Effects of Externally Applied, Cyclical, Low Magnitude Forces on Orthodontic Tooth Movement in Rats

Orthodontic tooth movement requires external orthodontic forces to be converted to cellular signals that result in the coordinated removal of bone on one side of the tooth (compression side) by osteoclasts, and the formation of new bone by osteoblasts on the other side (tension side). The length of orthodontic treatment can take several years, leading to problems of caries, periodontal disease, root resorption, and patient dissatisfaction. It appears that the velocity of tooth movement is largely dependent on the rate of alveolar bone remodeling. Pharmacological approaches to increase the rate of tooth movement are limited due to patient discomfort, severe root resorption, and drug-induced side effects. Recently, externally applied, cyclical, low magnitude forces (CLMF) have been shown to cause an increase in the bone mineral density of long bones, and in the growth of craniofacial structures in a variety of animal models. In addition, CLMF is well tolerated by the patient and produces no known adverse effects. However, its application in orthodontic tooth movement has not been specifically determined. Since factors that increase alveolar bone remodeling enhance the rate of orthodontic tooth movement, we hypothesized that externally applied, cyclical, low magnitude forces (CLMF) will increase the rate of orthodontic tooth movement. In order to test this hypothesis we used an in vivo rat orthodontic tooth movement model. Our specific aims were: Specific Aim 1: To develop an in vivo rat model for tooth movement. We developed a tooth movement model based upon two established rodent models (Ren and Yoshimatsu et al, See Figure 1.). The amount of variation of tooth movement in rats exposed to 25-60 g of mesial force activated viii from the first molar to the incisor for 4 weeks was calculated. Specific Aim 2: To determine the frequency dose response of externally applied, cyclical, low magnitude forces (CLMF) for maximal tooth movement and osteoclast numbers. Our working hypothesis for this aim was that the amount of tooth movement would be dose dependent on the frequency of application of the CLMF. In order to test this working hypothesis, we varied the frequency of the CLMF from 30, 60, 100, and 200 Hz, 0.4N, two times per week, for 10 minutes for 4 weeks, and measured the amount of tooth movement. We also looked at the number of osteoclasts for the different frequencies; we hypothesized an increase in osteoclasts for the dose respnse of different frequencies. Specific Aim 3: To determine the effects of externally applied, cyclical, low magnitude forces (CLMF) on PDL proliferation. Our working hypothesis for this aim was that PDL proliferation would increase with CLMF. In order to test this hypothesis we compared CLMF (30 Hz, 0.4N, two times per week, for 10 minutes for 4 weeks) performed on the left side (experimental side), to the non-CLMF side, on the right (control side). This was an experimental study with 24 rats in total. The experimental group contained fifteen (15) rats in total, and they all received a spring plus a different frequency of CLMF. Three (3) received a spring and CLMF at 30 Hz, 0.4N for 10 minutes. Six (6) received a spring and CLMF at 60 Hz, 0.4N for 10 minutes. Three (3) received a spring and CLMF at 100 Hz, 0.4N for 10 minutes. Three (3) received a spring and CLMF at 200 Hz, 0.4N for 10 minutes. The control group contained six (6) rats, and received only a spring. An additional ix three (3) rats received CLMF (30 Hz, 0.4N, two times per week, for 10 minutes for 4 weeks) only, with no spring, and were used only for histological purposes. Rats were subjected to the application of orthodontic force from their maxillary left first molar to their left central incisor. In addition some of the rats received externally applied, cyclical, low magnitude force (CLMF) on their maxillary left first molar. micro-CT was used to measure the amount of orthodontic tooth movement. The distance between the maxillary first and second molars, at the most mesial point of the second molar and the most distal point of the first molar (1M-2M distance) were used to evaluate the distance of tooth movement. Immunohistochemistry was performed with TRAP staining and BrdU quantification. Externally applied, cyclical, low magnitude forces (CLMF) do appear to have an effect on the rate, while not significant, of orthodontic tooth movement in rats. It appears that lower CLMF decreases the rate of tooth movement, while higher CLMF increases the rate of tooth movement. Future studies with larger sample sizes are needed to clarify this issue. CLMF does not appear to affect the proliferation in PDL cells, and has no effect on the number of osteoclasts.

