Higher Diametral Tensile Strength Research Articles

Comparative Evaluation of Bulk-Fill Composite Resins: Knoop Microhardness, Diametral Tensile Strength and Degree of Conversion.

PurposeBulk-fill composite resins were developed to reduce time and facilitate the restorative procedure. However, considering their recent introduction on the market and the new formulations, their performance still requires evaluation. This study aimed to evaluate Knoop microhardness (KHN), diametral tensile strength (DTS) and degree of conversion (DC) of three Bulk-Fill composite resins and a conventional one.Materials and MethodsSixty samples (n = 15; 8 mm ø x 4 mm height) were confectioned using a mold. Filtek Bulk-Fill (FBF), Tetric N-Ceram Bulk-Fill (TNC) and SonicFill 2 (SF2) were placed in 4 mm increments, and Filtek Z350 (FZ350) was placed in 2 mm increments. The KHN of top and bottom surfaces were tested using Knoop Hardness tester at 10 gf/10s. The DTS was tested under compressive load at 1.0 mm/min. The DC was measured by Fourier Transform Infrared (FTIR) spectroscopy. Differences in DTS and DC were analyzed by ANOVA and Tukey post hoc test. For KHN, Kruskal–Wallis and Wilcoxon tests were performed at α = 0.05.ResultsTop surfaces of all composite resins had higher KHN than bottom surfaces. At top and bottom surfaces, FZ350 showed higher KHN than TNC and SF2. The highest DTS was obtained by FBF, followed by FZ350 and SF2. The highest DC was obtained by SF2, the lowest one was obtained by FBF.ConclusionFrom Bulk-Fill composite resins, FBF presented the best KHN and DTS results. The SF2 showed the best DC. Further studies are required to ensure whether these differences can negatively influence the behavior of in vivo restorations.

Effect of sintering temperature on mechanical and bioactivity properties of bioactive glass and cordierite composite

In this study, a composite of bioactive glass (BG) and cordierite (BG-cord) was proposed to increase the strength and bioactivity of BG. Both BG and cordierite were separately synthesized with the method of glass melting, then, they were used to fabricate BG-cord with a variation of sintering temperature (600 to 1000 °C). The highest diametral tensile strength (DTS=30.54 MPa) was shown by the BG-cord with sintering temperature at 925 ºC. Bioactivity tests were conducted by soaking in Hank’s balanced salt solution (HBSS) for 7, 14, and 21 days. Apatite formation was examined by using a scanning electron microscope. The results showed that the sample showed good bioactivity with regards to the formation of apatite on the samples, confirmed by the detection of carbonate (C-O) and phosphate (P-O) absorption peaks by Fourier transform infrared spectroscopy and crystalline peaks in the X-ray diffraction pattern.

Mechanical evaluation of dental trauma splints fabricated using recently-developed photo-polymerizable composites.

This study aimed to determine functionality and mechanical properties of dental splints. Five splints were tested: a control splint Filtek Z350XT (ZF), two splints with G-Fix (GF) and Light Fix (LF), and two wire-composite splints with ZF (ZW) and Ortho Connect Flow (CW). Periotest values, elastic modulus, flexural, compressive, and diametral tensile strength were measured. ZW and CW showed no significant differences in flexibility in labial or occlusal pressure of upper central incisors. LF, GF, and ZF did not differ in labial or palatal pressure. ZW and CW had higher flexibility than LF, GF, and ZF. LF had the lowest flexural and compressive strength but the highest diametral tensile strength. This study showed that ZW and CW might be options for flexible splints, whereas LF and GF would be options for rigid splints. Additionally, CW and LF/GF might be simpler alternatives to ZW and ZF, respectively.

Experimental resin-based dual-cured calcium aluminate and calcium titanate materials for vital pulp therapy.

