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Purpose: To know the transmittance of light when wearing shading goggles and to protect eyes from blue light emitted from dental scanner when using CAD/CAM works or inducing polymerization reactions of dental resin with curing unit and infrared light occurred when melting Dental precious metal and non-precious metal alloys. Methods: By measuring and comparing the average transmittances of blue light, visible light and infrared ight by using UV-Vis Spectrophotometer analysis measuring instrument, I compared 3 GREEN Color Goggles worn when casting Dental precious metal and non-precious metal alloys, and compared each of YELLOW, ORANGE Color Goggles worn when using Dental CAD/CAM scanners and Light Curing(LED) the Dental resin. Results: In blue light range, YELLOW Color Goggles are more effective than ORANGE Color Goggles. In infrared light range, No.12 Goggles are more effective than No.10 and No.11 Goggles. Conclusion: When wearing blue light shading goggles to avoid harmful blue light occurred in using dental scanner and curing light, and when wearing infrared light shading goggles to avoid harmful infrared light during casting, to avoid the Side Effects like transmittance rate of blue light and infrared light goggles becomes too high to block appropriate amount of harmful light or too low that causing lower image clarity.

Purpose: The aim of this study was to investigate the influence of short and long duration sintering on microstructure and flexural strength of zirconia. Methods: To conduct three-point bending test, Zirconia specimens are milled according to ISO 6872 guidelines(N=18, n=9 per group). Two specimens group(n=8) is sintered for 10 hours(Standard schedule) and 3 hours(Speed schedule) at the peak temperature of 1550°C with silicon carbide sintering furnace. Flexural strength of specimens are measured by instron. After coating each specimen(n=1), microstructure of specimens is observed using Scanning Electron Microscope(SEM). T-test was utilized to statistically assess the data. Results: The mean and standard deviation value of the flexural strength for standard schedule group are 578.15±57.48Mpa, that of speed schedule are 465.9±62.34Mpa. T-test showed significant differences in flexural strength between two zirconia specimen group which applied standard schedule and speed schedule respectively(p<0.05). Conclusion: The result of this study showed that the increase in sintering time led to increased grain size, and also to a positive effect on the flexural strength.

Purpose: This in vitro study was conducted to evaluate the marginal and internal fit of three-unit Co-Cr frameworks fabricated by computer-aided metal milling and direct metal laser sintering(DMLS) systems in comparison to conventional casting method. Methods: Three-unit Co-Cr frameworks were fabricated by conventional wax up with casting(CWC), computer-aided metal milling(MM) and direct metal laser sintering(DMLS)(n=10 each). The marginal and internal fit of specimens were examined using a light-body silicone impression material. The thickness of light-body silicone was measured at eight reference points each, divided in the mesio distal and bucco lingual directions. All measurements were conducted by a stereomicroscope. Digital photos were taken at 150× magnification and then analyzed using a measurement software. The Kruskal-Wallis test and Bonferroni correction were used for analyzing the results. Results: The mean(SD) is ㎛ for fabrication methods, the mean marginal fit were recorded respectively, DMLS 39(27), followed by CWC 63(38), MM 220(128). and the mean internal fit CWC 95(47), DMLS 116(49), MM 210(152). In addition, the largest gap was found in the occlusal surface area among the internal measurement areas of all groups. Conclusion: As a result, the direct metal laser sintering method showed better marginal and internal fit than the metal milling method. The marginal and internal fit were statistically different according to the three fabrication methods(p<0.001). Except the MM group, the marginal fit of the CWC and DMLS groups was below the clinical standard of 120 ㎛. Based on the results of this study, it can be applied to clinical use in the future.

