Diametral Tensile Strength Research Articles

A Comparative Evaluation of Mechanical Properties of Four Different Restorative Materials: An In Vitro Study.

ABSTRACTObjectivesThe purpose of this study is to compare the mechanical properties (compressive strength (CS) and diametral tensile strength (DTS)) of four different restorative materials: conventional glass ionomer (Fuji IX), ClearFil AP-X, Filtex Z350-XT, and Cention N.Materials and methodsSpecimens (n = 80) were prepared from Fuji IX, ClearFil AP-X, Filtex Z350-XT, and Cention N for testing compressive strength and DTS.Statistical analysisResults obtained were subjected to one-way ANOVA and Tukey's post hoc test at significance (p < 0.001).ResultsThere were significant differences among restorative materials tested. ClearFil AP-X exhibits the highest mechanical properties (CS and DTS) and least values were obtained by the Fuji IX.ConclusionStrength is one of the most important criteria for the selection of a restorative material. Stronger materials better resist deformation and fracture, presenting more equitable stress distribution, greater probability, and greater stability of clinical success.How to cite this articleIftikhar N, Devashish, et al. A Comparative Evaluation of Mechanical Properties of Four Different Restorative Materials: An In Vitro Study. Int J Clin Pediatr Dent 2019;12(1):47–49.

Comparative evaluation of diametral tensile strength of phosphate-bonded investment (ringless) material by using air-drying method, conventional hot air oven, microwave oven, and combination of microwave and conventional oven: An in vitro study.

Aim:This study evaluated and compared the diametral tensile strength (DTS) of phosphate-bonded investment (PBI) material (ringless) used in removable cast partial denture fabrication.Settings and Design:Comparative - Invitro study.Materials and Methods:The PBI material, Wirovest used in this study was subjected to four different drying methods. A total of 80 specimens were prepared in a cylindrical form; 20 specimens were air dried for 2 h, 20 specimens were dried in a conventional oven at 230°C for 1 h, 20 specimens were dried in microwave oven at 600 W for 10 min, and remaining 20 specimens were dried first in microwave oven and then in conventional oven. The dried specimens were tested at 2-h interval for diametral compression at a crosshead speed of 0.5 cm/min.Statistical Analysis Used:Pairwise analysis.Results:The microwave drying technique and drying by combination method resulted in greater DTS, respectively.Conclusion:Within the limitation of this study, PBI specimens dried in microwave oven at 600W for 10 min increased the diametral strength and are also a time-saving procedure.

Evaluation of the effect of micro-hydroxyapatite incorporation on the diametral tensile strength of glass ionomer cements.

Aim:The aim of this study was to evaluate the effect of micro-hydroxyapatite (micro-HAP) incorporation on the diametral tensile strengths (DTSs) of a conventional glass ionomer cement (GIC) and a resin-modified glass ionomer cement (RMGIC).Materials and Methods:Forty disc-shaped specimens (diameter: 6.5 mm, height: 2 mm) were prepared into four groups (n = 10) as follows: group 1, conventional GIC; Group 2, GIC + micro-HAP (15 wt %); Group 3, RMGIC; and Group 4, RMGIC + micro-HAP (15 wt %). All the specimens were stored in distilled water for 24 h at room temperature. The DTSs of the specimens were measured using a universal testing machine. Data analysis was performed using one-way ANOVA and Tukey's test (P < 0.05).Results:No significant difference was found in the DTS of conventional GIC with and without micro-HAP incorporation (P > 0.05). Moreover, the DTS of RMGIC incorporated with micro-HAP was significantly lower than that of RMGIC without micro-HAP incorporation (P < 0.05).Conclusions:Micro-HAP incorporation did not affect the DTS of conventional GIC. The DTS of RMGIC was negatively influenced by the micro-HAP incorporation. Conventional GIC (with and without hydroxyapatite) exhibited a lower DTS than RMGIC (with or without hydroxyapatite).

Mechanical and optical properties of conventional restorative glass-ionomer cements - a systematic review.

