Monomers and filler content of resin-based crown and bridge materials

Use of a light-polymerized composite removable partial denture base for a patient hypersensitive to poly(methyl methacrylate), polysulfone, and polycarbonate: a clinical report

This article describes a light-polymerized composite denture base used for a patient with hypersensitivity to poly(methyl methacrylate) (PMMA), polysulfone (PSF), and polycarbonate (PC). A urethane-dimethacrylate (UDMA) composite was used as an alternative to fabricate both the denture base and the custom artificial teeth. Immediately after placing the new prosthesis, allergic symptoms disappeared from the patient's mucous membrane. The denture has functioned satisfactorily for more than 2.5 years without recurrence of the hypersensitivity.

Analysis of photopolymerization behavior of UDMA/TEGDMA resin mixture and its composite by differential scanning calorimetry

The aim of this study was to investigate the extent of polymerization (Ep) in terms of polymerization rate of UDMA/TEGDMA resin mixtures and its composite resin, by using a differential scanning calorimeter (DSC) technique employing a photopolymerization apparatus. The resin mixtures used in this study consisted of urethane dimethacrylate (UDMA) as a base monomer and triethyleneglycol dimethacrylate (TEGDMA) as a low viscosity monomer. The concentration of TEGDMA in the mixed monomer was varied to 0, 20, 40, 60, 80, and 100 mol %. Additionally, using a base monomer consisting of 60 mol % UDMA and 40 mol % TEGDMA, four kinds of composites with silica filler of 0, 20, 40, 60, and 70 wt %, were prepared in this study. The general reaction profile and Ep values were obtained from the DSC curves. Increasing the concentration of TEGDMA resulted in a decrease in the viscosity of the UDMA/TEGDMA mixture, a delay in the time to maximum polymerization rate, and an increase in the Ep values of the resin mixtures. Furthermore, Ep values decreased with increasing filler content between 0 and 60 wt % but did not decrease further between 60 and 70 wt %.

The influence of resin chemistry on a dental composite's biodegradation

Previous work reported that commercial dental composite resins containing a urethane-modified bisGMA (bisphenylglycidyl dimethacrylate)/TEGDMA (triethylene glycol dimethacrylate) (ubis) based monomer system showed a 10-fold reduction in the release of a bisGMA-derived product, bishydroxypropoxyphenyl propane (bisHPPP), as compared with that found for bisGMA/TEGDMA (bis) based composites after incubation with cholesterol esterase (CE). Unfortunately, these materials also differed substantially in filler type and content, making it impossible to directly relate any specific parameter to the differences in biodegradation levels. By controlling for filler content and type, the current study will seek to probe the biomolecular interactions between composite resin chemistry and esterase activity in order to help explain the observed differences in biodegradation levels between the ubis and bis resin systems. After 32 days of incubation, buffer and CE solutions were analyzed for degradation products using high-performance liquid chromatography, UV spectroscopy, and mass spectrometry. Both materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. In the CE groups, the ubis system showed a 2.6- to 86-fold reduction (dependent on the product) in the amount of isolated products relative to the bis system (p < 0.01). Scanning electron microscopy data also demonstrated the relative stability of the ubis system and X-ray photoelectron spectroscopy analysis showed a higher content of the ester bond at the surface of the bis samples. Fourier transform infrared data showed that both resins had similar conversions. Because both systems were identical except for their monomer systems, it was concluded that changes in biostability were associated with chemistry. Crosslinking, hydrophobicity, and solubility all relate to ubis's pro-stability.

