Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Pliability”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources
PubMed2004

Non-destructive characterization of resin-based filling materials using Electronic Speckle Pattern Interferometry.

OBJECTIVES: The aim of this study was to develop a non-destructive test for characterizing the modulus of resin-based filling materials. METHODS: Five different visible-light-cured composites (Filtek A110 [AO], Z100 [ZO], Filtek Z250 [ZT], F2000 [FT] and Filtek Flow [FF]; 3M-ESPE) were selected for this study. An ESPI (Electronic Speckle Pattern Interferometry) apparatus involving cantilever beam specimens (28 mm long, 8 mm wide and 2 mm thick) was developed for determining modulus. Out-of-plane displacement upon force application was measured using two focus region lengths (22 mm [EI1]; 11 mm [EI2]) and modulus (n = 7) was subsequently computed based on cantilever beam equations. Data was compared to those obtained from three-point-bend flexural testing (n = 7) based on ISO4049:2000 specifications [ISO]. Specimens were stored in distilled water at 37 degrees C for 1 week prior to evaluation for all tests. Results were analyzed using ANOVA/Scheffe's post-hoc tests (p < 0.05) and Pearson's correlation (p < 0.01). RESULTS: Modulus ranged from 5.53 to 13.99, 5.78 to 14.24 and 4.26 to 11.30 GPa for EI1, EI2 and ISO, respectively. For all three tests, the modulus of ZO and FT was significantly greater than ZT, which in turn was significantly greater than AO and FF. Correlation of EI1 and EI2 to ISO was significant, positive and very strong (r = 0.94 for EI1 and EI2). SIGNIFICANCE: ESPI may be a viable method of characterizing the modulus of resin-based filling materials. As it is a non-destructive test, time-dependent effects of composites can be determined using the same specimens leading to substantial time and material savings.

Analysis of Variance↗
PubMed2004

Synthesis and evaluation of HEMA-free glass-ionomer cements for dental applications.

OBJECTIVE: The objective of this study was to synthesize and characterize amino acid acrylate and methacrylate derivatives, use them to formulate light-cured glass-ionomer cements (LCGICs), and evaluate their mechanical strengths. MATERIALS AND METHODS: Acrylate and methacrylate derivatives of six amino acids were synthesized and characterized using FT-IR and 1HNMR spectroscopy. The LCGICs were formulated using a newly synthesized polymer having pendant methacrylate groups (in other words, a methacryloyl derived polymer or MDP), amino acid derivatives, water, and Fuji II LC glass. Compressive strength of the cements and viscosities of the resin liquids were used as screening tools in order to determine the optimal formulation. The specimens were conditioned in distilled water at 37 degrees C for 24 h prior to testing. RESULTS: The measured compressive strengths (MPa) of the cements were found to depend on the amino acid derivative used: acryloyl aspartic acid (268.5) > methacryloyl beta-alanine (259.1) = methacryloyl glutamic acid (254.5) = acryloyl beta-alanine (251.9) > acryloyl glutamic acid (238.8) > methacryloyl aspartic acid (210.9). Methacryloyl beta-alanine (MBA) was selected for further formulations due to its relatively low solution viscosity and high compressive strength. Effects of MDP content and power/liquid (P/L) ratio were significant. The formulation with a liquid composition of 50/25/25 (MDP/MBA/water) and P/L ratio of 2.7/1 was found to give optimal properties and handling of all the formulations studied. CONCLUSIONS: A novel HEMA-free LCGIC system based on amino acid derivatives has been developed. This system may eliminate potential cytotoxicity in current LCGICs caused by leached 2-hydroxyethyl methacrylate (HEMA). The optimal MBA-modified cements were 20% higher in compressive strength, 70% higher in diametral tensile strength (DTS) and 93% higher in flexure strength (FS), as compared to Fuji II LC cement.

Amino Acids↗
PubMed2004

Effects of polymerization initiator complexation in methacrylated beta-cyclodextrin formulations.

