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Materials have been developed to reduce the chipping of ceramic veneer and improve the esthetics of anterior ceramic veneered restorations. However, studies of the effects of material and substructure design on fracture resistance are sparse.The purpose of this in vitro study was to investigate the fracture resistance of metal-ceramic (MC), zirconia-feldspathic porcelain (ZC), and zirconia-lithium disilicate (ZL) anterior restorations and evaluate the effect of material and substructure design.After preparing and scanning artificial maxillary central incisor teeth, titanium abutments and restoration specimens (n=90) were fabricated. MC, ZC, and ZL materials were prepared with substructure designs A (two-third coverage of the palatal surface) and B (one-third coverage of the palatal surface). After cementation, the specimens were thermocycled (10 000 cycles, 5 and 55 °C). Fracture load measurements, failure mode analysis, energy dispersive X-ray spectroscopy (EDS), line scan analysis, fractography, finite element analysis (FEA), and Weibull analysis were performed. Two-way ANOVA was used to identify the effects of material and substructure design on fracture load. One-way ANOVA was used to identify significant differences of fracture load (α=.05).MC and ZL showed significantly higher fracture load than ZC (P.05). MC_A showed a significantly higher fracture load than MC_B (P.05). ZC_A exhibited the lowest Weibull modulus. FEA revealed that the maximum principal stress occurred near the loading area of the veneer. ZL displayed the lowest maximum principal stress among all the materials.ZL and MC_A exhibited more favorable fracture resistance. The substructure design of MC, with increased metal coverage of the palatal surface, improved fracture resistance significantly.

Statement of problem How axial displacement may be affected by the mechanical properties and internal discrepancy of a cement-retained implant-supported prosthesis is unclear. Purpose The purpose of this in vitro study was to assess the difference in internal discrepancy and axial displacement according to the prosthesis material in cement-retained prostheses splinting nonparallel implants. Material and methods Computer-aided design and computer-aided manufacture (CAD-CAM) titanium abutments were fabricated for a vertically placed implant and a 15-degree tilted implant. Three types of prostheses, in zirconia, cobalt-chromium (Co-Cr) alloy, and polymethylmethacrylate resin (PMMA), were fabricated (n=10). The internal discrepancy between the CAD-CAM titanium abutment and the prosthesis was measured by using the replica technique. After luting with an interim cement, they were mounted in Type IV gypsum. The specimens were cyclic loaded, and axial displacement of the prosthesis was measured after 3, 10, 100, and 106 cycles. The internal discrepancy and cumulative axial displacement were assessed by using a 3-way analysis of variance and repeated measures analysis of variance (α=.05). Results The internal discrepancy of the prosthesis did not differ based on the prosthesis material (P=.869); however, it was significantly different based on the measurement location, with the occlusal discrepancy (224 ±29 μm) being greater than the axial discrepancy (21 ±10 μm) (P Conclusions Prostheses made with high-elastic moduli materials exhibited less axial displacement than PMMA prostheses, even though the internal discrepancy was not different. Moreover, vertically placed implants presented a greater axial displacement of the prosthesis than implants with angled placement.

The mechanical and physical properties of implant screw access opening deteriorate if composite resin is not polymerized properly. Therefore, this study aimed to analyze the effect of using composite resin in implant access opening on the degree of conversion (DC).Two prosthetic materials (Co-Cr and zirconia), two types of composite resin (low and high viscosity), two light-cured resin depths (2 and 3 mm), and two polymerization methods (max-mode 10 s and mid-mode 20 s: 16 and 22 J/cm2, respectively) were considered (n = 192). The DC of the polymerized composite resin was measured through Fourier-transform infrared (FTIR) spectroscopy. The top and bottom surfaces of the polymerized composite resin body were observed through scanning electron microscopy. Multiple linear regression analysis and analysis of variance (ANOVA) were used to identify significant differences in DC (α = .05).The DC was lower when the low-viscosity composite resin (β = -0.431), light-polymerized resin depth of 2 mm (β = -0.430), zirconia prosthesis (β = -0.191), and mid-mode polymerization method (β = -0.164) were used. The resin type, depth of resin to be light-cured, prosthesis material, and polymerization method had an effect on the DC.Low-viscosity composite resin should be polymerized at a low irradiance and long polymerization time (such that the light-cured resin depth does not exceed 2 mm) to ensure proper composite resin polymerization in implant screw access opening. This article is protected by copyright. All rights reserved.

