• The korean journal of orthodontics
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• v.48 no.5
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• pp.339-345
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• 2018

Objective: The purpose of this study was to clarify the effects of continuous force application for extrusive tipping movement and occlusal interference on periapical root resorption in the rat mandibular first molar. Methods: We constructed an appliance comprising a titanium screw implant with a cobalt-chromium post as the anchorage unit and a nickel-titanium closed coil spring (50 cN) as the active unit. Force was applied on the mandibular left first molar of rats for 8 (n = 10) and 15 days (n = 10; experimental groups), with the tooth in occlusion. Five rats were included as a non-treated control group to examine the body effect of the appliance. Active root resorption lacunae, identified using tartrate-resistant acid phosphatase, were evaluated in terms of the length, depth, and area. Results: The rat mandibular first molars were mesially tipped and extruded in the occlusal direction. This mesio-occlusal tipping movement and occlusion resulted in the formation of a compression zone and active root resorption lacunae in the distoapical third of the distal roots. However, there was no significant difference in the amount of root resorption between the two experimental groups. The control group did not exhibit any active root resorption lacunae. Conclusions: Periapical root resorption was induced by continuous extrusive tipping force and occlusal interference in rat mandibular molars. These data suggest that we orthodontists had better take care not to induce occlusal interference during our orthodontic treatment.

• The korean journal of orthodontics
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• v.44 no.5
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• pp.263-267
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• 2014

Objective: To three-dimensionally elucidate the effects of occlusal hypofunction on the periodontal ligament and alveolar bone proper of rat molars by micro-computed tomography (micro-CT). Methods: Occlusal function in the molar area was restricted by attaching an anterior bite plate on the maxillary incisors and a metal cap on the mandibular incisors of 5-week-old male Wistar rats for 1 week. The periodontal ligament space and alveolar bone proper around roots of the mandibular first molar were assessed by histology and micro-CT. Results: The periodontal ligament space was narrower and the alveolar bone proper was sparser and less continuous in the hypofunction group than in the control group. Further, both the volume of the periodontal ligament and the volumetric ratio of the alveolar bone proper to the total tissue in the region of interest were significantly lower in the hypofunction group (p < 0.05). Conclusions: Occlusal hypofunction induces atrophic changes in the periodontal ligament and alveolar bone proper of rat molars.

• The korean journal of orthodontics
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• v.9 no.1
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• pp.111-115
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• 1979

The author intended to observe the developmental pattern in mandibular bone and condyle following the loss of function of molar with 5 week-old rats b y means of removing the crown of molar. The bjects were observed everyweek during six weeks. The results were as follows ; 1. Bone apposition was observed at the root apex and interadicular area of alveolar bone. 2. Development of bone substance in mandible tended to increase in the narrow bone trabeculae and fibrous bone substance. 3. Development of condylar head showed little difference from that of control group and development of calcified zone appeared more or less poorly.

• The korean journal of orthodontics
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• v.21 no.3
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• pp.521-541
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• 1991

The purpose of this study was to investigate the growth changes of the mandible and associated structure in response to postural hyperpropulsion and changes after removal of postural hyperpropulsor. The experimental animals were four-week-old Sprague-Dawley males rats. The animals were worn the postural hyperpropulsor diurnally for 10 hours per day. The animals were sacrified after 1-week, 2-week, 4-week postural hyperpropulsion and 4-week postural hyperpropulsion 4-week removal period. The growth changes of rat mandible and associated structures following postural hyperpropulsion on the growing rat mandible were observed biometrically, radiographically and histologically. The finding were as follows. 1. The angle between the chief axis of the bone trabeculae in the condyle and the mandibular plane of rats observed for 4 weeks after worn the hyperpropulsor for 4 weeks was directed posteriorly as compared with that of control rats. 2. The ratio of mandibular length to maxillary length of experimental rats was higher than that of control rats. 3. The tooth axis of mandibular first molar of rats worn the postural hyperpropulsor for 4 weeks was mesially inclined as compared with control rats. 4. Histologically, the cartilage layer at the superior region of the condyle of rats worn the postural hyperpropulsor for 2 weeks appeared thicker than that of same aged normal rats, and generalized increase of the cartilage layer was shown on the condyle of rats worn the postural hyperpropulsor for 4 weeks. 5. There was no significant histologic difference between rats observed for 4 weeks after worn the postural hyperpropulsor for 4 weeks (8 week experimental rats) and same aged normal rats. 6. The newly formed bone at anterior region of articular fossa of rats worn the postural hyperpropulsor for 2 weeks and 4 weeks was thicker than that of same aged normal rats.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.21 no.2
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• pp.165-179
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• 1991

