to
the lower contour of the lower vertebra involved in the
curvature was traced. Perpendicular lines to those just
described were then traced. The downward opening angle
between these two lines defined the angle of the curva-
ture. The greater the angle, the more curved that segment
of the spinal column.
Method Error
In order to evaluate the method error of the radi-
ographic procedure, two radiographs of four animals at
T0 were made after loosening and repositioning the rat.
The measurements of the first and the second radiographs
were taken and the method error was calculated using
DahlbergÕs formula22:
δ = √Σd2/2N
where dis the difference between the first and the
second measurement and Nis the number of double mea-
surements. In order to evaluate the error inherent to the
landmark identification on the radiographs, the same
measurements on 15 radiographs were taken once again
by the same operator a week later and the method error
calculated by using DahlbergÕs formula.
Data
The Statistical Package for Social Sciences program
(SPSS, Inc., Chicago, IL) was used to analyze the data.
Descriptive statistics included means and standard devia-
tions (SD) for each variable considered at T0, T1, and T2.
Since the data did not show a normal distribution, non-
parametric statistics were computed to test significance.
The difference between the test and control groups at
each experimental session (T0, T1, T2) was tested using
the Mann-Whitney ÒUÓ test, and FriedmanÕs two-way
analysis of variance (ANOVA) was used to test the sig-
nificant differences among the distances (mm) between
the reference points (the centers of the C4, T1, T6, T10,
and L4 vertebrae) and the true vertical from T0 to T2. The
Bonferroni corrected WilcoxonÕs signed rank test was
used as a post-hoc test to verify the significance of the
differences between T0-T1, T1-T2, and T0-T2, respec-
tively. Differences were considered significant at p<0.05.
Results
During the weeks from T0 to T1 and to T2, the rats
were observed carefully. During the hours soon after the
first occlusal pad was applied to the upper right molar, the
rats in the study group spent nearly all of their time open-
ing and closing their mouths. However, the presence of
the unilateral occlusal pad did not appear to impair their
activities. After the first occlusal pad was applied, they
were compelled to deviate their jaw-closing movements
to the right or the left side, in order to experience a more
stable occlusal condition. No difficulties in drinking,
feeding, or defending themselves were observed. When
the second occlusal pad was applied to the left upper
molar in order to rebalance the occlusion, the rats in the
study group experienced a new occlusal balance and after
a few tries, were able to open and close their mouths nor-
mally without deviation.
The observation of radiographs [Figure 10 (A-C) and
Figure 11 (A-C)] revealed that no change in the align-
ment of the spinal column occurred in any of the rats that
did not receive an occlusal pad. However, a change in the
alignment of the spinal column was observed in all of the
rats that received a unilateral occlusal pad. The deformi-
ties were similar to those found in human idiopathic sco-
liosis (Figure 10B and Figure 11B). The convexity of
the curve was directed to either side, with no consistent
preference. No rat developed limb paralysis or showed
difficulty in walking or running.
At T2, when the second occlusal pad was applied to the
left upper molar to rebalance the occlusion, radiographs
revealed the straightening of the spinal columns of all the
rats in the study group.
Error in landmark localization and in the radiographic
procedure was less than 5% of the total variance in the
whole sample for all the variables. The analysis of the
tracings on total body radiographs revealed no significant
differences in each variable between the study and the
control group at T0 and no significant changes in the
alignment of vertebrae from T0 to T1 and T2 in the con-
trol group (Table 1). On the contrary, significant changes
in the alignment of T6 vertebra (p<0.01) and T10 verte-
bra (p<0.05) were observed in the study group at T1,
compared with the results at T0 (Table 1).
D’ATTILIO ET AL. EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS
APRIL 2005, VOL. 23, NO. 2 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE 123
Finally, no significant changes in the alignment of the
spinal column were observed in the study group from T0
to T2, but significant changes in T6 vertebra and T10
vertebra were observed from T1 to T2 (respectively,
p<0.05 and p<0.02) (Table 1). At T1, rats in the study
group showed a significantly different alignment of
all vertebrae when compared with rats in the control
group (Table 1). The observation of radiographs re-
vealed that no significant change in the alignment of the
spinal column occurred in any of the rats on the lateral
plane (Table 2).
EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS D’ATTILIO ET AL.
