Corticision is a technique used to accelerate orthodontic tooth movement. This study investigated the effects of Corticision on paradental remodeling in cats undergoing orthodontic tooth movement. The results showed that Corticision led to less hyalinization of periodontal tissue and more direct bone resorption compared to orthodontic force alone. New bone formation was also accelerated with Corticision. Histologically, Corticision sites healed more rapidly with new bone formation filling defects. Quantitatively, Corticision increased the rate and amount of new bone formation up to 3.5 times compared to orthodontic force alone. Therefore, Corticision can be an efficient method to accelerate orthodontic tooth movement and associated al

1. Original Article
Effects of Corticision on Paradental Remodeling in
Orthodontic Tooth Movement
Su-Jung Kima; Young-Guk Parkb; Seung-Goo Kanga
ABSTRACT
Objective: To investigate the biologic effects of Corticision on alveolar remodeling in orthodontic
tooth movement.
Materials and Methods: In this study, 16 cats were divided into 3 groups: group A, only orthodontic force (control); group B, orthodontic force plus Corticision; and group C, orthodontic force
plus Corticision and periodic mobilization. Histologic and histomorphometric studies were performed on tissue specimens on days 7, 14, 21, and 28.
Results: Extensive direct resorption of bundle bone with less hyalinization and more rapid removal
of hyalinized tissue were observed in group B. The accumulated mean apposition area of new
bone on day 28 was observed to be 3.5-fold higher in group B than in the control group A.
Conclusions: Corticision might be an efficient procedure for accelerating orthodontic tooth movement accompanied with alveolar bone remodeling. (Angle Orthod. 2009;79:284–291.)
KEY WORDS: Corticision; Regional acceleratory phenomenon (RAP); Alveolar remodeling; Tooth
movement
INTRODUCTION
their biologic mechanism is based on the regional acceleratory phenomenon (RAP). In 1983, Frost7 demonstrated that regional noxious stimuli of sufficient
magnitude can result in markedly accelerated reorganizing activity in the osseous and soft tissues; he
termed this cascade of physiologic healing processes
as the RAP. This phenomenon is characterized by a
burst of the localized remodeling process, which accelerates healing, particularly following the surgical
wounding of cortical bone.
Surgical injury is a potentiating factor for the induction of RAP. The use of supplemental dentoalveolar
surgeries to accelerate tooth movement has been recommended. For rapid canine retraction, Liou and
Huang8 proposed periodontal ligament distraction, and
Iseri et al9 reported dentoalveolar distraction in accordance with the principles of distraction osteogenesis.
Selective alveolar decortication by Wilcko et al.10 invoked a RAP, leading to a transient osteoporotic condition. These modified surgical techniques were reported to be effective in reducing clinical orthodontic
treatment time. However, the actual drawback was little acceptance by patients due to the aggressive nature of these procedures, increasing postoperative discomfort, and the risk of complications.
‘‘Corticision’’ was introduced as a supplemental dentoalveolar surgery in orthodontic therapy to achieve
accelerated tooth movement with minimal surgical in-
Application of a mechanical force causes tooth
movement because of remodeling changes in the
paradental tissues. Recent cellular, molecular, and tissue-level studies1 on the biologic mechanism of tooth
movement suggest that a mechanical force is not the
only stimulus for inducing tooth movement. Although
clinical orthodontic systems generally use mechanical
forces to induce bone remodeling, the use of pharmaceutical,2–3 electromagnetic,4–5 laser,6 and surgical
stimuli in combination with the mechanical force for
accelerating orthodontic tooth movement has attracted
considerable scientific interest.
A common feature of these various stimuli is that
a
Assistant Professor, Department of Orthodontics, Oral Biology Research Institute, College of Dentistry, Kyung-Hee University, Seoul, Korea.
b
Professor and Chairman, Department of Orthodontics, Oral
Biology Research Institute, College of Dentistry, Kyung-Hee University, Seoul, Korea.
Corresponding author: Dr Seung-Goo Kang, Assistant Professor, Department of Orthodontics, College of Dentistry, KyungHee University, 1 Hoegi-Dong, Dongdaemoon-Ku, Seoul 130701, Korea
(e-mail: orthodrk@khu.ac.kr)
Accepted: April 2008. Submitted: February 2008.
