Effect of inorganic fillers on the light transmission through traditional or flowable resin-matrix composites for restorative dentistry

Sub-Nanoscale Caffeic Acid-Functionalized TiO2 Composite: Enhancing Mechanical Properties and Odontogenic Differentiation Capacity of Resin-Based Dental Restoration

Resin-based materials (RBMs) are widely applied in dentistry because they withstand the recurrent multi-dimensional force striking and the hydrolysis of teeth. Sub-nanoscale materials can enhance the mechanical strength and bioactivity of RBMs, but the effects are still limited and the mechanisms to enhance bioactivity remain unclear. Here, a TiO2-based sub-nanocomposite modified with caffeic acid (CA) to enhance mechanical robustness, structural stability, and bioactivity of RBMs is reported. This sub-nanocomposite can promote the proliferation, adhesion, and odontogenic differentiation of human dental pulp stem cells (hDPSCs) through specifically up-regulating the expression of genes related to cell-matrix adhesion, integrin-mediated signaling pathways, and collagen fibril organization. These effects lead to a better capacity for up-regulating odontogenic differentiation of RBMs.

Physical and Mechanical Properties of Bulk-fill Resin Composites Submitted to Additional Polymerization for Use in Semi-direct Restorations

Physical and mechanical properties of high-viscosity bulk-fill resin composites submitted to additional polymerization for semi-direct use were evaluated. Filtek Z350 XT, Aura Bulk Fill, Beautifil Bulk Restorative, Filtek One Bulk Fill Restorative, and Tetric N-Ceram Bulk Fill were submitted to additional polymerization to evaluate sorption, solubility, surface microhardness, surface roughness before and after simulated brushing, color stability after coffee staining, flexural strength, elastic modulus, and modulus of resilience. Filtek Z350 XT and Filtek One Bulk Fill Restorative showed higher sorption values, while Aura Bulk Fill showed higher solubility (p<0.0001). Microhardness values were significantly higher for Filtek Z350 XT (p<0.0001). Roughness increased after wear for all resins (p<0.05). All resins exhibited staining, with significantly higher ΔEab, ΔE00, and ΔWID values observed for Beautifil Bulk Restorative (p<0.0001). Flexural strength values were higher for Filtek Z350 XT and Filtek One Bulk Fill Restorative in comparison with the others (p<0.0001). Filtek One Bulk-Fill had higher elastic modulus and modulus of resilience values (p<0.0001). Physical and mechanical properties varied according to the composition. None of the bulk-fill resins showed surface microhardness and roughness properties after brushing similar to or superior to those of the conventional type. Color stability after staining depended on resin composition, with Beautifil Bulk Restorative showing more intense staining.

Long-Term Dentin Bonding Performance of Universal Adhesives: The Effect of HEMA Content and Bioactive Resin Composite

This study investigated the effects of resin composites (RCs) containing surface pre-reacted glass ionomer (S-PRG) filler on the dentin microtensile bond strength (μTBS) of HEMA-free and HEMA-containing universal adhesives (UAs). Water sorption (WS) and solubility (SL), degree of conversion (DC), and ion release were measured. The UAs BeautiBond Xtreme (BBX; 0% HEMA), Modified Adhesive-1 (E-BBX1; 5% HEMA), Modified Adhesive-2 (E-BBX2; 10% HEMA), and two 2-step self-etch adhesives (2-SEAs): FL-BOND II (FBII; with S-PRG filler) and silica-containing adhesive (E-FBII) were used. Teeth were restored with Beautifil Flow Plus F00 with S-PRG filler (BFP) and flowable resin composite with silica filler (E-BFP). μTBS was evaluated after 24 h and 6 months of water storage. WS and SL measurement followed ISO 4049:2019; spectroscopy measured DC; ICP-MS evaluated ion release. BBX and FBII presented the highest DC. The adhesives did not comply with the WS ISO requirements, but the bonding resin of 2-SEAs complied with the SL threshold. BFP released more ions than E-BFP. BFP positively affected the μTBS of UAs, regardless of HEMA concentration after 24 h, comparable to the 2-SEAs. The 6 months μTBS decrease depended on the adhesive and RC combination. HEMA did not affect the μTBS of UAs, while bioactive resins had a positive impact.