124 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE APRIL 2005, VOL. 23, NO. 2
Figure 10 (A-C)
Radiograph of one rat in the study group at T0 (A) before application of the composite; at T1 (B) one week after application of the composite; and at
T2 (C) one week after composite application on the balancing side. Note the convexity of curvature at T1, especially in the thoracic area.
ABC
Figure 11 (A-C)
Radiograph of one rat in the study group at T0 (A) before application of the composite; at T1 (B) one week after application of the composite; and at
T2 (C) one week after composite application on the balancing side. Note the convexity of curvature at T1, especially in the thoracic area. This rat
deviated to the opposite side from the rat in Figure 10.
ABC
Discussion
In the current study, the change in the occlusion of the
rats was brought about by using an occlusal bite pad
made of composite that was less than 0.5 mm in height.
In order to assure that the occlusal pad was made in the
same shape and size for the whole study sample, a quan-
titative method was followed. The same hollow plastic
cylinder of 0.5 mm in height was used to measure the
amount of composite to ensure the same amount was used
for all rats (Figure l). The same operator then spread the
composite resin over the whole occlusal surface of the
molar tooth for all the rats. Finally, particular care was
taken to make the second occlusal pad the same height as
the previous pad in the same animal, since this important
procedure allowed the restoration of normal occlusion.
The method employed for taking radiographs was mainly
conceived to assure the standardization and reproducibil-
ity of the radiographic procedure. In fact, the procedure
described in the Materials and Methods (points 1 and 2)
section allowed the researcher to employ the same posi-
tioning procedure for all the rats. The procedure described
in point 3 allowed for the exact repositioning of the rat
in the metal box as it was positioned for the first radi-
ograph. The aim of the positioning procedure was to
show the spinal curvature without error. The extremely
flexible nature of the ratÕs spine and the normal, exten-
sive thoracolumbar kyphosis necessitated very careful
positioning of each rat, because false-lateral curves could
have easily been generated, especially if the normal tho-
racolumbar kyphosis was misaligned. We realized that
any deviation of the kyphosis from the sagittal plane
could easily be misinterpreted as a long lateral curve in
the radiographs. Care was taken to eliminate false curves
by keeping the limbs symmetrical, keeping pelvic and
shoulder girdles parallel to each other, and ensuring that
the kyphosis was aligned in the sagittal plane as much as
possible. Since the evaluation of method error showed no
significant differences between a set of two radiographs
taken twice using this procedure and confirmed the valid-
ity of the method, the authors strongly recommend the
use of this procedure in future investigations of this type.
On the total body radiographs, the alignment of the
spinal column was defined as the distance (mm) between
the centers of C4, T1, T6, T10, and L4 vertebrae marked
on the radiographs and true verticalÑa line traced on the
radiographs parallel to the lateral margins and intersect-
ing the center of the pelvis (Figure 9). The greater the
distance, the more inclined that segment of the spinal
column was considered.
This method is unusual for the evaluation of scoliosis
angle, since CobbÕs angle is more frequently employed.
D’ATTILIO ET AL. EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS
APRIL 2005, VOL. 23, NO. 2 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE 125
Table 1
Spinal Column Misalignment (Mean and Standard Deviation Calculated as Distance Between the
Center of Vertebral Bodies and the Vertical Line) in the Both the Study and the Control Groups
T0 T1 T2 Difference
Vertebra Test Difference Control Test Difference Control Test Difference Control Test Control
C4 2.90±3.96 NS 3.20±3.99 -0.53±4.56 p<0.05 3.10±3.85 1.30±1.30 NS 2.87±3.96 NS NS
T1 2.60±4.51 NS 2.90±2.98 -1.63±5.37 p<0.01 2.83±3.80 1.37±1.37 NS 2.90±2.87 NS NS
T6 1.40±5.08* NS 1.73±4.77 -4.87±5.45‡ p<0.01 1.93±4.11 1.17±1.17 NS 1.87±4.84 p<0.05 NS
T10 0.67±4.94† NS 1.30±4.95 -6.07±10.35§ p<0.05 1.53±5.13 2.60±2.60 NS 1.30±5.03 p<0.01 NS
L4 0.57±3.36 NS 1.80±6.55 -4.10±7.05 p<0.05 0.67±2.70 -0.23±4.10 NS 0.67±3.70 NS NS
*Significantly different from T1 at p<0.01 level
†Significantly different from T1 at p<0.05 level
‡Significantly different from T2 at p<0.05 level
§Significantly different from T2 at p<0.02 level
CobbÕs angle is defined as the upper angle between the
perpendicular line to the tangent line to the superior con-
tour line of the first upper vertebra included in the patho-
logical curvature and the perpendicular line to the tangent
line to the inferior contour line of the first lower vertebra
included in the pathological curvature. The choice of
variables was made by the authors, because the variables
employed in our study appear to better show the level of
regional balance, instability, and alignment of the spinal
segments. CobbÕs angle, however, better clarifies the
shape of the whole scoliotic curvature. In order to evalu-
ate the level of regional changes rather than the degrees
of the whole curvature, the authors preferred to employ
this particular method. Among all the vertebrae, C4, T1,
T6, T10, and L4 were selected as indicators of spinal
column alignment; firstly, because they represent all the
segments in the spinal column of the rats (except for the
caudal spine segment); and secondly, because the dis-
tances between C4 and T1, T1 and T6, T6 and T10, T10
and L4 may be nearly considered the same. Rats, in fact,
normally have 30 vertebrae: seven cervical, twelve tho-
racic, seven lumbosacral and four caudal spine vertebrae.
