The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

STATEMENT OF PROBLEM. Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported. PURPOSE. The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM). MATERIAL AND METHODS. Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Sa ¨ckingen, Germany) were prepared in 40 mm (length) x 4 mm (width) x 3 mm (height) samples. Specimens were artificially aged in distilled water by heattreatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05). RESULTS. The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa. CONCLUSION. The monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government(MOST) (No. R01-2007-000-10977-0)

Improving shear bond strength of temporary crown and fixed dental prosthesis resins by surface treatments

This article is published with open access at Springerlink.comThis study evaluated the effect of surface treatments on the bond strength of repaired temporary resins. One-hundred flat-surfaced cylindrical specimens (Ø 7 mm × 12 mm) of each temporary resin (2 bis-acryl resins and 2 polymethyl-methacrylates) were prepared. The specimens were randomly divided into 10 groups (n = 10), according to the types of surface treatments: untreated, adhesive treated, silanated, silane + adhesive treated, hydrofluoric acid etched, laser treated, sandblasted, sandblasting + adhesive treated, sandblasting + silanated, and tribochemical silica coating + silanated. Each resin material of the same brand with cylindrical shape (Ø 3 mm × 3 mm) was polymerized onto the resin surfaces, and specimens were stored for 24 h in distilled water. The shear bond strengths were measured and failure modes were examined. All data were analyzed with a one-way ANOVA and multiple comparison Scheffé post hoc test (α = 0.05). For bis-acryl resins, the highest shear bond strength was observed in sandblasted group and the lowest was observed in the control group. Results show that the repair bond strength was improved for bis-acryl resin by 23 % than that of the control group due to the increase in surface roughness by sandblasting. However, chemical treatment did not improve repair bond strength. The surface treatment of bis-acryl resins with sandblasting seems to be promising for the improvement of repair bond strength.OAIID:oai:osos.snu.ac.kr:snu2015-01/102/2008003883/12ADJUST_YN:NEMP_ID:A078517DEPT_CD:861CITE_RATE:2.371FILENAME:j mater sci 201510 51(3) 1463-75.pdfDEPT_NM:치의학과SCOPUS_YN:YCONFIRM:

Effect of polishing and glazing on the color and spectral distribution of monolithic zirconia

PURPOSE : The aim of this study was to evaluate the effect of polishing and glazing on the color and spectral distribution of monolithic zirconia. MATERIALS AND METHODS : Forty-five monolithic zirconia specimens (16.3 mm × 16.4 mm × 2.0 mm) were fabricated and divided into 5 groups according to the number of A2-coloring liquid applications (Group I to V). Each group was divided into 3 subgroups according to the method of surface treatments (n=3): N: no treatment; P: polishing; G: glazing. Color and spectral distribution of five different areas of each specimen were measured according to CIELAB color space in the reflectance mode relative to the standard illuminant D65 on a reflection spectrophotometer. Data were analyzed using one-way ANOVA followed by Tukeys HSD test, Pearson correlation and regression analysis (α=.05). RESULTS : There was a significant difference in CIE L* between Subgroup N and P, and in CIE b* between Subgroup P and G in eachgroup. Spectral reflectance generally decreased in Subgroup P and G in comparison with Subgroup N. Color differences between Subgroup P and G were within the perceptibility threshold (ΔE*ab0.88, P<.001). CONCLUSION : A perceptible color difference can be detected after polishing of monolithic zirconia. Polishing decreases the lightness, and glazing also decreases the lightness, but increases the yellowness of monolithic zirconia.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/2008003883/11SEQ:11PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:2008003883ADJUST_YN:NEMP_ID:A078517DEPT_CD:861CITE_RATE:0FILENAME:j adv prosthodont 201308 5(3) 296-304.pdfDEPT_NM:치의학과EMAIL:[email protected]_YN:NCONFIRM:

Comparison between TiUniteTM and another oxidized implant using the rabbit tibia model

OAIID:oai:osos.snu.ac.kr:snu2007-01/102/2008003883/1SEQ:1PERF_CD:SNU2007-01EVAL_ITEM_CD:102USER_ID:2008003883ADJUST_YN:NEMP_ID:A078517DEPT_CD:861CITE_RATE:0FILENAME:J Korean Acad Prosthodont 2007 45(3) 339-44.pdfDEPT_NM:치의학과EMAIL:[email protected]_YN:NCONFIRM:

In vitro evaluation of fracture strength of zirconia restoration veneered with various ceramic materials

