Refractive indices of unfilled resin mixtures and cured composites related to color and translucency of conventional and low-shrinkage composites

Bis-EMA/Bis-GMA ratio effects on resin-properties and impregnated fiber-bundles

OBJECTIVES

To evaluate the effect of different ratios of Bis-EMA/Bis-GMA resin mixtures on the inherent viscosity and curing-related properties: including degree of cure (DC%), shrinkage strain, Knoop micro-hardness (KH) and flexural strength of resin-impregnated fiber-bundles.

METHODS

Bis-EMA/Bis-GMA monomers were mixed (by weight) in the following ratios: M1 = 30 %/70 %, M2 = 50 %/50 %, M3 = 70 %/30 %, and M4 = 100 %/0 %. Standard measurements were made of refractive index, viscosity, degree of conversion, shrinkage strain and Knoop hardness (KHN). For 60 % glass fiber-bundles impregnated with 40 % resin, three-point bending test for flexural strength and shrinkage strain were measured. Data were analyzed by One-way ANOVA and Bonferroni post-hoc tests (α = 0.05).

RESULTS

For resin mixtures, increasing Bis-EMA proportion decreased refractive index (p < 0.05), and viscosity (p < 0.05), and increased monomer conversion (DC%), shrinkage strain and KHN (p < 0.05). DC% increased after 1 h for all resin mixtures. The shrinkage strain and flexural strength of resin-impregnated fiber-bundles reduced with increased Bis-EMA.

SIGNIFICANCE

Monomeric mixtures with highest amounts of Bis-EMA showed enhancement in several clinically-relevant properties and polymerization of respective resin-impregnated glass fibers. This makes them potential candidates for impregnating glass fibers in fiber-reinforced restorations.

Effect of aging and fiber-reinforcement on color stability, translucency, and microhardness of single-shade resin composites versus multi-shade resin composite

OBJECTIVE

The purpose of this study was to evaluate the effect of aging and fiber-reinforcement on the color stability, translucency, and microhardness of single-shade resin composites versus multi-shade resin composite.

MATERIALS AND METHODS

Four resin composites (Filtek Z250, Omnichroma, Vittra APS Unique, Zenchroma) were tested. Three subgroups of specimens were prepared for each of the composites: control, polyethylene fiber-reinforcement, and glass fiber-reinforcement- groups (n = 10/per group). The samples were subjected to aging for 10,000 thermal cycles. Color differences (ΔE00 ) were calculated after aging. Relative translucency parameter (RTP00 ) and microhardness values were calculated before and after aging. A two-way analysis of variance and the generalized linear model was used (p < 0.05).

RESULTS

The lowest and highest ΔE00 values were found for Filtek Z250 (0.6 ± 0.2) and Omnichroma resin composites (1.6 ± 0.4), respectively. The ΔE00 value of the polyethylene fiber-reinforcement group (1.2 ± 0.6) was significantly higher than the ΔE00 value of the glass fiber-reinforcement group (1.0 ± 0.4, p < 0.001). The RTP00 value of the glass fiber-reinforcement group (1.92 ± 0.78) was significantly higher than the RTP00 value of the polyethylene fiber-reinforcement group (1.72 ± 0.77, p < 0.001). The highest microhardness values were found in glass fiber-reinforcement group (76.48 ± 17.07, p < 0.001).

CONCLUSION

Single-shade resin composites were more translucent, had higher color change, and lower hardness than multi-shade resin composite. For relative translucency and microhardness, statistical significance was found in the material and fiber type interaction. The glass fiber-reinforcement provided higher translucency, lower color change and higher microhardness values than polyethylene fiber-reinforcement group after aging. Thermocycling had a significant impact on the color stability, translucency parameter, and microhardness of the tested resin composite materials.

CLINICAL SIGNIFICANCE

Single-shade resin composite materials have greater color-changing potential. The glass fiber-reinforcement optimize resin material mechanical properties and color stability more than polyethylene fiber-reinforcement.