Enhancing 3D printed ceramic components: The function of dispersants, adhesion promoters, and surface-active agents in Photopolymerization-based additive manufacturing

In the domain of photopolymerization-based additive manufacturing (3D vat printing), ceramic photopolymer resins represent a multifaceted composite, predominantly comprising oligomers, ceramic fillers, and photoinitiators. However, the synergy between the ceramic fillers and polymer matrix, along with the stabilization and homogenization of the composite, is facilitated by specific additives, notably surface-active agents, dispersants, and adhesion promoters. Although these additives constitute a minor fraction in terms of volume, their influence on the final properties of the material is substantial. Consequently, their meticulous selection and integration are crucial, subtly guiding the performance and characteristics of the resultant ceramic matrix composites toward enhancement. This review delves into the array of dispersants and coupling agents utilized in the additive manufacturing of ceramic components. It elucidates the interaction mechanisms between these additives and ceramic fillers and examines how these interactions affect the additive manufacturing process. Furthermore, this review investigates the impact of various additives on the rheological behavior of ceramic slurries and their subsequent effects on the post-manufacturing stages, such as debinding and sintering. It also addresses the challenges and prospects in the optimization of dispersants and coupling agents for advanced ceramic additive manufacturing applications.

Monomer elution and shrinkage stress analysis of addition-fragmentation chain-transfer-modified resin composites in relation to the curing protocol

OBJECTIVE

The purpose was to compare the effects of rapid (3 s) and conventional (20 s) polymerization protocols (PP) of mono- and multichip LED curing units (LCU) on shrinkage stress (SS) and monomer elution (ME) in bulk-fill resin-based composites (RBC) with and without addition-fragmentation chain-transfer (AFCT) monomer.

METHODS

Cylindrical (5x4mm) specimens were prepared from two RBCs containing different AFCT monomers (Filtek OneBulk-FOB; Tetric PowerFill-TPF) and one without (Tetric EvoCeram Bulk-TEC). After soaking for 3, 10, and 14 days (75 % ethanol), ME was quantified using standard monomers by High-Performance Liquid Chromatography. SS was measured from the start of polymerization to 5 min using a Materials Testing Machine. The radiant exitance of LCUs was measured using a spectrophotometer. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).

RESULTS

AFCT-modification significantly decreased ME (p < 0.001). ME was reduced by half by day 10 and by one tenth by the end of the 14-day compared to the 3-day sampling. ME itself was dependent, whereas the percentage of monomers released was independent of the PP used (p > 0.05). FOB showed the lowest SS (p < 0.001), while there was no significant difference between TPF and TEC (p = 0.124). Both ME and SS were significantly influenced by material type and PP.

SIGNIFICANCE

The incorporation of the AFCT monomer reduced ME, but this was inversely related to a decrease in exposure time. SS values reduced by rapid PP in parallel with increasing ME values. The utilization of the AFCT molecule in conjunction with an appropriate resin-, initiator-system is of significant consequence for the kinetics of polymerization and the incorporation of monomers into the network.

Effect of barium silicate on mechanical properties, transmittance, and protein adsorption of resin for additive manufacturing containing zwitterionic polymer

STATEMENT OF PROBLEM

Studies on the effect of barium silicate on the material properties of additively manufactured (AM) resins containing 2-methacryloyloxyethyl phosphorylcholine (MPC) for dental applications are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the mechanical properties, transmittance, and protein adsorption of MPC-containing AM resin incorporated with different barium silicate contents and to compare these findings with those of a commercially available unfilled AM resin marketed for definitive restorations.

MATERIAL AND METHODS

Resins incorporating 6 wt% MPC and 4 different concentrations of barium silicate (10 wt%, MB10; 20 wt%, MB20; 30 wt%, MB30; and 40 wt%, MB40) were prepared. An MPC-containing resin with no filler was also prepared (0 wt%, MBN). Surface roughness (n=15), Vickers hardness (n=15), flexural strength and modulus (n=15), fracture toughness (n=15), transmittance (n=15), and protein adsorption (n=3) of the filled resin specimens were measured and compared with those of commercially available unfilled resin specimens. All data were analyzed using the Kruskal-Wallis and Dunn tests (α=.05).