Within the pulp and paper industry, the recycling of water to reduce water consumption leads to accumulation of colloidal material in the process water and greater risk of deposition. Resinous materials, arising from the wood extractives released during papermaking, form colloidal particles in solution that agglomerate and deposit onto the different surfaces within the mill. The formation of the resinous deposits, known as pitch, can be detrimental to the paper quality, process control and efficiency. A major factor in the colloidal stability of these substances is the presence of natural polymers originating from the wood and salts that accumulate in the process water as a result of increased system closure. To date, most work has looked at the stability of northern hemisphere woods. The work of this thesis explores the stability and formation of southern hemisphere Pinus radiata wood resins through the application of novel techniques. It investigates the factors that affect the stability of wood extractive colloids under varying conditions of ionic strength, ionic valency, shear, temperatures, pH, and mixtures of cations and wood polymers released from Pinus radiata thermomechanical pulp. Electron paramagnetic resonance (EPR) was used to study model wood extractive colloids. Nitroxides were chosen as EPR probes to gain a greater understanding of the different interior vs. surrounding parts of the colloidal droplet in order to assess current proposed models of the structure of the wood extractive colloid. Additionally, salt was added to solution in order to understand the macroscopic environmental interactions that the colloid experiences. A revised model for the colloid structure has been proposed to better explain the behaviour of the wood extractive colloids. Through the use of the photometric dispersion analyser (PDA), the coagulation kinetics for wood resins were determined. The coagulation kinetics allowed the stability factor (W) for the addition of various concentrations of salt to be determined with variation in a number of supernatant physiochemical factors (salt type, valency, temperature, pH, shear and simultaneous addition of multiple salts). Coagulation of a colloidal wood extractive solution by a single salt was found to follow the Schultz-Hardy rule, with the critical coagulation concentration (CCC) for a salt strongly influenced by salt valency (z). Addition of trivalent salts indicates that the affinity of aluminium and iron salts for the colloidal wood resin surface is greater than their affinity for hydrating water molecules. Changes in temperature and pH of an aqueous colloid suspension were observed to affect the concentration of salt required to destabilise the colloid, as expected from DLVO theory. An increase of the supernatant's pH resulted in an increase in the CCC for calcium. An increase in temperature resulted in an increased CCC for all salts tested. The degree of variation in CCC with temperature was found to be valency dependant. The stability of the colloidal wood resins was found to be highly dependent on the shear within the system. This aspect had not been reported before, particularly the effect of shear and metal ion valency. Increased shear within the system was found to decrease the CCC. The effect was found to be dependent on both the salt type and the valency of the metal ion. A change to the DLVO theory has been postulated to explain this. It is proposed that hydrodynamic forces need to be included in the relationship between the CCC and the counter ion charge: \\(CCC\\) `˜í¬± (˜í¬©z)^(-6˜ìvë)` or \\(CCC\\) `˜í¬± [z^(-6˜ìvë) + ˜í¬©]`; where `˜í¬©=f(G)` and `˜ìvë = g(G)`. The addition of multiple salts simultaneously to solution (essential for industrial colloids) was explored. The interaction between multiple salts and the colloids resulted in complex behaviour, both in destabilisation and restabilisation of the colloid. A nonlinear decrease in the CCC was found. Restabilisation of the colloids was observed to occur at high salt concentrations when two salts of differing valency were added. This restabilisation is thought to occur as a result of charge reversal mechanism by which metal cations are adsorbed onto the colloid surface. The coagulation kinetics for the addition of water-soluble wood polymers to the wood resins dispersions was determined in the same manner as the addition of salt through the use of the PDA. The interaction between the wood resin and the water-soluble wood polymer showed complex behaviour with two stages of destabilisation of the wood extractive colloids, separated by an apparently stable region. The behaviour was typical of aggregation by synthetic polymers: first, polymer bridging at low polymer additions caused colloid destabilisation with subsequent steric stabilisation of the colloids at medium concentration of the polymer, and then depletion flocculation was followed finally by depletion stabilisation at higher polymer concentrations. The deposition rate of colloidal wood resin onto hydrophobic and hydrophilic model surfaces was measured at the solid-liquid interface by impinging jet microscopy (IJM) and the effect of cation specificity in solution on deposition was quantified. On both model surfaces, the wood resin deposition was slightly faster with calcium ions than with magnesium at the same salt concentration (800 mg/L). The rate of colloidal wood resin deposition on hydrophobic surfaces was far greater (up to a 2.5 times) than on hydrophilic surfaces for both salts. Film thinning, or spreading of the wood resin particles, occurred on the hydrophobic surfaces with calcium and to a lesser extent with magnesium salt. The formation of oil films has not been previously reported.

PURPOSE The aim of this study is to compare the hardness according to the conditions of metal alloys. Moreover, the correlation between the cast crown hardness before and after wear testing and the degree of wear for each dental alloy was assessed. MATERIALS AND METHODS Cast crowns of three metal alloys (Co-Cr, gold, and Ni-Cr alloys) opposing smooth-surface monolithic zirconia were used. The Vickers microhardness of the ingot (which did not undergo wear testing) and the cast crown before and after wear testing were measured for each alloy. Two-way ANOVA and Scheffé tests were used to compare the measured hardness values. Moreover, the Pearson correlation coefficient was used to evaluate the relationship between the surface hardness and the wear of the cast crown (α=.05). RESULTS There was no significant difference in the hardness before and after wear testing for the gold alloy (P>.05); however, the hardness of the worn surface of the cast crown increased compared to that of the cast crown before the wear tests of Ni-Cr and Co-Cr alloys (P.05). CONCLUSION There was a significant difference in hardness between dental alloys under the same conditions. No correlation existed between the surface hardness of the cast crown before and after wear testing and the wear of the cast crown.