Dental Materials最新文献

Objectives

To compare the interfacial fracture toughness (IFT) with or without aging, of four different classes of CAD-CAM ceramic and composite materials bonded with self-adhesive resin cement to titanium alloy characteristic of implant abutments.

Methods

High translucent zirconia (Katana; KAT), lithium disilicate-based glass-ceramic (IPS. emax.CAD; EMX), polymer-infiltrated ceramic network material (PICN) (Vita Enamic; ENA), and dispersed filler composite (Cerasmart 270; CER) were cut into equilateral triangular prisms and bonded to titanium prisms with identical dimensions using Panavia SA Cement Universal. The surfaces were pretreated following the manufacturers’ recommendations and developed interfacial area ratio (Sdr) of the pretreated surfaces was measured. IFT was determined using the Notchless Triangular Prism test in a water bath at 36 °C before and after thermocycling (10,000 cycles) (n = 40 samples/material).

Results

IFT of the materials ranged from 0.80 ± 0.25 to 1.10 ± 0.21 MPa.m^1/2 before thermocycling and from 0.71 ± 0.24 to 1.02 ± 0.25 MPa.m^1/2 after thermocycling. There was a statistical difference between IFT of CER and the two top performers in each scenario: KAT and EMX before aging, and KAT and ENA after aging. Thermocycling significantly decreased IFT of EMX. The Weibull modulus of IFT was similar for all materials and remained so after thermocycling. Sdr measurements revealed that ENA (7.60)>Ti (4.97)>CER (2.85)>KAT (1.09)=EMX (0.96).

Significance

Dispersed filler CAD-CAM composite showed lower performance than the other materials. Aging only affected IFT of Li-Si glass-ceramic, whereas zirconia and PICN performed equally well, probably due to their chemical bonding potential and surface roughness respectively.

Objective:

To assess the prediction accuracy of recent optical and numerical models for the spectral reflectance and color of monolithic samples of dental materials with different thicknesses.

Methods:

Samples of dental resin composites of Aura Easy Flow (Ae1, Ae3 and Ae4 shades) and Estelite Universal Flow Super Low (A1, A2, A3, A3.5, A4 and A5 shades) with thicknesses between 0.3 and 1.8 mm, as well as Estelite Universal Flow Medium (A2, A3, OA2 and OA3 shades) with thicknesses between 0.4 and 2.0 mm, were used. Spectral reflectance and transmittance factors of all samples were measured using a X-Rite Color i7 spectrophotometer. Four analytical optical models (2 two-flux models and 2 four-flux models) and two numerical models (PCA-based and L*a*b*-based) were implemented to predict spectral reflectance of all samples and then convert them into CIE-L*a*b* color coordinates (D65 illuminant, 2°Observer). The CIEDE2000 total color difference formula ($\Delta E_{00}$) between predicted and measured colors, and the corresponding 50:50% acceptability and perceptibility thresholds ($A{T}_{00}$ and $P{T}_{00}$) were used for performance assessment.

Results:

The best performing optical model was the four-flux model RTE-4F-RT, with an average $\Delta E_{00}$ = 0.72 over all samples, 94.87% of the differences below $A{T}_{00}$ and 65.38% below $P{T}_{00}$. The best performing numerical model was L*a*b*-PCHIP (interpolation mode), with an average $\Delta E_{00}$ = 0.48, and 100% and 79.69% of the differences below $A{T}_{00}$ and $P{T}_{00}$, respectively.

Significance:

Both optical and numerical models offer comparable color prediction accuracy, offering flexibility in model choice. These results help guide decision-making on prediction methods by clarifying their strengths and limitations.

Polymerization shrinkage of bonded resin composite restorations will result in the development of curing contraction stresses during setting and can cause debonding of the restoration or failure of the surrounding tooth structure. However, the hygroscopic expansion that occurs after exposure of the restorative to the wet oral environment can compensate for this shrinkage.

Objectives

The purpose of this study was to determine the hygroscopic expansion of six commercial resin composites and relate it to their composition, mechanical properties, shrinkage, and contraction stress development.