ᮊ 2009 by The EH Angle Education and Research Foundation,
Inc.
Angle Orthodontist, Vol 79, No 2, 2009
284
DOI: 10.2319/020308-60.1

2. ‘‘CORTICISION’’ IN ORTHODONTIC TOOTH MOVEMENT
Table 1. Administration Schedule of Fluoresceins in Group IV
Injection Time
24
7
14
21
28
Hours before intervention
Days after intervention
Days after intervention
Days after intervention
Days after intervention
Fluorescein
Detected
Color
Oxytetracycline
Calcein
Alizarin red
Oxytetracycline
Alizarin red
Yellow
Green
Red
Yellow
Red
tervention. In this technique, a reinforced scalpel is
used as a thin chisel to separate the interproximal cortices transmucosally without reflecting a flap. Because
Corticision has the clinical value of accelerating tooth
movement, it is regarded as a convenient procedure
for both patients and orthodontists. The purpose of this
study was to elucidate the biologic effects of Corticision on alveolar remodeling in orthodontic tooth movement in cats.
MATERIALS AND METHODS
In this study, 16 domestic male cats weighing 2.8–
3.5 kg were used. The cats were divided into three
groups, designated as groups A, B, and C. Thirty-two
canine teeth were included in the experiments. The
treatment protocol for each group was as follows:
Group A: Only orthodontic force (control)
Group B: Orthodontic force plus Corticision
Group C: Orthodontic force plus Corticision and periodic mobilization
In all experimental animals, the group B and C treatment protocols were applied to the left and right maxillary canines, respectively. The control animals were
individually separated from the experimental ones to
rule out the possibility of systemic acceleratory phenomenon (SAP) following surgical injury. These three
groups were further divided into four subgroups according to the duration of force application: group I, 7
days; group II, 14 days; group III, 21 days; and group
IV, 28 days. The cats in group IV were intramuscularly
injected with oxytetracycline hydrochloride (Fluka, Chi-
285
na; yellow orange; 30 mg/kg), calcein (Fluka, Switzerland; green; 10 mg/kg), and alizarin red (Fluka, UK;
red; 30 mg/kg) to label the newly formed mineralized
bone for quantitative analysis. The injection schedule
is summarized in Table 1.
The maxillary second and third premolars on both
sides of all animals were connected with flowable
composite resin (3M Unitek, Monrovia, Calif) that was
extended onto the buccal surfaces to reinforce anchorage. Single buccal tubes (MBT, 3M Unitek) were
bonded to the buccal surface of third premolars with
Transbond (3M Unitek). Canine brackets (MBT, 3M
Unitek) were bonded to the maxillary canines, and a
0.016 ϫ 0.022-inch stainless steel sectional wire
(RMO, Denver, Colo) was passively inserted from the
canine brackets to the buccal tubes. The canines were
retracted using 0.010 ϫ 0.030-inch precalibrated
closed Sentalloy coil springs (Ormco Co, Orange, Calif)
(Figure 1B). The orthodontic force exerted by the appliance was 100 g at the beginning of the experiment.
The magnitude of force was checked every week and
was reactivated if required.
After local anesthesia, Corticision was performed on
the mesiobuccal, distobuccal, and distopalatal aspects
of both maxillary canines in the experimental groups
(Figure 1A). The mesiopalatal aspect was excluded
due to the extremely thin palatal bone with a suture
line, which had been confirmed in the cat skull. A reinforced surgical blade (No. 15T, Paragon, Sheffield,
UK) capable of making a surgical incision with a minimum thickness of 400 ␮m was employed. The blade
was positioned on the interradicular attached gingiva
at an inclination of 45Њ–60Њ to the long axis of the canine and was inserted gradually into the bone marrow
by malleting the blade holder penetrating the overlying
gingiva, cortical bone, and cancellous bone. The surgical injury was left 2 mm from the papillary gingival
margin in order to preserve the alveolar crest and was
extended 1 mm beyond the mucogingival junction because of the presence of a narrow attached gingiva in
cats. The blade was pulled out by a swing motion.
Mobilization was performed only on the right maxil-
Figure 1. Photographs of experimental canine in cat. (A) Corticision on the mesiobuccal side of the upper canine. (B) Orthodontic appliance
in place. (C) Additional manipulation.
