Rapid Maxillary Anterior Teeth Retraction En Masse by
Bone Compression: A Canine Model
Chufeng Liu1., Yang Cao2., Conghua Liu1., Jincai Zhang3, Pingping Xu4*
1Department of Orthodontics, Guangdong Provincial Stomatological Hospital, Southern Medical University, Guangzhou, China, 2Department of Orthodontics, Guanghua
College of Stomatology, Sun Yat-sen University, Guangzhou, China, 3Department of Periodontology, Guangdong Provincial Stomatological Hospital, Southern Medical
University, Guangzhou, China, 4Department of Oral and Maxillofacial Surgery, Guangdong Provincial Stomatological Hospital, Southern Medical University, Guangzhou,
Objective: The present study sought to establish an animal model to study the feasibility and safety of rapid retraction of
maxillary anterior teeth en masse aided by alveolar surgery in order to reduce orthodontic treatment time.
Method: Extraction of the maxillary canine and alveolar surgery were performed on twelve adult beagle dogs. After that, the
custom-made tooth-borne distraction devices were placed on beagles’ teeth. Nine of the dogs were applied compression at
0.5 mm/d for 12 days continuously. The other three received no force as the control group. The animals were killed in 1, 14,
and 28 days after the end of the application of compression.
Results: The tissue responses were assessed by craniometric measurement as well as histological examination. Gross
alterations were evident in the experimental group, characterized by anterior teeth crossbite. The average total movements
of incisors within 12 days were 4.6360.10 mm and the average anchorage losses were 1.2560.12 mm. Considerable root
resorption extending into the dentine could be observed 1 and 14 days after the compression. But after consolidation of 28
days, there were regenerated cementum on the dentine. There was no apparent change in the control group. No obvious
tooth loosening, gingival necrosis, pulp degeneration, or other adverse complications appeared in any of the dogs.
Conclusions: This is the first experimental study for testing the technique of rapid anterior teeth retraction en masse aided
by modified alveolar surgery. Despite a preliminary animal model study, the current findings pave the way for the potential
clinical application that can accelerate orthodontic tooth movement without many adverse complications.
Clinical Relevance: It may become a novel method to shorten the clinical orthodontic treatment time in the future.
Citation: Liu C, Cao Y, Liu C, Zhang J, Xu P (2011) Rapid Maxillary Anterior Teeth Retraction En Masse by Bone Compression: A Canine Model. PLoS ONE 6(10):
Editor: Samuel J. Lin, Harvard Medical School, United States of America
Received June 16, 2011; Accepted September 26, 2011; Published October 19, 2011
Copyright: ? 2011 Liu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The study was supported by the Guangdong Provincial Natural Science Fund (http://gdsf.gdstc.gov.cn/) (No. 8151026003000008) and Guangdong
Provincial Science & Technology Projects (http://www.gdstc.gov.cn/) (No. 2009B080701032, No. 2009B030801182). The funders had no role in study design, data
collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: email@example.com
. These authors contributed equally to this work.
Distraction osteogenesis (DO) is manifested as rapid new bone
growing by the mechanical stretching of the pre-existing bone tissue
which takes advantage of osseous remodeling capabilities of the
callus at the osteotomy and/or corticotomy sites. This innovative
concept of bone biology opens a new vista for minimally invasive
treatment of jaw deformities. So far, DO technique has achieved
great success in the treatment of severe bone deficiencies, including
micrognathia, sequelae of cleft lip and palate, and maxillofacial
bone defects. In stark comparison, very few advances have been in
using DO technique to treat excessive bone disorders such as
prognathism. Based on the mechanical principle of DO, it will be
fascinating to know the biological response when the bone is
imposed on the compression force by reverse activating of the
distractor, usually applied in DO for supplying the distraction force.
Maxillary protrusion is a common dentognathic deformity.
Orthodontics and orthodontics combined with anterior segmental
osteotomy are the common treatment strategies. The combined
orthodontic and anterior segmental osteotomy therapy can
markedly reduce the length of treatment over the conventional
orthodontic treatment and result in immediate improvement of the
facial profile. But its various postoperative complications including
ischemic necrosis of the anterior segment, wound dehiscence at the
osteotomy site, and devitalization of the teeth adjacent to the
osteotomy site deter many patients from seeking the treatment .
