Experimental Resin Composites Research Articles

Development of novel dental restorative composites with dibasic calcium phosphate loaded chitosan fillers

The incorporation of antimicrobial agents in restorative dental composites has the potential to slow the development of carious lesions. ObjectiveThe objectives of the present study were to develop experimental composite resins with chitosan or chitosan loaded with dibasic calcium phosphate anhydrous (DCPA) particles and to demonstrate their antimicrobial potential without loss of mechanical properties or biocompatibility. MethodsChitosan and chitosan/DCPA particles were synthetized by the electrospray method. Experimental composites were formulated by adding 0, 0.5, or 1.0 wt% particles into a resin matrix along with 60 wt% barium glass. The degree of conversion and mechanical properties were measured after 1 and 90 days of aging in water after photoactivation. Cytotoxicity and genotoxicity were evaluated using fibroblasts from dental pulp in conditioned medium. The antimicrobial activity against Streptococcus mutans was assessed by crystal violet biofilm assay. ResultsThe experimental restorative composites were not found to be cytotoxic or genotoxic, with cell viability of 93.1 ± 8.0% (p = 0.328) and 3.0 ± 0.8% micronucleus per group (p = 0.1078), respectively. The antimicrobial results showed that all composites with approximately 20% less biofilm (p < 0.001) relative to the control. No chitosan release was detected from the composites, suggesting direct contact of the bacteria with exposed chitosan particles on the surface was responsible for the observed antimicrobial effect. The addition of the chitosan and chitosan/DCPA submicrometer (<250 nm average diameter) particles to restorative composites did not change the degree of conversion, flexural strength, elastic modulus and fracture toughness compared to the control group after 90 days aging in water. SignificanceIt can be concluded that the addition of chitosan or chitosan/DCPA particles in the restorative composites induced antimicrobial activity without compromising the mechanical properties or biocompatibility of the composites.

Preparation and evaluation of a BisGMA-free dental composite resin based on a novel trimethacrylate monomer

ObjectiveThe use of the BisGMA as base monomer in dental composites has been questioned because of bisphenol A (BPA) is used as raw material in its synthesis, and BPA possess estrogenic potential associated to several health problems. This study describes the synthesis of the trimethacrylate tris(4-hydroxyphenyl)methane triglycidyl methacrylate (TTM) monomer and evaluate its effect when used as base monomer in the formulation of experimental photopolymerizable composite resins. MethodsThe TTM monomer was synthesized by a nucleophilic acyl substitution. Its chemical structure was confirmed via 1H and 13C NMR spectroscopy and FTIR spectroscopy. Experimental composite resins were formulated by mixing TTM, triethyleneglycol dimethacrylate (TEGDMA) and inorganic fillers. A BisGMA/TEGDMA based composite resin was prepared and used as control to compare several physicochemical properties. Cell viability assay was used for cytotoxicity evaluation. ResultsTTM was successfully synthesized with quantitative yields. The results showed that the TTM-based composite resin had similar values of flexural strength, elastic modulus, degree of conversion and polymerization shrinkage than the control (p > 0.05). Water sorption and solubility were statistically significantly higher than the control (p < 0.05), however they complied the requirements stablished by the ISO 4049. Finally, this study shows there were no statistically significant differences for the biocompatibility outcomes (p = 0.345). SignificanceTTM monomer could be potentially useful in the formulation of BisGMA free composite resins, which could mean to minimize the human exposure to BPA.

Light-Curing Units, Photoinitiators System, and Monomers on Physico-Mechanical Properties of Experimental Composite Resins

