Effect of hydrogen peroxide-based bleaching agents on the color dimensions and surface roughness of different milled restorative dental materials

PURPOSE

To compare the color dimensions, color discrepancies (ΔE00), and surface roughness of milled materials before and after the application of a bleaching agent.

MATERIAL AND METHODS

A total of 10 extracted molars were obtained. Each tooth was cut in transversal sections, to create discs (3 mm thick, 10 mm diameter) (control group). Disk specimens of 8 materials were fabricated: polymethyl methacrylate (PMMA) interim material (PMMA-Telio group), 2 resin nanoceramics: (RNC-Ultimate group) and (RNC-Cerasmart group), 2 hybrid ceramics: (HC-Shofu group) and (HC-Enamic group), lithium disilicate (LD-Emax group), zirconia reinforced glass ceramic (ZGC-Suprinity group), and zirconia (Zr group) (n=10). Color measurements were obtained using a spectrophotometer before and after applying 35% hydrogen peroxide-based bleaching agent. Pre- and post-bleaching surface roughness analysis were completed using a profilometer.

RESULTS

Significant L*, a*, b*, and ΔE00 values differences were found (P < .05). Color discrepancies (ΔE00) ranged from 0.30 ± 0.14 to 4.82 ± 0.10. The highest color discrepancies were measured on the PMMA-Telio group, while the lowest color discrepancies were computed on the ZGC-Suprinity, RNC-Ultimate, and RNC-Cerasmart. Significant surface roughness differences were found (P <.05). The largest increase of surface roughness values between the pre- and post-bleaching measurements was obtained in the PMMA-Telio group with a mean ΔSa value of 4.73 ± 3.02, while the largest decrease of surface roughness values between the pre- and post-bleaching measurements was obtained in the Zr-InCeram group with a mean ΔSa value of -1.58 ± 0.10.

CONCLUSIONS

The milled materials tested showed significant pre- and post-bleaching color and surface roughness discrepancies. Int J Prosthodont. doi: 10.11607/ijp.8359.

Adsorption Removal of Mo(VI) from an Aqueous Solution by Alumina with the Subsequent Regeneration of the Adsorbent

Industrial wastewater is the main source of an excessive amount of molybdenum (Mo) in natural ecosystems. It is necessary to remove Mo from wastewater before it is discharged into the environment. Molybdate ion(VI) is the most common form of Mo in natural reservoirs and industrial wastewater. In this work, the sorption removal of Mo(VI) from an aqueous medium was evaluated using aluminum oxide. The influence of such factors as the pH of the solution and the temperature was evaluated. Three adsorption isotherms, namely, Langmuir, Freundlich and Temkin, were used to describe the experimental results. It was found that the pseudo-first order kinetic model better fits the kinetic data of the adsorption process, and the maximum Mo(VI) adsorption capacity was 31 mg/g at 25 °C and pH 4. The thermodynamic parameters indicated that the process of Mo(VI) adsorption on Al₂O₃ was exothermic and spontaneous. It was shown that the adsorption of Mo strongly depends on pH. The most effective adsorption was observed at pH values below 7. Experiments on adsorbent regeneration showed that Mo(VI) can be effectively desorbed from the aluminum oxide surface into a phosphate solution in a wide range of pH values. After the desorption of Mo(VI) in a phosphate solution, alumina was found to be suitable for repeating the procedure at least five times.

Solid State Processing of BCZT Piezoceramics Using Ultra Low Synthesis and Sintering Temperatures