The more conventional and commonly-used orthodontic treat-
ment for maxillary protrusion heavily relies on the biological tooth
movement , which happens at a limited rate and thus prolongs
the treatment to 2 years for most patients . Even more time is
required for adult patients, who often wish their treatment could
be completed as soon as possible .
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In clinical studies, osteotomies or corticotomies, defined as the
osteotomies of the cortical bone, have been combined with
orthodontics to accelerate the tooth movement . Among these
procedures, alveolar corticotomies have been used for many years.
Selective buccal and lingual decortication of the alveolar bone is
commonly used to accelerate orthodontic tooth movement .
Several studies suggest that bone response with corticotomy occurs
by regional accelerated phenomenon (RAP), which induces
demineralization in the alveolar bone around the dental roots.
RAP is initially derived from the rare cases of fracture healing
[7,8]. The term ‘‘regional’’ refers to the demineralization of both
the cut site and the adjacent bone. The term ‘‘acceleratory’’ refers
to an intensified bone response in cuts which extends to the
marrow . This technique dramatically reduces the treatment
time because once the bone has demineralized, there is an
opportunity to move teeth rapidly through the demineralized bone
matrix before the alveolar bone remineralizes [5,6,10–13]. The
alveolar corticotomy technique has been modified over the years
to eliminate possible risks of the procedure, including periodontal
damage, devitalization of the teeth and osseous segments because
of inadequate blood supply.
Similar to DO, ‘‘distraction of periodontal ligament’’ was first
conceptualized in 1998  and later in 2002 another similar term
‘‘dentoalveolar distraction osteogenesis’’ was created . The
basic idea behind these concepts is to use a tooth-borne, custom-
made intraoral distraction device to move the canines at a rate of
0.5 to 1.0 mm per day towards the distal end after the first
premolar extraction. Their clinical applications prove to be
successful: the duration of orthodontic treatment is greatly
shortened by several months and no clinical and radiographic
evidence of complications such as root fracture, root resorption,
ankylosis, or periodontal problems is ever observed. However,
these reports mainly focus on the movement of a single tooth and
are confined in theoretical frame of DO.
Based on previous studies, we hypothesized that the maxillary
bone could be compressed to achieve rapid maxillary anterior
teeth retraction en masse. In this pilot study, a tooth-borne
distraction device is introduced to six maxillary anterior teeth to
investigate the feasibility and safety of rapid bulk adduction of
these teeth aided by modified alveolar corticotomy technique.
Since stronger force is needed to compress the bone than the single
tooth, its influence on root resorption and periodontal tissue is the
focus of this preliminary study.
All animals tolerated the operation and compressive procedures
fine and their wounds healed well without infection. Additionally,
the beagle dogs did not markedly lose weight. Though they
initially lost less than 5% of total weight, about 0.5–0.6 kg, 2 weeks
post-surgery, their weight recovered to preoperative levels 4 weeks
post-surgery. At 6-week post-surgery, the weight of some animals
even increased by 1.0 kg. The compressive devices remained in
place and intact until they were removed.
At the end of compression, anterior crossbite was evident in the
experimental group, whereas there was no obvious change in
control group. No loosening of teeth, soft tissue dehiscence or bone
necrosis in the operated region appeared. The total amounts of
incisor and premolar movements after consolidation for 1, 14 and
28 days are shown in Table 1. The average total movements of
incisors within 12 days were 4.6360.10 mm and anchorage losses
were 1.2560.12 mm. After 14 to 28 days of consolidation, the
average movements of incisors decreased slightly, but no
significant difference was found among the variables in after 1,
14 and 28 days of consolidation. Though the average mesial
movements of premolars (anchorage losses) increased slightly after
14 and 28 days of consolidation than those on day 1, no significant
difference was found among the variables.
Radiographic examination showed no evidence of complica-
tions in any of the animals, including root fracture, ankylosis, and
alveolar bone height resorption. However, root resorption was
found from the periapical radiographs of incisors in the
experimental group. There were slight lateral root surface
irregularities on the compression side and slight blunting of the
root apex of the third incisors (Fig. 4), whereas root resorption of
other incisors was not obvious. But all the incisor periodontal
ligaments increased in width after the compression in the
experimental group as compared with those before the compres-
sion and in the control group. No obvious dental root resorption
could be observed in the periapical radiographs of control group.