RESULTS

All experimental resins had higher surface roughness than the unfilled resin (P≤.048). MB40 had higher hardness, flexural strength, flexural modulus, and fracture toughness than most other groups (P≤.047). MB10 had higher transmittance than most other groups (P≤.012). All experimental resins had lower protein adsorption than the unfilled resin, regardless of the barium silicate content (P≤.023).

CONCLUSIONS

The experimental resin containing 6 wt% MPC and 40 wt% barium silicate showed better mechanical properties and lower protein adsorption than the resin with no MPC or ceramic fillers. Transmittance decreased with the increase of barium silicate in the resins.

Comparative Evaluation of Mechanical Properties and Color Stability of Dental Resin Composites for Chairside Provisional Restorations

Resin composites have become the preferred choice for chairside provisional dental restorations. However, these materials may undergo discoloration, changes in surface roughness, and mechanical properties with aging in the oral cavity, compromising the aesthetics, functionality, and success of dental restorations. To investigate the color and mechanical stability of chairside provisional composite resins, this study evaluated the optical, surface, and mechanical properties of four temporary restoration resin materials before and after aging, stimulated by thermal cycling in double-distilled water. Measurements, including CIE LAB color analysis, three-point bending test, nanoindentation, scanning electron microscopy (SEM), and atomic force microscopy (AFM), were conducted (n = 15). Results showed significant differences among the materials in terms of optical, surface, and mechanical properties. Revotek LC (urethane dimethacrylate) demonstrated excellent color stability (ΔE00 = 0.53-Black/0.32-White), while Artificial Teeth Resin (polymethyl methacrylate) exhibited increased mechanical strength with aging (p < 0.05, FS = 68.40 MPa-non aging/87.21 MPa-aging). Structur 2 SC (Bis-acrylic) and Luxatemp automix plus (methyl methacrylate bis-acrylate) demonstrated moderate stability in optical and mechanical properties (Structur 2 SC: ΔE00 = 1.97-Black/1.38-White FS = 63.20 MPa-non aging/50.07 MPa-aging) (Luxatemp automix plus: ΔE00 = 2.49-Black/1.77-White FS = 87.72 MPa-non aging/83.93 MPa-aging). These results provide important practical guidance for clinical practitioners, as well as significant theoretical and experimental bases for the selection of restorative composite resins.

Light transmittance through resin-matrix composite onlays adhered to resin-matrix cements or flowable composites

OBJECTIVE

The aim of this study was to evaluate the influence of the thickness of resin-matrix composite blocks manufactured by CAD-CAM on the light transmittance towards different resin-matrix cements or flowable composites.

METHODS

Sixty specimens of resin-matrix composite CAD-CAM blocks reinforced with 89 wt% inorganic fillers were cross-sectioned with 2 or 3 mm thicknesses. The specimens were conditioned with adhesive system and divided in groups according to the luting material, namely: two dual-cured resin-matrix cements, two traditional flowable resin-matrix composites, and one thermal-induced flowable resin-matrix composite. Specimens were light-cured at 900 mW/cm2 for 40s. Light transmittance assays were preformed using a spectrophotometer with an integrated monochromator before and after light-curing. Microstructural analysis was performed by optical and scanning electron microscopy (SEM). Nanoindentation tests were performed to evaluate mechanical properties for indirect evaluation of degree of monomers conversion.

RESULTS

Optical and SEM images revealed low thickness values for the cementation interfaces for the traditional flowable resin-matrix composite. The cement thickness increased with the size and content of inorganic fillers. The highest light transmittance was recorded for the onlay blocks cemented with the traditional flowable resin-matrix composites while a group cemented with the dual-cured resin-matrix cement revealed the lowest light transmittance. The elastic modulus and hardness increased for specimens with high content of inorganic fillers as well as it increased in function of the light transmittance.

CONCLUSIONS

The light transmittance of flowable resin-matrix composites was higher than that for resin-matrix cement after cementation to resin-matrix composites blocks. The type, size, and content of inorganic fillers of the luting material affected the thickness of the cement layer and light transmittance through the materials.

CLINICAL RELEVANCE

On chair-side light curing, the transmission of visible light can be interfered by the chemical composition and viscosity of the luting materials. The increase in size and content of inorganic fillers of resin-matrix composites and luting materials can decrease the light transmittance leading to inefficient polymerization.