Lead-free (Ba_0.92Ca_0.08) (Ti_0.95 Zr_0.05) O₃ (BCZT) ceramics were prepared by a solid-state route (SSR) using ultra-low synthesis (700 °C/30 min and 700 °C/2 h) and sintering temperatures (from 1150 °C to 1280 °C), due to prior activation and homogenization by attrition milling of the starting high purity raw materials for 6 h before the synthesis and of the calcined powders for 3 h before the sintering. The comparison of the thermal analysis of the mixture of the starting raw materials and the same mixture after 6 h attrition milling allowed to evidence the mechanisms of activation, resulting in a significant decrease of the perovskite formation temperature (from 854 °C down to 582 °C). The secondary phases that limit the functional properties of the ceramic and their evolution with the sintering conditions were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which allowed the design of a two-step sintering method to eliminate them. A pure tetragonal BCZT perovskite phase (P4mm, c/a = 1.004) and homogeneous ceramic microstructure was obtained for synthesis at 700 °C for 2 h and sintering with the use of a two-step sintering treatment (900 °C for 3 h and 1280 °C for 6 h). The best electromechanical properties achieved were d₃₃ = 455 pC/N, k_p = 35%, Q_m = 155.

New Ceramic Multi-Unit Dental Abutments with an Antimicrobial Glassy Coating

The choice of suitable materials and new designs in oral implantology and the subsequent enhancement of the characteristics of the dental implant developed is an important research topic with wide scope. The present work aims to develop a new multifunctional zirconia-ceria/alumina (Ce-TZP/Al₂O₃) composite with an antimicrobial glass-based coating to be used in multi-unit abutments compatible with commercially available Ti implants for peri-implantitis prevention. An airbrush spraying technique was effectively applied to coat the sintered ceramic composite starting from a glass powder suspension. This deposition technique was appropriate for obtaining continuous antimicrobial glass-based coatings with homogenous thickness (~35 µm) on ceramic dental implant components. The dental implant systems with the antimicrobial glassy coating were subjected to a mechanical integrity test following ISO 14801 to determine their long-term stability. The tested implant-coating structure seems to be stable under in vitro conditions with ultimate applied forces exceeding the maximum physiological occlusal loading force. This paper also presents a pilot clinical case report that shows peri-implant tissue around the mechanically stable glass coating with no signs of inflammation 1 year after implant insertion. This result is a preliminary probe of the durability and biological tolerance of the glassy material by the gingiva, as well as the antimicrobial effect on the peri-implant microbiota displayed by the coating.

Original vs compatible stock abutment- implant connection. An in vitro analysis of the internal accuracy and mechanical fatigue behaviour

PURPOSE

To assess the internal accuracy and mechanical behaviour under cyclic loading after artificial aging of implantsupported crowns restored with original stock abutments and two compatible non-original stock abutments.

METHODS

Forty-eight original internal hexagon connection implants were connected to different stock abutments. The samples were divided into three groups depending on the manufacturer of the abutment components (one original, two non-originals).Firstly, samples were cross-sectioned and observed by using Scanning Electron Microscope (SEM) to evaluate the internal accuracy in three different implant-abutment interface locations (platform, internal and screw). Further, cyclic fatigue loading was carried out according to the ISO Norm 14801 using dynamic testing machine under sinusoidal loads for 2,000,000 cycles at test frequencies of 2 Hz in air after thermocycling with 10,000 cycles at 5 °C and 55 °C in artificial saliva for aging simulation.

RESULTS

Original abutment components presented the highest percentage of surface with tight contact with the implant in the three implant-abutment interfaces studied. Additionally, original configuration showed highest fatigue limit value and fatigue strength exponent (280 N and -0.054) than non-original 1 (225 N and -0.109) and non-original 2 (200 N and -0.101).

CONCLUSION

Original abutment components provide better fit and mechanical results under cyclic loading than nonoriginal configurations. The results obtained in this study seem to suggest that the use of the original stock abutments to implants leads to a more homogeneous load distribution between the components that can influence the long-term success of the restorations.