This study was performed to understand the irradiation effects on the mandibular condyle and mandibular growth in developing white rats. Forty eight white male rats of the Sprague-Dawley strain aged 4 weeks, were devided into two groups; control group and experimental group. A single target dose of l0Gy of radiation was given to the mandibular condylar area and the observations of the photo analysis, radiologic, histopathologic and immunohistochemical study revealed as follows; 1. Animals killed one week after irradiation showed lesser increase in body weights, no difference in photo analysis and decreased thickness of cartilagenous layers of the condyle than the control group. 2. Two weeks after irradiation the weight increases were almost same in both irradiated and control groups and in photo analysis, the distance from Mental Foramen to Incisal tip (Mf-It) was longer than the controls. Repair processes were taken place in irradiated group, but the cartilagenous layers were thinner than the controls. 3. By the third week after exposure further repair was seen in the trabeculae and the distance from Condylion to Mandibular plane (Cd-Cd') was longer than the controls and the weight increases were almost same as the controls. 4. At 4 weeks after irradiation the cells of proliferating zone repaired to almost normal findings, but the cartilagenous cell layers were still thinner than the control animals. In photo analysis, the distances from Menton to Anterior Notch (Me-An), from First Molar to Mandibular plane (Fm-Fm') were shorter and the weight increases were lesser than the controls. 5. In the S-100 antibody, the positive cells were increased in number, but decreased reactivities were seen at the proliferating zone of the irradiated groups. In the Monoclonal Anti-Proteoglycan antibody and Type Ⅰ collagen antibody, the irradiated groups showed little decreased number of positive cells and in the Type Ⅱ collagen antibody, the differences between irradiated and control groups were undetectable in immunohistochemical study.

• The korean journal of orthodontics
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• v.16 no.1
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• pp.119-131
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• 1986

The purpose of the study is to note the effects of the resection of the lateral pterygoid muscle on the mandibular growth in the growing rats. Twenty four female Wistar rats were used in the experiment. They were divided into three groups: group 1 ; bilateral sham operation group 2 ; bilateral resenction of the lateral pterygoid muscle group 3 ; unilateral resection of the lateral pterygoid muscle (The right lateral pterygoid muscle was resected and the left one was sham-operated.) Groups 1&2 were sacrificed eight weeks lateral and group 3, four weeks later. All specimens were measured with calipers, and stained with hematoxylin and eosin. Groups 1 & 2 were compared with each other. In group 3, the right side was compared with the left. The results were as follows: 1. In the growing rats, the resection of the lateral pterygoid muscle was followed by a decrease of the mandibular growth. After eight weeks, the condyle-mental foramen distance, the angular process-mental foramen distance, the size of the condylar head, the supradentale-first molar distance, and the diameter of the symphysis were significantly smaller than the control. 2. Resection of the lateral pterygoid muscle resulted in decrease of the thickness of the cartilage layer and the prechondroblastic-chondroblastic layer after four weeks. 3. After eight weeks, group 1 and group 2 were not different significantly in the histologic sections. 4. The condylar cartilage was stabilized eight weeks after the experiment.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.25 no.2
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• pp.409-422
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• 1995

The purpose of this study was to investigate the effects of radiation on the formation of rat molar enamel at the developmental stage. The experimental animals were divided into five groups and were irradiated single dose of 396cGy ; 1 st group on 14th day of gestation, 2nd group on 19th day of gestation, 3rd group on 3 days after birth, 4th group on 8 days after birth, 5th group on 28 days after birth. The control and 1, 2, 3, and 4th experimental groups were sacrificed on 2, 4, and 6 weeks and the 5th groups were sacrificed on 1 day and 2 weeks after irradiation. Distal 1/2 and occlusal 1/3 enamel surface of lingual side of lingual cusp, and fractured surface of lingual side of lingual cusp in a longitudinal direction of the mandibular first molar were examined using scanning electron microscope. The following results were obtained. 1. The roughness of enamel surface and enamel hypoplasia were increased in a sequence of 4th, 1st, 2nd, and 3rd experimental group, and the enamel cracks were increased in the 1st and 2nd experimental group. 2. The pattern of enamel hypoplasia had a network form on the 1st and 2nd experimental group, and appeared a linear shape on the 3rd experimental group, and then the crator-like enamel defects were observed in all experimental groups (especially 1st and 2nd experimental group) except 5th. 3. Dentinoenamel junction showed the clear-cut and straight appearance except 5th experimental group. 4. There was no significant difference between 5th experimental and control group.

