Effect of low-temperature degradation on the mechanical and microstructural properties of tooth-colored 3Y-TZP ceramics.

The aim of the present study was to evaluate the effects of low-temperature degradation (LTD) induced by autoclaving on the mechanical and microstructural properties of tooth-colored 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP). In total, 162 disc-shaped 3Y-TZP specimens were prepared. Two-thirds of the specimens were shaded by either the infiltration or powder mixing methods while the remaining specimens were used without coloring. The specimens were autoclaved at 134 °C for 0, 10, and 100 h to induce LTD (n=18 for each group). Chemical compositions were analyzed with X-ray fluorescence spectroscopy. Biaxial flexural strength was measured using a piston-on-three-ball test. The surface fraction and penetration depth of the monoclinic phase were examined using X-ray diffraction and scanning electron microscopy, respectively. The tooth-colored 3Y-TZP specimens contained Fe2O3 and Er2O3 (infiltration technique), and Fe2O3 (powder mixing method) at concentrations of<0.5 wt%. The tooth-colored 3Y-TZP had higher strength than the non-colored material after 100 h of autoclaving. In terms of surface fraction and penetration depth, the generation of monoclinic phase was significantly lower in the tooth-colored 3Y-TZP than in the non-colored material. The tooth-colored 3Y-TZP possessed equivalent biaxial flexural strength to that of the non-colored material and higher resistance to LTD regardless of the coloring technique (infiltration technique or powder mixing method) when the coloring pigments were contained at concentrations used in the present study.

The influence of low-temperature degradation and cyclic loading on the fracture resistance of monolithic zirconia molar crowns.

The present study analyzed the kinetics of low-temperature degradation (LTD) in zirconia, and evaluated the influence of LTD and cyclic loading on the fracture resistance of monolithic zirconia molar crowns. Bar-shaped zirconia specimens were divided into nine groups and autoclaved at 134°C for 0-200h to induce LTD. The surface fraction and penetration depth of the monoclinic phase were examined using X-ray diffraction and scanning electron microscopy. Monolithic zirconia molar crowns were prepared for crown fracture testing. The crowns were autoclaved for 0-100h (n=6) and cemented to dies. Six crown-die samples that were not autoclaved and six samples that were autoclaved for 100h were subjected to cyclic loading with a load of 300N for 240,000 cycles. All samples were tested in a load-to-failure test. The monoclinic fraction on the surface increased with autoclaving time and reached a plateau after 50h. The depth of the monoclinic phase increased without reaching a plateau. The fracture load of the crowns significantly decreased from 5683N (SD: 342) to 3975N (SD: 194) after 100h of autoclaving. Cyclic loading did not significantly affect the fracture resistance of the crowns in all cases. Kinetic analysis showed no linear correlation between the surface fraction and depth of the monoclinic phase after 50h of autoclaving. Even though LTD increased the monoclinic phase, resulting in lower strength, the fracture resistance of the monolithic zirconia crowns was still sufficient to withstand the loading conditions in the molar regions.

On the surface elemental composition of non-corroded and corroded dental ceramic materials in vitro.

Dental ceramics are traditionally looked upon as inert materials. As many are glass phased, it may be hypothesized that they will be subjected to glass corrosion in aqueous environments. The aim of the study was therefore to analyze the surface elemental composition of glass-phased and all-crystalline ceramics, before and after low- and high-intensity, in vitro corrosion (milli-Q-water at 37+/-2 degrees C for 18 h and 4% acetic acid at 80+/-2 degrees C for 18 h, respectively). The analysis of the surface elemental composition was performed using ESCA. The hypothesis was confirmed. After high-intensity corrosion, the complete wash out of alkali ions, alkaline-earth ions and elemental alumina was found, leaving behind a surface totally dominated by silica. The all-crystalline ceramics, densely sintered alumina and yttria-partially stabilized tetragonal zirconia, displayed only minor surface changes, even after high-intensity corrosion. In comparison to the corrosion testing in acid, the corrosion process in milli-Q-water did not produce different results in principle, except for the lower magnitude of the depletion of alkali ions and the virtually unchanged level of elemental alumina. Unexpectedly, no substantial difference in surface degradation was found between the glass ceramic and the ordinary porcelain-fused-to-metal ceramic or between ceramics of higher sintering temperature and those of low or ultra-low sintering temperature. The composition and microstructure alone did not appear to provide a full explanation for the inter-individual differences in surface corrosion when exposed to comparable environmental conditions.

