• The korean journal of orthodontics
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• v.19 no.2
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• pp.57-73
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• 1989

The purpose of this study was to investigate the tissue response of the rat molar periodontium incident to intermittent orthodontic force. The author intended to observe the healing process of injured periodontium and the response of injured tissue to the resumed force. Oxytetracyclin 50mg/Kg was given to each rat intraperitonially. 5 days later, maxillary 1st molars were moved mesially from the incisors with closed coil spring of 100gram. 7 days later, the appliances were removed and 20mg/Kg of calcein were given intraperitonially to each rat. At the same time, maxillary left 1st molars of 15 rats were moved by the same method, but force was lowered to 20 gram. After 1 day, maxillary left 1st molars of another 15 rats were moved by the same method and 50mg/Kg of oxytetracycline was given intraperitonially. After 4 days, another 15 rats were treated as above. After 7 days, another 15 rats were treated as above. 1,4,7,10 and 14 days after change of force, 3 rats were sacrificed in each group respectively. 2 rats were decalcified, embedded in paraffin, and stained with hematoxylin-eosin stain and with Masson's trichrome stain. Another rat was embedded in polyester resin and undecalcified specimen were made. Microradiograms were taken with the undecalcified sections. Observations were made with light and fluorescence microscope. Following conclusions were made. 1. Connective tissue cells and vessels were infiltrated into the hyalinized tissue from the bony cleft and along the border of the hyalinized tissue with bone and root surface. At the same time, elimination of hyalinized tissue, bone and root resorption occurred. 2. Bone and root were resorbed directly and indirectly. 3. Hyalinized tissue was removed within 5 days after force removal. 4. Hyalinized zone was less extensive and easily removed as the rest period prolonged. 5. Hyalinized tissue developed more rapidly and extensively and lasted over 10 days as the force resumed on the already formed hyalinized tissue.

• The korean journal of orthodontics
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• v.13 no.2
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• pp.165-176
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• 1983

The hyalinized zone in compressed periodontal ligament seems to be an unavoidable aspect during certain phases of orthodontically produced tooth movement. And these hyalinized zones leads to a standstill of tooth movement. But when hyalinized zones disappears after a certain period of time and tooth movement is established. In the basic aspect of clinical science of orthodontics, it is very important, to study about the process involved and to establish whether a difference of periodontal response by the amount of the applied experimental force exists. The 35 Guineapigs were divided into the control group (5 animals) and the experimental group (Group I-Group VI 30 animals). The experimental tooth movement of Guineapig's maxillary incisors were carried out by rendering continuous force, 5g (Group I, Group II) 35g (Group III, Group IV), 100g (Group V, Group VI) respectively. 15 animals (Group I, Group III, Group V) were sacrificed one week after this experiment. Another 15 animals (Group II, Group IV, Group VI) were sacrificed one week after the removal of active appliences. At the end of the experimental periods, specimens containing tooth and adjacent periodontal structure were obtained and processed for light and electron microscopy. The results were as follows: 1. In Group I, cellular changes of pressured zones showed swollen mitochondria, dilation of rough surfaced endoplasmic reticulum (RER), vesicles and pyknosis of nucleus. 2. In Group III and Group V, the hyalinized tissues showed cell necrosis accompaning ruptures of cytoplasmic membrane and perinuclear envelope, large cytoplasmic vacuoles and many necrotic cell debris. 3. In Group IV and Group VI, hyalinized tissue were eliminated and the primitive mesenchymal cells and blood capillaries were proliferated. 4. In group V, the destruction of the collagenous fibers were observed, while in group I and group III were not observed. 5. In Croup IV and Group VI, the hyalinized zones were still remained partly.

• Imaging Science in Dentistry
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• v.31 no.4
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• pp.221-225
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• 2001

Purpose: To observe the relationship of bilaminar zone of temporomandibular joint retrodiscal tissues to the disc condition. Materials and Methods : The upper and lower stratum of bilaminar zone were identified on magnetic resonance open mouth images of 148 joints from 74 patients with disc displacements. Results: Both strata were identifiable in 105 joints which had disc displacement with reduction. Lower stratum was not identifiable in 35 joints which had disc displacement without reduction but 12 of 35 had hyalinized posterior attachment where the disc was. The 8 joints which had partial disc displacement without reduction showed identifiable lower stratum at the reducing site which was medial. Conclusion: Disruption or no identification of lower stratum which corresponds to the condylar portion of posterior attachment may be the sign of disc displacement without reduction.

