All ceramic restorations have had a more limited life expectancy than metal ceramic crowns because of their lower strength. The relatively lower strength has limited the use of all-ceramic crowns to the areas where occlusal loads are lower. Therefore many researches have been done to increase the strength of all-ceramic crowns. IPS Empress 2 is a new type of lithium disilicate glass-ceramic with enhanced physical characteristics which has been in use clinically since 1998. Previous researches reported that the flexural strength of all-ceramic material was greater than 300MPa, and all-ceramic crowns can be used in staining or layering technique. The objective of this study was to investigate the influence of the thickness of IPS Empress 2 ceramic on fracture strength. Both staining technique and layering technique was investigated. Vita VMK was used as control. For all three groups, five specimens each of 0.8mm, 1.0mm, 1.4mm, 1.8mm, and 2.2mm thickness (a total of 75 specimens) were prepared. Control group: Vita VMK Porcelain specimens were prepared with dentine ceramic and liquid glazing was done. Group I: IPS Empress 2 were prepared with staining technique and stained twice and glazed once. Group II : IPS Empress 2 were prepared with layering technique and glazed after wash firing. The thickness and diameter of the specimen were measured and controlled after specimen preparation. Biaxial Flexure Test (ASTM Standard F394-78) was adopted as this test method produces results least affected by the edge condition of the specimens. Fracture strength was measured with Instron Universal Testing Machine. Conclusions are as follow : 1. The fracture strength was increase in order of control group, test group I, test group II. 2. Fracture strength of the group I(Empress 2 Staining) was 65.54 N in 0.8mm, 155.2 N in 1.0mm, 233.5 N in 1.44mm, 434.5 N in 1.8mm, and 600.1 N in 2.2mm. 3. Fracture strength of the group II (Empress 2 Layering) was 190.0 N in 0.8mm, 283.5 N in 1.0mm, 437.2 N in 1.4mm, 732.0 N in 1.8mm, and 1115.0 N in 2.2mm. 4. No statistical difference was found in flexural strengths according to thickness in a specified group(p>0.05).
Ceramics* ; Crowns ; Dental Porcelain ; Dentin ; Fires ; Life Expectancy ; Lithium

No anstract available.
Magnetic Resonance Imaging* ; Spine*

No abstract available.
Peptic Ulcer*

All-ceramic restorations have become an attractive alternative to porcelain-fused-to-metal crowns. In-Ceram, and more recently IPS Empress 2 were introduced as a new all-ceramic system for single crowns and 3-unit fixed partial dentures. But their strength and marginal fit are still an important issue. This study evaluated the fracture resistance and marginal fit of three systems of 3 unit all-ceramic bridge fabricated on prepared maxillary anterior resin teeth in vitro. The 3 all-ceramic bridge systems were: (1) a glass-infiltrated, sintered alumina system (In-Ceram) fabricated conventionally, (2) the same system with copy-milled alumina cores (copy-milled In-Ceram), (3) a heat pressed, lithium disilicate reinforced glass-ceramic system (IPS Empress 2). Ten bridges of each system with standardized design of framework were fabricated. All specimens of each system were compressed at 55degree at the palatal surface of pontic until catastrophic fracture occurred. Another seven bridges of each system were fabricated with standard method. All of the bridge-die complexes were embedded in epoxy resin and sectioned buccolingually and mesiodistally. The absolute marginal discrepancy was measured with stereomicroscope at x50 power. The following results were obtained: 1. There was no significant difference in the fracture strength among the 3 systems studied. 2. The Weibull modulus of copy-milled In-Ceram was higher than that of In-Ceram and IPS Empress 2 bridges. 3. Copy-milled In-Ceram (112micrometer) exhibited significantly greater marginal discrepancy than In-Ceram (97micrometer), and IPS Empress 2 (94micrometer at P=0.05. 4. The lingual surfaces of the ceramic crowns showed smaller marginal discrepancies than mesial and distal points. There was no significant difference between teeth (incisor, canine) at P=0.05. 5. All-ceramic bridges of three systems appeared to exhibit sufficient initial strength and acceptable marginal fit values to allow clinical application.
Aluminum Oxide ; Ceramics ; Crowns ; Denture, Partial, Fixed ; Hot Temperature ; Lithium ; Tooth

Retinal changes of rabbit after intraocular injection of lidocaine(group I), lidocaine-epinephrine 1:50,000 (group II), and normal saline (group III) were studied with electron microscope. The results were as follows: 1. Intracellular edema of the cells of the inner nuclear layer and the inner one third of the outer nueler layer was observed. 2. The photoreceptor outer segments showed mild fragmentation. 3. Swelling of mitochondria and several phagosomes were observed in the cytoplasm of the pigment epithelium. 4. Above changes were reversible during the observation period of one week. 5. No significant differences between the groups I, II, and III were noted.
Cytoplasm ; Edema ; Epithelium ; Injections, Intraocular* ; Lidocaine* ; Mitochondria ; Phagosomes ; Retina* ; Retinaldehyde

