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PubMed2006

Fatigue of zirconia under cyclic loading in water and its implications for the design of dental bridges.

OBJECTIVES: The aim of this study was to evaluate the cyclic fatigue behavior of zirconia (3Y-TZP) in water and derive guidelines for the design of zirconia-based dental bridges with extended lifetime. METHODS: The subcritical crack growth parameters under aqueous and cyclic loading conditions were determined from Weibull distributions of the initial mechanical strength and of the lifetime of TZP specimens. The strength and lifetime data were obtained using a specially designed bending machine under simple and oscillatory loading conditions, respectively. RESULTS: The TZP components submitted to cyclic loading in water exhibited subcritical crack propagation at stress levels significantly ( approximately 50%) lower than the critical stress intensity factor (K(IC)=5.6 MPam(1/2)). In spite of this susceptibility to subcritical crack growth, calculations based on the fatigue parameters and on the stress applied on the prosthesis indicate that posterior bridges with zirconia frameworks can exhibit lifetimes longer than 20 years if the diameter of the bridge connector is properly designed. SIGNIFICANCE: This in vitro study indicates that partially stabilized zirconia (3Y-TZP) can withstand the severe cyclic loading and wet conditions typically applied in the molar region of the mouth and is therefore an appropriate material for the fabrication of all-ceramic multi-unit posterior bridges.

Ceramics↗
PubMed2006

Mechanical and fracture behavior of veneer-framework composites for all-ceramic dental bridges.

OBJECTIVES: High-strength ceramics are required in dental posterior restorations in order to withstand the excessive tensile stresses that occur during mastication. The aim of this study was to investigate the fracture behavior and the fast-fracture mechanical strength of three veneer-framework composites (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) for all-ceramic dental bridges. METHODS: The load bearing capacity of the veneer-framework composites were evaluated using a bending mechanical apparatus. The stress distribution through the rectangular-shaped layered samples was assessed using simple beam calculations and used to estimate the fracture strength of the veneer layer. Optical microscopy of fractured specimens was employed to determine the origin of cracks and the fracture mode. RESULTS: Under fast fracture conditions, cracks were observed to initiate on, or close to, the veneer outer surface and propagate towards the inner framework material. Crack deflection occurred at the veneer-framework interface of composites containing a tough framework material (TZP/Cercon S and Inceram-Zirconia/Vita VM7), as opposed to the straight propagation observed in the case of weaker frameworks (Empress 2/IPS Eris). SIGNIFICANCE: The mechanical strength of dental composites containing a weak framework (K(IC)<3 MPam(1/2)) is ultimately determined by the low fracture strength of the veneer layer, since no crack arresting occurs at the veneer-framework interface. Therefore, high-toughness ceramics (K(IC)>5 MPam(1/2)) should be used as framework materials of posterior all-ceramic bridges, so that cracks propagating from the veneer layer do not lead to a premature failure of the prosthesis.

Aluminum Oxide↗
PubMed2006

Cyclic fatigue in water of veneer-framework composites for all-ceramic dental bridges.

OBJECTIVES: Ceramic materials applied in dentistry may exhibit significant subcritical crack growth due to the severe cyclic loading in the aqueous environment encountered in the mouth during mastication. The authors report on the subcritical crack growth behavior of three dental restoration systems (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) under cyclic loading in water, in order to establish guidelines for the use and design of long-lifetime all-ceramic posterior bridges. METHODS: Inert strength and lifetime tests under cyclic loading in an aqueous environment were performed in a mechanical bending apparatus and evaluated with Weibull statistics. RESULTS: Subcritical crack growth occurred predominantly in the outer veneer layer of the veneer-framework composites. The apatite-based veneer (IPS Eris) was more susceptible to subcritical crack propagation compared to the feldspathic glass veneers (Cercon S and Vita VM7). SIGNIFICANCE: Dental restoration systems containing apatite-based veneers and weak frameworks (Empress 2/IPS Eris) are not recommended for the fabrication of all-ceramic bridges in the molar region. Conversely, veneer-framework systems consisting of feldspathic glass veneers and tough zirconia-based frameworks (TZP/Cercon S and Inceram-Zirconia/Vita VM7) may exhibit lifetimes longer than 20 years if the bridge connector is properly designed.