Objectives To perform a systematic review of test methodologies on conventional restorative glass-ionomer cement (GIC) materials for mechanical and optical properties to compare the results between different GICs.Material and Methods Screening of titles and abstracts, data extraction, and quality assessments of full-texts were conducted in search for in vitro studies on conventional GICs that follow the relevant specifications of ISO standards regarding the following mechanical and optical properties: compressive strength, flexural strength, color, opacity and radiopacity.Sources The Latin American and Caribbean Health Sciences (LILACS), Brazilian Bibliography of Dentistry (BBO) databases from Latin-American and Caribbean System on Health Sciences Information (BIREME) and PubMed/Medline (US National Library of Medicine - National Institutes of Health) databases were searched regardless of language. Altogether, 1146 in vitro studies were selected. Two reviewers independently selected and assessed the articles according to pre-established inclusion/exclusion criteria. Among all the properties investigated, only one study was classified as being of fair quality that tested compressive strength and was included. It was observed that many authors had not strictly followed ISO recommendations and that, for some properties (diametral tensile strength and microhardness), there are no guidelines provided.Conclusions It was not possible to compare the results for the mechanical and optical properties of conventional restorative GICs due to the lack of standardization of studies.

A comparison of antibacterial inhibitory effect on Streptococcus mutans and tensile strength between chitosan-based bonding adhesives and commercial products.

Adhesive bonding is the material used to attach a bracket to the enamel surface of the tooth. Streptococcus mutans contributes to enamel demineralization during orthodontic treatment. To analyze the antimicrobial inhibitory effect of Streptococcus mutans bacteria and tensile strength of chitosan and CaCO3-based adhesive bonding material. The investigation constituted laboratory experimental research featuring analytical observation and a random sampling method. The antibacterial inhibitory effect of chitosan and CaCO3-based adhesive bonding against Streptococcus mutans involved six groups: two control groups using commercial light cure and self-cure adhesive bonding products and four groups using adhesive bonding consisting of 75% CaCO3 + 17.6% Bis-GMA + 22.4% MMA with various percentages of chitosan composition (A1: 25%, A2: 50%, A3: 75%, and A4: 100%) each group consisting of two samples (n = 12). A diametric test was conducted consisting of three samples (n = 15) to measure the tensile strength of each group. Data were analyzed by a combination of one-way analysis of variance and least significant difference tests. The antibacterial inhibitory effect showed significant differences between groups (A1: 2.9467 ± 0.4163, A2: 3.6500 ± 0.6245, A3: 5.1267 ± 0.2517, A4: 4.7267 ± 0.9238; P = 0.0000; P < 0.05). A diametric tensile strength test confirmed significant differences between groups (A1: 7.2733 ± 5.0046, A2: 6.7667 ± 4.4346, A3: 6.4533 ± 2.9994, A4: 1.0058 ± 1.0058, K1: 15.6167 ± 3.1250; P = 0.009; P < 0.05). Chitosan-based adhesive bonding with good tensile strength has an antibacterial inhibitory effect against Streptococcus mutans.

Microstructural and diametral tensile strength evaluation of the zirconia-mullite composite

The purpose of the current research was to investigate the effect of duration of the mechanical activation process of starting materials on Vickers micro-hardness and diametral tensile strength of zirconia-mullite composites. Zirconia-mullite composites with 1:1 M ratio were fabricated by sintering of the mechanically activated kaolinite, gibbsite, and zircon powder mixture as inexpensive and convenient starting materials. Results of dynamic light scattering analysis showed that the mean particle size of the starting powders was reduced from 2.5 µm to 80 nm after 72 h of the mechanical activation process. X-ray diffraction analysis showed that zirconia and mullite were crystallized after 2 h thermal treatment at 1550 °C. Based on the semi-quantification results of X-ray diffraction patterns, increasing the duration of the milling process from 6 to 72 h had a positive effect on improving the amount of tetragonal zirconia in the final matrix. Scanning electron microscopy results revealed a fine and homogeneous distribution of zirconia particles in the mullite matrix after 72 h of the mechanical activation process. Increasing the duration of milling process from 6 h to 72 h had a remarkable effect in increasing the diametral tensile strength values from 30 to 220 MPa. Vickers micro-hardness values were also enhanced considerably from 7.30 to 11.12 GPa by increasing the milling time.