Orthodontic tooth movement in the prednisolone-treated rat

Adverse effects of corticosteroids on bone metabolism raise concerns as to whether steroid treatment may influence orthodontic movement. This study examined the effect of prednisolone on orthodontic movement using an established rat model. The corticosteroid treated group (N = 6) was administered prednisolone (1 mg/kg) daily, for a 12-day induction period; the control group (N = 6) received equivalent volumes of saline. On day 12, an orthodontic appliance was placed which exerted 30 g of mesial force to the maxillary first molar. Animals were sacrificed on day 24 and tooth movement was measured. Sagittal sections of the molars were stained with haematoxylin and eosin, and for tartrate-resistant acid phosphatase (TRAP) activity. While there were no significant differences in the magnitude of tooth movement between the 2 groups, steroid-treated rats displayed significantly less root resorption on the compression side and fewer TRAP-positive cells within the PDL space on the same side. This suggests steroid treatment suppressed elastic activity.

Experimental model of tooth movement in mice: A standardized protocol for studying bone remodeling under compression and tensile strains

During orthodontic tooth movement (OTM), alveolar bone is resorbed by osteoclasts in compression sites (CS) and is deposited by osteoblasts in tension sites (TS). The aim of this study was to develop a standardized OTM protocol in mice and to investigate the expression of bone resorption and deposition markers in CS and TS. An orthodontic appliance was placed in C57BL6/J mice. To define the ideal orthodontic force, the molars of the mice were subjected to forces of 0.1 N, 0.25 N, 0.35 N and 0.5 N. The expression of mediators that are involved in bone remodeling at CS and TS was analyzed using a Real-Time PCR. The data revealed that a force of 0.35 N promoted optimal OTM and osteoclast recruitment without root resorption. The levels of TNF-alpha, RANKL, MMP13 and OPG were all altered in CS and TS. Whereas TNF-a and Cathepsin K exhibited elevated levels in CS. RUNX2 and OCN levels were higher in TS. Our results suggest that 0.35 N is the ideal force for OTM in mice and has no side effects. Moreover, the expression of bone remodeling markers differed between the compression and the tension areas, potentially explaining the distinct cellular migration and differentiation patterns in each of these sites. (C) 2012 Elsevier Ltd. All rights reserved.

Advancements in the knowledge of induced tooth movement: idiopathic osteosclerosis, cortical bone and orthodontic movement

Movimentar ortodonticamente os dentes por áreas densas do trabeculado ósseo e pelas corticais pode requerer uma redução na intensidade e/ou na concentração das forças aplicadas. em parte, as forças ortodônticas aplicadas são dissipadas e reduzidas pela deflexão óssea que ocorre pelo discreto grau de elasticidade do tecido ósseo em condições de normalidade. Nas áreas de trabeculado denso e nas corticais, essa deflexão deve ser irrisória ou inexistente. Se não houver uma redução na intensidade das forças nessas regiões citadas, toda a força incidirá sobre a estrutura do ligamento periodontal, aumentando o risco de morte dos cementoblastos, hialinização e reabsorções radiculares. Novos trabalhos poderiam avaliar a prevalência dessas consequências em casuísticas selecionadas para essa finalidade, que, assim, deixariam de ser observações aleatórias.

A rat model for orthodontic translational expansive tooth movement

OBJECTIVES To present the development of an experimental model in rats for translational expansive tooth movement. SETTING AND SAMPLE Section of Periodontology at Department of Dentistry Aarhus University. Twenty male Wistar rats in two pilot experimental settings plus seven animals without any intervention serving as controls. MATERIAL AND METHODS The second molar (group P1) or the second and third molar (group P2) in the maxillae of the animals were moved buccally using transpalatal β-titanium springs. In the group P2, two spring types (high force and low force) and two preangulations (0° passive or 30° torsion moment) were tested. The amount and type of tooth movement achieved and the resulting skeletal effect were assessed on microCT images, histological analysis was performed on few selected specimens. RESULTS Expansive translational root movement amounting half a tooth width was achieved. Comparison of the amount of tooth movement at the right and left side of the maxilla showed that the expansion was rather symmetrical in the P2 group. Skeletal widening of the maxilla contributed in the P2 group to approximately one-third of the total root movement, whereas two-thirds were dental movement. CONCLUSION With the model used in the P2 group, further research on translational expansive tooth movement and its effect on the periodontium can be pursued. In models for orthodontic expansion, it is strongly recommended to separately evaluate skeletal and dental effects.