Aluminum Oxide↗
PubMed2006

Resistance to fracture and structural characteristics of different fiber reinforced post systems.

OBJECTIVES: The aim of this study was to investigate the ultrastructure and resistance to fracture of eight different types of fiber post, and to verify the existence of a correlation between structural characteristics and flexural strength. METHODS: Eight types of fiber post were selected for this study. Fiber Kor (Jeneric-Pentron), Para Post Fiber White (Colténe), Luscent Anchor (Dentatus), Twin-Luscent Anchor (Dentatus), Style Post (Metalor), DT White-Post (VDW), DT Light-Post (VDW) and ER Dentin Post (Brasseler). Ten posts of each experimental group were selected for a three-point bending test, and one was processed for SEM evaluation. A universal testing machine loading at an angle of 90 degrees was employed for the three-point bending test. The test was carried out until fracturing of the post. After fracture testing, the posts with the highest and the lowest values of flexural strength of each system were additionally processed for SEM analysis. SEM evaluation was performed using a PC-measurement program to assess the fiber/matrix ratio and fiber dimensions. RESULTS: The fracture load of the tested systems ranged from 60 to 96 N and the flexural strength from 565 to 898 MPa. DT White-Post and DT Light-Post (898 and 842 MPa, respectively) had significantly higher flexural strengths than the other posts. Style Post (565 MPa) showed a significantly lower flexural strength than all other posts. The differences in fiber diameter ranged from 8.2 to 21 microm and for the fiber/matrix ratio from 41 to 76%. Of the various structural characteristics investigated, only the fiber/matrix ratio showed a significant correlation to the flexural strength (r=0.922, p=0.003). SIGNIFICANCE: The FRC-posts investigated displayed significant differences with regard to fracture load and flexural strength. A strong and significant linear correlation between the fiber/matrix ratio and the flexural strength was found.

Composite Resins↗
PubMed2006

Modification of glass fibers to improve reinforcement: a plasma polymerization technique.

OBJECTIVES: This study evaluates the effect of plasma treated E-glass fiber to improve the mechanical properties of acrylic resin denture base material, polymethylmethacrlyate (PMMA). Plasma surface treatment of fibers is used as reinforcement in composite materials to modify the chemical and physical properties of their surfaces with tailored fiber-matrix bonding strength. METHODS: Three different types of monomer 2-hydroxyethyl methacrylate (HEMA), triethyleneglycoldimethylether (TEGDME) and ethylenediamine (EDA) were used in the plasma polymerization modification of glass fibers. A radiofrequency generator was used to sustain plasma in a glass vacuum chamber. Glass fibers were modified at the same glow-discharge power of 25 W and exposure time of 30 min for each monomer. Fibers were incorporated into the acrylic with 1% (w/w) loading except control group. Specimens were prepared using a standard mold of 3 cmx0.5 cmx0.8 cm in dimension with eight specimens in each group. Samples were subjected to a flexural strength test set up at a crosshead speed of 5mm/min. Scanning electron microscopy (SEM) was used to examine the microstructure and X-ray photoelectron spectroscopy (XPS) was used for chemical analysis of the surface. RESULTS: Data were analyzed by means of ANOVA and Duncan's tests. Test results revealed that fiber reinforcement had a significant effect on the flexural strength of the specimens (p<0.05). Among the fiber reinforced groups, plasma treatment with EDA monomer resulted in the most significant increase in flexural strength values (p<0.05). XPS results have shown an increasing number of nitrogenous compounds in EDA treated fibers. The chemical structure of the surface, especially with the increase in nitrogenous compounds could give an idea for the amine film deposition and SEM figures showed an increase in surface roughness. SIGNIFICANCE: The results showed that plasma treatment with EDA monomer was an effective alternative method of increasing the flexural strength of PMMA based denture base polymers through fiber reinforcement.

Analysis of Variance↗
PubMed2006

Synthesis and preparation of novel 4-arm star-shape poly(carboxylic acid)s for improved light-cured glass-ionomer cements.

