Assessment of Proliferation, Clonogenic Assay, and Osteogenic Differentiation of Human Periodontal Ligament Stem Cells Following Application of Orthodontic Forces

Context: The proliferation and differentiation of human periodontal ligament stem cells (hPDLSC) into other cell types are also mediated by mechanical stresses; they might offer therapeutic benefits in tissue regeneration and angiogenesis. Objectives: The study was planned to assess the proliferation, clonogenic potential, and osteogenic differentiation of human periodontal ligament stem cells (PDLSC) following the application of light and heavy orthodontic forces. Materials and Methods: A couple forces of 50 gm (light force) were applied on the 1st premolar on the one side and 250 gm (heavy force) on the contralateral side in the upper arch of patients requiring orthodontic treatment with extraction of all 1st premolars. After 30 days, periodontal tissues were scrapped from extracted teeth for the establishment of PDLSC in vitro. PDLC from the lower premolar teeth where no orthodontic force was applied acted as the control group. Morphology, viability, proliferating rate and population doubling time, clonogenicity, and alkaline phosphatase activity were analysed. Result: The osteogenic potential was confirmed by Alizarin red staining and the expression of the osteogenic markers by qRT?PCR. The morphology, growth kinetics, potency, and osteogenic lineage characteristics inferred the application of high force reduced the proliferative ability and osteogenesis of PDLSC, though the difference was not significant. Conclusion: The established PDLSCs demonstrated their MSC?like properties based on morphology, growth kinetics, colony forming ability, and AP activity. The culture?expanded PDLSCs showed their differentiation potential into osteocytes. The application of high force reduced the proliferative ability and osteogenesis of PDLSCs, variations were not significant.differentiation

Dynamic Analysis on Static-Vibration Coupled Loading in Accelerating Orthodontic Tooth Movement / 医用生物力学

Objective To analyze stress distributions on mandible bone and periodontal ligaments during acceleration of orthodontic tooth movement by mechanical vibration, and investigate the mechanism of static-vibration coupled loading to accelerate orthodontic tooth movement. MethodsThe finite element model including tooth, periodontal ligament, cancellous bone and cortical bone was established by Mimics，SolidWorks，Geomagic and ANSYS Workbench software. Conventional static orthodontic force and low-magnitude high-frequency mechanical vibration loads were applied to the finite element model for dynamic analysis. ResultsThe compression and tension zones of alveolar bone and periodontal tissues were identified based on Y-normal stress distribution of alveolar bone and periodontal tissues, which was periodic with the same frequency as the applied low-magnitude high-frequency vibration. The von Mises stress of alveolar bone and periodontal tissues also showed periodic changes, but the compression and tension zones of alveolar bone and periodontal tissues could not be identified based on von Mises stress distribution of alveolar bone and periodontal tissues. Conclusions In the field of orthodontics, Y-normal stress is a reasonable mechanical stimulus, and static-vibration coupled loading is an effective method for accelerating orthodontic treatment. The research findings can provide guidance for low-magnitude high-frequency mechanical vibration to accelerate orthodontic tooth movement.

Effect of orthodontic forces on root length of immature mandibular second premolars: a split-mouth randomized clinical trial

ABSTRACT Objective: To assess the effect of orthodontic forces on changes in root length of immature mandibular second premolars. Methods: Sixty-four mandibular second premolars (MSP) with immature apices (left and right sides) of 32 patients aged between 10 and 13 years were evaluated. Orthodontic treatment was started after obtaining periapical radiographs (T1) from the MSPs of each patient. Brackets were bonded, except the ones of MSPs (left or right by random as control MSP, and the other side as test MSP). After 9-12 months, a second periapical radiograph (T2) was obtained from the MSPs of each patient. Then, brackets were bonded to the control MSPs, which were not bonded before. After 18 ± 3 months, a third periapical radiograph (T3) was obtained. Changes in root length were evaluated by using a new formula. The test and control MSPs at T1, T2 and T3 were compared using repeated measures ANOVA and parametric tests. P-value smaller than 0.05 was statistically significant. Results: There was no significant difference between the test and control groups in the mean root length of MSP at T1 (p= 0.48) and T3 (p= 0.078). The root length at T2 (p= 0.001) was significantly different between test and control MSPs, and the test group showed longer root length than the control group. Conclusions: Orthodontic force applied for leveling and alignment of immature MSPs may not have destructive effects on the roots, and may accelerates root formation in short-term. Normal root length was achieved at the end of root development.

