Effect of silanation of fillers on their dispersability by monomer systems

Mechanical and Bioactive Properties of PMMA Bone Cement: A Review

Over the past few decades, poly(methyl methacrylate) (PMMA) based bone cement has been clinically used extensively in orthopedics for arthroplasty and kyphoplasty, due to its biocompatibility and excellent primary fixation to the host bone. In this focused review, we discuss the use of various fillers and secondary chemical moieties to improve the bioactivity and the physicochemical properties. The viscosity of the PMMA blend formulations and working time are crucial to achieving intimate contact with the osseous tissue, which is highly sensitive to organic or inorganic fillers. Hydroxyapatite as a reinforcement resulted in compromised mechanical properties of the modified cement. The possible mechanisms of the additive- or filler-dependent strengthening or weakening of the PMMA blend are critically reviewed. The addition of layered double hydroxides with surface functionalization appears to be a promising approach to enhance the bonding of filler with the PMMA matrix. Such an approach consequently improves the mechanical properties, owing to enhanced dispersion as well as contributions from crack bridging. Finally, the use of emerging alternatives, such as nanoparticles, and the use of natural biomolecules were highlighted to improve bioactivity and antibacterial properties.

Compositional boundaries for functional dental composites containing calcium orthophosphate particles

OBJECTIVES

To investigate the interrelationships among handling, degree of conversion (DC), mechanical behavior and Ca2+ release of composites containing dicalcium phosphate dihydrate (DCPD, CaHPO4.2H2O), as a function of total inorganic content and DCPD: glass ratio.

METHODS

Twenty-one formulations (1 BisGMA: 1 TEGDMA, in mols) with inorganic fractions ranging from zero to 50 vol% and different DCPD: glass ratios were evaluated for viscosity (parallel plate rheometer, n = 3), DC (near-FTIR spectroscopy, n = 3), fracture toughness/K1C (single-edge notched beam, n = 7-11) and 14-day Ca2+ release (inductively coupled plasma optical emission spectroscopy, n = 3). Data were analyzed by ANOVA/Tukey test (except viscosity, where Kruskal-Wallis/Dunn tests were used, α: 0.05).

RESULTS

Viscosity and DC increased with DCPD: glass ratio among composites with the same inorganic content (p < 0.001). At inorganic fractions of 40 vol% and 50 vol%, keeping DCPD content at a maximum of 30 vol% did not compromise K1C. Ca2+ release showed an exponential relationship with DCPD mass fraction in the formulation (R2 = 0.986). After 14 days, a maximum of 3.8% of the Ca2+ mass in the specimen was released.

CONCLUSION

Formulations containing 30 vol% DCPD and 10-20 vol% glass represent the best compromise between viscosity, K1C and Ca2+ release. Materials with 40 vol% DCPD should not be disregarded, bearing in mind that Ca2+ release will be maximized at the expense of K1C.

Investigation of Hydrothermally Stressed Silicone Rubber/Silica Micro and Nanocomposite for the Coating High Voltage Insulation Applications

Silicone rubber is a promising insulating material that has been performing well for different insulating and dielectric applications. However, in outdoor applications, environmental stresses cause structural and surface degradations that diminish its insulating properties. This effect of degradation can be reduced with the addition of a suitable filler to the polymer chains. For the investigation of structural changes and hydrophobicity four different systems were fabricated, including neat silicone rubber, a micro composite (with 15% micro-silica filler), and nanocomposites (with 2.5% and 5% nanosilica filler) by subjecting them to various hydrothermal conditions. In general, remarkable results were obtained by the addition of fillers. However, nanocomposites showed the best resistance against the applied stresses. In comparison to neat silicone rubber, the stability of the structure and hydrophobic behavior was better for micro-silica, which was further enhanced in the case of nanocomposites. The inclusion of 5% nanosilica showed the best results before and after applying aging conditions.

Chemical Characterisation of Silanised Zirconia Nanoparticles and Their Effects on the Properties of PMMA-Zirconia Nanocomposites

Objectives: The objective of this study was to investigate the mechanical properties of high-impact (HI) heat-cured acrylic resin (PMMA) reinforced with silane-treated zirconia nanoparticles. Methods: Forty-five PMMA specimens reinforced with zirconia were fabricated and divided into three groups: Pure HI PMMA (control group), PMMA reinforced with 3 wt.% of non-silanised zirconia nanoparticles and PMMA reinforced with 3 wt.% of silanised zirconia nanoparticles. Silanised and non-silanised zirconia nanoparticles were analysed with Fourier Transform Infrared (FTIR) Spectroscopy. For measuring the flexural modulus and strength, a Zwick universal tester was used, and for surface hardness, a Vickers hardness tester were used. Furthermore, raw materials and fractured surfaces were analysed using Scanning Electron Microscopy (SEM). A one-way ANOVA test followed by a post-hoc Bonferroni test was employed to analyse the data. Results: The results showed that the mean values for flexural strength (83.5 ± 6.2 MPa) and surface hardness (20.1 ± 2.3 kg/mm²) of the group containing 3 wt.% treated zirconia increased significantly (p < 0.05) in comparison to the specimens in the group containing non-treated zirconia (59.9 ± 7.1 MPa; 15.0 ± 0.2 kg/mm²) and the control group (72.4 ± 8.6 MPa; 17.1 ± 0.9 kg/mm²). However, the group with silanised zirconia showed an increase in flexural modulus (2313 ± 161 MPa) but was not significantly different (p > 0.05) from the non-silanised group (2207 ± 252 MPa) and the control group (1971 ± 235 MPa). Conclusion: Silane-treated zirconia nano-filler improves the surface hardness and flexural strength of HI PMMA-zirconia nanocomposites, giving a potentially longer service life of the denture base.