Methods

Short-term volumetric shrinkage and contraction stress of the different composites were measured by mercury dilatometry and a universal testing machine. The long-term contraction stress was measured by the deflection of a bilayer strip of metal and a resin composite, which were stored dry as well as wet to determine the effect of hygroscopic expansion. The curvature of the strip was measured by profilometry over a period of 3 months.

Results

The curvature of the strip correlated well (r² =0.74) with the initial contraction stress, showing that the contraction stress is an important factor in initial deformation. The water sorption in all specimens showed that the initial deformation, within 2–4 weeks after curing, was completely counteracted. A high correlation (r² =0.90) between deflection and relative water sorption was found, where the relative water sorption is defined as the absolute water sorption corrected for the inorganic filler volume of the composite.

Significance

Within a period of 2–4 weeks after curing most of the curing contraction stresses of resin composite restoratives will be released by hygroscopic expansion.

Objectives

The aim of this study was to assess the cytotoxicity of novel polymerization co-initiators and their effect on cytokine release from human dental pulp stem cells (hDPSCs), comparing them with commonly used co-initiators.

Methods

Cells were isolated from the dental pulp of healthy human third molars. The new co-initiators, namely HDa1, HD4, HD1, and MHPTm, were evaluated and compared with the compounds dimethylaminoethyl amine benzoate (EDAB) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). These compounds were diluted in dimethylsulfoxide (DMSO) at concentrations ranging from 1 to 8 mM. hDPSCs were seeded onto 96-well plates and incubated for 48 h. Subsequently, the cells were exposed to different concentrations of the co-initiators mentioned for 24 h. After this period, the culture medium was removed, and mitochondrial metabolism was evaluated using the MTT assay, while cytokine release (IL-1β, IL-6, IL-8, IL-10, TNF-α) was analyzed by the MAGPIX assay. Cells without exposure to the tested compounds served as controls. The data were analyzed using one-way ANOVA and Tukey’s test.

Results

The compounds showed low toxicity, with 8 mM concentration causing the most significant reduction in mitochondrial metabolism. MHPTm was the most toxic co-initiator tested (compound bearing an amine functionality). All compounds up-regulated TNF-α, IL-10, IL-6, and IL-8, with HD4 exhibiting the most pronounced increase in IL-6 and IL-8.

Significance

The newly proposed co-initiators demonstrated reduced impact on mitochondrial metabolism, comparable to some traditional co-initiators. Despite their lower toxicity, HD4 increased IL-6 and IL-8 release, suggesting its potential involvement in triggering an inflammatory reaction, particularly in the short term.

Objective

To formulate an experimental methacrylate-based photo-polymerizable resin for 3D printing with ytterbium trifluoride as filler and to evaluate the mechanical, physicochemical, and biological properties.

Methods

Resin matrix was formulated with 60 wt% UDMA, 40 wt% TEGDMA, 1 wt% TPO, and 0.01 wt% BHT. Ytterbium Trifluoride was added in concentrations of 1 (G_1 %), 2 (G_2 %), 3 (G_3 %), 4 (G_4 %), and 5 (G_5 %) wt%. One group remained without filler addition as control (G_C). The samples were designed in 3D builder software and printed using a UV-DLP 3D printer. The samples were ultrasonicated with isopropanol and UV cured for 60 min. The resins were tested for degree of conversion (DC), flexural strength, Knoop microhardness, softening in solvent, radiopacity, colorimetric analysis, and cytotoxicity (MTT and SRB).

Results

Post-polymerization increased the degree of conversion of all groups (p < 0.05). G_2 % showed the highest DC after post-polymerization. G_2 % showed no differences in flexural strength from the G_1 % and G_C (p > 0.05). All groups showed a hardness reduction after solvent immersion. No statistical difference was found in radiopacity, softening in solvent (ΔKHN%), colorimetric spectrophotometry, and cytotoxicity (MTT) (p > 0.05). G_1 % showed reduced cell viability for SRB assay (p < 0.05).

Significance

It was possible to produce an experimental photo-polymerizable 3D printable resin with the addition of 2 % ytterbium trifluoride as filler without compromising the mechanical, physicochemical, and biological properties, comparable to the current provisional materials.

Objectives

Considering the correlation between survival microenvironment of E. faecalis and acidic pH value, this study aimed to investigate the potential of utilizing pH-responsive DMAEM monomers and their copolymers with resin-based root canal sealers to inhibit E. faecalis.

