• The Journal of Korean Academy of Prosthodontics
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• v.45 no.2
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• pp.240-249
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• 2007

Statement of problem: A phenomenon of screw-loosening in implant abutment is frequently occurred in a single and multiple implant restoration. Purpose: This study was performed to evaluate an effect of abutment material on screw-loosening before and after a cyclic loading. In a single-tooth implant, different materials of abutment, Type III Gold alloy and Zirconium composite$(ZrO_2/Al_2O_3)$ were used. Material and method: The Gold alloy(Type III) and Zirconium composite$(ZrO_2/Al_2O_3)$ were used to make a superstructure of implant, the one of types of UCLA, Each group was constituted of 5 sample with a 30-degree offset angulated loading platform. The external hexagonal fixture was rigidly hel d in a special holding zig to ensure solid fixation without rotation during the tightening and a cyclic loading. A Titanium-alloy screw was used to connect and controlled to be tighten in 20Ncm torque by a digital torque gauge. A 20 times of consecutive closing/opening cycle were performed to evaluate the immediate torque loss. In 5 sample of each material group, an initial opening torque was recorded during 3 closing/opening cycle, then 2Hz, 200N, 1,000,000 cyclic loadings were performed, then a opening torque was evaluated. Result & Conclusion: 1. In this limited study, titanium alloy screw tightened in 20Ncm, a cold-welding phenomen on was not observed during the 20 times of closing/opening cycle(p=0.11, p=0.18). 2. In titanium alloy abutment screw, repeated opening and closing of the screw caused to progressive decrease of opening torque(p=0.014). 3. The difference in preload of screw between gold alloy abutment and ceramic$(ZrO_2/Al_2O_3)$ abutment was not significant(p=0.78). 4. The difference in torque loss of screw between gold alloy abutment and ceramic$(ZrO_2/Al_2O_3)$ abutment was not significant after 2Hz,200N, 1,000,000 cyclic loading(p=0.92). 5. In titanium alloy abutment screw tightened by 20Ncm, the screw loosening was not significant on each group after 2Hz, 200Ncm, 1,000,000 cyclic loading(p=0.59).

• Journal of Korean society of Dental Hygiene
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• v.9 no.1
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• pp.153-168
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• 2009

This study was executed to find out the outcome of Incremental Dental Care from September to November, 2004. 40 visitors to oral health center were examined on the oral conditions every week, seven times during above-mentioned period. Various tests were practiced in order to check their oral conditions before and after IDC such as tooth-brushing method/frequency/duration, calculus index, PHP index, halitosis and dental caries activity. Question and answer sheets were presented to student dental hygienists and 40 visitors respectively after IDC program. Results obtained are as follows. 1. Rotation method of toothbrushing increased from 27.8% to 88.9%. for men and increased from 27.3% to 95% for women. 2. Toothbrushing frequency increased from 2.8 times to 3.0 times a day for men and increased from 2.6 times to 3.1 times for women. Toothbrushing duration increased from 2.3 minutes to 2.8 minutes for men and increased from 2.1 minutes to 2.9 minutes for women. 3. Calculus index reduced from 0.5 to 0.1 for men and reduced from 0.7 to 0 for women. PHP index reduced from 3.7 to 3.0 for men and reduced 3.2 to 1.7 for women. However, halitosis didn't mark any significant difference before and after IDC. 4. Saliva buffering capacity of medium plus showed no change for men(94.5%), however increased from 95.4% to 100% for women. Dental caries activity of medium plus in S.mutans reduced by 4.3 times(72.2% to 16.7%) for men and reduced by 2 times(36.4% to 18.1%) for women. LB test results reduced by 1.5 times(50% to 33.3%) for men and reduced by 2.5 times(50% to 18.1%) for women. Alban's test results reduced by 1.4 times(83.3% to 61.1%) for men and reduced by 1.2 times(81.8% to 68.2%) for women. 5. All participants including visitors and students realized the importance of IDC and expressed a great satisfaction with IDC program. In conclusion, it is considered very necessary that IDC program should be maintained and extended to whole country so as to enhance the peoples' oral health conditions.

• The Journal of Korea Assosiation for Disability and Oral Health
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• v.7 no.1
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• pp.33-37
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• 2011

The ectopic eruption is defined as abnormal eruption which gives to displacement of the teeth and abnormal root resorption of adjacent teeth. The prevalence of ectopic eruption is reported to vary 2~6%, most of them are in the maxilla. Etiologic factors include narrow maxilla, large maxillary teeth, inclined eruption path of the first molar, retruded position of the maxilla and hereditary factor. Irreversible ectopic eruption where the second primary molar is lost often causes mesial tipping and rotation of the permanent molar, unfavorable occlusion and space deficiency for the second premolar. Ectopically erupted teeth should be treated early to maintain normal development of the dentition, harmony of facial growth and occlusal support. The method of the treatment are classified as follows : appliances that is positioned at the contact point for unlocking and the distal movement, fixed appliance that is connected to more than one tooth, and occlusion guiding method after disking or extraction of the second deciduous molar. A case report of a patient with bilaterally ectopic eruption of maxilla and mandible first permanent molar was present. Also, the patient who had experienced the chronic myelogenous leukemia, show various dental developmental complications. The ectopic eruption was treated with a Halterman appliance that was a effective way of correcting of ectopic eruption of the permanent first molar.

