Curing profile and marginal gap formation using a liner containing long-wavelength-absorbing photoinitiator: an in vitro study.

The aim was to evaluate the marginal-gap formation and curing profile of a new restorative technique using a liner with long-wavelength-absorbing photoinitiator (LWAP). Box-shaped preparations (6 mm × 4 mm × 4 mm) were made in third molars. All samples were treated with Clearfill SE Bond and divided into 4 groups (n = 5), according to restorative technique used: (1) incremental technique (INC-Technique); (2) camphorquinone-based liner (CQ-Liner) + bulk-fill resin composite; (3) LWAP-based liner (LWAP-Liner) + bulk-fill resin composite; and (4) bulk-fill technique without liner (BF-Technique). The marginal gaps (%) for all the samples were measured using micro-computed tomography. The restorations were cross-sectioned, and the degree of conversion (DC) and Knoop microhardness were evaluated at different depths (0.3, 1, 2, 3, and 4 mm). INC-Technique, CQ-Liner, and LWAP-Liner groups showed significantly fewer marginal gaps than those from the BF-Technique group. The BF-Technique specimens had the lowest DC and microhardness in depth. All the other techniques presented similar degree of conversion and microhardness at all the depths. The use of liners, regardless of the photoinitiator system, decreased the marginal-gap formation and improved the curing profile of bulk-filling restoration technique.

Effect of Thickness of Ceramic Veneers on Color Stability and Bond Strength of Resin Luting Cements Containing Alternative Photoinitiators.

PURPOSE: To evaluate the light transmittance of ceramic veneers of different thicknesses and verify their influence on the degree of conversion, color stability, and dentin bond strength of light-curing resin cements containing different photoinitiator systems. MATERIALS AND METHODS: Experimental resin cements were fabricated containing camphorquinone and amine (CQ-amine), TPO, Ivocerin (IVO), or TPO and Ivocerin (TPO-IVO). All photoinitiators were characterized by UV-Vis spectrophotometry. Disk-shaped lithium disilicate ceramic specimens that were 0.4, 0.7, and 1.5 mm in thickness were prepared using IPS e.max Press (Ivoclar Vivadent, shade LT/A2). Light transmittance through each specimen was measured using spectrophotometry. Specimens of each cement (n = 10) were made in a custom-designed mold and were light cured through each glass-ceramic disk using a multiwave LED (Bluephase G2, Ivoclar Vivadent). CS was evaluated using spectrophotometry before and after artificial aging with UV light. DC was evaluated using FTIR-spectroscopy. Dentin µSBS was evaluated using 0.75-mm-thick specimens that were light cured under the same protocol (n = 10). All data were submitted to two-way ANOVA and Tukey's test (α = 0.05; ß = 0.2). RESULTS: CQ-amine cements showed the highest color changes (p < 0.05) due to increased yellowing when compared to the amine-free cements (p < 0.05). However, all cements showed a significant color change after aging when cured through ceramics up to 1.5 mm thick (p < 0.05). The TPO-IVO cement showed the highest DC and the IVO cement showed a similar DC when compared to the CQ-amine cement. The TPO cement presented the lowest DC (p = 0.0377). No differences in mean dentin µSBS were found among the cements, except for the TPO cement, which presented a lower mean dentin µSBS (p = 0.0277). CONCLUSION: Amine-free cements containing Ivocerin and TPO seem to be a better alternative to CQ-amine cements, while not reducing either DC or dentin µSBS of amine-free cements. However, CQ-amine and amine-free cements still seem to change color over time.

The effect of combining photoinitiator systems on the color and curing profile of resin-based composites.

OBJECTIVE: To evaluate the effect of combining camphorquinone (CQ) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) on the color and curing profile of resin-based composites. METHODS: Experimental composites were produced with different CQ and TPO molar concentrations: CQ-only, 3CQ:1TPO, 1CQ:1TPO, 1CQ:3TPO, and TPO-only. Polywave LED was characterized using a beam profiler. Block-shaped samples (5mm×5mm×3mm depth) were cured in a custom-designed mold with a polywave LED positioned to compare the regions exposed to the 420-495nm and 380-420nm LED emittances. To map the cure profile, degree of conversion (DC) of longitudinal cross-sections from each block were evaluated by FT-NIR. Color, light-transmittance and light-absorption during curing were evaluated on specimens 1-3mm thick. Data were analyzed using ANOVA/Tukey's test (α=0.05; ß=0.2). RESULTS: Though the polywave LED beam profile was non-uniform, up to a depth of 2mm no differences in DC were found among the composites containing CQ with TPO added up to 50%, regardless of the position under the curing tip. Composites with higher TPO concentration showed a decrease in DC beginning with a depth of 1mm, while composites with higher or similar CQ concentrations did not show decreased DC until a depth of 3mm. Higher TPO concentration reduced initial yellowness and color change after curing; and lower CQ concentration decreased light-absorption at greater depths. SIGNIFICANCE: The combination of CQ with TPO added up to 50% reduced the yellowness and color change of composites after curing without affecting cure efficiency up to a depth of 2mm.