Since root resorption of the third incisor was most serious among
all incisors, it was focused in the following histological assessment.
In addition, lateral cephaloradiographs (Fig. 5) showed anterior
crossbite and slight introversion of the maxillary anterior teeth in
the experimental group.
The representative microphotographs of H&E stained sections
from the experimental group are shown in Figs 6, 7, 8. After 1-day
consolidation, the periodontal ligament was widened and the
fibroblasts and osteoblasts were accumulated on the tension side.
There appeared to be thin projection of bone spicules along the
direction of tooth movement. On the compression side, the
periodontium narrowed and a little hyalinization area and
undermining resorption could be observed. Considerable root
resorption was extended into the dentin, ranging from the
cementoenamel junction to the root apex. Obvious blood vessel
dilatation and congestion in the pulp could also be observed.
After 14-day consolidation, the periodontal ligament was still
widened and the new trabecular bone was striated. Superficial
osteoid calcified partly, and well-organized osteoblasts could be
seen on the tension side. The osteoclast-absorbed osseous tissue in
direct and undermining resorption was still seen on the
compression side. Except for significant inflammatory cell
infiltration, blood vessel dilatation and congestion markedly
decreased in the pulp than those on day 1. After 28-day
consolidation, the periodontal ligament on both sides reverted to
the normal status and new lamina dura formed. Partial repair,
with the resorption cavity walls partly covered with cementum,
was observed on the root surface. Using high-power microscopic
lens, some cementoblasts could be seen distributed on the repaired
Table 1. Amount of incisors distalizations and mesial
movement of the premolars.
Teeth movement (mm)
1-day4.5360.10 5.1460.05 4.0260.12 1.3260.12 1.1960.07 1.1260.05
14-day 4.4060.11 4.3260.08 4.9260.03 1.5860.08 1.4760.04 1.1460.03
28-day 4.5760.02 4.2660.10 4.0860.02 1.4460.04 1.2060.06 1.3960.07
A Canine Model of Rapid Anterior Teeth Retraction
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cementum. Most of the congestion in the pulp had disappeared
except for a small part of infiltrated inflammatory cells.
No change in bone remodeling was found in the H&E stained
sections of the control group (data not shown).
Because orthodontic tooth movement is the result of bone
remodeling secondary to the mechanical force and teeth usually
move at the rate of approximately 1 mm per month, distalizing the
anterior teeth can take up to 8 months and even longer for certain
adult patients . Clinical studies indicate that the duration of
orthodontic treatment is one of the most-complained issues among
the patients. Recently, several groups have reported that it is
possible to quickly move the canines into the first premolar
extraction sites based on the DO theory. In this study, a canine
model is successfully established for rapid maxillary anterior teeth
retraction en masse. We chose beagle dogs for several reasons.
Beagle dogs, a mammalian omnivore, show high similarity in their
teeth structure to human teeth. Specifically, the bone density of
their jaw and alveolar bone is similar to that of human’s and their
periodontal ligament is also similar to human tissues. In addition,
as model experimental dogs, beagle dogs are easy to tame, not
demanding on food, resistant to diseases, and have a high
tolerance to multiple anesthesia procedures. Due to their docile
nature, we could apply the daily distractor advancement and
check the experimental devices in their mouth without anesthesia.
In our model, all of the anterior teeth moved together for about
4.5 mm within 12 days, a rate much faster than the traditional
orthodontic tooth movement. All animals tolerated the experi-
mental procedures well without complications, such as root
fracture, ankylosis, loosening of teeth, soft tissue dehiscence,
alveolar bone losses or bone necrosis in the operated region. The
results of this preliminary animal model study suggest that it is
possible and safe to compress the maxillary bone and achieve
rapid bulk adduction of maxillary anterior teeth aided by the
modified alveolar corticotomy technique. The age of the beagle
dogs used in the study is 24 months, equivalent to 24 years old in
humans. Therefore the current results also suggest that corticot-
omy-assisted orthodontic treatment can be one optimal method
for adult maxillary protrusion patients because of its shorter
duration of treatment than those of conventional orthodontic
Classic orthodontic tooth movement can be divided into 3
periods: initial phase, lag phase, and postlag phase. Unlike the
classic tooth displacement curve , the dental distraction
response under heavy intermittent force is approximately a
straight line that cannot be divided . In this experiment, the
tooth displacement curve of the incisors was not studied during the
distraction. But after consolidation for a certain period, there was
some relapse based on the observation of teeth movement. During
the compression, a little bending of the screw and bar of the
distractor has been observed under the heavy intermittent force.
