Experimental Resin-based Composites Research Articles

Isolated effect of filler particle size on surface properties of experimental resin composites before and after toothbrush abrasion.

This study aimed to isolate the relationship between filler size and the surface properties of roughness and gloss before and after toothbrush abrasion for experimental resin-based composites (RBCs) containing uniform spherical fillers. Five experimental light-cured RBCs with different spherical filler sizes and three commercial RBCs were studied. Forty specimens were polished using silicon carbide papers. Gloss was measured after 0, 90, 180, and 360 min of simulated toothbrushing, and surface roughness was measured before and after 360 min of toothbrushing. Two-way ANOVA/Tukey's multiple comparison tests were used to compare the RBCs, and the correlation between particle size and surface roughness or gloss was also determined. After polishing and toothbrushing, RBCs with smaller fillers exhibited significantly higher gloss and lower surface roughness, and RBCs with larger fillers exhibited lower gloss and higher surface roughness. A significant correlation was found between filler particle size and gloss and surface roughness both before and after toothbrush abrasion. Gloss of RBCs containing fillers with larger particle sizes was significantly reduced. After toothbrushing abrasion, the surface roughness increased for all RBCs, except those containing the finest-sized fillers. The particle size of the filler is a critical determinant of the surface roughness and gloss of RBCs, after polishing and after toothbrushing. Increased surface roughness caused by toothbrush abrasion reduces the gloss of resin-based composites. Resin-based composites containing finer fillers best maintain glossiness after routine tooth brushing.

Physicochemical properties of experimental resin-based composites using tris(trimethylsilyl)silane associated with diphenyl iodonium hexafluorophosphate (DPIHP) salt

The purpose was to evaluate the effect of tris(trimethylsilyl)silane (TTMSS) associated with diphenyl iodonium hexafluorophosphate (DPIHP) on the polymerization shrinkage stress (PSS), mechanical properties, color change (CC), and degree of conversion (DC) of resin-based composites (RBCs). Experimental RBCs containing 35 wt% of organic matrix (10.2 wt% BisGMA, 11.1 wt% BisEMA10 and UDMA and 2.1 wt% TEGDMA) and 65 wt% filler (13 wt% fumed silica and 52 wt% BaBSiO2) were assigned to six groups: control (0.2 wt% CQ, 0.5 wt% DMAEMA); TD05 (0.2 wt% CQ, 0.5 wt% TTMSS, 0.5 wt% DPIHP); TD10 (0.2 wt% CQ, 1 wt% TTMSS, 0.5 wt% DPIHP); DTD (0.2 wt% CQ, 0.25 wt% of DMAEMA, 0.25 wt% TTMSS, 0.5 wt% DPIHP); DT (0.2 wt% CQ, 0.25 wt% DMAEMA, 0.25 wt% TTMSS); and T05 (0.2 wt% CQ, 0.25 wt% TTMSS). The experimental formulations were submitted to the following tests: DC; PSS; CC; rate of polymerization (Rp); depth of cure by Knoop hardness; flexural strength; and flexural modulus. TTMSS showed no effect on the DC, Rp, and mechanical properties of the RBCs. DMAEMA reacted with TTMSS and reduced the Rp; the RBCs containing no DMAEMA showed no reduction in CC. DT showed the lowest PSS mean value among the groups. TTMSS differed from DMAEMA only when used in combination with DPIHP, which significantly improved the DC, maximum Rp, and mechanical properties of the RBCs tested. Based on the artificial ageing results, TTMSS was ineffective in reducing CC in the RBCs tested.