OBJECTIVE: The objective of this study was to synthesize and characterize novel 4-arm star-shape poly(acrylic acid)s (poly(AA)s) via atom-transfer radical polymerization (ATRP) technique, tether in situ light-curable methacrylate functionalities onto the poly(AA) backbone, use these star-shape poly(AA)s to formulate the light-cured glass-ionomer cements (LCGICs), and evaluate the mechanical strengths of the formed cements. MATERIALS AND METHODS: The 4-arm poly(AA)s were synthesized using ATRP and tethered with either 2-isocyanatoethyl methacrylate (IEM) or glycidyl methacrylate (GM). The polymers were formulated with 2-hydroxyethyl methacrylte (HEMA) or methacryloyl beta-alanine (MBA), water, initiators, and Fuji II LC filler. Compressive strength (CS) was used as a tool to evaluate the formed cements. The specimens were conditioned in distilled water at 37 degrees C for 24h prior to testing. RESULTS: The 4-arm poly(AA) showed a lower viscosity as compared to its linear counterpart. Both IEM-tethered and GM-tethered 4-arm poly(AA) constructed LCGICs showed significantly high mechanical strengths. Both types of co-monomer and grafting agent dramatically affected the mechanical strengths. The MBA-containing poly(AA) cements exhibited much higher CS than the HEMA-containing cements. The IEM-tethered poly(AA) cements showed much higher CS and DTS than the GM-tethered cements. CONCLUSIONS: This study developed a novel light-curable 4-arm star-shape poly(AA) system. The system was 13% in CS, 178% in DTS and 123% in FS, compared to Fuji II LC.

Acrylic Resins↗
PubMed2006

Properties and cyclic fatigue of glass infiltrated tape cast alumina cores produced using a water-based solvent.

OBJECTIVE: The purpose of this study was to investigate the properties of tape cast alumina composite produced using a water-based solvent and its possible clinical use as an all ceramic crown system in a fixed partial denture. Durability of the system will be measured by fatigue test to simulate the masticating conditions of the oral cavity. METHODS: The optimal weight ratio of water-based alumina tape was determined by tensile strength, shrinkage ratio and durability. The coefficient of thermal expansion, fracture toughness, biaxial flexural strength and flexural strength after fatigue test of a composite produced from alumina tape at optimal weight ratios were determined and compared to In-Ceram alumina core (control). RESULTS: The weight ratio of alumina/(alumina+binder+plasticizer) of 0.84 and binder/(binder+plasticizer) of 0.5 was observed to be the optimal composition for achieving excellent composite properties. Coefficient of thermal expansion of the sintered alumina tape was observed to be 7.3x10(-6)/degrees C, and this value was increased to 7.5x10(-6)/degrees C after infiltrating the sintered tape with glass. The fracture toughness and biaxial flexural strength of glass infiltrated alumina tape was observed to be 4.6 MPa m(1/2) and 498 MPa, respectively. After cyclic loading for 10(2)-10(6) cycles, no significant change in the biaxial flexural strength was observed between the glass infiltrated alumina core and the In-Ceram alumina core (p>0.05). SIGNIFICANCE: The observed properties provide evidence that the water-based tape cast alumina-glass composite is suitable for clinical use as an all ceramic crown system in a fixed partial denture.

Aluminum Oxide↗
PubMed2006

The impact of hydrofluoric acid surface treatments on the performance of a porcelain laminate restorative material.

OBJECTIVES: Hydrofluoric (HF) acid etching increases the bond strength between composite resin and porcelain surfaces and has been advocated as a pre-cementation technique for ceramic restorations. The internal surface flaw distribution which is implicated in the premature failure of ceramic restorations is modified by the etching process and little agreement exists amongst researchers as to the appropriate etching regime. The purpose of the current study was to examine the impact of HF acid concentration and etching time on the performance of a low fusing feldspathic porcelain. METHODS: Sets of 30 Vitadur-Alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were etched with HF acid of three different concentrations (5, 10 and 20%) and for three different etching periods (45, 90 and 180s). Mean flexure strengths, standard deviations and the associated Weibull moduli (m) and characteristic stress (sigma(0)) were determined using bi-axial flexure (ball on ring). Contact profilometry was utilised to characterise the roughness of the etched porcelain surfaces. RESULTS: A univariate general linear analysis of means revealed a significant reduction in the mean strength values of the as-fired control compared with groups subjected to HF acid etching. Further significance (P<0.05) was discovered with the impact of acid concentration. Altering etching time also resulted in changes in the reliability of the fracture strength data. Contact profilometry demonstrated an increase in surface roughness following HF acid etching and an increase in roughness associated with increasing HF concentration. CONCLUSIONS: Etching of feldspathic porcelain is a dynamic process and the impact is dependent on substrate constitution, surface topography, acid concentration and etching time. A significant reduction of the flexural strength of a low fusing feldspathic porcelain has been demonstrated to result from etching and clear evidence exists that the nature of surface flaw modification is a function of etching time and HF acid concentration. Favourable combinations of HF acid concentration and etching time have been identified which enhance the reliability of the porcelain utilised although variability in clinical technique will result in the reduced reliability of porcelain laminate restorations in function.

