Influence of yttria content and surface treatment on the strength of translucent zirconia materials.

STATEMENT OF PROBLEM: Newly developed translucent zirconia materials have been used for anterior monolithic complete coverage restorations. Surface treatments can improve adhesion, as well as decrease or increase the strength of ceramics. However, information on the influence of surface treatments on the strength of translucent zirconias is sparse. PURPOSE: The purpose of this in vitro study was to measure and characterize the effects of different surface treatments, including airborne-particle abrasion, on the strength of different translucent 4 mol% and 5 mol% yttria-stabilized zirconia materials. MATERIALS AND METHODS: Disks (N=160) made from 4 types of translucent yttria-stabilized zirconia materials were surface-treated in 4 ways: Control groups were hand-polished with 2000-grit silicon carbide abrasive paper; as-machined; glass bead airborne-particle abraded; and alumina airborne-particle abraded. The biaxial flexural strength was measured by using a piston-on-3-ball test in a universal testing machine. The simple main effects of material type and surface treatment and their interaction on biaxial flexural strength were evaluated with 2-way ANOVA (α=.05). A priori, 1-way ANOVA and the Tukey multiple comparisons tests were used within material and treatment types (α=.05). Surface morphology was assessed by using scanning electron microscopy. Translucency, absolute transmittance, was measured by using a spectrophotometer. RESULTS: Two-way ANOVA revealed that the effects of zirconia type, surface treatment, and their interaction all significantly affected biaxial flexural strength (P<.001). One-way ANOVA revealed that the 4Y material was stronger than all 5Y materials, regardless of surface treatment; all 5Y materials were ranked from strongest to weakest as polished; as-machined, or glass bead abraded; and alumina abraded. The 4Y material was stronger when alumina abraded than when glass bead abraded. Scanning electron microscopy showed that as-polished surfaces were smoother than all others; as-machined and glass bead abraded surfaces displayed little difference; alumina abraded was the roughest; and differences among materials were not discerned. The 1-way ANOVA and multiple comparisons testing showed that the 4Y material had less absolute transmittance, approximately 5% less, than all the 5Y materials. CONCLUSIONS: Zirconia material type and surface treatment influenced the strength of translucent zirconia materials; a 4 mol% zirconia material was stronger than 5 mol% zirconia materials for all surface treatments tested; airborne-particle abrasion using alumina had a slight strengthening effect on a 4 mol% zirconia but had a weakening effect on 5 mol% materials; airborne-particle abrasion by using alumina produced the roughest surfaces on all materials; and the 4 mol% material was slightly less translucent than the 5 mol% materials.

Nitrate loads in sub-tropical headwater streams driven by intensive horticulture.

Nitrogen runoff from fertiliser intensive land uses has become an issue worldwide, contributing to algal blooms, hypoxic waters and aquatic biodiversity losses. This study assessed potential nutrient pollution from blueberry farms in subtropical Australia and examines whether nutrient loads were driven by groundwater discharge and/or surface water runoff. Streams downstream of eight blueberry farms were compared to eight nearby control sites without any blueberry activity. In the 90 day sample period, there were three rain events >90 mm day-1 that produced runoff sufficient to create flooding. Overall, the results revealed a clear link between blueberry farming and nitrogen runoff in headwater streams. While NOX (nitrate + nitrite) was the dominant nitrogen species downstream of blueberry farms, dissolved organic nitrogen (DON) was the dominant species in control sites. The concentrations and loads of NOx were one order of magnitude lower in the eight non-blueberry (6.3 ±â€¯2.0 µmol L-1; 1.6 ±â€¯1.2 kg N-NOX ha-1 yr-1) than the eight blueberry (56.9 ±â€¯14.2 µmol L-1; 21.8 ±â€¯8.0 kg N-NOX ha-1 yr-1) sites. NOX concentrations and loads were highest following rain events. Radon (222Rn, a natural groundwater tracer) observations and low nitrogen concentration in groundwater samples further suggest that surface runoff dominates the delivery of nitrogen to the creeks investigated. NOX concentrations and loads in creeks correlated with blueberry farm density. At >15% of blueberry land use in a catchment, there was a detectable influence in NOX concentrations and loads in the headwater streams. Assuming that our load estimates can be up-scaled to annual nitrogen creek exports, and that local farmers use the recommended amount of fertiliser (121 kg N ha-1 yr-1), between 18 and 25% of the used fertiliser was lost to the creeks. This implies that there are opportunities for decreasing the use of fertilisers in this catchment and managing any nitrogen that escapes to the creeks.