This study evaluated the physico-mechanical properties of experimental composite resins made with different resin matrix and light-curing units. Experimental composite groups were divided according to monomers (BisGMA + TEGDMA-BT and BisGMA + BisEMA + UDMA + TEGDMA-BBUT) and photoinitiator system (camphorquinone-CQ and 1-phenyl-1,2-propanedione-PPD). A quartz tungsten halogen (QTH) or light-emitting diode (LED) were used to light cure all materials. Knoop microhardness (n = 10) was determined using Knoop microhardness test. Compressive strength, diametral tensile strength, and Young modulus (n = 7) were obtained using a universal testing machine at crosshead speed of 1.0 mm/min. The data were submitted to a three-way ANOVA and the Tukey post-hoc test (α = 0.05). QTH presented the highest total irradiance values and similar total radiant exposure to LED. For the compressive strength test, BT-PPD light-cured with LED group showed the lowest mean value. BT-CQ light-cured with LED group exhibited the lowest diametral tensile strength results. The BBUT-composite resins presented lowest Young modulus values, with no statistical difference between light-curing units (QTH and LED) and photoinitiators system (CQ and PPD). Application of QTH or LED in BT-based composite resins with PPD photoinitiator generated suitable results regarding the physico-mechanical properties. Keywords: Biomaterials; blends; dental composites; polymerization; shrinkage

Degree of conversion of experimental resin composites containing bioactive glass 45S5: the effect of post-cure heating

Resin composites containing reinforcing inert glass fillers combined with bioactive glass (BG) can aid in the prevention of secondary caries, which is a major cause of failure of contemporary composite restorations. A series of previous studies on experimental resin composites filled with BG 45S5 has demonstrated that methacrylate resin polymerization can be impaired by the addition of unsilanized BG, leading to lower degrees of conversion (DC). In order to distinguish whether the polymerization inhibition is caused by a direct (temperature-independent) effect of BG or an indirect (temperature-dependent) effect of restricted mobility of reactive species, this study used Raman spectroscopy to evaluate the DC values of experimental composites post-cured at 37 °C and 150 °C. The potential of BG to adversely affect DC was highly dependent on the resin system. The highest DC reduction was observed in the resin system based on ethoxylated bisphenol A dimethacrylate (Bis-EMA), followed by bisphenol A glycidyl methacrylate (Bis-GMA). In contrast, the DC for urethane dimethacrylate (UDMA) was not compromised by BG. Increasing the mobility of reactive species by heating at 150 °C showed limited potential for increasing the DC in the Bis-EMA and Bis-GMA resin systems, indicating a direct inhibitory effect of BG on polymerization.

Effect of nanotitanium dioxide fillers addition on the compressive strength of an experimental composite resin core material

Effect of nanotitanium dioxide fillers addition on the compressive strength of an experimental composite resin core material

Evaluation of monomers derived from resorcinol as eluents of bisphenol A glycidyl dimethacrylate for the formulation of dental composite resins

ABSTRACTThe objective of this work was to synthesize two bio‐based monomers, using the resorcinol as raw material, and its effect as bisphenol A glycidyl dimethacrylate (Bis‐GMA) eluents on different chemical–physical and biological properties of experimental photopolymerizable composite resins. The acrylic 1,3‐phenylen diacrylic (1,3‐FDA) and methacrylic 1,3‐phenylen dimethacrylic (1,3‐FDMA) monomers were synthesized and fully characterized through FTIR and 1H‐NMR spectroscopies. Experimental photopolimerizable composites were formulated using Bis‐GMA/1,3‐FDA or Bis‐GMA/1,3‐FDMA as organic matrix. The materials were compared with a Bis‐GMA/TEGDMA resin‐based composite used as control. Polymerization kinetics was evaluated by means of FTIR spectroscopy. Polymerization stress was directly measured through a polymerization stress tester. The cell viability of the composites was evaluated using the MTT assay. One‐way analysis of variance and Tukey's test were used for statistical analysis. The materials formulated with the 1,3‐FDA monomer showed higher Rpmax values and lower polymerization stress values (p &lt; 0.05), while the flexural strength, water sorption, and solubility remained similar to the TEGDMA composite. Conversely, the materials formulated with the 1,3‐FDMA monomer showed a lower degree of conversion and statistically lower flexural strength (p &lt; 0.05). All materials exhibited a cellular viability close to 100%. Concerning the study conditions, the acrylic 1,3‐FDA monomer could be considered an alternative to TEGDMA in the formulation of photopolymerizable dental composite resins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48576.

