Resin based restorative dental materials: characteristics and future perspectives

Effects of 3 different light-curing units on the physico-mechanical properties of bleach-shade resin composites

Objectives

This study investigated the microhardness, flexural strength, and color stability of bleach-shade resin composites cured with 3 different light-curing units.

Materials and Methods

In this in vitro experimental study, 270 samples were fabricated of bleach and A2 shades of 3 commercial resin composites (Point 4, G-aenial Anterior, and Estelite Sigma Quick). Samples (n = 5 for each trial) were cured with Bluephase N, Woodpecker LED.D, and Optilux 501 units and underwent Vickers microhardness and flexural strength tests. The samples were tested after 24 hours of storage in distilled water. Color was assessed using a spectrophotometer immediately after preparation and 24 hours after curing. Data were analyzed using 3-way analysis of variance and the Tukey test (p ≤ 0.001).

Results

Samples cured with Optilux exhibited the highest and those cured with LED.D exhibited the lowest microhardness (p = 0.023). The bleach shade of Point 4 composite cured with Optilux displayed the highest flexural strength, while the same composite and shade cured with Sigma Quick exhibited the lowest (p ≤ 0.001). The color change after 24 hours was greatest for the bleach shade of G-aenial cured with Bluephase N and least for the A2 shade of Sigma Quick cured with Optilux (p ≤ 0.001).

Conclusions

Light curing with polywave light-emitting diode (LED) yielded results between or statistically similar to those of quartz-tungsten-halogen and monowave LED in the microhardness and flexural strength of both A2 and bleach shades of resin composites. However, the brands of light-curing devices showed significant differences in color stability.

Effects of Monomer Composition of Urethane Methacrylate Based Resins on the C=C Degree of Conversion, Residual Monomer Content and Mechanical Properties

(1) Background: This study investigated the influence of Bis-GMA, TEGDMA, UDMA, and two different polyethylene glycol (PEG)-containing, UDMO-based co-monomers on the Young’s modulus and flexural strength, degree of methacrylate C=C double bond conversion and residual monomer elution of experimental dental resins. (2) Methods: Urethane methacrylate-based monomer was synthesised via a radical chain growth polymerization mechanism using PEG in order to improve the mechanical properties. Dental resins were formulated using Bis-GMA, UDMA, or UDMO as base monomers combined with TEGDMA as a dilution monomer and DMAEM + CQ as the photo-initiator system. Degree of conversion (DC), mechanical properties, and residual monomer content of light-activated methacrylate resin formulations were evaluated and statistically analysed by ANOVA and a Tukey’s test. (3) Results: PEG-containing UDMO resins had lower Young’s modulus and elastic strength than UDMA-derived resin for all irradiation times. The highest DC (67,418%) was observed for the PEG-containing UDMO-based resin formulation when light cured for 40 s. For all samples, DC increased with the photo-polymerization time. The amount of residual monomer decreased after increasing the light-curing period from 20 to 40 s, resin with UDMO content 0.01 mol of PEG having the smallest amount of free eluted monomer. (4) Conclusions: A strong structure–property relationship exists in photo-cured dimethacrylate-based dental resins. The time and quantity of the photochemical initiation system can influence the physical–mechanical properties of the resins but also the monomers in their composition.

A novel methacrylate derivative polymer that resists bacterial cell-mediated biodegradation

This study tests biodegradation resistance of a custom synthesized novel ethylene glycol ethyl methacrylate (EGEMA) with ester bond linkages that are external to the central polymer backbone when polymerized. Ethylene glycol dimethacrylate (EGDMA) with internal ester bond linkages and EGEMA discs were prepared in a polytetrafluoroethylene (PTFE) mold using 40 μl macromer and photo/co-initiator mixture cured for 40 s at 1000 mW/cm² . The discs were stored in the constant presence of Streptococcus mutans (S. mutans) in Todd Hewitt Yeast + Glucose (THYE+G) media up to 9 weeks (n = 8 for each macromer type) and physical/mechanical properties were assessed. Initial measurements EGEMA versus EGDMA polymer discs showed equivalent degree of conversion (45.69% ± 2.38 vs. 46.79% ± 4.64), diametral tensile stress (DTS; 8.12± 2.92 MPa vs. 6.02 ± 1.48 MPa), and low subsurface optical defects (0.41% ± 0.254% vs. 0.11% ± 0.074%). The initial surface wettability (contact angle) was slightly higher (p ≤ .012) for EGEMA (62.02° ± 3.56) than EGDMA (53.86° ± 5.61°). EGDMA showed higher initial Vicker's hardness than EGEMA (8.03 ± 0.88 HV vs. 5.93 ± 0.69 HV; p ≤ .001). After 9 weeks of S. mutans exposure, EGEMA (ΔDTS-1.30 MPa) showed higher resistance to biodegradation effects with a superior DTS than EGDMA (ΔDTS-6.39 MPa) (p = .0039). Visible and scanning electron microscopy images of EGEMA show less surface cracking and defects than EGDMA. EGDMA had higher loss of material (18.9% vs. 8.5%, p = .0009), relative changes to fracture toughness (92.5% vs. 49.2%, p = .0022) and increased water sorption (6.1% vs. 1.9%, p = .0022) compared to EGEMA discs. The flipped external ester group linkage design is attributed to EGEMA showing higher resistance to bacterial degradation effects than an internal ester group linkage design methacrylate.

A fabric phase sorptive extraction method for the LC-UV determination of bisphenol A and leaching monomers from dental materials in human saliva

A rapid and simple fabric phase sorptive extraction (FPSE) procedure is developed for the simultaneous extraction of four monomers (Bisphenol A, BPA; Triethylene glycol dimethacrylate, TEGDMA; Urethane dimethacrylate, UDMA; Bisphenol A-glycidyl methacrylate, BisGMA) in human saliva, prior to the determination by high pressure liquid chromatography with an ultraviolet-visible detector. FPSE is a green sample preparation technique, harmonized with the principles of Green Analytical Chemistry (GAC), which utilizes a flexible surface, such as cellulose, chemically coated with a polymeric material using sol-gel technology. FPSE membranes are characterized by superior chemical stability and any solvent or solvent mixture can be used for elution. Among twelve different sol-gel coated membranes, an FPSE membrane coated with sol-gel polytetrahydrofuran (sol-gel PTHF) was found optimum to extract four target compounds from saliva samples, which were first centrifuged. Parameters with most significant impact on the extraction efficiency of FPSE including elution solvent, utilization of magnetic stirring, extraction time have been comprehensively studied and optimized. The studied compounds' separation was carried out by a Perfect Sil 120 ODS-2 chromatographic column (250 mm × 4.0 mm, 5 μm), using a mobile phase constituting of acetonitrile-water 70:30 % v/v (isocratic elution). The total analysis time was 10 min. Detection was achieved by an ultraviolet-visible detector at 220 nm. The method was validated in terms of sensitivity, linearity, trueness, precision, selectivity and stability of samples. For all four compounds, the limit of detection and the limit of quantification were 0.075 ng/μL and 0.25 ng/μL, respectively. Relative recovery rates were between 90.0 and 106.7%, while RSD values were <8.1 and 12% for interday and intraday repeatability, respectively. Youden & Steiner approach was applied to study method's ruggedness and reusability of the media was tested, which enhanced the green nature of technique.