Silane content influences physicochemical properties in nanostructured model composites

OBJECTIVE

To determine the effect of organosilane content on the physicochemical properties of model composites formulated with nano-sized fillers.

METHODS

Model composites were formulated with dimethacrylate-based monomers, a photoinitiator/co-initiator system and silicon dioxide nano-sized fillers treated with different amounts of 3-methacryloxypropyltrimethoxysilane (MPTS): 1.0 (G_1%), 2.0 (G_2%), 5.0 (G_5%), 7.5 (G_7.5%) and 10 (G_10%) wt.% relative to SiO₂. Non-silanized fillers (G_0%) were used in the control group. Degree of conversion (DC) was assessed by Fourier-transformed infrared spectroscopy (ATR-FTIR). Knoop hardness (KHN) and elastic modulus were determined before and after water storage for 4 months. Water sorption (Wsp) and solubility (Wsl) were calculated by successive mass determinations in analytical balance. Surface gloss and roughness were characterized before and after toothbrushing simulation.

RESULTS

With the exception of those fillers treated with 1% MPTS, DC was not dependent on the silane content. Within the silanized groups, G_1% showed the lowest initial and final KHN, without statistical difference from G_0%. The elastic modulus was not affected by the silane content, regardless of the storage condition, but those groups formulated with at least 5% silane presented improved values after storage. Silane content did not affect the WSl, but affected Wsp, in which those groups formulated with at least 2 wt.% of MPTS produced a more resistant material than G_0%. The use of treated particles with at least 2 wt.% of silane was able to produce materials that did not change their gloss after the brushing process. Additionally, these materials presented lower surface roughness than G_0% after the brushing process (p < 0.05).

SIGNIFICANCE

The concentration of MPTS affected the physicochemical properties of nano-filled composites. Therefore, 2 wt.% of silane was the optimized quantity to produce materials resistant to degradation, both in bulk and surface properties.

In Situ Ultraviolet Polymerization Using Upconversion Nanoparticles: Nanocomposite Structures Patterned by Near Infrared Light

In this paper, we report an approach to polymerization of a nanocomposite containing UV-polymerizable organic material and inorganic, NaYbF₄:Tm³⁺ core-based nanoparticles (NPs), which are optimized for upconversion of near infrared (NIR) to ultraviolet (UV) and blue light. Our approach is compatible with numerous existing UV-polymerizable compositions and the NaYF₄: Yb, Tm³⁺ core-based NPs are much more stable against harsh conditions than NIR organic photo-initiators proposed earlier. The use of a core-shell design for the NPs can provide a suitable method for binding with organic constituents of the nanocomposite, while maintaining efficient NIR-to-UV/blue conversion in the NaYbF₄ core. The prepared photopolymerized transparent polymer nanocomposites display upconversion photoluminescence in UV, visible and NIR ranges. We also demonstrate a successful fabrication of polymerized nanocomposite structure with millimeter/submillimeter size uniformly patterned by 980 nm irradiation of inexpensive laser diode through a photomask.

The quest for stable biomimetic repair of teeth: Technology of resin-bonded composites

The rationale leading to the present generation of resin composites is surveyed. There are many sub-classes such as flowable materials with specialized clinical indications. But a simplistic categorization of resin-composite materials is inappropriate. It is better to appreciate the factors that have driven recent developments. These include the search for low shrinkage composites and for greater depth of cure. Other necessary features are good handling behavior and sufficient strength for load-bearing situations. The esthetic challenge is for materials with superior and life-like optical properties and it is important to identify products that are good in every critical property. Nanotechnology has led to certain improvements, but the possibilities and limitations of nanoparticles must be appreciated. In all these developments, the structure and properties of the host tissues are a challenge and inspiration. Thus materials that can emulate the features of enamel and dentin are the goal of biomimetic design.

Antibacterial quaternary ammonium compounds in dental materials: A systematic review

OBJECTIVE

Quaternary ammonium compounds (QACs) represent one of the most effective classes of disinfectant agents in dental materials and resin nanocomposites. This reviews aims to give a wide overview on the research in the field of antibacterial QACs in dental materials and nanocomposites.

METHOD

An introduction to dental materials components as well as the microorganisms and methods of evaluation for the antimicrobial assays are presented. Then, the properties and synthesis route of QACs, as monomer and filler, are shown. Finally, antimicrobial monomers and fillers, specifically those contain quaternary ammonium salts (QASs), in dental materials are reviewed.

RESULTS

QACs have been used as monomer and micro/nanofiller in restorative dentistry. They possess one or more methacrylate functional groups to participate in polymerization reactions. QACs with multiple methacrylate groups can also be used as crosslinking agents. Furthermore, QACs with chain length from ∼12 to 16 have higher antimicrobial activity in cured dental resins. In general, increasing the chain length leads to a threshold value (critical point) and then it causes decrease in the antimicrobial activity.

SIGNIFICANCE

The current state of the art of dental materials and resin nanocomposites includes a wide variety of antimicrobial materials. Among them, QACs presents low cytotoxicity and excellent long-term antimicrobial activity without leaching out over time.

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%).

Functionalized pink Al2O3:Mn pigments applied in prosthetic dentistry

STATEMENT OF PROBLEM

The color of dental poly(methyl methacrylate) (PMMA) is conventionally rendered by organic and inorganic pigments, which are usually not bonded to the polymer network. Functionalized ceramic pigments can be used to color PMMA, allowing improved chemical interaction with the resin matrix.

PURPOSE

The purpose of this in vitro study was to synthesize, functionalize, and characterize pink manganese-doped alumina ceramic pigments. The hypothesis tested was that functionalized ceramic pigments would render pink coloration to a translucent PMMA without jeopardizing its mechanical properties.