RESUMO Objetivo: Avaliar o efeito das forças ortodônticas nas mudanças do comprimento radicular de segundos pré-molares inferiores com raízes incompletas. Métodos: Foram avaliados 64 segundos pré-molares inferiores (SPI) com raízes incompletas (lados direito e esquerdo da mandíbula) de 32 pacientes com idades entre 10 e 13 anos. O tratamento ortodôntico teve início após a obtenção de radiografias periapicais (T1) dos SPIs de cada paciente. Foram colados braquetes em todos os dentes, com exceção dos SPIs (do lado esquerdo ou direito, de forma aleatória, como grupo controle; e o SPI contralateral como grupo teste). Após 9 a 12 meses, uma segunda radiografia periapical (T2) foi obtida dos SPIs de cada paciente. Então, braquetes foram colados nos SPIs do grupo controle, que não haviam sido colados anteriormente. Após 18 ± 3 meses, uma terceira radiografia periapical (T3) foi obtida. As mudanças no comprimento radicular foram avaliadas por meio de uma nova fórmula. Os SPIs teste e controle foram comparados em T1, T2 e T3 usando ANOVA para medidas repetidas e testes paramétricos. Valores de p< 0,05 foram considerados estatisticamente significativos. Resultados: Não foi encontrada diferença significativa no comprimento radicular médio dos SPIs entre os grupos teste e controle em T1 (p= 0,48) e T3(p= 0,078). O comprimento radicular dos SPIs em T2 (p= 0,001) foi significativamente diferente entre os lados teste e controle, sendo que o grupo teste apresentou maior comprimento radicular do que o grupo controle. Conclusões: As forças ortodônticas aplicadas para o alinhamento e nivelamento de SPIs com raízes incompletas podem não ter efeitos danosos nas raízes, podendo, inclusive, acelerar a formação radicular em curto prazo. O comprimento radicular normal foi alcançado ao fim da formação radicular.

Effects of Moment-to-Force Ratio on Canine Translation by Numerical Analysis / 医用生物力学

Objective To study the influence of different moment-to-force ratios (M/F) and forces on canine displacement and periodontal ligament (PDL) stress. Methods A three-dimensional (3D) mandibular model was established based on CT images. The orthodontic force systems without a moment and with various M/F were applied to the canine for numerical calculation of its translation. An optimum force system to realize canine translation was validated by analyzing translation displacement of the canine in each case. Results The PDL stress increased with an increase in force magnitude in all cases. The PDL stress first decreased with an increase in the M/F before the M/F reached the optimum value (M/F=10.1 mm), and then increased with an increase in the M/F. The initial displacement of the canine was inclined movement, which was most close to translation when the precise optimum M/F was applied. Conclusions The canine movement requires an appropriate force to prevent root absorption, whereas the translation movement requires an optimal M/F value which is within the physiological range. Understanding the influence of force and moment on tooth translation can help to apply more reasonable orthodontic force system and design more reasonable orthodontic device.