Mechanical Properties of Polymer-Based Blanks for Machined Dental Restorations

The tremendous technological and dental material progress led to a progressive advancement of treatment technologies and materials in restorative dentistry and prosthodontics. In this approach, CAD/CAM restorations have proven to be valuable restorative dental materials in both provisional and definitive restoration, owing to multifarious design, improved and highly tunable mechanical, physical and morphological properties. Thus far, the dentistry market offers a wide range of CAD/CAM restorative dental materials with highly sophisticated design and proper characteristics for a particular clinical problem or multiple dentistry purposes. The main goal of this research study was to comparatively investigate the micro-mechanical properties of various CAD/CAM restorations, which are presented on the market and used in clinical dentistry. Among the investigated dental specimens, hybrid ceramic-based CAD/CAM presented the highest micro-mechanical properties, followed by CAD/CAM PMMA-graphene, while the lowest micro-mechanical features were registered for CAD/CAM multilayered PMMA.

Evaluation of the Behavior of Two CAD/CAM Fiber-Reinforced Composite Dental Materials by Immersion Tests

Fiber-reinforced composites are used as restorative materials for prosthetic oral rehabilitation. Gastroesophageal reflux disease (GERD) is an accustomed affection with various oral manifestations. This study aimed to evaluate the behavior of two high-performance CAD/CAM milled reinforced composites (Trinia™, TriLor) in artificial saliva at different pH levels through immersion tests, and to determine if changes in mass or surface morphology at variable pH, specific for patients affected by GERD, appear. After investigating the elemental composition and surface morphology, the specimens were immersed in Carter Brugirard artificial saliva for 21 days at different pH values (5.7, 7.6, and varying the pH from 5.7 to 3). The values of the weighed masses during the immersion tests were statistically processed in terms of mean and standard deviation. Results suggested that irrespective of the medium pH, the two composites presented a similar mass variation in the range of −0.18 (±0.01)–1.82 (±0.02) mg after immersion, suggesting their stability when in contact with artificial saliva, an aspect which was also highlighted by scanning electron microscope (SEM) analysis performed on the immersed surfaces. Novel composite biomaterials can be a proper alternative for metal alloys used for prosthetic frameworks in patients suffering from GERD.

Effect of post-irradiation polymerization on selected mechanical properties of six direct resins

This study evaluated the post-irradiation mechanical property development of six resin composite-based restorative materials from the same manufacturer starting at 1 h post irradiation, followed by 24 h, 1 week, and 1 month after fabrication. Samples were stored in 0.2M phosphate buffered saline until testing. Flexural strength, flexural modulus, flexural toughness, modulus of resiliency, fracture toughness, and surface microhardness were performed at each time interval. Mean data was analyzed by Kruskal Wallis and Dunn's post hoc testing at a 95% level of confidence (α=0.05). Results were material specific but overall, all resin composite material mechanical properties were found to be immature at 1 h after polymerization as compared to that observed at 24 h. It may be prudent that clinicians advise patients, especially those receiving complex posterior composite restorations, to guard against overly stressing these restorations during the first 24 h.

The Influence of Various Photoinitiators on the Properties of Commercial Dental Composites

The aim of this article was to compare the biomechanical properties of commercial composites containing different photoinitiators: Filtek Ultimate (3M ESPE) containing camphorquinone (CQ); Estelite Σ Quick (Tokuyama Dental) with CQ in RAP Technology^®; Tetric EvoCeram Bleach BLXL (Ivoclar Vivadent AG) with CQ and Lucirin TPO; and Tetric Evoceram Powerfill IVB (Ivoclar Vivadent AG) with CQ and Ivocerin TPO. All samples were cured with a polywave Valo Lamp (Ultradent Products Inc.) with 1450 mW/cm². The microhardness, hardness by Vicker's method, diametral tensile strength, flexural strength and contraction stress with photoelastic analysis were tested. The highest hardness and microhardness were observed for Filtek Ultimate (93.82 ± 17.44 HV), but other composites also displayed sufficient values (from 52 ± 3.92 to 58,82 ± 7.33 HV). Filtek Ultimate not only demonstrated the highest DTS (48.03 ± 5.97 MPa) and FS (87.32 ± 19.03 MPa) but also the highest contraction stress (13.7 ± 0.4 MPa) during polymerization. The TetricEvoCeram Powerfill has optimal microhardness (54.27 ± 4.1 HV), DTS (32.5 ± 5.29 MPa) and FS (79.3 ± 14.37 MPa) and the lowest contraction stress (7.4 ± 1 MPa) during photopolymerization. To summarize, Filtek Ultimate demonstrated the highest microhardness, FS and DTS values; however, composites with additional photoinitiators such as Lucirin TPO and Ivocerin have the lowest polymerization shrinkage. These composites also have higher FS and DTS and microhardness than material containing CQ in Rap Technology.

Comparative evaluation of Rheological characteristics of Giomers and other Nano-flowable resin composites in vitro

Objective

The purpose of this research was to determine the viscoelastic properties of a group of commercially available nano-flowable resin composites; and to explore the relation between these properties and the materials’ composition (with/without fluoride), filler size description (nano-filled, nanohybrid and submicron-filled) and filler loading (by volume).

Methods

Rheological measurements were performed using a rheometer. A Dynamic frequency sweep test was conducted to evaluate the complex viscosity, storage and loss moduli, loss tangent, and complex shear modulus at an angular frequency (ω) of 0.1–100 rad/s. Comparative evaluations of the nano flowable resin composites on rheological properties was performed, and statistically analyzed using one-way ANOVA.

Results

The results indicated that all the tested materials exhibited shear-thinning flow behaviour. As the shear rate increased, the complex viscosity of the nano-flowable composites decreased. The nanohybrid filled flowable resin composites exhibited the highest complex viscosity, while the nano-filled flowable resin composites exhibited the lowest value. The submicron-filled materials exhibited the lowest complex shear moduli and loss tangent values. Conclusions: The findings from the current study provided comprehensive evaluation of the rheological properties of different nano-flowable composites. The observed differences in rheological properties among the tested materials were independent of their fluoride content or filler size. Furthermore, no relationship was found between the complex viscosity of the tested nano-flowable resin composites and their filler volume.

Novel dental composite resin derived from rice husk natural biowaste: A systematic review and recommendation for future advancement

OBJECTIVES

This review aimed to summarize contemporary evidence related to dental composite resin derived from rice husk biowaste and its potential future advancement. This review paper included the techniques for synthesis, characterization, and preparation of rice husk composite resin. Focus was also given to the flexural strength and modulus, compressive strength, wear rate, hardness, surface roughness, color stability, polymerization shrinkage, degree of conversion, and their application onto root canal treated teeth.

MATERIAL AND METHODS

A search of English peer-reviewed literature (January 1960-February 2021) was conducted from electronic databases (PubMed Central, Cochrane, LILACS, Science Direct, Web of Science, SIGLE, EMBASE, EBSCO, Medline, and Google Scholar).

RESULTS

11 articles and a book section were finally selected for qualitative analysis. Studies concluded that the physicomechanical properties and the color stability of rice husk dental composites showed comparable results to conventional dental composites. Incorporation of zirconia nanopowder into rice husk dental composite increased the compressive strength and hardness values, associated with lower shrinkage, a high degree of conversion, and improved fracture strength when applied on root canal treated teeth.

CONCLUSIONS

Due to its low cost, eco-friendliness, and acceptable clinical performances, rice husk dental composite resin can be considered as an alternative to conventional composites.

CLINICAL SIGNIFICANCE

Dental composite resin derived from rice husk silica demonstrated excellent performance, which could potentially substitute currently available composite resins. This review will give new insight to clinicians and researchers on the usage of natural biowaste mass in the field of dental restorative materials.

Toothbrush Abrasion of Restorations Fabricated with Flowable Resin Composites with Different Viscosities In Vitro

The purpose of this study was to examine toothbrush-induced abrasion of resin composite restorations fabricated with flowable resin composites of different viscosities in vitro. In this study, six types of flowable resin composites with different flowability (Beautifil Flow F02, F02; Beautifil Flow F10, F10; Beautifil Flow Plus F00, P00; Beautifil Flow Plus F03, P03; Beautifil Flow Plus X F00, X00; and Beautifil Flow Plus X F03, X03) were used. For the toothbrush abrasion test, the standard cavity (4 mm in diameter and 2 mm in depth) formed on the ceramic block was filled with each flowable resin composite (n = 10) and brushed for up to 40,000 strokes in a suspension containing commercial toothpaste under the conditions of 500 g load, 60 strokes/min, and 30 mm stroke distance. After every 10,000 strokes, the brushed surface of the specimen was impressed with a silicone rubber material. The amount of toothbrush-induced abrasion observed on each impression of the specimen was measured using a wide-area 3D measurement device (n = 10). The viscosity was determined using a cone-and-plate rotational measurement system. Because of the effect of different shear rates on viscosity and clinical use, the values 1.0 and 2.0 s⁻¹ were adopted as data (n = 6). In this study, the results of the toothbrush abrasion test demonstrated no significant differences in the amount of toothbrush-induced abrasion among flowable resin composites used (p > 0.05). No significant correlation was reported between toothbrush-induced abrasion and viscosities of flowable resin composites.

Strategies toward development of antimicrobial biomaterials for dental healthcare applications

Several approaches for elimination of oral pathogens are being explored at the present time since oral diseases remain prevalent affecting approximately 3.5 billion people worldwide. Need for antimicrobial biomaterials in dental healthcare include but is not restricted to designing resin composites and adhesives for prevention of dental caries. Constant efforts are also being made to develop antimicrobial strategies for clearance of endodontic space prior root canal treatment and for treatment of periimplantitis and periodontitis. This article discusses various conventional and nanotechnology-based strategies to achieve antimicrobial efficacy in dental biomaterials. Recent developments in the design and synthesis of antimicrobial peptides and antifouling zwitterionic polymers to effectively lessen the risks of antimicrobial drug resistance are also outlined in this review. Further, the role of contemporary strategies such as use of smart biomaterials, ionic solvent-based biomaterials and quorum quenchers incorporated biomaterials in the elimination of dental pathogens are described in detail. Lastly, we mentioned the approach of using polymers to print custom-made three-dimensional antibacterial dental products via additive manufacturing technologies. This review provides a critical perspective on the chemical, biomimetic, and engineering strategies intended for developing antimicrobial biomaterials that have the potential to substantially improve the dental health.

Evaluation of Residual Monomers Eluted from Pediatric Dental Restorative Materials

Unreacted monomers eluted from resin-based restorative materials have been considered a reason of local and systemic adverse reactions. This study was designed to determine the effect of finishing and polishing procedures on the elution of Bis-GMA, TEGDMA, UDMA, and HEMA monomers from compomer and bulk-fill composite resins. Bulk-fill composite (3M ESPE GmbH, Seefeld, Germany) and compomer (Dentsply DeTrey GmbH, Konstanz, Germany) specimens with 3 × 4 mm diameters were prepared. The specimens were randomly divided into two groups, and finishing-polishing procedures were applied only to the experimental groups. Release of residual monomers was analyzed by using High-Performance Liquid Chromatography (HPLC) after 24, 48, and 72 hours. Repeated measures ANOVA and Tukey post hoc tests were used for comparisons. Finishing and polishing procedures had a significant effect on reducing the quantity of UDMA release in the Filtek™ Bulk Fill composite and Bis-GMA, HEMA, and TEGDMA in the Dyract XP compomer (p < 0.05). The restorative materials investigated here are not chemically stable after polymerization, and concentrations of eluted monomers may reach critical toxicity levels even after one restoration placement. Finishing and polishing procedures are mandatory to reduce residual monomers.

Physicochemical and biological evaluation of a triazine-methacrylate monomer into a dental resin

OBJECTIVES

This study aimed to (1) formulate blend resins with 2.5 or 5 wt.% of the methacrylate monomer 1,3,5-triacryloylhexahydro-1,3,5-triazine (TAT), and (2) to evaluate the blend resins regarding the physicochemical and biological properties.

METHODS

The base resin was formulated mixing 60 wt.% of bisphenol A glycol dimethacrylate and 40 wt.% of triethylene glycol dimethacrylate with photoinitiator/co/initiator system. TAT was added at 2.5 (G_2.5%) or 5 (G_5%) wt.%, and a group without TAT was used as control (G_ctrl). The resins were analyzed for degree of conversion (DC), Knoop hardness (KHN), softening in solvent (ΔKHN), ultimate tensile strength (UTS), contact angle, surface free energy (SFE), antibacterial activity against Streptococcus mutans biofilm formation, and cytotoxicity against human keratinocytes.

RESULTS

There was no difference for the DC (p = 0.676). The addition of TAT at 5 wt.% induced higher KHN (p<0.001), higher resistance against softening in solvent (p<0.001), and higher UTS (p = 0.04). There were no statistically significant differences for contact angle with water (p = 0.106), α-bromonaphtalene (p = 0.454), and SFE (p = 0.172). The higher the TAT concentration, the higher the antibacterial activity (p<0.001). G_2.5% showed no cytotoxicity compared to G_ctrl (p>0.05), and G_5% induced lower cell viability (p<0.05).

CONCLUSIONS

The addition of 2.5 wt.% of TAT is suitable for conveying antibacterial activity for dental resins without changing the physicochemical properties or impairing the cytotoxic effect.

CLINICAL RELEVANCE

Methacrylate monomers that decrease bacterial viability and copolymerize with the resin matrix are exciting approaches to developing therapeutic materials. TAT showed promising properties to may hamper and prevent carious lesions when incorporated into dental materials. Further evaluations with higher cariogenic challenges will be carried to analyze the formulated materials.

Molecular dynamics investigation of structural and mechanical properties of silica nanorod reinforced dental resin composites

In this work, molecular dynamics simulations are conducted to investigate the structural and mechanical properties of dental materials, i.e., the silica nanorod reinforced Bis-GMA/TEGDMA resin composite. The effects of loading content and size of the silica nanorods on the composite stiffness were performed by examining resin chain conformation, hydrogen bonds and matrix/filler binding energy. It is revealed that the presence of the silica nanorod causes polymer chain expansion, endowing the resins with higher stiffness. Moreover, the volumetric hydrogen bonds and binding energy increase considerably with the loading content, but decrease gradually with the diameter or show almost independence of the length. Furthermore, the composite moduli were quantified by the micromechanics models and the transverse moduli were well predicted by the Counto model, signifying a perfect bonding between the matrix and nanorod. The chain expansion and energetic matrix/filler interactions are believed to contribute to the significant mechanical reinforcement of the composites with the loading content. However, the length of the nanorod has a little effect on the composite moduli due to the unaltered interfacial interaction. In contrast, a smaller diameter is supposed to give a larger modulus, and this is not observed in this work due to the synergic effects of improved matrix/filler interaction and actual reduced filler volume fraction. The mechanical enhancement by the rod-like structures is more influenced by the loading content, but less so by the size of the nanorod, and it also exhibits superior mechanical performance as compared to nanoparticles. The findings thus extend the current understanding of the nanostructure and mechanical properties of silica nanorod reinforced dental resin composites from an atomic/molecular perspective.

Synthesis and Characterization of Novel Quaternary Ammonium Urethane-Dimethacrylate Monomers-A Pilot Study

Six novel urethane-dimethacrylate analogues (QAUDMAs) were synthesized and characterized. They consisted of the 2,4,4,-trimethylhexamethylene diisocyanate (TMDI) core and two methacrylate-terminated wings containing quaternary ammonium groups substituted with alkyl chains of 8, 10, 12, 14, 16, or 18 carbon atoms. QAUDMAs, due to the presence of quaternary ammonium groups, may have possible antibacterial effects. Since they showed satisfactory physicochemical properties, they will be subjected to further research towards the development of dental composites with a capacity to reduce secondary caries. The synthesis of QAUDMAs included three stages: (i) transesterification of methyl methacrylate (MMA) with N-methyldiethanolamine (MDEA), (ii) N-alkylation of the tertiary amino group with alkyl bromide, and (iii) addition of TMDI to the intermediate achieved in the second stage. The formation of QAUDMAs was confirmed by ¹H and ¹³C NMR. They were characterized for density (d_m), viscosity (η), refractive index (RI), glass transition temperature (T_g), polymerization shrinkage (S), and degree of conversion (DC). QAUDMAs were yellow, viscous resins (the η values ranged from 1.28 × 10³ to 1.39 × 10⁴ Pa·s, at 50 °C). Their RI ranged from 1.50 to 1.52, T_g from −31 to −15 °C, DC from 53 to 78%, and S from 1.24 to 2.99%, which is appropriate for dental applications.

Handling properties and surface characteristics of universal resin composites

OBJECTIVE

This study investigated the handling and surface characteristics of universal resin composites and determined the interrelations among the composites' handling, mechanical, and physical properties.

METHODS

Five recently introduced universal resin composites were tested. Twelve specimens per material were used to measure the stiffness and stickiness (handling properties) of the resin composite pastes. Additionally, surface properties (Knoop hardness number [KHN], surface roughness [Sa], surface gloss [SG], water contact angle [CA], and surface free energy [SFE]) of cured resin composites were determined in 12 specimens per material immediately after preparation (baseline) and after subjection to thermal cycles (TCs).

RESULTS

Handling and surface properties of the resin composites were material dependent. All the resin composites showed significantly lower KHN in the post-TC subgroups than that in the baseline subgroups. However, the influence of TC on the other surface properties was dependent on the material used. Some resin composites did not indicate any significant differences in Sa, SG, or CA between the baseline and post-TC groups.

SIGNIFICANCE

Although the resin composites in the baseline groups presented with different handling and surface properties, the surface properties of most of the composites were significantly affected by TC. Extremely strong positive or negative correlations were observed between stiffness and stickiness, KHN and Sa, KHN and SG, Sa and SG, and CA and SFE. Most correlations between the handling and surface properties were weak. Therefore, the selection of resin composites in clinical situations should be based on comprehensive consideration of their properties.

Synergistic Effect of Bioactive Inorganic Fillers in Enhancing Properties of Dentin Adhesives-A Review

Dentin adhesives (DAs) play a critical role in the clinical success of dental resin composite (DRC) restorations. A strong bond between the adhesive and dentin improves the longevity of the restoration, but it is strongly dependent on the various properties of DAs. The current review was aimed at summarizing the information present in the literature regarding the improvement of the properties of DAs noticed after the addition of bioactive inorganic fillers. From our search, we were able to find evidence of multiple bioactive inorganic fillers (bioactive glass, hydroxyapatite, amorphous calcium phosphate, graphene oxide, calcium chloride, zinc chloride, silica, and niobium pentoxide) in the literature that have been used to improve the different properties of DAs. These improvements can be seen in the form of improved hardness, higher modulus of elasticity, enhanced bond, flexural, and ultimate tensile strength, improved fracture toughness, reduced nanoleakage, remineralization of the adhesive-dentin interface, improved resin tag formation, greater radiopacity, antibacterial effect, and improved DC (observed for some fillers). Most of the studies dealing with the subject area are in vitro. Future in situ and in vivo studies are recommended to positively attest to the results of laboratory findings.

High-Power LED Units Currently Available for Dental Resin-Based Materials-A Review

The pursuit of less time-consuming procedures led to the development of high-power light-curing-units (LCU) to light-cure dental-resin-based-materials. This review aims to describe high-power light-emitting-diode (LED)-LCUs, by a bibliometric systematization of in vitro and in vivo studies. The research-question, by PICO model, aimed to assess the current knowledge on dentistry-based high-power LED-LCUs by analyzing to what extent their use can promote adverse events on materials and patients' oral condition when compared to low-power LED-LCUs, on daily dental practice. PubMed and B-on database search focused on high-power (≥2000 mW/cm2) LED-LCUs outputs. Studies assessing performance of high-power LED-LCUs for light-curing dental-resin-based-materials were included. From 1822 screened articles, 21 fulfilled the inclusion criteria. Thirty-two marketed units with high levels of radiant emittance (≥2000 mW/cm2 up to 6000 mW/cm2) were identified. Most output values vary on 2000-3000 mW/cm2. The highest output found was 6000 mW/cm2, in FlashMax™P3. Reports suggest that light-curing protocols with lower emittance irradiance and longer exposure outperforms all other combination, however in some clinical procedures high-power LED-LCUs are advocated when compared to low-power LED-LCUs. Moreover, long time exposures and over-curing can be dangerous to the biological vital pulp, and other oral tissues. Evidence showing that high-power LCUs are the best clinical option is still very scarce.

The relation between impact strength and flexural strength of dental materials

AIM

The aim of this study was to investigate whether there is a relation between impact strength and flexural strength of different composite and ceramic materials used in dental restorations.

MATERIALS AND METHODS

The three-point-bending test was used to determine the flexural strength and flexural modulus, and the Dynstat impact test was used to determine the impact strength of different composite and ceramic dental materials. The relation between the flexural strength and impact strength was mathematically investigated and a three-dimensional finite element analysis model of the impact test set-up was created to verify these results.

RESULTS

We found a relation between the impact strength, a_dU, the flexural strength, σ, and the flexural modulus, E, which can be represented by the formula: a_dU=λ_DK(σ²⁄E), where λ_DK is a constant dependent on the test set-up.

CONCLUSION

The obtained impact strength of materials is specific to the test set-up and dependent on the geometric configuration of the test set-up and the specimen thickness. The clinical significance of this investigation is that roughness and fatigue have far more influence on the impact strength than the flexure strength.

Effects of ionizing radiation on surface properties of current restorative dental materials

To investigate the impact of radiotherapy on surface properties of restorative dental materials. A conventional resin composite-CRC (Aura Enamel), a bulk-fill resin composite-BFRC (Aura Bulk-fill), a conventional glass ionomer cement-CGIC (Riva self cure), and a resin-modified glass ionomer cement-RMGIC (Riva light cure) were tested. Forty disc-shaped samples from each material (8 mm diameter × 2 mm thickness) (n = 10) were produced according to manufacturer directions and then stored in water distilled for 24 h. Surface wettability (water contact angle), Vickers microhardness, and micromorphology through scanning electron microscopy (SEM) before and after exposition to ionizing radiation (60 Gy) were obtained. The data were statistically evaluated using the two-way ANOVA and Tukey posthoc test (p < 0.05). Baseline and post-radiation values of contact angles were statistically similar for CRC, BFRC, and RMGIC, whilst post-radiation values of contact angles were statistically lower than baseline ones for CGIC. Exposition to ionizing radiation statistically increased the microhardness of CRC, and statistically decreased the microhardness of CGIC. The surface micromorphology of all materials was changed post-radiation. Exposure to ionizing radiation negatively affected the conventional glass ionomer tested, while did not alter or improved surface properties testing of the resin composites and the resin-modified glass ionomer cement tested.

Methacrylate peak determination and selection recommendations using ATR-FTIR to investigate polymerisation of dental methacrylate mixtures

Investigation of polymerisation kinetics using ATR-FTIR systems is common in many dental studies. However, peak selection methods to calculate monomer-polymer conversion can vary, consequently affecting final results. Thus, the aim of this study is to experimentally confirm which method is less prone to systematic errors. Three commercial restorative materials were tested-Vertise Flow (VF), Constic and Activa Bioactive Restorative Kids. Firstly, Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR) (Spectrum One, Perkin-Elmer, UK) spectra of monomers were acquired-10-methacryloyloxy decyl dihydrogen phosphate (10-MDP), bisphenol-A glycidyl dimethacrylate (Bis-GMA), 2-hydroxyethyl methacrylate (HEMA), triethyelene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) to investigate proportionality of methacrylate peak heights versus concentration. Spectral changes upon light exposure of 2 mm discs of the restorative materials (irradiated for 20 s, LED curing unit 1100-1330 mW/cm2) were assessed to study polymerisation kinetics (n = 3), with continuous acquisition of spectra, before, during and after light exposure. Peak differences and degrees of conversion (DC %) were calculated using 1320/1336, 1320/1350 and 1636/1648 cm-1 as reaction/reference peaks. Inferential statistics included a MANOVA and within-subjects repeated measures ANOVA design (5% significance level). Proportionality of methacrylate peak height to concentration was confirmed, with the 1320/1352 cm-1 peak combination showing the lowest coefficient of variation (8%). Difference spectra of the polymerisation reaction showed noise interference around the 1500-1800 cm-1 region. Across the different materials, DC % results are highly dependent upon peak selection (p<0.001), with higher variability associated to the 1636 cm-1. Significant differences in the materials were only detected when the 1320 cm-1 peak was used (p<0.05). Within the same materials, methods were significantly different for Constic and Activa (p<0.05). It is possible to conclude that the 1320 cm-1 peak is more adequate to assess polymerisation of methacrylates and is therefore recommended.

Effect of Modeling Resins on Microhardness of Resin Composites

Objectives  This study was aimed to determine the effects of modeling resins on the surface microhardness of composites.

Materials and Methods  Six resin-based composites (Charisma Smart, Estellite Asteria, CeramX-One SphereTEC, Admira Fusion, Filtek Ultimate, and Clearfil Majesty Es-2) and three wetting agents (Modeling Liquid, Composite Primer, and Modeling Resin) were investigated. In all, 240 specimens were prepared, and wetting agents were applied prior to light curing in the experimental groups. After 24 hours, specimens were polished and Vickers microhardness (VHN) values were measured.

Statistical Analysis  Shapiro–Wilk and two-way analysis of variance (ANOVA) were used for analyses ( p < 0.05).

Results  Both modeling resin and composites were determined to be effective factors ( p < 0.001). The control group showed the highest VHN (70.37 ± 7.94), followed by Modeling Liquid (64.68 ± 12.07), Composite Primer (59.84 ± 6.33), and Modeling Resin (58 ± 3.52 ^b ; p < 0.001). Filtek Ultimate showed the highest VHN (76.62 ± 9.78 ^c ), whereas Charisma Smart (58.87 ± 7.95), and Clearfil Majesty (67.27 ± 2.58) showed the lowest ( p < 0.001). Clearfil Majesty–Modeling Liquid (46.62 ± 5.33) and Charisma Smart–Composite Primer (50.81 ± 0.39) combinations showed the lowest VHN, whereas Filtek Ultimate–control (87.15 ± 2.12) and Filtek Ultimate–Modeling Liquid (84.24 ± 3.11) showed the highest ( p < 0.001).

Conclusion  All tested modeling resins decreased VHN value, and the amount of reduction varied among composites and wetting agents. It might be safer not to use wetting agents unless they are necessary.

An Evaluation of the Properties of Urethane Dimethacrylate-Based Dental Resins

Most of the dental materials available on the market are still based on traditional monomers such as bisphenol A-glycidyl methacrylate (Bis-GMA), urethane dimethacrylate (UDMA), triethyleneglycol dimethacrylate (TEGDMA), and ethoxylated bisphenol-A dimethacrylate (Bis-EMA). The interactions that arise in the monomer mixture and the characteristics of the resulting polymer network are the most important factors, which define the final properties of dental materials. The use of three different monomers in proper proportions may create a strong polymer matrix. In this paper, fourteen resin materials, based on urethane dimethacrylate with different co-monomers such as Bis-GMA or Bis-EMA, were evaluated. TEGDMA was used as the diluting monomer. The flexural strength (FS), diametral tensile strength (DTS), and hardness (HV) were determined. The impacts of material composition on the water absorption and dissolution were evaluated as well. The highest FS was 89.5 MPa, while the lowest was 69.7 MPa. The median DTS for the tested materials was found to range from 20 to 30 MPa. The hardness of the tested materials ranged from 14 to 16 HV. UDMA/TEGDMA matrices were characterized by the highest adsorption values. The overall results indicated that changes in the materials' properties are not strictly proportional to the material's compositional changes. The matrices showed good properties when the composite contained an equal mixture of Bis-GMA/Bis-EMA and UDMA or the content of the UDMA monomer was higher.

Molecular Interactions between Saliva and Dental Composites Resins: A Way Forward

Dentin and enamel loss related to trauma or especially caries is one of the most common pathological issues in dentistry that requires restoration of the teeth by using materials with appropriate properties. The composite resins represent dental materials with significant importance in today’s dentistry, presenting important qualities, including their mechanical behavior and excellent aesthetics. This paper focuses on the saliva interactions with these materials and on their biocompatibility, which is continuously improved in the new generations of resin-based composites. Starting from the elements involved on the molecular landscape of the dental caries process, the paper presents certain strategies for obtaining more advanced new dental composite resins, as follows: suppression of oral biofilm acids formation, promotion of remineralization process, counteraction of the proteolytic attack, and avoidance of cytotoxic effects; the relation between dental composite resins and salivary oxidative stress biomarkers is also presented in this context.