MATERIAL AND METHODS

Pink alumina powders doped with 1 or 2 mol% of manganese (Al₂O₃:Mn) were prepared by means of a polymeric precursor method. Pigment (Pig.) particles were functionalized with a silica coating method followed by silanation before preparation of PMMA-based composite resins (5 wt% pigment). The color of composite resins (Pig.1% and Pig.2%) and PMMA controls (Pink and translucent [Trans]) was evaluated (CIELab color coordinates), and their mechanical properties were tested (3-point bending).

RESULTS

The microstructure of the pigment particles showed approximately 55-nm nanocrystals of manganese-doped α-alumina clustered into irregular porous particles up to 60 μm. The composite resins and pink PMMA showed similar color parameters (CIE a* pink=20.1, Pig.1%=14.6, Pig.2%=16.0, Trans=0.19, P<.001; CIE b* Pink=17.0, Pig.1%=18.6, Pig.2%=19.0, Trans=2.52, P<.001). No statistical differences were observed in mechanical properties among groups (σ_f pink=98.4, Pig.1%=98.1, Pig.2%=98.8, trans=89.1, P=.136).

CONCLUSIONS

The addition of the functionalized pink ceramic pigments to a translucent PMMA yielded similar coloration to that of the regular pink PMMA used in dentistry and did not jeopardize its mechanical properties.

Isocyanato- and Methacryloxysilanes Promote Bis-GMA Adhesion to Titanium

In dentistry, adhesion promotion with 3-methacryloyloxypropyltrimethoxysilane is usually sufficient, but its hydrolytic stability is a continuous concern. The hydrolytic stability of an alternative, 3-isocyanatopropyltriethoxysilane, was compared with that of conventional 3-methacryloyloxypropyltrimethoxysilane. Two silanes, both in 0.1 and 1.0 vol-% in ethanol-water, were evaluated in the attachment of an experimental bis-phenol-A-diglycidyldimethacrylate (Bis-GMA) resin to grit-blasted (with two different systems) titanium. Silane hydrolysis was monitored by FTIR spectrometry. Bis-GMA resin was applied and photo-polymerized on titanium. The specimens were thermocycled (6000 cycles, 5–55°C). Surface analysis was carried out with scanning electron microscopy. Statistical analysis (ANOVA) showed that the highest shear bond was achieved with 0.1% 3-isocyanatopropyltriethoxysilane (12.5 MPa) with silica-coating, and the lowest with 1.0% 3-methacryloyloxypropyltrimethoxysilane (3.4 MPa) with alumina-coating. The silane, its concentration, and the grit-blasting method significantly affected the shear bond strength ( p < 0.05). SEM images indicated cohesive failure of bonding, and, in conclusion, 3-isocyanatopropyltriethoxysilane is a potential coupling agent.

Silica Coating of Nonsilicate Nanoparticles for Resin-Based Composite Materials

This study was designed to develop and characterize a silica-coating method for crystalline nonsilicate ceramic nanoparticles (Al₂O₃, TiO₂, and ZrO₂). The hypothesis was that the coated nonsilicate nanoparticles would stably reinforce a polymeric matrix due to effective silanation. Silica coating was applied via a sol-gel method, with tetraethyl orthosilicate as a silica precursor, followed by heat treatment. The chemical and microstructural characteristics of the nanopowders were evaluated before and after silica coating through x-ray diffraction, BET (Brunauer-Emmett-Teller), energy-dispersive x-ray spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy analyses. Coated and noncoated nanoparticles were silanated before preparation of hybrid composites, which contained glass microparticles in addition to the nanoparticles. The composites were mechanically tested in 4-point bending mode after aging (10,000 thermal cycles). Results of all chemical and microstructural analyses confirmed the successful obtaining of silica-coated nanoparticles. Two distinct aspects were observed depending on the type of nanoparticle tested: 1) formation of a silica shell on the surface of the particles and 2) nanoparticle clusters embedded into a silica matrix. The aged hybrid composites formulated with the coated nanoparticles showed improved flexural strength (10% to 30% higher) and work of fracture (35% to 40% higher) as compared with composites formulated with noncoated nanoparticles. The tested hypothesis was confirmed: silanated silica-coated nonsilicate nanoparticles yielded stable reinforcement of dimethacrylate polymeric matrix due to effective silanation. The silica-coating method presented here is a versatile and promising novel strategy for the use of crystalline nonsilicate ceramics as a reinforcing phase of polymeric composite biomaterials.

Photocurable, Antimicrobial Quaternary Ammonium-modified Nanosilica

In this study, novel, quaternary ammonium methacrylate-modified silica nanoparticles (QMSNs) were synthesized for the first time and proposed as possible antimicrobial particles for free-radical, photocurable monomers. Such monomers have the potential to polymerize with other methacrylate monomers and create antimicrobial polymers. The silica nanoparticles were modified by quaternary ammonium methacrylate functionality and incorporated at 0 to 10 wt% into a 1:1 (by mass) bisphenol A glycerolate dimethacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) resin. Thermal stability of the pristine and modified silica nanoparticles was examined by thermogravimetric analyses. Atomic force microscopy was used to investigate the size distribution and topography of the nanoparticles. For evaluation of the mechanical properties of the samples, flexural strength was measured using a 3-point bending test method. The flexural strength of the composites containing QMSNs increased with increasing modified silica content. The antimicrobial activity of samples was investigated against some standard microorganisms (Streptococcus mutans, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans), and then cytotoxicity and viability were quantified. Incorporation of 2.5% to 10% (by mass) QMSNs into BisGMA/TEGDMA demonstrated antimicrobial activity, but ≥5 wt% significantly reduced cell viability.

