Alveolar augmented corticotomy is effective in accelerating orthodontic tooth movement, but the effect only lasts for a relatively short time. Therefore, the purpose of this study was to investigate the underlying biology of the immediate periodontal response to orthodontic tooth movement after a corticotomy with alloplastic bone grafts. The results demonstrated that measurable tooth movement began as early as 3 days after the intervention in beagle dogs. Based on the results and histological findings, augmented corticotomy-facilitated orthodontic tooth movement might enhance the condition of the periodontal tissue and the stability of the outcomes of orthodontic treatment.
New appliances, materials, and mechanics of orthodontic treatment are being developed every day, but much of the biology of orthodontic tooth movement still needs to be clarified. Many adjunctive modalities are available to accelerate orthodontic tooth movement in humans, such as corticotomy [
The initial microscopic changes and early application of orthodontic force have been emphasized in corticotomy-facilitated orthodontic tooth movement [
The purpose of this study was to investigate the immediate periodontal response to a corticotomy with alloplastic bone grafts in beagle dogs.
Five adult male beagle dogs, weighing 10–13 kg, were used in the experiment, and their selection, care, and preparation, together with the surgical protocol, were carried out according to the guidelines for animal experiments (IRB no. KHMC-IACUC2012-024). They were caged separately under regulated conditions and fed a normal diet and water
For the preparation processes and surgical procedures, the animals were anesthetized with a mixture of tiletamine-zolazepam and xylazine, via intramuscular and intravenous injections using a catheter in the vessel of the ear.
Alginate impressions of each beagle were taken to make study models, and orthodontic appliances were custom-made for each model. The canine and fourth premolar teeth were banded to form anchor teeth, and a
Orthodontic appliances were custom-made for each study model. The canine and fourth premolar teeth were banded to form an anchor tooth, and a
Under general anesthesia, 2% lidocaine with 1 : 100,000 epinephrine was also infiltrated to the surgical sites. An intrasulcus incision was performed with a no. 12 blade from the canine tooth to the first molar, and a full-thickness flap was lifted. The circumscribing corticotomy (Figure
Surgical procedure. (a) Corticotomy: the circumscribing corticotomy was performed with a round bur (
All of the surgical procedures were performed under sterile conditions to prevent infection. After surgery, antibiotics and anti-inflammatory analgesics were administered by intramuscular injection twice a day for 6 days. A 1% chlorhexidine-gluconate solution dressing was applied simultaneously for infection control. A soft diet was supplied for 1 or 2 weeks and then a normal diet. Mechanical plaque control was performed once a week. The animals were euthanized with an overdose of thiopental sodium after 1 day, 3 days, 1 week, 2 weeks, and 4 weeks following the surgery (Figure
Schematic diagram describing the experiment design.
Following a predetermined time schedule, after the animals were killed, their maxillae and mandibles were dissected, and the sections containing the canine to the fourth premolar teeth were retrieved. The block specimens were rinsed in sterile saline and immediately immersed in 10% neutral-buffered formalin fixatives for 14 days. The block specimens were large, and rapid decalcification was performed for 6 days using 5% nitric acid because it is sufficiently strong [
Histological examinations were conducted using a light microscope (Olympus BX 51, Olympus, Tokyo, Japan) equipped with a DP controller 3.2.276.2 and DP manager 3.1.1.208 (Olympus, Tokyo, Japan). After microscopic examination, a photograph of each slide was taken with a digital camera (Olympus DP 71, Olympus, Tokyo, Japan). With imaging software (cellSens version 1.6, Olympus), we measured the buccal tipping angle (°) and distance (
Statistical data analysis was performed using the R programming language [
Figure
Box plots for the tooth movement measurements. (a) No statistically significant difference in the angular tooth movement was observed over time. (b) However, the linear measurements demonstrated statistically significant differences between 1 day and 3 days and between 2 weeks and 4 weeks after the start of the experiment.