Development of a fiber-reinforced material for fiber posts: Evaluation of stress distribution, fracture load, and failure mode of restored roots

Statement of problemThe biomechanical behavior of post-restored roots with an experimental fiber-reinforced composite resin is unknown. PurposeThe purpose of this in vitro study was to investigate the biomechanical behavior of an experimental composite resin (3-mm short glass fiber incorporated in methacrylate matrix with filler particles) used to produce the custom post itself or to reline fiber posts. Material and methodsFour testing groups (n=10) were created according to the root restoration method: FG, commercially available fiber post; FG+RC, fiber post relined with conventional composite resin; FG+EXP, fiber post relined with the experimental composite resin; and EXP, a custom post made of experimental composite resin. A three-dimensional finite element linear elastic analysis was performed by using geometric representations of groups, and the results were analyzed by von Mises (σvM) and maximum principal stress criteria. In sequence, 40 bovine incisors were assigned to these groups and subjected to a fracture load test (Instron 5965; 0.5 mm/min), and the failure mode was determined. ResultsThe EXP group showed more homogeneous stress distribution for σvM. ANOVA and the Tukey honestly significant difference (HSD) tests showed significant differences (P<.001) in fracture load (mean ±standard deviation; different superscript letters indicate statistical difference): FG+EXP (669.5 ±107.7)A; FG (620.7 ±59.2)A; EXP (506.5 ±27.0)B; FG+RC (452.7 ±81.6)B. No differences were found for failure mode (P=.595). ConclusionsThe experimental composite resin significantly increases fracture load when used to reline commercially available fiber posts and, irrespective of its use, presented lower stress concentration.

Effect of Synthesized Bis-GMA and UDMA Nanofibers on Cuspal Flexure, Microhardness, Wear, Surface Roughness and Color Stability of Experimental Resin-Composites

Objective: To study the cuspal flexure (CF), Vickers microhardness (HV), three-body wear (W), surface roughness (SR) and color stability (CS) of experimental resin-composites reinforced with Bis-GMA and UDMA nanofibers synthesized by electrospinning technique.Materials and methods: Bis-GMA (Bis-GMA+TEGDMA+PEGDMA) and UDMA (UDMA+PEGDMA) nanofibers were synthesized by wet electrospinning technique and characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). After being ball-milled to a nanoscale size (< 100 nm) in a ball-milling machine (Retsch – PM 400, Haan, Germany), these nanofibers were added to a prepared experimental resin-composite. This study was divided, according to the percent and type of added nanofibers, into eight groups (n=10/group except for color stability n=11): one control group, three groups reinforced with 7, 11 and 15 wt% Bis-GMA nanofibers and four groups reinforced with 7, 11, 15 and 20 wt% UDMA nanofibers. For each of these groups, CF, HV, W, SR and CS were studied. CF was studied by the digital image correlation method which analyzes the displacement of an object using a USB digital microscope with a built-in camera (COMET xS, Steinbichler Optotechnik GmbH, Neubeuern, Germany). HV was measured according to the ASTM E-384:1999 using a Digital Display Vickers Microhardness Tester (ZHVµ Micro Vickers Hardness Tester, Indentec Hardness Testing, Zwick Roell Co., Ltd. Atlanta, USA). W testing was carried out according to ISO/TS 14569:2001 using a custom-made cusp-on-disc sliding machine. Measurement of SR was performed according to ISO 25178-2:2012 and CS testing was carried out according to the regulations of ISO 4049; 2009 using a portable reflective spectrophotometer (X-Rite, model RM200QC, Neu-Isenburg, Germany). Data were collected and submitted to One-way ANOVA and post-hoc Tukey and Dunnett’s T3 tests with the significance level set at (p ≤ 0.05). Results: Pure forms of Bis-GMA (70-100 nm) and UDMA (50-100 nm) nanofibers were confirmed by SEM and FTIR. One-way ANOVA revealed significant differences between studied groups for CF, HV, W and SR (p = 0.001) but not for CS (p = 0.068). For both types of nanofibers, compared to the control group, reinforced groups showed lower CF, HV and SR and greater W results. For CS, there was no consistent trend of results of experimental groups that were comparable to that of control group. Within the range of added nanofibers (7-20 wt%), Bis-GMA nanofibers exhibited more favourable HV and W results than UDMA nanofibers, while the reverse was the case for CF and SR. Both nanofibers exhibited comparable CS results.Clinical Significance: A resin-composite reinforced with such nanofibers showing improved CF and unfavorably lower HV and more W should be used as a base layer and covered with a layer of another resin-composite with enhanced surface properties.

