• The Journal of Korean Academy of Prosthodontics
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• v.47 no.4
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• pp.406-415
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• 2009

Purpose: The purpose of this study was to compare the marginal fitness and fracture load of the zirconia copings according to the design with different thickness and coloration. Material and methods: The evaluation was based on 80 zirconia copings. Zirconia copings were fabricated in design with different thicknesses using CAD/CAM system (Everset, KAVO dental GmbH, Biberach, Germany). The designs of copings were divided into four groups. The first group consisted of copings with uniform thickness of 0.3 mm. The thickness in the second group was 0.3 mm on the buccal surface and 0.6 mm on the lingual surface. The third group consisted of coping with uniform thickness of 0.6 mm. The thickness in the fourth group was 0.6 mm on the buccal surface and 1mm on the lingual surface. Each group consisted of 10 colored and 10 uncolored copings. Half of the copings (40) processed with a milling system according to the specific design were sent to be given a color (A3) through saturation in special dye by a manufacturing company. Just after sintering, the marginal discrepancies of copings were measured on the buccal, lingual, mesial and distal surfaces of metal die, under a Video Microscope System (sv-35, Sometech, Seoul, Korea) at a magnification of $\times$ 100. It was remeasured after the adjusting of the inner surface. Next, all copings were luted to the metal dies using reinforced cement {GC FujiCEM (GC Corp. Tokyo, Japan)} and mounted on the testing jig in a Universal Testing Machine (Instron 4467, Norwood, MA, USA). The results were analyzed statistically using the one-way ANOVA test. Results: The obtained results were as follow: 1. The measured value of marginal discrepancy right after sintering was the greatest in the contraction of the buccal area in all groups, except for group I2. 2. There was no significant difference of marginal fitness among the groups in the colored zirconia group (P<.05). 3. When the marginal fitness among the groups in the uncolored zirconia group was considered, group II2 had the smallest marginal discrepancy. 4. When the colored and uncolored groups with the same design were compared, there was a significant difference between I1 and II1 groups. In group 2, 3, and 4, the uncolored zirconia had the greatest marginal fitness (P<.05). 5. After adjustment of inner surface, there was no significant difference in the marginal fitness in all groups when color and design of the zirconia coping were compared. 6. The fracture load of CAD/CAM zirconia copings showed significant difference in group 1, 2, 3, and 4. I4 and II4 had the strongest fracture load. 7. When groups with different color and same design were compared, all colored groups showed greater fracture load (P>.05), with no significance. Conclusion: There was difference in the marginal fitness according to the design and coloration of zirconia copings right after sintering, but it was decided that the copings may well be used clinically if the inner surface are adjusted. The copings should be thick enough for the reinforcement of fracture strength. But considering the esthetics of the visible surfaces (labial and buccal surface), the thickness of copings may be a little thin, without giving any significant effect on the fracture strength. This type of design may be considered when giving priority to preservation of tooth or esthetics.

• Journal of Technologic Dentistry
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• v.33 no.2
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• pp.129-136
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• 2011

Purpose: The purpose of this study was to investigate the transmittance differences of zirconium core due to thickness within the visible light spectrum. Methods: 36 specimens were divided into 3 groups (0.6mm, 0.8mm, 1.0mm) which have each 12 specimens. The size of specimens was 10mm high and 10mm wide. The transmittance of specimens are measured by spectrophotometer Model Cary 500 that can measure infrared-ray, visible wave and ultraviolet-ray. Results: The results shows that there was no significant difference between specimen's thickness and transmittance. Conclusion: The individual's color perception is personal and there are numerous factors that influence on it. In general, human eye can perceive the color of thing only within visible light spectrum but in this experiment through spectrophotometer there was no big difference between specimen's thickness and transmittance. To sum up, The most important factors were a layed porcelain structure and its thickness rather than core thickness in the porcelain crown.