OBJECTIVES: Methacrylated beta-cyclodextrin (MCD) is a candidate dental monomer that can complex molecules within its hydrophobic cavity. This study determined the effects of complexation of polymerization initiators such as camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (4E) with MCD on the flexural strength (FS) and degree of conversion (DC) of resulting dental composite formulations. METHODS: Complexation of CQ and 4E with MCD was studied by thin layer chromatography. A mass fraction of 44% 2-hydroxyethylmethacrylate or triethyleneglycoldimethacrylate was mixed separately with a mass fraction of 56% MCD to produce a workable formulation. The mixture was activated with varied amounts of CQ and 4E. One part by mass of the activated resin formulation was mixed with three parts by mass of glass filler. Specimens for FS were prepared by filling molds with composites and curing for 2 min. The cured specimens were immersed in 37 degrees C water for 24 h and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. DC in MCD-based resin formulations was measured with a differential photocalorimeter under nitrogen. RESULTS: MCD appears to form inclusion complexes with CQ and 4E. As a result, FS and DC of MCD-based composites vary significantly as a function of the concentration of polymerization initiators used in the formulations. SIGNIFICANCE: Complexation of polymerization initiators with MCD can influence the FS and DC in MCD-based dental formulations and should be taken into consideration when evaluating MCD as a dental monomer.

Aminobenzoates↗
PubMed2004

Role of investment interaction layer on strength and toughness of ceramic laminates.

OBJECTIVES: The aim of this study was to test the hypothesis that the interaction of a core ceramic with investment material can significantly reduce the flexural strength and the fracture toughness of core/veneer ceramic laminates. METHODS: Ceramic composites were prepared from experimental core and experimental veneer and Empress 2 core and Empress 2 veneer ceramics. Four divesting techniques were used for each bilayer ceramic group. Core surfaces were etched with 1% HF solution for 15 or 30 min and grit blasted with 100 microm Al2O3 particles for 15 or 30 s. The effect of treatment on strength was analyzed statistically by means of two-way ANOVA. A linear regression graph was made for each group to analyze the relationship between flexural strength and the dimensions of critical cracks. RESULTS: The four surface divesting treatments produced no significant differences (p > 0.05) between the mean flexural strengths and the mean fracture toughnesses. However, groups with different core/veneer combinations showed statistically significant differences (p < or = 0.05) between the mean flexural strengths and between the mean fracture toughnesses. The Empress 2 core/experimental veneer combination exhibited the greatest fracture toughness values. The Empress 2 core/Empress 2 veneer combination exhibited the lowest mean fracture toughness and lowest mean flexural strength. SIGNIFICANCE: The investment interaction layer does not have a significant effect on the flexural strength and fracture toughness of the bilayer ceramic laminates for interfaces that are coherent and well bonded. However, the core/veneer combination of materials does affect the strength of bilayer ceramic laminates. The existence of global residual stress is the most likely reason for the observed strength increases.

Acid Etching, Dental↗
PubMed2004

Physical and mechanical properties of an experimental dental composite based on a new monomer.

OBJECTIVE: The purpose of this study was to investigate the physical and mechanical properties of a dental composite based on BTDMA, a new dimethacrylate monomer based on BTDA (3,3',4,4'-benzophenone tetracarboxylic dianhydride), and to compare these with the properties of a composite based on commonly used Bis-GMA monomer. METHODS: Experimental composites were prepared by mixing the silane-treated filler with the monomers. The prepared pastes were inserted into the test molds and heat-cured. Light-cured composites were also prepared using camphorquinone and amine as photoinitiator system. Degree of conversion of the light-cured and heat-cured composites was measured using FTIR spectroscopy. The flexural strength, flexural modulus, diametral tensile strength (DTS), water sorption, water contact angle, microhardness and thermal expansion coefficient of the prepared composites were measured and compared. Water uptake of the monomers was also measured. RESULTS: The results showed that the mechanical properties of the new composite are comparable with the properties of the Bis-GMA-based composite but its water sorption is higher. BTDMA as a monomer containing aromatic rings and carboxylic acid groups in its structure gives a composite with good mechanical properties. There is a close relation between the contact angle, water sorption of the cured composite and water uptake of their monomers. SIGNIFICANCE: Finding new monomers as alternatives for Bis-GMA have been a challenge in the field of dental materials and any investigation into the properties of new composites would be beneficial in the development of dental materials.