Nanotechnology in dentistry today

A review was done of nanotechnology as it applies to dentistry today. Information was gathered from literature search, research data and material inserts in products.Nanotechnology deals with the physical, chemical and biological properties of structures and their components at nanoscale dimensions. One of the biggest contributionS to restorative and aesthetic dentistry has been nanocomposites. These composites are characterized by filler-particle sizes ≤ 100 nm and offer aesthetic and strength advantages over the current microfilled and hybrid resin-based composites. Nanoparticles for coating implant surfaces and the nanopatterning of dental implants is leading to better osseointegration and improved physiologic functions of implants, while nanophase hydroxyapatite has improved its adaptation into bone graft sites. Nano-biochips are now making oral cancer screening and diagnosis of diseases by saliva easier and more affordable.

Bioactive glass particulate filler composite: Effect of coupling of fillers and filler loading on some physical properties

OBJECTIVES

The aim of this study was to investigate the effect of silanization of biostable and bioactive glass fillers in a polymer matrix on some of the physical properties of the composite.

METHODS

The water absorption, solubility, flexural strength, flexural modulus and toughness of different particulate filler composite resins were studied in vitro. Five different specimen groups were analyzed: A glass-free control, a non-silanized bioactive glass, a silanized bioactive glass, a non-silanized biostable glass and a silanized biostable glass groups. All of these five groups were further divided into sub-groups of dry and water-stored materials, both of them containing groups with 3wt%, 6wt%, 9wt% or 12wt% of glass particles (n=8 per group). The silanization of the glass particles was carried out with 2% of gamma-3-methacryloxyproyltrimethoxysilane (MPS). For the water absorption and solubility tests, the test specimens were stored in water for 60 days, and the percentages of weight change were statistically analyzed. Flexural strength, flexural modulus and toughness values were tested with a three-point bending test and statistically analyzed.

RESULTS

Higher solubility values were observed in non-silanized glass in proportion to the percentage of glass particles. Silanization, on the other hand, decreased the solubility values of both types of glass particles and polymer. While 12wt% non-silanized bioactive glass specimens showed -0.98wt% solubility, 12wt% silanized biostable glass specimens were observed to have only -0.34wt% solubility. The three-point bending results of the dry specimens showed that flexural strength, toughness and flexural modulus decreased in proportion to the increase of glass fillers. The control group presented the highest results (106.6MPa for flexural strength, 335.7kPA for toughness, 3.23GPa for flexural modulus), whereas for flexural strength and toughness, 12wt% of non-silanized biostable glass filler groups presented the lowest (70.3MPa for flexural strength, 111.5kPa for toughness). For flexural modulus on the other hand, 12wt% of silanized biostable glass filler group gave the lowest results (2.57GPa).

SIGNIFICANCE

The silanization of glass fillers improved the properties of the glass as well as the properties of the composite. Silanization of bioactive glass may protect the glass from leaching at early stage of water storage.

Mechanical properties of hydroxyapatite whisker-reinforced bis-GMA-based resin composites

OBJECTIVE

To evaluate the reinforcement efficacy of hydroxyapatite (HA) whiskers in bis-GMA-based dental restorative composites and determine the effect of volume fraction on the mechanical properties.

METHODS

Silanized HA whiskers and nano-scale powder were mixed in various proportions with bis-phenol A-glycidyl methacrylate (bis-GMA)-based polymer pastes. Equal parts of initiator and accelerator pastes were then mixed by hand. After curing at 25 ± 2 °C and storage in distilled water at 37 °C for 24h, elastic modulus, fracture strength and work-to-failure in three-point bending, fracture toughness using a notchless triangular prism fracture method, and Vickers hardness were determined. Data were examined by means of one-way analysis of variance and linear regression.

RESULTS

Reinforcing efficacy was significantly dependent on filler morphology. Whiskers had good dispersibility and wettability with bis-GMA-based polymer, conferring good reinforcement and toughening, significantly better than did the HA nano-scale powder.

SIGNIFICANCE

HA whiskers provided better mechanical properties in bis-GMA-based composites compared with the nano-scale powder. Such whisker-reinforced materials may be beneficial compared with currently used dental restorative materials.

Synthesis and study of physical properties of dental light-cured nanocomposites using different amounts of a urethane dimethacrylate trialkoxysilane coupling agent

OBJECTIVE

The purpose of this work was the study of the effect of the amount of a urethane dimethacrylate silane (UDMS) coupling agent on physical properties of dental light-cured resin nanocomposites based on Bis-GMA/TEGDMA (50/50 wt/wt) matrix and Aerosil OX50 as filler.

METHODS

Silica nanoparticles (Aerosil OX 50) used as filler were silanized with 5 different amounts of UDMS 1.0, 2.5, 5.0, 7.5 and 10 wt% relative to silica. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (60 wt%) were mixed with a Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of light cured composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by DMA analyzer. Measurements were taken in samples stored, immediately after curing, in water at 37°C for 24 h. Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water of 75 vol% for 30 days. Thermogravimetric analysis of composites was performed in nitrogen atmosphere from 50 to 800°C.

RESULTS

Almost all of used amount of silane remained chemically bounded on the surface of silica particles, forming a layer around them, which have dense accumulation of methacrylate groups. No significant statistic difference was found to exist between the degree of conversion values of composites with different silane contents. The composite with the lowest amount of UDMS (1.0 wt%) showed the lower flexural strength value, the higher static and dynamic elastic modulus values and the higher sorbed liquid value and solubility.

SIGNIFICANCE

The optimum concentration of UDMS seems to be that of 2.5 wt%. Higher concentrations of UDMS did not improve the properties of composites.

Effect of mechanical properties of fillers on the grindability of composite resin adhesives

INTRODUCTION

The purpose of this study was to investigate the effect of filler properties on the grindability of composite resin adhesives.

METHODS

Six composite resin products were selected: Transbond XT (3M Unitek, Monrovia, Calif), Transbond Plus (3M Unitek), Enlight (Ormco, Glendora, Calif), Kurasper F (Kuraray Medical, Tokyo, Japan), Beauty Ortho Bond (Shofu, Kyoto, Japan), and Beauty Ortho Bond Salivatect (Shofu). Compositions and weight fractions of fillers were determined by x-ray fluorescence analysis and ash test, respectively. The polished surface of each resin specimen was examined with a scanning electron microscope. Vickers hardness of plate specimens (15 × 10 × 3 mm) was measured, and nano-indentation was performed on large filler particles (>10 μm). Grindability for a low-speed tungsten-carbide bur was estimated. Data were compared with anlaysis of variance (ANOVA) and the Tukey multiple range test. Relationships among grindability, filler content, filler nano-indentation hardness (nano-hardness), filler elastic modulus, and Vickers hardness of the composite resins were investigated with the Pearson correlation coefficient test.

RESULTS

Morphology and filler size of these adhesives showed great variations. The products could be divided into 2 groups, based on composition, which affected grindability. Vickers hardness of the adhesives did not correlate (r = 0.140) with filler nano-hardness, which showed a significant negative correlation (r = -0.664) with grindability.

CONCLUSIONS

Filler nano-hardness greatly influences the grindability of composite resin adhesives.

Update on Dental Nanocomposites

Dental resin-composites are comprised of a photo-polymerizable organic resin matrix and mixed with silane-treated reinforcing inorganic fillers. In the development of the composites, the three main components can be modified: the inorganic fillers, the organic resin matrix, and the silane coupling agents. The aim of this article is to review recent studies of the development of dental nanocomposites and their clinical applications. In nanocomposites, nanofillers are added and distributed in a dispersed form or as clusters. For increasing the mineral content of the tooth, calcium and phosphate ion-releasing composites and fluoride-releasing nanocomposites were developed by the addition of DCPA-whiskers or TTCP-whiskers or by the use of calcium fluoride or kaolinite. For enhancing mechanical properties, nanocomposites reinforced with nanofibers or nanoparticles were investigated. For reducing polymerization shrinkage, investigators modified the resin matrix by using methacrylate and epoxy functionalized nanocomposites based on silsesquioxane cores or epoxy-resin-based nanocomposites. The effects of silanization were also studied. Clinical consideration of light-curing modes and mechanical properties of nanocomposites, especially strength durability after immersion, was also addressed.

Shrinkage Stresses Generated during Resin-Composite Applications: A Review

Many developments have been made in the field of resin composites for dental applications. However, the manifestation of shrinkage due to the polymerization process continues to be a major problem. The material's shrinkage, associated with dynamic development of elastic modulus, creates stresses within the material and its interface with the tooth structure. As a consequence, marginal failure and subsequent secondary caries, marginal staining, restoration displacement, tooth fracture, and/or post-operative sensitivity are clinical drawbacks of resin-composite applications. The aim of the current paper is to present an overview about the shrinkage stresses created during resin-composite applications, consequences, and advances. The paper is based on results of many researches that are available in the literature.

The effect of five silane coupling agents on the bond strength of a luting cement to a silica-coated titanium

OBJECTIVES

The adhesive performance of five silane coupling agents in adhering resin composite cement (3M ESPE) to silica-coated titanium was evaluated. Titanium was tribochemically silica-coated by using the Rocatec system.

METHODS

Two volume percent solutions of 3-acryloyloxypropyltrimethoxysilane (Toray Dow Corning Silicone), N-[3-(trimethoxysilyl)propylethylenediamine] (Dow Corning), 3-mercaptopropyltrimethoxysilane (Toray Dow Corning Silicone) and bis-[3-(triethoxysilyl)propyl]polysulfide (Dow Corning) were prepared in 95 vol.% acidified ethanol and allowed to activate (hydrolyze). A pre-activated ca. 2 vol.% 3-methacryloyloxypropyltrimethoxysilane (ESPE Sil) was used as a control. The silanes were applied onto silica-coated titanium slides. Chemical activation reactions of the silanes were monitored by Fourier transform infrared spectrometry (Perkin-Elmer Spectrum One). RelyX ARC (3M ESPE) resin composite cement stubs were applied and photo-polymerized onto silica-coated titanium. The specimens were thermo-cycled (6000 cycles, 5-55 degrees C).

RESULTS

Statistical analysis (ANOVA) showed that the highest shear bond strength (n=8 per group) value after thermocycling, 14.8 MPa (S.D. 3.8 MPa), was obtained with 2.0 vol.% 3-acryloyloxypropyltrimethoxysilane. Silanization and results with 3-methacryloyloxypropyltrimethoxysilane (control, ESPE Sil) did not statistically differ from 3-acryloyloxypropyltrimethoxysilane, 14.2 MPa (S.D. 5.8). The lowest shear bond strength was 7.5 (S.D. 1.9) MPa for N-[3-(trimethoxysilyl)propylethylenediamine] and 7.5 (S.D. 2.5) MPa for bis-[3-(triethoxysilyl)propyl]polysulfide. Both the type of silane (p<0.001) and storage conditions affected significantly the shear bond strength values (p<0.001). All silanes became activated according to the infrared spectroscopic analysis.

SIGNIFICANCE

Silanization with 3-acryloyloxypropyltrimethoxysilane or 3-mercaptopropyltrimethoxysilane might offer an alternative for bonding a luting cement to silica-coated titanium.