Preparation and Assessment of Antimicrobial Property of Resin Based Composites Impregnated with Proanthocyanidin and Titanium Dioxide

OBJECTIVE: To synthesize three experimental resin based composites (RBCs) out of a commercial preperation (Control) by impregnating into each a fixed weight (0.01%) of titanium dioxide (TiO2) and three different weight % (0.01, 0.02 and 0.03) of proanthocyanidin (PA) and to compare antibacterial property, from the zones of inhibition of streptococcus mutans (S. mutans), of the specimen restorations made in the experimental and control RBCs. METHODOLOGY: In the first phase, Streptococcus mutans were isolated and identified from the oral cavity of patients and identified on the basis of morphogenic appearance of colonies and confirmed through catalase test and microscopic examination. Isolates were then incubated and cultured for sensitivity. Specimens for control and experimental RBCs were made through a metallic mold having 2mm thickness and 5mm diameter for all the 4 groups. Specimen restorations made in the commercial as supplied RBC acted as the control (Group A). Specimen restorations in the Group B, C, and D were made in each of the experimental RBCs modified with 0.01% proanthocyanidin (PA) and 0.01% titanium dioxide (TiO2), 0.02% PA and 0.01% TiO2 and 0.03% PA and 0.01% TiO2. The antimicrobial property of all the specimen restorations in all the groups was evaluated by Bauer-Kirby (Disc Diffusion) method through the formation of zones of inhibition of S. mutans colonies on blood agar plates. Data were computed using SPSS version 21 for descriptive statistics and analyzed using one-way ANOVA with p value 0.05 taken as significant. RESULTS: The range of the zone of inhibition for specimen RBC restorations (N= 12) containing PA and TiO2 was 0.00 for Group A, 10-12mm for Group B, 12-14mm for Group C and 9-10mm for Group D. The mean inhibition zone for the experimental restoration specimens was 11±2mm for Group B, 12.7±1mm for Group C and 9.7±1mm for Group D compared to no inhibition zones (0.00 mm) with the control RBC Group A. The order of the inhibition zones from maximum to minimum was Group C > Group B > Group D > Group A. The differences between the mean values for the control and the experimental RBC restoration specimens were significant (p < 0.000). The specimen restorations in the Group D appeared under cured and could impact on their mechanical properties. CONCLUSION: Irrespective of the mentioned concentrations, impregnating PA and TiO2 rendered the RBC antimicrobial. RBC restorations made with the experimental RBC with 0.02% PA and 0.01% TiO2 proved relatively more effective in terms of antimicrobial effect. KEY WORDS: dental materials, resin based dental restorations, antibacterial resin based composite, proanthocyanidin, titanium dioxide.

Synthesis and characterization of graphene oxide-zirconia (GO-ZrO2) and hydroxyapatite-zirconia (HA-ZrO2) nano-fillers for resin-based composites for load-bearing applications

ObjectivesThe study aims to synthesize two different types of nano-fillers based on zirconia (ZrO2), which was functionalized with graphene oxide (GO-ZrO2), and hydroxyapatite (HA-ZrO2), and to implement them in an experimental methacrylate matrix containing new dimethacrylic oligomers. MethodsNano-particles were synthesized via a modified Hummer’s method and a sol-gel route. Bisphenol A-glycidyl methacrylate oligomers (Bis-GMA336[0–1]) were synthesized from an epoxy resin that reacted with methacrylic acid in the presence of a basic catalyst. Traditional dental glass-fillers (Barium oxide/BaO and Barium fluoride/BaF2) were synthesized to create an experimental resin-based composite (RBC) used as reference. Filler morphology was evaluated via Transmission Electron Microscopy. RBCs were characterised by real-time Fourier transform infrared spectroscopy (degree of cure/DC, polymerisation kinetics), real-time spectrometry (light transmittance), 3-point bending test (flexural strength and modulus, Weibull parameters), and depth-sensing indentation test (plastic and elastic deformation parameters). ResultsThe synthesized nanohybrid fillers proved good dispersing performance. Mechanical properties and materials’ reliability are within or above the mean values reported in the literature for RBCs. Addition of HA-ZrO2-fillers resulted in a decrease light transmission, DC and mechanical properties. Except for the HA-ZrO2 RBC, materials showed a high resistance to softening in solvent. ConclusionsThe synthesis of GO-ZrO2 and HA-ZrO2 nanohybrid particles and their implementation in experimental RBCs has proven successful. Adjustments of the light transmission through suitable co-fillers in addition to GO-ZrO2 as well as adjustments of the amount of HA-ZrO2 are necessary to enable reduced curing time (<20 s). Clinical significanceThe addition of nanofillers with tailor-made properties can help improving the performance of modern restoratives.