This paper evaluates the physicochemical and biological properties of experimental resin-based dual-cured calcium aluminate (CA) and calcium titanate (CTi) materials for vital pulp therapy (VPT). The experimental dual-cured materials were obtained as two pastes: a) Bis-EMA 10, PEG 400, DHEPT, EDAB, camphorquinone, and butylated hydroxytoluene; and b) fluoride ytterbium, Bis-EMA 10, Bis-EMA 30, benzoyl peroxide, and butylated hydroxytoluene. The materials were divided into six groups based on the added calcium component: MTA (MTA®, Angelus); CLQ (Clinker-Fillapex®, Angelus); CA (calcined at ,1200°C in pastes a and b); CA800 (calcined at 800°C in paste a); CA1200 (calcined at 1,200°C in paste a); and CTi (paste a). The real-time degree of conversion and rate of polymerization (n = 3), diametral tensile strength (n = 10), hydrogen potential (n = 15), calcium ion release (n = 10), water sorption and solubility (n = 10), and cell viability (n = 6) were evaluated. One- and two-way ANOVA and Tukey's post hoc test were used in the analysis of the parametric data, and Kruskal-Wallis and Dunn's multiple tests were used to analyze the nonparametric data (α = 0.05). CLQ, CA800 and CA1200 had the highest diametral tensile strength. The water solubility of MTA was similar to that of CA800, CA1200 and CTi. CA800 and CA1200 resulted in cell viabilities similar to those of MTA and CLQ. The experimental dual-cured CA-based material that calcined at 800°C showed physicochemical and biological properties suitable for VPT, and similar to those of MTA.

Influence of activation mode, fatigue, and ceramic interposition on resin cements’ diametral tensile strength

This study evaluated the influence of activation modes, on Diametral Tensile Strength (DTS) of dual cured resin cements subjected to a Mechanical Fatigue test (MF). Four dual-cured resin cements (RelyX UNICEM [U], RelyX ARC [A], ENFORCE [E] and Nexus 2 [N]) were activated by three different curing modes as follows: Self-Curing (SC), Dual Cure activation with photoactivation executed directly (DC) and Dual Cure activation with Photoactivation Through Porcelain (DCTP). After 24 hours, half of the sample was subjected to 30.000 fatigue cycles at 1 Hz frequency and 12 N load. Then, all specimens were subjected to DTS test in Instron Universal Testing Machine and data were analyzed by three-way ANOVA and Tukey's Test (5%). The results of DTS test means (MPa) and standard deviation, for each cement factor activated by SC, DC and DCTP was respectively: U (28.12 ± 5.29; 37.44 ± 6.49 and 40.10 ± 4.39), A (49.68 ± 8.42; 55.12 ± 5.16 and 63.43 ± 6.92), E (49.12 ± 3.89; 56.42 ± 8.88 and 56.96 ± 6.45) and N (61.89 ± 11.21; 59.26 ± 9.47 and 62.56 ± 10.93). Turkey's test indicated that DC is related to the highest DTS values; Nexus 2 DTS remained the same independently of activation mode and that the Porcelain disk interposition enhanced DTS only for RelyX ARC the ANOVA statistical test indicated that MF didn't alter the DTS values for all experimental groups. MF results clinical implication is that all cements tested exhibited, in an immediate loading, good cross linked bonds quality.

The evaluation of the mechanical characteristics of the synthesized glass-ionomer cements (GICs): the effect of hydroxyapatite and fluorapatite nanoparticles and glass powders