Characterization of adsorbed silane on fillers used in dental composite restoratives and its effect on composite properties

The purpose was to study the effect of silane treatment of fillers on viscosity, flexural strength, and hydrolytic degradation of experimental dental composite resins fabricated with these fillers. The fillers consisted of a mixture of barium glass and amorphous silica. The resin was mainly based on ethoxylated bisphenol A dimethacrylate and polycarbonate dimethacrylate. The adsorption of silane on the filler surface was characterized by FTIR. There was significant correlation between the adsorbed silane on filler surface and the silane concentration in silane/methanol solution used for filler treatment. The silane concentration varied from 0.75 to 14% by weight. An increase in silane concentration led to a decrease in viscosities of the corresponding composite resins. The flexural strengths of composites with silanated fillers were greater than that of composites with unsilanated fillers: however, no significant difference was found between the flexural strengths of various silanated groups. The resistance to hydrolytic degradation of different composites increased when the fillers were treated with silane and was the highest at 1.1% silane.

Rheological properties of resin composites according to variations in monomer and filler composition

OBJECTIVES

The aim of this study was to investigate the effects of monomer and filler composition on the rheological properties related to the handling characteristics of composites.

METHODS

A resin matrix in which Bis-GMA was blended with TEGDMA at a ratio of 6:4, was mixed with silane-treated Barium glass (0.7 and 1.0 microm), 0.04 microm fumed silica or 0.5 microm round silica. The type and content of incorporated fillers were varied to achieve different viscosity levels of the experimental composites. Steady shear and dynamic oscillatory shear tests were performed with a rheometer. The viscosity (eta) of the resin matrix, the storage shear modulus (G'), loss modulus (G''), complex modulus (G*), loss tangent (tandelta), phase angle delta and complex viscosity (eta*) of the composites were evaluated as a function of frequency omega=0.1-100 rad/s. To investigate the effect of temperature on viscosity, a temperature sweep test was also performed.

RESULTS

Resin matrices were Newtonian fluids and all experimental composites exhibited pseudoplasticity. The viscosity exponentially increased as the percentage of filler volume was increased, but decreased with increasing temperature. For identical filler volumes, as the filler size decreased, viscosity increased. The effect of filler size on the viscosity was intensified with increasing filler content, and the increased filler content reduced the tandelta.

SIGNIFICANCE

The rheological properties of composites related to handling characteristics were greatly influenced by the formulation of the monomer and filler, shear rate and temperature. The locus of frequency domain phasor plots, G(*)(omega)e(idelta)=G(*)(omega) angledelta, in a complex plane was a valuable method for representing the viscoelastic properties of the composites.

Evaluation of mechanical properties of Z250 composite resin light-cured by different methods

This study evaluated some mechanical parameters of Z250 composite resin using different light-curing methods. Ten specimens were prepared for each mechanical test group with different dimensions according to the test. Light-curing was performed by: a). continuous light (800mW/cm²-40s); b). exponential light (0-800mW/cm²-40s); c). intermittent light (2s-600mW/cm²; 2s without light-80s); d). stepped light (10s-150mW/cm²; 30s-650mW/cm²); e). PAC (1320mW/cm²-3s); f). LED (350mW/cm²-40s). After 24 ± 1 h, the specimens were loaded at a crosshead speed of 0.5 mm/min until fracture. The mechanical properties were calculated and analyzed by ANOVA and Tukey test (5%). The results showed that the highest compressive strength values were found for the continuous, exponential, intermittent and stepped light methods, whereas PAC and LED obtained the lowest values. LED, stepped light, PAC, exponential and continuous light presented the highest values for diametral tensile strength. The intermittent light showed the lowest value, which was significantly lower than the value obtained for LED only. Flexural strength results were not significantly different between all light-curing methods. Finally, the highest modulus of elasticity values were obtained for LED, exponential, continuous and intermittent light, whereas PAC and stepped light showed the lowest values. The mechanical properties were affected by light-curing methods employed.

Bioactive bone cements containing nano-sized titania particles for use as bone substitutes

Three types of bioactive polymethylmethacrylate (PMMA)-based bone cement containing nano-sized titania (TiO2) particles were prepared, and their mechanical properties and osteoconductivity are evaluated. The three types of bioactive bone cement were T50c, ST50c, and ST60c, which contained 50 wt% TiO2, and 50 and 60 wt% silanized TiO2, respectively. Commercially available PMMA cement (PMMAc) was used as a control. The cements were inserted into rat tibiae and allowed to solidify in situ. After 6 and 12 weeks, tibiae were removed for evaluation of osteoconductivity using scanning electron microscopy (SEM), contact microradiography (CMR), and Giemsa surface staining. SEM revealed that ST60c and ST50c were directly apposed to bone while T50c and PMMAc were not. The osteoconduction of ST60c was significantly better than that of the other cements at each time interval, and the osteoconduction of T50c was no better than that of PMMAc. The compressive strength of ST60c was equivalent to that of PMMAc. These results show that ST60c is a promising material for use as a bone substitute.

Thermo-hydrolytic stability of core foundation and restorative composites

STATEMENT OF PROBLEM

The use of weak and less durable materials in restoring teeth may result in weak restorations unable to withstand intraoral conditions.

PURPOSE

The purposes of this study were to evaluate the effect of thermo-hydrolytic stress on the flexural strength and flexural modulus of core foundation composites with direct restorative composites and determine mass percentage of filler content.

MATERIAL AND METHODS

A total of 216 specimens, from 9 brands of commercially available composites (Coreflo, DC Core, Photocore, APX, Litefil II A, Surefil, TPH Spectrum, Z100, and Z250) were fabricated following ISO Standard 4049. Flexural strength (MPa) and flexural modulus (GPa) were determined on bar-shaped specimens (25 x 2 x 2 mm) before and after storage in boiling water for 24 hours (n=12). The filler content in composite was determined by incineration using a thermogravimetric analyzer. The data were analyzed using 2-way analysis of variance and the Student t test (alpha=.05).

RESULTS

Filler content of the tested composites was 66.6 to 81.8 mass %. Significant differences in both flexural strength and flexural modulus existed among materials, the effect of boiling and interaction (P<.05). Coreflo, DC Core, Z100, and Z250 demonstrated a significant decrease in flexural strength after boiling (P<.05). Z250 showed a significant decrease in flexural modulus after boiling (P=.001), while Surefil showed a significant increase in flexural modulus (P=.007).