Effect of Bioactive Composites on Microhardness of Enamel Exposed to Carious Challenge.

This study verified if experimental composites containing calcium phosphate nanoparticles exert a protective effect against enamel demineralization. Three experimental resin-based composites containing 60 vol% of fillers were manipulated. Filler phase was constituted by silanized barium glass and 0%, 10% or 20% (by volume) of dicalcium phosphate dihydrate (DPCD) nanoparticles functionalized with the monomer triethylene glycol dimethacrylate (TEGDMA). Cavities (10 x 2 x 2 mm) were prepared in bovine enamel and restored using one of the experimental materials (n=10). Specimens were exposed to pH cycling (demineralizing solution: pH 5.0/4h, remineralizing solution: pH 7.0/20h, 14 days). Enamel Knoop microhardness (100g/10s) was measured on the surface (SH) and after transversal sectioning up to 90 μm depth (cross-sectional microhardness, CSH). Microhardness values and the percent of microhardness loss were analyzed ANOVA/Tukey test and Student's paired t-test (alpha: 5%). The materials did not differ in respect to SH. Enamel adjacent to DCPD-containing composite restorations showed smaller reductions in CSH (-1.2% to -3.5%) than the enamel from control group (-12.5%), while CSH of enamel restored with resin-modified glass ionomer was similar to the other groups (-4.5%). DCPD-containing composites reduced enamel demineralization in comparison to a conventional composite.

Effect of fiber incorporation on the contraction stress of composite materials.

This study aimed to assess the effects of fiber incorporation on the contraction stress (CS), time to gelation (TG), and temperature rise (TR) features of two experimental resin-based composites (RBCs) in comparison to those of bulk-fill RBCs and conventional RBCs in simulated, clinically relevant cavities. CS over 300s, TG and TR were assessed by a stress-strain analyzer (SSA T80) in two cavity configurations (2 × 4 × 4mm3/4 × 4 × 4mm3/configuration value [Formula: see text] and [Formula: see text]) for two experimental RBCs, eight bulk-fill RBCs (EverX Posterior, Filtek Bulk Fill, SDR, SonicFill, Tetric EvoCeram Bulk Fill, Venus Bulk Fill, X-tra base, and X-tra Fill) and one RBC (Filtek Supreme XTE) by light curing (1200mW/cm2) (n = 10). The experimental materials used were based on EverX Posterior with modifications made to the fiber and filler content. Statistical analyses were performed via ANOVA; multiple pair-wise comparisons were performed via Tukey's test, and homogeneous subsets were identified ("multcomp" package, R). CS values ranged from 1.00 to 4.07MPa (2 × 4 × 4mm3) and from 0.97 to 2.49MPa (4 × 4 × 4mm3); TG values ranged from 1.31 to 4.05s (2 × 4 × 4mm3) and from 1.39 to 3.84s (4 × 4 × 4mm3). SDR values showed lowest stress values in both cavity configurations. The experimental composite with fibers presented significantly higher stress values than did the experimental composite without fibers. Bulk-fill RBCs showed lower levels of stress than did conventional RBCs. The incorporation of fibers had no positive impact on the CS and TG. Appropriate material selection may be essential to clinical success because certain RBCs exhibit higher CS, TG, and TR values.

Streptococcus mutans biofilm formation and release of fluoride from experimental resin-based composites depending on surface treatment and S-PRG filler particle fraction

To evaluate fluoride release and biofilm formation on resin-based composites (RBCs) including surface pre-reacted glass ionomer (S-PRG) filler particles. Specimens were prepared from experimental RBCs including different fractions of S-PRG fillers (0/10/30/50/70% w/v). RBCs were light cured against mylar strips (MYL), and 50% of the specimens were additionally polished to a high gloss (POL). Surface roughness (SR), surface free energy (SFE) and fluoride release were determined. Streptococcus mutans biofilm formation (SMBF) was simulated for 48 h and 120 h; adherent viable biomass was assessed using an MTT-based assay. The highest SR was identified for POL specimens manufactured from the RBC with a filler fraction of 70%. For all specimens and surface treatments, polishing caused an increase in surface free energy. For both MYL and POL specimens, increasing the filler fraction coincided with an increased release of fluoride; a higher release of fluoride was identified for POL specimens with filler fractions of 50% and 70% in comparison to their MYL counterparts. Release of fluoride was lower after 120 h than after 48 h. No differences in SMBF were identified between MYL and POL specimens with identical filler fractions after 48 h of biofilm formation; with increasing filler fractions, a tendency towards decreasing SMBF was observed. After 120 h, less SMBF was identified for POL specimens with filler fractions of 30%, 50% and 70% in comparison to corresponding MYL specimens. The inclusion of S-PRG fillers and an effective surface treatment may reduce biofilm formation on RBCs.