Preparation of experimental resin composites with an anti-adhesion effect against S. mutans using branched silicone methacrylate

The purpose of this study was to prepare anti-bacterial experimental resin composites with synthesized branched silicone methacrylate (BSM), and evaluate the influence of BSM on the physiochemical properties of the experimental resin composites. BSM was synthesized through a reaction between branched amino silicone and isocyanatoethyl methacrylate, and it was incorporated into 2,2-bis [4- (2-hydroxy-3-methacryloxy-propoxy)phenyl] propane (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA) (50 wt/50 wt) with a series of concentrations to form resin matrices. The experimental composites (EC) were then prepared by mixing different resin matrices with silaned BaAlSiO2 fillers. The double bond conversion, volumetric shrinkage, and mechanical properties of the prepared experimental resin composites were measured among groups with different BSM concentrations. A bacterial adhesion assay for bacteria colony counting was conducted using Streptococcus mutans. The results showed that all of the experimental resin composites had nearly the same double bond conversion ranging from 60.9 ± 0.3% to 62.4 ± 1.3% (p > 0.05). BSM could reduce the volumetric shrinkage of experimental resin composites, and composites with 20 wt% and 30 wt% of BSM in the resin matrix had the lowest volumetric shrinkage (p < 0.05). The flexural strength would be impaired after adding 30 wt% of BSM into the resin matrix of experimental resin composites, and BSM had no negative influence on the flexural modulus in this study. The water contact angles on the surfaces of BSM-containing composites were all higher than that on the surface of control group (p < 0.05), and followed a trend of increasing with the increase of the BSM concentration. S. mutans adherence on the surfaces of the EC-10%, EC-15%, EC-20% and EC-30% groups were significantly lower compared with the control group. This work suggested that the hydrophobic resin composites incorporating of BSM could reduce S. mutans adhesion and possibly increase the longevity of resin composite restorations.

In vitro evaluation of multi-walled carbon nanotube reinforced nanofibers composites for dental application

The goal of this study was to evaluate the mechanical properties of an experimental composite resin filled with nylon-6 nanofibers (N6), nylon-6 nanofibers with multi-walled carbon nanotubes (N6-MWCN) or with pre-polymerized resin at different concentrations. The fillers/particles were obtained from nanofibers produced by electrospinning technique or from pre-polymerized composite resin. The fillers were distributed in the composite resin in four different mass fractions (2.5, 5.0, 10.0, and 20.0%), totaling 12 groups. The volumetric polymerization shrinkage (VPS), composite film thickness (CRFT), flexural strength (FS) and elastic (E) modulus of the composite resins were calculated. The data were evaluated using two-way ANOVA and Tukey test (p < .05). The interaction concentration*filler material was statistically significant for the VPS (p = .0008) and for FS (p = .0001). The smallest VPS was observed in 20% concentration without a difference to 10% for N6-MWCN particles. For FS, N6-MWCN in 2.5 and 5.0% presented the highest values (116.4 ± 9.32; 118.5 ± 7.72). Both factors (p = .0001) were significant for CRFT. Higher concentration (20%) showed a higher film thickness. E modulus was similar for all conditions, with p = .0590 for filler material and p = .3987 for concentration. The most indicated composite reinforcement in order to achieve suitable flexural strength with decreased polymerization shrinkage is the use of pre-polymerized composite-based material at a concentration of 20%. N6-MWCNT particles in 2.5 or 5% concentrations should be incorporated to produce a composite resin presenting adequate strength associated with reduced film thickness.