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3. 286
lary canines (group C) using a pincet immediately following Corticision and was repeated every 3 days
throughout the experimental period. Postoperative
care included gentamicin (DaeSung Co, Seoul, Korea;
0.1 mL/kg) injections for 3 days, tooth brushing, and
daily hexamedine (Bukwang Co, Seoul, Korea) irrigation.
Tissue blocks were resected from the separated
maxillae, including the canines, the surrounding paradental tissues, and Corticision site. They were fixed in
10% neutral buffered formalin, decalcified in 10% ethylene diamine tetraacetic acid (EDTA) solution, dehydrated in a series of ethyl alcohol concentrations, embedded in paraffin, and longitudinally sectioned in the
mesiodistal direction parallel to the direction of orthodontic force application. The 4-␮m sectioned slices
were examined under a light microscope with hematoxylin and eosin stain and Masson’s trichrome stain.
For the histomorphometric analysis, nondecalcified
specimens were prepared from the group IV cats.
These were examined under an ultraviolet (UV) fluorescent microscope (Olympus BH-2, Olympus Co, Tokyo, Japan) with a UV filter (␭ ϭ 515 nm). Microphotographs of all specimens were obtained using a digital
charge-coupled-device (CCD) camera (KAPPA
PS30C) and were processed by a computer (Intel
Pentium, 4.2 GHz). An outline of the labeled bone was
traced from the microphotographs, and the areas of
newly formed mineralized bone were measured using
an image analysis software (Metreo version 2.5, KAPPA Image Base, KAPPA Optoelectronics, Accusoft
Co, Gleichen, Germany). A subsequent examination
of the slides by an oral pathologist confirmed these
evaluations.
RESULTS
Light microscopic findings of the compression side
are shown in Figure 2. In the control group, extensive
hyalinization of the periodontal ligament (PDL) and indirect resorption of the bundle bone adjacent to the
compressed PDL was observed from the marrow
spaces on day 7. On day 14, indirect resorption was
widespread, and areas of local unresorbed bundle
bone were observed with the remaining hyalinized
PDL. These findings corresponded to the lag phase of
tooth movement. On day 21, resorption activity in the
existing bundle bone ceased temporarily, causing
markedly wide and traumatic PDL. In the Corticision
group, the compressed PDL on day 7 contained less
hyalinized tissue and more viable PDL cells than in the
control group. Multinucleated osteoclast-like cells appeared on the margin of the bundle bone adjacent to
the compressed PDL, thereby resulting in direct bone
resorption subjacent to these cells. On day 14, the
Angle Orthodontist, Vol 79, No 2, 2009
KIM, PARK, KANG
wide area of old bundle bone was resorbed leading to
the development of large resorption cavities with increased recruitment of osteoclast-like cells. This facilitated the resumption of tooth movement followed by
tissue remodeling as well as osteoid formation on the
tension side.
The microscopic findings of the tension side are
shown in Figure 3. In the control group, band-like osteoid formation was observed on day 7, which is associated with slow tooth movement including the
movement within the PDL. New bone formation associated with stretched Sharpey’s fibers and proliferative PDL cells was observed on day 14. The osteoblasts gradually flattened and developed into quiescent lining cells, and a few of them became embedded
in the newly formed bone matrix on day 21. In the
Corticision group, spike-like osteoid formation associated with rapid tooth movement was observed along
with proliferative PDL cells and active osteoblasts on
day 7. The osteoblasts were plump and vigorous and
produced a thick layer of osteoid. On day 14, the number of osteoblasts and new osteocytes increased in
the actively forming bone matrix. This newly formed
bone containing multiple newly developed marrow
spaces was easily distinguishable from the old lamellar bone. The process of lamellation by the remodeling
of the new bone had progressed on day 21.
The microscopic appearance of the healing processes at the Corticision site is shown in Figure 4.
After 21 days, healing progressed in group B at the
mesiobuccal aspect of the injury site. New bone developed at the site of the bone defect, and lamellation
of the new bone was almost complete at this stage.
On the contrary, the surgical gap was still wide, and
both the resorption and the apposition of bone continued in group C.
