Zirconia changes after grinding and regeneration firing.

STATEMENT OF PROBLEM: Despite improvements in computer-aided design and computer-aided manufacturing (CAD-CAM) systems, grinding during either laboratory procedures or clinical adjustments is often needed to modify the shape of 3 mol(%) yttria-tetragonal zirconia polycrystal (3Y-TZP) restorations. However, the best way to achieve adjustment is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the microstructural and crystallographic phase changes, flexural strength, and Weibull modulus of a 3Y-TZP zirconia after grinding with or without water cooling and regeneration firing. MATERIAL AND METHODS: Ninety-six bar-shaped specimens were obtained and divided as follows: as-sintered, control; as-sintered with regeneration firing; grinding without water cooling; grinding and regeneration firing with water cooling; and grinding and regeneration firing. Grinding (0.3 mm) was performed with a 150-µm diamond rotary instrument in a high-speed handpiece. For regeneration firing, the specimens were annealed at 1000°C for 30 minutes. The crystalline phases were evaluated by using x-ray powder diffraction. A 4-point bending test was conducted (10 kN; 0.5 mm/min). The Weibull modulus was used to analyze strength reliability. The microstructure was analyzed by scanning electron microscopy. Data from the flexural strength test were evaluated using the Kruskal-Wallis and Dunn tests (α=.05). RESULTS: Tetragonal-to-monoclinic phase transformation was identified in the ground specimens; R regeneration firing groups showed only the tetragonal phase. The median flexural strength of as-sintered specimens was 642.0; 699.3 MPa for as-sintered specimens with regeneration firing; 770.1 MPa for grinding and water-cooled specimens; 727.3 MPa for specimens produced using water-cooled grinding and regeneration firing; 859.9 MPa for those produced by grinding; and 764.6 for those produced by grinding and regeneration firing; with statistically higher values for the ground groups. The regenerative firing did not affect the flexural strength. Weibull modulus values ranged from 5.3 to 12.4. The SEM images showed semicircular cracks after grinding. CONCLUSIONS: Adjustments by grinding in 3Y-TZP frameworks should be performed with water cooling, and regeneration firing should be undertaken to obtain a more reliable material.

Surface properties of Ti-35Nb-7Zr-5Ta: Effects of long-term immersion in artificial saliva and fluoride solution.

STATEMENT OF PROBLEM: The mechanical properties of new titanium alloys with an elastic modulus closest to cortical bone have been studied. However, potentially damaging conditions experienced in the oral cavity, such as fluoride ions, can initiate a localized or crevice process of corrosive degradation in the alloy surfaces. PURPOSE: The purpose of this in vitro study was to evaluate the effects of long-term immersion in artificial saliva or in fluoride solution on mean roughness (Ra), Vickers hardness, and topography of the new titanium alloy Ti-35Nb-7Zr-5Ta (TNZT) compared with those of cp Ti and Ti-6Al-4V (TAV). MATERIAL AND METHODS: Disks (N=210) were divided into cp Ti, TAV, and TNZT and subdivided according to the following treatments: no immersion (N(-), control), immersion in artificial saliva (S), and immersion in fluoride (F) during periods equivalent to 5, 10, 15, and 20 years. The Ra and Vickers hardness were measured with a profilometer and a hardness tester. The topography was analyzed by scanning electronic microscopy. Data were compared using the Kruskal-Wallis and Dunn tests (α=.05). RESULTS: Values of Ra and hardness were significantly different among the metals (Ra: TAV

In vitro comparisons of casting retention on implant abutments among commercially available and experimental castor oil-containing dental luting agents.

STATEMENT OF PROBLEM: Although cement-retained implant prostheses are widely used, the quantification of optimal retention remains controversial, and new dental luting agents should be evaluated. PURPOSE: The purpose of this study was to compare, in vitro, the casting retention on implant abutments after cementation with 3 commercially available luting agents and an experimental luting agent (castor oil polyurethane, COP) with variable weight percentages (wt%) of calcium carbonate (CaCO3). MATERIAL AND METHODS: Seventy-two palladium-silver cast copings were fabricated and divided into 6 groups: Temp Bond interim cement (TB); zinc phosphate cement (ZP); Rely X ARC resin cement (RX); pure COP (COP); COP + 10% wt% CaCO3 filler (COP 10); and COP + 50% wt% CaCO3 filler (COP 50). After cementation, the specimens were stored in distilled water at 37°C for 24 hours and subjected to removal force tests in a universal testing machine (5 kN; 0.5 mm/min). Statistical analyses were performed with the Kruskal-Wallis and Student-Newman-Keuls tests (α=.05). RESULTS: The median values of casting retention (N) were as follows: TB=57.20 ±10.4; ZP=343.56 ±50.3; RX=40.07 ±9.7; COP=258.98 ±41.4; COP 10=466.57 ±79.3; and COP 50=209.63 ±31.4. The Kruskal-Wallis test showed significant differences among the groups (P<.01). TB and RX had the lowest mean retention values; COP, COP 10, and COP 50 were equal to ZP, and COP 10 had the highest retention. CONCLUSIONS: The casting retention on implant-abutments provided by COP was similar to that of copings cemented with zinc phosphate and may be influenced by the addition of calcium carbonate.

Development of binary and ternary titanium alloys for dental implants.