Methods

Broth microdilution assay, crystal violet staining and qPCR were performed to evaluate antibacterial effects of DMAEM monomers against E. faecalis at different pH. Methacrylate-resin based root canal sealers were prepared and copolymerized with DMAEM. The flow, solubility, water sorption, apical sealing ability and cytotoxicity of sealers were investigated to optimize formulation. The anti-E. faecalis effects of DMAEM copolymers with sealers were evaluated by direct contact test, colony-forming unit counting and live/dead staining.

Results

DMAEM monomers inhibited the growth, biofilm formation and virulence factors expression of E. faecalis in a concentration- and pH-dependent manner. Incorporation of 1.25 % and 2.5 % DMAEM into experimental sealers would not affect the flowability, solubility and periapical sealing ability (P > 0.05), but increased the water sorption of sealers (P < 0.01). Cells viability was higher than 90 % in both 1.25 % and 2.5 % DMAEM groups at pH 7.0. DMAEM copolymers with sealers reduced E. faecalis counts, inhibited biofilm formation and decreased live cells within the biofilm in response to pH values.

Significance

DMAEM monomers and their copolymers with resin-based sealers possessed antibacterial and antibiofilm effects on E. faecalis in response to pH values. DMAEM is promising to inhibit intraradicular E. faecalis in response to its acidic survival environment and maintain low cytotoxicity under neutral conditions, ensuring their biosafety in case of inadvertent entry into periapical tissues.

Objectives

This multicenter study aimed to evaluate visual-instrumental agreement of six color measurement devices and optimize three color difference equations using a dataset of visual color differences (∆V) from expert observers.

Methods

A total of 154 expert observers from 16 sites across 5 countries participated, providing visual scaling on 26 sample pairs of artificial teeth using magnitude estimation. Three color difference equations (ΔE*_ab, ∆E₀₀, and CAM16-UCS) were tested. Optimization of all three equations was performed using device-specific weights, and the standardized residual sum of squares (STRESS) index was used to evaluate visual-instrumental agreement.

Results

The ΔE*_ab formula exhibited STRESS values from 18 to 40, with visual-instrumental agreement between 60 % and 82 %. The ∆E₀₀ formula showed STRESS values from 26 to 32, representing visual-instrumental agreement of 68 % to 74 %. CAM16-UCS demonstrated STRESS values from 32 – 39, with visual-instrumental agreement between 61–68 %. Following optimization, STRESS values decreased for all three formulas, with ΔE^’ demonstrating average visual-instrumental agreement of 79 % and ∆E₀₀ of 78 %. CAM16-UCS showed average visual-instrumental agreement of 76 % post optimization.

Significance

Optimization of color difference equations notably improved visual-instrumental agreement, overshadowing device performance. The optimzed ΔE^’ formula demonstrated the best overall performance combining computational simplicty with outstanding visual-instrumental agreement.

The clinical failure mode of dental crown ceramics involves radial cracking at the interface, driven by the surface tension generated from the flexure of the ceramic layer on the subsurface. This results in a reduced lifespan for most all-ceramic dental crowns. Therefore, investigating optimal material combinations to reduce stress concentration in dental crown materials has become crucial for future successful clinical applications. The anisotropic complex structures of natural materials, such as nacre, could potentially create suitable strong and damage-resistant materials. Their imitation of natural structural optimisation and mechanical functionality at both the macro- and micro-levels minimises weaknesses in dental crowns. This research aims to optimise cost-effective, freeze-casted bioinspired composites for the manufacture of novel, strong, and tough ceramic-based dental crowns. To this end, multilayer alumina (Al₂O₃) composites with four different polymer phases were tested to evaluate their bending behaviour and determine their flexural strength. A computational model was developed and validated against the experimental results. This model includes Al₂O₃ layers that undergo gentle compression and distribute stress, while the polymer layers act as stress relievers, undergoing plastic deformation to reduce stress concentration. Based on the experimental data and numerical modelling, it was concluded that these composites exhibit variability in mechanical properties, primarily due to differences in microstructures and their flexural strength. Furthermore, the findings suggest that bioinspired Al₂O₃-based composites demonstrate promising deformation and strengthening behaviour, indicating potential for application in the dental field.