We speculate that the flexibility of the distractor may be related to
teeth relapse but the exact mechanism needs further studies.
The mechanism of rapid maxillary anterior teeth
retraction en masse achieved by bone compression
Rapid maxillary anterior teeth retraction en masse achieved by
bone compression in this study is different from the technique of
‘‘distraction of periodontal ligament’’ developed by Liou et al. 
or ‘‘dentoalveolar distraction osteogenesis’’ by Kisnisci et al. ,
both of which are essentially based on the principles of DO.
Despite distalization of the teeth to the extraction sites is targeted
by all three techniques, an extra process of compressing the palatal
bone at the same time of decortication is introduced in this study,
which distinguishes the present technique from the other two.
Moreover, the current maxillary anterior teeth retraction en masse
in the form of teeth-premaxilla complex is quite different from the
single tooth by Liou et al  and dentoalveolar distraction by
Kisnisci et al .
In the dental distraction studies from the above two groups,
heavy intermittent force is applied to the canines with screws. The
bend and fracture of the interseptal bone are believed to be the
main reasons for rapid canine retraction . However, several
studies suggest that bone formation with corticotomy-assisted
tooth movement occurs by RAP, a term initially coined to describe
the rare cases of fracture healing [7,9]. Several mechanisms of
RAP have been proposed, including a decrease in the osteoblast
cell number, cell proliferation responses, neovascularization, and
local and systemic mediators. Corticotomy-assisted tooth move-
ment is associated with lack of hyalinization and early tartrate-
resistant alkaline phosphatase staining . The variability in
tooth movement rate is affected by the presence of hyalinization
[20,21]. In this study, less hyalinization was observed on the
compression side of the experimental group. It might be the result
of RAP, which was associated with increased systemic inflamma-
tion markers  and a shift in the number of osteoclast and
osteoblast cell populations resulting in an osteopenic effect .
The mechanism for different periodontal tissue changing and
osteotomic healing between the experiment and control groups
under compressive force is next major question. The profiles of
chemokines, such as the osteoprotegerin/receptor activator of
nuclear factor-kB ligand signaling system, expressed in osteoclasts
and osteoblasts for osteogenesis in response to mechanical stress
have been examined and will be reported in another article as a
follow-up study of this canine model.
The loss of posterior teeth anchorage is less even if there is only
a little relapse during the four weeks of immobilized observation,
therefore achieving a high clinical level of anchorage. The
traditional view believes that most of the loss of posterior teeth
anchorage is caused by excessive orthodontic stress. But in the
course of rapid tooth movement in the distraction of periodontal
ligament and DAD, the majority of molars actually do not move to
the mesial. Only a small number of teeth have minute mesial
movements with almost no loss of anchorage . Liou et al.
believe that this can be explained by the time gap between the
stress application on the canine and anchorage teeth. After the
alveolar bone is partially removed and the resistance is reduced, as
the canine is moved rapidly to the distal end, the anchorage teeth
still remain in the lag phase of tooth movement during the second
and third weeks. In this case, the loss of anchorage is minimal.