Analysis of Variance↗
PubMed2004

Evaluation of fracture toughness of a fiber containing dental composite after flexural fatigue.

OBJECTIVE: The purpose of this study was to examine the effect of cyclic loading in four different environments on the fracture toughness of a fiber reinforced resin composite. METHODS: The specimens were 3 x 3 x 25 mm3 bars polished with 320 grit SiC paper. A 60 degrees v-notch was machined 1 mm deep at the midspan of each bar. The specimens were loaded in air, artificial saliva, water, and a 50/50 by volume mixture of ethanol and water at a frequency of 5 Hz with sinusoidal loads cycling between 10 and 20 N for 1, 1000, 10,000 and 100,000 cycles. Specimens were also aged for 4 months in each respective media. Following cyclic loading, the specimens were tested in three-point loading. Statistical analysis consisted of four 2-way ANOVAs followed by Tukey's HSD inference, and two 3-way ANOVAs followed by two-sample t-tests. RESULTS: The ANOVAs indicated no difference in the means of fracture toughness for the set numbers of cycles, but a significant difference for the aging solutions and the aging times. SIGNIFICANCE: Statistical analysis showed a significant decrease of fracture toughness from unaged to aged specimens when aged in air, saliva, and 50/50 ethanol/water. The latter showed the most pronounced decrease. The effect of the 50/50 by volume mixture of ethanol and water would appear to attack the resin matrix and/or the bond between the resin matrix and the filler, which resulted in the observed decrease in fracture toughness. In addition, the significant decrease in fracture toughness following aging is attributed to residual matrix stress around the large fiber filler particles resulting in separation of the fiber filler from the resin matrix.

Air↗
PubMed2004

Flexural properties of denture base polymers reinforced with a glass cloth-urethane polymer composite.

OBJECTIVES: A newly designed light-cured reinforcement made from urethanemethacrylate oligomer and woven glass cloth has orthotropic anisotropy. This is produced for incorporation into the outermost position under the greatest tension in denture base resins. In this study, the flexural properties of self-, heat-, and light-curing reinforced resins were determined. METHODS: The silanized glass cloth was soaked in urethanemethacrylate oligomer containing camphorquinone and 2-(dimethylamino)ethylmethacrylate. It was sandwiched between two pieces of polyethylene film and pressed to form a reinforcement sheet 0.3 mm in thickness, which was light-cured and prepared using four different surface conditions: with or without the polyethylene film and with or without a bonding agent. The reinforcement sheet was fixed in a fluorocarbon resin mold 3 mm in thickness, which was filled with self-, heat-, or light-curing resin and cured. The cured laminated plate was cut for flexural testing (40 x 7 x 3 mm3). A three-point flexural test was carried out at a crosshead speed of 2 mm/min and a span length of 30 mm. In this study, the glass fiber content was measured at percentages by weight because it was not possible to determine accurately the volume of the various polymers. RESULTS: The baseline flexural strengths of the self-, heat-, and light-curing resins were 76.2, 68.6, and 55.6 MPa, respectively, and these values were increased to 271.7, 216.4, and 266.5 MPa by the reinforcement sheet. The baseline flexural moduli of self-, heat-, and light-curing resins were 2.0, 2.4, and 2.1 GPa, respectively. These values were increased to 7.2, 5.1, and 6.6 GPa by the reinforcement sheet. SEM photographs revealed good impregnation of the glass fiber within the polymer matrix. SIGNIFICANCE: The differences in the flexural strengths and flexural moduli of the control and reinforced specimens were significant (p < 0.01).