Effects of background color and restoration depth on color adjustment potential of a new single-shade resin composite versus multi-shade resin composites

The objectives of this study was to evaluate the effects of background color and restoration depth on color adjustment potential of a new single-shade resin composite versus multi-shade resin composites. Two multi-shade resin composites (Spectrum TPH3 and Clearfil AP-X) marked A2 shade and a new single-shade resin composite (Charisma Diamond One) were tested. Four base shades (A1, A2, A3, and A3.5) of the same resin composite (Filtek Z250) were selected as different background colors. Dual specimens with 1-, 2-, and 3-mm restoration depth and single specimens of all materials were fabricated. CIE color coordinates were measured using a spectrophotometer, then color differences (∆E00) and translucency parameter (TP00) were calculated using the CIEDE2000 formula. Independent observers performed visual scoring. CAP-I and CAP-V values were calculated according to ΔE00 and visual scoring. The results revealed that CAP-I and CAP-V were significantly affected by resin composite type, background color, and restoration depth. CAP-I and CAP-V decreased as restoration depth increased at the same background color for all materials. Charisma Diamond One had the highest CAP-I and CAP-V values at all background colors and restoration depths, with the highest TP00 value. These findings demonstrated that color adjustment potential was dependent on resin composite type, background color, and restoration depth, so shade selection is indispensable for multi-shade resin composites. Charisma Diamond One exhibited the highest color adjustment potential and the most pronounced color shifting, contributing to simplifying the process of shade selection and improving the efficiency of clinical work.

Instrumental and visual evaluation of the color adjustment potential of different single-shade resin composites to human teeth of various shades

OBJECTIVE

The study aims to evaluate the color adjustment potential (CAP-I, CAP-V) of different single-shade resin composites.

MATERIALS AND METHODS

The shades of 40 human incisors were determined using a spectrophotometer, with the teeth divided into four groups of the same shade (n = 10). The following single-shade resin composites were tested: Omnichroma, Charisma Diamond One, Vittra Unique, and Essentia Universal. The specimens were prepared as "dual" and "single." Standardized cavity preparations (diameter, 7 mm; depth, 2 mm) were prepared in human incisor teeth and then restored for dual specimens. Composite duplicates of human incisors were prepared with resin composites for single specimens (n = 10). The color match of these specimens to that of unrestored human incisors was compared, and the color difference (ΔE*) was calculated. Independent observers conducted a visual evaluation of the specimens and scored them. CAP-I and CAP-V values were determined. A one-way analysis of variance test was used for statistical analysis (p < 0.05).

RESULTS

There was no statistically significant difference between the CAP-V and CAP-I values of the tested single-shade resin composites (p > 0.05). All the materials tested had acceptable color-matching potential.

CONCLUSIONS

In terms of color matching, there were no significant differences between the different tooth shades of all the tested resin composites.

CLINICAL RELEVANCE

Single-shade resin composites have acceptable CAP. The use of single-shade resin composites can reduce in-chair clinical times by minimizing the time spent on shade selection.

Color Assessment of Feldspathic Ceramic with Two Different Thicknesses, Using Multiple Polymeric Cements

The purpose of this study was to evaluate the color changes of feldspathic ceramics CEREC Blocs (Dentsply Sirona, Milford, DE, USA) when cemented with different luting agents, while varying the ceramic thickness. Seventy ceramic discs of feldspathic ceramic (A2 shade) were obtained with 0.5 and 0.8 mm thicknesses. Seventy composite discs (A3 shade) 1 mm in thickness were used as substrates. After being polished and conditioned, the ceramic and composite discs were cemented with different resin cements and a flowable composite: Variolink^® Esthetic Light, Neutral and Warm (Ivoclar Vivadent, Schaan, Liechtenstein); RelyX^TM Veneer B0.5, Translucent and A3 Opaque/yellow shades (3M Oral Care, St. Paul, MN, USA); G-aenial^® Universal Flow A2 (GC Europe, Leuven, Belgium). Color difference (ΔE) was determined using a spectrophotometer. A two-way ANOVA and multiple comparisons were performed using the Bonferroni method with a 95% confidence interval. Variolink^® Neutral showed the highest ΔE (15.12 ± 0.71) and RelyX^TM Veneer A3 the lowest value (1.59 ± 0.33). There are no statistically significant differences between the two ceramic thicknesses for Variolink^® Light (p = 0.230) and RelyX^TM Veneer B0.5 (p = 0.318) cements. The feldspathic ceramic final color is influenced by the cement used and the ceramic thickness. The use of different cements in a thin ceramic has a clinically significant impact on the final esthetic result.