Therefore, to prevent the loss of anchorage, the authors emphasize
that the canine should be drawn to the intended position within
three weeks. This view has been generally proved by current
The root apices of the third incisors were not intact and clear in
most of the periapical films of the experimental group. Although
periapical radiographs are still an important tool available for
detecting root resorption in daily clinical practice, they are not
adequate enough to accurately measure resorption. Tissue slices
are frequently used to evaluate root resorption. It is generally
accepted that some root resorption will occur with any orthodontic
tooth movement, and various conditions may affect root
resorption . Microscopic examination of the current slices
showed some serious external root resorption of the third incisors
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in the experimental group, especially after 12 days of compression
and 1 day of consolidation. Partial repair was observed after
consolidation for 28 days. We have treated another batch of beagle
dogs with 0.75 mm per day compression and found similar results
of root resorption and repair (data not shown). Numerous studies
have attempted to describe root resorption repair sequences [25–
27]. According to Owman-Moll et al. , approximately 75% of
root resorption will be repaired by the formation of cellular
cementum on the resorbed surface of the dentin. This process of
forming resorption lacunae followed by cementum ‘‘healing’’ is
considered normal and does not predicate root resorption, unless
the ability of cementum regeneration is less than the extent of
resorption lacunae formation. In general, the duration of the
applied force is a far more critical factor for the root resorption
than the magnitude of the force [29–32]. In spite of the heavy
force applied, the incisors were distalized for only 12 days in this
study. It appears that the initial strain on the teeth resulted in
resorption lacunae formation as previously reported, and that later
cementum repair can occur as predicted. Therefore, the current
findings imply the normal process of transitory rather than
permanent root resorption. The long-term effects of current
treatments on root resorption need further study. In addition, this
study indicates that the third incisor is typically the foothold of all
incisors. A three-dimensional finite element analysis is necessary to
disclose the strain distribution over the compression area in order
to avoid harmful stress on the third incisor.
A modest and transient inflammatory response in the pulp is
observed after routine application of orthodontic force in a
previous study . But in this study, the pulp response was much
more evident. Blood vessel dilatation and congestion in the pulp
with significant inflammatory cell infiltration was obvious one day
after the compression ended. Although the symptoms ameliorated
with the time, there were still a small part of infiltrated
inflammatory cells after consolidation for 28 days. But no necrosis
was observed. Long-term effects on pulp vitality after rapid
movement have not been described in the literature. Liou et al.
 demonstrates that the pulp is still vital in an animal
experimental research even if the tooth was moved rapidly at
the rate of 1.2 mm per week. Therefore, pulp vitality deserves
This study is a preliminary study on the feasibility of rapid
maxillary anterior teeth retraction en masse with a compressive
device. Before this method can be applied clinically, many issues
need to be addressed by future studies. First, the extent of pulp
inflammation and root resorption, two common symptoms under
conventional orthodontic force, need to be closely monitored.
Under conventional treatment, these two symptoms are often
healed or restored when orthodontic force is stopped, suggesting
that they can be tolerated by the body and are acceptable by
clinicians. Although the force applied in our study is heavier than
that used in traditional orthodontic treatment, we still observed
restorative responses of the teeth. This phenomenon indicates that
pulp inflammation and root resorption may also be acceptable in
our model. To further minimize the occurrence of these two
symptoms, we suggest reducing force from 1 compression/day,
0.5 mm/time, which was used in this study, to 2 compressions/
day, 0.25–0.35 mm/time.
Another important issue is pain level. Although we did not
analyze pain level in this study, animals did not show any
abnormal behavior, suggesting that the postoperative pain was not
severe. Furthermore, the daily distractor advancement was applied
in the absence of anesthesia or coercive measures. Held gently in
an experimenter’s hand, although beagle dogs did try to avoid the
advancement, they nevertheless endured the operation well. This
observation suggests that the discomfort or pain induced by our
procedure is within the tolerable range. This is similar to the
reactions of clinical patients under distraction osteogenesis.
Furthermore, in future clinical applications, to make patients
more comfortable, the metal band used in this study can be
replaced with periodontal splinting, which is smaller and more
aesthetically acceptable. In addition, the distraction device applied
in this study can also be replaced with a smaller, more refined
Through animal experiments, this study proves that it is feasible
and safe to achieve rapid maxillary anterior teeth retraction en
masse with a compressive device and aided by modified alveolar
surgical methods. Active bone deposition in the tension area and
bone resorption in the compression area ensured rapid teeth
movement. But root resorption and pulp inflammation were
observed during the distraction. Although they partially recovered
after consolidation, the long-term effects on root resorption, pulp
vitality, and periodontal tissue health need further evaluation.
Under this compressive force, whether the process of callus healing
will change or not and what is the underlying mechanism are the
next major questions we plan to solve.
