Iodonium salt improves the dentin bonding performance in an experimental dental adhesive resin

The aim of this study was to evaluate the influence of an iodonium salt on the immediate and long-term microtensile bond strength to dentin of an experimental dental two-step, self-etching adhesive system. A model dental adhesive resin was formulated using bisphenol A glicidyl dimethacrylate (Bis-GMA), triethylene glicol dimethacrylate (TEGDMA), and hydroxyethyl methacrylate (HEMA), which was polymerized using four combinations of photo-initiators and coinitiators. A group using only camphorquinone (CQ), two binary systems (CQ and ethyl 4-dimethylamine benzoate (CQ+EDAB), CQ and diphenyliodonium hexafluorphosphate (CQ+DPIHFP)) and a ternary system (CQ+EDAB+DPIHFP) was investigated. Clearfil SE Bond (CSEB) was used as a commercial reference. Bond strength to bovine dentin was assessed through microtensile bond tests measured in MPa in a universal testing machine. The beam specimens were stored in distilled water at 37 °C for 24 h and 1 year. Two-way ANOVA and Student–Newman–Keuls' post-hoc tests were used to compare means of groups (α=5%) and failure modes classified under magnification. After 24 h, the ternary system showed a bond strength similar to that of the binary system CQ+EDAB and the commercial material. After 1 year of storage, the μTBS values of the group CQ+EDAB+DPIHFP showed a bond strength significantly higher (p<0.05) than those of the CQ, CQ+DPIHFP, and CQ+EDAB groups and no difference from that of the CSEB group. The ternary photo-initiator system with iodonium salt maintained increased bond strength to dentin of model self-etching adhesive systems after 1 year of aging.     

Bi-colored zirconia as dental restoration ceramics

Machinable zirconia blocks with gradient colors are fundamental for fabrication of full-contour esthetic dental restorations. The aim of this study was to process and evaluate bi-colored zirconia ceramics as a pilot dental material by using well-established techniques. Two commercially available partially stabilized zirconia granules, one undoped and one doped with 0.202 wt% Fe₂O₃, resulted in white and yellow colors after sintering, respectively. Bi-colored zirconia was fabricated by two-step dry pressing of both zirconia granules one above the other to form green bodies, followed by cold isostatic pressing (CIP) and, a two-step pressureless sintering finally at 1450 °C. The dilatometer results showed that the Fe₂O₃ doped zirconia sintered slightly rapid, but the difference of shrinkage between two powders was <1%. Sintered bars achieved full density, 6.018 g/cm³ (～99%TD), without cracks in the ～1 mm color gradient zone. The microstructures were characterized by scanning electron microscopy (SEM) and careful observation of both surface and interior provided no obvious structural difference of either grains or pores among the three distinct regions, comprising white, yellow and color gradient zone. Vickers hardness of bi-colored zirconia was ～13.1 GPa, with no obvious difference in the three regions. The four-point bending strength of the bi-colored zirconia bars was 745.5±159.6 MPa, which appeared noticeably lower than that of the single-colored references being above 1000 MPa. Fractographic analysis revealed that in most of the cases (60%) the fracture was initiated at the color gradient zone, where large voids with high coordination numbers, agglomerates with critical size and concentration of irregular grains with porous surfaces were observed. Above all, bi-colored zirconia ceramics prepared by the improved technique could meet the basic requirements of dental materials. The ways of minimizing the defects within bi-colored blocks should be developed for the production of esthetic zirconia ceramics of high strength and reliability.     

Effect of iron on the properties of sulfated zirconia

Sulfated zirconia has found several industrial applications, mainly for catalyzing reactions which require acidic sites. In order to control the properties of this solid, the effect of iron on the sulfated zirconia properties was studied in this work. Samples with different iron to zirconium molar ratios were prepared by the sol–gel method, followed by sulfation and characterization by several techniques. It was found that all iron ions go into zirconia when Fe/Zr ≤ 0.4. However, when higher amounts of iron (Fe/Zr ≥ 0.8) are added, hematite is segregated. Different phases can be obtained depending on the iron content and on the sulfur presence. Iron increases the specific surface areas of both sulfated and pure zirconia but does not affect the incorporation of sulfate groups as compared to pure zirconia. Iron also makes the solids thermally more stable and modifies the sulfated zirconia surface creating acidic sites with medium strength. Therefore, it is possible to control the acidity of the solid doping the sulfated zirconia with iron. All these changes are very useful for catalytic applications.     