Composite Resins↗
PubMed2004

Effects of strain rate and temperature on the mechanical properties of resin composites.

OBJECTIVE: To evaluate the effects of strain rate and temperature on the mechanical properties of resin composite restorative materials (RCs) and to investigate the construction of temperature--strain rate equivalence 'master curves'. METHODS: Four visible light-cured resin composite RCs, all of shade A3, were used: Heliomolar Radiopaque (HR) and Tetric Ceram (TC) (Ivoclar, Schaan, Liechtenstein), Filtek Z250 (FZ) (3M, St Paul, MN, USA) and Prodigy Condensable (PR) (Kerr, Orange, CA, USA). Bar specimens (10 x 1.5x 16.0 mm3) were cured for 50 s at an irradiance of 500 mW cm(-2) and were randomly distributed into groups of six for each type of material. All specimens were stored in artificial saliva at pH 6, for 7d. The specimens tested at 12, 24 and 37 degrees C were stored at the corresponding temperature but those tested at 0 degrees C were stored at 24 degrees C. Three-point bend tests for flexural strength (F), flexural modulus of elasticity (E) and total energy to failure (W) were performed at cross-head speeds (XHS) of 0.1, 1.0, 10, 50 and 100 mm min(-1) for all materials as well as at 0.01, 0.03, 0.2 and 0.5 mm min(-1) for some materials. RESULTS: There was a common pattern of behavior across materials. At constant temperature, F showed a slight variation with cross-head speed, with a broad peak in the region of 1-10 mm min(-1). E, on the other hand, showed a more marked and steady increase with XHS at all temperatures except at 0 degrees C, where it tended to level off above about 10 mm min(-1). In contrast, the values of W showed a decline with increasing XHS, except at 37 degrees C where an initial rise followed by a decline was observed. At constant XHS, increase in temperature caused a small, but highly significant (P < 10(-3)) decline in F but a marked decline in E. W, again in contrast to Fand E, showed a general increase with temperature. A master curve model for the temperature-strain-rate equivalence was fitted to the E and W data (all P < 10(-5)) and the fitted parameters interpreted in terms of strain rate and temperature sensitivity. SIGNIFICANCE: The mechanical properties of RCs are very sensitive to the test conditions of strain rate and temperature. This implies that properties determined at any temperature other than 37 degrees C, or at only one cross-head speed (or only one strain rate) are inadequate to describe their behavior in service. The master curve principle is applicable to RCs and can be used, inter alia, to determine property values under other than tested conditions. Conditions of testing in regard to XHS and temperature, as well as other factors, should clearly be stated to enable proper comparisons between studies, but more importantly the use of standardized test conditions is overdue.

Acrylic Resins↗
PubMed2004

Interface effects on mechanical properties of particle-reinforced composites.

OBJECTIVES: Effective bonding between the filler and matrix components typically improves the mechanical properties of polymer composites containing inorganic fillers. The aim of this study was to test the hypothesis that composite flexural modulus, flexure strength, and toughness are directly proportional to filler-matrix interfacial shear strength. METHODS: The resin matrix component of the experimental composite consisted of a 60:40 blend of BisGMA:TEGDMA. Two levels of photoinitiator components were used: 0.15, and 0.5%. Raman spectroscopy was used to determine degree of cure, and thermogravimetry (TGA) was used to quantify the degree of silane, rubber, or polymer attachment to silica and glass particles. Filler-matrix interfacial shear strengths were measured using a microbond test. Composites containing glass particles with various surface treatments were prepared and the modulus, flexure strength, and fracture toughness of these materials obtained using standard methods. Mechanical properties were measured on dry and soaked specimens. RESULTS: The interfacial strength was greatest for the 5% MPS treated silica, and it increased for polymers prepared with 0.5% initiator compared with 0.15% initiator concentrations. For the mechanical properties measured, the authors found that: (1) the flexural modulus was independent of the type of filler surface treatment, though flexural strength and toughness were highest for the silanated glass; (2) rubber at the interface, whether bonded to the filler and matrix or not, did not improve toughness; (3) less grafting of resin to silanated filler particles was observed when the initiator concentration decreased. SIGNIFICANCE: These findings suggest that increasing the strength of the bond between filler and matrix will not result in improvements in the mechanical properties of particulate-reinforced composites in contrast to fiber-reinforced composites. Also, contraction stresses in the 0.5 vs 0.15% initiator concentration composites may be responsible for increases in interfacial shear strengths, moduli, and flexural strengths.

