Earticle

Purpose: The present study was performed to investigate the effect of abutment inclined angle on the marginal fit of zirconia all-ceramic crown. Methods: The Ti abutments with 3 different inclined angle(2°, 4° and 6°) were fabricated. The zirconia copings were fabricated for each abutment by using dental CAD/CAM system. The manufactured zirconia copings were duplicated through silicone replica technique, and a replicated specimen was sectioned in the center of buccolingual and mesio-distal axial to measure the marginal fit by using a stereo microscope. The results were analyzed using a one-way ANOVA with SPSS 22.0 for Windows(α=0.05). Results: On the bucco-lingual axial, marginal fit was the RL3(41.5±3.4㎛), RL2(44.3±4.3㎛) and RL1(47.5±5.7㎛), respectively. On the mesio-distal axial, marginal fit was the RL3(41.1±3.7㎛), RL2(45.7±5.3㎛) and RL1(46.2±4.5㎛), respectively. One-way ANOVA showed statistically significant difference between groups for marginal fit(p<0.05). Conclusion: For marginal fit of the abutments inclined angle, RL3 specimen was superior. The abutment inclined angle had influence on marginal fit of the zirconia copings. The marginal fit of each group were within clinically acceptable range.

Purpose: The purpose of this study is to evaluate the marginal gap of all-ceramic crowns fabricated by CERECⓇ in-office CAD/CAM system. Methods: The mandibular first molar was selected as the abutment for the experiments. Thirty working models were prepared. VITA Mark Ⅱ(VM) and VITA Enamic(VE), LAVA Ultimate(LU) blocks were milled using CEREC MCXL with CEREC 3D system to construct 10 crowns for each groups. To measure marginal gap, milled restorations were examined under digital microscope with scale under 160x magnifications. The results were statistically analyzed using the one-way ANOVA and Tukey’s HSD test(α=0.05). Results: There was no significant difference in the marginal gap regarding to ceramic materials (p>0.05). Conclusion: Single crowns fabricated using CEREC in-office CAD/CAM system provided clinically acceptable marginal gap. This confirmed that the type of ceramic material used does not determine the precision of fit of a prosthesis.

Purpose: Currently advanced in Dental CAD/CAM technology increase a use of Co-Cr sinter metal block at Dental CAD/CAM part traditionally it has been being used with metal casting method. There is an advantage that can leave out a step of investment and casting as well as reducing a working time to compare with conventional casting method in a dry milling. Methods: In this research, compare a deformation of before and after sinter result of Co-Cr sinter metal block. Design a specimen figure by 3D CAD software and transformed it to a STL file can be used at Dental CAD/CAM. With a transformed STL file, milled a Co-Cr sinter metal specimen by using a Dental CAD/CAM dry milling machine. It arrived at the following conclusions after measuring an outer form and thickness of a machined specimen and then after sinter measure it again in a way of before sinter measurement method. Results: It is confirmed that there is no error while a 3D design figure specimen is transformed to a Dental CAD data. It is observed that there is no error at Co-Cr sinter metal specimen which consider a length of single coping and bridge. Conclusion: It is observed that there is no deformation at a specimen of AS05 and AB05 are made of 0,5mm thickness. On the other hand, the out of range of deformation is observed at a specimen of AS10 and AB10 which are made of 1mm thickness.

Purpose: The aim of this research was to evaluate the influence of different surface treatments on the shear bond strength of zirconia ceramic to composite resin. Methods: Seventy two cylinder-shape (diameter: 5 mm; height: 12 mm) blocks of experimental industrially manufactured Y-TZP ceramic were abraded with 125㎛ Al2O3 particles and randomly divided into 4 groups. All the materials were categorized as group Gc(control group - composite resin veneering on zirconia surface), Gr - composite resin veneering after surface treatment of Rocatec system (3M ESPE, Seefeld, Germany) group; Gz - composite resin veneering after surface treatment of Zirconia primer (Z-primer, Bisco, U.S.A) group; Gm - composite resin veneering after surface treatment of zirconia primer (Monobond plus, ivoclar vivadent AG, Liechtenstein) group. Two different zirconia primers and Rocatec system were used to zirconia cylinders (n=16) onto the zirconia surface. Zirconia specimens, polished and roughened, were pretreated and composite bilayer cylinders bonded using conventional adhesive techniques. Results: Shear bond strengths were analyzed using single-factor ANOVA(p<0.05). Bond strength values achieved after airbone particle abrasion and zirconia surface pre-treatments(p<0.05). Conclusion: Shear bond strength tests denmonstrated that zirconia primer is a viable method to improved bond strength between zirconia ceramic core and veneering composites.