Purpose: This study is to compare the flexural strength and modulus by inserting a mesh and stick type fiberglass reinforcement into resin specimens. Methods: Wax specimens (length 64 mm, width 39 mm, thickness 5 mm) are prepared according to ISO 20795-1:2013. Mesh type and stick type glass fiber reinforcements were prepared. The prepared wax specimens were used plaster and flask for investment. The flask was separated and the wax was removed. The heat curing resin was injected into the flask, and then a mesh type and stick type fiberglass reinforcement were inserted. The prepared resin specimen was cut into three equal parts (length 64 mm, width 10 mm, thickness 3.3 mm). The mesh type glass fiber reinforcement (MT group) and the stick type glass fiber reinforcement (ST group) were classified into two groups. The prepared specimen was measured using a universal testing machine (UTM). The data were analyzed by Mann-Whitney U test, and the significance level was set to 0.05. Results: In the flexural strength, the ST group was higher than the MT group, and there was a significant difference between the two groups (p<0.05). In the flexural modulus, the ST group was higher than the MT group, and there was a significant difference between the two groups (p<0.05). Conclusion: The stick-type glass fiber increased the flexural strength than the mesh-type glass fiber reinforcement.

Purpose: A study analysed the stress distribution of abutment screw and supporting bone of fixture by the tightening torque force of the abutment screw within clinical treatment situation for the stability of the dental implant prosthesis. Methods: The finite element analysis was targeted to the mandibular molar crown model, and the implant was internal type 4.0 ㎜ diameter, 10.0 ㎜ length fixture and abutment screw and supporting bone. The occlusal surface was modeled in 4 cusps and loaded 100 N to the buccal cusps. The connection between the abutment and the fixture was achieved by combining three abutment tightening torque forces of 20, 25, and 30 Ncm. Results: The results showed that the maximum stress value of the supporting bone was found in the buccal cortical bone region of the fixture in all models. The von Mises stress value of each model showed 184.5 MPa at the 20 Ncm model, 195.3 MPa in the 25 Ncm model, and 216.5 MPa in the 30 Ncm model. The contact stress between the abutment and the abutment screw showed the stress value in the 20 Ncm model was 201.2 MPa, and the 245.5 MPa in the 25 Ncm model and 314.0 MPa in the 30 Ncm model. Conclusion: The increase of tightening force within the clinical range of the abutment screw of the implant dental prosthesis was found to have no problem with the stability of the supporting bone and the abutment screw.

Purpose: This study compares how accurately the specimen produced by the machining method and the rapid prototyping method is produced and how much dimensional error occurs with the finished casting body, and presents the results as experimental comparative data. Methods: Specimens produced using a digital processing method were cast by a conventional dental casting process, and dimensional changes of the finished casting body were measured to compare shrinkage and expansion. Results: In the control group that did not artificially induce large swelling, the dimensional error was the smallest, and the shrinkage and expansion reactions cannot be elimainated in all processes. Conclusion: The shrinkage and expansion depend on the given conditions, so if there is a change in the traditional dental casting process, it is necessary to adjust all the parameters to obtain an accurate casting body.

Purpose: This study is to compare and analyze the shrinkage of the specimen after UV irradiation of UV cured resin at 5, 15, and 30 minutes. Methods: A cylindrical UV cured specimen was produced using a stainless steel mold. UV cured resin specimens were prepared in three groups: 5 minutes cured (5M), 15 minutes cured (15M), and 30 minutes cured (30M). The measurement was made in total 3rd. The measurement was made in total 3rd. The primary measurement was made after 24 hours using a digital measuring instrument. The 2nd and 3rd measurements were deposited in a constant temperature water bath and the shrinkage was measured. The measured data was calculated by referring to the ASTM C326 linear measurement calculation method. T-test and One-way ANOVA were performed to test the significance between groups. The post-test was conducted with Tukey (α=0.05). Results: When the inner diameter and the outer diameter of the three groups not placed in the water bath were compared and analyzed, the contraction was the smallest at 6.8% in the 5M group, and the contraction was the largest at 7.3% in the 30M group. In the outer diameter, the contraction of the 5M group was the smallest at 3.5%, and the contraction of the 30M group was the largest at 4.5%. Shrinkage decreased in all three groups immersed in a water bath for 3-7 days. Conclusion: In the UV cured resin specimen, the shrinkage increased as the amount of UV irradiation increased.