MgNb2 O6 Modified K0.5 Na0.5 NbO3 Eco-Piezoceramics: Scalable Processing, Structural Distortion and Complex Impedance at Resonance

In this work, piezoceramics of the lead-free composition K0.5 Na0.5 NbO3 with an increasing amount of MgNb2 O6 (0, 0.5, 1, 2 wt.%) were prepared through conventional solid-state synthesis and sintered in air atmosphere at 1100 °C. The effect of magnesium niobate addition on structure, microstructure and piezoelectric properties was evaluated. The ceramics maintain the orthorhombic Amm2 phase for all compositions, while an orthorhombic Pbcm secondary phase was found for increasing the concentration of MgNb2 O6 . Our results show that densification of these ceramics can be significantly improved up to 94.9 % of theoretical density by adding a small amount of magnesium-based oxide (1 wt.%). Scanning electron microscopy morphology of the 1 wt.% system reveals a well-packed structure with homogeneous grain size of ∼2.72 μm. Dielectric and piezoelectric properties become optimal for 0.5-1.0 wt.% of MgNb2 O6 that shows, with respect to the unmodified composition, either higher piezoelectric coefficients, lower anisotropy and relatively low piezoelectric losses (d33 =97 pC N-1 ; d31 =-36.99 pC N-1 and g31 =-14.04×10-3  mV N-1 ; Qp (d31 )=76 and Qp (g31 )=69) or enhanced electromechanical coupling factors (kp =29.06 % and k31 =17.25 %).

Original versus nonoriginal cast-to-gold abutment-implant connection: Analysis of the internal fit and long-term fatigue performance

STATEMENT OF PROBLEM

Restoring implants with nonoriginal abutments is common. However, studies that evaluated compatible abutments with long-term fatigue performance are lacking.

PURPOSE

The purpose of this in vitro study was to assess the internal fit and the cyclic fatigue life after artificial aging of 3 implant-abutment configurations restored with 1 original and 2 compatible nonoriginal cast-to-gold abutments.

MATERIAL AND METHODS

Forty-eight original internal hexagon connection implants were connected to 3 different brands of abutments (n=16): 1 original to the implant system and the other 2 with nonoriginal abutments. Internal fit and the percentage of surface with tight contact were assessed by scanning electron microscopy in 12 cross-sectioned specimens (n=4) at 3 different areas (platform, internal, and screw). Thirty-six implant-abutment-crown specimens (n=12) were immersed in artificial saliva and thermocycled for 10 000 cycles between 5 °C and 55 °C. Subsequently, a cyclic load test, as per International Organization for Standardization (ISO) Standard 14 801, was completed in a universal testing machine at 2 Hz in air.

RESULTS

The original abutments presented the best fit and highest percentage of tight contact in the internal areas. In addition, the original abutments showed the lower cyclic fatigue strength degradation and the highest long-term success.

CONCLUSIONS

Occlusal loads are transferred more homogenously through the system when original abutments are used because of the better fit between the internal components, leading to increased fatigue resistance.

Fatigue fracture resistance of titanium and chairside CAD-CAM zirconia implant abutments supporting zirconia crowns: An in vitro comparative and finite element analysis study

STATEMENT OF PROBLEM

Zirconia abutments with a titanium base are promising candidates to substitute for titanium abutments based on clinical studies reporting good short-term survival rates. However, information on the long-term performance of zirconia abutments supporting ceramic crowns is scarce.

PURPOSE

This in vitro comparative and finite element analysis study compared the fatigue life performance of ceramic computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic restorations and zirconia abutments fabricated with a chairside workflow connected to a titanium interface versus titanium abutments.

MATERIAL AND METHODS

Twenty-two internal connection implants were divided into 2 groups, one with a zirconia abutment and monolithic ceramic zirconia crown (ZZ) and the other with a titanium abutment and zirconia crown (TiZ). They were subjected to a fatigue test to determine the fatigue limit and fatigue performance of each group as per International Organization for Standardization (ISO) 14801. Microstructural analysis of the fracture surfaces was conducted by using a scanning electron microscope (SEM). Simulations of the in vitro study were also conducted by means of finite element analysis (FEA) to assess the stress distribution over the different parts of the restoration.

RESULTS

The fatigue limit was 250 N for the TiZ group and 325 N for the ZZ group. In both groups, the screw was the part most susceptible to fatigue and was where the failure initiated. In the zirconia abutment models, the stress on the screw was reduced.