Effects of a low-shrinkage methacrylate monomer and monoacylphosphine oxide photoinitiator on curing efficiency and mechanical properties of experimental resin-based composites.

This study investigated the degree of conversion, depth of cure, Vickers hardness, flexural strength, flexural modulus and volumetric shrinkage of experimental composite containing a low shrinkage monomer FIT-852 (FIT; Esstech Inc.) and photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO; Sigma Aldrich) compared to conventional composite containing Bisphenol A-glycidyl methacrylate (BisGMA) and camphorquinone-amine photoinitiator system. The degree of conversion was generally higher in FIT-based composites (45-64% range) than in BisGMA-based composites (34-58% range). Vickers hardness, flexural strength and modulus were higher in BisGMA-based composites. A polywave light-curing unit was generally more efficient in terms of conversion and hardness of experimental composites than a monowave unit. FIT-based composite containing TPO showed the depth of cure below 2mm irrespective of the curing light. The depth of cure of FIT-based composite containing CQ and BisGMA-based composites with either photoinitiator was in the range of 2.8-3.0mm. Volumetric shrinkage of FIT-based composite (0.9-5.7% range) was lower than that of BisGMA-based composite (2.2-12% range). FIT may be used as a shrinkage reducing monomer compatible with the conventional CQ-amine system as well as the alternative TPO photoinitiator. However, the depth of cure of FIT_TPO composite requires boosting to achieve clinically recommended thickness of 2mm.

Influence of matrix and filler fraction on biofilm formation on the surface of experimental resin-based composites.

The aim of this study was to investigate the impact of resin matrix chemistry and filler fraction on biofilm formation on the surface of experimental resin-based composites (RBCs). Specimens were prepared from eight experimental RBC formulations differing in resin matrix blend (BisGMA/TEGDMA in a 7:3 wt% ratio or UDMA/aliphatic dimethacrylate in a 1:1 wt% ratio) and filler fraction (no fillers; 65 wt% dental glass with an average diameter of 7 or 0.7 µm or 65 wt% SiO2 with an average diameter of 20 nm). Surface roughness, surface free energy, and chemical surface composition were determined; surface topography was visualized using atomic force microscopy. Biofilm formation was simulated under continuous flow conditions for a 48 h period using a monospecies Streptococcus mutans and a multispecies biofilm model. In the monospecies biofilm model, the impact of the filler fraction overruled the influence of the resin matrix, indicating lowest biofilm formation on RBCs with nano-scaled filler particles and those manufactured from the neat resin blends. The multispecies model suggested a more pronounced effect of the resin matrix blend, as significantly higher biofilm formation was identified on RBCs with a UDMA/dimethacrylate matrix blend than on those including a BisGMA/TEGDMA matrix blend but analogous filler fractions. Although significant differences in surface properties between the various materials were identified, correlations between the surface properties and biofilm formation were poor, which highlights the relevance of surface topography and chemistry. These results may help to tailor novel RBC formulations which feature reduced biofilm formation on their surface.