The goal of this research is to examine the influence that incorporation of synthesized hydroxyapatite (HA) and fluorapatite (FA) nanoparticles has on the synthesis and mechanical characteristics of glass-ionomer cements (GICs). In this research, HA and FA nanoparticles were synthesized through wet-chemical precipitation method. The obtained inorganic nanoparticles were evaluated with XRD, SEM, TEM, and STA analyses. The glass powder of the GIC (G1 and G2) were synthesized with two different formulations, and in addition, the polymer of GIC, acrylic-itaconic copolymer, was prepared in this research. The synthesized GIC components were appraised employing XRD and STA (for glass component) and FTIR and H-NMR (for polymer component). HA and FA nanoparticles were then added into the powder component (G1 and G2) at 5% and 8 wt%, and unblended powder was utilized as a control. Compressive strength (CS) and diametral tensile strength (DTS) before and after 1, 7, and 28 days of storage in distilled water were investigated utilizing a universal testing machine. Surface microhardness after 1 and 7 days of storage in distilled water was measured utilizing Vickers microhardness tester. Also, setting and working time was determined as specified in the ASTM standard. The obtained results showed that the calcined HA and FA nanoparticles have an ellipsoid-like morphology, and their mean crystallite sizes were measured as 24 and 30 nm, respectively. The mechanical results of the modified GICs, following the addition of HA and FA (5 and 8 wt%) into the glass ionomer cement and 28 days storage in distilled water, exhibited statistically higher CS (64–70 and 66–72 MPa, respectively). Also, higher DTS was observed, at about 7.5–10.5 and 8.5–12 MPa, respectively. The microhardness of the GICs containing HA and FA nanoparticles (5 wt%) increased by 6.5 and 14%, respectively. In addition, the working time and setting time by adding the 5 wt% nanoparticles reduced about 12 and 19% for HA and 13.5 and 18% for FA, respectively. Finally, it can be concluded that the synthesized GICs containing HA and FA nanoparticles provide enhanced mechanical properties to restorative dental materials.

Mechanical properties of resin-based cements with different dispensing and mixing methods

Statement of problemResin-based cements are frequently used in clinical practice. To reduce time and technique sensitivity, manufacturers have introduced the same brand of cement with different dispensing methods. The effect of this change on properties of the cement is unknown. PurposeThe purpose of this in vitro study was to evaluate the mechanical properties of resin-based cements with different dispensing systems. Material and methodsSpecimens of resin-based cements (n=14) PANAVIA SA Cement Plus Handmix, PANAVIA SA Cement Plus Automix, RelyX Unicem Handmix, RelyX Unicem 2 Automix, G-CEM Capsule Automix, G-CEM LinkAce Automix, Variolink II Handmix, and Variolink Esthetic Automix were prepared for each mechanical test. They were examined after thermocycling (n=7/subgroup) for 20000 cycles as to fracture toughness (FT) (ISO standard 6872; single-edge V-notched beam method), compressive strength (CS) (ISO 9917-1), and diametral tensile strength (DTS). The specimens were mounted and loaded at a crosshead rate of 1 mm/min (0.5 mm/min for FT) with a universal testing machine until failure occurred. The 2-and 1-way ANOVA followed by the Tukey HSD post hoc test were used to analyze data for statistical significance (α=05). ResultsThermocycling had a significant effect in reducing the FT property of all resin-based cements except RelyX Unicem 2 and G-CEM LinkAce (P<.05). Variolink II and G-CEM LinkAce showed better FT properties than their automixed counterparts (P<.05). The overall CS of all automixed resin-based cements was better than that of their hand-mixed counterpart, except for Variolink II. PANAVIA SA Automixed and G-CEM LinkAce had higher DTS than their hand-mixed counterparts (P<.05). ConclusionsChanging the dispensing method alters the mechanical properties of resin-based cements. The clinical significance of these results is yet to be determined.

Comparison of Design Method for Making Composite of (PMMA/HA/Sericin)

Biomaterial components (PMMA/HA/Sericin) are composite biomaterial that have complemented each other, which HA is able to improve the mechanical properties, biocompatible and osteoconductivity. PMMA has the ability biocompatible with human tissue and easy manipulated, while sericin can improve cell viability. Analysis of the composite composition is important to do more in depth, but the design method in the analysis of research also has significant impact in generating research output and prediction output. Analysis of the design method to determine the method of designing the optimal research was needed. This research used 3 factors: Poly methyl methacrylate (PMMA) powder (with concentration of 40% to 60%), Hydroxyapatite (HA) powder (with concentration of 10% to 25%) and Sericin (with concentration of 0.16% to 0.32%). This research is done to identify the effect of individual components of the composite and analyze the design method to obtain the best of diametral tensile strength (DTS) with a small error. The result of two methods was found that the 2k factorial design method give higher DTS (PHS401032 = 25.49MPa) than that of Taguchi method (PHS601532 = 24.82MPa). The error of 2k Factorial design method between validation and model prediction is 0.27%, which smaller than Taguchi method (7.45%).