Fabrication of pure octacalcium phosphate blocks from dicalcium hydrogen phosphate dihydrate blocks via a dissolution–precipitation reaction in a basic solution

Octacalcium phosphate (OCP) blocks are attractive as bone substitutes because of their excellent biocompatibility. They can be fabricated from precursor ceramic blocks via a compositional conversion process. Herein, high-purity OCP blocks were fabricated through a dissolution–precipitation reaction from precursor blocks of dicalcium hydrogen phosphate dihydrate (DCPD) immersed in a 1.00-mol/L basic phosphate solution of disodium hydrogen phosphate (NaAP; pH ∼ 9) at 70 °C for 2 days. The results showed that they were completely converted to OCP blocks comprising interlocking ribbon-like crystals while maintaining their shape. The diametral tensile strength of the obtained OCP blocks was ∼6 MPa, which was significantly higher than that of OCP blocks fabricated from calcium sulfate as the precursor.

Titanium dioxide and modified titanium dioxide by silver nanoparticles as an anti biofilm filler content for composite resins

ObjectiveThe aim of this study was to evaluate the antibacterial activity of a composite resin modified by TiO2 and TiO2/Ag nanoparticles and their influence over different properties. MethodsTiO2 and TiO2/Ag NPs were synthesized by polymeric precursor and microwave-assisted hydrothermal methods and then, characterized by different techniques. Direct contact test was performed using Filtek™ Z350XT blended with 0.5; 1 and 2% (wt.) of NPs against Streptococcus mutans to determine the best concentration to the other tests. After that, the modified composite resin was tested against S. mutans 7-day biofilm (CFU/mL). Also, compressive and diametral tensile strength (n=40), degree of conversion (n=25) and surface roughness (n=50) was performed. The data were analyzed by ANOVA and Tukey’s test for multiple comparison at 5% significance level. ResultsThe direct contact test demonstrates that by increasing the nanoparticle content, the bacterial growth is significantly reduceed (p<0.05). The inclusion of 2% of TiO2/Ag NPs significantly decreased (p<0.05) the biofilm accumulation of S. mutans on the composite resin surface compared to the control Group. The TiO2 NPs treated with an organosilane increased compressive strength of composite resin (p<0.05). Degree of conversion remained unchanged (p>0.05) and the surface roughness increased with the NPs (p<0.05), except for the TiO2 by polymeric precursor Group (p>0.05). SignificanceThe development of an antibacterial dental restorative material that hinder S. mutans biofilm without sacrificing the mechanical and physical properties is desirable in dental material science.

Dental cement's biological and mechanical properties improved by ZnO nanospheres

Metal oxide nanoparticles are a new class of important materials used in a wide variety of biomedical applications. Bulk zinc oxide (ZnO) particles have been used for temporal or permanent luting cement because of their excellent mechanical strength and biocompatibility. ZnO nanoparticles have distinct optical and antibacterial properties and a high surface-to-volume ratio. We investigated the mechanical and antibacterial properties of luting cement with different ratios of ZnO nanospheres. We showed that luting cement with 5% and 10% ZnO nanospheres was less soluble in low-pH (pH 3) artificial saliva. Antibacterial activity was 40% higher for Streptococcus mutans and 90% higher for Porphyromonas gingivalis when >10% (w/v) of the bulk particles were replaced with ZnO nanospheres in ZnO polycarboxylate cement. ZnO nanospheres were also biocompatible with mammalian cells. Additionally, the compressive strength was 1.2 times greater and the diametral tensile strength was 1.5 times greater for cements with 10% ZnO nanospheres than for conventional ZnO polycarboxylate cement. We propose a new method for improving dental luting cement by integrating it with ZnO nanospheres. This method simultaneously adds their greater antibacterial, mechanical, and acid resistance properties and retains an outstanding degree of biocompatibility.

Effect of titanium tetrafluoride addition on the physicochemical and antibacterial properties of Biodentine as intraorfice barrier