Permeability of different types of medical protective gloves to acrylic monomers

Dental personnel and orthopedic surgeons are at risk when manually handling products containing methyl methacrylate (MMA). Dental products may also contain cross-linking agents such as ethylene glycol dimethacrylate (EGDMA) or 1,4-butanediol dimethacrylate (1,4-BDMA). Skin contact with monomers can cause hand eczema, and the protection given by gloves manufactured from different types of material is not well known. The aim of this study was to determine the breakthrough time (BTT, min) as a measure of protection (according to the EU standard EN-374-3) for a mixture consisting of MMA, EGDMA and 1,4-BDMA. Fifteen different gloves representing natural rubber latex material, synthetic rubber material (e.g. nitrile rubbers), and synthetic polymer material were tested. The smallest monomer MMA permeated within 3 min through all glove materials. A polyethylene examination glove provided the longest protection period to EGDMA and 1, 4-BDMA (> 120 min and 25.0 min), followed by the surgical glove Tactylon (6.0 min and 8.7 min) and the nitrile glove Nitra Touch (5.0 min and 8.7 min). This study showed that the breakthrough time (based on permeation rate) cannot be regarded as a 'safe limit'. When the permeation rate is low, monomers may have permeated before BTT can be determined. Using double gloves with a synthetic rubber inner glove and a natural rubber outer glove provided longer protection when the inner glove was rinsed in water before placing the outer glove on top.

From vulcanite to vinyl, a history of resins in restorative dentistry

This article provides historical background on the development of resin-based dental restorative materials. With an understanding of the evolution of these materials, clinicians can better appreciate both the complexity of and similarities among the wide variety of resins and polymerization techniques available today. Common problems associated with the use of resin-based materials are explained, and more advanced resin-based systems currently under development are briefly reviewed.

Effects of filler composition and surface treatment on the characteristics of opaque resin composites

The effects of filler composition and surface treatment of titanium dioxide (TiO2) on the shear bond strength to noble metal and mechanical properties of opaque dental resin composites were assessed. A series of fillers for resin composites were prepared with untreated TiO2 or treated silica/alumina-coated TiO2 with silane coupling agent; these fillers were replaced with silanized SiO2 in increasing amounts. Each of various powder compositions were mixed with the liquid and applied to the surface of a silver-palladium-copper-gold (Ag-Pd-Cu-Au) alloy and light cured. A light-activated resin-veneering composite material was placed on top with the use of a brass ring mold and light cured. Specimens were stored at 37 degrees C in water for a period of 24 h. Additionally some specimens were thermocycled at 4 degrees C and 60 degrees C in water baths for 1 min each for 5000 cycles before shear mode testing was performed. Light-activated opaque resin composites containing filler with specific filler compositions of 50 wt% of untreated TiO2-50 wt% of silanized SiO2 (untreated TiO2(50)) and 40 wt% of untreated TiO2-60 wt% of silanized SiO2 (untreated TiO2(40)) showed higher shear bond strengths to the Ag-Pd-Cu-Au alloy than any other specific compositions when no thermocycling was involved. Surface treatment of TiO2 filler and TiO2(50)- and TiO2(40)-opaque resin composites prepared thereof showed significantly higher shear bond strengths than untreated TiO2(50)- and TiO2(40)-opaque resin composites when subjected to thermocycling. Surface-treated opaque resin composite had significantly higher compressive and flexural strength than untreated opaque resin composite after immersion in water for 1 month. Scanning electron microscopy of the fractured opaque resin composite surface showed an interface failure between TiO2 and the matrix resin for untreated composite, and cohesive failure within the resin for surface-treated composite. Surface-treated TiO2(50) and TiO2(40) may be clinically useful as the filler for light-activated opaque dental resin composites.