Purpose: The purpose of this study is to evaluate the effect of two different oblique mechanical loading to occlusal surfaces of cement retained implant on the stress distributions in surrounding bone, using 3- dimensional finite element method. Methods: A 3-dimensional finite element model of a cement retained implant composed of three unit implants, simplified ceramic crown and supporting bone was developed according to the design of ement retained implant for this study. two kinds of surface distributed oblique loads(100 N) are applied to following occlusal surfaces in the single crowns; 1) oblique load on 2 occlusal points(50N for each buccal cusp, 2 buccal cusps exist), 2) oblique load on 4 occlusal points(25N for each buccal and lingual cusp, 2 buccal and 2 lingual cusps exist) Results: The results of the comparison of the stress distributions on surrounding bone are as follows. In the condition of oblique load on 2 occlusal points, VMS was 741.3 Mpa in the M1(Ø4.0×13㎜) model and 251.2 Mpa in the M2(Ø5.0×13㎜) model. It means the stress on the supporting bone is decreased. The results of oblique load on 4 occlusal points are similar to this one. Conclusion: Increasing the diameter of the implant fixture is helpful to distribute the stress on the supporting bone. Also, to obtain the structural stability of the supporting bone, it is effective to distribute the load evenly on the occlusal surface of crown in producing single crown implant.

Purpose: The dental implant should be enough to endure chewing load and it’s required to have efficient design and use of implant to disperse the stress into bones properly. This study was to evaluate the stress distribution on a supporting bone by lengths and diameters of the implant fixture. Methods: The modeling and analysis of stress distribution was used for the simple molar porcelain crown model by Solidworks as FEM program. It was designed on applying with tightening torque of 20 Ncm of a abutment screw between a cement retained crown abutment and a fixture. The fixtures of experimental model used 10, 13㎜ by length and 4, 5㎜ by diameter. A external vertical loading on the two buccal cusps of crown and performed finite element analysis by 100 N. Results: The maximum von Mises stress(VMS) of all supporting bone models by fixture length and diameter were concentrated on the upper side of supporting compact bone. The maximum stress of each model under vertical load were 164.9 ㎫ of M410 model, and 141.2 ㎫ of M413 model, 54.3 ㎫ of M510 model, 53.6 ㎫ of M513 model. Conclusion: The stress reduction was increase of fixture’s diameter than it’s length. So it’s effective to use the wider fixture as possible to the conditions of supporting bone.

Purpose: It is to compare and evaluate the change of the wear rate and phase variation of the Zirconia before and after the sintering after the grinding by a high speed equipment manufactured for the Zirconia. Methods: The specimen of the sintered Zirconia was manufactured as size of 15㎜×15㎜×2㎜. The grinding has been applied to each of all pieces of each test groups for a minute fit for each condition at same speed of 50,000 rpm by a diamond bur at high speed handpiece with injection of the air and water. For the observation of the surface before and after the sintering of the each test piece, the cross section of it was observed as 100 magnification by a scanning electron microscope after it was coated by PT, and the diffraction analysis was performed by XDR to compare the crystal phase of the Zirconia. The average surface roughness value of all specimens were evaluated. The wear test was performed at room temperature by applying a load of 1kg for 120,000 cycles for the chewing period 6 months. Wear was analyzed for the enamel cusps by measurement of the vertical substance loss with a laser scanner. Conclusion: The phase variation from the tetragonal phase to the monoclinic phase was confirmed in the test group of the pre-sintered Zirconia after the grinding, and the value of the surface roughness and the wear rate was increased in experimental group.

Purpose: This study was conducted to examine the color stability of temporary prosthetic materials for dental CADCAM. Method: 2 kinds of existing acrylic resin temporary filling materials and 2 kinds of polymer prosthetic materials for dental CAD-CAM were used for testing, and five specimens respectively were absorbed in soy sauce, red pepper paste, and coffee. A Chroma Meter was used as analysis equipment. The color change of the specimens was observed to calculate ΔE value throughout 2 days, 3 days, 4 days, and 5 days and this was analyzed and the following result was obtained. Results: Snap’s ΔE value was bigger than Vipi block(p<0.05). Red pepper paste had the largest impact on the color change of resin(ΔE), followed by soy sauce and coffee(p<0.000). With the passage of time, ΔE value was inversely(-) related and decreased somewhat(p<0.000).