Epidermal growth factor in liposomes may enhance osteoclast recruitment during tooth movement in rats

Objective: To evaluate the effects of local administration of epidermal growth factor (EGF) located within liposomes on recruitment of osteoclasts during mechanical force in rats. Materials and Methods: An orthodontic elastic band was inserted between the left upper first and second molars, to move mesially the first molar. Rats were randomly divided into 4 groups (n = 8): EGF (2 ng/mu L) located within liposomes (group 1), liposomes only (group 2), soluble EGF (2 ng/mu L; group 3), or vehicle alone (group 4). The solutions were injected into the region of the root furcation of the left first molar after elastic band insertion. Tooth movement was measured using a plaster model of the maxilla, and the number of osteoclasts recruited at the pressure side of the first molar was histologically evaluated. Results: Intergroup analysis showed that there was no significant difference between group 2 and group 4 (P >.05) and between group 1 and group 3 (P >.05). However, group 1 and group 3 exhibited greater differences in tooth movement than group 2 and group 4 (P <.05). On the other hand, group 1 showed greater tooth movement than groups 2 and 4 with statistical significance (P <.01). The increase in the number of osteoclasts in group 1 was significantly higher than in the other groups (P <.05). Conclusion: Exogenous EGF-liposome administration has an additive effect when compared with soluble EGF on the rate of osteoclast recruitment, producing faster bone resorption and tooth movement.

Tooth Movement Activates the Central Amygdala and the Lateral Hypothalamus by the Magnitude of the Force Applied

Objective: To determine if the magnitude of the force used to induce incisor tooth movement promotes distinct activation in cells in the central amygdala (CEA) and lateral hypothalamus (LH) of rats. Also, the effect of morphine on Fos immunoreactivity (Fos-IR) was investigated in these nuclei. Materials and Methods: Adult male rats were anesthetized and divided into six groups: only anesthetized (control), without orthodontic appliance (OA), OA but without force, OA activated with 30g or 70g, OA with 70g in animals pretreated with morphine (2 mg/kg, intraperitoneal). Three hours after the onset of the experiment the rats were reanesthetized and perfused with 4% paraformaldehyde. The brains were removed and fixed, and sections containing CEA and LH were processed for Fos protein immunohistochemistry. Results: The results show that in the control group, the intramuscular injection of a ketamine/xylazine mixture did not induce Fos-IR cells in the CEA or in the LH. Again, the without force group showed a little Fos-IR. However, in the 70g group the Fos-IR was the biggest observed (P < .05, Tukey) in the CEA and LH compared with the other groups. In the 30g group, the Fos-IR did not differ from the control group, the without OA group, and the without force group. Furthermore, pretreatment with morphine in the 70g group reduced Fos-IR in these regions. Conclusions: Tooth movement promotes Fos-IR in the CEA and LH according to the magnitude of the force applied. (Angle Orthod. 2010;80:111-115.)

Differential expression of osteoblast and osteoclast chemmoatractants in compression and tension sides during orthodontic movement

Orthodontic tooth movement is achieved by the remodeling of alveolar bone in response to mechanical loading, and is supposed to be mediated by several host mediators, such as chemokines. In this study we investigated the pattern of mRNAs expression encoding for osteoblast and osteoclast related chemokines, and further correlated them with the profile of bone remodeling markers in palatal and buccal sides of tooth under orthodontic force, where tensile (T) and compressive (C) forces, respectively, predominate. Real-time PCR was performed with periodontal ligament mRNA from samples of T and C sides of human teeth submitted to rapid maxillary expansion, while periodontal ligament of normal teeth were used as controls. Results showed that both T and C sides exhibited significant higher expression of all targets when compared to controls. Comparing C and T sides, C side exhibited higher expression of MCP-1/CCL2, MIP-1 alpha/CCL3 and RANKL, while T side presented higher expression of OCN. The expression of RANTES/CCL5 and SDF-1/CXCL12 was similar in C and T sides. Our data demonstrate a differential expression of chemokines in compressed and stretched PDL during orthodontic tooth movement, suggesting that chemokines pattern may contribute to the differential bone remodeling in response to orthodontic force through the establishment of distinct microenvironments in compression and tension sides. (C) 2008 Elsevier Ltd. All rights reserved.

Celecoxib treatment does not alter recruitment and activation of osteoclasts in the initial phase of experimental tooth movement

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Microscopic evaluation of induced tooth movement in traumatized teeth: an experimental study in rats