Relation of dental composite formulations to their degradation and the release of hydrolyzed polymeric-resin-derived products

This article reviews the principal modes of dental composite material degradation and relates them to the specific components of the composites themselves. Particular emphasis is placed on the selection of the monomer resins, the filler content, and the degree of monomer conversion after the clinical materials are cured. Loss of mechanical function and leaching of components from the composites are briefly described, while a more detailed description is provided of studies that have considered the chemical breakdown of materials by agents that are present in the oral cavity, or model the latter. Specific attention will be given to the hydrolysis process of monomer and composite components, i.e., the scission of condensation-type bonds (esters, ethers, amides, etc.) that make up the monomer resins, following reaction of the resins with water and salivary enzymes. A synopsis of enzyme types and their sources is outlined, along with a description of the work that supports their ability to attack and degrade specific types of monomer systems. The methods for the study of biodegradation effects are compared in terms of sensitivity and the information that they provide. The impact of biodegradation on the ultimate biocompatibility of current materials is discussed from the perspective of what is known to date and what remains to be studied. The findings of the past decade clearly indicate that there are many reasons to probe the issue of biochemical stability of composite resins in the oral cavity. The challenge will now be to have both industry and government agencies take a pro-active approach to fund research in this area, with the expectation that these studies will lead to a more concise definition of biocompatibility issues related to dental composites. In addition, the acquired information from such studies will generate the development of alternate polymeric chemistries and composite formulations that will require further investigation for use as the next generation of restorative materials with enhanced biostability.

Analysis of composite type and different sources of polymerization light on in vitro toothbrush/dentifrice abrasion resistance

OBJECTIVES

This study examined toothbrush/dentifrice abrasion of a photo-activated prosthetic composite (dentin and enamel variations) for the purpose of evaluating the influence of polymerization sources on abrasive wear.

METHODS

A photo-activated prosthetic composite material (Artglass) was assessed. Dentin and enamel variations were polymerized using a proprietary photo-curing unit with two xenon stroboscopic lamps (UniXS), and other enamel specimens were polymerized either with a laboratory photo-curing unit with three fluorescent tubes or with a high intensity unit with two metal halide lamps. All specimens were stored in water for 14days and subjected to toothbrush/dentifrice abrasion (350g vertical load) using an abrasive slurry (Colgate Fluoriguard) and a toothbrush (Oral-B 40). The amount of vertical loss and the surface roughness of the specimens after 20,000 strokes were determined by profilometer. Average values of groups of five specimens were compared using analysis of variance (ANOVA) and Sheffe's S intervals (p<0.05).

RESULTS

When polymerizing with the proprietary unit, the abrasion and surface roughness of the enamel material required respective means of 34.08microm (+/-3.66) and 1.00microm (+/-0.08), and the those of the dentin material required means of 42.02microm (+/-5.62) and 1.23microm (+/-0.20). Both abrasion and surface roughness after toothbrushing of the enamel material were significantly smaller than were those of the dentin material. The abrasion of specimens polymerized with the metal halide unit required a mean of 23.89microm (+/-6.17) and demonstrated minimal wear.

CONCLUSIONS

The use of a high intensity metal halide photo-curing unit effectively enhanced the abrasion resistance of the composite. Surfaces of restorations should be covered with the enamel material in order to achieve smoothness and wear resistance.

Curing depth of four composite veneering materials polymerized with different laboratory photo-curing units

Post-curing properties of composite materials are influenced by the type of base monomer, activation system, filler content, and also by the type of light source employed. This study examined curing depth of four composite veneering materials polymerized by means of two different high-intensity photo-curing units for the purpose of evaluating the curing performance of the combinations of composite material and photo-curing unit. Two microfilled and two hybrid composite materials designed for prosthetic veneer were assessed. The composite materials were cured using two photo-curing units, one with a xenon light source and one with two metal halide light sources, and exposure periods varied from 20 to 90 s. Curing depth of the materials was determined with a scraping technique described by the International Organization for Standardization (ISO 4049). Three-factor analysis of variance revealed that the depth of cure was influenced by the type of composite material as well as by the photo-curing unit, and also by the exposure period (P = 0.0001). A microfilled composite material (Dentacolor) demonstrated the greatest depth of cure (4.69 mm) after 90 s irradiation with a metal halide unit (Hyper LII). Of the two photo-curing units, the metal halide curing unit consistently exhibited greater depth of cure than the xenon curing unit (Dentacolor XS). Longer exposure increased the depth of cure for all combinations.