Purpose: Observation of Oxide Film Formation and Bonding Strength according to surface treatment of Co-Cr Alloy for porcelain fused to Metal. Methods: metal specimens 0.5㎜×25㎜×4㎜ in size were made using Co-Cr alloys for porcelain fused to metal crown (Heraenium P, Tae jung Medis). Dental porcelain 0.5㎜×25㎜×4㎜ in size was sintered on the metal specimens after changing the etching time, sandblasting condition, and heat treatment temperature. Subsequently, the bonding strength was compared by the three-point flexural strength test using a universal testing machine (UTM) to observe the fracture surface and oxidized layers. Results: With regard to the experimental group treated with acid-etching, Specimen 1 treated for 25 minutes (B- 3) showed the highest bonding strength, and Specimen 2 treated only with sandblasting showed the most excellent bonding force at 3.5 bar (C-3). With regard to the experimental group treated with sandblasting at 3.5 bar after acid-etching for 25 minutes, Specimen 3 with heat treatment at 980℃ (D-3) showed the highest bonding strength. Conclusion: The specimen which went through both sandblasting and etching, showed an excellent ceramicmetal bond strength.

Purpose: The purpose of this study were to evaluate the quality of dental prostheses printed by 3-dimensional printing system. Methods: Mater model was prepared and ten study models were fabricated. Ten single crowns were printed by 3D-printing system(Resin group) and another ten single crowns using casting method were manufactured(Metal group). The marginal adaptation of single crowns were measured using by silicone replica technique. Silicone replicas were sectioned four times. The marginal adaptations were evaluated using by digital microscope. Statistical analyses were performed with Mann-Whitney test(α=0.05). Results: Mean ± standard deviations of all marginal adaptations were 92.1(20.0)㎛ for Metal group and 69.7(12.3)㎛ for Resin group. Two groups were no statistically significant differences(p>0.05). Conclusion: Marginal adaptation of single crowns printed by 3D-printing system were ranged within the clinical recommendation.

Purpose: The purpose of this study was to know of photopolymerization effect of self-etch dual-cured resin cement on different transmittance and thickness of zirconia disks. Methods: The two types of transparent and opaque zirconia speciments were prepared. The five speciments of each groups were seperated with 0.5㎜ and 1.0mm thickness. Degree of conversion(DC) were studied by FT-IR spectroscopy using ATR method before and after irradidaion for 40 sec. Results: The relative DC was showed the higher results of ZS5 as compared with ZS10 (p < 0.05). And OP5 and OP10 were lower results than ZS10 (p < 0.05). Conclusion: The photopolymerization effect of dual-cured resin cement were affected by the transmittance and thickness of zirconia.

Purpose: This study introduces the production process of dog’s dental prosthesis using an automated dental prosthetics technology. The occlusal interaction of dog’s dental prosthesis was observed. Methods: This study was proceeded with dog’s the mandibular first molar teeth. The 3D CAD designed to 3D model specimens was observed by CAD software. and The specimens designed to 3D model specimens was observed occlusal interaction by using articulator. Results: Occlusal contact point in prosthetic specimens were observed in buccal surface. and 98% of the size of the crown is the best occlusal relationship. Conclusion: Observation of occlusal relations result to 98% of the size of the crown is the best.

Purpose: The purpose of this study is to discover the recognition of dental technicians on MSDS and to research the furnishing rate of Material Safety Data Sheet (MSDS) in dental laboratories. Method: 104 dental technicians who were self-written questionnaire. The results were analyzed by SPSS 12.0. The answers to the questionnaire underwent frequency analysis, chi-square test were performed. Results: The result of cross analysis on the occurrence of occupational diseases according to whether MSDS is furnished showed that the group with MSDS furnished had 37.8% of damages due to their occupation, but the group with MSDS unfurnished had 65.7% of damages due to their occupation, which displayed a significant difference(p<0.05). The result of cross analysis on whether the education about chemicals according to whether MSDS is furnished showed there were relatively more responses of no education on the types and characteristics of chemicals, the effect on human body and its risk, emergency measure when exposed to risk, the treating and storing methods and the disposal methods. In addition, there were significant differences on whether all the above education was done between the group with MSDS furnished and the group without MSDS(p<0.000). Conclusion: In order to secure safe working environment of dental technicians and to reduce occurrence of damage caused by chemicals, the related education is necessary. The recognition of dental technicians on MSDS and furnishing rate is increasing but still insufficient, so the related organizations need to establish education and PR measures for prevention of damage.