In the current study, the radiographs at T1 were taken
one week after the positioning of the first occlusal pad,
and those at T2 one week after the second occlusal pad
was applied. The choice of a week as the period for wear-
ing the unilateral occlusal pad and, then, the second
occlusal pad, was made by considering the average life-
span of a man at 70 years and of a rat at three years and
the average time necessary in humans for the appearance
of the first symptoms of temporomandibular joint pathol-
ogy after an alteration of occlusion, which was calculated
(Dr. Farrar to Dr. DÕAttilio in a personal communication,
1984) to be six months.
Expressing the month and years in days and laying out
the following proportion:
25550 days: 180 days = 1085 days : x days,
the result of x=7.64 days is obtained.
After a week from the application of the second occlusal
bite pad, all the rats in the study as well as in the control
group underwent another radiograph to evaluate the
effects induced on the spinal column by rehabilitation of
the occlusal plane.
There are a number of theories on the etiology and
pathogenesis of idiopathic scoliosis. These theories
include genetic,23 musculoskeletal,24-25 metabolic, and
chemical factors,26 as well as abnormalities of the central
nervous system.27 Based upon these theories, many inves-
tigators have sought to produce scoliotic curves in several
species using a variety of techniques.1-15
The assumption on which this study was based is that
there is an anatomical and functional relationship between
the stomatognathic apparatus and the spinal column. This
relationship is hypothesized by several authors based
upon various observations16,28-31:
1. Neurophysiological principles of convergence
and sensitization: A constant input, such as a nociceptive
input, on second-order neurons may increase the sensitiv-
ity of these neurons. Then, non-nociceptive neural
impulses from other areas within the same segment,
which converge onto these neurons, may give rise to
altered sensations from these areas. For the craniocervi-
cal region, for example, a constant nociceptive input
from, the upper part of the trapezius muscle can lead to an
increased sensitivity of the spinal trigeminal nucleus and,
consequently, non-nociceptive stimuli from the mastica-
tory system would then lead to painful sensations from
the trigeminal region.28 This occurs as the different input
converges onto the nucleus caudal portion of the trigemi-
nal spinal tract nucleus.29 As a consequence, in a recent
study a significantly higher prevalence of cervical spinal
pain was observed in a group of patients with cran-
iomandibular pain than in a matched control group with-
out craniomandibular pain. The prevalence of cervical
spine pain was higher in patients with craniomandibular
arthrogenous pain (64%) than in patients with cran-
iomandibular myogenous pain (58%) or with both myo-
genous and arthrogenous pain (53%);16
EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS D’ATTILIO ET AL.