PURPOSE: Fracture of the veneering material of zirconia restorations frequently occurs in clinical situations. The purpose of this in vitro study was to compare the fracture strengths of zirconia crowns veneered with various ceramic materials by various techniques.MATERIALS AND METHODS: A 1.2 mm, 360° chamfer preparation and occlusal reduction of 2 mm were performed on a first mandibular molar, and 45 model dies were fabricated in a titanium alloy by CAD/CAM system. Forty-five zirconia copings were fabricated and divided into three groups. In the first group (LT) zirconia copings were veneered with feldspathic porcelain by the layering technique. In the second group (HT) the glass ceramic was heat-pressed on the zirconia coping, and for the third group (ST) a CAD/CAM-fabricated high-strength anatomically shaped veneering cap was sintered onto the zirconia coping. All crowns were cemented onto their titanium dies with Rely X™ Unicem (3M ESPE) and loaded with a universal testing machine (Instron 5583) until failure. The mean fracture values were compared by an one-way ANOVA and a multiple comparison post-hoc test (α=0.05). Scanning electron microscope was used to investigate the fractured interface.RESULTS: Mean fracture load and standard deviation was 4263.8±1110.8 N for Group LT, 5070.8±1016.4 for Group HT and 6242.0±1759.5 N for Group ST. The values of Group ST were significantly higher than those of the other groups.CONCLUSION: Zirconia crowns veneered with CAD/CAM generated glass ceramics by the sintering technique are superior to those veneered with feldspathic porcelain by the layering technique or veneered with glass ceramics by the heat-pressing technique in terms of fracture strength.OAIID:oai:osos.snu.ac.kr:snu2012-01/102/2008003883/4SEQ:4PERF_CD:SNU2012-01EVAL_ITEM_CD:102USER_ID:2008003883ADJUST_YN:NEMP_ID:A078517DEPT_CD:861FILENAME:J Adv Prosthodont 201208 4(3) 162-9.pdfDEPT_NM:치의학과EMAIL:[email protected]_YN:NCONFIRM:

The reliability of an easy measuring method for abutment convergence angle with a computer-aided design (CAD) system

PURPOSE. The purpose of this study was to evaluate the intra-rater reliability and inter-rater reliability of three different methods using a drawing protractor, a digital protractor after tracing, and a CAD system. MATERIALS AND METHODS. Twenty-four artificial abutments that had been prepared by dental students were used in this study. Three dental students measured the convergence angles by each method three times. Bland-Altman plots were applied to examine the overall reliability by comparing the traditional tracing method with a new method using the CAD system. Intraclass Correlation Coefficients (ICC) evaluated intra-rater reliability and inter-rater reliability. RESULTS. All three methods exhibited high intra-rater and inter-rater reliability (ICC>0.80, P<.05). Measurements with the CAD system showed the highest intra-rater reliability. In addition, it showed improved inter-rater reliability compared with the traditional tracing methods. CONCLUSION. Based on the results of this study, the CAD system may be an easy and reliable tool for measuring the abutment convergence angle.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/2008003883/3SEQ:3PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:2008003883ADJUST_YN:NEMP_ID:A078517DEPT_CD:861CITE_RATE:0FILENAME:j adv prosthodont 201406 6(3) 185-93.pdfDEPT_NM:치의학과SCOPUS_YN:NCONFIRM:

Measuring abutment convergence angles using stereovision dental image processing system

PURPOSE. The purpose of this study was to develop a dental image processing system using a three-dimensional (3D) camera and stereovision technology. The reliability of the system for measuring axial wall convergence angles was evaluated. MATERIALS AND METHODS. The new system predicted 3D coordinate points from 2D images and calculated distances and angles between points. Two examiners measured axial wall convergence angles for seven artificial abutments using a traditional tracing-based method (TBM) and the stereovision-based method (SVBM). Five wax abutment models of simplified abutment forms were made and axial wall convergence angles of wax models were measured by both methods. The data were statistically analyzed at the level of significance, 0.05. RESULTS. Intraclass correlation coefficients showed excellent intra-examiner and inter-examiner reliabilities for both methods. Bland-Altman plots and paired t-tests showed significant differences between measurements and true values using TBM; differences were not significant with SVBM. CONCLUSION. This study found that the SVBM reflected true angle values more accurately than a TMB and illustrated an example of 3D computer science applied to clinical dentistry.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/2008003883/6SEQ:6PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:2008003883ADJUST_YN:YEMP_ID:A078517DEPT_CD:861CITE_RATE:.631DEPT_NM:치의학과SCOPUS_YN:YCONFIRM:

Initial in vitro bacterial adhesion on dental restorative materials

Objectives: The purpose of this study was to evaluate initial bacterial adhesion on several restorative materials with similar roughness.Materials and Methods: Sixty cylindrical slabs were prepared from four restorative materials: zirconia (Zr), alumina-toughened zirconia (Al-Zr), type III gold alloy (Au), and cp-titanium (Ti). All the materials were polished until a mirror-like shine was achieved. The average surface roughness and topography were determined by atomic force microscopy. Contact angles were measured to calculate surface free energyby the sessile drop technique. After the formation of a salivary pellicle, S. sanguinis, S. gordonii, and S. oralis were inoculated onto the specimens and incubated for 4 h. Quantification of the adherent bacteria was performed by crystal violet staining technique and resazurin reduction assay. One-way ANOVA and Tukeys post hoc test were adopted for statistical analysis. The level of significance was 0.05.Results: The Ra values determined with atomic force microscopy for all specimens were lower than 5 nm. Surface free energy increased in the order of Al-Zr, Zr, Ti, and Au. Differences were significant between the investigated materials in both crystal violet absorbance and fluorescence intensities. Gold alloy showed the highest values for all bacterial strains (p<0.05).Conclusions: Zirconia, alumina-toughened zirconia, and titanium may be more suitable than gold alloy as an abutment material with respect to the initial bacterial adhesion and subsequent advance of peri-implantitis.OAIID:oai:osos.snu.ac.kr:snu2012-01/102/2008003883/6SEQ:6PERF_CD:SNU2012-01EVAL_ITEM_CD:102USER_ID:2008003883ADJUST_YN:NEMP_ID:A078517DEPT_CD:861CITE_RATE:1.861FILENAME:Int J Artif Organs 201212 35(10) 773-9.pdfDEPT_NM:치의학과EMAIL:[email protected]_YN:YCONFIRM: