Sorption, solubility, shrinkage and mechanical properties of “low-shrinkage” commercial resin composites

Preparation of Al-doped mesoporous silica spheres (Al-MSSs) for the improvement of mechanical properties and aging resistance of dental resin composites

OBJECTIVE

The purpose of this study was to synthesize Al-doped mesoporous silica spheres (Al-MSSs) and evaluate the effect of them as functional fillers on the mechanical properties and aging resistance of dental resin composites.

METHODS

Al-MSSs were prepared by a two-step method. The effect of Al-MSSs on the performance of the composites was evaluated using neat resin matrix, commercial composites 3M Z350XT and samples containing mesoporous silica spheres (MSSs) and nonporous silica spheres (NSSs) as control. The neat resin matrix consisted of resin monomer (Bisphenol A glycerolate dimethacrylate/triethylene glycol dimethacrylate, 49.5/49.5, wt%) and photoinitiator (camphor quinone/Ethyl-4-dimethylaminobenzoate, 0.2/0.8, wt%). The mechanical properties (flexural strength, flexural modulus, compressive strength and microhardness) of them were evaluated by a universal testing machine and microhardness tester. The mechanical stabilities of the prepared composites in wet environment were evaluated by immersing them in deionized water at 37 °C. In addition, we evaluated the effect of Al-MSSs on other properties of the dental resin composites such as polymerization shrinkage, degree of conversion, curing depth, contact angle, water sorption and solubility according to ISO 4049: 2019.

RESULTS

The synthesized Al-MSSs possessed good dispersibility with an average particle size of about 505 ± 16 nm. The mechanical properties of resin composites gradually increased with the increase of the loading amounts of inorganic fillers. The reinforcing effect of Al-MSSs was similar to that of MSSs and better than that of the NSSs groups at the same filler loading. After aging in deionized water at 37 °C for 30 days, the mechanical properties of all resin composites decreased. However, the decrease percentage of the composites filled with Al-MSSs was significantly lower than the other groups, indicating that the stability of the dental composites in wet environments was significantly improved by the Al-MSSs fillers. Furthermore, Al-MSSs had no obvious influence on the biocompatibility and other properties of dental resins.

SIGNIFICANCE

The prepared Al-MSSs could effectively improve the mechanical properties and aging resistance without sacrificing other physic-chemical properties of dental resin composites.

High Refractive Index, Low Birefringence Holographic Materials via the Homopolymerization of 1,2-Dithiolanes

High refractive index, low birefringence photopolymers were created via the radical-mediated, ring opening homopolymerization of 1,2-dithiolane functionalized monomers and were subsequently evaluated as holographic recording media. This investigation systematically characterized the reaction kinetics, thermodynamics, and volume shrinkage of the 1,2-dithiolane homopolymerization as well as the optical transparency, refractive index, birefringence, and holographic performance of multifunctional 1,2-dithiolane functionalized monomers and their resultant polymers. Real-time kinetic and thermodynamic analyses of a monofunctional 1,2-dithiolane monomer, lipoic acid methyl ester (LipOMe), indicated rapid monomer conversion, exceeding 90% in 60 s, with an overall enthalpy of reaction of 18 ± 1 kJ/mol. The ring-opening polymerization resulted in low shrinkage (10.6 ± 0.3 cm3/mol dithiolane) and a significant bulk refractive index increase (0.030 ± 0.003). The resulting photopolymers exhibited high optical transparency, minimal haze, and negligible birefringence, suggesting the potential of 1,2-homopolymers as optical materials. To further explore the specific capabilities for use as high-performance holographic recording applications, several multifunctional monomers were synthesized with the ethanedithiol lipoic acid monomer (EDT-Lip2) selected for experimentation. Holographic diffraction gratings written using this monomer achieved a peak-to-mean refractive index modulation of 0.008 with minimal haze and birefringence.

Release of contraction stress of dental resin composites by water sorption

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.

Bulk-fill composite in challenging cavities: conversion rate, solubility, and water absorption analysis

In a deep, curved cavity, polymerization of a bulk fill composite can be challenging. The aim of this study was to investigate the solubility, water absorption, and conversion rate of bulk-fill composite samples prepared using molds with various slope angles. Bulk-fill composite resin (Filtek One Bulk Fill) was placed into cylindrical Teflon molds with a depth of 4 mm, angled at varying degrees (90°, 75°, 60°, 45°). Two different LED light-curing units (VALO Cordless, iLed Curing Light) were used to cure the samples. Polymerizations were performed at three different distances (0 mm, 2 mm, and 4 mm). Five samples per group were used, resulting in a total of 24 groups. The Fourier Transform Infrared Spectrometer was utilized to evaluate the conversion levels of the samples. Water sorption and solubility values were determined by storing the composites in distilled water at 37 °C for 21 days. The VALO light-curing unit applied closest to samples inserted in a 90° angulation mold had the highest mean degree of conversion (41.55%), while iLED light-curing unit group that applied from 4 mm to the samples inserted in a 45° angulation mold had the lowest mean conversion (8.97%). The angle of the cavity and the distance at which the light-curing unit is applied significantly affected bulk-fill composite resin conversion. In addition, the choice of light-curing unit impacted the conversion levels. However, with the tested conditions, the water sorption and solubility values of polymerized composite resin samples remain unaffected by these factors.

Effect of layering strategy and prolonged water aging on masking ability of composite resins

STATEMENT OF PROBLEM

Layered composite resins may adequately mask discolored substrates. However, whether color changes that occur over time affect masking ability is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of layering and water aging on the masking ability of 2 composite resins.

MATERIAL AND METHODS

Disk specimens (1.5 mm-thick and shade A1) from Charisma Diamond (CD) and Filtek Z350XT (Z350) were made according to the composite resin shade combination used in the layering strategies: bilayer for CD (enamel/dentin) and for Z350 (enamel/body and enamel/dentin) and trilayer for Z350 (enamel/body/dentin) (n=5). Color measurements were obtained with a spectrophotometer over an A3.5 ceramic substrate, and the whiteness index for dentistry (WID) was calculated. The specimens were aged in water at 37 °C and evaluated at different times: 24 hours, 1 week, 1 month, 2 months, 6 months, 12 months, 18 months, and 24 months. CIEDE2000 color differences (ΔE00) and WID differences (ΔWID) were calculated and interpreted by 50:50% color and whiteness perceptibility and acceptability thresholds. Changes among strategies and aging times were analyzed using the Kruskal-Wallis test (α=.05). Contrasts were made using the Mann-Whitney U test with Bonferroni correction (α=.001).

RESULTS

ΔE00 decreased from 24 hours to 2 months of aging. From 2 months onwards, ΔE00 increased for all layering strategies and times, without significant changes in lightness for CD (P>.004). Overall, for the CD restorative system, an increase in ΔWID was observed after 1 month of aging (P<.001), while for the Z350 restorative system, ΔWID decreased after aging (P<.001), except for the Z350 bilayer strategy (enamel + dentin) at 1 week and 2 months (P>.004). For all layering strategies and aging times, color differences were higher than the 50:50% perceptibility threshold for ΔE00 and, after 6 months, higher than the 50:50% acceptability threshold for ΔE00 and the 50:50% whiteness acceptability threshold.

CONCLUSIONS

The ability of the tested composite resins to mask a discolored substrate was affected by the layering approach applied and by prolonged water aging.

Investigation of aging resistance for dental resin composites with and without glass flakes

OBJECTIVES

Outstanding physical-mechanical properties and aging resistance are key requirements for dental resin composite since it will be placed in the oral environment for a long time. In this work, a new dental resin composite mainly modified by glass flakes was fabricated, and the aging resistance was evaluated by comparing with commercial composites without glass flakes.

MATERIALS AND METHODS

The new dental resin composite was produced through hand blending of inorganic glass flakes/Si-Al-borosilicate glass (58wt%:7wt% of dental resin composite), POSS-MA (5wt% of resin matrix), Bis-GMA/TEGDMA(64.4wt%:27.6wt% of resin matrix), and CQ/EDMAB (0.9wt%:2.1wt% of resin matrix) together. The flexural strength, elasticity modulus, and hardness, as well as wear were tested for evaluating the aging resistance of different dental resin composite.

RESULTS

Among 6 kinds of commercial composites in this study, after 6-month water storage, the maximum percentage of performance degradation is that the flexural strength decreased 39.96%, elasticity modulus decreased 51.53% and hardness decreased 12.52%. In contrast, the new synthesized material decreased 14.53%, 20.88%, and 0.61%, respectively, and performed lesser wear depth compared to some other groups (P < 0.05).

CONCLUSIONS

It was observed that the new dental resin composite performed better performance stability and wear resistance when compared with commercial dimethacrylate-based or low shrinkage dental resin composite tested in this study.

CLINICAL RELEVANCE

This possibly paves a path for designing tailored dental composite for practical application. Since the aging resistance of dental resin composite modified by glass flakes is superior, it has the potential to be used for promoting the durability of dental resin composite.

Bioactive Dental Resin Composites with MgO Nanoparticles

Photoactivating dental resin composites have been the most prevailing material for repairing dental defects in various clinical scenarios due to their multiple advantages. However, compared to other restorative materials, the surface of resin-based composites is more susceptible to plaque biofilm accumulation, which can lead to secondary caries and restoration failure. This study introduced different weight fractions (1, 2, 5, 10, and 15%) of magnesium oxide nanoparticles (MgONPs) as antibacterial fillers into dental resin composites. Multifarious properties of the material were investigated, including antibacterial activity against a human salivary plaque-derived biofilm, cytotoxicity on human gingival fibroblasts, mechanical and physicochemical properties as well as the performance when subjected to thermocycling aging treatment. Results showed that the incorporation of MgONPs significantly improved the composites' anti-biofilm capability even at a low amount of 2 wt % without compromising the mechanical, physicochemical, and biocompatibility performances. The results of the thermocycling test suggested certain of aging resistance. Moreover, a small amount of MgONPs possibly made a difference in enhancing photoactivated polymerization and increasing the curing depth of experimental resin composites. Overall, this study highlights the potential of MgONPs as an effective strategy for developing antibacterial resin composites, which may help mitigating cariogenic biofilm-associated secondary caries.

Tailoring the monomers to overcome the shortcomings of current dental resin composites - review

Dental resin composites (DRCs) have become the first choice among different restorative materials for direct anterior and posterior restorations in the clinic. Though the properties of DRCs have been improved greatly in recent years, they still have several shortcomings, such as volumetric shrinkage and shrinkage stress, biofilm development, lack of radio-opacity for some specific DRCs, and estrogenicity, which need to be overcome. The resin matrix, composed of different monomers, constitutes the continuous phase and determine the performance of DRCs. Thus, the chemical structure of the monomers plays an important role in modifying the properties of DRCs. Numerous researchers have taken to design and develop novel monomers with specific functions for the purpose of fulfilling the needs in dentistry. In this review, the development of monomers in DRCs were highlighted, especially focusing on strategies aimed at reducing volumetric shrinkage and shrinkage stress, endowing bacteriocidal and antibacterial adhesion activities as well as protein-repelling activity, increasing radio-opacity, and replacing Bis-GMA. The influences of these novel monomers on the properties of DRCs were also discussed.

Microleakage Evaluation of Two Methacrylate-Based Composites (GC Kalore and Luna SDI) in Class II Restorations: A Laboratory Study

Objective

In recent years, dental composite resins such as tooth-colored restoration are frequently used to restore dental cavities, coronal fractures, and congenital defects. This study aimed to evaluate the microleakage of two methacrylate-based composites (GC Kalore and Luna SDI) in class II restorations.

Materials and Methods

In this experimental study, a total of 18 intact human premolars previously extracted for periodontal and orthodontic reasons were randomly divided into two groups. Similar class II cavities (box only) were prepared on all teeth and restored with two different composites. In group 1, a bonding agent (Single Bond 2-SB2; 3M ESPE) and Luna SDI composite in mesial cavities and GC Kalore composite in distal cavities were used. In group 2, Single Bond 2 and GC Kalore composite in mesial cavities and Luna SDI composite in distal cavities were applied. They were then subjected to 2000 thermal cycles in a water bath between 5-55°C (dwell time: 30 seconds in every bath and transfer time: 10 seconds). Then, they were immersed in a 2% basic fuchsin dye solution for 24 hours. After rinsing with water, they were sectioned mesiodistally and evaluated for microleakage using a stereomicroscope.

Results

Independent t-test (Mann-Whitney test) showed no statistically significant difference for microleakage in mesial and distal class II restorations between GC Kalore composite and Luna SDI composite (p = 1.000) (p= 0.852). A total of 83.4% of the Luna SDI composite samples and 66.6% of the GC Kalore composite had a microleakage score of ≤3 in class II cavities.

Conclusion

In the present study, marginal microleakage was found mainly at the gingival floor extending to 1/3 of the axial wall for the Luna SDI composite and GC Kalore composite. Furthermore, no statistically significant difference was found between the microleakage of the Class II cavities restored with Luna SDI composite and GC Kalore composite.

Comparative of flexural strength, hardness, and fluoride release of two bioactive restorative materials with RMGI and composite resin

Aim: This study was fulfilled to evaluate the flexural strength, micro-hardness, and release of two fluoride ions of bioactive restorative materials (Cention N and Activa Bioactive), a resin modified glass ionomer (Fuji II LC), and a resin composite (Filtek z250). Methods: Forty samples from four restorative materials (Activa Bioactive, Fuji II LC, Cention N, and Filtek Z250) were provided according to the current standards of ISO 4049/2000 guide lines. Subsequently, the samples were stored for 24 hours and 6 months in artificial saliva, and successively, flexural strength and micro-hardness of the samples were measured. For each studied groups the pH was decreased from 6.8 to 4 in storage solution. The rate of changes in fluoride ion release was measured after three different storage periods of 24 hours, 48 hours, and 6 months in distilled water, according to the previous studies’ method. Two-way ANOVA, One-way ANOVA, Tukey HSD Pair wise comparisons, and independent t-tests were used to analyze data (α= 0.05). Results: The highest flexural strength and surface micro-hardness after 24 hours and also after 6 month were observed for Cention N(p<0.001).Flexural strength of all samples stored for 6 months was significantly lower than the samples stored for 24 hours(p<0.001). The accumulative amount of the released fluoride ion in RMGI, after six-month storage period in distilled water was considerably higher (p<0.001) than 24 hours and 48 hours storage. The amount of fluoride ion release with increasing acidity of the environment (from pH 6.8 to 4) in Fuji II LC glass ionomer was higher than the bioactive materials (p<0.05). Conclusion: The flexural strength of RMGI was increased after storage against the Activa Bioactive,Cention N and Z250 composite. Storage of restorative materials in artificial saliva leads to a significant reduction in micro hardness. The behavior and amount of released fluoride ions in these restorative materials, which are stored in an acidic environment, were dependent on the type of restorative material.

Low-Shrinkage Resin Matrices in Restorative Dentistry-Narrative Review

Dimethacrylate-based resin composites restorations have become widely-used intraoral materials in daily dental practice. The increasing use of composites has greatly enhanced modern preventive and conservative dentistry. They have many superior features, especially esthetic properties, bondability, and elimination of mercury and galvanic currents. However, polymeric materials are highly susceptible to polymerization shrinkage and stresses that lead to microleakage, biofilm formation, secondary caries, and restoration loss. Several techniques have been investigated to minimize the side effects of these shrinkage stresses. The primary approach is through fabrications and modification of the resin matrices. Therefore, this review article focuses on the methods for testing the shrinkage, as well as formulations of resinous matrices available to reduce polymerization shrinkage and its associated stress. Furthermore, this article reviews recent cutting-edge developments on bioactive low-shrinkage-stress nanocomposites to effectively inhibit the growth and activities of cariogenic pathogens and enhance the remineralization process.

Preparation of Ca doped wrinkled porous silica (Ca-WPS) for the improvement of apatite formation and mechanical properties of dental resins

The purpose of this work was to fabricate and characterize Ca doped wrinkled porous silica (Ca-WPS), and evaluate their effect on the mineralization and mechanical properties of resin composites as functional fillers. Ca-WPS were prepared by sol-gel method and characterized by scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption measurements. The mineralization properties of the prepared Ca-WPS particles and the resin composites with different amount of Ca-WPS were evaluated by simulated body fluid (SBF) immersion method. The mechanical properties (flexural strength, flexural modulus, compressive strength and microhardness) of the dental resins containing unimodal Ca-WPS fillers and bimodal Ca-WPS fillers with nonporous silica were evaluated by a universal testing machine. Results showed that after immersing in SBF for 5 d, apatite formed on the surface of Ca-WPS and composites containing Ca-WPS fillers, indicating the excellent mineralization property of the prepared Ca-WPS. The mechanical properties of the dental resins increase with the increase of the proportion of unimodal Ca-WPS fillers. The dental resins with bimodal Ca-WPS fillers showed better mechanical properties than the group with only nonporous fillers at the same filler loading (60 wt%). Among all the samples, the dental composites filled with bimodal fillers (mass ratio of Ca-WPS: nonporous silica = 10:50, total filler loading 60 wt%) exhibited the best mechanical performance. The flexural strength, flexural modulus, compressive strength and microhardness of these samples were 26.96%, 42.75%, 16.04% and 54.1% higher than the composites with solid silica particles alone, respectively. Thus, the prepared Ca-WPS could effectively improve the apatite formation and mechanical properties of resin composites.

A novel resin cement to improve bonding interface durability

Bonding failure is one of the main causes of failure of dental restorations. The bonding strength, aging resistance, and polymerization shrinkage of cement can affect the stability of the bonding interface and lead to marginal microleakage. To reduce the bonding failure rate of restorations, a novel polyurethane (PU) cement was designed to improve the mechanical properties, hydrophobicity, degree of conversion (DC), polymerization shrinkage, bond strength and aging resistance of cement by introducing isophorone diisocyanate (IPDI) and hydroxyethyl methacrylate (HEMA) and adjusting the polyester : polyether ratio to increase the degree of cross-linking. Experimental results verified that the novel PU could increase the mechanical properties and thermal stability of the cement, reduce polymerization shrinkage during the curing reaction, improve the bonding performance and DC, endow the cement with hydrophobic properties, and improve its ability to resist aging in the salivary environment to maintain the long-term stability of interfacial bonding under the influence of comprehensive factors. The results of this study provide a new direction and insights to reduce microleakage and improve the success rate of restorations.

Bonding failure is one of the main causes of failure of dental restorations.

Effect of post-curing light exposure time on the physico-mechanical properties and cytotoxicity of 3D-printed denture base material

OBJECTIVE

This study investigated the effect of post curing light exposure time on the physico-mechanical properties and cytotoxicity of a 3D-printed PMMA-based denture material in comparison to a conventional heat-cured alternative as a control.

METHODS

3D-printed specimens were fabricated followed by post-curing for 0, 5, 10 or 20 min at 200 W and light wavelength range of 390-540 nm. Heat-cured specimens were fabricated using a standard protocol. Specimens were placed in artificial saliva at 37 ℃ for 48 h (immediate groups) and 6 months (aged group), then evaluated flexural strength/modulus, fracture toughness, microhardness, and degree of conversion. Water sorption and solubility was assessed after 28 days. Flexural strength, flexural modulus, and fracture toughness were tested through three-point bending tests, while the surface hardness was tested using Vickers's test. Fractured specimens were viewed by scanning electron microscope (SEM). Cytotoxicity in term of cell viability was evaluated using human oral fibroblasts.

RESULTS

Flexural strength/modulus, fracture toughness and surface hardness significantly improved with the increase in light curing time up to 20 min. The same pattern of improvement was found with degree of conversion, water sorption, solubility, and cell viability. There was no significant difference (p < 0.01) between heat-cured material and 3D specimens post-cured for 20 min in term of flexural strength/modulus, surface hardness, and degree of conversion at the two-storage time points.

SIGNIFICANCE

Generally, the physico-mechanical properties of the 3D-printed denture base material improve as post curing time increases up to 20 min which exhibited comparable performance as the conventional heat-cured control.

Comparative evaluation of the effect of thermocycling on the mechanical properties of conventionally polymerized, CAD-CAM milled, and 3D-printed interim materials

STATEMENT OF PROBLEM

Studies on the energy absorption characteristics by means of elastic and plastic material deformation of interim materials are lacking.

PURPOSE

The purpose of this in vitro study was to compare the effect of different thermocycling periods on the flexural strength (σ_fs), resilience (U_r), and toughness (U_T) of conventionally polymerized, computer-aided design and computer-aided manufacturing (CAD-CAM) milled, and 3-dimensionally (3D) printed interim materials.

MATERIAL AND METHODS

Rectangular specimens (n=30 for each material) were fabricated from autopolymerized polymethyl methacrylate (PMMA), bis-acryl resin (Bis-acryl), CAD-CAM polymethyl methacrylate-based polymer (CAD-CAM/Milled), and 3D-printed composite resin (3D-Printed). Each material was divided into 3 groups (n=10) according to the applied thermocycling (5 °C to 55 °C) procedure: control (0 cycles), 2500, and 10 000 cycles. Parameters of the materials such as σ_fs, U_r, and U_T were tested in a 3-point bend test according to International Organization for Standardization (ISO) 10477. Data were statistically analyzed with the Shapiro-Wilk test followed by Kruskal-Wallis test, the Mann-Whitney U test, the Friedman test, and Wilcoxon signed-rank test (α=.05).

RESULTS

The tested material and thermocycling had a statistically significant influence on the σ_fs, U_r, and U_T values (P<.05). PMMA showed the lowest mean σ_fs, U_r, and U_T values (P<.05), and CAD-CAM/Milled showed σ_fs values similar to those of 3D-Printed at all thermocycling periods. CAD-CAM/Milled showed the highest U_r values at 10 000 cycles and the highest U_T values at all thermocycles. No significant differences were found in the mean change of σ_fs and U_r of CAD-CAM/Milled among different thermocycling periods.

CONCLUSIONS

The results suggested that digitally fabricated interim materials had better mechanical properties than conventionally polymerized materials and that milled materials had the highest stability in maintaining their initial capacity to absorb energy.

Evaluation of the Water Sorption and Solubility Behavior of Different Polymeric Luting Materials

Objective: The study evaluated the water sorption (WSP) and water solubility (WSL) characteristics of different luting agents over a 180-day water storage period. Materials and Methods: Nine luting materials, i.e., conventional resin cement: Panavia F (PF), Rely X ARC (RA), self-adhesive resin cement: Rely X Unicem (RU), Breez (BZ), Maxcem Elite (MX), BisCem (BC) and resin-modified glass ionomer cement: FujiCem (FC), FujiPlus (FP) Rely X luting plus (RL) were assessed and fifty-two-disc specimens of each material were fabricated. All specimens were desiccated until a constant weight (W0) was reached. Thirteen specimens for each luting material were then randomly assigned to one of the four water immersion periods (7, 30, 90, and 180 days). After each period, the specimens were removed from the water and weighed to get W1. The samples were again desiccated for a second time and W₂ was measured. Both WSP and WSL were determined by the following equations: WSP (%) = (W₁ − W₂) × 100/W₀ and WSL (%) = (W₀ − W₂) × 100/W₀. Assessments were performed following ISO standards. ANOVA was used to assess the effect of luting agent and time period on water sorption and solubility. Pair-wise comparisons were adjusted using Tukey’s multiple comparison procedure. A significance level of 0.05 was used for all statistical tests. Results: The highest mean WSP and WSL (WSP/WSL) were demonstrated by resin-modified glass-ionomers (RL 18.32/3.25, FC 17.08/4.83, and FP 14.14/1.99), while resin luting agents showed lower WSP and WSL results (PF 1.6/0.67 and RA 1.76/0.46), respectively. The self-adhesive agents exhibited a wide range of WSP and WSL values (RU 1.86/0.13, BZ 4.66/0.93, and MX 3.68/1.11). Self-adhesive cement showed lower WSP and WSL compared with the resin-modified glass-ionomers (p < 0.05). All the materials reached equilibrium after 90-days. Conclusions: Resin-based luting materials have the lowest sorption and solubility. Rely X Unicem self-adhesive luting materials were comparable to resin luting materials for WSL and WSP. Resin-modified glass-ionomer showed the highest water sorption and solubility compared with both resin and self-adhesive materials.

Improper Light Curing of Bulkfill Composite Drives Surface Changes and Increases S. mutans Biofilm Growth as a Pathway for Higher Risk of Recurrent Caries around Restorations

How dentists cure a resin-based material has deleterious effects on the material's properties and its interaction with surrounding dental tissues. Biofilm accumulation has been implicated in the pathogenesis of carious lesions around dental restorations, with its composition manifesting expressed dysbiosis in patients suffering from dental caries. To evaluate the influence of varying radiant exposure on the degree of conversion (DC%), Streptococcus mutans biofilm growth, and surface roughness of bulk-fill composites under different light-curing conditions. Two light-curing units (LCU) at 600 and 1000 mW/cm² were used to simulate curing conditions with different angulations (∢20° and ∢35°) or 2 mm-distance displacements of the LCU tip. The radiant exposure (RE) was assessed, and the composites were analyzed for DC%. Biofilm formation was induced over the bulk-fill composites and analyzed via colony-forming units counting and scanning electron microscopy (SEM). The surface roughness was analyzed via a profilometer and SEM after biofilm formation. Curing conditions with different angulation or displacement decreased RE compared to the "optimal condition". The moderately (∢35°) angulated LCU tip and low (600 mW/cm²) radiant emittance significantly reduced the DC% (p < 0.05). The difference in DC% between the top and bottom of the composites ranged from 8 to 11% for 600 mW/cm² and 10 to 20% for 1000 mW/cm². Greater S. mutans biofilm and surface changes were found in composites with non-optimal RE delivery (e.g., tip displacement and angulation) (p < 0.05). Inadequate polymerization of bulk-fill composites was associated with more biofilm accumulation and surface topography changes. Overall, non-optimally performed curing procedures reduced the amount of delivered RE, which led to low DC%, more biofilm formation, and higher surface roughness. The improper light-curing of bulk-fill composites compromises their physicochemical and biological properties, which could lead to inferior clinical performance and reduced restorative treatments' longevity.

Interface analysis after fatigue loading of adhesively luted bundled fiber posts to human root canal dentin

OBJECTIVES

The aim of this study was to assess the fatigue loading behavior and fracture resistance of endodontically treated teeth restored with adhesively luted bundled fiber posts in comparison to solid fiber posts. Image analysis (2D and 3D) was applied to evaluate modes of failure and to characterize susceptible parts of the post-and-core interface.

METHOD

Crowns of 72 human similar-sized central upper incisors were removed and roots received a conventional root canal filling prior to establishing 4 groups of core build-up: No Post group (nP) received a 4 mm deep filling made of composite inside the canal with no dental post, fiber post group (FP) received a conventional solid post, and two experimental groups received bundles of 6 (FB6) or 12 (FB12) 0.3 mm thin fiber posts, respectively. Posts were placed adhesively inside the root canal using a dual-curing build-up composite in combination with a self-etch adhesive, the latter was also used for nP group. Upon completion of core build-ups, all teeth received full-ceramic crowns that recreated the original tooth form. Samples were subjected in a 135° angle to thermo-mechanical loading (TML) for 1.2 Mill. chewing cycles followed by static load tests (fracture resistance). Fracture modes as well as intracanal failure modes with respect to failed interfaces were analyzed using optical and electron microscopy (SEM). Microcomputer tomography (μCT) was used to exemplary compare pre and post TML geometries.

RESULTS

Static load test was significantly different between groups (p < 0.0005; Kruskal-Wallistest). Pairwise comparison showed that the nP group (221 ± 103N) failed at significantly lower forces compared to the FP (454 ± 184N), FB6 (477 ± 250N) and FB12 (478 ± 260N) groups (p ≤ 0,001; Mann-Whitney-U-test). Fracture modes were significantly affected by the presence or absence of a post (p ≤ 0,016; Chi-square test) revealing increased incidence of restorable fractures at the cervical region for nP group. Microscopic analysis revealed more intracanal failures at interfaces between post surfaces and composite for solid posts, whereas fiber bundled posts mostly failed at the interfaces between composite and dentin. Micro-CT analysis showed no alterations of the root-post-and-core structure after TML except slight deformations of occasionally entrapped voids.

CONCLUSION

Fracture resistance and fracture modes were significantly affected by the presence or absence of a post, whereas the investigated post groups did not differ from each other. However intracanal failure revealed differences in adhesive failures between solid fiber posts and bundled fiber posts. Deformations of entrapped voids, revealed by micro-Ct analyses after TML, lead to the assumption that applied forces result in alterations in the regions of voids.

Antimicrobial potential of resin matrices loaded with coffee compounds

This study evaluated the biological behavior of the coffee compounds Trigonelline (T), chlorogenic acid (C), and nicotinic acid (N), correlating with their release from a resin matrix. Minimum inhibitory concentration (MIC) was evaluated against Streptococcus mutans UA159, and cytotoxicity was assessed by methyl tetrazolium salt on OD-21 cells. Resin matrices (bisphenol A-glycidyl-dimethacrylate/triethylene glycol-dimethacrylate 70/30 wt%, camphorquinone/ethyl 4-dimethyl aminobenzoate 0.5/1 wt%) were doped with coffee compounds in different concentrations (10/20/30/40/50 wt%), performing 15 groups (T10-T50, C10-C50, N10-N50), and a control group with no coffee compound. Degree of conversion (DC%) was analyzed by Fourier transform infrared spectroscopy. Antimicrobial properties were evaluated by bioluminescence (Luciferase assay). The release from loaded matrices was analyzed over time (24 hr, 6, 14, 21 and 28 days), using high-performance liquid chromatography (HPLC). Data were submitted to ANOVA/Tukey's test (α = 0.05). MIC for T and C was 6 mg/ml, and 4 mg/ml for N. None of them were cytotoxic. Only T50 and C50 showed lower DC% than control (α < 0.05). Some groups (T30/T40/T50/C40/C50/N50) were strongly antimicrobial, reducing bacterial activity approximately five times compared to control (α < 0.05). For T30, T40, T50, C40, and C50, the HPLC showed a release above or closer to MIC values mainly in 24 hr, but for N50, up to 28 days. In conclusion, the coffee compounds presented antimicrobial activity, depending on their concentration when added in resin matrices, being found a correlation with their release.

Effect of over the counter mouthwashes with and without alcohol on sorption and solubility of bulk fill resins

Background

Composites sorption and solubility can be precursors of several chemical and physical processes, which lead to deleterious effects on the polymer structure. This study evaluated the effect of mouthwashes with and without alcohol on the sorption and solubility of conventional and low viscosity bulk fill resins.

Material and Methods

Four types of Bulk Fill resins (Filtek™ Bulk Fill, X-tra Fil, Filtek™ Bulk Fill Flow and X-tra Base) were submitted to the following mouthwashes: Listerine Cool Mint and Periogard (containing alcohol) and Listerine Zero and Periogard (alcohol-free). The specimens were stored in the mouthwashes for seven days. Solubility and sorption tests were performed according to ISO 4049. Data were analyzed using two-way-ANOVA, followed by Tukey Test. The data were grouped, and a paired t-test was performed to evaluate the effect of alcohol on the properties studied. The p was fixed at 5%.

Results

Resins immersed in alcohol-containing mouthwashes had higher values of sorption and solubility, with the highest sorption rate for X-Tra Base in Listerine Cool Mint treatment (p<0.05). Flow type resins showed higher sorption than conventional viscosity resins, irrespective of the mouthwash used (p<0.05).

Conclusions

Alcohol-containing mouthwashes affected sorption and solubility of bulk fill resins and the composites that presented worse and better performance regarding the studied properties were X-Tra Base and Filtek™ Bulk Fill, respectively.

Key words:Solubility, Sorption, Mouthwashes, Bulk-fill composites.

Biomechanical and biological evaluations of novel BPA-free fibre-reinforced composites for biomedical applications

This aim was to assess the biomechanical and biocompatibility properties of novel glass fibre-reinforced composites (FRCs) with a fluorinated urethane dimethacrylate (FUDMA) resin. Three ratios of FUDMA/TEGDMA (30/70 wt%, 50/50 wt%, 70/30 wt%) and two ratios of control FRCs with bis-GMA/TEGDMA (50/50 wt% and 70/30 wt%) containing long silanized E-glass fibres were prepared. Despite 70 wt% bis-GMA-FRC showed a significantly higher flexural strength (p < 0.05), 50 wt% FUDMA- and bis-GMA-FRCs were not differ from each other. The greatest surface hardness and weight increase after water storage were found in 70 wt% and 30 wt% FUDMA-FRCs, respectively. No significant difference was found in water sorption and solubility among all groups. Average surface roughness was 1.80 ± 0.05 μm, while 70 wt% FUDMA-FRC exhibited the greatest contact angle (p > 0.05). Viabilities and ALP activities of MC3TC-E1 cells in all FUDMA-FRCs were higher than bis-GMA-FRCs after 5 days. To conclude, the novel FUDMA-FRCs are potential substitutes that exhibited superior cytocompatibility properties but comparable biomechanical properties to bis-GMA-FRCs.

Young's modulus and Poisson ratio of composite materials: Influence of wet and dry storage

In the oral environment dental materials are subject to a wet condition what might in time change their elastic properties. In this article, we evaluated the influence of the storage condition (dry versus wet) on the Young's modulus and the Poisson ratio in compression of three composite materials. The data of the Young's modulus and Poisson ratio published of dental composite materials are not always comparable, due to different test methods and sample dimensions influencing the results. Therefore, we established the degree of exactness of the results out of the test set-up used. Since the present study depicted differences of the properties after dry and wet storage, the elastic properties should be measured after wet storage. The bonding between the matrix and the filler particles showed to have an influence on the elastic properties and on the influence of a wet environment.

The synergistic effects of SrF2 nanoparticles, YSZ nanoparticles, and poly-ε-l-lysin on physicomechanical, ion release, and antibacterial-cellular behavior of the flowable dental composites

Resin-based pit-and-fissure sealants (flowable resin composites) were formulated using bisphenol-A-glycerolatedimethacrylate (Bis-GMA)-triethylene glycol dimethacrylate-(TEGDMA)-diurethanedimethacrylate (UDMA) mixed monomers and multiple fillers, including synthetic strontium fluoride (SrF₂) nanoparticles as a fluoride-releasing and antibacterial agent, yttria-stabilized zirconia (YSZ) nanoparticles as an auxiliary filler, and poly-ε-l-lysin (ε-PL) as an auxiliary antibacterial agent. Based on the physical, mechanical and initial antibacterial properties, the formulated nano-sealant containing 5 wt% SrF₂, 5 wt% YSZ and 0.5 wt% ε-PL was selected as the optimal specimen and examined for ion release and cytotoxicity. The results showed an average release rate of 0.87 μg·cm^-2·day^-1 in the aqueous medium (pH 6.9) and 1.58 μg·cm^-2·day^-1 in acidic medium (pH 4.0). The maximum cytotoxicity of 20% toward human bone marrow mesenchymal stem cells (hMSCs) was observed according to the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) cytotoxicity assay and acridine orange staining test. A synergy between SrF₂ nanoparticles and ε-PL exhibited a better antibacterial activity in terms of colony reduction compared to the other samples. However, the inclusion of SrF₂ and ε-PL caused mechanically weakening of the sealants that was partly compensated by incorporation of YSZ nanoparticles (up to 10 wt%).

Light Transmittance and Polymerization of Bulk-Fill Composite Materials Doped with Bioactive Micro-Fillers

This study investigated the effect of bioactive micro-fillers on the light transmittance and polymerization of three commercially available bulk-fill resin composites. These were mixed with 20 wt% bioactive glass 45S5, Portland cement, inert dental barium glass, or nothing (controls). Composites were photo-activated and light transmittance through 4 mm thick specimens was measured in real time. Moreover, degree of conversion (DC) and Knoop hardness (KHN) were assessed. Light transmittance of all bulk-fill composites significantly decreased (p < 0.05) with addition of 20 wt% bioactive glass 45S5 but not when inert barium glass was added. For bulk-fill composites modified with Portland cement, light irradiance dropped below the detection limit at 4 mm depth. The DC at the top surface of the specimens was not affected by addition of bioactive or inert micro-fillers. The bottom-to-top ratio of both DC and KHN surpassed 80% for bulk-fill composites modified with 20 wt% bioactive or inert glass fillers but fell below 20% when the composites were modified with Portland cement. In contrast to Portland cement, the addition of 20 wt% bioactive glass maintains adequate polymerization of bulk-fill composites placed at 4 mm thickness, despite a decrease in light transmittance compared to the unmodified materials.

The effect of aging methods on the fracture toughness and physical stability of an oxirane/acrylate, ormocer, and Bis-GMA-based resin composites

PURPOSE

To determine the effect of aging methods on the fracture toughness of a conventional Bis-GMA-based resin composite (Filtek Supreme), an ormocer-based resin composite (Admira), and an experimental hydrophobic oxirane/acrylate interpenetrating network resin system (OASys)-based composite.

METHODS

A 25 × 5 × 2.8-mm stainless-steel mold with 2.5 mm single-edge center notch, following ASTM standards [E399-90], was used to fabricate 135 specimens (n = 15) of the composite materials and randomly distributed into groups. For the baseline group, specimens were fabricated and then tested after 24-h storage in water. For the biofilm challenge, specimens were randomly placed in a six-well tissue culture plate and kept at 37 °C with bacterial growth media (Brain Heart Infusion (BHI); Streptococcus mutans) changed daily for 15 days. For the water storage challenge, specimens were kept in 5 ml of deionized distilled autoclaved water for 30 days at 37 °C. μCT evaluation by scanning the specimens was performed before and after the proposed challenge. Fracture toughness (K_Ic) testing was carried out following the challenges.

RESULTS

μCT surface area and volume analyses showed no significant changes regardless of the materials tested or the challenge. Filtek and Admira fracture toughness was significantly lower after the biofilm and water storage challenges. OASys mean fracture toughness values after water aging were significantly higher than that of baseline. Toughness values for OASys composites after biofilm aging were not statistically different when compared to either water or baseline values.

CONCLUSION

The fracture toughness of Bis-GMA and ormocer-based dental resin composites significantly decreased under water and bacterial biofilm assault. However, such degradation in fracture toughness was not visible in OASys-based composites.

CLINICAL SIGNIFICANCE

Current commercial dental composites are affected by the oral environment, which might contribute to the long-term performance of these materials.

New generation bulk-fill resin composites: Effects on mechanical strength and fracture reliability

PURPOSE

To investigate the mechanical performance and fracture reliability of new generation, bulk-fill resin composites of different viscosities.

METHODS

Forty sound maxillary premolars were prepared into Class I cavities comprised of 5 mm width × 5 mm length × 5 mm thickness. The teeth were randomly allocated into four groups (n = 10) according to the restorative material: Negative control - without restoration; Positive control - conventional resin composite (Opallis; FGM) was applied using increments of up to 2.0 mm-thick; Bulk-Regular - bulk-fill resin composite of regular viscosity (Opus Bulk Fill; FGM) was applied using a single increment of 5 mm-thick; and Bulk-Flow - a low-viscosity bulk-fill resin composite (Opus Bulk Fill Flow; FGM) was applied as the first increment with ∼3.5 mm-thick, followed by two final increments of Opallis (∼1.5 mm-thick). The teeth were stored at 37 °C, for 24 h, and submitted to a mechanical testing machine (DL500; EMIC) under a compressive loading. Work of fracture (W_f) was also obtained. All data were analyzed using ANOVA and Tukey (α = 5%). Reliability of restorations and probability of failure were analyzed by Weibull analysis.

RESULTS

The non-restored teeth showed the weakest behavior of the study. All the restored groups demonstrated similar mechanical properties to each other (p ≥ 0.242). The positive and negative controls failed exclusively within the cohesiveness of enamel/dentin, whereas the bulk-fill-based restorations showed a mixture of cohesive and mixed failures. The restored groups showed an overall similar reliability, although the Bulk-Regular group demonstrated greater characteristic strength than the positive control.

CONCLUSION

The novel bulk-fill resin composites of low and regular viscosities show promising application in the restoration of Class I cavities in premolars, demonstrating similar mechanical performance and reliability as compared with restorations prepared using conventional resin composites. From the bulk-fill materials, the version with regular viscosity presented the greatest compliant behavior of the study.

Antibacterial resin-based composite containing chlorhexidine for dental applications

OBJETICVE

The aim of this study was to develop a composite material with antibacterial activity using MMT loaded with clorhexidine (CHX). For that it was used a BisGMA/TEGDMA matrix and added low concentration of MMT/CHX. The aim was to evaluate the drug release capacity of MMT, and not to provide reinforcement.

METHODS

Six experimental composites were made with organic matrix of BisGMA/TEGDMA in equal proportions by weight. The composites received organophlizated montmorillonite with or without CHX. The concentrations were 2,5; 5 or 10% by weight. Degree of conversion (DC) was evaluated using FTIR (peak 6165 cm-1; n=5). Specimens for flexural properties (10×2×1mm) were immediate tested (24h). Elastic modulus(E) and flexural strength (FS) was measured using the three point bending test (n=10). Inibition halo was used to test the antibacterial activity against Staphylococcus aureus, Streptococcus mutans, and Porphyromonas gingivalis (n=5 for each bacteria). The inhibition of biofilm formation (BF) was evaluated by inserting polymerized disc of composite in to a culture media colonized with Streptococcus mutans (n=10). The release of CHX was measured using ultraviolet (255nm) for 10 days (n=5). The data of degree of conversion was analysed using Kruskal-Wallis/ Mann-Whitney, and the other variables using two-way ANOVA/Tukey, always considering a global level of significance of 5%.

RESULTS

DC ranged from 71% to 74%. E ranged from 5.7 to 8.1GPa. FS ranged from 61.4 to 74.7MPa. There were no statistical differences among the groups for all the variables. For the three bacteria tested the composites with CHX loaded presented inhibition of growth for all concentration, except for 2,5% that did not inihibited the growth of P. gingivalis. BF was lower for the groups with 10% MMT/CHX, all groups presented BF, even those without CHX loaded. All concentrations presented release off CHX during all the 28 days analyzed.

CONCLUSIONS

Within the limitation of this study it can be concluded that: all concentrations tested presented release of CHX and reduced BF. All concentration presented antibacterial activity for the three bacteria tested, except for 2,5% that did not inhibit the growth of P. gingivalis. The presence of MMT with CHX loaded did not interfere in the properties evaluated.

The Silorane-based Resin Composites: A Review

This article aims to review the research done on the silorane-based resin composites (SBRC) regarding polymerization shrinkage and contraction stresses and their ability to improve the shortcomings of the methacrylate-based resin composites (MRBC). Special attention is given to their physical and mechanical properties, bond strength, marginal adaptation, and cusp deflection. The clinical significance of this material is critically appraised with a focus on the ability of SBRC to strengthen the tooth structure as a direct restorative material. A search of English peer-reviewed dental literature (2003-2015) from PubMed and MEDLINE databases was conducted with the terms "low shrinkage" and "silorane composites." The list was screened, and 70 articles that were relevant to the objectives of this work were included.

The influence of simulated aging on the color stability of composite resin cements

STATEMENT OF PROBLEM

Data for the color stability of dual-polymerized and light-polymerized resin cements used in esthetic dentistry are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the color stability of 4 types of composite resin cements after water aging.

MATERIAL AND METHODS

Specimens (n=30) of each resin cement (Variolink Esthetic LC, RelyX Ultimate DC, Nexus 3 DC, Nexus 3 LC) were prepared. The shade selected was Light+ for Variolink Esthetic, B 0.5 for RelyX Ultimate, and White for both Nexus 3 DC and LC. All 120 specimens were aged by water for 30 days at 37°C under dark conditions, using a thermocycling machine. The specimens' color characteristics (L*, luminosity; a*, red-green; b*, yellow-blue) and color differences (ΔE) were measured with a spectrophotometer before day 0, after day 1, and after 30 days of immersion. Statistical analysis used ANOVA and Tukey post hoc tests (α=.05).

RESULTS

Considering ΔE<3.3 as clinically acceptable, results showed significant color variations for all cements (RelyX Ultimate=3.69; Nexus 3 LC=3.76; Nexus 3 DC=5.34), except for Variolink Esthetic (0.88). However, this variation was significantly less when day 1 was considered the baseline measurement, showing clinically acceptable ΔE values for all types of cement.

CONCLUSIONS

Water aging had a significant effect on color stability; most color variations occurred in the first 24 hours of polymerization, with relatively nonsignificant variations afterwards.

Properties of Experimental Dental Composites Containing Antibacterial Silver-Releasing Filler

Secondary caries is one of the important issues related to using dental composite restorations. Effective prevention of cariogenic bacteria survival may reduce this problem. The aim of this study was to evaluate the antibacterial activity and physical properties of composite materials with silver sodium hydrogen zirconium phosphate (SSHZP). The antibacterial filler was introduced at concentrations of 1%, 4%, 7%, 10%, 13%, and 16% (w/w) into model composite material consisting of methacrylate monomers and silanized glass and silica fillers. The in vitro reduction in the number of viable cariogenic bacteria Streptococcus mutans ATCC 33535 colonies, Vickers microhardness, compressive strength, diametral tensile strength, flexural strength, flexural modulus, sorption, solubility, degree of conversion, and color stability were investigated. An increase in antimicrobial filler concentration resulted in a statistically significant reduction in bacteria. There were no statistically significant differences caused by the introduction of the filler in compressive strength, diametral tensile strength, flexural modulus, and solubility. Statistically significant changes in degree of conversion, flexural strength, hardness (decrease), solubility (increase), and in color were registered. A favorable combination of antibacterial properties and other properties was achieved at SSHZP concentrations from 4% to 13%. These composites exhibited properties similar to the control material and enhanced in vitro antimicrobial efficiency.

Hygroscopic expansion of self-adhesive resin cements and the integrity of all-ceramic crowns

OBJECTIVE

Low pH neutralization and subsequent remnant hydrophilicity can lead to hygroscopic expansion of self-adhesive resin cements (SARCs) after water storage. The aim of this in vitro study was to investigate the effects of hygroscopic expansion of SARCs, used as luting and partial core build-up material, on integrity and cement gap thickness increase of all-ceramic CAD/CAM crowns.

METHODS

Human third molars (n=48) were prepared and anatomical all-ceramic CAD/CAM crowns were manufactured (VITABLOCS Mark II, VITA Zahnfabrik). Crowns internal surfaces were HF etched and silanized. The prepared teeth with their respective crowns were divided into 6 groups (n=8). In groups 1, 3 and 5 the coronal dentin was removed to simulate a partial core build-up. Groups 1 and 2 were luted with iCEM (Heraeus Kulzer), 3 and 4 with RelyX Unicem 2 Automix (3M), 5 and 6 with Variolink Esthetic DC (Ivoclar Vivadent). All specimens were dual cured and stored in distilled water at 37°C. Crown integrity was controlled at baseline and in regular intervals until 180 days. Cement gap thickness was measured using an optical 3D scanner (ATOS Triple scan, GOM) at baseline and after 180 days. Crown integrity was statistically analysed using Kaplan-Meier survival analysis and cement gap thickness increase using two-way ANOVA (α=0.05).

RESULTS

After 180 days storage, crack formation was observed in all specimens of group 1 (mean survival time of 85.5 days), in one specimen of group 2 and in two specimens of group 4. Two-way ANOVA analysis revealed a statistically significant interaction between material type and build-up on cement gap size increase for iCEM.

SIGNIFICANCE

Within the limits of this study, the application of SARCs with low pH neutralization as partial build-up material under CAD/CAM crowns is not recommended for clinical use.

Fracture Resistance of Ceramic Crowns Supported with Indirect Chair-side Composite Cores

Aims and Objectives

To evaluate the influence of indirect chair-side polymerization of resin composite cores on the fracture resistance of overlaying IPS e.max Press crowns.

Materials and Methods

Root canals of 60 extracted premolars were prepared to receive #2 fiber posts after the crowns were sectioned 2 mm above the cervical line. In Groups 1-3 (n = 10 each), posts were luted to the prepared dowel spaces using self-adhesive resin cement. Resin composite cores were then bonded and incrementally built-up using Filtek Z250 XT, Filtek P60, and Filtek P90 resin composites. In Groups 4-6 (n = 10 each), the fabricated post-core systems were subjected to post-curing heat and pressure treatment before cementation to their respective teeth using self-adhesive resin cement. Another 10 sound premolars served as control. All teeth in the test and control groups were then subjected to standardized preparation to receive IPS e.max Press crowns before testing their fracture resistance and the mode of restorations' failure. The collected results were statistically analyzed using ANOVA, Kruskal-Wallis, and Tukey's tests on the past software used at α = 0.05 to stand on the significance of the detected differences.

Results

Significant differences were detected between the fracture resistance of teeth in different groups (ANOVA, P = 2.857E-35). Crowns in Groups 4-6 provided higher fracture resistance than those in Groups 1-3 (Tukey's test, P < 0.05). Crowns in Groups 4 and 6 provided higher fracture resistance than the control, while those in Groups 2 and 3 provided lower fracture resistance than the control (Tukey's test, P < 0.05).

Conclusion

Indirect composite cores improved the fracture resistance of IPS e.max Press crowns when compared to directly fabricated post and cores. The directly and indirectly polymerized nanohybrid, methacrylate-based composite (Filtek Z250 XT) cores yielded the highest fracture resistance for the utilized all-ceramic crowns.

Chemical and Mechanical Properties of Experimental Dental Composites as a Function of Formulation and Postcuring Thermal Treatment

This study evaluated the influence of formulation and thermal treatment on the degree of conversion, fracture toughness, flexural strength, and elastic modulus of experimental composites. Six composites were analyzed at BisGMA : TEGDMA molar ratios of 1 : 1 and 7 : 3 with filler at 30, 50, and 70 wt%. The degree of conversion was analyzed by Fourier transform infrared spectroscopy, fracture toughness was measured using the single-edge notched beam, and flexural strength and elastic modulus were measured with the 3-point bend test. For all tests, one-half of the specimens received thermal treatment at 170°C for 10 min. Data were analyzed by the Kruskal-Wallis or ANOVA/Tukey's test (α = 5%). The 1 : 1 BisGMA : TEGDMA ratio showed higher properties than the 7 : 3 ratio. Although the material with 70% filler had a conversion lower than the one with 50%, it showed higher mechanical properties. The thermal treatment improved all properties in all materials. Therefore, the use of an equimolar ratio of BisGMA : TEGDMA can be paired with 70 wt% filler to design dental composites that possess increased advantageous physical and chemical properties. Furthermore, the simple and low-cost method of thermal treatment proposed for use in clinical dentistry has been shown to effectively improve the properties of all evaluated materials.

Preparation and characterization of silane-modified SiO2 particles reinforced resin composites with fluorinated acrylate polymer

A series of fluorinated dental resin composites were prepared with two kinds of SiO₂ particles. Bis-GMA (bisphenol A-glycerolate dimethacrylate)/4-TF-PQEA (fluorinated acrylate monomer)/TEGDMA (triethylene glycol dimethacrylate) (40/30/30, wt/wt/wt) was introduced as resin matrix. SiO₂ nanopartices (30nm) and SiO₂ microparticles (0.3µm) were silanized with 3-methacryloxypropyl trimethoxysilane (γ-MPS) and used as fillers. After mixing the resin matrix with 0%, 10%, 20%, 30% SiO₂ nanopartices and 0%, 10%, 20%, 30%, 40%, 50% SiO₂ microparticles, respectively, the fluorinated resin composites were obtained. Properties including double bond conversion (DC), polymerization shrinkage (PS), water sorption (W_p), water solubility (W_y), mechanical properties and cytotoxicity were investigated in comparison with those of neat resin system. The results showed that, filler particles could improve the overall performance of resin composites, particularly in improving mechanical properties and reducing PS of composites along with the addition of filler loading. Compared to resin composites containing SiO₂ microparticles, SiO₂ nanoparticles resin composites had higher DC, higher mechanical properties, lower PS and lower W_p under the same filler content. Especially, 50% SiO₂ microparticles reinforced resins exhibited the best flexural strength (104.04 ± 7.40MPa), flexural modulus (5.62 ± 0.16GPa), vickers microhardness (37.34 ± 1.13 HV), compressive strength (301.54 ± 5.66MPa) and the lowest polymerization (3.42 ± 0.22%).

Comparative abrasive wear resistance and surface analysis of dental resin-based materials

OBJECTIVE

The objective of this study was to assess the surface properties (microhardness and wear resistance) of various composites and compomer materials. In addition, the methodologies used for assessing wear resistance were compared.

MATERIALS AND METHODS

This study was conducted using restorative material (Filtek Z250, Filtek Z350, QuiXfil, SureFil SDR, and Dyract XP) to assess wear resistance. A custom-made toothbrush simulator was employed for wear testing. Before and after wear resistance, structural, surface, and physical properties were assessed using various techniques.

RESULTS

Structural changes and mass loss were observed after treatment, whereas no significant difference in terms of microhardness was observed. The correlation between atomic force microscopy (AFM) and profilometer and between wear resistance and filler volume was highly significant. The correlation between wear resistance and microhardness were insignificant.

CONCLUSIONS

The AFM presented higher precision compared to optical profilometers at a nanoscale level, but both methods can be used in tandem for a more detailed and precise roughness analysis.

Characterization of fluoride releasing restorative dental materials

This study aimed to evaluate and compare certain mechanical properties, Vickers-hardness, water sorption, fluoride-release, shrinkage-stress and wear of five commercial fluoride-releasing restorative materials (Dyract, CompGlass, BEAUTIFIL II, ACTIVA-Restorative, and GC Fuji II LC), in relation to their microstructural characteristics. Mechanical properties were determined for each material following ISO standards. A wear test was conducted with 15,000 chewing cycles using a dual-axis chewing simulator. Daily fluoride-release was measured during the first 10 days by using a fluoride ion selective electrode. Scanning electron microscopy (SEM) was used to evaluate the microstructure of each material. Results were statistically analysed using ANOVA followed by post hoc Tukey's test. ACTIVA-Restorative exhibited the highest fracture toughness (1.1 MPa m^1/2) among the materials tested. BEAUTIFIL II presented the highest flexural strength (145 MPa) which was not significantly different (p>0.05) from CompGlass and Dyract. Highest fluoride-release measurement was located for GC Fuji II LC among other tested materials.

Characteristics of low polymerization shrinkage flowable resin composites in newly-developed cavity base materials for bulk filling technique

The purpose of this study was to evaluate polymerization shrinkage and other physical properties of newly-developed cavity base materials for bulk filling technique, with the brand name BULK BASE (BBS). Polymerization shrinkage was measured according to ISO/FDIS 17304. BBS showed the significantly lowest polymerization shrinkage and significantly higher depth of cure than conventional flowable resin composites (p<0.05). The Knoop hardness, flexural strength and elastic modulus of that were significantly lower than conventional flowable resin composites (p<0.05). BBS had the significantly greatest filler content (p<0.05). SEM images of the surface showed failure of fillers. The lowest polymerization shrinkage was due to the incorporation of a new type of low shrinkage monomer, which has urethane moieties. There were no clear correlations between inorganic filler contents and polymerization shrinkage, flexural strength and elastic modulus. In conclusion, the low polymerization shrinkage of BBS will be useful for cavity treatment in dental clinics.