Purpose: This study aimed to investigate the effects of the sintering conditions of zirconia core on the adaptability. Methods: Ten specimens of each of commercial brand of zirconia(Razor 1100, U&C international, Seoul, Korea) were made and sintered under three different conditions. Specimens were divided into three subgroup(n=10) and sintered with various total time(1hr, 3hr, 9hr) at the maximum temperature(1500℃). The digitized data was superimposed with 3D inspection software to quantitatively obtain the adaptation of a zirconia core, and visual differences were confirmed with a color map. The root mean square(RMS) values of group were statistically analyzed with one-way ANOVA(α=0.05). Results: The overall adaptation of the zirconia cores were as follows; ss-1hr: 36.18±5.2㎛, ss-3hr: 39.55±3.9㎛, cs-9hr: 46.62±4.3㎛. They were statistically significant differences between groups for adaptation(p<0.05). Conclusion: Based on the results of this study, it could be considered that sintering condition of 1500℃ and 1~3 hour is recommended for the better marginal and internal fit. Speed sintering can be widely utilized to fabricate zirconia prothesis as the properties of those almost are to dentistry uses.

Purpose: The aim of this study is to observe the compressive fracture strength of the crown according to the direction of the occlusal force of the mandibular canine and carnassial of the small dog. Methods: The abutment models of mandibular canine and carnassial were prepared, specimens of zirconia, PMMA and Ni-Cr alloy were produced. The experimental jig was fabricated with Co-Cr alloy and buried in acrylic resin after make tilt to specified angle. The specimen was attached to a jig and loaded using a universal testing machine until the specimen fractured. Results: The compressive fracture strengths of CXZ and CXP specimens were found to be 999.21 ± 31.15 N on average and 731.42 ± 59.13 N on average. And CZZ and CZP specimens were 730.48 ± 70.14 N on average and 377.65 ± 11.87 N on average. CXN and CZN specimens were not fractured. In addition, MZZ and MZP specimens were 746.46 ± 50.75 N and 258.64 ± 31.86 N on average. The MZN specimens were not fractured. Conclusion: Zirconia has compressive fracture strength that can be applied to small dog's canine and Carnassial prosthetics, while PMMA has inadequate strength to small dog's carnassial prosthesis.

Purpose: This study is for the prosthesis of dog. Observed the occlusal relation between the small dog canine and carnassial teeth. The direction of the bite force was analyzed by 3D FEM(finite element method). Methods: The mandibular canine and carnassial of dog were tested. The skull of dog was contact point confirmed by dental CAD. The skull of dog was scaned using CT and a 3D model was created. The 3D model was analyzed ABAQUS. Closing movement has been 100N, 200N, 300N, 500N, 1000N, 1500N. The Direction of bite force was confirmed. Results: As occlusal force increased, the direction of bite force appeared to (-y), (-x,-y,-z), (-x,-y), (-x,-y,+z), (-x,-y,+ z), (+x,-y) in mandibular left canine. And the direction was seen at (+x, -y), (+x,-y,-z), (+x,-y), (-x,-y,+z), (-x,-y,+z), (+x,-y). When the occlusal load is 100 N, 200 N, 300 N, 500 N, the direction of the mandibular carnassial appears as (-x, -y, -z), and when the occlusal load is 1000 N, 1500 N, the direction appears as (-x,-y). Conclusion: The mandibular canine showed irregularities in the coordinates of the direction of the bite force, and the mandibular carnassial showed regularity in the coordinates of the direction of the bite force.