ObjectiveTo evaluate the influence of titanium tetrafluoride (TiF4) incorporation on the physicochemical and antibacterial properties of Biodentine (BD; Septodont, Saint Maur des Faussés, France) as an intraorfice barrier material. MethodsThree different proportions of TiF4 powder were used with BD; 1wt%, 2wt%, and 3wt%; respectively. BD without TiF4 addition was used as the control group. The setting time (ST) was determined using Gillmore needle apparatus. Diametral tensile strength (DTS) and fracture resistance were measured in a universal testing machine. Solubility was assessed using mass variation after 7days water storage. The hardness test was conducted using Vickers microhardness tester. The antibacterial activity was assessed using direct contact test against Enterococcus faecalis. Radiopacity was assessed and expressed in thickness of aluminum. Surface topography and elemental composition of modified BD were also assessed. The pH of soaking water was measured up to 168h. Data of tested properties were analyzed using one-way analysis of variance, the paired t-test, two-way repeated measures analysis of variance, and Tukey post hoc tests (P<0.05). ResultsBD-incorporating 2wt% TiF4 revealed the highest surface microhardness, DTS, and fracture resistance compared with the unmodified group (P<0.001). Higher concentrations of TiF4 (3wt%) compromised the solubility and prolonged the ST of BD (P<0.05). Bacterial growth of BD-incorporating TiF4 was significantly reduced when compared with the control group (P<0.05). The tested materials induced alkalization of the soaking water that decreased with time. SignificanceBiodentine-incorporating TiF4 (1wt% and 2wt%) is a promising intraorfice barrier material with enhanced physicochemical and antibacterial properties.

Effect of phytic acid on the setting times and tensile strengths of calcium silicate-based cements.

This study aimed to evaluate and compare the effect of 1% phytic acid as a mixing medium on the setting times and diametral tensile strengths of different calcium silicate-based cements. Specimens for four experimental groups (n=20/each) were fabricated by mixing ProRoot MTA® (Dentsply) and Biodentine® (Septodont) powders with their original liquids or with 1% phytic acid. Half of the samples in each group were immediately subjected to setting time tests, whereas the remaining half was subjected to the diametral tensile strength test after 3weeks. When mixed with their original liquids, the setting time of MTA was significantly longer than that of Biodentine® (P<0.05). When mixed with phytic acid, the initial and final setting times of both test materials significantly decreased (P<0.05). The diametral tensile strength of Biodentine® was significantly greater than that of MTA (P<0.05). However, phytic acid had no effect on this outcome (P>0.05).

Fabrication of self-setting β-TCP granular cement using β-TCP granules and sodium hydrogen sulfate solution.

Bridging beta-tricalcium phosphate (β-TCP) granules with dicalcium phosphate dihydrate (DCPD) creates a porous, interconnected β-TCP granular cement (GC) that is useful for reconstructing bone defects: the interconnected pores can accelerate new bone ingrowth and the set cement prevents the loss of granules from the bone defect area. However, the setting time of β-TCP GC in an acidic calcium phosphate solution is too short (<1 min) for handling in clinical applications, such as in orthopedic surgery. To address this issue, we sought to optimize the setting time of β-TCP GC using β-TCP granules and NaHSO4 solution, as [Formula: see text] is a known inhibitor of DCPD formation. Both DCPD and calcium sulfate dihydrate (CSD) precipitated on the surface of β-TCP granules and bridged β-TCP granules to one another. Increasing NaHSO4 concentration (from 0.5 mol/L to 5 mol/L) led to an increase in the amount of precipitant from 2.6 ± 0.2% to 21.6 ± 1.3% for DCPD and 1.3 ± 0.3% to 10.1 ± 0.5% for CSD. The diametral tensile strength was also increased from 0.03 ± 0.01 MPa to 2.0 ± 0.1 MPa with increasing NaHSO4 concentration. When 2 mol/L NaHSO4 solution was used as the liquid phase, setting time became 5.3 ± 0.2 min, which is suitable for handling in clinical applications to repair bone defects. In conclusion, β-TCP GC using NaHSO4 solution as the liquid phase has good potential value as bone augmentation cement.

Ion release, antimicrobial and physio-mechanical properties of glass ionomer cement containing micro or nanosized hexametaphosphate, and their effect on enamel demineralization.