Effect of proanthocyanidin incorporation into dental adhesive on durability of resin–dentin bond

BackgroundProanthocyanidin has shown to have beneficial effects on dentin bonding via its collagen cross-linking and protease inhibitory effects.ObjectiveThis study evaluated the effect of incorporation of 1–3% PA into a dental adhesive on durability of resin–dentin bond.Materials and methodsThe experimental adhesive was first formulated by combining 50 wt% comonomer mixtures with 50 wt% ethanol. PA was then added to the ethanol-solvated adhesive to yield three groups of adhesives at concentrations of 1.0 wt%, 2.0 wt% and 3.0 wt%. The PA-free adhesive served as control. Flat dentin surfaces from forty extracted third molars were etched with 32% phosphoric acid and the specimens were randomly assigned to one of the four adhesive groups. Two layers of experimental adhesives were applied to etched dentin and light-cured for 20 s after solvent evaporation. Composite build-ups were performed using Filtek Z250 (3M ESPE). The bonded teeth were divided into three subgroups for different methods of storage: (1) 24 h indirect water exposure (IE), (2) 6 M IE and (3) 6 M direct water exposure (DE). After the designated period of water storage, the bonded teeth were sectioned into 0.9 mm×0.9 mm beams for bond strength testing. Bond strength data were evaluated by two-way ANOVA and Tukey׳s tests (α=0.05). Interfacial nanoleakage was examined using a field-emission scanning electron microscopy. Two-way ANOVA and Tukey׳s tests were used to examine the effects of PA concentration and water exposure on bond strength and percentage of nanoleakage (α=0.05).ResultsTwo-way ANOVA showed that the factors, water exposure and PA concentration had a significant effect on bond strength (p<0.001). Interaction between the two factors was also significant (p<0.001). Bond strength of all four adhesives decreased with PA concentrations and ageing. Type of water exposure had no effect on the bond strength of PA-incorporated adhesive; while direct water exposure significantly reduced the bond strength of PA-free adhesive. Conversely, the factors, water exposure and PA concentration showed a significant effect on nanoleakage percentage (p<0.001). Interaction between the two factors was not significant (p>0.05).ConclusionIncorporation of proanthocyanidin into a dental adhesive did not prevent resin–dentin bond degradation over time.     

Slow crack growth and hydrothermal aging stability of an alumina-toughened zirconia composite made from La2O3-doped 2Y-TZP

A very tough zirconia matrix is interesting to fabricate alumina-toughened zirconia (ATZ) and composites generally processed from 3Y-TZP do not exhibit very high toughness. The strategy of lowering the yttria content to increase toughness however is normally associated with an increased hydrothermal aging susceptibility. In this work, a 0.4 mol% La₂O₃ doped 2Y-TZP matrix was investigated to realize a 20 wt.% alumina toughened zirconia composite with a substantially high aging resistance. The higher transformation toughening in the composite shifted the V-K_I towards higher K_I values, while preserving the slope of the curve, resulting in a threshold K_I0 of 4.0 MPa m^1/2 and fracture toughness (K_IC) of 7.1 MPa m^1/2. These composites can offer a better compromise between aging and crack resistance than traditional 3Y-TZPs and plain ATZ composites without La₂O₃ doping.     

Assessment of the initial and aged dentin bond strength of universal adhesives

This study evaluated the effect of mechanical loading on microtensile bond strengths (μTBS) of universal adhesives to dentin and quantified adhesive dentin penetration using micro-Raman spectroscopy. Human molars had occlusal dentin exposed and were allocated into eight groups: All-Bond Universal and Scotchbond Universal using etch-and-rinse and self-etch approaches, Adper Prompt L-Pop, Adper Single Bond Plus, Clearfil SE Bond, and Optibond FL. Following bonding procedures and build-ups, specimens were either stored in water at 37 °C for 24 h or mechanically loaded (50,000 cycles, 50 N) prior to μTBS test. Additional teeth were prepared for micro-Raman analysis of adhesive penetration and FE-SEM. Data were analyzed by two-way ANOVA and Tukey׳s post hoc test (P<0.05). Mechanical loading had no deleterious effect on μTBS with the exception of Adper Prompt L-Pop. Incomplete infiltration of the demineralized dentin was noticed for adhesives using the etch-and-rinse approach and for Scotchbond Universal in the self-etch approach.     