• Imaging Science in Dentistry
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• v.33 no.2
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• pp.79-83
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• 2003

Purpose : To assess the relationship between the direction of the indicating rod of the radiographic stent for ideal prosthetic design and the actual possible path of implant fixture placement when residual ridge resorption is considered. Materials and Methods: The study materials consisted of 326 implant sites (male 214 cases and female 112 cases) from a total of 106 patients (male 65 patients and female 41 patients) who desired implant prostheses. Computed tomography of patients were taken and reformatted using ToothPix/sup (R)/ software. Bony defects, bony sclerosis, the change of the direction of indicating rod, and root proximity of the adjacent teeth were examined on the CT-derived images. Results: The rate of the irregular crestal cortex was relatively high on premolar and molar area of maxilla. Mandibular molar area showed relatively high rate of focal sclerosis on the area of implant fixture insertion. The position of the indicating rods were relatively acceptable on the molar areas of both jaws. However, the position of the indicating rods should be shifted to buccal side with lingual rotation of the apical end on maxillary anterior teeth and premolar area. Conclusion: Clinically determined rod direction and position of the indicating rod for implant placement was not always acceptable for insertion according to the reformatted CT images. The pre-operative treatment plan for implant should be determined carefully, considering the state of the alveolar bone using the reformatted CT images.

• Imaging Science in Dentistry
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• v.40 no.2
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• pp.69-74
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• 2010

Purpose : The research was performed to predict the three dimensional relationship between the impacted mesiodens and the maxillary central incisors and the proximity with the anatomic structures by comparing their panoramic images with the CT images. Materials and Methods : Among the patients visiting Seoul National University Dental Hospital from April 2003 to July 2007, those with mesiodens were selected (154 mesiodens of 120 patients). The numbers, shapes, orientation and positional relationship of mesiodens with maxillary central incisors were investigated in the panoramic images. The proximity with the anatomical structures and complications were investigated in the CT images as well. Results : The sex ratio (M : F) was 2.28 : 1 and the mean number of mesiodens per one patient was 1.28. Conical shape was 84.4% and inverted orientation was 51.9%. There were more cases of anatomical structures encroachment, especially on the nasal floor and nasopalatine duct, when the mesiodens was not superimposed with the central incisor. There were, however, many cases of the nasopalatine duct encroachment when the mesiodens was superimpoised with the apical 1/3 of central incisor (52.6%). Delayed eruption (55.6%), crown rotation (66.7%) and crown resorption (100%) were observed when the mesiodens was superimposed with the crown of the central incisor. Conclusion : It is possible to predict three dimensional relationship between the impacted mesiodens and the maxillary central incisors in the panoramic images, but more details should be confirmed by the CT images when necessary.

• Progress in Medical Physics
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• v.12 no.1
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• pp.51-58
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• 2001

Synchrotron radiation (SR) has several advantages over convetional x-rays, including its phase, collimation, and high flux. A synchrotron radiation beamline 5C1 at Pohang Light Source (PLS) was recently built for imaging applications. We have shown that a SR imaging system is useful in imaging microscopic structures. SR with broad-band energy spectrum were adjusted to an object by Si wafers and their energy were approximately ranging from 6 keV to 30 keV. SR were passed through an object and finally transformed into visible lights by CdWO$_4$ scintillator screen. The visible lights which were reflected at an angle of 90 degrees by gold plated mirror were detected by a CCD camera and the image data were acquired using image acquisition system. A high-resolution phantom, capacitor, adult tooth, child tooth, cancerous breast tissue, and mouse lumbar vertebra were imaged with SR imaging system. The Objects were rotated within the field of view of the CCD detector, and their projection image data were obtained at 250 steps over 180 degrees rotation. Image reconstructions were carried out in a PC by using IDLTM(Research systems, Inc., US) program. The spatial resolution of the images acquired by the SR imaging system was measured with a high-resolution chart manufactured for several micrometer resolution. The specimens were also imaged with conventional x-ray radiography system to compare the image quality of radiography obtained with the SR imaging system. The results showed more structural details and high contrast images with SR imaging system than conventional x-ray radiography system. The SR imaging system may have a potential for imaging in biological researches, material applications, and clinical radiography.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.2
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• pp.213-230
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• 2008

The aim of this study was to analyze the initial movement and the stress distribution of each tooth and periodontal ligament during the lingual lever-arm retraction of 6 maxillary incisors using FEA. Two kinds of finite element models were produced: 2-properties model (simple model) and 24-properties model (multi model) according to the material property assignment. The subject was an adult male of 23 years old. The DICOM images through the CT of the patient were converted into the 3D image model of a skull using the Mimics (version 10.11, Materialise's interactive Medical Image Control System, Materialise, Belgium). After series of calculating, remeshing, exporting, importing process and volume mesh process was performed, FEA models were produced. FEA models are consisted of maxilla, maxillary central incisor, lateral incisor, canine, periodontal ligaments and lingual traction arm. The boundary conditions fixed the movements of posterior, sagittal and upper part of the model to the directions of X, Y, Z axis respectively. The model was set to be symmetrical to X axis. Through the center of resistance of maxilla complex, a retraction force of 200g was applied horizontally to the occlusal plane. Under this conditions, the initial movements and stress distributions were evaluated by 3D FEA. In the result, the amount of posterior movement was larger in the multi model than in the simple model as well as the amount of vertically rotation. The pattern of the posterior movement in the central incisors and lateral incisors was controlled tipping movement, and the amount was larger than in the canine. But the amount of root movement of the canine was larger than others. The incisor rotated downwardly and the canines upwardly around contact points of lateral incisor and canine in the both models. The values of stress are similar in the both simple and multi model.