• International Journal of Oral Biology
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• v.36 no.1
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• pp.31-35
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• 2011

Teeth develop via a reciprocal induction between the ectomesenchyme originating from the neural crest and the ectodermal epithelium. During complete formation of the tooth morphology and structure, many cells proliferate, differentiate, and can be replaced with other structures. Apoptosis is a type of genetically-controlled cell death and a biological process arising at the cellular level during development. To determine if apoptosis is an effective mechanism for eliminating cells during tooth development, this process was examined in the rat mandible including the developing molar teeth using the transferase-mediated dUTP-biotin nick labeling (TUNEL) method. The tooth germ of the mandibular first molar in the postnatal rat showed a variety of morphological appearances from the bell stage to the crown stage. Strong TUNEL-positive reactivity was observed in the ameloblasts and cells of the stellate reticulum. Odontoblasts near the prospective cusp area also showed a TUNEL positive reaction and several cells in the dental papilla, which are the forming pulp, were also stained intensively in this assay. Our results thus show that apoptosis may take place not only in epithelial-derived dental organs but also in the mesenchyme-derived dental papilla. Hence, apoptosis may be an essential biological process in tooth development.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.1
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• pp.25-31
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• 2001

The purpose of this study was to investigate the distribution and fluorescence intensity of vasoactive intestinal polypeptide immunoreactive (VIP-IR) cells in rat trigeminal ganglion following pulp extirpation of rat mandibular molar. The animals were divided into control group(n=6) and experimental group(n=6). The experimental animals were sacrificed at 14 days after pulp extirpation. The trigeminal ganglion was removed and immersed in the 4% paraformaldehyde in 0.1M phosphate buffer. Serial frozen sections about $20{\mu}m$ in thickness were cut with a cryostat. The immunofluorescence staining was performed. The rabbit anti-VIP(1 : 8,000) was used as primary antibody and fluorescene isothiocynate(FITC) conjugated anti-rabbit IgG(1 : 80) as secondary antibody. The slides were observed under confocal laser scanning microscope (CLSM). Unprocessed optical sections were obtained and stored on a optical disk. Color pictures were printed by a video copy processor. The results were as follows; 1. The positive ratio of VIP-IR cells in mandibular part of trigeminal ganglion were 7.40% in control group and 28.42% in experimental group(14 days after pulp extirpation). 2. The relative fluorescence intensity of VIP-IR cells in mandibular part of trigeminal ganglion were 87.78 in control group and 138.65 in experimental group. The relative fluorescence intensity of experimental group was 58% higher than that of control group. 3. In optical serial section analysis of VIP-IR cells of experimental group, most of the 9 sections showed high fluorescence intensity. At high magnification, axons of the experimental group displayed greater VIP-IR than in the control group, and the positive cells were mainly of medium size. The result indicate that number and fluorescence intensity of VIP-IR cells were increased in the mandibular part of trigeminal ganglion following pulp extirpation of mandibular molar, and it suggests that VIP could play a role in processing of nociception.

• Journal of Periodontal and Implant Science
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• v.31 no.2
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• pp.317-332
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• 2001

The purpose of this study was to investigate effects of the natural coral(NC) and the hydroxyapatite/calcium sulfate hemihydrate(HA/CS) on an early stages of wound healing in the rat periodontal fenestration defects. In this experiment, twelve male rats(Mean : 520g in BW) aged 8 to 9 months were used. Experimental periodontal fenestration defects were surgically created with tapered fissure bur at the buccal surface of the left mandibular 1st, 2nd molars. The buccal aspects of molar roots were carefully denuded of their periodontal ligament through a bony window created in the left mandibles of rats under general anesthesia. Each experimental periodontal fenestration defect was grafted with natural coral and HA/CS, randomly. An area without bone graft was assigned for negative control group. At 10,35 days, rats were serially sacrificed via intracardiac perfusion with 2.5% glutaraldehyde and specimens were processed with Hematoxylin-Eosin stain for light microscopic evaluation. The results of this study were as follows : 1. The defect areas were filled with dense connective tissues at 10 days in control group. But in the test(NC, HA/CS)groups, the connective tissues around graft materials were formed more loosely and the response of inflammation by graft materials itself was not found. 2. The defect areas were filled with new osteoid tissues and new cementum was not formed on the cut root surface at 35 days in the control group. 3. New osteoid tissue formation was more prominent at 35 days in control than test groups. 4. The NC and HA/CS particles were encapsulated by loose connective tissues at 10 days and by dense connective tissues at 35 days, respectively. 5. In the test groups, resorption of graft particles was not found through the experimental time. From the above results, natural coral and hydroxyapatite/calcium sulfate hemihydrate may be biocompatible and osteoconductive and have a weak adverse reaction to the periodontal tissues.