126 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE APRIL 2005, VOL. 23, NO. 2
Table 2
Spinal Column Curvature (Mean and Standard Deviation) Calculated as the Downward Opening
Angle on Lateral Radiographs in Both the Study and the Control Groups
T0 T1 T2
Mean SD T0vs.T1 Mean SD T1vs.T2 Mean SD T0vs.T2
Control group 6.67 4.68 NS 6.53 4.36 NS 6.60 4.60 NS
Study group 6.73 4.25 NS 5.40 2.99 NS 8.00 4.09 NS
2. Anatomical details: There is an anatomical rela-
tionship between the mandible and the cervical column,
since the cranium and mandible have muscular and liga-
ment attachments to the cervical area. The function of the
head, neck, and jaws is closely interrelated, forming a
combined functional system.28 Festa, et al.30 observed a
significant correlation between mandibular length and
cervical lordosis angle on lateral skull radiographs (in
natural head position) in Caucasian adult women with a
skeletal class II malocclusion. The longer the mandibular
body was, the straighter the cervical column appeared to
be.30 In a group of 50 Caucasian adult women with inter-
nal derangement, compared with a control group of 50
Caucasian women without internal derangement, cephalo-
metric tracings on lateral skull radiographs in natural
head position showed a significantly lower cervical lor-
dosis angle (p<0.05).31
Based on these observations, which underline an
anatomical and a neurophysiological interrelationship
between the spinal column and the stomatognathic appa-
ratus, the purpose of this study was to evaluate any
changes occurring in the positioning of the spinal column
on the frontal plane in a group of rats, both when the
occlusion was experimentally altered and following reha-
bilitation of the condition. Many transversal studies
reported a history or the presence of cross-bite in young
patients with idiopathic scoliosis.17,20 In the current study,
the alteration to the occlusion was performed in such a
way as to induce the rat into a cross-bite occlusal rela-
tionship.
The most important findings of this study were that the
functional cross-bite induced by a unilateral occlusal pad,
caused a significant change in the alignment of the T6
vertebra (p<0.01, from T0 to T1) and T10 vertebra
(p<0.05, from T0 to T1) in the group of treated rats and,
what is more important, this change disappeared at T2,
when the second occlusal pad was applied to the other
side. In fact, no significant difference was observed
between T0 and T2. Between group analysis revealed sig-
nificant differences in the alignment of all the vertebrae
considered at T1 (Table 1). This evidence leads to the
postulate that an occlusal functional cross-bite might con-
tribute to experimental scoliosis in rats. Interestingly,
scoliosis curvature observed in the rats of the study group
involved a long thoracic curve, and the spinal deformities
were similar to scoliosis observed after lesions induced in
the hypothalamus, produced by Yamada, et al.32 and to
scoliosis induced in a group of bipedal rats using pinealec-
tomy by Machida, et al.14
However, the associations between the occlusal fea-
tures and lesions in the hypothalamus or melatonin defi-
ciency secondary to pinealectomy are unknown. The
occurrence of scoliosis in our sample was probably asso-
ciated with the fact that a normal spine requires a precise
and delicate mechanical balance of equilibrium and pos-
tural tone. Disturbances in the primary structures, support
structures, position of the spine, and related neural or
muscular components could possibly result in develop-
ment of scoliosis. The result obtained may be considered
a movement of adaptation that occurs in relationship to
the constraints imposed by morphology and degrees of
freedom of each joint, as well as the elasticity and archi-
tecture of the surrounding soft tissue. These adaptations
may be specific to the constraints imposed by muscle
tissue in reference to a new occlusal equilibrium and, in
consequence, affect the overall geometry of the spinal
column. These adaptations may reflect a strategy used by
the neuromuscular system to move the center of gravity
over the sacral base and within the base of support, pro-
viding a horizontal vestibular and visual frame of refer-
ence. At the time of the initial evaluation, the rats had no
discrepancy in their occlusion, but after the cross-bite
was induced, they all showed a curvature of the spine.
We noted that the convexity of the observed curve was
directed to either side, with no consistent preference, sug-
gesting that the side of the curve cannot be predicted, or
more probably, that the sample in this investigation was
too small to study the probability of spinal inclination to
one side or the other. Further investigations, using larger
samples, could possibly clarify the real mechanism of
these findings and forecast the direction of spinal column
inclination.
The mechanism may be related to the consequential tilt
of the first cervical vertebra (Cl) that affects the tilt of
adjacent vertebra, destabilizing the vertical alignment of
the spine, changing the functionality of each muscle, and
in the end, an asymmetrical distribution could then affect
the orientation of the vertebrae, contributing to the func-
tional deformity of the spine.21-22
Although from our observations it could be assumed
that the current study mechanism induced vertebral mis-
alignment, our sample was possibly too small to predict
the side of vertebral inclination.