Effects of artificial aging on the biaxial flexural strength of Ce-TZP/Al2O3 and Y-TZP after various occlusal adjustments

The aim of this study was to determine the effect of aging on the biaxial flexural strength (BFS) of Ce-TZP/Al₂O₃ and Y-TZP after occlusal adjustment. NanoZr block (Ce-TZP/Al₂O₃ nanocomposite) and Katana zirconia block (Y-TZP) were prepared by milling with the aid of CAD/CAM into disk-shaped specimens. For each type of zirconia, 16 specimens were prepared without grinding for the control group (diameter of 16 mm and thickness of 1.20±0.05 mm, mean±SD), while 48 specimens were prepared for 3 experimental groups (n=16 each; 16 mm in diameter and 1.50±0.05 mm thick) with different types of surface grinding: superfine diamond bur (group I), zirconia stone bur (group II), and zirconia stone and fine polishing bur (group III). These specimens underwent an aging process in a steam autoclave for 5 h at 0.2 MPa and 134 °C, and then X-ray diffractometry was applied along with measurements of surface roughness and BFS. After occlusal adjustment, the monoclinic phase percentage increased in 3 experimental groups. Overall the increase was greater for Ce-TZP/Al₂O₃ than for Y-TZP. The Ra value showed similar changes for both types of zirconia. Following the aging process, Y-TZP showed a greater increase in the monoclinic phase percentage, but the change was not statistically significant. The Ra value showed similar changes in both types of zirconia, with no significant differences between before and after the aging process. The results of the BFS test showed that applying the aging process after grinding significantly increased the strength of both types of zirconia, with Ce-TZP/Al₂O₃ being significantly stronger than Y-TZP. The specimens treated by a superfine diamond bur exhibited the highest BFS in the four tested groups. Ce-TZP/Al₂O₃ had a higher BFS and greater resistance to low-temperature degradation than did Y-TZP.     

The antibacterial and physicochemical properties of a one-step dental adhesive modified with potential antimicrobial agents

This study investigated the effect of antimicrobial agents on the antibacterial potential of a one-step dental adhesive. Zinc silicate microparticles (ZnSi), silver microparticles (Ag), or essential oil of tea tree (terpinen-4-ol, Tr) were added at 0.5 wt% or 1 wt%. Additional analysis included pH, degree of C=C conversion (DC), translucency parameter (TP), water sorption/solubility (W_SR/SL), morphology of bonded interfaces, and dentin microtensile bond strengths (µTBS) after 24 h or 6 months. Antibacterial potential was assessed using a microcosm biofilm model. Data were statistically analyzed at α=0.05. DC, W_SR/SL, and bonding morphology were not affected by antimicrobial incorporation. ZnSi and Ag increased pH and improved immediate µTBS, generating more stable dentin bonds after 6 months. Tr showed the poorest results for µTBS. Ag 1% was the adhesive with lower TP. In general the best antibiofouling results were observed for Ag 0.5 wt%, although all antibacterial agents showed some antibiofouling effect.     

Effect of methyl methacrylate monomer on bond strength of denture base resin to acrylic teeth

Bond failures at the acrylic teeth and denture base resin interface are still a common clinical problem in prosthodontics. The effect of methyl methacrylate (MMA) monomer on the bond strength of three types of denture base resins (Acron MC, Lucitone 550 and QC-20) to two types of acrylic teeth (Biotone and Trilux) was evaluated. Twenty specimens were produced for each denture base resin/acrylic tooth combination and were randomly divided into control (acrylic teeth received no surface treatment) and experimental groups (MMA was applied to the surface of the acrylic teeth for 180 s) and were submitted to shear tests (1 mm/min). Data (MPa) were analyzed using three-way ANOVA/Student's test (α=0.05). MMA increased the bond strength of Lucitone denture base resins and decreased the bond strength of QC-20. No difference was detected for the bond strength of Acron MC base resin after treatment with MMA.     