Composite Resins↗
PubMed2005

Degree of conversion and flexural properties of a dendrimer/methyl methacrylate copolymer: design of experiments and statistical screening.

OBJECTIVES: The aim of this study was to investigate the effect of photosensitive initiator and activator concentrations on the degree of conversion and flexural properties of an experimental photopolymerized dental copolymer containing dendrimer. METHODS: The experimental resin system consisted of a dendrimer with 12 methacrylate groups and methyl methacrylate in a mass ratio of 80:20. The initiator and activator used were camphorquinone and 2-(N,N-dimethylamino)ethyl methacrylate, whose concentrations varied individually from 1 to 4 wt%. The degree of conversion was determined with FTIR spectroscopy, and flexural strength and flexural modulus with the three-point bending test. The experiments were designed and analyzed, and the results plotted with Modde 5.0 software. RESULTS: The highest degree of conversion was obtained with 2.5 wt% initiator and activator concentrations, the highest flexural strength with 2.5 wt% initiator and 1.0 wt% activator concentration, and the highest flexural modulus with 1.0 wt% initiator and activator concentrations. SIGNIFICANCE: The results indicated that the degree of conversion increased, and flexural strength and flexural modulus decreased, with increasing initiator and activator concentrations. The high concentrations of initiator probably inhibited the transmittance of the active wavelengths to the depths of the samples (the inner filter effect), resulting in inhomogeneous conversion and thus decreased mechanical properties.

Elasticity↗
PubMed2005

The effect of core:dentin thickness ratio on the bi-axial flexure strength and fracture mode and origin of bilayered dental ceramic composites.

OBJECTIVES: The aim of the current study was to assess the effect of core:dentin thickness ratio on the flexure strength, fracture mode and origin of bilayered dental ceramic composite disc specimens. METHODS: Sets of 30 bilayered composite discs with core:dentin thickness ratio of 2:1, 1:1 and 1:2 were tested in bi-axial flexure with both the reinforcing core and veneering dentin loaded in tension. Mean flexure strengths, standard deviations and associated Weibull Moduli (m) were determined. A combination of optical and scanning electron microscopy was employed for identification of the fracture mode and origin. RESULTS: The core:dentin ratio influenced the bi-axial flexure strength and reliability of the flexure strength data when both the reinforcing core and veneering dentin porcelain were tested in tension. The strength and reliability was increased for a core:dentin thickness of 2:1. The number of fracture fragments, the frequency of occurrence of specimen delaminations, Hertzian cone formations and sub-critical radial cracking in the bilayered dental ceramic composite disc shaped specimens was also dependent on the core/dentin ratio and the surface loaded in tension. CONCLUSIONS: Core:dentin thickness ratio influences the bi-axial flexure strength and fracture mode and origin in bilayered dental ceramic composite specimens.

Ceramics↗
PubMed2004

Fracture behavior of lithia disilicate- and leucite-based ceramics.