Effect of Nanofiller Loading on Cure Efficiency and Potential Color Change of Model Composites.

OBJECTIVES: To evaluate the effect of nanofiller loading on cure efficiency and potential color change of experimental composites. MATERIALS AND METHODS: Four different polymeric materials were produced using the same organic matrix blend. To this matrix, different amounts of 0.05 µm fumed silica filler were added: no filler, 13, 52, and 65wt%. Fourier transform infrared spectroscopy was used to evaluate the degree of conversion (DC) for each composite using near-IR analysis, and spectrophotometry according to CIELab chromatic space was used to evaluate the color change.To induce color change, composites were artificially aged with exposure to cycles of UV-B light for 300 hours. Trasmission electron microscopy was used to illustrate nanoffiler aglomeration in the resin matrix. Data were analyzed using correlation analysis (α = 0.05). RESULTS: There was an excellent inverse linear correlation between filler wt% and either DC or color change. Greater changes to red (+Δa) and yellow (+Δb) were observed as the filler wt% increased. CONCLUSIONS: A higher percentage of nano-sized filler particles in dental resin composites directly affects their cure efficiency and potential for color change. CLINICAL SIGNIFICANCE: The increase in filler particle loading negatively affected monomer conversion and color stability of resin-based composites. As reduced filler loading results in poorer mechanical properties, to enhance color stability, resin-based composites should be formulated by making the refractive index of the polymeric matrix more closely match that of the filler throughout the polymerization process. (J Esthet Restor Dent, 2016).

Effect of different photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths.

OBJECTIVES: To evaluate the effect of photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths. METHODS: Model resin-based composites were associated with diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO) or camphorquinone (CQ) associated with 2-(dimethylamino) ethyl methacrylate (DMAEMA), ethyl 4-(dimethyamino) benzoate (EDMAB) or 4-(N,N-dimethylamino) phenethyl alcohol (DMPOH). A narrow (Smartlite, Dentisply) and a broad spectrum (Bluephase G2, Ivoclar Vivadent) LEDs were used for photo-activation (20 J/cm(2)). Fourier transform infrared spectroscopy (FT-IR) was used to evaluate the cure efficiency for each composite, and CIELab parameters to evaluated color stability (ΔE00) after aging. The UV-vis absorption spectrophotometric analysis of each photoinitiator and reducing agent was determined. Data were analyzed using two-way ANOVA and Tukey's test for multiple comparisons (α=0.05). RESULTS: Higher cure efficiency was found for type-I photoinitiators photo-activated with a broad spectrum light, and for CQ-systems with a narrow band spectrum light, except when combined with an aliphatic amine (DMAEMA). Also, when combined with aromatic amines (EDMAB and DMPOH), similar cure efficiency with both wavelength LEDs was found. TPO had no cure efficiency when light-cured exclusively with a blue narrowband spectrum. CQ-systems presented higher color stability than type-I photoinitiators, especially when combined with DMPOH. CONCLUSIONS: After aging, CQ-based composites became more yellow and BAPO and TPO lighter and less yellow. However, CQ-systems presented higher color stability than type-I photoinitiators, as BAPO- and TPO-, despite their higher cure efficiency when photo-activated with corresponding wavelength range. CLINICAL SIGNIFICANCE: Color matching is initially important, but color change over time will be one of the major reasons for replacing esthetic restorations; despite the less yellowing of these alternative photoinitiators, camphorquinone presented higher color stability.

Effect of low shrinkage monomers on physicochemical properties of dental resin composites.