Production and characterization of self-colored dental zirconia blocks

The objective of this study is to produce and characterize self-colored dental zirconia blocks by using zirconia raw material having Fe₂O₃ content. Five different compositions with different amounts of Fe₂O₃ were prepared by using two different raw materials. The shaped samples were sintered at 1500 °C for 2 h. Color differences, phase formations, microhardness, fracture toughness, and microstructures of the specimens were investigated. Self-colored zirconia blocks and frameworks of desired physical and mechanical properties for dental restorations can be produced by using zirconia raw material having Fe₂O₃ content.     

Texturing of 3Y-TZP zirconia by electrophoretic deposition in a high magnetic field of 17.4 T

Ceramics can be textured during colloidal processing by aligning the suspended particles in a strong magnetic field and retaining this alignment in the green body. Attempts to align tetragonal zirconia particles however were not successful, not even in 12 T magnetic fields. In the current work, monoclinic zirconia was successfully aligned with its (1 0 0) plane perpendicular to the magnetic field direction by electrophoretic deposition (EPD) in a 17.4 T field. Moreover, textured tetragonal zirconia was developed by reactive sintering of undoped pure monoclinic zirconia and co-precipitated 8 mol% yttria-stabilized zirconia. The sintered tetragonal zirconia inherited the alignment of the monoclinic zirconia particle precursor and aligned with its (0 0 1) plane perpendicular to the magnetic field direction. The toughness of the (0 0 1)-oriented 3Y-TZP along the [0 0 1] direction of the textured zirconia was 65% higher than normal to it and 48% higher than the randomly oriented material.     

Reaction mechanisms of synthesis and decomposition of fluorapatite–zirconia composite nanopowders

The reaction mechanisms of formation and decomposition of fluorapatite?zirconia composite nanopowders were investigated after the mechanochemical process and subsequent thermal treatment. Experimental results indicated that formation of fluorapatite?zirconia composite nanopowders proceeded in several steps. In the first stage, phosphoric acid formed immediately upon addition of phosphorous pentoxide to the reaction mixture. Afterwards, anhydrous dicalcium phosphate was generated as a result of reaction between reagents with phosphoric acid. The synthesis progressed by the formation of the stoichiometrically deficient hydroxyfluorapatite?zirconia composite at milling times between 5 and 15 min. Ultimately, the fluorapatite?zirconia composite nanopowder was obtained after 300 min of milling. Results revealed that the annealing process led to a decomposition of fluorapatite to tricalcium phosphate and calcium fluoride, and to the transformation of monoclinic zirconia to the tetragonal form. Field emission scanning electron microscope observations showed that the milled sample was composed of fine particles with a mean particle size of about 45 nm after 300 min of milling. Besides, the mean particle size increased progressively due to crystal growth in the temperature range above 900 °C. According to the gained data, reaction mechanism steps were proposed to clarify the reactions occurring during the above-mentioned solid state process.     

Influence of dentin biomodification with epigallocatechin-3-gallate on the bond strength of self-etch adhesive: Twelve-month results

To evaluate the effectiveness of dentin biomodification with epigallocatechin-3-gallate (EGCG) on the resin-dentin bonds over time. Twenty seven extracted human third molars were prepared to expose a flat dentin surface and divided into 3 groups (n=9). Dentin surfaces were dried and treated with 20 µL aliquots of either distilled water (control); 2% chlorhexidine digluconate solution (CHX) or 0.1% EGCG aqueous solution. Solutions were rubbed for 60 s followed by bonding with Adper Easy One, and 5-mm-thick resin crown build-up. Bonded teeth were stored in distilled water for 24 h and then longitudinally sectioned to obtain bonded sticks. One-third of the specimens were immediately subjected to a microtensile bond strength test in tension at 0.5 mm/min, while the remaining specimens were tested after six and twelve months of storage in distilled water at 37 °C. Data were analyzed with Two-way ANOVA and Holm–Sidak method. After 24 h of storage, mean bond strength values were not significantly different among all groups (p>0.05). Bond strengths of EGCG and CHX remained stable after 6 and 12 months. (p>0.05). To conclude, pretreatment with EGCG or CHX preserved the bonding of Adper Easy One to dentin after six and twelve months of storage.     