OBJECTIVE: This study was designed to characterize the fracture behavior of ceramics and test the hypothesis that variation in strength is associated with a variation in fracture toughness. METHODS: The following four groups of 20 bar specimens (25 x 4 x 1.2 mm) were fabricated (ISO standard 6872): E1, a hot-pressed leucite-based core ceramic (IPS Empress); E2, a hot-pressed lithia-based core ceramic (IPS Empress 2); ES, a hot-pressed lithia-based core ceramic (Experimental); and GV, a glass veneer (IPS Empress2 body). Specimens were subjected to four-point flexure loading in 37 degrees C distilled water. Fractographic analysis was performed to determine the fracture origin (c) for calculation of fracture toughness (KIC). Weibull analysis of flexure strength (sigma) data was also performed. RESULTS: Differences in mean sigma and KIC were statistically significant for E1 and GV (p<0.05). These differences are associated with processing effects and composition. SIGNIFICANCE: The higher mean sigma and KIC values of E2 and ES core ceramics suggest potentially improved structural performance compared with E1 although the Weibull moduli of E1 and E2 are the same.

Aluminum Silicates↗
PubMed2005

Fatigue resistance and structural characteristics of fiber posts: three-point bending test and SEM evaluation.

OBJECTIVES: The aim of the present study was to assess the fatigue resistance of different types of fiber posts, and to observe their ultrastructure through scanning electron microscopy (SEM) before and after undergoing the fatigue test. METHODS: Eight types of fiber posts were selected for this study. Easypost (Group 1), Para Post Fiber White (Group 2), FibreKor (Group 3), Ghimas White (Group 4), DT Light-Post radiopaque (Group 5), FRC Postec (Group 6), Luscent Anchors (Group 7), Snowpost (Group 8). Ten out of fifteen posts in each group were used for the fatigue test, and the other five were processed for SEM. A three-point bending machine, loading at an angle of 90 degrees and a frequency of 3 Hz was employed for fatigue testing. The test was carried out until two million cycles were completed or until fracturing of the post. SEM evaluation was performed using a three-step scale method to assess the fiber/resin ratio and fiber dimension. RESULTS: The fatigue test showed statistically significant differences among the different posts. Groups 5 and 6 performed better than all the other groups, withstanding practically all the stipulated number of load cycles. All the other posts fractured before the end of the test. SEM observations of the surface integrity of the fiber posts showed that Groups 4-6 obtained better scores for both longitudinal sections and cross-sections. SIGNIFICANCE: There was a large variation in the response of different kinds of fiber posts a fatigue resistance test. The absence of correlation between results of fatigue testing and parameters of structural integrity suggests that the latter mostly reflect random variations in the fiber post manufacturing process.

Composite Resins↗
PubMed2005

Properties of eight methacrylated beta-cyclodextrin composite formulations.

OBJECTIVES: Methacrylated beta-cyclodextrins (MCDs) are novel candidate dental monomers if all or some of the hydroxyl groups of beta-cyclodextrin are substituted with methacrylate groups. The main objective of this study was to evaluate mechanical properties of a number of composite formulations having MCDs as novel dental comonomers. The properties determined were flexural strength (FS), volumetric shrinkage (VS), and degree of conversion (DC). METHODS: A mass fraction of 50% of MCD monomers was mixed with a mass fraction of 50% each of a series of dimethacrylate or monomethacrylate diluent comonomers to produce consistent formulations of a workable viscosity. For comparison a resin mixture of a mass fraction of 50% Bis-GMA and a mass fraction of 50% triethyleneglycol dimethacrylate (a typical dental resin mixture) was also studied. The mixtures were activated with camphorquinone and ethyl 4-dimethylamino benzoate. One part by mass of each activated resin formulation was mixed with three parts by mass of glass filler. Samples for the FS tests were prepared in (2 x 2 x 25) mm3 molds by light-curing the composites for 2 min on each side. The cured samples were immersed in 37 degrees C water for 24 h, and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. VS was measured by a computer-controlled mercury dilatometer. DC was measured by near-infrared spectroscopy. RESULTS: The properties of the MCD-based composites depended on the kind of diluent used. With these MCD monomers, diluents of triethyleneglycol dimethacrylate, 1,10-decamethylenediol dimethacrylate, or benzyl methacrylate yielded the best composite properties. SIGNIFICANCE: Although not yet fully optimized, MCD-based composite formulations containing triethyleneglycol dimethacrylate, 1,10-decamethylenediol dimethacrylate, or benzyl methacrylate yielded flexural strength and volumetric shrinkage values were comparable to those of the Bis-GMA/triethyleneglycol dimethacrylate controls. These findings lend support for further development and evaluations of polymerizable cyclodextrin derivatives for use in dental materials.