Investigations on the adhesion of new composites for restoring cervical lesions using energy dispersive X-ray analysis and scanning electron microscopy

Restoration of noncarious cervical lesions with resin composites is one of the treatment options, but the retention of the restorations located at the crown-root junction is still a cause of clinical concern. The aim of this study was to evaluate the adhesive properties of three experimental resin composites and two commercial materials used to restore cavities prepared on extracted teeth as well as to determine the relative elemental composition of these materials. We tested the null hypothesis, which considered that the adhesive behaviours of different resin composites did not differ. The microleakage test using tracers showed that all tested materials exhibited some degree of dentinal microleakage, although they all had good dentinal adhesion. The results failed to reject the null hypothesis. The scanning electron microscopy revealed completely adapted adhesive interfaces underneath the restorations along with well-developed hybrid layers depending on the adhesive system. Energy dispersive X-ray analysis analyses showed that the restorative materials have similar chemical compositions, with some differences between the samples from the same material. The results support the implementation of experimental resins in clinical settings.

Evaluation of the Degree of Conversion, Residual Monomers and Mechanical Properties of Some Light-Cured Dental Resin Composites.

The novelty of this study consists in the formulation and characterization of three experimental dental composites (PM, P14M, P2S) for cervical dental lesion restoration compared to the commercial composites Enamel plus HRi® - En (Micerium S.p.A, Avengo, Ge, Italy), G-ænial Anterior® - Ge, (GC Europe N.V., Leuven, Belgium), Charisma® - Ch (Heraeus Kulzer, Berkshire, UK). The physio-chemical properties were studied, like the degree of conversion and the residual monomers in cured samples using FTIR-ATR (attenuated total reflectance) and HPLC-UV (ultraviolet detection), as well as the evaluation of the mechanical properties of the materials. The null hypothesis was that there would be no differences between experimental and commercial resin composites regarding the evaluated parameters. Statistical analysis revealed that water and saliva storage induced significant modifications of all mechanical parameters after three months for all tested materials, except for a few comparisons for each type of material. Storage medium seemed not to alter the values of mechanical parameters in comparison with the initial ones for: diametral tensile strength (DTS-saliva for Ge and PM, compressive strength (CS)-water for Ch, DTS-water and Young’s modulus YM-saliva for P14M and YM-water/ saliva for P2S (p > 0.05). Two of the experimental materials showed less than 1% residual monomers, which sustains good polymerization efficiency. Experimental resin composites have good mechanical properties, which makes them recommendable for the successful use in load-bearing surfaces of posterior teeth.

The effect of excitation laser power in Raman spectroscopic measurements of the degree of conversion of resin composites

ObjectivesTo evaluate the effect of excitation laser power in Raman spectrometry by comparing the spectra and the degree of conversion (DC) values obtained using excitation powers between 300 and 1000mW. MethodsFive commercial and three experimental resin composites were light cured at 1200mW/cm2 for 10–20s from a commercial blue-violet LED dental curing unit. Raman spectra were collected from composite specimens within 9min after light-curing. The excitation laser (1064nm) was focused on the spot of 0.4mm in diameter. The following powers were used for specimen excitation (mW): 300, 400, 600, 800, and 1000. From Raman spectra, the DC values were calculated and compared among different laser powers. Also, vector-normalized Raman spectra collected using the lowest excitation power (300mW) were compared to those collected using the maximum excitation power (1000mW). ResultsVarying the excitation laser power between 300 and 1000mW resulted in statistically significant differences in both the DC values and the intensity of particular spectral features. The effect of varying laser power on Raman spectra and obtained DC values was material-dependent. The DC values measured within an individual material using different laser powers varied between 3.2 and 7.2% (absolute DC difference). The spectral bands affected by variations in laser power were assigned to symmetric and asymmetric stretching of −CH2 (2900-3100cm−1), symmetric stretching of aliphatic CC (1640cm−1) and scissoring of C–H (1458cm−1). SignificanceThe DC can be artificially elevated through increasing excitation laser power. This effect should be considered in Raman spectroscopic evaluations of DC in specimens during ongoing post-cure polymerization.