Purpose: The purpose of this study was to conduct a cost accounting of implant prosthesis according to the fabrication activities. Methods: In this study, the cost price of implant prosthesis fabrication activities was calculated by the bottom-up costing approach for material and labor cost and the top-down costing approach for expenses and other. Results: The total cost price was estimated to 220,000 ~ 310,000 won per one implant prosthesis. By product, the screw type was estimated to 220,000 ~ 230,000 won, and when the stent and tray were included, it was 260,000 ~ 270,000 won, which increased about 40,000 won. And, the cement type with more material and labor time was estimated to 250,000 ~ 260,000 won, and when the stent and tray were included, it was about 300,000 won. Conclusion: In terms of the fabrication cost ratio by items, it was shown that material cost and labor cost accounted for about 40% and 30% of the total cost structure for resin case, respectively, which was the opposite for porcelain. It was shown that expenses and general administrative expenses accounted for about 15%, and profits were about 11% ~ 14% in both cases.

Purpose: The purpose of this study is the tooth decay ratio of the children and adolescents in four rural areas of Kyrgyzstan. Methods: Oral examinations were conducted 2,677 children and adolescents in Nizhniy chuy, Bokonbayevo, Chon Tash and Arashan from March 2017 to November 2019. It was investigated decayed tooth ratio(DT), decay permanent tooth ratio(DPT) and missing permanent tooth ratio(DMT) according to ages and areas by direct observation of the oral cavity. Results: In all areas, the rate of all children and adolescents aged 6 to 14 had very high DT of more than 94 percent overall. Furthermore, it was showed that high DPT rates above 78% on average and DMT over 8 years old in Chon Tash and Arashan. Conclusion: These results are higher than the average of DT, DPT and DMT in OECD countries. In order to promote oral health of children and adolescents, increased interest in oral health and policy measures at the Kyrgyzstan government level are considered urgent.

Purpose: The purpose of this study was to investigate dental technicians’ awareness of infections and to enhance their interest and commitment towards infection prevention. Methods: A self-reported questionnaire survey was conducted among dental technicians. Total of 195 responses were used for analysis. A cross-tabulation analysis was used to compare dental technicians’ awareness of infections according to their levels of education on infection prevention (α=0.05). Results: Dental technicians were educated on infection prevention (40.5%). Most participants received infection prevention education from school (29.8%). Dental laboratories had an infection control guideline (34.9%). Dental technicians were not aware of infection risks at their workplaces or believed that they were not at risk of infections at their workplaces (59.3%). Conclusion: Dental technicians must be consistently educated on infection prevention and control through systematic education at school and wider promotion through media. Research is needed to economically and efficiently improve equipment used by dental technicians and to protect them from infectious diseases. A budget for infection prevention must also be determined. Institutional measures such as providing support for dental technicians at the policy level and developing a basic infection prevention manual are necessary. Solving these issues not only protects dental technicians from infections but also allows them to provide high-quality medical services.

Purpose: The purpose of this study is to examine decision factors to start orthodontic treatment with male and female undergraduates having experience in orthodontic treatment at a dental clinic or hospital because of malocclusion. Methods: A survey was carried out to investigate decision factors to begin orthodontic treatment with 330 male and female undergraduates attending universities located in Daegu Metropolitan City or Gyeongsangbuk-do who had experience in orthodontic treatment at a dental clinic or hospital because of malocclusion, and out of 330 questionnaire sheets, total 294 (89.1%) sheets were employed for analysis after excluding ones unreliably or erroneously answered. Results: According to the results of analyzing decision factors for orthodontic treatment, such factors as ‘a dentistry-related person’s suggestion’, ‘feeling necessity on one’s own’ are found to be significantly higher in students majoring in health units than those having non-dental health majors, and students residing in small and medium cities are influenced more significantly by this decision factor, ‘an acquaintance’s suggestion’, than those living in farming and fishing villages or big cities, and students who started orthodontic treatment at elementary school were more significantly influenced by the factor, ‘feeling necessity through the public media’. Conclusion: Among the factors influencing their decision on orthodontic treatment, no influence was found in sexual difference, and each of the decision factors influenced them considerably according to the difference of their residence, economic power, majors, or time to start orthodontic treatment.