Protein characterisation of salivary and plasma biofilms formed in vitro on non-corroded and corroded dental ceramic materials.

Dental ceramics are generally regarded as low-adhesive materials. Different ceramics may, however, differ in composition and physico-chemical surface properties, which may be changed after corrosion. The aim of this study was to examine the adsorption of proteins onto specimens of different ceramic materials after the incubation in saliva and plasma before and after in vitro corrosion. In addition, the topography of the biofilm was examined by AFM. Surface-bound proteins were desorbed and analysed by polyacrylamide gel electrophoresis (PAGE) and immunoblotting using antibodies to saliva and plasma proteins. Silver-stained gels indicated differences in the adsorption of proteins. Differences in surface roughness at the nanometer level did not, however, seem to be correlated to the protein adsorption. After corrosion, unchanged or increased protein staining was generally seen in the gels and Western blots. The reactions for salivary amylase and proline-rich proteins varied between the different materials. Albumin and fibrinogen were identified in samples from all materials tested. Fibronectin and in specific IgA were more sparsely seen. No saliva but all plasma proteins were identified in the alumina and yttria-stabilised zirconia samples and reduced protein reactions were obtained after corrosion.

Factors affecting the shear bond strength of bonded composite inlays.

PURPOSE: This article analyzes the influence of different pretreatments on the bond strength between inlays and the resin cement of three different composite inlay systems: Z-100, Targis, and Art Glass. MATERIALS AND METHODS: Four separate treatments of the composite-bonding agent interface were investigated: (1) untreated surface, (2) grinding, (3) sandblasting, and (4) sandblasting followed by silane treatment. Surface topography, roughness, and shear bond strength were evaluated using digital scanning electron microscopy, confocal laser scanning profilometry, and a Lloyd LRX equipped for shear bond testing, respectively. RESULTS: The bond strength is presented both with respect to composite surface pretreatment and with respect to different composite inlay systems. Independent of the composite inlay system, the sandblasted and silane-treated surface was found to give the highest bond strength values, followed by the sandblasted and ground surfaces. The untreated surface showed the lowest bond strength. For pretreated surfaces, Targis showed the highest (P < 0.05) bond strength values, followed by Art Glass and Z-100. This distribution, however, was reversed for the untreated interface, where Z-100 showed the highest bonding strength (P < 0.05). CONCLUSION: Surface pretreatment and roughness as well as the inlay material have an impact on the bond strength and the retention of composite inlays.

Water sorption and flexural properties of a composite resin cement.

PURPOSE: The aim of this study was to assess the water sorption and determine the influence of water on flexural properties of a composite resin cement of 2 different viscosities. MATERIALS AND METHODS: A dual-cured composite resin cement of 2 different viscosities was tested according to International Standards Organization standards for dental composite materials. The samples tested for water sorption were stored in distilled water for 7 or 60 days. The samples tested for flexural properties were divided into 2 groups and stored either wet in distilled water or dry for 1, 7, or 60 days. After storage, a flexural test was performed with 3-point bending equipment. RESULTS: A significant increase in water sorption for both viscosities was registered as the storage time increased, but no significant difference between the 2 viscosities was recorded. Significantly lower strength and modulus were found for specimens that were wet stored for 60 days compared with the dry-stored ones, and significant changes in deflection at break were also registered. There were no differences in flexural properties between the 2 viscosities. Because of the lubricant and plasticizing effect of water on composite resin materials, the secant modulus and deflection at break seem to be valid methods to describe the complete deflection behavior. CONCLUSION: Water has an important effect on the flexural properties of composite resin cement after 60 days of storage time. No significant differences in water sorption and flexural properties were found between the high and low viscosities of the composite resin cement studied.

Surface energy of non-corroded and corroded dental ceramic materials before and after contact with salivary proteins.