Effects of polishing procedures on optical parameters and surface roughness of composite resins with different viscosities

The aims of this study were to evaluate the optical properties of flowable and injectable composites after polishing, such as translucency (translucency parameter [TP], TP₀₀), opalescence (OP-BW), chroma (C*ab), refractive index (RI), and change in surface roughness (Ra, Rz). Ninety disc-shaped samples were prepared from micro-hybrid, flowable, and injectable composites and divided into 3 groups according to the polishing systems (n=10). The RI was measured with an Abbe refractometer, and optical measurements were performed with a spectrophotometer. The surface roughness was measured with a two-dimensional profilometer. Data were analyzed with the generalized linear model method and two-way analysis of variance. The results showed that the polishing procedure did not significantly impact the RI (p=0.987). Injectable composite had the highest translucency (TP=28.67; TP₀₀=13.49) and opalescence (OP-BW=13.11); showed the lowest C*ab value (17.95). Also, the effects of the composite type and polishing procedure on surface roughness were statistically significant (p=0.047 and p<0.001).

Optical characteristics of experimental dental composite resin materials

OBJECTIVES

To derive the K-M optical coefficients of experimental composites and compare the inherent CIE L*, a* and b* color parameters, translucency parameters and both perceptibility and acceptability thresholds.

METHODS

Experimental composites were prepared with 4 base-monomers: Bis-GMA, UDMA, Bis-EMA and Fit852 with TEGDMA used as a co-monomer and 3 filler:resin fractions (50:50wt%, 60:40wt% and 70:30wt%). The optical absorption (K) and scattering (S) coefficients over the visible spectra were derived. Corrected reflectivity spectra were calculated using the corrected Kubelka-Munk reflectance model and were used to calculate CIE color parameters (X, Y, Z) values. Translucency parameter (TP) was calculated using the CIEDE2000 color difference. A three-way repeated measures ANOVA was used to analyze the CIE L*a* and b* color parameters at infinite thickness. A two-way ANOVA was used to analyze the translucency parameter at 2 mm thickness. Pairwise comparisons were assessed using Bonferroni-corrected Student's t-tests. For all statistical testing α = 0.05 was used. Color parameters (ΔE₀₀) were calculated for every experimental composite using the CIEDE2000 color differences. Perceptibility threshold (PT), acceptability threshold (AT) and translucency differences (ΔTP) were used to compare experimental composites in both filler fraction within every resin and every resin within each filler fraction.

RESULTS

The statistical analysis revealed a 3-way interaction (P < 0.0001) between base monomer, filler and direction factors. For the translucency parameter, when comparing filler fraction within base monomers, there were statistically significant differences between the filler fraction within all base monomers. The analysis of color differences (ΔE₀₀) of base monomers within filler fraction revealed that the comparison between experimental composites where beyond the acceptability threshold. The comparison of the differences in translucency parameter (ΔTP) of base monomers within filler fraction were beyond the perceptibility threshold, except between base monomers UT and FT.

SIGNIFICANCE

Different base monomer and filler fraction combination influences the optical characteristics of experimental composites such as: light transmission, translucency, and color appearance.

Effects of whitening gels on color and surface properties of a microhybrid and nanohybrid composite

The aim of this study was to compare color changes, surface roughness and gloss of a microhybrid and nanohybrid composite whitened in a simulated in-office or at-home procedure using 40% hydrogen peroxide or 16% carbamide peroxide, respectively. CIELab coordinates were measured before, during and after treatment using VITA EasyShade V (VITA) and ∆E₀₀ calculated. Surface roughness was measured using a surface roughness tester (SJ210; Mitutoyo). Gloss was measured using a gloss checker (IG-331; Horiba). At-home whitening resulted in ∆E₀₀ of 1.23±0.49 (microhybrid) and 1.01±0.76 (nanohybrid). In-office exposure resulted in ∆E₀₀ of 0.69±0.38 (microhybrid) and 0.72±0.50 (nanohybrid). There were no significant differences in ∆E₀₀, surface roughness and gloss between whitening protocols (p>0.05). Color changes of a microhybrid and nanohybrid composite following simulated in-office or at-home whitening reached CIEDE2000 50:50% perceptibility but not acceptability threshold. Surface roughness and gloss of the microhybrid and nanohybrid composite were not affected by whitening.