• Journal of Technologic Dentistry
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• v.33 no.4
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• pp.313-321
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• 2011

Purpose: The purpose of this study was to compare color parameters of different fabrication method of Lava ceram powder, Lava DVS blocks, IPS e.max ceram and IPS e.max zirpress. Methods: The three available shades(A1, A2, A3.5) of Lava & Kavo zirconia blocks were examined. For each of three colors, three different thickness were tested, 5 times of measurement frequency. The measurements were made using a spectrophotometer equipped with an integrating sphere using the CIE $L^*$, $a^*$, $b^*$ colorimetric system. Results: Lava build-up group and Lava DVS group showed clinically perceived color difference, on the other hand IPS e.max build-up group and IPS e.max zirpress group did not show clinically perceived color difference to shade allowed on core. When the thickness of porcelain veneer increased from Lava and IPS e.max groups, color differences(${\Delta}E$) were decreased. Conclusion: All-ceramic system has color characteristics that clinicians have to consider when selecting materials. Also, manufacturers of different porcelain systems must make every effort to achieve color reproducibility.

• Journal of dental hygiene science
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• v.12 no.4
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• pp.368-374
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• 2012

Dental CAD (computer-aided design)/CAM (computer-aided manufacturing) systems facilitate the use of zirconia core for all-ceramic crown. The purpose of this study was to evaluate the marginal and internal fit of zirconia core fabricated using a dental CAD/CAM system and to compare the fit of metal cores by a conventional method. Ten identical cases of single coping study models (abutment of teeth 11) were manufactured and scanned. Ten zirconia cores were fabricated using dental CAD/CAM system. An experienced dental technician fabricated 10 samples of metal cores for the control group using the lost wax technique. Marginal and internal fit was measured by the silicone replica technique. Fit was measured with magnification of 160 using a digital Microscope. Margin, rounded chamfer, axial wall and incisal fits were measured for comparison. T-test of independent sample for statistical analysis was executed with SPSS 12.0 for Windows (SPSS Inc., Chicago, IL, USA) (${\alpha}$=0.05). The mean (SD) for marginal, rounded chamfer, axial wall and incisal were: $97.0\;(25.3){\mu}m$, $104.0\;(22.0){\mu}m$, $59.6\;(21.4){\mu}m$ and $124.8\;(33.3){\mu}m$ for the zirconia core group, and $785.2\;(18.4){\mu}m$, $83.8\;(15.1){\mu}m$, $42.7\;(9.6){\mu}m$ and $83.4\;(14.4){\mu}m$ for the metal core group. T-test showed significant differences between groups for margin (p<.001), rounded chamfer (p<.001), axial wall (p<.001) and incisal (p<.001). But zirconia core group observed that the marginal and internal fit values in the present study were within clinically acceptable range.

• Journal of Technologic Dentistry
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• v.35 no.1
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• pp.57-64
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• 2013

Purpose: Waste parts of zirconia blocks and powders were remained after CAD/CAM process. In order to make these residual zirconia fit for practical use, zirconia single cores were produced by drain casting process. Methods: Remained zirconia blocks were reduced to powders with zirconia mortar, and screened with 180 mesh sieve. Zirconia slip was prepared from waste parts of zirconia by ball milling. Plaster molds for forming cores by slip casting were also prepared. Formed cores were removed from mold after partial drying. Dried cores were biscuit fired at $1,100^{\circ}C$ for 1hour. Biscuit fired cores were treated with tools to control the fitness and thickness. Finished cores were $2^{nd}$ fired at $1,500^{\circ}C$ for 1hour. Microstructure of cross section of core was observed by SEM. Results: When mill pot was filled with 100g of zirconia and alumina mixed powder, 300g of zirconia ball, and 180g of distilled water, the optimum slip for drain casting was obtained. Gypsum plaster for ceramic forming was more suitable then yellow stone plaster for casting process. SEM photograph showed the microstructure of fully dense with uniform grain size of zirconia and well dispersed alumina grains into the zirconia matrix. Conclusion: Zirconia single cores were produced by drain casting process. Drain casting is useful process to make these residual zirconia fit for practical use. Further study will be focused on the preparation of the bridge type cores by casting.