Acid Etching, Dental↗
PubMed2006

Characterization of sintered TCP sheets with various contents of binder prepared by tape-casting technique.

OBJECTIVES: The purpose of this study was to investigate the effect of binder content on the characterization of sintered tricalcium phosphate (TCP) sheets prepared by the tape-casting technique. METHODS: Poly(acrylic acid)-based binder was added at four contents: 5, 10, 15, or 30 mass%, to a beta-TCP aqueous slurry. The TCP green sheets were fabricated with the prepared TCP slurry by the tape-casting technique, and were sintered at 1200 degrees C for 2h. The sintered TCP sheets were characterized by field-emission scanning electron microscope (FE-SEM) observation, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectrometry. Apatite precipitation on the sintered TCP sheet surface in Hanks' balanced salt (HBS) solution at pH 7.4 was monitored over 14 days at 37 degrees C. RESULTS: A TCP green sheet with 5 mass% binder content had insufficient flexibility before sintering, and that with 30 mass% binder content had a problem in controlling the viscosity of slurry. FE-SEM observation showed that no differences in grain size existed in the various sintered TCP sheets. Measurement of XRD and FT-IR showed the presence of alpha-TCP phase in the various sintered TCP sheets, and same crystallographic structure was observed among various sintered TCP sheets. After 14 days immersion in HBS solution, the surfaces of sintered TCP sheets were completely covered with precipitated apatite crystals. SIGNIFICANCE: The binder content of 10 or 15 mass% is suitable for sintering TCP sheets. The sintered TCP sheet prepared by the tape-casting technique is a promising material as bone substitute.

Acrylic Resins↗
PubMed2006

Effect of short-term water storage on the elastic properties of some dental restorative materials--A resonant ultrasound spectroscopy study.

OBJECTIVES: This study was aimed to determine if short-term water storage would change elastic properties of dental composite materials. METHODS: Particulate filler composite resin and continuous unidirectional E-glass FRC materials were photopolymerized and additionally post-polymerized by heat for testing elastic properties with the Resonance Ultrasound Spectroscopy method as a function of time in water storage. The test specimens were stored in 37 degrees C water for up to 30 days. RESULTS: About 1% weight increase due to water sorption was observed in both materials with both polymerization methods. Water sorption did not change the resonance frequencies towards lower values, indicating no significant decrease in elastic properties in these materials. Because of high damping of the polymer composite materials leading to wide resonance peaks and low number of the recorded peaks, accurate determination of the elastic properties was not possible. SIGNIFICANCE: Results suggest that the most likely explanation for the previously observed decrease in bending stiffness of FRC materials is the decreased yield limit of the hydrated polymer matrix. It is important to recognize that water sorption has the effect on mechanical properties of dental composite materials by changing the yield limit of the matrix rather than by changing the elastic properties of the material.

Absorption↗
PubMed2006

Immediate versus water-storage performance of Class V flowable composite restoratives.

OBJECTIVES: The aims of this investigation were to clarify the effects of 24h water-storage and finishing time on mechanical properties and marginal adaptation to a Class V cavity of eight modern flowable resin-composites. METHODS: Eight flowable composites, plus two controls (one microfilled and one hybrid composite), were investigated with specimen sub-groups (n = 10) for each property measured. The principal series of experiments was conducted in model Class V cavities with interfacial polishing either immediately (3 min) after setting or after 24 h water-storage. After the finishing procedure, each tooth was sectioned in a buccolingual direction through the center of the restoration, and the presence or absence of marginal-gaps was measured (and then summed for each cavity) at 14 points (each 0.5 mm apart) along the cavity restoration interface (n = 10 per group; total points measured = 140). The shear bond-strengths to enamel and to dentin, and flexural strengths and moduli data were also measured at 3 min and after 24 h water-storage. RESULTS: For all flowable composites, polished immediately after setting, 14-30 summed gaps were observed (controls: 64 and 42). For specimens polished after 24 h, a significantly (p < 0.05) reduced number of 8-17 summed gaps occurred for only 3 flowable composites; whereas for 5 flowable composites there were non-significantly-different (p > 0.05) numbers (11-17) of summed gaps (controls: 28 and 22). After 24h storage, shear bond-strengths to enamel and to dentin, flexural strengths and moduli increased highly significantly (p < 0.001) for all materials, except Silux Plus. SIGNIFICANCE: A post-cure interval of 24 h resulted in enhanced mechanical and adhesive properties of flowable dental composites. In a minority of cases there was also a reduced incidence of marginal-gap formation. However the latter effect may be partly attributed to 24 h delayed polishing, even though such a delay is not usual clinical practice.