UNLABELLED: The aim of this study was to evaluate the effect of low shrinkage monomers on physicochemical properties of dental resin composites. Two low shrinkage resin composites: one with a crosslink branching monomer (Kalore, GC Corp) and a novel monomer (Venus Diamond, Heraeus Kulzer) were compared to a conventional resin composite formulation (Filtek Z250, 3M/ESPE). The volumetric shrinkage was evaluated by µCT analysis (n=5) and the physicochemical properties by degree of C=C conversion (DC), flexural strength (FS) and Young's modulus (YM) (n=10). All samples were light cured by a LED device (Radii, SDI) with 16 J/cm2. The results were analysed by one-way ANOVA and Tukey test for multiple comparisons (α=0.05). No statistical difference was found between µCT shrinkage values to Kalore (1.8%) and Venus Diamond (1.7%) (p≥0.05); Z250 presented statistical highest shrinkage value (2.0%). Kalore presented higher statistical DC (60.8%) than Venus Diamond (49.5%) and Z250 (49.6%). No statistical difference was found between FS or YM properties to Venus Diamond and Z250; Kalore presented statistical lowest FS and YM properties (p≥0.05). CONCLUSION: Using novel monomers seem to reduce polymerization shrinkage without affecting the physicochemical properties evaluated of resin composites rather than using crosslink branching monomers.

Effect of Different In Vitro Aging Methods on Color Stability of a Dental Resin-Based Composite Using CIELAB and CIEDE2000 Color-Difference Formulas.

PURPOSE: To evaluate the effect of different in vitro aging methods on color change (CC) of an experimental dental resin-based composite using CIELAB (ΔEab ) and CIEDE2000 (ΔE00 ) color-difference formulas. MATERIALS AND METHODS: The CC was evaluated with a spectrophotometer (CM700d, Konica Minolta, Tokyo, Japan) according to the CIE chromatic space. Disk-shaped specimens (Φ = 5 × 1 mm thick) (N = 10) were submitted to different in vitro aging methods: 30 days of water aging (WA); 120 hours of ultraviolet light aging (UVA); or 300 hours of an accelerated artificial aging (AAA) method with cycles of 4 hours of UV-B light exposure and 4 hours of moisture condensation to induce CC. The temperature was standardized at 37°C for all aging methods. CC was evaluated with ΔEab and ΔE00 formulas. Differences in individual Lab coordinates were also calculated. Data for the individual color parameters were submitted to one-way analysis of variance and Tukey's test for multiple comparisons (α = 0.05). RESULTS: All in vitro aging methods tested induced CC, in the following order: WA: ΔEab = 0.83 (0.1); ΔE00 = 1.15 (0.1) < AAA: ΔEab = 5.64 (0.2); ΔE00 = 5.01 (0.1) < UVA: ΔEab = 6.74 (0.2); ΔE00 = 6.03 (0.4). No changes in L* or a* coordinates were ≥1; the methods with UV aging showed a yellowing effect due a large positive change in b*. CONCLUSIONS: All in vitro aging methods tested induced a CC, but to different extents. Changes in color followed similar trends, but with different absolute values when calculated with the CIELAB and the CIEDE2000 formulas. CLINICAL SIGNIFICANCE: Establishing the efficacy of different artificial aging methods and differences between color change using CIELAB and CIEDE2000 formulas are important to standardize color stability evaluations and facilitate the comparison of outcomes from different studies in the literature.

Nanoleakage of fiber posts luted with different adhesive strategies and the effect of chlorhexidine on the interface of dentin and self-adhesive cements.

The aim of this in vitro study was to evaluate the nanoleakage of fiber posts luted using different adhesive strategies and to investigate the effect of 2% chlorhexidine (CHX) on nanoleakage at the resin-dentin interfaces of self-adhesive cements. The self-adhesive and etch-and-rinse adhesive groups tested demonstrated similar results with regard to nanoleakage. Pretreatment with CHX promoted an adequate seal at the resin-dentin interface for self-adhesive cements.

Minimally invasive cosmetic dentistry: smile reconstruction using direct resin bonding.

Discrepancies in tooth size and shape can interfere with smile harmony. Composite resin can be used to improve the esthetics of the smile at a low cost while offering good clinical performance. This article presents an approach for restoring and correcting functional, anatomic, and esthetic discrepancies with minimal intervention, using composites and a direct adhesive technique. This conservative restorative procedure provided the patient with maximum personal esthetic satisfaction.