CAD-FE modeling and analysis of class II restorations incorporating resin-composite, glass ionomer and glass ceramic materials

OBJECTIVES

To investigate the influence of specific resin-composite, glass ceramic and glass ionomer cement (GIC) material combinations in a "multi-layer" technique to replace enamel and dentin in class II mesio-occlusal-distal (MOD) dental restorations using 3D-Finite Element Analysis (FEA).

METHODS

Four 3D-FE models (A-D) of teeth, adhesively restored with different filling materials, were created and analyzed in comparison with a 3D model (E) of a sound lower molar. Models A, B & C had "multilayer" constructions, consisting of three layers: adhesive, dentin replacement and enamel replacement. Model A: had a low modulus (8GPa) composite replacing dentin and a higher modulus (12GPa) composite replacing enamel. Model B: had a GI cement replacing dentin and a higher modulus (12GPa) composite replacing enamel. Model C: had a low modulus (8GPa) composite replacing dentin and a very high modulus (70GPa) inlay replacing enamel. Model D: had a lithium disilicate inlay replacing both dentin and enamel with a luting cement base-layer. Polymerization shrinkage effects were simulated and a load of 600N was applied. All the materials were assumed to behave elastically throughout the entire deformation.

RESULTS

Model A showed the highest stress distribution along all the adhesive interfaces of the shrinking resin-based materials with a critical condition and failure risk marginally and internally. Model D, by contrast, showed a more favorable performance than either of the multilayer groups (A-C). Stress and displacement plots showed an elastic response similar to that obtained for the sound tooth model. Model B and Model C performed according to their bilayer material properties. The use of a non-shrink dentin component simulating a GIC clearly affected the shrinkage stress at the basis of the Model B; while the bulk resin composite having a 12GPa Young's modulus and linear polymerization shrinkage of 1% strongly influenced the biomechanical response in the bucco-lingual direction.

SIGNIFICANCE

Direct resin-based composite materials applied in multilayer techniques to large class II cavities, with or without shrinking dentin layers, produced adverse FEA stress distributions and displacements. An indirect lithium disilicate inlay used to replace lost dentin and enamel in posterior restored teeth generated lower stress levels, within the limits of the elastic FEA model.

Flowable composites for restoration of non-carious cervical lesions: Results after five years

OBJECTIVES

To evaluate the clinical performance of two flowable composites for restoration of Class-V non-carious cervical lesions (NCCLs), one with novel (N'Durance^® Dimer Flow, Septodont; ND) and one with modified conventional matrix composition (Filtek™ Supreme XTE Flow, 3M-ESPE; FS). The null hypothesis was that both flowable composite materials perform equally regarding clinical quality and survival.

METHODS

50 patients received one ND and one FS restoration of NCCLs in premolars using Clearfil Protect Bond (Kuraray) as an adhesive without additional selective enamel etching. Restorations were evaluated at baseline (BL), after 30 and 60 months employing selected original FDI criteria and refined FDI criteria by separate evaluation of enamel and dentine margins. Non-parametric statistical analyses and χ² tests were applied (α=0.05).

RESULTS

38 patients with both restorations under risk were available for the 60-mo recall (recall rate: 76%). At 60-mo, 94.7% of ND and 84.2% of FS restorations were rated clinically acceptable. No significant differences for all selected FDI criteria were recorded between ND and FS at each examination time point except for the criteria surface lustre at 60-mo, where FS showed significantly better results. No significant differences over time could be detected for both materials. There was a trend for more deterioration along the enamel margins than along the dentine margins (criteria marginal staining and marginal adaptation).

SIGNIFICANCE

Within the limitations of the study, the null hypothesis that materials perform equally could not be rejected. Both flowable composites performed similarly regarding clinical performance.

The Influence of Water Sorption of Dental Light-Cured Composites on Shrinkage Stress

The contraction stress generated during the photopolymerization of resin dental composites is the major disadvantage. The water sorption in the oral environment should counteract the contraction stress. The purpose was to evaluate the influence of the water sorption of composite materials on polymerization shrinkage stress generated at the restoration-tooth interface. The following materials were tested: Filtek Ultimate, Gradia Direct LoFlo, Heliomolar Flow, Tetric EvoCeram, Tetric EvoCeram Bulk Fill, Tetric EvoFlow, Tetric EvoFlow Bulk Fill, X-tra Base, Venus BulkFil, and Ceram.X One. The shrinkage stress was measured immediately after curing and after: 0.5 h, 24 h, 72 h, 96 h, 168 h, 240 h, 336 h, 504 h, 672 h, and 1344 h by means of photoelastic study. Moreover, water sorption and solubility were evaluated. Material samples were weighted on scale in time intervals to measure the water absorbency and the dynamic of this process. The tested materials during polymerization generated shrinkage stresses ranging from 6.3 MPa to 12.5 MPa. Upon water conditioning (56 days), the decrease in shrinkage strain (not less than 48%) was observed. The decrease in value stress in time is material-dependent.

Full in-vitro analyses of new-generation bulk fill dental composites cured by halogen light

The objective of this study was to investigate the full in-vitro analyses of new-generation bulk-fill dental composites cured by halogen light (HLG). Two types' four composites were studied: Surefill SDR (SDR) and Xtra Base (XB) as bulk-fill flowable materials; QuixFill (QF) and XtraFill (XF) as packable bulk-fill materials. Samples were prepared for each analysis and test by applying the same procedure, but with different diameters and thicknesses appropriate to the analysis and test requirements. Thermal properties were determined by thermogravimetric analysis (TG/DTG) and differential scanning calorimetry (DSC) analysis; the Vickers microhardness (VHN) was measured after 1, 7, 15 and 30days of storage in water. The degree of conversion values for the materials (DC, %) were immediately measured using near-infrared spectroscopy (FT-IR). The surface morphology of the composites was investigated by scanning electron microscopes (SEM) and atomic-force microscopy (AFM) analyses. The sorption and solubility measurements were also performed after 1, 7, 15 and 30days of storage in water. In addition to his, the data were statistically analyzed using one-way analysis of variance, and both the Newman Keuls and Tukey multiple comparison tests. The statistical significance level was established at p<0.05. According to the ISO 4049 standards, all the tested materials showed acceptable water sorption and solubility, and a halogen light source was an option to polymerize bulk-fill, resin-based dental composites.

Effect of Mouthwashes on Solubility and Sorption of Restorative Composites

Objective

Composites sorption and solubility can be precursors of several chemical and physical processes, which lead to deleterious effects on the polymer structure. This study evaluated the effect of mouthwashes on solubility and sorption of composite resins.

Materials and Methods

Forty-two specimens of each evaluated composite (Filtek Bulk Fill Flow, Opallis Flow, Durafill VS, and Filtek Z350) were prepared and randomized into seven groups for each solution (mouth rinses with and without alcohol and distilled water) and stored for seven days. Solubility and sorption tests were performed according to ISO4049. Data were analyzed using 2-way-ANOVA followed by Tukey's test for means comparison (α = 0.05). In addition, paired t-test was performed to analyze the alcohol effect on the studied composite resin properties.

Results

Listerine Cool Mint (containing alcohol in its composition) caused the greatest degree of sorption for all composites tested in comparison to other rinses, while for solubility this behavior was observed for Opallis Flow and Durafill VS composite resins (p < 0.05). Regarding the composites, Opallis Flow showed the highest sorption and solubility values in general (p < 0.05).

Conclusion

Overall, the sorption and solubility of composites were higher in mouthwashes containing alcohol in its composition, with Opallis Flow being the most affected composite resin.