Fatigue behavior of the resinous cement to zirconia bond.

PURPOSE: Resinous cements are widely used for luting zirconia restorations. Adhesive failures have occurred at the cement/zirconia interface, rather than at the cement/dentin interface, suggesting that the cement/zirconia bond may lack durability; however, few comprehensive, comparative evaluations of fatigue effects have been reported. The rate of fatigue-induced loss of bond strength may be a more important predictor of long-term success than a single snapshot of bond strength after an arbitrary number of thermocycles. Previous studies have failed to identify trends by investigating bond strengths at several different numbers of cycles. This may result in invalid conclusions about which cements have superior bond strengths. The purpose of this study was to investigate the effects of artificial aging by thermocycling and resinous cement type on bond strengths to zirconia. MATERIALS AND METHODS: The effect of the number of thermocycles (0, 1, 10, 100, 1000, and 10,000) on the bond strengths of five resinous cements, two of which were used with and without a primer, and an oxygen-inhibiting gel, was studied. Specimens were randomly assigned to thermocycle number/cement-type test groups. Because zirconia has a very low thermal diffusivity, exceptionally long thermocycle dwell times were used. Cylinders of zirconia were bonded end-to-end. One end of each bonded specimen was insulated, specimens were thermocycled and tested in shear, and bond strengths were calculated and analyzed. RESULTS: Two-way ANOVA revealed that the effects of cement type, the number of thermocycles, and their interaction all significantly affected bond strength (p < 0.0001). By 10,000 cycles, most cements had lost at least half of their initial bond strengths, and two cements effectively recorded zero bond strengths. Failure modes were cement specific, but adhesive modes predominated. Fatigue resistance of two cements was greatly improved by use of a primer and an oxygen-inhibiting gel, as recommended by their respective manufacturers. CONCLUSIONS: Both the type of resin cement and the number of thermocycles influenced bond strength. Fatigue through thermocycling affected different cement types in different ways. Some materials displayed more rapid loss of bond strength than others. Cements differed in their failure modes.

Ultrasound imagery for dental implant diagnosis and treatment planning in a porcine model.

STATEMENT OF PROBLEM: Currently, there is no commercially available method to provide non-invasive, non-ionizing, real-time imaging of the gingival form and bony architecture of implant sites, before, during, and after implant placement. PURPOSE: The purpose of this study was to demonstrate the feasibility of 2-dimensional (2-D) ultrasound imaging of soft and hard tissues for implant diagnosis and treatment planning. MATERIAL AND METHODS: A sector scanning ultrasound system was applied. Five representative clinical features (implant in an edentulous ridge, single implant tooth replacement, implant dehiscence, tooth dehiscence, and mental foramina) were created or identified in each of the 5 porcine jaws, which were then covered with soft tissue and imaged in an acoustic water tank. RESULTS: All of the 5 model features, in all 5 jaws, were clearly visible with the ultrasound. Most objects were visible over a large range of positions and angles. Each of the features, as well as the soft tissue and bone surfaces, were recognized by specific acoustic signatures, with the same signature recurring for each object type among all 5 of the jaw specimens. All implants were highly reflective and clearly visualized. CONCLUSIONS: A 2-D sector scanning ultrasound system was demonstrated to be capable of imaging representative features for implant treatment planning in a porcine model; these included implants placed in edentulous ridges; implants placed for single tooth replacement; implants with simulated dehiscences; teeth with simulated dehiscences; and mental foramina. Specific acoustic signatures for these features were defined. Qualitative differences between ultrasound and other dental imaging techniques were described.