Influence of Different Conditioning Treatments on the Bond Integrity of Root Dentin to rGO Infiltrated Dentin Adhesive. SEM, EDX, FTIR and MicroRaman Study

The present study aimed to synthesize and equate the mechanical properties and dentin interaction of two adhesives; experimental adhesive (EA) and 5 wt.% reduced graphene oxide rGO) containing adhesive. Scanning electron microscopy (SEM)-Energy-dispersive X-ray spectroscopy (EDX), Micro-Raman spectroscopy, push-out bond strength test, and Fourier Transform Infrared (FTIR) spectroscopy were employed to study nano-bond strength, degree of conversion (DC), and adhesive-dentin interaction. The EA was prepared, and rGO particles were added to produce two adhesive groups, EA-rGO-0% (control) and rGO-5%. The canals of sixty roots were shaped and prepared, and fiber posts were cemented. The specimens were further alienated into groups based on the root canal disinfection technique, including 2.5% sodium hypochlorite (NaOCl), Photodynamic therapy (PDT), and ER-CR-YSGG laser (ECYL). The rGO nanoparticles were flake-shaped, and EDX confirmed the presence of carbon (C). Micro-Raman spectroscopy revealed distinct peaks for graphene. Push-out bond strength test demonstrated highest values for the EA-rGO-0% group after NaOCl and PDT conditioning whereas, rGO-5% showed higher values after ECYL conditioning. EA-rGO-0% presented greater DC than rGO-5% adhesive. The rGO-5% adhesive demonstrated comparable push-out bond strength and rheological properties to the controls. The rGO-5% demonstrated acceptable DC (although lower than control group), appropriate dentin interaction, and resin tag establishment.

Structure-dependent antimicrobial mechanism of quaternary ammonium resins and a novel synthesis of highly efficient antimicrobial resin

The demand for powerful and multifunctional water-treatment materials and reagents is increasing, because we are facing worse raw water quality, various tolerant bacteria, and risky disinfection by-products (DBPs) in drinking water. Quaternary ammonium resins (QARs) are promising candidates for water disinfection and purification, but their limited bactericidal capacities are difficult to improve because of the lack of guidelines for enhancing antibacterial efficiency. Therefore, we first systematically studied the structure-dependent antimicrobial mechanism of QARs and found that the best resin skeleton is acrylic-type, the optimal bactericidal alkyl is hexyl or octyl, the most applicable sizes are 80-100 meshes, the best counter anion is iodide ion, and the optimum quaternization reagent is iodoalkane. Moreover, the antibacterial capacity was demonstrated to depend on surficial N⁺ groups, correlating with surficial N⁺ charge density (R² of 0.98) but not with exchange capacity (R² of 0.26), physical adsorption of resin skeleton, or electrostatic adsorption of N⁺ groups. Based on these principles, we synthesized a new resin, Ac-81, with a surficial antibacterial design, which simultaneously exhibited better antimicrobial efficiency (two orders of magnitude) as well as higher contaminant removal potential (61.92%) compared to the traditional Ac-8C antibacterial resin. Furthermore, the new resin showed remarkable broad-spectrum antibacterial effects against Gram-negative E. coli and P. aeruginosa and Gram-positive B. subtilis and S. aureus in simulated water and actual water. Simultaneously, water quality was significantly improved, with HCO₃^-, SO₄^2-, TN, TP, and TOC reduced by 79-90%, >99%, 66-85%, >99%, and 22-26%, respectively. Ac-81 is characterized by facile reusability, high treatment capacity of 1500 bed volume, and good adaptability for treating actual water, providing a promising alternative for drinking-water disinfection and purification.

Surface degradation effects of carbonated soft drink on a resin based dental compound

Dental compounds and restorative materials undergo surface degradation and erosion from exposure to a variety of dietary substances. In this study we investigated changes in the surface properties of Rebaron, a hard denture reline material (HDRM), following timed immersion in carbonated soft drinks to determine its durability in a common acidic environment. Samples were prepared and immersed in a carbonated soft drink (or its components) for 6, 12, or 24 h. Surface structure and mechanical properties were characterized using Atomic Force Microscopy (AFM). Raman spectroscopy was used to identify changes in the HDRM surface chemistry following exposure to the test solutions. AFM revealed that prolonged exposure led to pit formation and a subsequent increase in surface roughness, from 302.02 ± 30.20 to 430.59 ± 15.07 nm Ra, following a 24 h exposure. Young's modulus values decreased from 9.3 ± 7.0 to 0.53 ± 0.26 GPa under the same conditions, demonstrating a softening and embrittlement of the HDRM sample. Raman results revealed that immersion in the carbonated soft drink or acidic solution changed the nature of the HDRM structure, converting the HDRM surface chemistry from primarily hydrophobic to hydrophilic. Our study indicates that sustainability and durability of Rebaron HDRM are significantly reduced by prolonged exposure to carbonated (acidic) soft drink, resulting in deformation and degradation of the material surface.

Effect of myricetin on odontoblast-like cells and its potential to preserve resin-dentin Bonds

Stabilization of the resin-dentin interface to increase the durability of adhesive dental restorations is a challenging task. The use of naturally occurring collagen crosslinking agents has been proposed to prevent degradation of the hybrid layer. Myricetin (MYR) is a flavonoid with a wide variety of beneficial effects and it has been used for the treatment of different systemic pathologies. The chemical structure of MYR makes it a powerful antioxidant, an inhibitor of matrix metalloproteinase (MMP) activity, and a collagen cross-linker. This study presents MYR as a novel treatment in operative dentistry to stabilize the resin-dentin interface by inhibiting MMPs and crosslinking the collagen. Viability tests carried out using a resazurin assay showed that MYR had no cytotoxic effects on human odontoblast-like cells and the phenotype was preserved. Fluorometric MMP activity assay and fluorescence microscopy revealed that the MMPs in the demineralized dentin were effectively inhibited by the application of MYR (600 μM for 120 s). A microtensile bond strength test was performed immediately and after six months of storage. The bond strength to dentin was not affected by MYR and was preserved over time. Demineralized dentin beams were evaluated to determine the dentin biomodification using microtensile strength and elastic modulus assays. MYR improved the biomechanical behavior of the demineralized dentin similarly to glutaraldehyde, a recognized crosslinking agent. These findings indicated that MYR acts as an MMP inhibitor, collagen cross-linker, and preserver of the bond strength. Furthermore, MYR is an ethanol-soluble molecule with a lower molecular weight than the other polyphenols; hence, it can be applied for a short time and diffuses deeply through the dentin without any associated cytotoxicity. This molecule has beneficial effects on the biological and mechanical behavior of the resin-dentin interface and may be used to effectively stabilize the hybrid layer in a clinical setting.

Effects of Different Amine Activators on the Monomer Conversion, Biaxial Flexural Strength, and Color Stability of Experimental Provisional Dental Restorations

Objective  The aim was to assess the effect of different amine activators including N, N-dimethyl-p-toluidine (DMPT) or Na-N-tolyglycine glycidyl methacrylate (NTGGMA) on chemical-activated monomer conversion, biaxial flexural strength (BFS), and color stability of composites for provisional dental restorations.

Materials and Methods  Two formulations of composites containing either DMPT (D-temp) or NTGGMA (N-temp) were prepared. The degree of monomer conversion was assessed. The BFS of the materials was tested using the ball-on-ring testing jig. The color difference (∆E ₀₀ ) of the materials after immersion in water was also determined. The commercial comparisons were Unifast (UF), Protemp (PT), Luxacrown, and Luxatemp (LT).

Results  The monomer conversion of D-temp (57.4 ± 1.3%) was comparable to that of N-temp (59.0 ± 1.3%). The conversion of both D-temp and N-temp were higher than that of PT (48.1 ± 3.4%) and LT (48.0 ± 1.6%). BFS of both D-temp (164.2 ± 18.1 MPa) and N-temp (168.6 ± 8.9 MPa) were comparable but higher than that of UF (119.8 ± 13.6 MPa). ∆E ₀₀ of D-temp (2.7 ± 0.7) and N-temp (2.5 ± 0.8) were comparable but higher than that of other commercial materials (0.6–1.2).