Influence of resin matrix on the rheology, translucency, and curing potential of experimental flowable composites for bulk-fill applications

OBJECTIVE

To propose monomer formulations that show an optimal degree of conversion as a function of depth for bulk-fill applications.

METHODS

Four resin blends were formulated with methacrylate-based monomers: BisGMA + TEGDMA (control); BisEMA + BisGMA + TEGDMA (BisEMA-based); UDMA + BisGMA + TEGDMA (UDMA-based) and BisEMA + UDMA + BisGMA + TEGDMA (BisEMA + UDMA-based). For each material, a photoinitiating system and silanized filler particles were added. The rheological analyses were performed with a rotational rheometer using the cone/plate geometry. CIELab coordinates were assessed over black and white backgrounds using a bench spectrophotometer (SP60, X-Rite) to calculate the translucency parameter (TP) for samples with 0.5, 4, and 6 mm thickness. The degree of CC conversion (DC) was determined by infrared spectroscopy (FTIR/ATR) at 0.05 mm (top), 4, and 6 mm depths (bottom), and the bottom-to-top ratio was considered. A broad spectrum-based LED was used for light activation. Analysis of variance and Tukey's test (95%) were performed on the results.

RESULTS

The materials tested showed pseudoplastic and thixotropic behavior and a predominance of viscous effects over elastics. The control resin yielded the lowest viscosity for the entire shear rate investigated, followed by the BisEMA-based, BisEMA + UDMA-based, and UDMA-based group, which had the highest viscosity. The UDMA-based material showed the lowest TP as a function of thickness. Both the materials' formulations and depths significantly influenced the DC. The UDMA-based group promoted the highest DC ​​on the top (71 ± 1%) and 4 mm depth (68 ± 1%) but exhibited lower bottom-to-top DC ratio. The BisEMA + UDMA-based material promoted the highest bottom-to-top DC ratio at 4 mm (99%) and 6 mm (97%).

SIGNIFICANCE

The resin matrix interferes in the rheological behavior, translucency parameter, and polymerization capacity as a function of depth. The material formulated with the addition of UDMA and BisEMA demonstrated the highest curing potential as a function of depth and can be useful for bulk-fill applications.

Expanding Monomers as Anti-Shrinkage Additives

Commonly, volumetric shrinkage occurs during polymerizations due to the shortening of the equilibrium Van der Waals distance of two molecules to the length of a (significantly shorter) covalent bond. This volumetric shrinkage can have severe influence on the materials’ properties. One strategy to overcome this volumetric shrinkage is the use of expanding monomers that show volumetric expansion during polymerization reactions. Such monomers exhibit cyclic or even oligocyclic structural motifs with a correspondingly dense atomic packing. During the ring-opening reaction of such monomers, linear structures with atomic packing of lower density are formed, which results in volumetric expansion or at least reduced volumetric shrinkage. This review provides a concise overview of expanding monomers with a focus on the elucidation of structure-property relationships. Preceded by a brief introduction of measuring techniques for the quantification of volumetric changes, the most prominent classes of expanding monomers will be presented and discussed, namely cycloalkanes and cycloalkenes, oxacycles, benzoxazines, as well as thiocyclic compounds. Spiroorthoesters, spiroorthocarbonates, cyclic carbonates, and benzoxazines are particularly highlighted.

Optical behavior of one-shaded resin-based composites

OBJECTIVE

To evaluate optical properties, and translucency and opalescence parameters of one-shaded resin-based composites.

METHODS

Three one-shaded resin composites (OM - Omnichroma; VP - Venus Pearl; and VD - Venus Diamond) and a group-shaded resin composite (FU- Filtek Universal A2) were used. Three composite discs from each material were fabricated for each of the following thickness: 0.5, 1.0 and 2.0 mm. Diffuse reflectance was measured against white and black backgrounds using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Translucency parameter (TP) was calculated using ΔE_ab^* and ΔE₀₀. Scattering (S) and absorption (K) coefficients and transmittance (T%) were calculated using Kubelka-Munk's equations, and a reflection spectrophotometer was used to measure the opalescence parameter (OP). Data was statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient.