Enhancing glass ionomer cement features by using the HA/YSZ nanocomposite: A feed forward neural network modelling

Despite brilliant properties of glass ionomer cement (GIC), its weak mechanical property poses an obstacle for its use in medical applications. The present research aims to formulate hydroxyapatite/yttria-stabilized zirconia (HA/YSZ) in the composition of GIC to enhance mechanical properties and to improve fluoride release of GIC. HA/YSZ was synthesized via a sol–gel method and characterized by applying X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photo-emission spectroscopy (XPS) and simultaneous thermal analysis (STA) along with transmission electron microscopy (TEM) methods. The synthesized nanocomposite was mixed with GIC at a fixed composition of 5wt%. The effect of different weight percentages of YSZ:HA on GIC was investigated by measuring the compressive strength, diametral tensile strength, microhardness and fluoride release. The results showed that, after 1 and 7 days of setting, the 20wt% nanohydroxyapatite/80wt% stabilized zirconia cement exhibited higher compressive strength (1857–245MPa), higher diametral tensile strength (11–14MPa) and greater microhardness (104–106MPa) as compared with the pure GIC (65–88MPa in compressive strength, 5–9.5MPa in diametral tensile strength and 70–89MPa in microhardness). The reinforced cement, also, exhibited higher fluoride release compared with pure GIC.The artificial neural network (ANN) was trained for modeling the system. Results obtained by ANN have proved to be completely in accordance with expectations.

An in vitro Evaluation of Diametral Tensile Strength and Flexural Strength of Nanocomposite vs Hybrid and Minifill Composites cured with Different Light Sources (QTH vs LED)

Composites always remained the target of discussion due to lot of controversies around it. Mechanical properties are one of them. With the introduction of new technology and emergence of various composites which combine superior strength and polish retention, nanocomposites have led to a new spark in the dentistry. A recent curing unit LED with various curing modes claims to produce higher degree of conversion. The aim of this study was to evaluate the diametral tensile strength and flexural strength of nanocomposite, hybrid and minifill composites cured with different light sources (QTH vs LED). Seventy-two samples were prepared using different specially fabricated teflon molds, 24 samples of each composite were prepared for the diametral tensile strength (ADA specification no. 27) and the flexural strength (ISO 4049) of the 12 samples, six were cured with LED (Soft Start curing profile) and other six with QTH curing light and tested on a universal testing machine. The nanocomposite had highest diametral tensile strength and flexural strength which were equivalent to the hybrid composite and superior than the minifill composite. With the combination of superior esthetics and other optimized physical properties, this novel nanocomposite system would be useful for all posterior and anterior applications.

Novel experimental cements for use on the dentin-pulp complex

This aim of this study was to evaluate the physicochemical and biological properties of novel experimental cements (Hybrid, Paste and Resin) based on synergistic combinations of existing materials, including pH, diametral tensile strength (DTS) and cytotoxicity comparing them with mineral trioxide aggregate (MTA - Angelus®) and a glass ionomer cement (GIC) developed at our laboratory. For the physicochemical and biological tests, specimens with standard dimensions were produced. pH measurements were performed with digital pH meter at the following time intervals: 3, 24, 48 and 72 h. For the DTS test, cylindrical specimens were subjected to compressive load until fracture. The MTT assay was performed for cytotoxicity evaluation. Data were analyzed by ANOVA and Tukey's test (α=0.05). Paste group showed pH values similar to MTA, and Hybrid group presented pH values similar to GIC (p>0.05). The tested materials showed pH values ranging from alkaline to near neutrality at the evaluated times. MTA and GIC showed similar DTS values. The lowest and highest DTS values were seen in the Paste and Resin groups, respectively (p<0.05). Cell viability for MTA and experimental Hybrid, Paste and Resin groups was 49%, 93%, 90% and 86%, respectively, when compared with the control group. The photo-cured experimental resin cement showed similar or superior performance compared with the current commercial or other tested experimental materials.