Novel method for the synthesis of a β-tricalcium phosphate coating on a zirconia implant

A novel method for the synthesis of a thin β-tricalcium phosphate (β-TCP) coating on zirconia implants has been developed. The synthesis procedure involves two steps: (i) rapid wet-chemical deposition of a biomimetic CaP coating and (ii) subsequent post-deposition processing of the biomimetic CaP coating, which includes a heat treatment at 900 °C followed by a short sonication in a water bath. The obtained β-TCP coating showed a uniform and dense morphology with a thickness of ≈500 nm and displayed a roughness in the nanometre range (R_a = 28 nm). The β-TCP coating demonstrated an apatite-mineralization ability in a simulated body fluid and enhanced the adsorption of serum proteins on the zirconia. Moreover, the β-TCP coating adhered firmly to the zirconia substrate, developing a notable scratch resistance (L_c = 97 N) and tensile strength (52 MPa) and showed strong resistance towards mechanical forces present during implantation of the coated zirconia implant into the artificial bone.     

Speed sintering translucent zirconia for chairside one-visit dental restorations: Optical,mechanical, and wear characteristics

The fabrication of zirconia dental restorations is a time-consuming process due to traditional slow sintering schemes; zirconia (Y-TZP) produced by these conventional routes are predominantly opaque. Novel speed sintering protocols have been developed to meet the demand for time and cost effective chairside CAD/CAM-produced restorations, as well as to control ceramic microstructures for better translucency. Although the speed sintering protocols have already been used to densify dental Y-TZP, the wear properties of these restorations remain elusive. Fast heating and cooling rates, as well as shorter sintering dwell times are known to affect the microstructure and properties of zirconia. Thus, we hypothesize that speed sintered zirconia dental restorations possess distinct wear and physical characteristics relative to their conventionally sintered counterparts. Glazed monolithic molar crowns of translucent Y-TZP (inCoris TZI, Sirona) were fabricated using three distinct sintering profiles: Super-speed (SS, 1580 °C, dwell time 10 min), Speed (S, 1510 °C, dwell time 25 min), and Long-term (LT, 1510 °C, dwell time 120 min). Microstructural, optical and wear properties were investigated. Crowns that were super-speed sintered possessed higher translucency. Areas of mild and severe wear were observed on the zirconia surface in all groups. Micropits in the wear crater were less frequent for the LT group. Groups S and SS exhibited more surface pits, which caused a scratched steatite surface that is associated with a greater volume loss. Tetragonal to monoclinic phase transformation, resulting from the sliding wear process, was present in all three groups. Although all test groups had withstood thermo-mechanical challenges, the presence of hairline cracks emanating from the occlusal wear facets and extending deep into the restoration indicates their susceptibility to fatigue sliding contact fracture.     

Low temperature degradation resistant nanostructured yttria-stabilized zirconia for dental applications

When used in prosthetic dentistry, zirconia encounters severe durability issues due to low temperature degradation: exposure to humidity results in a transition from tetragonal to monoclinic phase, associated to disruptive integrity loss. Recently it has been shown that size-induced stabilization helps maintaining zirconia in tetragonal form, when the grain size is reduced to the nano-range. Objective of this work is to demonstrate the applicability of High Pressure Field Assisted Sintering (HP-FAST) to the preparation of dense, nanostructured samples of tetragonal yttria stabilized zirconia, with yttria content between 0.5 and 3 mol% and showing resistance to low temperature degradation. The yttria stabilized zirconia nanopowders were prepared by a hydrothermal method. Sintering by HP-FAST was performed at 900 °C in 5 min, under a pressure of 620 MPa. Resistance to low temperature degradation was tested at 134 °C, under vapor pressure, for up to 40 h. Both pristine and aged samples were characterized by X-ray diffraction, high-resolution scanning electron microscopy and nanoindentation tests in continuous stiffness measurement mode. The sintered samples presented a grain size between 20 and 30 nm and low or null monoclinic content. Both parameters resulted unaffected by ageing. The best results in terms of phase composition and mechanical properties have been obtained with the material containing 1.5 mol% of yttria. These results induce to reconsider the use of yttria stabilized zirconia as material for dental prosthetic systems requiring long-term durability.     