Synthesis of Bis-GMA and UDMA Nanofibers for Reinforcing Experimental resin-composites: Influence on Degree of Conversion, Depth of Cure, Flexural Strength, Flexural Modulus and Fracture Toughness

Objectives: To study the degree of conversion, depth of cure, flexural strength, flexural modulus and fracture toughness of experimental resin-composites reinforced with Bis-GMA and UDMA nanofibers synthesized by electrospinning technique.Materials and methods: Bis-GMA (Bis-GMA+TEGDMA+PEGDMA) and UDMA (UDMA+PEGDMA) nanofibers were synthesized by wet electrospinning technique and characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). After ball-milling to a nanoscale size (< 100 nm) in a ball-milling machine (Retsch – PM 400, Haan, Germany), these nanofibers were added to a prepared experimental resin-composite. According to the percent and type of added nanofibers, this study was divided into eight groups (n=10/group): one control group, three groups reinforced with 7, 11 and 15 wt% Bis-GMA nanofibers and four groups reinforced with 7, 11, 15 and 20 wt% UDMA nanofibers. For each of these groups, the degree of conversion (DC), depth of cure (DoC), flexural strength (FS), flexural modulus (Ef) and fracture toughness (FT) were studied. DC was studied using the FTIR method (FTIR, Model: EQUINO X55, Bruker, Germany). DoC was measured according to ISO 4049: 2009a. FS testing (and Ef calculation) was carried out according to ISO 4049:2009 by a three-point bending test. FT testing was conducted according to ISO/FDIS 6872:2007. Data were collected and submitted to One-way ANOVA and post-hoc Tukey test with the significance level set at (p ≤ 0.05).Results: Pure forms of Bis-GMA (70-100 nm) and UDMA (50-100 nm) nanofibers were confirmed by SEM and FTIR. One-way ANOVA revealed significant differences for flexural strength (p = 0.001), flexural modulus (p = 0.001) and fracture toughness (p = 0.001) but not for neither degree of conversion (p = 0.078) nor depth of cure (p = 0.879). For both types of nanofibers, compared to the control group, reinforced groups showed greater FS and FT and comparable DC and DoC results. For Ef, except the group reinforced with 7 wt% Bis-GMA,all groups exhibited lower values than that of the control group. Within the range of studied properties, Bis-GMA nanofibers exhibited more favourable results than UDMA nanofibers.Conclusions: Synthesis if Bis-GMA and UDMA nanofibers could be successfully accomplished by electrospinning to be used for resin-composite reinforcement. At a certain ratio (7 wt%), these fibers recorded improvement in FS and FT while keeping Ef, DC and DoC unchanged.

Reinforcement of dental resin composite via zirconium hydroxide coating and phosphate ester monomer conditioning of nano-zirconia fillers

ObjectivesThe present study aimed to evaluate effects of conditioning with the phosphate ester monomer 10-methacryloyloxydecyl dihydrogen phosphate (MDP), with and without precoating with zirconium hydroxide for nano-size zirconia fillers, on mechanical properties of dental resin composites. Materials and methodsNano-zirconia fillers coated with or without zirconium hydroxide [Zr(OH)4] were prepared. Transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to observe the coating and to characterize Zr(OH)4 coating on the zirconia filler surface. Zirconia fillers with or without Zr(OH)4 coating were conditioned with MDP and were subsequently used to prepare experimental resin composites. XPS was used to analyze the Zr-O-P bonds on the filler surface after MDP conditioning. Moreover, three-point bending strength and elastic modulus of prepared resin composites were measured, and Weibull analysis was performed. Resin composites without addition of zirconia fillers and the ones with addition of untreated or silane conditioned-zirconia fillers were set as controls. Cell counting kit (CCK)-8 was used to test cell cytotoxicity of these zirconia fillers-containing experimental resin composites. ResultsNano-zirconia fillers were coated with Zr(OH)4 through chemical deposition. FTIR and XPS analysis confirmed the increase of hydroxyl groups after Zr(OH)4 coating. XPS detected the highest contents of Zr-O-P bonds on MDP-conditioned zirconia fillers with pre-Zr(OH)4 coating, followed by MDP-conditioned zirconia fillers. Resin composite with added MDP-conditioned zirconia fillers with and without Zr(OH)4 coating exhibited greater three-point bending strength, elastic modulus values, and Weibull moduli. According to the cytotoxicity classification, resin composites containing experimental zirconia fillers were considered to have no significant cell cytotoxicity. ConclusionNano-zirconia fillers conditioned with MDP, with or without precoating with Zr(OH)4, improve the mechanical properties of resin composites, and are potentially safe for clinical use.