Bicuspid↗
PubMed2006

Contact versus flexure fatigue of a fiber-filled composite.

OBJECTIVE: The intent of this project was to examine the effect of two different modes of fatigue loading, contact and flexure, on the flexure strength of a dental composite. METHODS: The composite was Restolux (a fiber-filled composite) formed as bars 3 mm x 3 mm x 25 mm in size. The cyclic loading ranges were 30-50, 60-80, and 90-110 N for contact loading and 20-40 and 40-60 N for the flexure loading. Number of cycles completed was 1, 1000 or 100,000 in four different media: air, water, artificial saliva, and a 50/50 mixture of water and ethanol. Specimens were aged in sealed polyethylene containers in their respective media for 4 months at 37 degrees C. RESULTS: Statistical analysis indicated a significantly lower flexure strength for the specimens flexure loaded versus contact loaded. For the flexure loaded specimens, the number of cycles had no significant effect, but the aging, load, and the media were all significant. For the contact loaded specimens, a significant effect was observed for the media, aging, and cycles completed, but no effect for the different cycling loads. SIGNIFICANCE: In summary, the decrease in flexure strength from flexure loading was mainly affected by the aging media, whereas, the decrease from contact loading was attributed mainly to the number of cycles.

Air↗
PubMed2006

Restoring cervical lesions with flexible composites.

OBJECTIVES: Flexure at the tooth cervix has been suggested to dislodge cervical restorations more rapidly. The objective of this randomized controlled clinical trial was to test the hypothesis that a higher composite flexibility better withstands tooth flexure stress. METHODS: One hundred and forty-two non-carious cervical lesions were restored with composites with contrasting stiffness. Seventy-one patients randomly received two cervical restorations placed following two out of the three experimental groups: (1) the three-step etch-and-rinse adhesive Permaquick applied with the stiff micro-hybrid composite Amelogen Hybrid (PMQ/A-Hy, Ultradent), (2) Permaquick applied with the more flexible micro-filled composite Amelogen Microfill (PMQ/A-Mi, Ultradent), or (3) the 'golden standard' three-step etch-and-rinse adhesive Optibond FL applied with the micro-hybrid composite Prodigy (O-FL/Pro, Kerr). RESULTS: The recall rate at 7 years was 80%. No statistically significant difference was found for any of the parameters evaluated neither between both adhesives, nor between both composites (McNemar, p>0.05). Eleven percent of the O-FL/Pro restorations were clinically unacceptable due to loss of retention (5.5%) and severe marginal discoloration (5.5%). In the PMQ-group, 22% of the PMQ/A-Mi restorations (8% loss of retention, 5% severe enamel margin defects, 3% severe dentin margin defects, 6% severe marginal discoloration, 3% extreme sensitivity) and 19% of the PMQ/A-Hy restorations (13% loss of retention, 3% severe enamel margin defects, 3% severe marginal discoloration) needed repair or replacement. SIGNIFICANCE: The clinical performance of the three adhesive/composite combinations was good and reliable during the 7-year clinical trial. It was concluded that the composite stiffness does not affect the clinical longevity of cervical composite restorations.

Composite Resins↗
PubMed2006

Fracture toughness determination of two dental porcelains with the indentation strength in bending method.