Effect of orthodontic traction on the microstructure of dental enamel / 南方医科大学学报

OBJECTIVE@#To investigate the effect of orthodontic traction on the microstructure of dental enamel.@*METHODS@#Forty-eight isolated premolars were randomly divided into 6 groups (=8), including Group A (blank control group), in which the teeth were bonded with the orthodontic brackets without any loading force; Groups B1, B2, and B3 where the teeth were bonded with the orthodontic brackets using clinical adhesives and loaded with 50 g force for 6 months, 200 g force for 6 months, and 200 g force for 1 month, respectively; and Groups C1 and C2, where the teeth were bonded with straight wire brackets using light curing bonding and chemical curing bonding techniques, respectively. All the teeth were embedded with non-decalcified epoxy resin. Scanning electron microscope (SEM), atomic force microscope (AFM), and energy spectrometer (EDS) were used to analyze interface morphology and elemental composition of the teeth sliced with a hard tissue microtome.@*RESULTS@#Compared with those in Group A, the teeth in the other 5 groups showed increased adhesive residue index with microcracks and void structures on the enamel surface under SEM; AFM revealed microcracks on the enamel surface with angles to the grinding direction. A larger loading force on the bracket resulted in more microcracks on the enamel interface. The interface roughness differed significantly between Groups A and C2, and the peak-to-valley distance differed significantly between Groups A, C, and C2.@*CONCLUSIONS@#Orthodontic traction can cause changes in the microstructure of normal dental enamel.

Finite element analysis of maxillary anterior teeth retraction of posterior teeth with different alveolar bone absorption heights under orthodontic force / 华西口腔医学杂志

OBJECTIVE@#This study applied the direct orthodontic force system to explore the applicability of the finite element method in the simulation of alveolar bone absorption and analyze periodontal stress distribution and the overall displacement trend.@*METHODS@#The horizontal balanced alveolar bones of model 2, 3 and 4 were reduced by 2, 4, and 6 mm by deleting elements in reference to the established height of the normal alveolar bone model 1. Then, stress distribution on the posterior set of teeth and initial total tooth displacement under the simulated load of 1.47 N of orthodontic force were investigated.@*RESULTS@#The total displacement of posterior teeth increased and parodontium Von Mises stress gradually increased as the alveolar bone height decreased. The total displacement trend and parodontium stress drastically increased when alveolar bone absorp-tion reached the height of 4 mm.@*CONCLUSIONS@#When treating patients with alveolar bone loss, stress should be avoided or drasti-cally reduced to prevent irreversible damage to periodontal tissue and to improve the quality of medical treatment.

A biomechanical case study on the optimal orthodontic force on the maxillary canine tooth based on finite element analysis / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Excessive forces may cause root resorption and insufficient forces would introduce no effect in orthodontics. The objective of this study was to investigate the optimal orthodontic forces on a maxillary canine, using hydrostatic stress and logarithmic strain of the periodontal ligament (PDL) as indicators. Finite element models of a maxillary canine and surrounding tissues were developed. Distal translation/tipping forces, labial translation/tipping forces, and extrusion forces ranging from 0 to 300 g (100 g=0.98 N) were applied to the canine, as well as the force moment around the canine long axis ranging from 0 to 300 g·mm. The stress/strain of the PDL was quantified by nonlinear finite element analysis, and an absolute stress range between 0.47 kPa (capillary pressure) and 12.8 kPa (80% of human systolic blood pressure) was considered to be optimal, whereas an absolute strain exceeding 0.24% (80% of peak strain during canine maximal moving velocity) was considered optimal strain. The stress/strain distributions within the PDL were acquired for various canine movements, and the optimal orthodontic forces were calculated. As a result the optimal tipping forces (40-44 g for distal-direction and 28-32 g for labial-direction) were smaller than the translation forces (130-137 g for distal-direction and 110-124 g for labial-direction). In addition, the optimal forces for labial-direction motion (110-124 g for translation and 28-32 g for tipping) were smaller than those for distal-direction motion (130-137 g for translation and 40-44 g for tipping). Compared with previous results, the force interval was smaller than before and was therefore more conducive to the guidance of clinical treatment. The finite element analysis results provide new insights into orthodontic biomechanics and could help to optimize orthodontic treatment plans.