The Effects of Colored Pigments on the Translucency of Experimental Dental Resin Composites.

Colored pigments are incorporated into dental resin composites to produce clinically acceptable shades for restorative materials but studies on their effects on translucency are rare. The aim of this study was to examine the effects of the addition of different colored pigments on the translucency of experimental dental resin composites. 12 types of experimental dental resin composites containing different concentrations of red and yellow iron oxide pigments were formulated and light-cured. Total and diffuse translucency as well as CIE L*a*b* values were measured and the color differences were calculated. There was a statistically significant difference in the translucency values between the composites with no pigments and the composites with increasing concentrations of the pigments (p<0.05). The translucency decreased as the concentration of the pigments increased. However at pigment concentrations greater than 0.02%, the translucency of the composites reached a plateau and ceased to be influenced by the addition of the pigments (p⟨0.05). All color differences were in the range of 3.62-16.00 ΔE*ab unit. The pigments used in this study can influence the translucency of the experimental resin composites and should be considered as an important factor by clinicians to achieve optimal esthetic restorative outcome.

The effect of adding a new monomer “Phene” on the polymerization shrinkage reduction of a dental resin composite

ObjectiveA new photocurable monomer, “Phene” (N-methyl-bis(ethyl-carbamate-isoproply-α-methylstyryl)amine) was synthesized and incorporated into Bis-GMA/TEGDMA with the aim of reducing polymerization shrinkage swithout detriment to the physical properties and wearing of the resin composites. MethodsPhene was synthesized through a 2-step reaction route, and its structure was confirmed by FT-IR and 1H-NMR spectra. Phene was incorporated into Bis-GMA/TEGDMA (50/50, wt/wt) with a series of mass fraction (from 0 wt% to 40 wt%). Experimental resin composites were prepared by mixing 29 wt% of resin matrix to 71 wt% of particulate-fillers. Degree of conversion (DC) was determined by FT-IR analysis. The volumetric shrinkage (VS) was calculated as a buoyancy change in distilled water by means of the Archimedes principle. Polymerization shrinkage-stress (SS) was measured using the tensilometer technique. The flexural strength (FS), modulus (FM), and fracture toughness (FT) were measured using a three-point bending setup. A wear test was conducted with 15000 cycles using a dual-axis chewing simulator. Wear depth was measured by a three-dimensional (3D) non-contact optical-profilometer. ResultsANOVA analysis showed that when mass fraction of Phene in resin matrix was more than 10 wt%, the obtained resin composite formulation had lower DC, VS and SS than control resin composite (p < 0.05). In general, the experimental resin composites had comparable FS and FM (p > 0.05) when the mass fraction of Phene in resin matrix was not more than 20 wt %. Resin composite with 20 wt% Phene had the lowest wear depth and fracture toughness values. SignificanceThe overall tested properties prove that including Phene up to 20 wt% into Bis-GMA/TEGDMA resin could be potentially useful in the formulation of low-shrinkage resin composites.

Efficacy of Yttrium (III) Fluoride Nanoparticles in Orthodontic Bonding.

