Effects of polymerization initiator complexation in methacrylated beta-cyclodextrin formulations.

OBJECTIVES: Methacrylated beta-cyclodextrin (MCD) is a candidate dental monomer that can complex molecules within its hydrophobic cavity. This study determined the effects of complexation of polymerization initiators such as camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (4E) with MCD on the flexural strength (FS) and degree of conversion (DC) of resulting dental composite formulations. METHODS: Complexation of CQ and 4E with MCD was studied by thin layer chromatography. A mass fraction of 44% 2-hydroxyethylmethacrylate or triethyleneglycoldimethacrylate was mixed separately with a mass fraction of 56% MCD to produce a workable formulation. The mixture was activated with varied amounts of CQ and 4E. One part by mass of the activated resin formulation was mixed with three parts by mass of glass filler. Specimens for FS were prepared by filling molds with composites and curing for 2 min. The cured specimens were immersed in 37 degrees C water for 24 h and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. DC in MCD-based resin formulations was measured with a differential photocalorimeter under nitrogen. RESULTS: MCD appears to form inclusion complexes with CQ and 4E. As a result, FS and DC of MCD-based composites vary significantly as a function of the concentration of polymerization initiators used in the formulations. SIGNIFICANCE: Complexation of polymerization initiators with MCD can influence the FS and DC in MCD-based dental formulations and should be taken into consideration when evaluating MCD as a dental monomer.     

Properties of improved glass-ionomer cement formulations.

The properties of variants of the ASPA cement are described. Improved manipulative and hardening properties are obtained by the incorporation of chelating co-monomers to the polyelectrolyte liquid and by replacing polyacrylic acid by alternative polyalkenoic acids.     

Stress-relaxing composite ligature wires: formulations and characteristics.

A stress-relaxing composite ligature was developed that has both mechanical and esthetic characteristics that make it attractive for use in orthodontics. The neutrally-colored polymer-polymer composite was created by encasing ultra-high molecular weight poly(ethylene) fibers in a poly(n-butyl methacrylate) polymer, which was formulated from a polysol and an optimal benzoin ethyl-ether concentration. The resulting composite ligature exhibited a tensile strength more than twice that of dead-soft stainless steel ligature, and a stress-relaxation decay significantly greater than stainless steel ligature. With these characteristics, the material could be used as an orthodontic ligature when tooth movement with negligible friction due to ligation is desired. A Maxwell-Weichert model predicted the load-decay profiles that ultimately resulted in the general loss of frictional forces with time.     

Microleakage evaluation of eight composite resins

Four-hundred forty-four true hinge axis locations were made and compared to various arbitrary locations. Statistical determinations of probability were made from the population sample. It was found that any chosen artibrary location would not reliably represent the true anatomic hinge axis.     

Effect of methacrylated chitosan incorporated in experimental composite and adhesive on mechanical properties and biofilm formation

The lifespan of a resin‐based restoration is limited, with the main reason for failure being secondary caries. Biofilm formation at the tooth–material interface is a necessary etiological agent for caries development. Dental materials with antimicrobial properties may reduce formation of biofilm and thus increase the longevity of restorations. This study aimed to investigate the effect of methacrylated chitosan (CH‐MA), incorporated into the polymeric network of an experimental dental composite and adhesive, on biofilm growth of Streptococcus mutans and to assess the mechanical properties of the modified materials. The methacrylation of low‐molecular‐weight chitosan was achieved and biofilm studies confirmed the antibacterial effect of the modified polymer in solution. Methacrylated chitosan was incorporated into an experimental composite and adhesive, and the modified materials reduced the formation of S. mutans biofilm. The incorporation of CH‐MA did not alter the bond strength of the adhesives. However, the amount of CH‐MA in composite that is required to elicit an antibacterial response challenges the mechanical properties of the material. The hardness and flexural strength of the composite decreased with increasing amounts of CH‐MA. However, flexural strength values still met the requirement in the ISO standard.     

Scanning electron microscope investigation of in vivo performance of eight composite resins.

Retention. At 6 months, five restorations were lost due to retention failure. The remaining restorations were retained to 24 months and/or 30 months. The study of one material was discontinued because of numerous retention failures. Marginal wear. Facial wear along the margin in the center portion of the restoration was appreciably greater than lingual, proximal, and incisal wear. In general, most composite resins began to display evidence of wear during the first 6 months of service. Over the study period, three restorations were lost because of excessive marginal wear. Surface texture. Most materials were clinically acceptable with regard to surface texture over the course of the study. Extended studies of greater durations are indicated.     

Properties of microfilled and visible light-cured composite resins.