Changes of signal transducer and activator of transcription 1 expression in the anterior cingulate cortex under orthodontic force in rats / 口腔疾病防治

Objective@# To study the change of STAT1 expression in the anterior cingulate cortex on rats under orthodontic force, and to further explore the roles of STAT1 and related JAK-STAT1 signaling pathway in the mediation and regulation of pain during tooth movement. @*Methods@#112 male Sprague-Dawley (SD) rats (225±25 g) were used in this study. They were randomly divided into experimental groups (96 rats) and control groups (16 rats). All rats were installed bilateral maxillary device for tooth movement models. Rats in the experimental groups were applied 80g orthodontic force on both sides and were divided into six subgroup 4 h, 12 h, 24 h, 2 d, 3 d, 7 d, with 16 rabbits in each subgroup. The control groups were only installed the same orthodontic devices, without the application of orthodontic force. Brain tissue of the anterior cingulate cortex was isolated after 4 h, 12 h, 24 h, 2 d, 3 d, 7 d since experiment, and the expression level of STAT1 and p-STAT1 was analyzed with the method of immunofluorescence and PCR. @*Results @#For the immunofluorescence result, there was significant difference in STAT1 expression between control groups and different experimental groups at different time points in total (P < 0.05). The STAT1 expression amount in the 4 h group decreased significantly when compared with the control group (P < 0.05); to the 2 d group, the difference is still statistically significant (P < 0.01). 3 d group, 7 d group and control group had no statistically significant difference. The STAT1 expression amount in 4 h group, 12 h group, 24 h group was significantly lower than that in 3 d and 7 d groups, differences were statistically significant (P < 0.05). The STAT1 expression in the 2 d group was significantly lower than that of 7 d (42.35 ± 5.77) group, the difference was statistically significant (P < 0.05). There was significant difference in p-STAT1 expression between control groups and different experimental groups at different time points in total (F = 623.518, P < 0.05). The p-STAT1 expression amount in experimental groups were higher than that in the control group (P < 0.05). The p-STAT1 expression in 4 h group was lower than that in 12 h and 24 h group and higher than that in 2 d, 3 d and 7 d groups, of which the differences were statistically significant (P < 0.05). The p-STAT1 expression in 12 h group was lower than that in 24 h group and higher than that in 2 d, 3 d and 7 d groups, of which the differences were statistically significant (P < 0.05). For the PCR result, the expression of mRNA in STAT1 of experimental groups of 4 h, 12 h, 24 h, 2 d, 3 d, 7 d and the control groups were not statistically significant (P > 0.05).@*Conclusions @#After applying orthodontic force, the expression of STAT1 decreased transiently and the expression of p-STAT1 increased transiently. The reduction of STAT1 was probably caused by the phosphorylation of STAT1 and decrease in the translation level of STAT1, rather than changes in the transcriptional levels. The orthodontic pain might be related with the activation of STAT1 into phosphorylated STAT1.

Changes in force associated with the amount of aligner activation and lingual bodily movement of the maxillary central incisor / 대한치과교정학회지

OBJECTIVE: The purposes of this study were to measure the orthodontic forces generated by thermoplastic aligners and investigate the possible influences of different activations for lingual bodily movements on orthodontic forces, and their attenuation. METHODS: Thermoplastic material of 1.0-mm in thickness was used to manufacture aligners for 0.2, 0.3, 0.4, 0.5, and 0.6 mm activations for lingual bodily movements of the maxillary central incisor. The orthodontic force in the lingual direction delivered by the thermoplastic aligners was measured using a micro-stress sensor system for the invisible orthodontic technique, and was monitored for 2 weeks. RESULTS: Orthodontic force increased with the amount of activation of the aligner in the initial measurements. The attenuation speed in the 0.6 mm group was faster than that of the other groups (p < 0.05). All aligners demonstrated rapid relaxation in the first 8 hours, which then decreased slowly and plateaued on day 4 or 5. CONCLUSIONS: The amount of activation had a substantial influence on the orthodontic force imparted by the aligners. The results suggest that the activation of lingual bodily movement of the maxillary central incisor should not exceed 0.5 mm. The initial 4 or 5 days is important with respect to orthodontic treatment incorporating an aligner.