Purpose: This study aimed to generate 3-D occlusal curvatures and evaluate the relationship between the occlusal curvatures and mandibular occlusal morphology factors. Methods: Mandibular dental casts from 25 young adult Korean were scanned as a virtual dental models with a 3- D scanner(Scanner S600, Zirkonzahn, Italy). The curve of Spee, curve of Wilson, and Monson’s sphere were generated by fitting a circle/sphere to the cusp tips using a least-squares method. The mandibular mesiodistal cusp inclination, buccolingual cusp inclination, and tooth wear parameters were measured on the prepared virtual models using RapidForm2004(INUS technology INC, Seoul, Korea). Wilcoxon signed-rank test was performed to test side difference, and Spearman’s rank correlation coefficients were investigated to verify the correlation between occlusal curvatures and correlated factors (a=0.05). Results: The mean radii of curve of Spee were 83.09±33.94 in the left side and 79.00±28.12㎜ in the right side. The mean radii of curve of Wilson were 66.82±15.87㎜ in the mesial side and 47.87±9.40㎜ in the distal side with significantly difference between mesiodistal sides(p<0.001). The mean radius of Monson ’s sphere was 121.85±47.11㎜. Most of the cusp inclination parameters showed negative correlation for the radius of Monson’ sphere(p<0.05). Especially, the buccolingual cusp inclinations in mesial side of molar showed high correlation coefficients among the factors(p<0.05). Conclusion: The radius of Monson’s sphere was greater than the classical 4-inch values, and the buccolingual cusp inclinations in mesial side of molar can be considered as one of the main factors correlating with the radius of Monson’s sphere.

Purpose: The purpose of this study aims to improve self-confidence, satisfaction and self fulfillment of dental technology students through practical skills competitions to meet the levels required by the industry. Method: The questionnaire was composed of 12 general characteristics, 23 self-efficacy, 25 practice satisfaction, 5 self-satisfaction, 12 self fulfillment out of 77 questions. The reliability of the surveys showed Cronbach’α=0.893 on the self-efficacy, Cronbach’α=0.871 on the practice satisfaction, Cronbach’α=0.857 on self- satisfaction and Cronbach’ α=0.941 on self fulfillment. Results: Before and after the test result comparison showed a statistically significant difference for both men and women according to the general characteristics. Women’s progress was higher than for men. The thought about dental technicians has changed for the better and showed a statistically significant difference. Subjects who have 3.1~3.5 school record showed the highest score on job skills, self-efficacy, practice satisfaction, self-satisfaction and self fulfillment according to the the general characteristics, and 3.6 ~ 4.0, 3.0 or less and 4.1 ~ 4.5 in order. Conclusion: This study was conducted with dental technology students who participated in practical skills competitions after 10 week 40 hours training in D college, and the results were as follows. Practical training improved the job performance, self-efficacy, practice satisfaction, self-satisfaction and self fulfillment improved significantly.

Purpose: The purpose of this study is to investigate the analysis blended learning interesting and satisfaction on students majoring in dental techniques. Method: The study subject were 181 students from Gimcheon university. Data for this survey was obtain by selfadministration method. This questionnaire consist of lecture°Øs interesting and satisfaction when using an blended learning in the lecture. SPSS 22.0 was used. Analysis of frequency was used and two sammple t- test was used to identify significantly different blended interesting and sataisfaction within the grade. Multiple regression was used to which interestings affect the satisfaction. Results: First, there were significant differences in the grade among the blended interesting and sataisfaction, while on differences in participation satisfaction(p<0.05). Second, The correlation coefficient is 0.714 between blended interesting and staisfaction, Third, Multiple regression showed that the lecture°Øs interesting applying blended learning affects the satisfaction(p<0.05). Conclusion: Given the findings of the study, lecture applying blended learning seem to be efficient education programs to improve lecture's interesting & satisfaction.

Purpose: This study is to analyse the job seeking stress, to see the relationship Between Job Seeking Stress and career decision-making self-efficacy in students of department of dental technology. Method: For this, the students of department of dental technology in daegu and daejeon and wonkwang university selected at May 2016. A question investigation was used in a entry method of self-estimation. Furthermore a total of 151 person was used as final analysis data. Statical analysis was performed with SPSS 22.0. An analysis of frequency, two sample t-test, one-way ANOVA, Multiple regression was used. Results: Firstly, personal expenses affected beneficially statistically the Job Seeking Stress (p<.05). Secondly, sex, Score, Major satisfaction, personal expenses affected beneficially statistically the career decision-making selfefficacy( p<.05). Thirdly, University environment and academic stress in the Job Seeking Stress affected beneficially statistically the career decision-making self-efficacy(choice target). Conclusion: The study found out that there was significant effect when increased to university environment and academic stress in Job Seeking Stress, the career decision-making self-efficacy was decreased. So the study proved that when helping students facing difficulties due to the career decision-making self-efficacy, it is important to decreased their university environment and academic stress.