After sintering and autoglazing, the surface free energy of seven different dental ceramic materials was determined by contact angle measurements using a Dynamic Adsorption Tester and three different standard probe liquids before and after in vitro corrosion and also before and after incubation with human whole saliva. The surface free energy was calculated from the Young-Dupré equation, and the polar and non-polar components were determined. The total surface free energy (range 50 +/- 5 mN/m) did not differ significantly between the different ceramic materials or between corroded and non-corroded specimens. The basicity of the surface persisted after corrosion, although reduced to a lower level, which probably reflects ion exchange processes at the exposed surfaces. After saliva incubation, the basic (gamma-) component of the surface free energy increased, which may be interpreted as the result of salivary proteins binding to the predominantly basic (gamma-) surface with their anionic groups, orienting their cationic sites towards the bulk phase. Selective adsorption of proteins to biosurfaces will no doubt influence both microbiological colonisation and cell adhesion, although the exact mechanisms are not known.

Surface corrosion of dental ceramics in vitro.

The objective of this study was to evaluate possible structural surface changes in different dental ceramic materials in a provocative corrosive environment in vitro. On the basis of compositional and microstructural differences, seven dental ceramic materials were selected for the test. After sintering and autoglazing, the surface roughness of the specimens was evaluated by confocal laser profilometry. A specially designed specimen holder made it possible to locate the same surface area before and after contact with the corrosive solution. The surface topography was additionally analysed using scanning electron microscopy. All the ceramic materials displayed evidence of surface structural changes on the exposed surfaces, but to varying degrees. Traditional leucite-containing feldspathic porcelains displayed an increase in surface roughness compared with baseline conditions when kept in 4% acetic acid at 80 degrees C for 18 h. Micro-crystalline and non-crystalline ceramic materials, on the other hand, demonstrated a smoother surface or just a minor increase in surface roughness. Whether or not the smoother post-corrosion appearance of certain ceramic materials is indicative of a true increase in corrosion resistance or is merely the result of an uniformly progressive corrosive process will be the object of future studies.

Two years of clinical experience with Procera titanium crowns.

PURPOSE: The purpose of the study were to evaluate the clinical performance of the Procera porcelain-fused-to-titanium crown system in general practice during a 2-year period, and to evaluate the performance of a new low-fusing porcelain as a veneering material on titanium. MATERIALS AND METHODS: A number of consecutive complete-coverage crowns (40) in 25 patients (14 women and 11 men) with a mean age of 53.1 years (range 35 to 79 years) were made according to the Procera (Nobel Biocare) technique in a 3-month period. The titanium copings were fabricated from solid rods of pure titanium using spark erosion and copy-milling technique, whereafter they were veneered with a new type of low-fusing ceramic material. The crowns were evaluated using the CDA criteria at baseline and after 2 years. RESULTS: The general failure rate was low and was restricted to one carious lesion, one porcelain fracture, and one loss of a crown resulting from failure of retention of a post and core. The most frequent single reason that the "excellent" color level was not recorded was a "too-high value." A slightly dull or granular porcelain surface was observed both at baseline and after 2 years. Overall, the responses of the patients were positive. CONCLUSION: Within the limitations of the study it can be concluded that porcelain-veneered Procera titanium crowns can be used as an alternative to other porcelain-fused-to-metal systems. However, conclusions should be made with caution from the results of this study because of the limited number of patients and crowns and the short observation period.

Microhardness and surface topography of a composite resin cement after water storage.

PURPOSE: The aims of this study were to assess changes in the microhardness and surface roughness of a dual-cured composite resin cement after water storage for different periods of time. MATERIALS AND METHODS: Sixty specimens were divided into four groups comprising high- and low-viscosity cement specimens stored either dry or in water for 1 to 60 days. Microhardness and surface roughness measurements were made after 1, 7, and 60 days of storage. RESULTS: It was found that that although interactions complicated the interpretation of the results, the water-stored samples had a significantly lower microhardness compared to the dry-stored specimens for every time interval. In addition, the high-viscosity specimens had a significantly higher microhardness compared to the low-viscosity specimens. An increased microhardness was found for all groups, except for the low-viscosity, water-stored specimens after 60 days of water storage, which was attributed to an effect of the chemical postcuring process. Although difficult to evaluate from a clinical point of view, the laser profilometry analysis revealed that a significantly increased surface roughness was found after water storage and increased storage time that was possibly caused by a deterioration of the resin-matrix surface. CONCLUSION: For the permanency of the interfacial luting material, a high microhardness value seems to be important.