RESULTS

Spectral distributions of S, K and T were wavelength dependent, showing significant differences between materials of the same thickness and for different thicknesses of the same material (p < 0.001). OM showed the greatest translucency values for all thicknesses. Translucency decreased as thickness increased with statistically significant differences (p < 0.005). Values of ΔTP_ab and ΔTP₀₀ between thicknesses were above of translucency thresholds for all materials. VP and VD showed the lowest OP values.

SIGNIFICANCE

One-shaded resin-based composites showed different optical behavior than the group-shaded resin-based composite. Understanding the optical behavior of the one-shaded resin-based composites is essential to optimize their clinical performance.

Optical properties and colorimetric evaluation of resin cements formulated with thio-urethane oligomers

OBJECTIVE

The aim of this study was to evaluate the color parameters and optical properties of resin cements (RCs) formulated with thio-urethanes (TUs).

MATERIALS AND METHODS

Six TUs were synthesized by combining thiols (pentaerythritol tetra-3-mercaptopropionate [PETMP] or trimethylol-tris-3-mercaptopropionate [TMP]) with di-functional isocyanates (1,6-Hexanediol-diissocyante [HDDI] [aliphatic-AL] or 1,3-bis(1-isocyanato-1-methylethyl) benzene [BDI] [aromatic-AR] or Dicyclohexylmethane 4,4'-Diisocyanate [HMDI] [cyclic-CC]). TUs (20 wt%) were added to a BisGMA/UDMA/TEGDMA matrix. Filler was introduced at 60 wt%. Fluorescence was evaluated through an UV-light emitting equipment. Coordinates L*, a*, and b* were obtained in the black and white reflectance to evaluate the contrast ratio (CR) and translucency parameter (TP₀₀ ). The coordinates obtained from transmittance were used to evaluate lightness (L*), chroma (C*), color difference (ΔE₀₀ ) after 6 month, and whiteness index for Dentistry (WI_D ).

RESULTS

RCs formulated with TUs presented significantly higher CR, and fluorescence (with T_AR). Significantly lower C*, L*, and TP₀₀ (except for P_AR and T_AL) were also observed in RCs containing TUs. ΔE₀₀ were not significant among the materials. WI_D was not influenced.

CONCLUSION

RCs composed by TU oligomers present higher CR and lower translucency. The material also present higher fluorescence depending on the oligomer used.

CLINICAL SIGNIFICANCE

The use of thio-urethanes to formulate resin cements can ensure a luting material with improved potential to mask colored substrates due to the higher contrast ratio and lower translucency obtained. A final higher fluorescence of restoration is also expected with the use of specific oligomer.

Translucency and color stability of resin composite and dental adhesives as modeling liquids - A one-year evaluation

The aim of this study is to evaluate the influence of modeling liquids on the translucency and color shade of resin composites (RCs) after one year of storage. RC specimens were prepared using either a conventional insertion technique (control; without modeling liquid) or a restorative dental modeling insertion technique (RDMIT) with dental adhesives as modeling liquids (Scotchbond™ Multi-Purpose [SBMP; 3M ESPE] or Adper™ Single Bond 2 [SB; 3M ESPE]). The initial colors of the specimens were obtained with a digital spectrophotometer and the CIEL*a*b* color system, after which specimens were stored (37°C) in distilled water or red wine for 12 months. Color measurements were reassessed after 6 and 12 months of storage, and scanning electron microscopy was performed after 12 months. Translucency and color change (ΔE*) were calculated and analyzed using ANOVA and Tukey's test (α = 5%). RC samples prepared via RDMIT showed a translucency similar to that of control samples. ΔE* was also less intense for RCs containing SBMP than for RCs containing SB. Specimens stored in wine showed a clear pattern of degradation, especially in the control group, and surface degradation seemed to be less intense for specimens prepared with SBMP and SB than for specimens without. Specimens stored in water did not show clear evidence of surface degradation. RDMIT appears to be an interesting approach to reduce ΔE* in RCs over time without negative effects on the translucency of the material. However, the modeling liquid should feature a hydrophobic composition, similar to that used in the SBMP group, the achieve the best results.