Effect of silicon and heat-treatment temperature on the morphology and mechanical properties of silicon - substituted hydroxyapatite

The precipitation method was used to synthesize silicon-substituted hydroxyapatite with different Si contents of 0.4, 0.8 and 1.6 wt.% (0.4, 0.8 and 1.6Si-HA) using silicon acetate [Si(OCOCH 3) 4] as a Si source. As-synthesized hydroxyapatite (HA) and Si-HA powders/bulks were heat-treated at different temperatures of 1150, 1200 and 1250 °C for 1 h. Pure 0.4Si-HA and 1.6Si-HA were obtained after heat-treatment at all temperatures, whilst α-TCP phase was formed in the 0.8Si-HA sample after heat-treatment at 1250 °C. SEM observation clearly showed that the substitution of Si in HA inhibited the grain growth of Si-HA even at high heat-treatment temperatures (1200 or 1250 °C). The highest diametral tensile strength (DTS) of 15.93 MPa was obtained in the 1.6Si-HA sample after heat-treatment at 1250 °C.

Microstructure and properties of polyhydroxybutyrate-calcium phosphate cement composites

AbstractThe biopolymer (polyhydroxybutyrate) microparticles-calcium phosphate composites were prepared by mechanical mixing of the basic composite components with the addition of hardening liquid after ethanol-composite mixture suspension moulding. The composite microstructures were more compact than the pure cement samples as confirmed by the lower values of specific areas and mesopore volumes. Both the specific areas and mesopore volumes decreased with soaking time in a simulated body fluid. The low polyhydroxybutyrate degradation in composites was found after soaking in simulated body fluid, which was terminated after one week. The formation of a dense apatite layer bonded directly to the surface of polyhydroxybutyrate microparticles was observed. The highest diametral tensile strength (13 MPa) and compressive strength (95 MPa) values of up to 50 % higher than in pure cement were measured in samples with 10 % of polyhydroxybutyrate. The addition of polyhydroxybutyrate microparticles had no effect on the setting time.

Synthesis and characterization of a novel fast-set proline-derivative-containing glass ionomer cement with enhanced mechanical properties

In this study, a methacryloyl derivative of l-proline was synthesized, characterized and incorporated into a conventional glass ionomer cement (GIC) with a polyacid composition. Subsequently, the effects of incorporation of synthesized N-methacryloyl-proline and terpolymer on the GIC’s mechanical and working properties were studied. 1-Methacryloylpyrrolidone-2-carboxylic acid was synthesized and used in a polymerization reaction with acrylic acid and itaconic acid in order to form terpolymer which was used in Fuji II commercial GIC formulations. Chemical structural characterization of the resulting products was performed using 1H nuclear magnetic resonance and Fourier transform infrared spectroscopy. The viscosity and molecular weight of the terpolymer were also measured. The mechanical strength properties of the modified GICs were evaluated after 24 h or 1 week of immersion in distilled water at 37 °C. Analysis of variance was used to study the statistical significance of the mechanical strengths and working properties, and to compare them with a control group. Results showed that N-methacryloyl-proline modified GICs exhibited significantly higher compressive strength (CS; 195–210 MPa), higher diametral tensile strength (DTS; 19–26 MPa) and higher biaxial flexural strength (38–46 MPa) in comparison to Fuji II GIC (161–166 MPa in CS, 12–14 MPa in DTS and 13–18 MPa in biaxial flexural strength). The working properties (setting and working time) of the modified samples showed that the modified cement was a fast-set cement. It was concluded that a novel amino acid-containing GIC has been developed in this study with 27%, 94% and 170% increases in values for compressive, diametral tensile and biaxial flexural strength, respectively, in comparison to commercial Fuji II GIC.