Ceramic inlay systems: some clinical aspects.

Due to their inertness and unsurpassed aesthetic properties, ceramic materials are increasingly used as inlay materials. Based on a questionnaire, the frequency and character of complications related to ceramic inlay therapy were assessed and some important pitfalls and clinical relevant factors discussed. A majority of the dentists performed between 1 and 10 ceramic inlays per month using several different ceramic materials. As many as 85% of the dentists had observed complications in connection with ceramic inlays. Most frequency reported was hypersensitivity of a transient nature (15%). The material revealed an overall inlay fracture frequency of 5%, but the individual variations were high. Tooth fracture, loss of retention and other complications such as secondary caries, endodontic envolvement, colour mismatch and a surface and edge deterioration occurred with a varying but lower frequency. Failure analysis revealed a large number of causative factors among which cavity and inlay design, bonding procedures, selection of luting material and proper case selection were regarded as the most important. Due consideration to the strength of remaining tooth substance was found to be important in reducing the problem of hypersensitivity and the risk of tooth and inlay fracture.

Restitution of enamel after interdental stripping.

This paper studies the effect of interdental stripping on the enamel surface and evaluates methods to restitute the treated surface. Extracted teeth mounted in a semielastic material were subjected to stripping by different kinds of steel strips. The treated enamel surfaces were then polished in several different ways. The effects were studied by SEM and profilometry. It was concluded that the coarsest strips produced irregularities of such a magnitude that polishing had very limited effect. Polishing starting with coarse polishing strips followed by gradually finer gave the best result. An increase in number of strokes and use of all grades of polishing strips slightly improved the result.

Microleakage of indirect composite inlays. An in vitro comparison with the direct technique.

Microleakage occurring around directly and indirectly made class-II composite restorations was evaluated on extracted human premolars. Before the evaluation was made, the teeth were thermocycled and stained with an organic dye. Direct class-II composite restorations demonstrated extensive microleakage at their dentin cavosurface margins. Indirect class-II composite inlays luted with a dual-curing composite cement displayed much less microleakage than restorations made using the direct technique. The use of glass-ionomer cement rather than composite cement as the luting material resulted in more microleakage. Rather than being a true microleakage, the leakage of glass-ionomer cement might be the result of a diffusion of the water-soluble organic dye in the water-based cement. The results suggest that the indirect composite technique is superior to the direct technique when it comes to reducing microleakage.

A clinical evaluation of ceramic laminate veneers.

The objective of this study was to make a clinical quality evaluation of resin-bonded ceramic veneers placed in general practice. Ceramic veneers were evaluated by four independent examiners according to the California Dental Association guidelines for evaluation of dental care. In addition, bleeding and margin index and mode of tooth preparation were recorded. None of the veneers had been replaced and only two had fractured. Almost all veneers received a satisfactory rating regarding surface, color, and margin integrity. More than half of the veneers had a satisfactory anatomical form. The bleeding index was comparable to that reported for other types of crowns. An equigingival or subgingival margin was most common.

Cytotoxicity of corroded and non-corroded dental silver amalgams.

The cytotoxicity of one conventional and four non-gamma 2-amalgams was studied in a cell culture system, using the Millipore filter method. Before testing set amalgam specimens were kept in distilled water or in artificial saliva at pH 4, 5, or 7 for up to 28 wk to produce a corrosion layer on the test surface. Non-corroded set amalgam specimens was also tested. None of the noncorroded, set amalgams showed any sign of surface accumulation of cytotoxic products whereas the corroded amalgams showed varying degrees of cytotoxicity. Generally, the non-gamma 2-amalgams gave a more pronounced cytotoxic effect than the conventional amalgam. When the corrosion procedure was carried out at pH 7, the various non-gamma 2-amalgams showed different degrees of cytotoxicity. It appears that the difference in cytotoxic effect between the non-gamma 2-amalgams and the conventional amalgam as well as the differences among the various non-gamma 2-amalgams could be related to variation in the retention of corrosion products deposited on the amalgam surface.