STATEMENT OF PROBLEM: Recently, resin cements have become more widely used and have been accepted as prominent luting cements. Current resin cements exhibit less microleakage than conventional luting cements. However, the constant contact with water and exposure to occlusal forces increase microleakage even in resin cements inevitably. Most bonding resins have been modified to contain a hydrophilic resin such as 2-hydroxyethylmethacrylate (HEMA) to overcome some of the problems associated with the hydrophobic nature of bonding resins. By virtue of these modifications, bonding resins absorb a significant amount of water, and there may also be significant stresses at bonding interfaces, which may adversely affect the longevity of restorations. Therefore the reinforcement of water stability of resin cement is indispensable in future study. PURPOSE: This study was conducted to examine the influence of water retention on microleakage of two resin cements over the period of 6 months. MATERIALS AND METHODS: 32 ex acted human teeth were used to test the microleakage of a single full veneer crown. Two resin cements with different components and adhesive properties - Panavia F (Kuraray Co., Osaka, Japan) and Super-Bond C&B (Sun Medical Co., Kyoto, Japan)- were investigated. The storage medium was the physiological saline solution changed every week for 1 month, 3 months, and 6 months. One group was tested after storage for 1 day. At the end of the each storage period, all specimens were exposed to thermocycling from 5.C to 55.C of 500 cycles and chewing simulation of 50,000 cycles, and then stained with 50% silver nitrate solution. The linear penetration of microleakage was measured using a stereoscopic microscope at x 40 magnification and a digital traveling micrometer with an accuracy of +/-3 um. Values were analyzed using two-way ANOVA test, Duncan's multiple range tests (DMRT). RESULTS: Statistically significant difference of microleakage was shown in the 3-month group compared with the 1-day or 1-month group in bot systems (p<0.05) and there were statistically significant differences in microleakage between the 3-month group and the 6-month group in both systems (p<0.05). The two systems showed different tendency in the course of increased microleakage during 3 months. In Panavia F, microleakage increased slowly throughout the periods. In Super-Bond C&B, there was no significant increase of microleakage for 1 month, but there was statistically significant increase of microleakage for the next 2 months. For the mean microleakage for each period, in the 3-month group, microleakage of Super-Bond C&B was significantly greater than that of Panavia F. On the other hand, in the 6-month group, microleakage of Panavia F was significantly greater than that of Super-Bond C&B (p<0.05). CONCLUSION: Within the limitation of this study, water retention of two different bonding systems influence microleakage of resin cements. Further studies with the longer observation periods in viro are required in order to investigate water stabilty and the bonding durability of the resin cement.
Adhesives ; Bite Force ; Crowns ; Hand ; Humans ; Longevity ; Mastication ; Resin Cements* ; Silver Nitrate ; Sodium Chloride ; Tooth ; Virtues ; Water*

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 Sackingen, Germany) were prepared in 40 mm (length) x 4 mm (width) x 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225degrees C 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 (alpha= .05). RESULTS: The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125degrees C for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150degrees C, 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 100degrees C. 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 175degrees C. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.
Aged ; Aging ; Aluminum Oxide ; Ceramics ; Collodion ; Dental Porcelain ; Electrons ; Humans ; Phenothiazines ; Tokyo ; Water ; X-Ray Diffraction ; Yttrium ; Zirconium

No abstract available.
Pregnancy, Heterotopic*

This investigation evaluated the fracture toughness (KIC) of eight currently available core materials, and relate the fracture toughness value to fractography analysis and surface characteristics using a atomic force microscope (AFM). Single-edge notched (SEN) test specimens (n=10) and compact tension (CT) test specimens (n=10) were prepared conforming to the ASTM Standard E-399 for a high copper amalgam, three composite core materials (Core-Max II, Core Paste, Bisfil Core), two reinforced composite core materials (Ti-Core, Ti-Core Natural), a resin-modified glass ionomer core material (Vitremer), and a conventional glass ionomer core material (Ketac-Molar). The specimens were tested with an Instron Universal Testing Machine. The maximum loads were measured to calculate the fracture toughness (KIC). Thereafter, fracture surfaces of SEN specimens of each material were investigated for fractography analysis using scanning electron microscope. And, disc-shaped specimens with 1mm thickness were fabricated for each material and were investigated under AFM for surface morphology analysis. The results were as follows : 1. Bisfil Core showed the highest mean fracture toughness regardless of test methods. 2. For the tooth-colored materials, Ti-Core Natural exhibited the highest fracture toughness. 3. Ketac Molar showed a significantly low fracture toughness when compared with the amalgam and the composite resin core materials (p<0.05). 4. The fracture toughness values obtained with the single-edge notched test, except Ketac Molar, were higher than those obtained in the compact tension test. 5. SEM revealed that the fracture surface of high fracture toughness material was rougher than that of low fracture toughness material. 6. AFM revealed that the surface particles of the composite resins were smaller in size, with a lower surface roughness than the glass ionomer core materials.
Composite Resins ; Copper ; Glass ; Molar

No abstract available.
Animals ; Gram-Negative Bacteria* ; Interleukin-2* ; Mice*