OBJECTIVE: This study was to investigate the influence of the bending test configurations and the crosshead displacement speeds on the fracture toughness (K(Ic)) of dental porcelains obtained with the indentation strength in bending (ISB) method. METHODS: The strength of the dental veneering porcelains Duceram and Sintagon Zx, Vickers' indented at a load of 2 kg was measured at a crosshead speed of 0.5mm/min with three test configurations, which were 3-point, 4-point, and biaxial bending. Two more groups of Sintagon Zx were tested the same way, but at speeds of 0.1, and 0.05 mm/min, respectively. Both porcelains, the three crosshead speeds, and the three test configurations were compared statistically. RESULTS: Duceram had a higher toughness than Sintagon Zx with all three test configurations and there was no significant difference between three test configurations with either porcelain. Within the crosshead speed groups of Sintagon Zx, a significant difference was found only in the 0.5mm/min group between the 3-point, and 4-point configurations. Within the configuration groups, significant differences were found between all speeds with the 3-point configuration and only between the highest and lowest speed with the 4-point and the biaxial tests. CONCLUSION: The crosshead displacement speed can cause statistically different results of fracture toughness obtained with the ISB method.

Analysis of Variance↗
PubMed2006

Material characteristics of a novel shrinkage-free ZrSiO(4) ceramic for the fabrication of posterior crowns.

OBJECTIVE: To confirm the clinical applicability of a novel ZrSiO(4) (zircon) based shrinkage-free ceramic material, the flexural strength, fracture toughness and chemical solubility were tested. In addition, the fracture load of full crowns made from this material was tested after cyclic thermomechanical loading. METHODS: Flexural strength of 12 specimens was measured using a biaxial bending test. Fracture toughness was measured using 10 slotted box shaped specimens. The specimens were fractured using a universal testing machine; fracture loads were recorded. A chemical solubility test was performed in accordance with ISO norm 6872. Additionally, 32 ZrSiO(4) all-ceramic crowns were fabricated on extracted caries-free human molars. Sixteen Empress 2 and 16 PFM crowns served as a reference control. After artificial aging of 1.2 million cycles in the chewing simulator, the survival rate of the crowns was determined. The fracture load of all surviving specimens was obtained by loading the crowns until fracture in a universal testing machine. RESULTS: A flexural strength of 328MPa was found. The fracture toughness of the ZrSiO(4) ceramic was 5.16MPam(0.5). The chemical solubility amounted to 7.2microg/cm(2). All specimens survived the chewing simulation (survival rate: 100%); no crowns had to be re-cemented. A mean fracture strength of 1790N was found for Everest HPC for Empress 2 crowns, 1715N for Empress 2 crowns and 2416N for PFM crowns. Fracture loads of PFM crowns were significantly higher than for Empress 2 crowns (P=0.032) as well as ZrSiO(4)-crowns (P=0.007). There was no significant difference between ZrSiO(4)-crowns and Empress 2 crowns (P=0.743). SIGNIFICANCE: At the present stage, Everest HPC can be recommended for the fabrication of single crowns as an alternative to conventional PFM and other all-ceramic crowns, because its fracture strength exceeds average masticatory forces in the posterior region.

Bite Force↗
PubMed2006

Influence of the bonder on the adhesion of porcelain to machined titanium as determined by the strain energy release rate.

OBJECTIVE: To determine the adhesion at the titanium-porcelain interface using a fracture mechanics approach, and to investigate the bonding mechanism using SEM. METHODS: Specimens of five different titanium-porcelain and one base metal-porcelain bonding systems were prepared for a four-point bending interfacial delaminating test on a universal testing machine. The pre-cracked specimen was subjected to load and the strain energy release rate (G, J/m(2)) was calculated from the critical load to induce stable crack extension in each system. The interface for the various materials was investigated in an SEM and compared. RESULTS: The titanium-porcelain with Gold Bonder showed the highest G-value (72.39+/-13.21J/m(2)) among the groups whilst titanium-porcelain with cross-cut-bur preparation showed the lowest (5.78+/-1.39J/m(2)). The former was significantly higher than that of Wiron 99 (base-metal, BEGO, Germany) porcelain (40.01+/-6.67J/m(2)), a clinically accepted bonding system for many years. The G-values of porcelain fused to titanium-Rocatec, titanium-sandblasted and/or titanium-GC-Bonder were 10.81+/-1.49, 12.64+/-3.01 and 35.74+/-5.20J/m(2), respectively. SEM images of the interface fracture crack path for the different bonders enabled the mechanisms responsible for the differences in strain energy release rates to be appreciated. CONCLUSION: The strain energy release rate (G) of titanium-porcelain with a Gold Bonder interface layer was highest among the five different systems.