Physical and mechanical properties of four commercial micro-filled composite resins, a visible light-cured composite resin, and a conventional composite resin were investigated. Isocap, Isopast, and Superfil were similar in most properties. Compared with Concise, they had lower values of inorganic filler content and modulus of elasticity and higher values of water sorption, depth of indentation, and linear coefficient of thermal expansion. The properties of Silar were between those of Concise and the other microfilled composite resins. Fotofil had lower values of modulus of elasticity, water sorption, and linear coefficient of thermal expansion than Concise.     

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.     

Mechanical properties of denture base resin cross-linked with methacrylated dendrimer

Objectives

The aim of this study was to investigate the mechanical properties of denture base resin cross-linked with methacrylated dendrimer.

Methods

The test specimens (3 mm × 10 mm × 65 mm) were fabricated from autopolymerizing resin with the powder/liquid ratio of 10 g/7 ml. The monomer liquid of resin was applied with the mixture of methylmethacrylate and crosslinker dendrimer (DD1) or crosslinker ethyleneglycol dimethacrylate (EGDMA) with five different volume percentages (vol%). The dendrimer crosslinker in this study is a methacrylated molecule (MW = 3617 g/mol) with 12 methacrylate groups. Quantity of crosslinkers varied from 1.1 to 9.1 vol%. The specimens (n = 8/group) were polymerized in distilled water maintained at 55 °C under pressure of 0.4 MPa for 20 min. Test specimens were stored dry at room temperature before testing. The flexural strength (MPa) and flexural modulus (GPa) was measured with three-point bending test at a crosshead speed of 5 mm/min. Surface microhardness (MHN) of matrix area of polymer (n = 8/group) was measured with a load of 245.3 mN by 10 s. Data were analyzed with two-way ANOVA.

Results

ANOVA showed that the addition of DD1 had a significantly higher effect (p < 0.05) on flexural modulus and hardness of matrix area than EGDMA but on flexural strength (p > 0.05). The effect of quantity differences of crosslinker was statistically significant only on flexural strength (p < 0.05).

Significance

The results of this study suggest that dendrimer-crosslinked resin gives better stiffness than that of EGDMA.     

低聚合收缩复合树脂的性能及其应用

聚合收缩是复合树脂的主要缺陷之一,易引起复合树脂与牙体之间形成间隙,产生釉质裂纹和牙尖移动,导致充填失败。近年来,一种以矽油基底基环氧化物为基质成分的新型复合树脂,以低聚合收缩率为特点,成为研究的热点。本文就这种新型复合树脂的性能和粘接等方面作一综述。     

Rheology of urethane dimethacrylate and diluent formulations.

OBJECTIVE: The purpose of this study was to measure the viscosity of resin formulations and investigate the relationship between diluent percentage and temperature. METHODS: Resin formulations were prepared using UDMA and either TEGDMA or HEMA, or HPMA, as diluents at different percentages. Viscosities were obtained with a Bohlin Rheometer at 23 degrees C for all formulations, and at 37 and 60 degrees C for selected formulations. RESULTS: The viscosity of the formulations exhibited Newtonian behaviour and decreased as the percentage of the diluent monomer increased, especially up to 40% of diluent. Linear regressions relating log(viscosity) and mass percent diluent, were obtained in the range 20-80% diluent. Viscosity also decreased as the temperature increased. Activation energies were calculated from Arrhenius plots, and ranged from 16.2-23.4 kJ mol-1. SIGNIFICANCE: The viscosity of the resins controls the flow properties and thus has a significant effect on the deployment of the respective monomers.     

Properties of a new carvable composite dental filling material

The chemical principles and physical properties of a new composite system, which apparently cures in a two-step process to allow time for hand carving to the proper anatomic contours, are described. The new material appears to have better in vitro wear resistance than an older composite filling material.     

Properties of titanium dioxide-polymer composite with titanate coupling agents

Titanium dioxide-polymethacrylate composites were prepared with triethyleneglycol dimethacrylate (TEGDMA), 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylexane (UDMA) and rutile structure titanium dioxide. The coupling agents used were isopropyldimethacrylisostearoyl titanate (KR7), isopropyltri (dioctylphosphate) titanate (KR12) and 4-methacryloxyethyl trimellitate anhydride (4-META). Compressive and transverse strengths of composites were determined under various experimental conditions. Compressive strength of composite with KR 7-treated titanium dioxide was higher than that with untreated titanium dioxide. Transverse strength of the composite with 4-META-treated titanium dioxide was higher than that with untreated titanium dioxide. Both compressive and transverse strengths increased when the titanium dioxide was treated with the mixture of KR7 and 4-META. Scanning electron microscopic observations of fractured composite surfaces showed titanium dioxide polymer interface failure with untreated specimens and polymer cohesive fracture with KR7 + 4-META-treated specimens. The results suggest that titanium dioxide treated with both KR7 and 4-META is useful as a pigment of the opaque material of fixed prosthodontic composite.     