Effect of dopants and sintering temperature on microstructure and low temperature degradation of dental Y-TZP-zirconia

Accelerated ageing of dental TZP were investigated at 134 °C for 2 h under 2.3 bar water vapor pressure. The TZP blanks were sintered in the range from 1350 to 1580 °C. The average grain size of 1350 and 1400 °C sintered materials were <0.3 μm whereas higher sintering temperatures led to larger grain sizes. The grain size and dopants influence the stability of tetragonal phase of zirconia under LTD conditions. The Y-TZP with average grain sizes <0.3 μm did not reveal the martensitic tetragonal-monoclinic phase transformation after ageing, whereas zirconia with grain sizes larger 0.3 μm showed fractions of monoclinic phase. Alumina and Ceria stabilized grain size and Y-TZP against LTD. Y-TZP with low amounts of Fe₂O₃ (<0.15%) used for coloring did not show any detrimental effects under LTD conditions. As the Y-TZP ceramics with grain size larger than 0.3 μm are not stable under LTD conditions they are not recommended for long term use in moist environment.     

Improvement in sinterability and phase stability of hydroxyapatite and partially stabilized zirconia composites

Composites of hydroxyapatite with partially stabilized zirconia with MgO or MgF₂ were pressureless sintered between 1000 °C and 1300 °C. The reactions and transformations of phases were verified by X-ray diffraction. For the hydroxyapatite and zirconia composites with MgO, calcium from the hydroxyapatite diffused into the zirconia phase, and the hydroxyapatite decomposed to tri-calcium phosphate at sintering temperatures higher than 1000 °C. Above about 1200 °C, CaZrO₃ was formed. Composites containing the MgF₂ decomposed slower than the composites with MgO, which was verified by the changes in the lattice volume of the hydroxyapatite left in these composites. Fluorine ions in MgF₂ diffused into hydroxyapatite, which resulted in thermal stability at high sintering temperatures. Composites with MgF₂ had higher hardness than those with MgO. The lowest porosity was found in a composite initially containing 10 wt% partially stabilized zirconia and 5 wt% MgF₂.     

Reactions in hydroxylapatite–zirconia composites

Sintered composites of hydroxylapatite (HA) and zirconia were studied with X-ray diffraction and scanning electron microscopy (SEM). Addition of zirconia caused increased decomposition of the HA in composites sintered at 1100 °C and 1300 °C, forming tricalcium phosphate phases (TCP). The volume of the unit cell of HA increased as the concentration of zirconia in the composites increased. These results are explained as resulting from exchange of Ca²⁺ and ZrO²⁺ ions between the HA and the zirconia. The porosity of the sintered composites increased with increase in zirconia concentration in the composites, probably because of water formed by the decomposition of the HA.     

Formic acid as additive for the preparation of high-performance FePO4 materials by spray drying method

High-performance ferric phosphate (FePO₄), with well-defined ellipsoid morphology and uniform particle size distribution, is successfully fabricated via a green spray drying method with formic acid as additive. It is found that the added formic acid plays a crucial role for the formation of the well-distributed FePO₄ particles. Benefited by the outstanding structure and properties of ferric phosphate prepared above, a high performance of lithium iron phosphate (LiFePO₄) has been prepared. It exhibits high capacity, especially at high charging/discharging rate (158.4 mAh g⁻¹ at 0.2 C and 107.3 mAh g⁻¹ at 10 C), and excellent cycling stability (without capacity fading after cycling for 200cycles at 1 C). All these impressive electrochemical performance could be ascribed to the FePO₄ precursor, and further attributed to the addition of formic acid, which may play as a template, resulting in the well-defined morphology, uniform particles size distribution, hierarchical pore structure, and high surface area of the ferric phosphate.