Comparisons of orthodontic root resorption under heavy and jiggling reciprocating forces during experimental tooth movement in a rat model / 대한치과교정학회지

OBJECTIVE: Root mobility due to reciprocating movement of the tooth (jiggling) may exacerbate orthodontic root resorption (ORR). "Jiggling" describes mesiodistal or buccolingual movement of the roots of the teeth during orthodontic treatment. In the present study, buccolingual movement is described as "jiggling." We aimed to investigate the relationship between ORR and jiggling and to test for positive cell expression in odontoclasts in resorbed roots during experimental tooth movement (jiggling) in vivo. METHODS: Male Wistar rats were divided into control, heavy force (HF), optimal force (OF), and jiggling force (JF) groups. The expression levels of cathepsin K, matrix metalloproteinase (MMP)-9 protein, interleukin (IL)-6, cytokine-induced neutrophil chemoattractant 1 (CINC-1; an IL-8-related protein in rodents), receptor activator of nuclear factor κB ligand (RANKL), and osteoprotegerin protein in the dental root were determined using immunohistochemistry. RESULTS: On day 21, a greater number of root resorption lacunae, which contained multinucleated odontoclasts, were observed in the palatal roots of rats in the JF group than in rats from other groups. Furthermore, there was a significant increase in the numbers of cathepsin K-positive and MMP-9-positive odontoclasts in the JF group on day 21. Immunoreactivities for IL-6, CINC-1, and RANKL were stronger in resorbed roots exposed to jiggling than in the other groups on day 21. Negative reactivity was observed in the controls. CONCLUSIONS: These results suggest that jiggling may induce ORR via inflammatory cytokine production during orthodontic tooth movement, and that jiggling may be a risk factor for ORR.

Integrins and Reorganization of Osteoclast Cytoskeleton under Orthodontic Force.

Integrins are mechanoreceptors and mediate mechanotransduction by transferring forces into focal adhesions. Osteoclastogenesis starts with adhesion to the bone matrix, leading to cytoskeleton reorganization that is important for osteoclast polarization and migration. However, there are several signaling pathways mediating this process, and integrins have been shown to be important signaling molecules participating osteoclastogenesis. Particularly, integrins have played an important role in both force transduction and osteoclastogenesis. This paper reviewed the findings on the relationship between integrins and reorganization of osteoclast cytoskeleton under orthodontic force.

Role of interleukin-6 in orthodontically induced inflammatory root resorption in humans / 대한치과교정학회지

OBJECTIVE: To determine the interleukin (IL)-6 levels in gingival crevicular fluid (GCF) of patients with severe root resorption after orthodontic treatment and investigate the effects of different static compressive forces (CFs) on IL-6 production by human periodontal ligament (hPDL) cells and the influence of IL-6 on osteoclastic activation from human osteoclastic precursor (hOCP) cells in vitro. METHODS: IL-6 levels in GCF samples collected from 20 patients (15 and 5 subjects without and with radiographic evidence of severe root resorption, respectively) who had undergone orthodontic treatment were measured by ELISA. The levels of IL-6 mRNA in hPDL cells and IL-6 protein in conditioned medium after the application of different uniform CFs (0, 1.0, 2.0, or 4.0 g/cm2 for up to 72 h) were measured by real-time PCR and ELISA, respectively. Finally, the influence of IL-6 on mature osteoclasts was investigated by using hOCP cells on dentin slices in a pit-formation assay. RESULTS: Clinically, the IL-6 levels were significantly higher in the resorption group than in the control group. In vitro, IL-6 mRNA expression significantly increased with increasing CF. IL-6 protein secretion also increased in a time- and magnitude-dependent manner. Resorbed areas on dentin slices were significantly greater in the recombinant human IL-6-treated group and group cultured in hPDL cell-conditioned medium with CF application (4.0 g/cm2) than in the group cultured in hPDL cell-conditioned medium without CF application. CONCLUSIONS: IL-6 may play an important role in inducing or facilitating orthodontically induced inflammatory root resorption.

