• Journal of Oral Medicine and Pain
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• v.37 no.4
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• pp.251-256
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• 2012

With today's heightened interest in quality of life, leisure and sports activities were popular in the general public. Accordingly, the incidence of oral and maxillofacial injury are also rising. Use of a mouth protector to prevent the trauma of the oral and maxillofacial region is growing in importance, and among the mouth protector the mouthguard is the most commonly used. Mouthguard has been suggested to protect injuries by (1) preventing tooth injuries by absorbing and deflecting blows to the teeth; (2) shielding the lips, tongue, and gingival tissues from laceration; (3) preventing opposing teeth from coming into violent contact; (4) providing the mandible with resilient support, which absorbs an impact that might fracture the unsupported angle or condyle of the mandible; (5) preventing neck and cerebral brain injuries. Although mouthguard is effective for prevention of oral and maxillofacial injury, it is not widespread to athletes or general public and they are lack of awareness about the importance of mouthguard. We present the types and materials of mouthguard, things to consider when mouthguard fabrication, and the usage. This should be helpful in awareness about the importance and popularization of mouthguard.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.2
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• pp.308-319
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• 2003

Mechanical forces are known to have an effect on bone formation, maintenance and remodeling, and there is evidence that the development of the mandibular condyle in the rat or mouse is influenced by altered functional force. However, studies are lacking in molecular-biologic mechanism such as the identification of differentiation factor induced from functional force. Here a mouse model was used to investigate the functional stress-responsive gene or factors which is related to the altered force by comparing the expression genes of functional state and hypo-functional state of the mouse mandible. ICR mice were provisioned with either a soft, mushy diet (soft-diet group) or hard rat pellets (hard-diet group) beginning at weaning for the alteration of functional force and subsequently sacrificed at 89 days of age. Incisor of mice in group 1 were trimmed twice a week to reduce occlusal forces. After killing the animals, mandibular bone including condyle were collected for RNA extraction, subtractive hybridization, northern blot analysis and mRNA in-situ hybridization. The results as follows; 1. A total of 39 clones were sequenced, and 11 individual sequence types were subsequently identified by subtractive hybridization, as 28 clones were represented twice in the analyzed sets. 2. Consequently four candidate clones, FS-s (functional stress-specific)2, -5, -18, and -22 were identified and characterized by homolgy search and northern analysis. Four of these clones, FS-s2, -5, -18, and -22, were shown to be expressed differentially in the hard-diet group. 3. Histologic sections showed that osteoblastic activity along the bone trabeculae and active bone remodeling were significantly lower in soft than in hard diet animals. A soft diet seems to enable a longer period of endochondral ossification in the mandibular condyle. 4. Although the mRNAs of FS-s2, -5, -18, and -22 were expressed rarely by cells of the soft-diet group, highest expression was detected in the cells of the hard-diet group. Together with the above results, it is suggested that FS-s2, -5, -18, and -22 could act as an important factors controlling the tissue changes in response to functional stress. The exact functional significance of these findings remains to be established.

• The korean journal of orthodontics
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• v.26 no.3
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• pp.255-265
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• 1996

The purpose of this study was to investigate if there were a significant difference between cephalometric measurements of mandibular position derived from a centric occlusion tracing compared to those of a converted centric relation tracing in the Class III malocclusion. The sample consisted of 25 Class III malocclusion and 25 normal occlusion persons who had no orthodontic treatment. The records included an lateral cephalometrics in centric occlusion, centric relation and centric occlusion bite registration and diagnostic casts mounted on the SAM II articulator in CR. The amount of CR-CO discrepancy of condyle was recorded using a MPI(Mandibular Position Indicator, MPI $200^{(R)}$, Great Lakes Orthodontics, USA). The conversion of the CO cephalogram to CR using the MPI readings was performed on the Conversion work sheet. Measures of mandibular position were chosen for the purpose of this study. The comparison of the difference between CO and CR cephalometric measurements in the normal occlusion and Class III malocclusion group were studied. The results were as follows: 1. In the features of CR-CO discrepancy of the condyle, the condyle was displaced posterior and inferior when the teeth were in centric occlusion. The horizontal component(${\Delta}X$) in Class HI malocclusion group was greater than the vertical component(${\Delta}Z$) and also greater than the horizontal component(${\Delta}X$) in normal occlusion group. There was no statistically significant correlation between MPI measurements and the groups of normal occlusion and Class III malocclusion group. 2. In the comparison of the cephalometric measurements in each group, Normal occlusion group showed significant difference in measurements such as ANB, Facial angle, Facial convexity and ODI. Class HI malocclusion group showed significant difference in measurements such as ANB, Facial angle, Facial convexity, ODI, SNB, APDI, L1-FP and it had more significance than the normal occlusion group. 3. The Value of cephalometric measurements was significantly different between CO and CR but there were no differences between the groups of normal occlusion and Class III malocclusion. The results of this study suggest that if the discrepancies are greater than the amount of normal displacement from clinically captured centric relation, centric relation should be considered as the starting point for proper diagnosis and treatment planning.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.28 no.5
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• pp.404-416
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• 2006

Purpose : This study was to clarify the changes in mandibular condyle after unilateral mandibular distraction osteogenesis throughout histological changes and expression of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of matrix metalloproteinase-2 (TIMP-2). Materials & Methods : Intraoral distractors were placed via submandibular incision in 8 dogs. Two unoperated animals served as controls. Distraction was performed five days after osteotomy as a rate of 0.5 mm twice per day for 10 days. Two animals were sacrificed on 7, 14, 28, and 56 days after completion of distraction, respectively. Ipsilateral condyles were harvested and processed for histological and immunohistochemical examinations. Results : The condyle cartilage is separated into four layers: fibrous layer, proliferative layer, hypertrophic layer, and calcified layer. At 7 days and 14 days after distraction, the condylar cartilage showed the decreased thickness of the articular cartilage and reduced cellularity. At 28 days after distraction, there was an increase in cellularity of fibrous, proliferative, and hypertrophic layer. However, it demonstrated reduced cellularity compared to the control. At 56 days of after distraction, the articular cartilage was an almost normal histologic structure. Positive Safranin-O staining, indicative of sulfated proteoglycans, was examined in the condylar cartilge of nonloaded control. At 7 days and 14 days after distraction, the sulfated proteoglycans is almost completely depleted from the noncalcified part of the condylar cartilage. At 28 days after distraction, there was an increase in Safranin-O staining intensity. However, the staining intensity of the experimental condyle was weaker than that of the control. At 56 days of after distraction, the condylar cartilage showed almost normal Safranin-O staining pattern. In control condyle, MMP-2 immunostaining was seen in fibrous, proliferative, and hypertrophic layer of condylar cartilage, however, it demonstrated lack of staining in fibrous and proliferative layer. At 7 days and 14 days after distraction, strong MMP-2 immunoreactivity was seen in the fibrous, proliferative and hypertrophic layer of the condylar cartilage. At 28 days after distraction, MMP-2 immunostaining was seen in the fibrous and hypertrophic layer of condylar cartilage, however, their immunoactivity was reduced. At 56 days after distraction, MMP-2 immunoreactivity showed almost normal immunostaining pattern. In control condyle, TIMP-2 immunostaining was primarily seen in fibrous and hypertrophic layer of condylar cartilage, however, it demonstrated lack of staining in proliferative layer. At 7 days after distraction, very weak TIMP-2 immunoreactivity appeared in fibrous, proliferative and hypertrophic layer of the condylar cartilage. At 14 days after distraction, weak TIMP-2 immunoreactivity was seen in the fibrous, proliferative and hypertrophic layer of the condylar cartilage. At 28 days after distraction, TIMP-2 immunoreactivity was increased in the fibrous and hypertrophic layer of condylar cartilage. At 56 days after completion of distraction, TIMP-2 immunoreactivity showed almost normal immunostaining pattern. Conclusions : The results show that short-term outcome of physiologic distraction osteogenesis may lead to degenerative changes in the condylar cartilage. These alterations in the condylar cartilage may be considered as a pressure-related degeneration of the cartilage tissue. However, the long-term results suggest that the condylar cartilage display repair activity after mandibular distraction osteogenesis.

• Journal of Dental Rehabilitation and Applied Science
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• v.17 no.4
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• pp.283-305
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• 2001

The purpose of this study was to analyze the stress distribution of condylar regions and edentulous mandible with implant-supported cantilever prostheses on the certain conditions, such as amount of load, location of load, direction of load, fixation or non-fixation on the condylar regions. Three dimensional finite element analysis was used for this study. FEM model was created by using commercial software, ANSYS(Swanson, Inc., U.S.A.). Fixed model which was fixed on the condylar regions was modeled with 74323 elements and 15387 nodes and spring model which was sprung on the condylar regions was modeled with 75020 elements and 15887 nodes. Six Br${\aa}$nemark implants with 3.75 mm diameter and 13 mm length were incorporated in the models. The placement was 4.4 mm from the midline for the first implant; the other two in each quardrant were 6.5 mm apart. The stress distribution on each model through the designed mandible was evaluated under 500N vertical load, 250N horizontal load linguobuccally, buccal 20 degree 250N oblique load and buccal 45 degree 250N oblique load. The load points were at 0 mm, 10 mm, 20 mm along the cantilever prostheses from the center of the distal fixture. The results were as follows; 1. The stress distribution of condylar regions between two models showed conspicuous differences. Fixed model showed conspicuous stress concentration on the condylar regions than spring model under vertical load only. On the other hand, spring model showed conspicuous stress concentration on the condylar regions than fixed model under 250N horizontal load linguobuccally, buccal 20 degree 250N oblique load and buccal 45 degree 250N oblique load. 2. Fixed model showed stress concentration on the posterior and mesial side of working and balancing condylar necks but spring model showed stress concentration on the posterior and mesial side of working condylar neck and the posterior and lateral side of balancing condylar neck under vertical load. 3. Fixed model showed stress concentration on the posterior and lateral side of working condylar neck and the anterior and mesial side of balancing condylar neck but spring model showed stress concentration on the anterior sides of working and balancing condylar necks under horizontal load linguobuccally. 4. Fixed model showed stress concentration on the posterior side of working condylar neck and the posterior and lateral side of balancing condylar neck but spring model showed stress concentration on the anterior side of working condylar neck and the anterior and lateral side of balancing condylar neck under buccal 20 degree oblique load. 5. Fixed model showed stress concentration on the anterior and lateral side of working condylar neck and the posterior and mesial side of balancing condylar neck but spring model showed stress concentration on the anterior side of working condylar neck and the anterior and lateral side of balancing condylar neck under buccal 45 degree oblique load.. 6. The stress distribution of bone around implants between two models revealed difference slightly. In general, magnitude of Von Mises stress was the greatest at the bone around the most distal implant and the progressive decrease more and more mesially. Under vertical load, the stress values were similar between implant neck and superstructure vertically, besides the greatest on the distal side horizontally. 7. Under horizontal load linguobuccally, buccal 20 degree oblique load and buccal 45 degree oblique load, the stress values were the greatest on the implant neck vertically, and great on the labial and lingual sides horizontally. After all, it was considered that spring model was an indispensable condition for the comprehension of the stress distributions of condylar regions.