The clinical management of orthodontic patients with dental trauma before or during the treatment is mainly founded on clinical experience, expert opinions, and individual case reports. It is proposed in the literature that teeth sustaining mild trauma with minor damage to the periodontium (e.g. subluxation) should be followed for a period of time before being subjected to orthodontic forces. A minimum period of 3 months has been proposed. In this study, we used an animal model to investigate whether shorter observation periods could be established in case of mild trauma. The periradicular region of rat molars was examined microscopically to determine the biological events of tooth movement started 15 and 30 days after intentional subluxation using an experimental method to induce dentoalveolar trauma. Thirty adult male Wistar rats were assigned to 6 groups (n = 5): Group 1 (control no trauma/orthodontic movement); Group 2: the animals received an orthodontic device and were sacrificed after 7 days; Groups 3 and 4: dentoalveolar trauma (subluxation) was experimentally induced by the application of an axial force of 900 cN on the occlusal surface of the maxillary right first molar, and the animals were sacrificed after 22 and 37 days, respectively; and Groups 5 and 6: 15 and 30 days, respectively, after force application, an orthodontic device was installed and the rats were sacrificed 7 days later. In G5 and G6, the periodontal ligament and pulp tissue were rich in cellular elements and blood vessels, the alveolar bone was preserved, and the root surface presented only very small areas of surface resorption (cementum), maintaining the characteristics of normality. In conclusion, the microscopic alterations in the gingival and periodontal tissues in response to an experimentally induced mild dentoalveolar trauma simulating subluxation were not sufficient to contraindicate starting the orthodontic movement 15 and 30 days after trauma.

Influence of Orthodontic Dental Movement on the Healing Process of Teeth With Periapical Lesions

The purpose of this study was to histomorphologically evaluate (in dog's teeth) the influence of tooth movement in the healing of chronic periapical lesions. Thirty roots of incisors and premolars of two dogs (1-year-old) were used in this research. After pulpectomy, the root canals remained exposed to the oral environment for 6 months for achievement of periapical lesions. Twenty root canals were biomechanically prepared and received a calcium hydroxide dressing for 14 days before being filled with gutta-percha points and Sealapex sealer. After root canal treatment, some incisors were submitted to orthodontic movement, whereas the other roots remained without orthodontic movement. The orthodontic appliance was removed at 5 months and 15 days after treatment, the dogs were killed 15 days later and the specimens were prepared for histomorphological analysis. The results showed that the orthodontic movement delayed, but did not hinder, the periapical healing process. (J Endod 2006;32:115-119)

Effect of alendronate sodium on tooth movement in ovariectomized rats

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Celecoxib treatment does not alter recruitment and activation of osteoclasts in the initial phase of experimental tooth movement

In a previous study, we reported that the short-term treatment with celecoxib, a nonsteroidal anti-inflammatory drug (NSAID) attenuates the activation of brain structures related to nociception and does not interfere with orthodontic incisor separation in rats. The conclusion was that celecoxib could possibly be prescribed for pain in orthodontic patients. However, we did not analyze the effects of this drug in periodontium. The aim of this follow-up study was to analyze effects of celecoxib treatment on recruitment and activation of osteoclasts and alveolar bone resorption after inserting an activated orthodontic appliance between the incisors in our rat model. Twenty rats (400420 g) were pretreated through oral gavage with celecoxib (50 mg/kg) or vehicle (carboxymethylcellulose 0.4%). After 30 min, they received an activated (30 g) orthodontic appliance, set not to cause any palate disjunction. In sham animals, the appliance was immediately removed after introduction. All animals received ground food and, every 12 h, celecoxib or vehicle. After 48 h, they were anesthetized and transcardiacally perfused through the aorta with 4% formaldehyde. Subsequently, maxillae were removed, post-fixed and processed for histomorphometry or immunohistochemical analyses. As expected, incisor distalization induced an inflammatory response with certain histological changes, including an increase in the number of active osteoclasts at the compression side in group treated with vehicle (appliance: 32.2 +/- 2.49 vs sham: 4.8 +/- 1.79, P<0.05) and celecoxib (appliance: 31.0 +/- 1.45 vs sham: 4.6 +/- 1.82, P<0.05). The treatment with celecoxib did not modify substantially the histological alterations and the number of active osteoclasts after activation of orthodontic appliance. Moreover, we did not see any difference between the groups with respect to percentage of bone resorption area. Taken together with our previous results we conclude that short-term treatment with celecoxib can indeed be a therapeutic alternative for pain relieve during orthodontic procedures.

Induced tooth movement: standardization of terms to describe the effects of forces on the periodontal ligament: compression/Traction instead of Pressure/Tension

There is no reason for Dentistry to use different terms for phenomena defined in Physics, the specific field in which concepts associated with forces are established and adapted. In place of pressure/tension, the compression/traction pair should be used. This study defines each one of these terms and justifies their use. Our contemporary world demands standardized criteria, methods, measures, concepts and terms to ensure that study protocols, results and applications are used in the same way in any country or area of human action.