Properties of microfilled composite resins as influenced by filler content

Two series of composite resins were prepared with a light-cured urethane dimethacrylate matrix to which varying amounts of two types of silanated silica particles were added. One series contained volume fractions ranging from 15.8 to 28.8% silica particles of 20 nm in diameter (Type I filler) and the other series volume fractions of from 24 to 49.4% of an agglomerated silica particle of 40 nm in diameter (Type II filler). Tests were conducted to determine the effect of filler level on: depth of cure as determined by hardness measurements; color stability in both UV light and water; water sorption with time; hardness; compressive strength; strain behavior in slow compression; and resistance to toothbrush abrasion and wear by hydroxyapatite. Analysis of the data obtained for these two microfilled series indicate that increased filler levels result in trends for increased depth of cure, color stability, hardness, compressive strength, and stiffness, while water sorption and resistance to both toothbrush abrasion and wear by hydroxyapatite were reduced. These trends were more pronounced for the Type II filler series than for the Type I filler series. However, there was a greater differential in filler levels within the Type II series than within the Type I series.     

Properties of opaque resin composite containing coated and silanized titanium dioxide

Titanium dioxide (TiO2) is mainly used as a pigment in opaque resin composites for application to the surface of a metal framework. The hypothesis in this paper is that particles of silica/alumina (SiO2/Al2O3)-coated TiO2 treated with a silane coupling agent could bond effectively with resin monomers of opaque resin composites. Untreated TiO2 was used as the control filler. Compressive and flexural strength specimens were prepared by the heat-curing method, because these bulk specimens could not be made by the typical photo-curing method. The treated composite had significantly higher compressive and flexural strengths than the untreated composite after 6 months' immersion in water. Scanning electron microscopy of the fractured composite surfaces showed an interface failure between TiO2 and resin for the untreated composite and cohesive failure within the resin for the treated composite after 6 months' immersion. The light-activated opaque resin composite containing treated TiO2 exhibited significantly higher bond strength to a noble dental alloy after 5000 thermal cycles than that containing untreated TiO2. Thus, silanized SiO2/Al2O3-coated TiO2 appears to be clinically useful as a filler of opaque resin composites.     

聚酸改性复合树脂的性能及其在口腔中的应用

聚酸改性复合树脂(复合体)是较新的一种牙色修复材料,其组分中不含水,固化方式包括光固化和化学固化两种。复合体具有一定的吸水性和释放氟能力,会影响其机械性能以及在临床中的应用。本文就复合体的组成、吸水性、机械性能、释氟性及临床应用等方面作一综述。     

Properties of a dental resin composite with a spherical inorganic filler

This study compared the mechanical properties, generalized wear resistance and polymerization shrinkage of a resin composite filled with spherical inorganic filler to other commercial resin composites. Six dental resin composites were tested, including a submicron filled composite (Estelite sigma, Estelite), 1 nano-composite (Filtek Supreme, Supreme), 2 microfilled composites (Heliomolar; Renamel Microfill, Renamel) and 2 microhybrid composites (Esthet X Improved; Tetric Ceram). Compressive strength (CS), diametral tensile strength (DTS), flexural strength (FS), flexural modulus (FM), generalized wear resistance (WV) and polymerization shrinkage (PS) were evaluated for the 6 materials. The specimens were cured according to the manufacturers' instructions in appropriate molds, stored (37 degrees C water, 24 hours), then tested on an Instron testing machine (0.5 mm/minute). PS was tested according to the Archimedes method at 1, 24 and 48 hours continually after polymerization. Data were analyzed by analysis of variance. The results showed that CS values ranged from 252 to 298 MPa, DTS ranged from 35 to 54 MPa, FS from 73 to 140 MPa, FM from 4.8 to 11.1 GPa, WV from 0.037 to 0.086 mm(3) and PS at 24 hours from 2.17 to 3.96 vol%. Composite had statistically significant influence on the in vitro properties tested. Estelite performed similarly to nano-composite and microhybrid composites in mechanical properties and generalized wear resistance, while Estelite and Supreme had the lowest PS among the materials tested. The 2 microhybrid materials had similar properties, while the 2 microfilled composites were different for most properties tested. Overall, the microfilled composites had lower strength than the other composites except Renamel for CS. All the materials had a similar shrinkage pattern in that about 99% of shrinkage occurred in less than 24 hours.     

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后牙复合树脂(posterior composite resin)是指用于涉及到牙齿牙合面修复的材料,要求具有较高的抗压强度、弯曲强度、断裂韧性和耐磨损性。随着复合树脂的发展,后牙复合树脂的性能及临床应用效果不断得到提高。本文概述了目前市售后牙复合树脂的临床效果,以及在减小聚合收缩和提高耐磨损性方面的研究进展。