Fluorescent microscopic findings are shown in Figure 5. Triple-fluorochrome labeled surfaces are an index of new mineralized bone formation. The lines demarcated the amount of new bone formed 7, 14, 21,
and 28 days after treatment. While sharp and thin labeling lines were evident on the alveolar wall ahead
of the direction of tooth movement in the control group,
diffuse and thick lines were observed in groups B and
C. These thick bands implied that the formation rate
of new bone was accelerated at the time of fluorochrome injection. The amount and the rate of bone
formation were similar in groups B and C, except for
the remodeling pattern. In group B, active remodeling
of the lamellar bone was observed to occur around the
new Haversian systems at days 14–21; this was indicated by multiple concentric circles labeled in red
(stained by first alizarin red) and yellow (subsequently
stained by second oxytetracycline).
The histomorphometric analysis indicated that the

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‘‘CORTICISION’’ IN ORTHODONTIC TOOTH MOVEMENT
Figure 2. Microphotographs of periodontal tissue on compression side (100ϫ): (A) Control group on day 7. (B) Group B on day 7. (C) Group
C on day 7. (D) Control group on day 14. (E) Group B on day 14. (F) Group C on day 14. (G) Control group on day 21. (H) Group B on day
21. (I) Group C on day 21. Arrows mean the direction of bone resorption. The compressed PDL in the Corticision group contained less
hyalinized tissue and more viable cells than the control group, resulting in direct bone resorption. (A–I) Hematoxylin and eosin (H&E) stain. b
indicates alveolar bone; p, PDL; r, root; h, hyalinization.
mean apposition length (mm) and accumulated mean
apposition area (mm2/mm) were higher in the experimental groups than in the control group during all experimental periods (Figure 6). The mean apposition
rate of the control group peaked on day 21 after demonstrating low values for the first 14 days, while it
peaked earlier, ie, on day 14 in the experimental
groups (Figure 7). There was no remarkable difference
in the accumulated apposition area between groups B
and C; however, it was 3.5-fold higher in group B
(0.2771 mm2/mm) than in the control group (0.0798
mm2/mm; Table 2).
DISCUSSION
Corticision could activate catabolic remodeling in the
direction of tooth movement. This was represented by
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KIM, PARK, KANG
Figure 3. Microphotographs of bone resorbing cells on compression side on day 14 (400ϫ): (A) Control group. (B) Group C. The resorption
lacunae with osteoclast-like cells (small arrows) headed against the direction of tooth movement (large arrow) in the control group (undermining
resorption), but headed for the direction of tooth movement in group C (frontal resorption). p indicates PDL; TM, the direction of tooth movement.
Figure 4. Microphotographs of periodontal tissue on tension side (100ϫ): (A) Control group on day 7. (B) Group B on day 7. (C) Group C on
day 7. (D) Control group on day 14. (E) Group B on day 14. (F) Group C on day 14. (G) Control group on day 21. (H) Group C on day 21.
More rapid formation and maturation of osteoid tissue was seen in the experimental groups than in the control group. (A–F) Hematoxylin and
eosin (H&E) stain. (G–H) Masson’s trichrome stain. b indicates alveolar bone; p, PDL; r, root; ot, osteoid tissue; ob, old bone; nb, new bone.
extensive direct resorption of bundle bone with less
hyalinization and more rapid removal of hyalinized tissue in group B than in the control group. Corticision
accelerated the anabolic remodeling activity as well.
On day 28, mean apposition area of the mineralized
bone was observed to be 3.5-fold higher in group B
Angle Orthodontist, Vol 79, No 2, 2009
than in the control group. Histologic findings revealed
neither pathologic changes in the paradental tissues
nor root resorption following ‘‘Corticision.’’
For accelerating orthodontic tooth movement, it is
essential to minimize hyalinization of the PDL tissue
or to stimulate the removal process of the hyalinized

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‘‘CORTICISION’’ IN ORTHODONTIC TOOTH MOVEMENT
Figure 5. Microphotographs of the alveolar bone healing at the Corticision site with hematoxylin and eosin (H&E) stain (40ϫ). (A) Group B on
day 21. (B) Group C on day 21. Arrows mean the injury site. Delayed healing of the bone defect was seen in group C.