CONCLUSIONS

Chairside CAD-CAM zirconia abutments with a titanium base supporting zirconia crowns had higher fatigue fracture resistance compared with that of titanium abutments.

Zirconia Reduced Graphene Oxide Nano-Hybrid Structure Fabricated by the Hydrothermal Reaction Method

In this work, we report an available technique for the effective reduction of graphene oxide (GO) and the fabrication of nanostructured zirconia reduced graphene oxide powder via a hydrothermal method. Characterization of the obtained nano-hybrid structure materials was carried out using a scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The confirmation that GO was reduced and the uniform distribution of zirconia nanoparticles on graphene oxide sheets during synthesis was obtained due to these techniques. This has presented new opportunities and prospects to use this uncomplicated and inexpensive technique for the development of zirconia/graphene nanocomposite powders.

The Influence of Wire Electrical Discharge Machining Cutting Parameters on the Surface Roughness and Flexural Strength of ZrO2/TiN Ceramic Nanocomposites Obtained by Spark Plasma Sintering

In this work, we characterized the mechanical and electrical properties of zirconia-based ceramic nanocomposites reinforced with 30 and 40 vol. % TiN and fabricated by spark plasma sintering. In addition to their improved mechanical performance, these compositions have sufficient electrical conductivity to allow wire electrical discharge machining (WEDM). The influence of WEDM variables on the roughness and the mechanical strength of samples was analyzed after each cut. The experimental results showed that the roughness of machined surfaces can be reduced by variations in WEDM manufacturing regimes, and, consequently, a drastic drop in flexural strength of workpieces can be avoided. Furthermore, the composites with higher content and homogeneous distribution of the conductive phase exhibited better surface quality as well.

Mechanical fatigue behaviour of different lengths screw-retained restorations connected to two designs prosthetic connection level

The aim of this work is to compare the mechanical fatigue behaviour of different crown heights of single crown implant restorations made over two different internal hexagonal titanium dental implant connection levels. Two different groups of internal hexagonal connection were studied: (a) TL group (N = 26) included implants with a transmucosal connection (12.2 mm height and 4.8 mm width) and (b) BL group (N = 26) composed by implants at a bone level connection (10 mm height and 3.8 mm width). Two subgroups (N = 13) were established for each connection level according to crown heights (TL10 = 10 mm, TL15 = 15 mm, BL12 = 12 mm, BL17 = 17 mm). Dynamic load tests were carried out according to ISO Norm 14801. Failed samples and fracture surfaces were analysed with an optical and scanning electron microscope (SEM). The fatigue limit and the fatigue strength degradation (fatigue strength exponent) decreases with increasing crown height (5 mm) in both groups of internal hexagonal titanium dental implant connection levels. Consequently, the mechanical integrity of internal hexagonal dental implants varies with the height of the crown. An increase of 5 millimetres in the crown height appears to significantly decrease the fatigue life of both types of dental implants.

Unprecedented simultaneous enhancement in damage tolerance and fatigue resistance of zirconia/Ta composites

Dense (>98 th%) and homogeneous ceramic/metal composites were obtained by spark plasma sintering (SPS) using ZrO₂ and lamellar metallic powders of tantalum or niobium (20 vol.%) as starting materials. The present study has demonstrated the unique and unpredicted simultaneous enhancement in toughness and strength with very high flaw tolerance of zirconia/Ta composites. In addition to their excellent static mechanical properties, these composites also have exceptional resistance to fatigue loading. It has been shown that the major contributions to toughening are the resulting crack bridging and plastic deformation of the metallic particles, together with crack deflection and interfacial debonding, which is compatible with the coexistence in the composite of both, strong and weak ceramic/metal interfaces, in agreement with predictions of ab-initio calculations. Therefore, these materials are promising candidates for designing damage tolerance components for aerospace industry, cutting and drilling tools, biomedical implants, among many others.