• The korean journal of orthodontics
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• v.30 no.3 s.80
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• pp.317-333
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• 2000

The purpose of this study was to determine the proliferative activity of the osteoblasts and fibroblasts in the midpalatal area and to investigate the adjacent periodontal tissues of individual tooth following rapid expansion of the palate. Ten young adult dogs, aged approximately ten months, were used in the experiment. The experimental design was consisted of 1 week expansion group(Group E1, 3 dogs), 2 week expansion group(Group E2, 3 dogs), 2 week expansion and 2 week retention group(Group E3, 3 dogs), and control group(Group C, 1 dog). For each group, expansion screw was activated one time per day(1/4 turn;$90^{\circ}$) following Hyrax-screw application. The experimental animals in each group were sacrificed at 1, 2 and 4 weeks following palatal expansion. Maxillary tissue blocks were obtained and prepared ior the histomorphologic and immunohistochemical studies. Light mcroscope, polarizing microscope, and soft X-ray apparatus were used in this study, and following results were obtained. 1. In polarizing microscopic study, the expansion groups(E1 & E2) showed blue color representing bone resorption and new bone formation in midpalatal suture area. E3 groups skewed less blue color compared to the E1 and E2 group. But yellow color increased by calcification in the E3 groups. 2. Immunohistochemical study revealed that positive responses of the osteoblasts to PCNA and undifferentiated fibroblasts to EGF in E1 group were somewhat increased. Positive response to PCNA and EGF were increased in fibroblasts and the osteoblasts forming new bone in E2 group. In E3 group, the positive response cell concentrated the periphery of edge of palatal process in both PCNA and EGF. 3. Throughout the expansion period(E1 & E2), light microscopic study showed the edges of the extensive resorption and new palatal processes, indicating bone remodeling within the suture. E3 group exhibited less remodeling of midpalatal suture area. E2 group and E3 group showed cementum formation and resorption at the apex of 3rd premolar and 1st molar E3 group exhibited extensive hyalinized zone on the cervical portion of buccal side of 1st molar. 4. Soft X-ray analysis of E1 group showed hypomineralized defect and microfractures in various parts of the suture areas when compared with control animals. There was no significant difference in the degree of mineralization in the midpalatal suture region between the C and E3 groups. Tooth axis showed tipping of 3rd premolar and 1st molar in the E2 group and E3 group. Based upon these experimental results, it is concluded that the undifferentiated mesenchymal cells always presented in midpalatal suture area following RPE. Differentiated osteoblasts and fibroblasts possess proliferating cellular activity until the 2 week retention period. The posterior teeth are tend to tip buccally as RPE force applied. Retention group exhibited irreversible response with severe hyalinized zone on the buccal surface of the first molar.

• The korean journal of orthodontics
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• v.25 no.1 s.48
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• pp.101-110
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• 1995

The purpose of this study was to observe the tissue response to the orthodontic force applied immediately after buccal horizontal subapical osteotomy of maxilla. Five mongrel cats weighing about 2.5 Kg were used for this experiment. The left upper canine and premolar of each cat served as a experimental side and the right ones as a control side. On the experimental side, a 100gm orthodontic force was applied between the upper canine and premolar immediately after the osteotomy. On the control side, the same orthodontic force was applied without the osteotomy. After 7days, the experimental animals were sacrificed. The results were as follows: 1. In the pressure zones of the experimental group, significant increase of osteoclasts and direct resolution along the alveolar bone surface was observed as compared with those of the control group. 2. In the pressure 2ones of the experimental group, a less extensive hyalinized zone was observed than those of the control group. 3. In the pressure zones of both group, no root resorption was found. 4. Tn the tension zones of the experimental group, new bone deposition increased along the alveolar bone surface as compared with those of the control group. In conclusion, the results suggest the possibility that early orthodontic treatment after orthognathic surgery may have some benefits if the stability of the repositioned segment at surgery is secured.