This is a pilot, animal model study to achieve rapid anterior
teeth movement en masse. If it can be applied to the clinic, it will
greatly reduce the duration of orthodontic treatment. But we
should also note that the compressive device is too big to make
patients feel comfortable and the alveolar surgical method which
involves the upper jaw may deter patients from seeking the
treatment. Therefore, there is still a long way to go to apply this
method to clinical use.
Materials and Methods
Twelve 24-month-old male beagle dogs, weighing 12–16 kg
were selected in this study. They all had intact maxillary and
mandibular permanent teeth showing normal occlusion and good
systemic and periodontal health at the beginning of the
experiments. The animals were housed in an animal facility with
a controlled environment at the Animal Experiment Center of Sun
Yat-sen University and fed with standard laboratory diet and free
access to drinking water. The housing, care, and experimental
protocols were in accordance with the guidelines of the Medical
Institutional Animal Care and Use Committee of Sun Yat-sen
University. After arrival at the facility, all animals were
quarantined for no less than one week. The protocol was
approved by the Academic and Medical Ethic Committee of
Guangdong Provincial Stomatological Hospital, Southern Medical
University (Permit Number: 2008025).
The first dog was used to standardize the procedures and
optimize the efficiency of the interventions; the remaining 11 dogs
started the experiments 4 weeks later. Before each intervention,
the animals were sedated with 3% sodium pentobarbital (30 mg/
kg, intramuscularly, Merck, Germany).
Fabrication of the compressive device
The cone-shaped tooth coronals of the third incisors and
premolars made it difficult to keep the experimental device in
place, so coronal preparation was first carried out with a high-
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speed turbo drill to increase the retention on both sides of the third
incisors and the second and third premolars. The light-curing
composite resin (3 M, USA) was then applied to shape the coronal
contour into a column. Finally, the bilateral maxillary impressions
were taken with a rubber-based impression material (Heraeus
Kulzer Dental, Germany) and an individual tray made of self-
curing acrylic resin. Based on the cast, individual bands for the
anterior teeth and premolars were fabricated. The bands of the
anterior teeth as well as the second and third premolars were
designed united to strengthen the anchorage.
The distractor was designed on the basis of an orthodontic
expander (Xinye Dental Odontological Materials, China), which
was activated using a key. A half turn (180u) activation of the screw
could produce 0.5 mm of distal movement (Fig. 1). The length of
the screw was designed according to the distance between the third
incisor and the second premolar. The custom-made distractor was
soldered on the third incisors bands against the second premolars
to setup the complete tooth-borne compressive device (Fig. 2).
Before cementing the compressive device, alveolar surgery was
All surgical procedures were performed under general anesthe-
sia with sodium pentobarbital and local infiltrated anesthesia with
2% lidocaine hydrochloride (Mingxing Pharmaceutical, China).
Under aseptic conditions, following the maxillary canine extrac-
tion, the labial and palatal cortical plates of the extraction sockets
were grinded and removed with a round carbide bur on both sides,
and extended obliquely towards the lower lateral margin of the
pyriform aperture to weaken its resistance.If the nasopalatal
neurovascular bundle was well protected, the palatal mucoperios-
teal flap was elevated from the palatal alveolar crest of the six
anterior teeth to the apical region to expose the cortical bone
around them. The corticotomy was performed with a round
carbide bur inserted just into the marrow space under water
cooling, and the palatal corticotomy cut stopped right at the
extraction sockets laterally. Then a horizontal labial incision was
made parallel to the gingival margin of the maxillary incisors
beyond the depth of the vestibule. After the lower margin of the
pyriform aperture was exposed, corticotomy was performed with a
small round carbide bur along the margin to connect the bilateral
extraction sockets (Fig. 3). Additionally, a titanium mini-plant as a
marker was placed in the palatal middle of the distal margins of
the first two maxillary molars, which was vertical to the palatal
bone surface. The palate mucoperiosteal flap was repositioned and
the wound was secured by interrupted 1-0 silk sutures after
corticotomy. Another marker was placed in the middle of the root
apex of two upper central incisiors, which was vertical to the labial
surface. The tooth-borne compressive device was then cemented
in place. After that, both sides of the mandibular canines were
delivered in order to avoid interfering with the occlusion. All
animals were daily administered penicillin G (800,000 units,
intramuscularly) as antibiotic prophylaxis for one week.