tissue. Considering that it is impossible to control the
force magnitude clinically not to produce hyalinization,
in the view of a biologic approach rather than a mechanical control, the lag phase of tooth movement can
be shortened by stimulating the removal of hyalinized
tissue. This can be attributed to the RAP because it
stimulates cell-mediated responses around the tooth,
thereby providing a favorable microenvironment for tissue remodeling. Various researchers have focused on
controlling the microenvironment of the alveolar bone
by using the RAP in an attempt to reduce tissue resistance.10 The transient osteoporotic condition involved increased release of calcium, decreased bone
density, and increased bone turnover, all of which
would facilitate tooth movement.11 This mechanism
based on the RAP differed from the classical concepts
of tooth movement such as the pressure-tension theory,12 bone-bending theory,13 mechanostat theory,14
and bony block movement in corticotomy.15
It is important that the cortical bone itself is not a
barrier or resistance to orthodontic tooth movement.
Garg16 emphasized that the RAP is primarily a phenomenon observed in the cortical bone. This new concept of cortical remodeling enabled the continuous advancement of supplemental surgical procedures involving minimal and conservative interventions. Germec et al 17 revealed that single-sided partial
corticotomy in the mandible appeared to be sufficient
to stimulate rapid tooth movement.
Corticision minimized the degree of the surgical injury by excluding flap reflection. Only mucoperiosteal
flap reflection without any decortication, as studied by
Yaffe et al,18 could serve the RAP, resulting in widening of the periodontal ligament space and tooth mobility without any force application. However, the possible complications after flap surgery, such as crestal
bone resorption and bone dehiscence were troublesome.18 Frost7 stated that the duration and intensity of
the RAP are proportional to the extent of injury and
soft tissue involvement in the injury. Hence, it was nec-
Table 2. Measurements for Histomorphometric Analysis
Group
Group A
(Control)
Group B
(Corticision)
Group C
(Corticision
and Mobilization)
Measurements
Mean
Mean
SD
Mean
Mean
SD
Mean
Mean
SD
apposition length, mm
apposition area, mm2/mm
apposition length, mm
apposition area, mm2/mm
apposition length, mm
apposition area, mm2/mm
7 Days
14 Days
21 Days
28 Days
Total
0.0140
0.0118
0.0041
0.0723
0.0600
0.0220
0.0452
0.0472
0.0154
0.0375
0.0283
0.0177
0.0860
0.0738
0.0484
0.1015
0.1030
0.0505
0.0421
0.0396
0.0034
0.0371
0.0635
0.0255
0.0672
0.0528
0.0422
0.0015
0.0001
0.0000
0.0736
0.0798
0.0390
0.0801
0.0795
0.0385
0.0950
0.0798
0.0262
0.2690
0.2771
0.0337
0.2940
0.2808
0.0366
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KIM, PARK, KANG
Figure 6. Microphotographs of fluorescence on tension side at 28 days after ‘‘Corticision.’’ (A) Control group. (B) Group B. (C) Group C. More
new bone was formed in the experimental groups than in the control group. p indicates PDL; ob, old bone; nb, new bone.
Figure 7. (A) Mean apposition rate and (B) accumulated mean apposition area on tension side. The mean apposition area was 3.5-fold higher
in group B than in the control group.
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8. ‘‘CORTICISION’’ IN ORTHODONTIC TOOTH MOVEMENT
essary to investigate whether Corticision was a logical
modification to sufficiently elicit the RAP for accelerating tooth movement.
Clinically, additional manipulation intended to
lengthen the duration of the RAP is initiated immediately after Corticision and repeated every 2 weeks
thereafter. In this experiment, it was performed every
3 days considering the difference in the time cycle between humans and cats. This manipulation would involve the interception of the lamellation process of woven bone at the injury site and provide repeated microdamage. However, the effect of periodic manipulation on the remodeling of alveolar bone proper and
on the rate of tooth movement could not be elucidated.
Although additional manipulation would delay the healing process at the injury site, this was insufficient to
last the duration of the RAP and the SAP.
CONCLUSIONS
• Corticision stimulated orthodontic tooth movement in
28 days by accelerating the rate of alveolar bone
remodeling.
• The biologic exploration of Corticision is crucial for
broadening the scope of orthodontics by reducing
the treatment duration.
ACKNOWLEDGMENT
Supported by the Kyung-Hee University Research fund in
2005 (20051041), Seoul, Korea (ROK).
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