After 1 day of orthodontic movement, a microphotograph of the buccopalatal/lingual section (Figure
Microphotograph of a buccopalatal/lingual section of the 1-day experiment. (a) Maxilla. (b) Higher magnification of (a). On the pressure side, the PDL was compressed. (c) Higher magnification of (b). Extravasation of RBC was observed. (d) Mandible. (e) Higher magnification of (d). Compression of the PDL was shown, and reduced capillaries were identified. (f) Higher magnification of (e). The number of cells was reduced, and grafted MBCP+ particles were lost in the process of making the histological section; the red
At 3 days, the PDL was more severely compressed and fewer cells were found in the PDL space (Figure
Microphotograph of a buccopalatal/lingual section of the 3-day experiment. (a) Maxilla. (b) Higher magnification of (a). On the pressure side, the PDL was more severely compressed. (c) Higher magnification of (b). Few cells were observed in the PDL space. (d) Mandible. (e) Higher magnification of (d). In common with the maxilla, the PDL was severely more compressed on the pressure side. (f) Higher magnification of (d). Extravasation of RBC was observed in the PDL space. (g) Tension side at the lingual bone crest. The tension side showed abundant cells compared with the pressure side. (h) Higher magnification of (g). Active osteoblasts forming new bone were observed. Grafted MBCP+ particles were lost in the process of making the histological section; the red
At 1 week after the start of the experiment, most of grafted MBCP+ particles were well maintained (Figure
Microphotograph of a buccopalatal/lingual section of the 1-week experiment. Most of the grafted MBCP+ particles were well maintained. (a) Maxilla. (b) Higher magnification of (a). On the pressure side, the PDL space was wider than at 3 days. (c) Higher magnification of (b). Extravasation of RBC was observed in the PDL space. (d) Tension side at the palatal bone crest. The tension side showed abundant cells compared with the pressure side and a widened PDL space. (e) Higher magnification of (d). Abundant PDL fibroblasts were seen. (f) Higher magnification of (d). Active osteoblasts forming a new bone were observed. (g) Mandible. Most of the grafted MBCP+ particles were well maintained. (h) Higher magnification of (g). Pressure side. The PDL was compressed. (i) Higher magnification of (g). The tension side showed a widened PDL space. Masson’s trichrome stain. Original magnification was ×12.5 for (a) and (g), ×100 for (b), (d), (h), and (i), and ×400 for (c) and (f).
At 2 weeks, undermining resorption and a resorption bay were observed on the buccal pressure side (Figures
Microphotograph of a buccopalatal/lingual section of the 2-week experiment. (a) Maxilla. Most of the grafted MBCP+ particles were well maintained. (b) Higher magnification of (a) at the crest area. Undermining resorption on the pressure side was observed. (c) Higher magnification of (b). Extravasation of RBC was observed in the PDL space. Resorption bays, which indicate undermining resorption on the pressure side, were also observed. (d) Higher magnification of (a) at the buccal bone surface. New bone formation surrounding the grafted MBCP+ particles was observed. Grafted MBCP+ particles were bridged by newly formed bone. (e) Higher magnification of (d). Abundant osteoblasts were forming new bone. (f) Higher magnification of (a). Osteoblasts were forming a new bone island. (h) Higher magnification of (a). Grafted particles encircled by new bone were bridged with the buccal bone surface. (j) Higher magnification of (a). New bone was formed in the PDL space at the buccal tension area. New bone was formed from the bone. (l) Mandible. Most of the grafted MBCP+ particles were well maintained. (m) Higher magnification of (l) at the crest area. Grafted particles were resorbed by osteoclasts. (n) Higher magnification of (m). (o) Higher magnification of (l). (p) Higher magnification of (l). Bone and root surface resorption by osteoclasts were observed. (q) Higher magnification of (l). Undermining resorption at the buccal bone in the PDL area was observed. (r) Higher magnification of (q). Many osteoblasts filled the resorption bay. (s) Higher magnification of (l). Active new bone formation was found at the buccal bone surface in the apical area. (t) Higher magnification of (s). Many osteoblasts were forming a new bone encircling the grafted MBCP+ particles. (u) Higher magnification of (s). Osteoclastic and osteoblastic activities were both observed. (v) Higher magnification of (l). New bone islands were formed. (w) Higher magnification of (v). (x) Higher magnification of (v). Abundant osteoblasts were actively forming new bone islands. Masson’s trichrome stain. Original magnification was ×12.5 for (a) and (l); ×100 for (b), (d), (f), (h), (j), (m), (o), (q), (s), and (v), and ×400 for (c), (e), (g), (i), (k), (n), (p), (r), (t), (u), (w), and (x).