To evaluate the effects of hexametaphosphate microparticles (mHMP) or nanoparticles (nHMP) incorporated in glass ionomer cement (GIC) on antimicrobial and physico-mechanical properties, fluoride (F) release, and enamel demineralization. HMP solutions were obtained at concentrations of 1, 3, 6, 9, and 12%, for screening of antimicrobial activity. Next, mHMP or nHMP at 6, 9, and 12% were incorporated into a resin-modified GIC and the antibacterial activity was evaluated. The resistance to diametral tensile and compressive strength, surface hardness, and degree of monomer conversion as well as F and HMP releases of GICs were determined. Furthermore, specimens were attached to enamel blocks and submitted to pH-cycling, and mineral loss was determined. Parametric and non-parametric tests were performed, after checking data homoscedasticity (p < 0.05). HMP solutions at 6, 9, and 12% demonstrated the best antibacterial activity. GIC containing HMP showed better antibacterial effects at 9 and 12% for nHMP. Regarding F and HMP releases, the highest levels of release occurred for groups containing 9 and 12% nHMP. With the increase in HMP concentration, there was lower mineral loss. However, the incorporation of mHMP or nHMP in GIC reduced values of physico-mechanical properties when compared to the control GIC. nHMP improves antimicrobial activity and fluoride release, and decreases enamel demineralization, but reduces the physico-mechanical properties of GIC. The association of GIC/HMP could be an alternative material for patients at high risk for dental caries and could be indicated for low-stress regions or provisional restorations.

Mechanical and Bioactive Properties of Mullite Reinforced Pseudowollastonite Biocomposite

Bioactive composites consist of pseudowollastonite and mullite synthesized from natural resources was developed for bone implant applications. To realize such applications, a mechanical test of these composites and in vitro bioactivity in SBF solution were studied. The present paper reports pseudowollastonite synthesized from the rice husk ash and limestone reinforced with 10, 20 and 30 wt. % of mullite. Influence of sintering temperature, phase composition, morphology towards mechanical properties of various pseudowollastonite-mullite (PSW-M) composites was examined prior to the bioactivity test. It was found that pseudowollastonite with the addition of 20 wt. % of mullite sintered at 1150°C gave the best result for diametral tensile strength (DTS) and hardness with the value of 8.8 ± 0.15 MPa and 3.79 ± 0.13 GPa, respectively. The obvious increment in the mechanical strength was due to the formation of liquid phase CaAl2O3 during sintering at 1150°C. In addition, the formation of fibrous apatite (HA) layer of amorphous calcium phosphate (ACP) with Ca/P ratio 1.8 on PSW20M sample confirmed the good bioactivity of the composite.

Fabrication of octacalcium phosphate block through a dissolution-precipitation reaction using a calcium sulphate hemihydrate block as a precursor.

Although octacalcium phosphate (OCP) powder and a collagen/gelatin composite demonstrate good potential as bone substitutes, an OCP block has not been fabricated to date. In this study, the feasibility of fabricating an OCP block was evaluated through a dissolution-precipitation reaction using a calcium sulfate hemihydrate (CSH) block as a precursor. When the block was immersed in a phosphate salt solution, its composition changed to that of OCP, while its structure was maintained. The diametral tensile strength (DTS) of the OCP block was 1.0 ± 0.2 MPa. The macroporosity and microporosity of the OCP block were 33.4 ± 4.5% and, 69.0 ± 1.6%, respectively. New bone attached well to the OCP block, and this block was partially replaced by bone 2 weeks after implantation. Four weeks after implantation, the surface of the OCP block was nearly covered with new bone and ~30% of the block was replaced by new bone, while no replacement by bone was observed in the case of a hydroxyapatite (HAp) block used as a control. It is concluded that OCP blocks are potentially suitable for their use as artificial bone substitutes.

The influence of filler amount on selected properties of new experimental resin dental composite

Abstract Aim of the study was to evaluate the influence of filler amounts on mechanical properties and contraction stress of light-curing experimental composite. Hardness, flexural strength, diametral tensile strength of material filled with 40, 50 or 60 wt. % of silanized silica were tested. The contraction stress was measured after 24 h by means of photoelastic study. The addition of 40-60 wt. % filler to composite caused significant increase in hardness, Young’s modulus and flexural strength. The DTS, after incorporating filler into polymer matrix, was valued at ~26 MPa. The composite containing 40 wt. % of filler demonstrated significantly lower contraction stress in comparison to neat resin and filled &gt; 50 wt. % of silica.

Mineral Trioxide Aggregate Mixed with 5-Aminolevulinic Acid for the Photodynamic Antimicrobial Strategy in Hard Tissue Regeneration.