CONCLUSION

Within the limitations of this study, it can be concluded that composites were affected differently by moist heat stress. Some composites showed a degradation of flexural properties while some retained flexural properties. Stability of the composites varied among brands.

Shear bond strength of Bis-GMA resin and methacrylated dendrimer resins on silanized titanium substrate

OBJECTIVES

The study compared the bond strengths of three resins, Bis-GMA and two novel experimental methacrylated polyester dendrimer resins to grit-blasted titanium substrate with three silanes.

METHODS

Two commercial dental silanes (ESPE Sil and Monobond-S) and an experimental 0.5 vol% 3-methacryloxypropyltrimethoxysilane were applied to grit-blasted Ti substrates. Light-polymerizable resins of Bis-GMA and methacrylated dendrimer were applied to the grit-blasted Ti substrate with polyethylene molds. The substrates with resin stubs (n = 10) were thermocycled (6000 cycles, 5-55 degrees C) or kept in water (37 degrees C, 24 h). The shear bond strength of the resin was measured at a crosshead speed of 1.0 mm min(-1). The surface examination, before and after silanization, was made with a scanning electron microscope (SEM). The silane reactions on the Ti surface were monitored by Fourier transform infrared spectrometry.

RESULTS

Statistical analysis (ANOVA) showed that the highest shear bond for thermocycled samples was obtained for Bis-GMA with Monobond-S (19.4 MPa, standard deviation (SD) 7.1 MPa), and after water storage with a laboratory-made silane (26.4 MPa, SD 8.1 MPa). The dendrimer and Bis-GMA resins conferred equal bonding properties to grit-blasted titanium after thermocycling. The silane, resin type, and storage conditions significantly affected the shear bond strength (p < 0.001 for all factors). SEM images suggested a mainly cohesive type of bonding failure.

SIGNIFICANCE

A dendrimer based resin and the Bis-GMA resin systems conferred statistically equivalent bonding properties to silica-coated Ti after thermocycling.

Processing and properties of porous poly(L-lactide)/bioactive glass composites

Porous poly(L-lactide)/bioactive glass (PLLA/BG) composites were prepared by phase separation of polymer solutions containing bioactive glass particles (average particle size: 1.5 microm). The composite microstructures consist of a porous PLLA matrix with glass particles distributed homogeneously throughout. Large pores (>100 microm) are present in a network of smaller (<10 microm) interconnected pores. The porous microstructure of the composites was not significantly influenced by glass content (9 or 29 vol%), but silane pretreatment of the glass resulted in better glass incorporation in the matrix. Mechanical tests showed that an increase in glass content increased the elastic modulus of the composites, but decreased their tensile strength and break strain. Silane pretreatment enhanced the increase in modulus and prevented the decrease in tensile strength with increasing glass content. Composites soaked in simulated body fluid (SBF) at body temperature formed bone-like apatite inside and on their surfaces. The silane pretreatment of glass particles delayed the in vitro apatite formation. This bone-like apatite formation demonstrates the composites' potential for integration with bone.

EDX fluorescence analysis and SEM observations of resin composites

The purpose of this study was to evaluate the filler compositions of recently available light-cured resins. The composition of each resin paste was evaluated using an energy dispersive X-ray fluorescence spectrometer. Scanning electron microscopic observation of the polymerized resin pastes was also conducted. The main component of each resin composite was Si, while the other elements detected were Al, Ba, Sr, Zr, and K. These elementary compositions differed among the resin pastes used. Three different types of filler morphology were observed; splintered, prepolymerized and splintered, and spherical. The results of this study have thus characterized recently developed resin composites based on their filler elements and morphology.

Surface treatment of injectable strontium-containing bioactive bone cement for vertebroplasty

A novel injectable bioactive bone-bonding cement (SrHAC) composed of strontium-containing hydroxyapatite (Sr-HA) as the inorganic filler and bisphenol A diglycidylether dimethacrylate (Bis-GMA) as the organic matrix for vertebroplasty was developed previously. In this study, the Sr-HA powders were surface treated with methyl methacrylate (MMA) to improve the interface integration of the two phases. After surface treatment, the compression strength and Young's modulus, which were tested after immersion in distilled water at 37 degrees C for 24 h according to ISO 5833, were increased by 68.65 % (p <.001) and 31.02% (p <.001), respectively. The bending strength and bending stiffness of the bioactive bone cement were significantly improved by 54.44% (p <.001) and 83.90% (p <.001). In addition, the handling property of the cement was also enhanced. In vitro biomechanical testing showed that the stiffness of the fractured spine recovered to 82.5% (p <.01) of the intact condition after cementation with surface-treated SrHAC. The failure load of the spine cemented with original and MMA-treated SrHAC improved by 14.25% (p <.05) and 46.91% (p <.05) in comparison with the fractured spines. Results from this study revealed that the MMA-treated SrHAC has a better mechanical effect for orthopedic applications.

Silane treatment effects on glass/resin interfacial shear strengths

OBJECTIVE

Methacrylic resin-based dental composites normally use a bifunctional silane coupling agent with an intermediary carbon connecting segment to provide the interfacial phase that holds together the organic polymer matrix with the reinforcing inorganic phase. In this study, fiber pull-out tests were used to measure the interfacial bond strength at the fiber-matrix interface.