Performance of the experimental resins and dental nanocomposites at varying deformation rates

The aim of the present study was to evaluate the bi-axial flexural strength of experimental unfilled resins and resin-based composites at varying deformation rates following 1-week dry, 1-week wet, and 13-week wet storage regimes. A total of 270 disc-shaped specimens (12mm diameter, 1mm thickness) of either unfilled resins or experimental resin-based composites comprising of three groups (n=90) were fabricated. Three groups of each unfilled resin and resin-based composites (n=90) were stored for 1week under dry conditions, and at 1 and 13weeks under wet conditions (37±1°C) before testing. The bi-axial flexural strength of each unfilled resin and resin-based composites group was determined at a 0.1, 1, and 10mm/min deformation rate (n=30). The unfilled resins revealed a deformation rate dependence following all storage regimes; however, the addition of fillers in the unfilled resins modified such reliance following the 1-week dry and 13-week wet storage regimes. In contrast, a lower bi-axial flexural strength of the 1-week wet resin-based composites specimens at a 0.1mm/min deformation rate was identified. A lower bi-axial flexural strength of the 1-week wet resin-based composites specimens at a low deformation rate suggests that premature failure of resin-based composites restorations might occur in patients with parafunctional habits, such as bruxism.

The in vitro wear behavior of experimental resin-based composites derived from a commercial formulation

ObjectiveTo investigate the short- and long-term in vitro wear resistance of experimental resin-based composites (RBCs) derived from a commercial formulation. MethodsSix experimental RBCs were manufactured by manipulating the monomeric resin composition and the filler characteristics of Grandio (Voco GmbH, Cuxhaven, Germany). The Oregon Health Sciences University (OHSU) oral wear simulator was used in the presence of a food-like slurry to simulate three-body abrasion and attrition wear for 50,000, 150,000 and 300,000 cycles. A three-dimensional image of each wear facet was created and the total volumetric wear (mm3) and maximum wear depth (μm) were quantified for the RBC and antagonist. Statistical analyses of the total volumetric wear and maximum wear depth data (two- and one-way analyses of variance (ANOVA), with Tukey's post hoc tests where required) and regression analyses, were conducted at p=0.05. ResultsTwo-way ANOVAs identified a significant effect of RBC material×wear cycles, RBC material and wear cycles (all p<0.0001). Regression analyses showed significant increases in the total volumetric wear (p≤0.001) and maximum wear depth data (p≤0.004) for all RBCs with increasing wear cycles. SignificanceDifferences between all RBC materials were evident after ≥150,000 wear cycles and antagonist wear provided valuable information to support the experimental findings. Wear simulating machines can provide an indication of the clinical performance but clinical performance is multi-factorial and wear is only a single facet. Employing experimental RBCs provided by a dental manufacturer rather than using self-manufactured RBCs or dental products provides increased experimental control by limiting the variables involved.

The influence of monomeric resin and filler characteristics on the performance of experimental resin-based composites (RBCs) derived from a commercial formulation

ObjectiveTo explore experimental RBCs derived from a successful commercially available RBC (Grandio) to investigate resin monomer blend and filler parameters (volume fraction, density and diameter) on RBC performance. MethodSix experimental RBCs modified from a commercial RBC were tested. The three-point flexure strength (σ3) and modulus (E) data was determined for groups of 20bar-shaped specimens, prepared in a custom-made knife-edge split aluminum mold and irradiated using a modification of the ISO 4049 protocol. The biaxial flexure strength (BFS) and top and bottom Vickers hardness number (VHN) determination was performed on disc-shaped specimens (n=20). Normal distribution of the σ3, E, BFS and top and bottom VHN data was verified using the Shapiro–Wilk's test. Paired groups were compared using independent samples t-test for the individual tests investigated (σ3, E, BFS and top and bottom VHN) at a significance level of P<0.05. ResultsA significant decrease in the mean σ3 (P<0.011) and mean E (P<0.001) were identified on increasing the filler fraction (from 71.4 to 74.5vol%) or increasing the mean filler diameter (from 1.5 to 2.5μm). Increasing the filler density resulted in a significant increase in the mean σ3 (P<0.001), mean E (P<0.001) and mean top VHN (P≤0.001). Replacing the monomeric blend with an ormocer blend significantly reduced the mean σ3, E, BFS and top and bottom VHNs (all P<0.001). SignificanceFor each RBC monomeric resin and filler (type, density and diameter) combination employed, a finite filler volume fraction exists. Operating at the finite filler volume fraction increases the difficulty in improving the mechanical properties of the RBCs tailored from a commercial product.