New ZrO2/Al2O3 Nanocomposite Fabricated from Hybrid Nanoparticles Prepared by CO2 Laser Co-Vaporization

Alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) are currently the materials of choice to meet the need for tough, strong, and bioinert ceramics for medical devices. However, the mechanical properties of ZrO₂/Al₂O₃ dispersion ceramics could be considerably increased by reducing the corresponding grain sizes and by improving the homogeneity of the phase dispersion. Here, we prepare nanoparticles with an intraparticular phase distribution of Zr_(1−x)Al_xO_(2−x/2) and (γ-, δ-)Al₂O₃ by the simultaneous gas phase condensation of laser co-vaporized zirconia and alumina raw powders. During subsequent spark plasma sintering the zirconia defect structures and transition alumina phases transform to a homogeneously distributed dispersion of tetragonal ZrO₂ (52.4 vol%) and α-Al₂O₃ (47.6 vol%). Ceramics sintered by spark plasma sintering are completely dense with average grain sizes in the range around 250 nm. Outstanding mechanical properties (flexural strength σ_f = 1500 MPa, fracture toughness K_Ic = 6.8 MPa m^1/2) together with a high resistance against low temperature degradation make these materials promising candidates for next generation bioceramics in total hip replacements and for dental implants.

In vitro and in vivo evaluation of a new zirconia/niobium biocermet for hard tissue replacement

Metals and ceramics are commonly used in orthopaedics, dentistry and other load bearing applications. However, the use of ceramic matrix composites reinforced with biocompatible metals for heavy load-bearing hard tissue replacement applications has not previously been reported. In order to improve the reliability and the mechanical properties of biomedical implants, new zirconia-Nb composites have been recently developed. The aim of this study was to investigate the biological tolerance of these new zirconia/Nb biocermets implants with both in vitro and in vivo approaches. At first, human bone marrow derived mesenchymal stem cells were cultured on sintered biocermet discs with polished surfaces and were compared with responses to niobium metal. In vitro, the biocermets showed no deleterious effect on cell proliferation, extra-cellular matrix production or on cell morphology. Furthermore, the biocermet showed a higher percentage of cell proliferation than Nb metal. On the other hand, the bone response to these new zirconia/Nb biocermets was studied. Cylinders of biocermets, as well as commercially Nb rod were implanted in the tibiae of New Zealand white rabbits. All the animals were euthanatized after 6 months. The specimens were processed to obtain thin ground sections. The slides were observed in normal transmitted light microscope. A newly formed bone was observed in close contact with material surfaces. No inflamed or multinucleated cells were present. This study concluded that zirconia/Nb composites are biocompatible and osteoconductive. The ceramic-metal composite has even better osteointegration ability than pure Nb. In conclusion, zirconia-Nb biocermet is suitable for heavy load-bearing hard tissue replacement from the point of view of both mechanical properties and biocompatibility.

Mechanical performance of a biocompatible biocide soda-lime glass-ceramic

A biocompatible soda-lime glass-ceramic in the SiO2-Na2O-Al2O3-CaO-B2O3 system containing combeite and nepheline as crystalline phases, has been obtained at 750°C by two different routes: (i) pressureless sintering and (ii) Spark Plasma Sintering. The SPS glass-ceramic showed a bending strength, Weibull modulus, and toughness similar values to the cortical human bone. This material had a fatigue limit slightly superior to cortical bone and at least two times higher than commercial dental glass-ceramics and dentine. The in vitro studies indicate that soda-lime glass-ceramic is fully biocompatible. The in vivo studies in beagle jaws showed that implanted SPS rods presented no inflammatory changes in soft tissues surrounding implants in any of the 10 different cases after four months implantation. The radiological analysis indicates no signs of osseointegration lack around implants. Moreover, the biocide activity of SPS glass-ceramic versus Escherichia coli, was found to be >4log indicating that it prevents implant infections. Because of this, the SPS new glass-ceramic is particularly promising for dental applications (inlay, crowns, etc).