Modification of conventional glass-ionomer cements with N-vinylpyrrolidone containing polyacids, nano-hydroxy and fluoroapatite to improve mechanical properties

Objective The objective of this study was to enhance the mechanical strength of glass-ionomer cements, while preserving their unique clinical properties. Methods Copolymers incorporating several different segments including N-vinylpyrrolidone (NVP) in different molar ratios were synthesized. The synthesized polymers were copolymers of acrylic acid and NVP with side chains containing itaconic acid. In addition, nano-hydroxyapatite and fluoroapatite were synthesized using an ethanol-based sol–gel technique. The synthesized polymers were used in glass-ionomer cement formulations (Fuji II commercial GIC) and the synthesized nanoceramic particles (nano-hydroxy or fluoroapatite) were also incorporated into commercial glass-ionomer powder, respectively. The synthesized materials were characterized using FTIR and Raman spectroscopy and scanning electron microscopy. Compressive, diametral tensile and biaxial flexural strengths of the modified glass-ionomer cements were evaluated. Results After 24 h setting, the NVP modified glass-ionomer cements exhibited higher compressive strength (163–167 MPa), higher diametral tensile strength (DTS) (13–17 MPa) and much higher biaxial flexural strength (23–26 MPa) in comparison to Fuji II GIC (160 MPa in CS, 12 MPa in DTS and 15 MPa in biaxial flexural strength). The nano-hydroxyapatite/fluoroapatite added cements also exhibited higher CS (177–179 MPa), higher DTS (19–20 MPa) and much higher biaxial flexural strength (28–30 MPa) as compared to the control group. The highest values for CS, DTS and BFS were found for NVP-nanoceramic powder modified cements (184 MPa for CS, 22 MPa for DTS and 33 MPa for BFS) which were statistically higher than control group. Conclusion It was concluded that, both NVP modified and nano-HA/FA added glass-ionomer cements are promising restorative dental materials with improved mechanical properties.

Effects of incorporation of hydroxyapatite and fluoroapatite nanobioceramics into conventional glass ionomer cements (GIC)

Hydroxyapatite (HA) has excellent biological behavior, and its composition and crystal structure are similar to the apatite in the human dental structure and skeletal system; a number of researchers have attempted to evaluate the effect of the addition of HA powders to restorative dental materials. In this study, nanohydroxy and fluoroapatite were synthesized using an ethanol based sol–gel technique. The synthesized nanoceramic particles were incorporated into commercial glass ionomer powder (Fuji II GC) and were characterized using Fourier transform infrared and Raman spectroscopy, X-ray diffraction and scanning electron microscopy. Compressive, diametral tensile and biaxial flexural strengths of the modified glass ionomer cements were evaluated. The effect of nanohydroxyapatite and fluoroapatite on the bond strength of glass ionomer cement to dentin was also investigated. Results showed that after 1 and 7 days of setting, the nanohydroxyapatite/fluoroapatite added cements exhibited higher compressive strength (177–179 MPa), higher diametral tensile strength (19–20 MPa) and higher biaxial flexural strength (26–28 MPa) as compared with the control group (160 MPa in CS, 14 MPa in DTS and 18 MPa in biaxial flexural strength). The experimental cements also exhibited higher bond strength to dentin after 7 and 30 days of storage in distilled water. It was concluded that glass ionomer cements containing nanobioceramics are promising restorative dental materials with both improved mechanical properties and improved bond strength to dentin.