• Journal of Technologic Dentistry
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• v.35 no.3
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• pp.193-200
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• 2013

Purpose: In this study, in order to provide objective standard of the mixed concentration of the zirconia coloring-liquids, compare the shade differences after colored zirconia blocks from different concentrations. Methods: After immersion for 2 minutes zirconia specimen ($1.5{\times}1.5{\times}0.6{\pm}0.01mm$) in coloring-liquids that produced different concentrations, were sintered in furnace dedicated. Then, it was measured in spectrophotometer and Shadepilot. It has been determined mean and standard deviation of the color difference for each group, and verified by one-way ANOVA using the (version12.0) SPSS WIN Program the difference in shade according to the concentration at the significance level of 95% confidence, it conducted a Tukey's multiple range test to post-test. Results: The mean of $L^*$ was decreased toward LN35 group, however the mean of $a^*$ and $b^*$ was increased(p<.05). There is a statistically significant difference in the results of $L^*$ post hoc test of each group was LN15-LN30/LN35, LN20-LN30/LN35, LN25-LN30/LN35, and LN30-LN35 group. The $a^*$ group, it was found that there is a statistically significant difference in all groups for each(p<.05). The $b^*$ group, it was found that there is a statistically significant difference in all groups except the LN25-LN30(p<.05). Conclusion: In order to make effective use of the coloring-liquids of zirconia, the device objective, accurate concentration measurement is required, from the present study, we presented evidence basic to this.

• Journal of Technologic Dentistry
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• v.32 no.4
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• pp.327-335
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• 2010

Purpose: The purpose of this study was to investigate the correlation between zirconia core thickness and color tone blocking of discolored tooth and metal post. Methods: For this study, we made 20-porcelain sample and 4-metal sample( liechtenstein IPS e.max) bonded to zirconia core of different thickness with cement(Relyx ARC-3M USA)for produce discolored. We measured the color-spectral characteristics, using Shadepilot equipment(Degudent USA).We measured it with Shadepilot equipment set by automated average mode in 3 times And applied the average value obtained from 2 times of measurement in the middle of each sample. Results: As a result of analysing color-spectral characteristics on zirconia core sample, Depending on the thickness of zirconia core, the value of brightness(${\Delta}L*$:color-spectral characteristic) was increased within limited range, value of ${\Delta}a*$, ${\Delta}b*$ was decrease. Conclusion: Consequently, we obtained the following results: Changes of sample color were observed depending on the thickness of zirconia, but the range of change did not exceed the scope range of shade guide. The case of metal posts, shade guide color D2 were observed in 0.5mm of zirconia core thickness. As a result, in case of porcelain, increasing the zirconia thickness of 0.3mm or more is unnecessary for color blocking effect, in case of metal post, considering the discolored tooth, thickness of zirconia with at least 0.5mm or more is recommended.

• Journal of Technologic Dentistry
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• v.34 no.2
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• pp.75-81
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• 2012

Purpose: All ceramic crown, made from zirconia instead of metal for core material, is recognized the best esthetical prosthesis. Recently, high-priced zirconia blocks and expensive CAD/CAM machines come into use for making zirconia core. In this study, slip casting process is adapted to evaluate the possibility of the recycling the remained parts of zirconia block after machining. Methods: Remained zirconia blocks were reduced to powders with zirconia mortar, and screened with 180 mesh sieve. Passed powders were ball milled under various conditions to obtain the optimum zirconia slip for casting. Solid casting method was used for casting the specimens with plaster mold. Formed specimens were dried and biscuit fired at $1,000^{\circ}C$ for 1 hour. Biscuit fired specimens were finished with exact shape of square pillar. Finished specimens were fired from $1,200^{\circ}C$ to $1,550^{\circ}C$ at $50^{\circ}C$ intervals for 1 hour. Linear shrinkage, apparent porosity, water absorption, bulk density, and flexural strength were tested. Microstructures were observed by SEM. Results: Above examinations indicated that the optimum firing temperture was $1,500^{\circ}C$, and when fired at this temperature for 1 hour, apparent porosity was 0% and flexural strength was 680MPa. SEM photomicrographs showed uniform 200~300nm grain size, which is equal with microcture of sintered commercial zirconia block. when compare 24% linear shrinkage of cast specimen with 20% linear shrinkage of CAD/CAM machined block, it was estimated that the size controlling of cast core was not so difficult. Conclusion: According to the all of this experimental results, the cast zirconia core produced from the remained parts of zirconia block was possible to use for all ceramic denture.