Bone loss at implant with titanium abutments coated by soda lime glass containing silver nanoparticles: a histological study in the dog

The aim of the present study was to evaluate bone loss at implants connected to abutments coated with a soda-lime glass containing silver nanoparticles, subjected to experimental peri-implantitis. Also the aging and erosion of the coating in mouth was studied. Five beagle dogs were used in the experiments. Three implants were placed in each mandible quadrant: in 2 of them, Glass/n-Ag coated abutments were connected to implant platform, 1 was covered with a Ti-mechanized abutment. Experimental peri-implantitis was induced in all implants after the submarginal placement of cotton ligatures, and three months after animals were euthanatized. Thickness and morphology of coating was studied in abutment cross-sections by SEM. Histology and histo-morphometric studies were carried on in undecalfied ground slides. After the induced peri-implantitis: 1.The abutment coating shown losing of thickness and cracking. 2. The histometry showed a significant less bone loss in the implants with glass/n-Ag coated abutments. A more symmetric cone of bone resorption was observed in the coated group. There were no significant differences in the peri-implantitis histological characteristics between both groups of implants. Within the limits of this in-vivo study, it could be affirmed that abutments coated with biocide soda-lime-glass-silver nanoparticles can reduce bone loss in experimental peri-implantitis. This achievement makes this coating a suggestive material to control peri-implantitis development and progression.

Radiologic evaluation of bone loss at implants with biocide coated titanium abutments: a study in the dog

The objective of the present study is to evaluate bone loss at implant abutments coated with a soda-lime glass containing silver nanoparticles subjected to experimental peri-implantitis. Five beagle dogs were used in the experiments, 3 implants were installed in each quadrant of the mandibles. Glass/n-Ag coted abutments were connected to implant platform. Cotton floss ligatures were placed in a submarginal position around the abutment necks and the animals were subject to a diet which allowed plaque accumulation, and after 15 weeks the dogs were sacrificed. Radiographs of all implant sites were obtained at the beginning and at the end of the experimentally induced peri-implantitis. The radiographic examination indicated that significant amounts of additional bone loss occurred in implants without biocide coating, considering both absolute and relative values of bone loss. Percentages of additional bone loss observed in implants dressed with a biocide coated abutment were about 3 times lower (p<0.006 distal aspect; and p<0.031 at mesial aspect) than the control ones. Within the limits of the present study it seems promising the use of soda-lime glass/nAg coatings on abutments to prevent peri-implant diseases.

Inhibitory effect on in vitro Streptococcus oralis biofilm of a soda-lime glass containing silver nanoparticles coating on titanium alloy

This paper reports the effect of soda-lime-glass-nAg coating on the viability of an in vitro biofilm of Streptococcus oralis. Three strains (ATCC 35037 and two clinical isolates from periodontitis patients) were grown on coated with glass, glass containing silver nanoparticles, and uncoated titanium alloy disks. Two different methods were used to quantify biofilm formation abilities: crystal violet staining and determination of viable counts. The influence of the surface morphology on the cell attachment was studied. The surface morphology was characterized by scanning electron microscopy (SEM) and using a profilometer. SEM was also used to study the formation and the development of biofilm on the coated and uncoated disks. At least a >99.7% inocula reduction of biofilm respect to titanium disks and also to glass coated disks was observed in the glass-nAg coated disks for all the studied strains. A quantitative evaluation of the release of silver was conducted in vitro to test whether and to what extend the biocidal agent (silver) could leach from the coating. These findings suggest that the biofilm formation of S. oralis strains is highly inhibited by the glass-nAg and may be useful for materials which require durable antibacterial effect on their surfaces, as it is the case of dental implants.

Nanostructured ceramic oxides with a slow crack growth resistance close to covalent materials

Oxide ceramics are sensitive to slow crack growth because adsorption of water can take place at the crack tip, leading to a strong decrease of the surface energy in humid (or air) conditions. This is a major drawback concerning demanding, long-term applications such as orthopaedic implants. Here we show that a specific nanostructuration of ceramic oxides can lead to a crack resistance never reached before, similar to that of covalent ceramics.