Conclusion  The use of DMPT or NTGGMA showed negligible effect on monomer conversion, BFS, and color stability of the experimental provisional restorations. The conversion and BFS of the experimental materials were in the range of that obtained from commercial bis-acryl-based materials. However, the color stability of the experimental materials was lower than that of commercial materials.

The Photoinitiators Used in Resin Based Dental Composite-A Review and Future Perspectives

The presented paper concerns current knowledge of commercial and alternative photoinitiator systems used in dentistry. It discusses alternative and commercial photoinitiators and focuses on mechanisms of polymerization process, in vitro measurement methods and factors influencing the degree of conversion and hardness of dental resins. PubMed, Academia.edu, Google Scholar, Elsevier, ResearchGate and Mendeley, analysis from 1985 to 2020 were searched electronically with appropriate keywords. Over 60 articles were chosen based on relevance to this review. Dental light-cured composites are the most common filling used in dentistry, but every photoinitiator system requires proper light-curing system with suitable spectrum of light. Alternation of photoinitiator might cause changing the values of biomechanical properties such as: degree of conversion, hardness, biocompatibility. This review contains comparison of biomechanical properties of dental composites including different photosensitizers among other: camphorquinone, phenanthrenequinone, benzophenone and 1-phenyl-1,2 propanedione, trimethylbenzoyl-diphenylphosphine oxide, benzoyl peroxide. The major aim of this article was to point out alternative photoinitiators which would compensate the disadvantages of camphorquinone such as: yellow staining or poor biocompatibility and also would have mechanical properties as satisfactory as camphorquinone. Research showed there is not an adequate photoinitiator which can be as sufficient as camphorquinone (CQ), but alternative photosensitizers like: benzoyl germanium or novel acylphosphine oxide photoinitiators used synergistically with CQ are able to improve aesthetic properties and degree of conversion of dental resin.

Optimization of Plasmonic Gold Nanoparticle Concentration in Green LED Light Active Dental Photopolymer

Gold nanoparticles (AuNPs) display surface plasmon resonance (SPR) as a result of their irradiation at a targeted light frequency. SPR also results in heat production that increases the temperature of the surrounding environment, affecting polymerization. The aim was to investigate the SPR effect of AuNPs on a dimethacrylate-based photopolymer system. The tested composites were designed to overlap the illumination required for the polymerization and the plasmon effect. The 5 nm-sized dodecanethiol capped AuNPs were applied in different concentrations in the matrix that were irradiated with green light (λ = 532 nm), where the Irgacure 784 photoinitiator also absorbs the light. The plasmonic effect was investigated for the refractive index change by surface plasmon resonance imaging (SPRi) supplemented by ellipsometry. Moreover, optical transmission and transmission electron micrographs (TEM), diametral tensile stress (DTS), and confocal Raman spectroscopy was performed to determine the degree of conversion (DC) at 1.0, 1.4, and 2.0 mW/cm2 light intensities. It was found that the optimal conditions were at 0.0208 wt% AuNPs concentration and 1.4 mW/cm2 light intensity at which the refractive index change, DTS, and DC data were all maximal. The study confirmed that AuNPs are applicable to improve the polymerization efficiency of dental composite resin.

A Low-Viscosity BisGMA Derivative for Resin Composites: Synthesis, Characterization, and Evaluation of Its Rheological Properties

This study aimed to synthesize new bisphenol A-glycidyl methacrylate (BisGMA) derivatives, targeting a reduction in its viscosity by substituting one of its OH groups, the leading cause of its high viscosity, with a chlorine atom. Hence, this monochloro-BisGMA (mCl-BisGMA) monomer was synthesized by Appel reaction procedure, and its structure was confirmed using Fourier transform infrared spectroscopy, ¹H and ¹³C-nuclear magnetic resonance spectroscopy, and mass spectroscopy. The viscosity of mCl-BisGMA (8.3 Pa·s) was measured under rheometry conditions, and it was found to be more than 65-fold lower than that of BisGMA (566.1 Pa·s) at 25 °C. For the assessment of the viscosity changes of model resins in the presence of mCl-BisGMA, a series of resin matrices, in which, besides BisGMA, 50 wt % was triethylene glycol dimethacrylate, were prepared and evaluated at 20, 25, and 35 °C. Thus, BisGMA was incrementally replaced by 25% mCl-BisGMA to obtain TBC0, TBC25, TBC50, TBC75, and TBC100 blends. The viscosity decreased with temperature, and the mCl-BisGMA content in the resin mixture increased. The substantial reduction in the viscosity value of mCl-BisGMA compared with that of BisGMA may imply its potential use as a dental resin matrix, either alone or in combination with traditional monomers. However, the various properties of mCl-BisGMA-containing matrices should be evaluated.

Evaluation of physico-mechanical properties and filler particles characterization of conventional, bulk-fill, and bioactive resin-based composites

OBJECTIVE

This study evaluated physical and mechanical properties and characterized the filler particles of seven composites.

MATERIALS AND METHODS

Filtek Supreme (FS, 3M Oral Care), Forma (FO, Ultradent), Charisma Diamond (CD, Kulzer), Spectra Smart (SS, Dentsply), Filtek Bulk Fill (FB, 3M Oral Care), Tetric N-Ceram Bulk Fill (TB, Ivoclar), and Cention N (Ivoclar) in self- (CNSC) or dual-curing (CNDC) were evaluated. Fillers size, shape, and content were analyzed by scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDX). Disk-shaped specimens (n = 5) were prepared for sorption (SP) and solubility (SL). Flexural strength and elastic modulus were tested at 24 h and 12 months (n = 10). Degree of conversion (DC%) and maximum rate of polymerization (Rp^max) were evaluated using micro-Raman spectroscopy. SP and SL results were submitted to Kruskal-Wallis one-way ANOVA and Dunn's pairwise test (α = 0.05). Mechanical properties were analyzed by 2-way ANOVA and Tukey's test (α = 0.05). DC% of CNSC and CNDC was compared by independent t-test (α = 0.05). Rp^max results were analyzed by 1-way ANOVA and Tukey's test (α = 0.05).

RESULTS

The composites differed regarding filler size, shape, and content. CD and CNSC showed lower SP than FS. SS had lower SL than CNSC and CNDC. CNDC presented higher DC% than CNSC. CD, TB, and CNDC showed the highest Rp^max. TB, CNSC, and CNDC showed the lowest 24-h flexural strengths. Mechanical properties of CD did not decrease, while FO, TB, and CNSC showed a significant reduction after storage.

CONCLUSIONS

Monomer composition and fillers characteristics greatly influenced the physico-mechanical properties of the tested composites.