OBJECTIVE: The aim of this study was to develop binary and ternary titanium (Ti) alloys containing zirconium (Zr) and niobium (Nb) and to characterize them in terms of microstructural, mechanical, chemical, electrochemical, and biological properties. METHODS: The experimental alloys - (in wt%) Ti-5Zr, Ti-10Zr, Ti-35Nb-5Zr, and Ti-35Nb-10Zr - were fabricated from pure metals. Commercially pure titanium (cpTi) and Ti-6Al-4V were used as controls. Microstructural analysis was performed by means of X-ray diffraction and scanning electron microscopy. Vickers microhardness, elastic modulus, dispersive energy spectroscopy, X-ray excited photoelectron spectroscopy, atomic force microscopy, surface roughness, and surface free energy were evaluated. The electrochemical behavior analysis was conducted in a body fluid solution (pH 7.4). The albumin adsorption was measured by the bicinchoninic acid method. Data were evaluated through one-way ANOVA and the Tukey test (α=0.05). RESULTS: The alloying elements proved to modify the alloy microstructure and to enhance the mechanical properties, improving the hardness and decreasing the elastic modulus of the binary and ternary alloys, respectively. Ti-Zr alloys displayed greater electrochemical stability relative to that of controls, presenting higher polarization resistance and lower capacitance. The experimental alloys were not detrimental to albumin adsorption. SIGNIFICANCE: The experimental alloys are suitable options for dental implant manufacturing, particularly the binary system, which showed a better combination of mechanical and electrochemical properties without the presence of toxic elements.

Streptococcus mutans adhesion to titanium after brushing with fluoride and fluoride-free toothpaste simulating 10 years of use.

PURPOSE: To assess the influence of fluoride on the adhesion of Streptococcus mutans to titanium using an experimental paradigm simulating 10 years of brushing. MATERIALS AND METHODS: Commercially pure titanium (cpTi) and titanium alloy (Ti-6Al-4V) disks (6 mm in diameter and 4 mm thick) were mirror-polished and randomly assigned to one of the following six groups (n = 6): immersion (I) or brushing (B) in deionized water (groups IW [control] and BW), fluoride-free toothpaste (groups IT and BT), or fluoridated toothpaste (groups IFT and BFT). Specimens subjected to immersion were statically submerged into the solutions without brushing. For the brushed specimens, a linear brushing machine with a soft-bristled toothbrush was used. The experiments lasted a total of 244 hours. Before and after treatment, the specimens were analyzed under an atomic force microscope to determine the mean roughness (Ra) and the mean of the maximum peak-to-valley heights of the profile (Rtm). The disks were contaminated with standard strains of S mutans in well plates with brain-heart infusion broth. Adhesion was analyzed based on the numbers of colony-forming units (CFU/mL) of adhered viable cells using scanning electronic microscopy. Differences in CFU/mL between the groups were analyzed by one-way analysis of variance. RESULTS: Immersion did not affect either surface. As suggested by Ra and Rtm, BW, BT, and BFT induced changes on the surface of cpTi, whereas only BT and BTF induced changes on the surface of Ti-6Al-4V. No significant differences were observed regarding CFU/mL among the cpTi or Ti-6Al-4V groups. S mutans adhesion was similar for all surfaces. CONCLUSIONS: The changes in titanium induced by 10 years of simulated brushing with fluoride toothpaste did not increase the adhesion of S mutans.

Titanium surface topography after brushing with fluoride and fluoride-free toothpaste simulating 10 years of use.

OBJECTIVES: To conduct a controlled study contrasting titanium surface topography after procedures that simulated 10 years of brushing using toothpastes with or without fluoride. METHODS: Commercially pure titanium (cp Ti) and Ti-6Al-4V disks (6 mm Ø×4 mm) were mirror-polished and treated according to 6 groups (n=6) as a function of immersion (I) or brushing (B) using deionised water (W), fluoride-free toothpaste (T) and fluoride toothpaste (FT). Surface topography was evaluated at baseline (pretreatment) and post-treatment, using atomic force microscope in order to obtain three-dimensional images and mean roughness. Specimens submitted to immersion were submerged in the vehicles without brushing. For brushed specimens, procedures were conducted using a linear brushing machine with a soft-bristled toothbrush. Immersion and brushing were performed for 244 h. IFT and BFT samples were analysed under scanning electron microscope with Energy-Dispersive X-ray Spectroscopy (EDS). Pre and post-treatment values were compared using the paired Student T-test (α=.05). Intergroup comparisons were conducted using one-way ANOVA with Tukey post-test (α=.05). RESULTS: cp Ti mean roughness (in nanometers) comparing pre and post-treatment were: IW, 2.29±0.55/2.33±0.17; IT, 2.24±0.46/2.02±0.38; IFT, 2.22±0.53/1.95±0.36; BW, 2.22±0.42/3.76±0.45; BT, 2.27±0.55/16.05±3.25; BFT, 2.27±0.51/22.39±5.07. Mean roughness (in nanometers) measured in Ti-6Al-4V disks (pre/post-treatment) were: IW, 1.79±0.25/2.01±0.25; IT, 1.61±0.13/1.74±0.19; IFT, 1.92±0.39/2.29±0.51; BW, 2.00±0.71/2.05±0.43; BT, 2.37±0.86/11.17±2.29; BFT, 1.83±0.50/15.73±1.78. No significant differences were seen after immersions (p>.05). Brushing increased the roughness of cp Ti and of Ti-6Al-4V (p<.01); cp Ti had topographic changes after BW, BT and BFT treatments whilst Ti-6Al-4V was significantly different only after BT and BTF. EDS has not detected fluoride or sodium ions on metal surfaces. CONCLUSIONS: Exposure to toothpastes (immersion) does not affect titanium per se; their use during brushing affects titanium topography and roughness. The associated effects of toothpaste abrasives and fluorides seem to increase roughness on titanium brushed surfaces.