At 4 weeks after the start of the experiment, new bone formation along the PDL formed a new buccal bone wall on the pressure side (Figure
Microphotograph of a buccopalatal/lingual section of the 4-week experiment. (a) Maxilla. Most of the grafted MBCP+ particles were well maintained. New bone formation along the PDL formed a new buccal bone wall. ((b) and (c)) Higher magnification of (a) at the crest area. (d) Higher magnification of (a). The bone-derived mesenchymal matrix bordered the PDL-derived mesenchymal matrix. A new bone island was formed in the center of the bone-derived mesenchymal matrix. (e) Higher magnification of (d). Osteoblasts and osteocytes were observed. (f) Higher magnification of (a). The grafted MBCP+ particles were bridged with newly formed bone in the bone-derived mesenchymal matrix on the buccal side. (g) Higher magnification of (f). Entrapped osteocytes and aggregated osteoblasts were observed. (h) Higher magnification of (a). (i) Higher magnification of (h). New bone was formed in the center of the grafted MBCP+ particles at the buccal side. ((j) and (l)) Higher magnification of (a). The palatal tension side at the crestal (j) and apical (l) areas. ((k) and (m)) Higher magnification of (j) and (l), respectively. Aggregated osteoblasts and active form of osteoblasts were seen. (n) Mandible. (o) Higher magnification of (n) at the crestal area. New bone forming a buccal bone wall and crest was observed. (p) Higher magnification of (n). Native bone (red star) and new bone (yellow star). (q) Higher magnification of (n). New bone (yellow star) was formed on the outer and inner surface of the native bone (red star). ((r), (s), and (t)) Higher magnification of (n). The outer portion of the bone-derived mesenchymal matrix. Grafted MBCP+ particles were bridged by the newly formed bone. Masson’s trichrome stain. Original magnification was ×12.5 for (a) and (n), ×100 for (b), (c), (d), (f), (h), (j), (l), (o), (p), (q), (r), (s), and (t), and ×400 for (e), (g), (i), (k), and (m).
The biological mechanism by which the tooth movement is facilitated after a corticotomy has been suggested to be mediated by a regional acceleratory phenomenon [
In most experiments in dogs or rats, corticotomy-facilitated tooth movement was observed at a rate of about 1 mm per month, which was almost double that observed on the control side [
Despite the similar pattern between the angular and linear changes, the linear measurements exhibited a statistically significant difference while the angular changes did not. Linear measurements are assessed between two points while degrees of angles are measured between three points, from which a variation in angular measurements can be produced. This may be the cause of the larger variation in angular measurements than in linear measurements.
A typical cell-free zone on the pressure side and an inflammatory reaction were seen on the 1- and 3-day slides (Figures
On the 1-week slide, we observed that the PDL space was widened at the pressure side compared with that of the 3-day slide (Figure
Interestingly, new bone surrounding the graft materials was observed on the compression side on the 2-week slides (Figure
From the findings of the 4-week sections, the new bone formation in the center of the MBCP+ graft material on the buccal side was very distinctive (Figures
The slides taken at 2 and 4 weeks did not show a distinctive loss of periodontal attachment, and the small areas of root resorption that were seen were not significant.
Orthodontic patients have complained about the length of their treatment, and it has become necessary to develop adjunctive methods to tackle this problem [
Although there is no doubt that this procedure could align teeth within a shorter period of time [
The combination of corticotomy with an alveolar graft was introduced by Wilcko et al. and is referred to as accelerated osteogenic orthodontics or periodontally accelerated osteogenic orthodontics [
Tooth movement that was thought to be difficult or impossible to produce in the past has become possible due to the development of orthodontic mechanics and new appliances and materials. Therefore, orthodontic treatment is mainly limited by the scope of the alveolar bone, and orthognathic surgery is required when this limit is exceeded. If an augmented corticotomy could increase the alveolar bone volume, this would help patients who have a limited amount of supporting alveolar bone.
Augmented corticotomy surgery is not free from some morbidity. It also requires a skilled clinician, and there may be some discomfort to patients and additional costs.
The findings from this study suggest that measurable tooth movement starts as early as 3 days after augmented corticotomy-facilitated orthodontic treatment and that this procedure might enhance the condition of periodontal tissue and the stability of orthodontic treatment outcomes.
The authors declare that they have no conflict of interests. The authors also certify that no financial support was received from commercial sponsors to conduct this study or the preparation of this paper.
Hyung-Joo Choi and Dong-Yeol Lee contributed equally to this study.
This work was supported by the National Research Foundation of Korea, funded by the Korean government (Grant no. 2012R1A5A2051388).