Evaluation of Synergic Potential of rGO/SiO2 as Hybrid Filler for BisGMA/TEGDMA Dental Composites

Graphene and graphene oxide based nanomaterials have attained immense significance in research because of their matchless physiochemical characteristics. Although potential biomedical applications of graphene have been extensively studied, however, dentistry related applications were rarely explored. This study aimed to investigate the effect of various percentages of surface modified reduce graphene oxide (S-rGO) in combination with SiO₂ nanoparticles (bulk filler) on numerous physio-mechanical characteristics of acrylate-based (BisGMA/TEGDMA: 1:1 by wt.) composites. BisGMA/TEGDMA reinforced with 30 wt.% surface modified fumed-silica (S-A200) was considered as control group (base composite). Various concentrations (0, 0.5, 1, 2, 4 wt.%) of S-rGO were incorporated into the base composite via solution casting and high-speed mixing. The obtained composites were characterized for rheological properties before curing by using Rheometer (Anton Paar, USA) in the oscillatory mode under a frequency sweep over a range of angular frequency of 0.1–100 rad/s at 25 °C. The degree of conversion (DC) was measured by using Fourier transform infrared spectroscopy (FTIR). A Nano-indentation test was carried out to obtain nano-hardness and elastic modulus. The surface roughness was measured by optical microscope (Bruker^®), 3D non-contact surface profilometer. The structural and morphological properties were studied by using Scanning Electron Microscopy (SEM). The mean and standard deviation were calculated and a simple mean comparisons test was performed for comparison using SPSS. The results revealed that the addition of a tiny proportion of S-rGO considerably increased the nano-indentation hardness, elastic modulus and DC. Conversely, a gradual reduction in viscosity was observed with increasing S-rGO concentration. The study demonstrates that a small fraction of S-rGO in combination with SiO₂ could enhance physical, mechanical and rheological properties of acrylate based composites. Thus S-rGO/SiO₂ combination could be used as a potential hybrid filler for dental nanocomposites.

Evaluation of degree of conversion, rate of cure, microhardness, depth of cure, and contraction stress of new nanohybrid composites containing pre-polymerized spherical filler

The aim of the present study was to characterize nanohybrid and nanofilled composites in terms of degree of conversion (DC), rate of cure (RC), microhardness (Vickers hardness number; VHN), depth of cure, and contraction stress (CS). Ceram.X® universal- A3, duo enamel E2, and duo dentin D3 composites were compared to Tetric EvoCeram® and FiltekTMSupreme XTE composites of equivalent dentin and enamel shades under a 40 s photopolymerization protocol. DC was measured by infrared spectroscopy, calculating RC from the kinetic curve. Top and bottom VHN were determined using a Vickers indenter, and bottom/top surface ratio (Vickers hardness ratio; VHR) calculated. CS vs. time was assessed by a universal testing machine and normalized for the specimen bonding area. All materials showed DC  < 60%, Ceram.X® composites reaching higher values than the other composites of corresponding shades. RC at 5 s of photopolymerization was always higher than that at 10 s. All the Ceram.X® composites and the lighter-shaded Tetric EvoCeram® and FiltekTMSupreme XTE composites reached the RC plateau after 25 s, the remaining materials showed a slower kinetic trend. Tetric EvoCeram® and FiltekTMSupreme XTE composites displayed the softest and the hardest surfaces, respectively. Differently from darker-shaded materials, the universal and the three enamel-shaded composites resulted optimally cured (VHR >  80%). The tested composites differed in CS both during and after light cure, Tetric EvoCeram® and FiltekTMSupreme XTE composites displaying the highest and the lowest CS, respectively. Only the Ceram.X® universal-A3 reached a CS plateau value. The tested composites exhibited material-dependent chemo-mechanical properties. Increasing the curing time and/or reducing the composite layer thickness for dentin-shaded composites appears advisable.

Rapid Fabrication of Sterile Medical Nasopharyngeal Swabs by Stereolithography for Widespread Testing in a Pandemic

The 3D printing of nasopharyngeal swabs during the COVID-19 pandemic presents a central case of how to efficiently address a break in the global supply chain of medical equipment. Herein a comprehensive study of swab design considerations for mass production by stereolithography is presented. The retention and comfort performance of a range of novel designs of 3D-printed swabs are compared with the standard flocked-head swab used in clinical environments. Sample retention of the 3D swab is governed by the volume, porosity density, and void fraction of the head as well as by the pore geometry. 3D-printed swabs outperform conventional flock-head swabs in terms of sample retention. It is argued that mechanically functional designs of the swab head, such as corkscrew-shaped heads and negative Poisson ratio heads, maximize sample retention and improve patient comfort. In addition, available designs of swab shafts for an optimized sample collection procedure are characterized. The study is conducted in vitro, using artificial mucus, covering the full range of human mucus viscosities in a 3D-printed model of a nasal cavity. The work sets the path for the resilient supply of widespread sterile testing equipment as a rapid response to the current and future pandemics.

Effect of Different Polishing Systems on the Surface Roughness and Gloss of Novel Nanohybrid Resin Composites

Objectives  To evaluate the surface roughness and gloss of three nanohybrid resin composites after polishing with three different polishing systems.

Materials and Methods  A total number of 112 disc specimens (10 × 3 mm) were prepared from nanohybrid—Empress Direct (ID), Grandio (GR), Filtek Z350 (Z350) and a microhybrid resin composite restorative materials—Filtek Z250 (Z250). Following 24-hour storage in 37°C distilled water, each composite group ( n = 28) was assigned into four groups ( n = 7) according to finishing/polishing (F/P) system: Mylar strip, Optrapol, Politip, and Sof-Lex (SL). The surface roughness (Ra, mm) was measured by a novel three-dimensional method using an image analysis software attached to an environmental scanning electron microscope. A glossometer was used to measure the surface gloss.

Results Statistical analysis used was ANOVA test. Two-way Anova test revealed that the “type of composite” and “F/P techniques” had a significant effect on both surface roughness and gloss of the tested resin composite materials ( p < 0.05). Tukey’s post hoc test showed that ID, GR, and Z350 revealed lower surface roughness and higher surface gloss than Z250 within the same polishing system ( p < 0.05). Sof-Lex polishing discs produced the lowest surface roughness and highest surface gloss values compared with Optrapol and Politip ( p < 0.05).

Conclusion  The tested F/P systems provided comparable surface roughness and gloss for nanohybrid composites. The Sof-Lex system provided the best surface roughness and gloss for nanohybrid composites.

Dental Composition Modified with Aryloxyphosphazene Containing Carboxyl Groups

A modifier consisting of the mixture of cyclotriphosphazenes containing 4-allyl-2-methoxyphenoxy and β-carboxyethenylphenoxy moieties was developed for administration with acrylate dental restorative compositions. The synthesized compounds were characterized by ¹H and ¹³C NMR spectroscopy and MALDI-TOF mass spectrometry. The optimal conditions to combine the modifier with the starting dental mixture consisting of bis-GMA and TGM-3 were revealed by differential scanning calorimetry (DSC) method. Properties of the cured modified compositions were evaluated for the compliance with requirements of ISO 4049:2019. It was found that these compositions possess the increased adhesion to dental tissues and cure depth and the decreased water sorption and water solubility. The values of elastic modules, destructive compressive stress and microhardness were also increasing along with the increased content of the modifier in the composition.

Validation of a Simple HPLC-UV Method for the Determination of Monomers Released from Dental Resin Composites in Artificial Saliva

Bisphenol-A (BPA), bisphenol A glycerolate dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA) are organic monomers that can be released from dental composites into the oral cavity. Over specific concentrations, they can act as endocrine disruptors or cause toxic effects. The purpose of this work is to develop and validate an analytical method to determine BPA, Bis-GMA, TEGDMA, and UDMA monomers released from synthetic dental resins in artificial saliva. The method was validated before its application to new hybrid ceramic materials used in computer-aided design and computer-aided manufacturing (CAD/CAM) restorations to determine the release of monomers in various time intervals (e.g., 24 h, and 7, 14, 30, and 60 days), both in methanolic solutions, as well as in artificial saliva. Chromatographic analysis was performed isocratically on a Perfect Sil Target ODS-3 analytical column (250 mm × 4.6 mm, 5 µm) with CH3CN/H2O, 58/42% v/v as mobile phase within 23 min. The developed method was validated in terms of selectivity, linearity, accuracy, and precision.