Influence from deformation history of NiTi shape-memory-alloy arch-wires on orthodontic force / 医用生物力学

Objective To evaluate the influence from deformation history of arch-wires on its orthodontic force. MethodsA finite element model including brackets and arch-wires in free status was built, and the position of brackets under clinical condition was obtained through laser scanning on the plaster dental model. Based on the finite element method, the brackets were moved to the clinical position through two different movement pathways, using a thermal-mechanical shape-memory-alloy model of arch-wires. The orthodontic force obtained from the two pathways were then compared and analyzed. Results The relative differences in the orthodontic force obtained from the two pathways were significant, with a range from 0.3 to 8.0. The influence of deformation pathway on the orthodontic force was reduced if the arch-wire was first overloaded and then unloaded to the clinical condition，but reduction of the orthodontic force varied at different positions of arch-wires, and the relative differences might increase at certain positions. Conclusions The deformation history of arch-wires has some direct relation with the orthodontic force produced on the NiTi shape-memory-alloy, and the evaluation on the orthodontic force should trace its deformation history.

The autotransplantation of an anklyosed maxillary canine / 대한치과보존학회지

The clinical diagnosis of ankylosis can be made only when the affected tooth gives positive evidence of an inability to move. The inability to move is demonstrated either as a failure of the tooth to move with normal vertical dental alveolar growth or a failure of the tooth to move when the tooth is subjected to an orthodontic force system. This case report describes the autotransplantation of an ankylosed maxillary canine.

Partial pulp necrosis caused by excessive orthodontic force / 대한치과보존학회지

As the dental pulp is encased with a rigid, noncompliant shell, changes in pulpal blood flow or vascular tissue pressure can have serious implication for the health of pulp. Numerous studies have demonstrated that orthodontic force application may influence both blood flow and cellular metabolism, leading degenerative and/or inflammatory responses in the dental pulp. The aim of this case report is to present a case about tooth with chronic periapical abscess which showed normal vital responses. Excessive orthodontic force is thought to be the prime cause of partial pulp necrosis. Owing to remaining vital tissue, wrong dianosis can be made, and tooth falsely diagnosed as vital may be left untreated, causing the necrotic tissue to destroy the supporting tissuses. Clinician should be able to utilize various diagnostic tools for the precise diagnosis, and be aware of the endodontic-orthodontic inter-relationship.

Autogenous transplantation of tooth with complete root formation / 대한치주과학회지

PURPOSE: Autogenous transplantation of teeth can be defined as transplantation of teeth from one site to another in the same individual, involving transfer of impacted or erupted teeth into extraction sites or surgically prepared sockets". Successful autogenous transplantation of teeth depends upon a complex variety of factors. Such factors include damage to the periodontal ligament of the donor tooth, residual bone height of the recipient site, extra-oral time of tooth during surgery. Schwartz and Andreasen previously reported that autogenous transplantation of teeth with incomplete root formation demonstrated higher success rate than that of teeth with complete root formation. Gault and Mejare yielded similar rate of successful autogenous transplantation both in teeth with complete root formation and in teeth with incomplete root formation when appropriate cases were selected. This case report was aimed at the clinical and radiographic view in autogenous transplantation of teeth with complete root formation. MATERIALS AND METHODS: Patients who presented to the department of periodontics, Chonnam National University Hospital underwent autogenous transplantation of teeth. One patient had vertical root fracture in a upper right second molar and upper left third molar was transplanted. And another patient who needed orthodontic treatment had residual root due to caries on upper right first premolar. Upper right premolar was extracted and lower right second premolar was transplanted. Six months later, orthodontic force was applied. RESULTS: 7 months or 11/2 year later, each patient had clinically shallow pocket depth and normal tooth mobility. Root resorption and bone loss were not observed in radiograph and function was maintained successfully. CONCLUSION: Autogenous transplantation is considered as a predictive procedure when it is performed for the appropriate indication and when maintenance is achieved through regular radiographic taking and follow-up.