The use of slow heating and slow cooling regimens to strengthen porcelain fused to zirconia.

STATEMENT OF PROBLEM: Porcelain fused to zirconia prostheses are widely used. However, porcelain chipping, spalling, fracture, and delamination are common clinical problems. Residual stresses of thermal origin have received attention, but clear data and firing guidelines remain absent. PURPOSE: The purpose of this study was to measure the influence of heating and cooling protocols on the strength of porcelain fused to zirconia. MATERIAL AND METHODS: A modified 4-point flexural testing technique was used to measure strength, and porcelain buttons were bonded to the beam between the 2 central loading points. Beams (n=54) were made of a tetragonal polycrystalline zirconium dioxide that was partially stabilized with an yttria core and a feldspathic dental porcelain. Three different heating rates and 3 different cooling regimens were used during firing. Two-way analysis of variance (ANOVA) was used to evaluate the 2 main effects of the heating and cooling regimens and their interaction with the delamination force (α=.05). The Tukey multiple comparisons test was used to identify differences among heating or cooling regimens. RESULTS: During loading, the porcelain buttons separated from the zirconia beams because of delamination within the porcelain, which was close to the porcelain to zirconia interface. ANOVA revealed that the effects of the cooling regimen and heating rate had statistically significant effects on failure load (P<.05). The effect of the cooling regimen was greater than that of the heating regimen. CONCLUSIONS: Slow cooling and slow heating regimens should be used when firing porcelain to zirconia. Cooling regimens were found to be more influential than heating rates. Failure was localized to the porcelain adjacent to the porcelain-zirconia interface, not to the interface itself, indicating that the residual stresses of thermal origin within the porcelain dominated. The preparation of zirconia with 50 µm aluminum oxide at a pressure of 0.34 MPa was sufficient to prevent interfacial failure.

A phase I/II study of pemetrexed and vinorelbine in patients with non-small cell lung cancer.

PURPOSE: Pemetrexed and vinorelbine are active antineoplastic agents in non-small cell lung cancer (NSCLC). Phase I objectives include maximum tolerated dose (MTD) and recommended phase II dose determination, and pharmacokinetics of the pemetrexed-vinorelbine doublet in locally advanced or metastatic solid tumor patients (pts). Phase II objectives include tumor response evaluation, efficacy, and toxicity for first-line treatment of advanced NSCLC. EXPERIMENTAL DESIGN: Phase I pts received pemetrexed (day 1, 300-700 mg/m2) and vinorelbine (days 1 and 8, 15-30 mg/m2) every 21 days. Pharmacokinetics determined at cycle 1. Beginning with dose-level 3, folic acid and Vitamin B12 supplementation were given. RESULTS: Thirty-one phase I pts were enrolled. MTD was pemetrexed 700 mg/m2 and vinorelbine 30 mg/m2; and recommended phase II dose was pemetrexed 500 mg/m2 and vinorelbine 30 mg/m2. When administered in combination, pemetrexed and vinorelbine pharmacokinetics were consistent with single-agent administration. Thirty-seven (36 chemonaive) phase II NSCLC pts received pemetrexed-vinorelbine. Evaluable tumor response was 40%, with intent-to-treat 38%. One drug-related death occurred from febrile neutropenia with Staphylococcal infection. Grade 3/4 hematologic toxicities were neutropenia (65%) and febrile neutropenia (11%), while prevalent grade 3/4 non-hematologic toxicity was fatigue (27%). CONCLUSION: The pemetrexed-vinorelbine combination is well tolerated and shows activity as first-line treatment in advanced NSCLC patients.