Aminolevulinic acid (ALA) based photodynamic antimicrobial strategy can provide good antimicrobial effects and be used for medical applications. The aim of this study was to apply this strategy to Mineral Trioxide Aggregate (MTA), which is commonly used as a filling material for root endings and by doing so, to increase the bactericidal capability of MTA, as well as to investigate its characterization, cytocompatibility, and odontogenic differentiation potential. MTA is known to be a derivative of calcium silicate (CS). In this study, MTA specimens with or without ALA and light treatment were prepared. Diametral tensile strength values (DTS), setting durations, X-ray diffraction (XRD) spectra, apatite-mineralization, and antimicrobial abilities of the MTA, were also analyzed. Human dental pulp cells (hDPCs) can proliferate into the newly formed matrix and differentiate into odontoblasts to reinforce and strengthen the root. Levels of hDPCs proliferation and its odontogenic capabilities when cultured on MTA with ALA and light treatment, and the percentages of cells existing in the various cell cycle stages, were further evaluated in this study. The results indicated that MTA added ALA with light treatment had greater antibacterial ability and cytocompatibility, compared to MTA alone. A higher percentage S phase of the cells cultured on MTA added ALA with light treatment was observed. Furthermore, hDPCs cultured on MTA added ALA with light treatment had the highest expression levels of the odontoblastic differentiation markers. ALA has great antimicrobial efficiency and is a potential material for future medical applications. ALA-based photodynamic antibacterial strategy applied in the MTA has great antibacterial ability, cytocompatibility, and odontoblastic differentiation potential, and can facilitate the development of root canal treatment.

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.

Physical–mechanical evaluation of a microhybrid and a nanofilled composite light activated by quartz-halogen tungsten and light-emitting diode

The aim of this study was to characterize organic and disperse phase of a microhybrid (Mh – Filtek Z250) and a nanofilled (Nf – Filtek Z350) dental composite and analyze the influence of two LCUs (QHT-quartz-halogen tungsten and LED – light-emitting diode) on its physical–mechanical properties (degree of conversion, polymerization shrinkage, Vickers hardness and diametral tensile strength). Surface morphology was studied by scanning electron microscopy. The disperse phase content was measured using thermogravimetric analysis (TGA) and the organic fractions were qualitatively analyzed by nuclear magnetic resonance spectroscopy. Physical–mechanical properties were analyzed varying dental composite and LCU: Mh-QHT, Nf-QHT, Mh-LED and Nf-LED. The degree of conversion was evaluated using Raman spectrophotometry and polymerization shrinkage was measured by water picnometry. Mechanical behavior was analyzed by Vickers microhardness and diametral tensile testing. Scanning electron microscopy analysis showed similar microstructure of the materials mainly composed with different-sized particles dispersed within methacrylate matrix. Thermogravimetric analysis shows 80.13% of inorganic fraction for microhybrid composite and 75.29% for nanofilled. Nuclear magnetic resonance analysis showed similar organic structure for composites and did not show the presence of the monomer TEGDMA. Different light sources did not influence the tested properties, but considering different composites, nanofilled showed the highest degree of conversion (Gr 2:77%, Gr 4: 79.4%). The study shows that when the optimum radiant exposure (24 J/cm2) was used for polymerization of composites, regardless of the polymerization source, the properties of these resin materials showed satisfactory and similar results in relation to the conversion of polymers, polymerization shrinkage and mechanical behavior.

Effect of resin thickness and light-curing distance on the diametral tensile strength of short fibre-reinforced resin composite

This study analyzed the effect of short fibre-reinforced resin composite (SFRC) thickness and light-curing distance on diametral tensile strength. A total of 40 disk-shaped SFRC specimens 3 and 4 mm thick and 6 mm in diameter (n = 20) were divided into two different light-curing distance groups of 2 and 4 mm (n = 10), respectively. All specimens were polymerized using a light-emitting diode (LED) curing unit at irradiance 800 mW/cm2 for 20 s. Specimens were tested using a universal testing machine to determine the diametral tensile strength. Diametral tensile strengths were 43.04 ± 1.53 and 41.77 ± 1.79 MPa in the 3-mm thickness groups with 2- and 4-mm light-curing distances, respectively, compared with 42.30 ± 1.77 and 39.46 ± 1.90 MPa, respectively, in the 4-mm thickness groups. There was a significant difference in diametral tensile strength in the 4-mm thickness group with a 4-mm light-curing distance using one-way analysis of variance (ANOVA) and post-hoc Fisher’s least significant difference (LSD) tests. It is concluded that SFRC thickness and light-curing distance have an effect on diametral tensile strength.