• Journal of Technologic Dentistry
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• v.42 no.3
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• pp.213-219
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• 2020

Purpose: This study aimed to identify the impact of physical surface roughing with a polishing tool onto the pre-sintering yttria-stabilized tetragonal zirconia polycrystals (TZP) core and liner treatment for chemical bonding on the bond strength of TZP core and veneering ceramic. Methods: Overall, 80 specimens were classified into two groups (non-liner, NL; and usingliner, UL ) depending on the use of liner, and these two groups were then subclassified into four groups depending on the polishing tool used. (1) Non-liner groups: NS, non-liner+stone point; NC, non-liner+carbide bur; NP, non-liner+paper cone point; NT, non-liner+silicon point. (2) Using-liner groups: US, using-liner+stone point; UC, using-liner+carbide bur; UP, usingliner+paper cone point; UT, using-liner+silicon point. The pre-sintering surface roughing values and shapes were observed, and after burning up the veneering ceramic, the shear bond strength was measured using a universal testing machine. For significance testing, a one-way analysis of variance and Tukey's multiple comparison test were conducted. An optical microscope was used to observe the fracture plane, and the following results were obtained. Results: Surface roughness NP (4.09±0.51 ㎛) represented a higher value than other groups (p<0.001). In shear bond strength, NS (35.21±1.44 MPa) of the NL group showed the highest bond strength (p<0.001). The UL group did not show a statistically significant difference between groups (p=0.612). Conclusion: Our study findings reveal that the bond strength of TZP core and veneering ceramic was improved by pre-sintering physical surface treatment than by chemical bonding with liner surface treatment.

• Journal of Korean Dental Hygiene Science
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• v.5 no.1
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• pp.13-19
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• 2022

Background: In this study, zirconia copings were fabricated by setting clinically acceptable inner values for prostheses using computer-aided design/computer-aided manufacturing (CAD/CAM). The processed copings were evaluated for the marginal and internal fit of each abutment shape with a CAD program using the silicone replica technique. Methods A total of 20 copings was produced by selecting models commonly used in clinical practice. After injecting the sample, the minimum thickness, internal adhesion interval, and distance to the margin line were set to 0.5, 0.05, and 1.00 mm using a dental CAD program, respectively. It was measured using a 2D section function in a three-way program of the silicon replication technology. Although the positions and number of measurements of the anterior and posterior regions differed, nine parts of each pre-tube were designated and measured by referring to a previous study to compare the two samples. Results As a result, the average margin of the mesial, distal, and buccal (labial) surfaces was 59.90 ㎛ in the anterior region and 60.40 ㎛ in the posterior region. The mean axial wall margin was 67.25 ㎛ in the anterior region and 69.25 ㎛ in the posterior region. In occlusion, the anterior teeth (77.70 ㎛), posterior teeth (77.60 ㎛), and both anterior and posterior regions were within the clinically acceptable range. Conclusion The edge and inner fit of zirconia coping manufactured using the CAD/CAM system showed clinically applicable results. To reduce errors and increase accuracy, materials and machine errors that affect the manufacture of prosthetics should be investigated. Based on our results, the completeness of prosthetics could increase if the inner value and characteristics of the material are adjusted when applied in clinical practice.