Analysis of Variance↗
PubMed2005

Evaluation of sub-critical fatigue crack propagation in a restorative composite.

OBJECTIVES: Fracture is a major reason for clinical failure of dental restorations. Many clinical fractures are likely to be preceded by a slow sub-critical crack propagation. The purpose of this study was to determine slow crack propagation in a restorative composite. METHODS: Notched composite (Z100, 3M ESPE) specimens were fatigued in a four-point bending test. The notch (1 mm) was created by embedding a sharpened razor blade in the specimen mold. The specimens were load-cycled at 5 Hz between -5 and -30 N until failure. Displacement and load were recorded during the fatigue tests and used to derive crack propagation based on beam-compliance. RESULTS: The number of cycles until failure ranged between 34 and 82,481. In the last 1500 cycles prior to final fracture, the beam compliance increased consistently, indicating sub-critical crack propagation. It was calculated from the compliance change that the crack length increased 8% (77 +/- 14 microm) before final failure. The crack growth rate during sub-critical crack propagation was determined as a function of the stress intensity for the last 1500 cycles before fracture. SIGNIFICANCE: A method is presented to determine slow crack propagation using a four-point bending test. Although fatigue lifetime varied widely, stable crack growth prior to fracture was consistent. This consistency allowed formulation of stress-based crack propagation relationships that can be used in concert with numerical simulations to predict composite restoration performance. The large variation found for specimen lifetime was attributed to the initiation process that precedes sub-critical crack propagation.

Compliance↗
PubMed2005

In vitro cuspal deflection and microleakage of maxillary premolars restored with novel low-shrink dental composites.

OBJECTIVES: The development of novel low-shrink resin-based composites (RBCs) may offer a potential reduction in polymerisation shrinkage stresses generated at the tooth/restoration interface compared with current methacrylate RBCs. In vitro cuspal deflection and microleakage of meiso-occlusal-distal (MOD) cavities restored with experimental oxirane and silorane (EXL596 and H1) and methacrylate (Z100 and Filtek Z250) RBCs were assessed. METHODS: Standardised pre-molar MOD cavities were prepared (n = 10) and restored with each material. The flexure of buccal and palatal cusps was recorded 0.1 h following irradiation utilising a differential transformer deflection gauge. Each restored tooth was subjected to a thermocycling regime and microleakage of tooth sections were assessed following 24 h immersion in 0.2% fuschin dye. The degree of conversion (DC) of each RBC material was also assessed using Fourier transform infrared (FTIR) spectroscopy following 0.1, 0.5, 1, 4, 24 and 48 h post-irradiation. RESULTS: A total cuspal deflection was observed for EXL596 (2.5 +/- 0.9 microm) and H1 (6.0 +/- 1.8 microm) compared with Z100 (20.0 +/- 4.7 microm) and Filtek Z250 (16.5 +/- 3.3 microm) following 0.1 h. The cavities restored with EXL596 displayed significantly higher microleakage than any other RBC and H1 exhibited non-significant and significantly decreased microleakage compared with Z100 and Filtek Z250, respectively. The DC of EXL596 and H1 was significantly decreased compared with Z100 and Filtek Z250 following 0.1, 0.5 and 1 h. SIGNIFICANCE: The 'living' polymerisation associated with the novel oxirane and silorane RBCs and the associated decrease in cuspal deflection may suggest a decrease in the magnitude of polymerisation shrinkage stress at the tooth/restoration interface. The decreased DC following 0.1 h of the oxirane compared with the methacrylate RBCs has provided information on the cure rate of cationic and free-radical polymerisation mechanisms, respectively. The inadequate marginal seal of cavities restored with EXL596 would preclude its use as a dental restorative. The reduction in cuspal deflection and decrease in microleakage of cavities restored with H1 compared with Filtek Z250 may be advantageous in terms of marginal integrity following placement. However, the non-significant difference in microleakage between the H1 and Z100 may only present modest decreases in the deleterious effects of shrinkage stress.