An effect of immediate orthodontic force on palatal endosseous appliance(C-Palatal PlateTM) in beagle Dog / 대한치과교정학회지

This study was performed to investigate the effect of immediate orthodontic force on soft and hard tissues surrounding C-Palatal PlateTM in beagle Dog. Immediately after this appliance was implanted on the midpalate of 4 adult beagle Dogs, 400gm continuous orthodontic force was applied. Experimental animals were euthanized at 8weeks, 18weeks, and 22weeks (including post-removal healing time of 4weeks), and a control animal was euthanized at 8weeks after implantation without orthodontic force application. The appliance and the surrounding tissue were studied radiographically, macroscopically, and histologically. The results were as follows : 1. The lateral radiographs taken after euthanasia showed very slight displacement of the vertical plate in the experimental animals, compared with the control animal. Mobility test of all animals confirmed primary stability without any increase of mobility during experimental period. 2. No pathologic changes were found in the healing condition of covering soft tissue and bone-screw interface in experimental animals as well as a control animal. 3. Osseointegration was achieved in the bone-screw interface in 8weeks after implantation and the amount of osseointegration increased in 18weeks. There was little difference of osseointegration between the compression side and the tension side. 4. In the marginal bone area, slight bone apposition and resorption were found regardless of compression and tension side, while there was no change in the control animal. 5. Both 8week-animal and 18week-animal showed the new bone apposition along the surface of screws which were perforated into the nasal cavity, while the control animal showed no change. 6. After 4weeks of plate removal, the covering epithelium was repaired intactly, while the connective tissue showed loose and irregular rearrangement and the connective tissue capsule remained. The C-Palatal PlateTM manifested sufficient anchorage capacity in the context of histological study as well as clinical outcomes, when immediate orthodontic force was applied after implantation.

The effect of early loading on the direct bone-to-implant surface contact of the orthodontic osseointegrated titanium implant / 대한치과교정학회지

The orthodontic osseointegrated titanium implant, a kind of intraoral skeletal anchorage can be an alternative to tooth-borne anchorage, in case that the conventional tooth-borne anchorage is not available or the anchorage is critical. This study was conducted to elucidate the effect of early loading on the osseointegration of the orthodontic titanium implant and the healing process of the impaired bone at the site of implant after removing it. In two adult beagle dogs 24 osseointegrated titanium implants were inserted into the alveolar bone, with 12 implants placed in each dog. In dog1, 6 out of 12 implants were loaded with 200-300gm of force immediately after placing, and the remaining 6 implants were not loaded for 4weeks. In dog2, all 12 implants had healing period of 4weeks, and then were loaded with 200-300gm of force for another 4weeks. Following an observation period of 4 and 8 weeks, the animals were sacrificed. Then the implants and the surrounding bone of dog1 and dog2 were removed, respectively. Undecalcified sections along the long axis of implant were made and the degree of osseointegration was examined under the light microscope. The results were as follows. 1. In the histologic features of tissues around implants anchored in dog1, there was no difference between immediately loaded implants and unloaded implants. Immature woven bone was ingrowing into the thread spaces from the original compacta and in direct contact with the implant surface in part. 2. The premature loading just after 4weeks healing period did not halt the progress of the osseointegration between bone and implant surface. The woven bone around the implants was maturing into the lamellar bone which resembled the structure of the original compacta at the end of 8weeks observation period. 3. Most implants with the inflammed surrounding mucosa were lost or mobile. The mobile implants were encapsulated by fibrous connective tissue which separated the implant surface from the bone. 4. The impaired bone at the site of the implant failed to anchor was showing recovery without inflammatory reaction 2weeks after removing, with the immaure woven bone lined by active osteoblasts and osteoid. Based on the results of this study, the integration of this orthodontic implant seemed to be impaired by the inflammation of the tissue surrounding the implant rather than by early loading on implant, and increased with time lapsed after placing the implant. The use of implant described in this report can be recommended as an orthodontic anchorage unit immediately after insertion under the careful control of orthodontic force applied and plaque.