Adhesives↗
PubMed2006

Preliminary study on chitosan modified glass ionomer restoratives.

OBJECTIVES: The aim of this study was to investigate the effect of chitosan (CH), a biocompatible polysaccharide, on the flexural strength of glass ionomer restoratives (GIR) and on the release of fluoride ions from GIR. METHODS: Commercial GIR (Vidrion, SS White) has been modified by adding chitosan (CH, Fluka). Samples containing 0.0044, 0.012, 0.025 and 0.045wt% CH were prepared, molded and weighed. For flexural strength, sets of 10 specimens 10mmx2mmx2mm of commercial and CH modified GIR were prepared. Differences were analyzed by the one-way analysis of variances (ANOVA) test, at significance level 0.05. The data were also analyzed by post hoc Tukey's HSD for unequal n (Spjotvoll/Stoline) test. Scanning electron microscopy analyses were performed on the composites cryo-fracture surfaces. For the fluoride release tests and medium pH determination, discs with 10mm diameter and 2mm height were prepared in a PTFE mold placed between two glass slides. Samples were weighed in order to normalize each material test group. At least 10 samples of each material were prepared. Approximately 5min after preparation the discs were transferred into individual glass flasks containing 50mL of distilled water. The concentration of released fluoride was determined as a function of time by means of a fluoride ion selective electrode Orion 94-09 SC connected to an Ionanalyser (Orion Research Inc., USA). The medium pH was monitored as a function of time at (25+/-1 degrees C), using a Digimed DM20 potentiometer (Digicrom Instrumentos, Brazil) equipped with a combined glass electrode. Ellipsometric measurements were performed to quantify the thickness of adsorbed polymer (poly(acrylic acid) or the mixture of poly(acrylic acid) with CH). RESULTS: The addition of 0.0044wt% of CH led to a significant increase in the flexural resistance. CH contents higher than 0.022wt% led to poor performance. For the same period of time the amount of fluoride ions released from CH modified GIR was much larger than that released from commercial GIR. CH catalyzed the fluoride release from GIR to the medium, especially from those with 0.0044wt% of CH. As a consequence, the medium pH increased from 5.0 to 6.3. A model based on the formation of a polymeric network around the inorganic particles was proposed to explain the experimental findings. The adsorption of CH and poly(acrylic acid) onto planar Si/SiO(2) substrates was quantified and supported the proposed model. SIGNIFICANCE: The results presented here showed that the flexural strength of a commercial GIR can be considerably improved by the addition of a tiny amount of CH. Moreover, in the presence of CH, the release of fluoride ions from GIR is catalyzed.

Acrylic Resins↗
PubMed2006

Flexural properties of endodontic posts and human root dentin.

OBJECTIVES: To evaluate the flexural modulus and flexural strength of different types of endodontic post in comparison with human root dentin. METHODS: Three different types of fiber-reinforced composite (FRC) posts and three metal posts each comprising 10 specimens (n=10) and 20 dentin bars were loaded to failure in a three-point bending test to determine the flexural modulus (GPa) and the flexural strength (MPa). Three randomly selected fiber posts of each group were evaluated using a scanning electron microscope (SEM) to illustrate the differences in mode of fracture. Data were subjected to a one-way ANOVA to determine significant differences between groups and the Bonferroni t-test multiple comparison was applied to investigate which mean values differed from one another with significance levels of P<0.05. RESULTS: The flexural modulus recorded for the dentin bars was 17.5+/-3.8 GPa. The values for posts ranged from 24.4+/-3.8 GPa for silica fiber posts to 108.6+/-10.7 GPa for stainless steel posts. The flexural strength for dentin was 212.9+/-41.9 MPa, while the posts ranged from 879.1+/-66.2 MPa for silica fiber posts to 1545.3+/-135.9 MPa for cast gold posts. The ANOVA test analysis revealed significant differences between groups (P<0.05) for flexural modulus and flexural strength mean values. SIGNIFICANCE: FRC posts have an elastic modulus that more closely approaches that of dentin while that for metal posts was much higher. The flexural strength of fiber and metal posts was respectively four and seven times higher than root dentin.

Carbon↗