METHODS

Glass fibers (approximately 30 microm diameter, 8 x 10 (-2)m length, MoSci) were silanated using various concentrations (1, 5 and 10%) of either 3-methacryloxypropyl-trimethoxysilane (MPS) or glycidoxypropyltrimethoxy-silane (GPS) in acetone (99.8%). Rubber (poly(butadiene/acrylonitrile), amine terminated, M(w) 5500) molecules were also attached to the fiber surface via GPS molecules. The resin was comprised of a 60/40 mixture of Bis-phenol-A bis-(2-hydroxypropyl)-methacrylate (BisGMA) and tri (ethylene glycol) dimethacrylate (TEGDMA). A bead of resin approximately 2-4 x 10(-3)m in embedded length was placed on the treated fibers and light cured. The load required to pull the fiber out of the resin was converted to shear bond strength.

RESULTS

Interfacial shear strengths were greater for silanated specimens compared with unsilanated, and for MPS compared with GPS. The same set of samples soaked in 50:50 (v/v) mixtures of ethanol and distilled water for a period of 1 month showed a decrease in properties.

SIGNIFICANCE

A positive correlation was found between the amount of silane on the filler surface and the property loss after soaking. Rubber treatment provided improvement in interfacial strength. 5% MPS samples had the highest strength both in soaked as well as unsoaked samples.

The effect of filler loading and morphology on the mechanical properties of contemporary composites

STATEMENT OF PROBLEM

Little information exists regarding the filler morphology and loading of composites with respect to their effects on selected mechanical properties and fracture toughness.

PURPOSE

The objectives of this study were to: (1) classify commercial composites according to filler morphology, (2) evaluate the influence of filler morphology on filler loading, and (3) evaluate the effect of filler morphology and loading on the hardness, flexural strength, flexural modulus, and fracture toughness of contemporary composites.

MATERIAL AND METHODS

Field emission scanning electron microscopy/energy dispersive spectroscopy was used to classify 3 specimens from each of 14 commercial composites into 4 groups according to filler morphology. The specimens (each 5 x 2.5 x 15 mm) were derived from the fractured remnants after the fracture toughness test. Filler weight content was determined by the standard ash method, and the volume content was calculated using the weight percentage and density of the filler and matrix components. Microhardness was measured with a Vickers hardness tester, and flexural strength and modulus were measured with a universal testing machine. A 3-point bending test (ASTM E-399) was used to determine the fracture toughness of each composite. Data were compared with analysis of variance followed by Duncan's multiple range test, both at the P<.05 level of significance.

RESULTS

The composites were classified into 4 categories according to filler morphology: prepolymerized, irregular-shaped, both prepolymerized and irregular-shaped, and round particles. Filler loading was influenced by filler morphology. Composites containing prepolymerized filler particles had the lowest filler content (25% to 51% of filler volume), whereas composites containing round particles had the highest filler content (59% to 60% of filler volume). The mechanical properties of the composites were related to their filler content. Composites with the highest filler by volume exhibited the highest flexural strength (120 to 129 MPa), flexural modulus (12 to 15 GPa), and hardness (101 to 117 VHN). Fracture toughness was also affected by filler volume, but maximum toughness was found at a threshold level of approximately 55% filler volume.

CONCLUSION

Within the limitations of this study, the commercial composites tested could be classified by their filler morphology. This property influenced filler loading. Both filler morphology and filler loading influenced flexural strength, flexural modulus, hardness, and fracture toughness.

Improved filler-matrix coupling in resin composites

Ineffective silane coupling between filler and matrix within dental composites is prone to accelerated in vivo degradation. In this study, we examined to what degree a procedure involving chemical decontamination of filler prior to silanization could improve the filler-matrix bonding, and thus the physico-mechanical properties, of composites. X-ray photoelectron spectroscopy revealed that filler-matrix coupling largely depended upon siloxane bridge (Si-O-Si) formation between the silica surface and the silane molecule, rather than on intermolecular bonding between adjacent silane molecules. Pre-silanization decontamination based upon boiling silica in 0.05-5% sodium peroxodisulfate, followed by ultrasonic rinsing in acetone, most effectively decontaminated filler. Consequently, it significantly improved the bonding of silane molecules to silanol groups at the silica surface. Experimental composites produced following pre-silanization decontamination of filler revealed a diametral tensile strength that was resistant to degradation by thermocycling.

Effect of filler fraction and filler surface treatment on wear of microfilled composites

OBJECTIVES

The aim of this study was to determine the effect of filler content and surface treatment on the wear of microfilled composites.

METHODS

Four microfilled composites with different filler contents (A=20, B=25, C=30, and D=35 vol.%) were made with a light-cured resin (Bis-GMA/UDMA/TEGDMA). The surface treatment of the colloidal silica in each varied: F=functional silane, NF=non-functional silane, U=untreated. Silux Plus served as a control. Specimens were made in steel molds and cured in a light curing unit Triad II (40s/side). Abrasion and attrition wear were evaluated in vitro in a wear tester (OHSU oral wear simulator) with an abrasive slurry (poppy seeds + PMMA) and a human enamel antagonist. The average of five specimens was computed and compared using a ANOVA/Tukey's test at P < or = 0.05. The surface of the wear patterns and the distribution of filler particles were examined using a scanning electron microscope and digital imaging.

RESULTS

As filler volume increased, wear was reduced regardless of filler treatment. Amounts of wear for specimens C and D were significantly lower than specimens A and B. Composites with functional silane treated microfiller (Group F) produced significantly less wear than those with non-functional microfiller (Group NF) at 30 and 35 vol.%, and less than the untreated microfiller (Group U) at 30 vol.%. Scanning electron microscopy of specimens of group NF showed large filler agglomerates (size > 1 microm) in the resin matrix, while specimens of group F and U showed fewer agglomerates. Digital imaging analysis revealed small filler clusters (size < or = 1 microm) in the resin matrix of all specimens.

SIGNIFICANCE

Wear resistance of microfilled composites is enhanced by higher filler volumes irrespective of surface treatment, but good filler/matrix adhesion is needed to minimize wear.