Diametral tensile strength of composite resins submitted to different activation techniques

The aim of this study was to evaluate the diametral tensile strength (DTS) of composite resins submitted to different curing techniques. Four composite resins were tested in this study: Targis (Ivoclar), Solidex (Shofu), Charisma (Heraeus-Kulzer) and Filtek Z250 (3M Espe). Sixty-four cylindrical specimens were prepared and divided into eight groups according to each polymerization technique (n = 8). The indirect composite resins (Targis and Solidex) were polymerized with their respective curing systems (Targis Power and EDG-lux); Charisma and Filtek Z250 were light-cured with conventional polymerization (halogen light) and additionally, with post-curing systems. Specimens were stored in artificial saliva at 37 degrees C for one week. DTS tests were performed in a Universal Testing Machine (0.5 mm/min). The data were statistically analyzed by ANOVA and Duncan tests. The results were (MPa): Z250/EDG-lux: 69.04 feminine; Z250/Targis Power: 68.57 feminine; Z250/conventional polymerization: 60.75b; Charisma/Targis Power: 52.34c; Charisma/conventional polymerization: 49.17c; Charisma/EDG-lux: 47.98c; Solidex: 36.62d; Targis: 32.86d. The results reveal that the post-cured Z250 composite resin showed the highest DTS means. Charisma composite presented no significant differences when activation techniques were compared. Direct composite resins presented higher DTS values than indirect resins.

Influence of activation modes on diametral tensile strength of dual-curing resin cements

In metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. The effect of the lack of photoactivation on the strength of these cements has been rarely studied. This study evaluated the influence of activation modes on the diametral tensile strength (DTS) of dual-curing resin cements. Base and catalyst pastes of Panavia F, Variolink II, Scotchbond Resin Cement, Rely X and Enforce were mixed and inserted into cylindrical metal moulds (4 x 2 mm). Cements were either: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated through mylar strips (chemical and photo-activation = dual-cured groups) (n = 10). After a 24 h storage in 37 masculineC distilled water, specimens were subjected to compressive load in a testing machine. A self-curing resin cement (Cement-It) and a zinc phosphate cement served as controls. Comparative analyses were performed: 1) between the activation modes for each dual-curing resin cement, using Students t test; 2) among the self-cured groups of the dual-curing resin cements and the control groups, using one-way ANOVA and Tukeys test (alpha = 0.05). The dual-cured groups of Scotchbond Resin Cement (53.3 MPa), Variolink II (48.4 MPa) and Rely X (51.6 MPa) showed higher DTS than that of self-cured groups (44.6, 40.4 and 44.5 MPa respectively) (p < 0.05). For Enforce (48.5 and 47.8 MPa) and Panavia F (44.0 and 43.3 MPa), no significant difference was found between the activation modes (p > 0.05). The self-cured groups of all the dual-curing resin cements presented statistically the same DTS as that of Cement-It (44.1 MPa) (p > 0.05), and higher DTS than that of zinc phosphate (4.2 MPa). Scotchbond Resin Cement, Variolink II and Rely X depended on photoactivation to achieve maximum DTS. In the absence of light, all the dual-curing resin cements presented higher DTS than that of zinc phosphate and statistically the same as that of Cement-It (p > 0.05).

Analysis of strength properties of light-cured resin composites

Objectives: To determine and correlate the compressive and tensile strengths of resin composites, to scale their failure probability and to analyze their failure mode under combined state of stresses. Methods: Ten brands of composites were tested for compressive and diametral tensile strengths. A recently introduced device for testing of pure shear stresses was modified to adapt to smaller specimens. Uniformity of pure shear stress distribution in the significant section was verified by a photoelastic model. Loading specimens in pure shear up to failure determined their mode of fracture under combined state of stresses. Results: Diametral tensile strength yielded values that were 20% of their respective compressive strength. Multiple comparison test indicated that strength properties of the tensile strength test were much more sensitive in predicting differences between resin composites when compared to a compressive strength test. Pertac (Espe) had the highest compressive strength, Graft LC (GC) and Z-100 (3M) had the highest diametral tensile strength. No correlation was found between tensile and compressive strengths. The Weibull modulus disclosed differences in the liability of the materials to fracture. When combined state of stresses were applied through the pure shear test, failure of each specimen occurred at the principal tensile planes. Significance: Compressive strength cannot predict the ability of the resin composite to withstand tensile stresses. The importance of compressive strength is limited as failure of a brittle material occurs in tension.