Our study evaluated the adhesion strength and antibacterial effect of a conventional orthodontic composite resin blended with yttrium fluoride (YF₃) nanoparticles. Yttrium fluoride nanoparticles (NP) were added to the conventional orthodontic composite resin (Transbond XT) at concentrations of 1%, 2%, and 3% (w/w), and the blended composite resins were labeled as NP1, NP2, and NP3, respectively. A total of 60 extracted human premolars was randomly allocated to four groups of 15 samples (n = 15). Orthodontic brackets were bonded using the conventional (control) and experimental composite resins (NP1, NP2, and NP3). The adhesion strengths of the composite resins were determined using a universal testing machine. The debonding sites were assessed and scored using the adhesive remnant index (ARI). The antibacterial effect of YF₃ nanoparticles against Streptococcus mutans was assessed by the viable cell counting method. For the same, 40 composite disc specimens were prepared using the control and experimental composite resins (n = 10). The data was analyzed by one-way ANOVA and Tukey's post hoc analysis. In all the tests, the significance level was determined to be 0.05. The highest adhesion strength values were found in the control group (11.61±0.23) and the lowest values were found in the NP3 group (10.49±0.17). A significant difference was observed between the control and experimental groups, NP2 and NP3 (P < 0.05). NP1 group showed insignificant (P = 0.388) adhesion strength values compared with the control group. There was no significant difference between the ARI scores of the conventional and experimental groups (P > 0.05). The highest colony forming units (CFU) were found in the control group (75.85±1.15) and the lowest CFU were found in the NP1 group (2.24±1.14). A significant difference between the mean CFU of the conventional and experimental composite groups was observed (P < 0.05). Despite higher antibacterial activity in the NP1 group compared with NP2 (P = 0.146) and NP3 (P = 0.117), the difference was not significant. Similarly, no significant difference was observed between NP2 and NP3 groups (P = 0.97). Our results suggested that yttrium fluoride nanoparticles, blended with a conventional resin at 1% concentration, demonstrated significant antibacterial effect and did not compromise adhesion strength.

Reinforcing experimental resin-composites with synthesized zirconia and alumina nanofibers: evaluation of cuspal flexure, flexural strength, flexural modulus and fracture toughness

Aim: This study evaluated cuspal flexure, flexural strength, flexural modulus and fracture toughness of experimental resin-composites reinforced with zirconia and alumina nanofibers. Zirconia and alumina nanofibers were synthesized by wet electrospinning technique. Characterization of these nanofibers was carried out by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy that confirmed pure forms of zirconia nanofibers (50–100 nm in diameter) and alumina nanofibers (70–100 nm in diameter). Materials and methods: The study was divided into seven groups (n = 10/group) according to the type and percentage of added nanofibers: control group, three groups reinforced with 2, 4 and 6 wt% zirconia nanofibers and more three groups reinforced with 2, 4 and 6 wt% alumina nanofibers. Results: A one-way analysis of variance revealed significant differences between the studied groups (P = 0.000) for all investigated properties. Mean cuspal flexure ranged between 0.13 and 0.36% with markedly lower values for groups with higher percentages of nanofibers. For flexural strength, data ranged between 98 and 168 MPa, for flexural modulus between 7.6 and 17.04 GPa, and for fracture toughness between 1.16 and 3.51 MPa m1/2 with greater values recorded for nanofibers-reinforced groups. Conclusion: Zirconia nanofibers were superior to alumina nanofibers in reducing cuspal flexure and improving the studied mechanical properties.

Effect of Nanotitanium Dioxide Fillers Addition on yhe Compressive Strength of Experimental Composite Rein Core Material

Purpose: The objective of this study was to prepare an experimental dental composite resin core material loaded with prepared nanotitanium dioxide fillers and to evaluate the compressive strength of the experimentally prepared composite materials Materials and methods: prepared nanotitanium dioxidefillers, commercial nanosilica were used as a filler added to the experimentally prepared resin matrix and commercially available resin core material Nexcomp was used as a control. Preparation and characterization of a nanotitanium dioxide fillers through the following techniques: X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy analysis, Scanning electron microscopic (SEM) analysis, EDX analysis,Transmission electron microscopy (TEM) analysis, and Thermal gravimetric analysis (TGA). then added to the prepared resin matrix BisGMA: TEDGMA(70%:30%) mixed with 0.5 wt% camphorquinone and 0.5 wt% ethyldimethyl amine. Testing of compressive strength was done. Results: revealed that there was no significant difference in the compressive strength between the experimental and Nexcomp core composite. Conclusions: It was concluded that experimental core composite showed a comparable mechanical properties to a commercial nanocomposite core resin regarding Compressive strength