Bicuspid↗
PubMed2005

Interpretation of bond failure through conversion and residual solvent measurements and Weibull analyses of flexural and microtensile bond strengths of bonding agents.

OBJECTIVES: An inverse correlation between initial acetone content of bonding agents and microtensile bond strength (MTBS) has previously been reported. Here it was investigated whether the inferior MTBS of acetone-rich bonding agents was caused by flaws and low adhesive layer strength, insufficient to resist polymerization shrinkage stresses of the overlying composite. METHODS: Bonding solutions with (27-67) mass fraction% acetone were dried for 10 s or 30 min. Specimens for infrared (IR) spectroscopy and flexural strength (FS) were cured for 10 s (cure mode 1) to represent the adhesive layer properties when polymerizing the composite resin or for 10 s plus an additional 60 s through composite resin (cure mode 2) to represent adhesive layer properties when testing the bond strength. Degree of conversion (DC) and residual acetone content were evaluated for films by mid-IR and bulk specimens by near-IR spectroscopy. FS and MTBS data using these bonding solutions were interpreted by Weibull statistics and ANOVA (alpha = 0.05). RESULTS: In bulk specimens, initial and residual acetone content were positively correlated (P = 0.003). FS in cure mode 1 was significantly lower than in cure mode 2 and decreased with increasing initial acetone content, while DC remained consistent, suggesting pores from acetone evaporation as flaw initiating sites affecting the mechanical adhesive properties. SIGNIFICANCE: From DC and Weibull analyses of MTBS and FS, early low strength of the adhesive layer and shrinkage stresses acting on pre-existing flaws are suggested as critical factors affecting the dentin/adhesive bond strength.

Acetone↗
PubMed2005

The span length and cross-sectional design affect values of strength.

OBJECTIVES: The aim of this study was to determine experimentally flexural strength and flexural modulus of fiber-reinforced composite (FRC) with different cross-sectional designs and diameters and tested with different span lengths. METHODS: Continuous FRC test specimens (n = 6) were made with two different cross-sectional designs, namely circular and rectangular. The resin matrix of FRC was polymerized with a hand light-curing unit followed by a light-curing oven polymerization. Three-point flexural test for determination of ultimate flexural strength and flexural modulus of the dry test specimens was made with different span lengths for rectangular specimens and diameters for circular specimens. Thus, the span length/diameter ratio (L/D) was changed. RESULTS: Flexural strength and flexural modulus of specimens with rectangular cross-section varied from 540 to 792 MPa and 9.8 to 20.3 GPa being the highest with the group of the 20 mm span length and the lowest with the group of the 10 mm span length. Flexural strength and flexural modulus of circular cross-section specimens varied from 847 to 1286 MPa and 19.9 to 36.6 GPa being the highest with 1.5 mm cross-section and the lowest with 2.8 mm cross-section. SIGNIFICANCE: It was concluded, that by increasing the L/D ratio, the flexural strength and flexural modulus values in MPa increased and the maximum fracture load values in N decreased. Reporting the L/D ratio is essential for interpretation of flexural strength and flexural modulus values of small size test specimens.

Bisphenol A-Glycidyl Methacrylate↗