The relationship between the cervical part of the spinal
column and the stomatognathic apparatus has been previ-
ously shown by several authors. For example, in a
cephalometric study of adult Caucasian females in skele-
tal class II, Festa, et al.30 showed a significant correlation
between mandibular length and cervical lordosis angle.
DÕAttilio, et al.31 also showed a significantly lower cervi-
cal lordosis angle in patients with internal derangement
when compared to a control group of patients without
internal derangement. Moya, et al.33 investigated the
effect of an occlusal stabilization splint on craniocervical
D’ATTILIO ET AL. EXPERIMENTALLY INDUCED MALOCCLUSION IN RATS
APRIL 2005, VOL. 23, NO. 2 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE 127
relationships in 15 patients with muscle spasms in the
sternocleidomastoid and trapezius muscles. Their patients
underwent two lateral skull radiographs, with and with-
out a splint inserted in the mouth. They found that soon
after the insertion of the splint, the device caused a sig-
nificant extension of the head on the cervical spine and a
significant decrease in cervical spine lordosis. Hellsing,
et al.34 studied 125 children, aged 8, 11, and 15 years, for
the development of cervical lordosis (measured on lateral
skull radiographs), thoracic kyphosis, and lumbar lordo-
sis (measured using a kyphometer) and showed a highly
significant correlation between the thoracic and lumbar
curvatures and a negative correlation between the inclina-
tion of the lower part of the cervical spine (from the
fourth to the sixth vertebra) to a true vertical and the tho-
racic curvature.
In a follow-up investigation, Hellsing, et al.35 showed
an association between thoracic kyphosis and some cran-
iofacial morphological variables. The curvature of the
thoracic spine increased with facial prognathism and the
anteroposterior dimension of the mandible. This may
suggest that the curvature of the thoracic spine has a com-
pensatory mechanism in maintaining body balance.
Although these results concerned humans and may be not
appropriate for describing postural adaptations in rats,
they might suggest a close relationship between the stom-
atognathic apparatus and the spinal column which could
be valid for all vertebrate animals. Based on the findings,
the scoliotic curvature observed in our sample was prob-
ably related to the consequential tilt of the first cervical
vertebra (C1) which affects the tilt of adjacent vertebra,
destabilizing the vertical alignment of the spine.
Limitations of the Study
This study must be considered a pilot investigation
because of the small sample, and because the results did
not make clear any long-term effects of the occlusal pad
on spinal alignment, since the period for wearing the first
or the second occlusal pad was only one week. No con-
clusions about the possible application of the results to a
human model were possible, since the results of the cur-
rent study were based upon a quadruped model (rat)
which could influence the development of particular
mechanisms of adaptation. Further research in this area
will clarify the relationship between occlusion and the
functional aspects of body posture and the spinal curva-
ture in bipedal vertebrate animals and in humans.
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Dr. Maria R. Filippi received her M.D. degree from the University of
Chieti, Italy in 1992. She is currently a staff member in the Department of
Orthodontics and Gnathology, School of Dentistry, University of Chieti.
Dr. Beatrice Femminella received her D.D.S. degree in 2000 from the
Faculty of Dentistry, University of Chieti, Italy. She is currently a staff
member in the Department of Orthodontics and Gnathology, School of
Dentistry, University of Chieti.
Dr. Felice Festa is the director of the Department of Orthodontics and
Gnathology, School of Dentistry, and a full professor of orthodontics at
the University of Chieti, Italy. He is also director of post graduate
courses in clinical gnathology and orthodontics at the same university.
He received his M.D. degree from the University of Rome in 1979, a
D.D.S. degree from the same university in 1982, and earned an M.S. in
orthodontics in 1985 from the University of Cagliari. In 2001, he was
nominated National Referee Professor in Orthodontics at the Professor
National College. Dr. Festa has authored many clinical and research
articles.
Dr. Simona Tecco received her D.D.S. degree in 1999 from the Faculty
of Dentistry, University of Chieti, Italy. Since then she has been an
assistant in the Department of Orthodontics and Gnathology at the same
university. Dr. Tecco is working toward a Ph.D. degree in oral pathology
prevention at the University of Chieti, Italy.
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APRIL 2005, VOL. 23, NO. 2 THE JOURNAL OF CRANIOMANDIBULAR PRACTICE 129