• The korean journal of orthodontics
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• v.20 no.2
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• pp.319-331
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• 1990

The purpose of this study was to help examining force system, optimal treatment, and prevention of relapse. Orthodontic force was generated by electromagnets, therefore duration could be freely controlled, and applied for 4 days in dogs. Force magnitude was 200gm and 50gm. duration was contious and intermittent. Intermittent duration was divided into 2 kinds of types in on/off, 1 mininute/1 minute, 10 seconds/1 minute. The results were as follows: 1. In the intermittent group to which force was applied for 10 seconds and ceased for 1 minute, osteoclast was not observed. 2. In the intermittent group to which 200gm of force was applied for 1 minute and ceased for 1 minute, there was blood circulation in periodontal space on pressure side, but mild hyalinized zone was observed. 3. More number of total osteoclast was counted in the pressure side of continous group to which 200gm of force was applied than in any other groups. 4. More number of frontal osteoclast was counted in the pressure side of intermittent group to which 200gm was applied for 1 minute and ceased for 1 minute than in any other groups. 5. On tension side, less periodontal space widening, more new bone and secondary cementum formation were observed in the intermittent group to which force was applied for 1 minute and ceased for 1 minute than in the continous group.

• The korean journal of orthodontics
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• v.23 no.2 s.41
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• pp.199-216
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• 1993

The purpose of this study was to quantify the biologic effects of the tensile forces from helical springs across the maxillary incisors on the periodontal tissues of rats. 39 Sprague-Dawlely rats were divided into a control group(3 rats) and three experimental groups(36 rats)-group 1, pressured with a light force(50-75g), group 2, with a heavy force(250-300g) and group 3, with a hen force(250-300g) plus laser irradiation. Autoradiographic and histopathologic observations were performed in 12, 24, 48 and 96 hours after force application. The result were as follow : 1. Hyalinized zone of periodontal ligament began to appear at pressure side in 12 hours in group 2 and group 3 ; all decreased in 96 hours except in group 2. 2. Alveolar bone resorption began to appear in 12 hours in group 2 and group 3 ; Group 2 showed more resorption than group 1 and no difference to group 3. 3. Tearing of periodontal ligament and vascular dilatation began to appear at tension side in 12 hours in all groups ; Group 2 showed more changes than group 1 and no difference to group 3 ; Decrease began to appear in 96 hours. 4. New bone formation began to appear at tension side in 12 hours and increased more and more ; No differences were shown of groups 5. New capillary proliferation began to appear at pressure side in 12 hours ; The changes were the greatest in group 3, group 2, group 1, in that order. 6. Positive reaction of cells to $[^3H]-thymidine$ was the greatest in 24 hours of all groups and decreased with times i Group 2 showed more reaction than group 1 and no difference to group 3.

• The korean journal of orthodontics
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• v.27 no.4 s.63
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• pp.559-568
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• 1997

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 4issues. 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 canine and 1st molar and control group contained contralateral teeth of same animal. The .018'x.022' 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 microscopy 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, peridontal 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. Aftter the 28-day retention, the periodontal fibers are normally repaired. A lot of TRAP(+) osteoclasts md increased alveolar bone resorption were observed in pressure side, and AP(+) osteoblast and increased new bone formation were observed in tension side.

• The korean journal of orthodontics
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• v.29 no.5 s.76
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• pp.551-562
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• 1999

This study was undertaken to investigate the relation between orthodontic force magnitude and the amount of tooth movement. And more light force application for reducing root resorption Twenty-four rats were divided into three experimental groups(A, B, C) based on force magnitude and application method. Springs of 50g force were applied to A group, springs of 100g force were applied to B group and springs of 25g force were applied to C group initially, and after 4 days springs of C group were changed to springs of 50g force. Two kinds of $sentally^{(R)}$(GAC U.S.A.) closed coil spring, 50g and 100g, were used. And we made 25g springs by heat treatment process of 50g springs. Each spring was inserted between the maxillary central incisor and the maxillary left first molar. Amounts of tooth movement were measured everyday by digital caliper($Digimatic^{(R)}$, Mitutoyo, Japan) under inhalation anesthesia for 15 days. After 15 days, all rats were sacrificed and histological samples were obtained with Hematoxyline-Eosin stain and Masson's trichrome stain. Following conclusion were made; 1. Group B showed the mean cumulative tooth movement of $2.19{\pm}0.41mm$ at 15th day, which was greatest among three groups, followed by group C($2.06{\pm}0.10mm$), group A($1.90{\pm}0.49mm$) respectively. however, there was no statistically difference among three groups. 2. All groups showed general tooth movement pattern and A, B, C group finished lag phase at 9th, 8th, 7th day, but there was no statistical significance. 3. Group A,B,C showed root resorption and especially group B showed the most severe root resorption and group C showed milder root resorption than other groups. According to the above results, large initial force with the development of a flirty widespread hyalinized zone may cause severe root resorption, so initial force should be applied lightly to reduce hyalinized area and eventually root resorption and then increased force will induce efficient tooth movement.