A study on the expression of vascular endothelial growth factor in tension side of rat molar periodontal ligament following experimental tooth movement / 대한치과교정학회지

This study was performed to analyse the expression of VEGF and it's receptor(VEGFR) in the tension side of the periodontal ligament following orthodontic tooth movement. Upper first molars of Sprague-Dawley rats were moved medially using closed coil spring for 1, 2, 24 hours and 3, 7, 14 days. H&E staining, immunohistochemical staining and in situ hybridization methods were used to analyse the change of the expression of VEGF and VEGFR. The results from this study were as follows : 1. Following tensional force, periodontal ligament showed elongation of fibers, compression and congestion of vessels and regional hemorrhage. These tissue changes were recovered within 3 days of force application. New bone formation was seen after 3 days of force application and continued for the remaining experimental periods. 2. Following tensional force, VEGF and VEGF mRNA expression was increased in the periodontal ligament cells, osteoblasts and cementoblasts. This change was followed by increased vasculature in the periodontal ligament. 3. After 3 days of tensional force, VEGF and VEGF mRNA expression was confined mainly to the osteopaths and the periodontal ligament cells adjacent to the alveolar bone. After 2 weeks of force application, VEGF and VEGF mRNA expression was reduced to the level of control sample. 4. VEGFRs(Flt-1, Flk-1) showed similar expression pattern and it's expression was mainly seen in the endothelial cells and osteoblasts. Following tensional force VEGFR expression was increased in the endothelial cells and osteoblasts. In conclusion, in the tension side of the periodontal ligament, ligament cells, osteoblast and cementoblast showed increased expression of VEGF & VEGF mRNA. It preceded the increase of vasculature and new bone formation. The increased expression of VEGF mRNA in cementoblast may induce periodontal vessels, which distribute mainly the bone side half of periodontal ligament, grow in the direction of tensional force. Increased expression of VEGFR & VEGFR mRNA not only in endothelial cell but in osteoblast, osteocyte and periodontal cells showed VEGF acts not only in paracrine manner but in autocrine one.

A study on the changes of periodontal tissue after orthodontic tooth movement in young adult dogs / 대한치과교정학회지

For orthodontic tooth movement, optimal orthodontic force should be maintained without periodontal breakdown and alveolar bone should be remodeled physiologically. Therefore, To obtain proper occlusion through tooth movement within alveolar bone, we should know the biomechanics of teeth and supporting tissues. The present study was performed to observe histologic changes of periodontal tissue immediately after application of orthodontic force and during the retention period in growing young adult dogs. In this study, experimental group contained between mandibular left canie and 1st molar and control group contained contralateral teeth of same animal. The .018"x.22" stainless steel closed coil spring(Dentaurum Co.) was ligated on the experimental teeth at initial 200gm-force from mandibular canine to 1st molar. The animals(4 to 6 months aged young adult dogs) were sacrificed on 0, 14, 28 days after the finish of appliance activation, and then tissue samples were divided into hematoxylin-eosin(HE) staining section, ground section, alkaline phosphatase(ALP) staining section, and tartrate-resistant acid phosphatase(TRAP) staining section. Thereafter, the preparations were examined under light microsopy. The following results were obtained: 1. Immediately after the finish of appliance activation, the periodontal space was increased in tension side, but decreased in pressure side compared to that of control. The hyalinized zone was also observed in the periodontium. 2. After the 14-day retention, periodontal space was decreased in tension side and slightly increased in pressure side compared to that of immediately after the finish of appliance activation. The hyalinized zone was repaired and a few osteoblasts showing slightly new bone formation were seen. Osteoblasts were scarcely observed along the alveolar bone. 3. After the 28-day retention, the periodontal fibers are normally repaired. A lot of TRAP(+) osteoclasts and increased alveolar bone resorption were observed in pressure side, and AP(+) osteoblast and increased new bone formation were observed in tension side.