The animals were randomly assigned to the experimental or
the control group. For nine dogs as the experimental group in the
study, their distractors were activated immediately after the
surgery because the time span was critical for the teeth
movement. The distractors were activated 0.5 mm per day,
continuously for 12 days to distalize the anterior teeth. After the
teeth movement was completed, the distractors were left in place
for consolidation. The remaining three dogs as the control group
received no compression. Three animals in the experimental
group were randomly selected to be euthanized by excess
anesthesia after consolidation for 1 day, 14 days and 28 days,
Figure 1. Custom-made appliance for distraction.
Figure 2. Occlusion comparison of experiment groups before
and after the treatment. (a, b) before the treatment. (c, d) after the
treatment. Occlusal views show that the upper incisors were retracted
after 12 days of distalization.
Figure 3. Areas of corticotomy (brown). (a) area on the palatal side.
(b) area on the buccal side.
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respectively. And one in the control group was sacrificed at the
last day of consolidation. Each dog underwent radiographic and
histological examinations after sacrifice.
The dog was placed in a custom-made box with the head fixed
outside. The periapical radio videography (RVG) of maxillary
incisors were taken immediately after the surgery (before the
compression) and before sacrifice. The X-ray tube (Planmeca
Intra, Finland) was positioned 5 cm from the animal’s teeth. The
machine settings were 63 kV, 8 mA with 2 s exposure time. A
digital lateral cephaloradiograph was obtained with another X-ray
tube (Sirona, Germany) 7 cm from the animal’s right-side face and
the machine settings were 73 kV, 15 mA and 9.4 s exposure time.
The changes in the periodontal ligaments, alveolar bone
deposition and resorption, root resorption of the maxillary teeth,
as well as anterior occlusion were evaluated before and after the
The maxillary segments, including the maxillary incisors and
extraction sockets, were dissected after removing the compressive
device and fixed in 10% formalin for 48 h and then decalcified
with 10% EDTA for 60 days. After decalcification, the specimens
were imbedded in paraffin, sectioned sagittally (6 to 8 mm) with a
microtome, and stained with hematoxylin and eosin (H&E). The
histological observation was performed using a conventional
bright-field light microscope (Olympus CX41, Japan) and the
images were captured by a camera (Olympus Q Imaging
MicroPublisher 5.0 RTV, Japan). The changes in the periodontal
ligaments, alveolar bone deposition and resorption, root resorption
Figure 4. Periapical films of maxillary anterior teeth. (a) control
group. (b) experiment group. The films show some root defects on the
compressive side of the third incisors in the experiment group after
compression for 12 d and consolidation for 1 d. All the periodontal
ligament space was thicker in the experimental group than the control
Figure 5. Cephalometric films of experiment group before and
after treatment. (a) before the treatment. (b) after compression for
12 d and consolidation for 1 d. The films show a little introversion on
incisors after 12 days of distalization.
Figure 6. Histological microphotographs of compressive side
of third incisiors in experiment groups. Each panel includes two
pictures of H&E staining with the amplifications of 1006(left) and 4006
(right). (a) alveolar resportion after compression for 12 d and
consolidation for 1 d. (b) root defects deep into the dentine after
compression for 12 d and consolidation for 1 d. (c) after 28 d of
consolidation, repaired cementum covering the root defects and some
cementoblasts distributed inside.
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of the maxillary teeth, and pulp condition were evaluated after the
Teeth movement measurement
The distance between the reference markers on the palatal and
the united points of the maxillary central incisor bands was
measured to 0.02 mm with a sliding caliper (Sanfeng, Japan). So
was the mesial margin of the bands on the second premolars with
the palatal markers.
The statistical analysis was performed using SPSS 13.0 program
(PASW, USA) and the results were shown as mean 6 standard
The authors are especially grateful to Drs. Zhiyong Zhang and Rongjian
Pan (Department of Radiology, Guangdong Provincial Stomatological
Hospital, Southern Medical University, Guangzhou, China) for their
precious contribution to the radiographic examination of this study. The
authors also thank Mr. Bingkun Ye for his great work on the fabrication of
compressive devices used in this study.
Conceived and designed the experiments: PX. Performed the experiments:
CL YC CL PX. Analyzed the data: PX JZ. Contributed reagents/
materials/analysis tools: PX. Wrote the paper: CL.
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