Properties of four composite veneering materials polymerized with different laboratory photo-curing units

This study examined properties of four composite veneering materials polymerized with two different photo-curing units for the purpose of evaluating curing performance of the combination of composite material and curing unit. Two microfilled (Dentacolor and Thermoresin LC II) and two hybrid (Cesead II and Solidex) composite materials designed for prosthetic veneer were selected. The respective light sources of the units were a xenon (Dentacolor XS) and a metal halide (Hyper L II) lamp. The composite materials were exposed with the photo-curing unit for 60 s on each side (i.e. from top and bottom). Knoop hardness, compressive strength, flexural strength, flexural modulus, water absorption and water solubility were determined according to standardized testing methods. The specimens exposed with the metal halide unit generally exhibited greater Knoop hardness number, and compressive strength and lower solubility than those exposed with the xenon unit. A microfilled material (Thermoresin LC II) cured with the metal halide unit exhibited significantly improved results for all tests as compared with the same material cured with the xenon unit.

Filler content and gap width after luting of ceramic inlays, using the ultrasonic insertion technique and composite resin cements. An in vitro study

The effect of ultrasonic insertion on the filler content and the gap width for two brands of composite resin luting agents, intended for luting with the ultrasonic insertion technique, were studied after MOD ceramic inlays (Cerec) had been placed. In addition, the internal and marginal gap widths were determined after MOD ceramic inlays (Celay) bad been luted on extracted premolars with this technique. No statistically significant differences (P > 0.05) were observed for either brand between the filler content obtained from the internal surfaces, from the excess luting agent, or from the luting agent as delivered. There were no statistically significant differences (P > 0.05) between the final internal and marginal gap widths when the two brands of luting agent were compared with each other. Except for the final occlusal and internal gap widths obtained for the inlays luted with the Sono-Cem luting agent, no statistically significant differences (P > 0.05) were observed between the gap widths at the different locations determined. Thus, the ultrasonic insertion technique used did not significantly influence the filler ratio of the hybrid luting agents studied. Judged by the findings in this study, the properties of luting agents seem to greatly influence the final marginal and internal gap widths.

How different curing methods affect mechanical properties of composites for inlays when tested in dry and wet conditions

The purpose of this investigation was to evaluate the differences in the mechanical properties of 3 composite materials in relationship to the intraoral and extraoral curing techniques of direct and indirect (inlay) restorations, and how the mechanical properties are affected by water sorption. Creep characteristics in compression as well as the stress-strain relationship at a constant loading rate both in compression and flexure, were determined. A secondary aim was to investigate the influence of filler content and monomer composition on the mechanical properties. The results are presented as creep curves and as values for elastic moduli, ultimate strength, and ultimate strain. The materials were cured with 2 curing methods. Method A was light curing with a handheld curing unit, and method B was curing in light curing ovens. Water sorption increased the creep values for all types of specimens. Curing in light ovens (method B) gave significantly lower creep values at high stresses than curing with a handheld curing unit (method A). Water sorption decreased the modulus and ultimate strength values for specimens cured with method A. The ultimate strength values also differed for dry and wet specimens cured with method B. There were no general differences in compressive and flexural stress-strain properties between specimens cured according to the methods A and B.

A metal halide light source for laboratory curing of prosthetic composite materials

A high-intensity laboratory photo-curing unit has been developed with the aim of improving the post-curing properties of composite veneering materials. This study introduces the structure of the curing unit and examines the resulting properties of a representative composite material. The curing unit is equipped with two metal halide lamps that radiate both ultraviolet and visible light. Unlike conventional metal halide lamps for industrial use, these metal halide lamps radiate an increased intensity of visible radiation. Properties of a microfilled composite veneering material cured with the new metal halide unit were ascertained. A xenon photo-curing unit was also used as a control. The specimens cured with the metal halide unit exhibited greater Knoop hardness numbers and flexural moduli as compared with those cured with the xenon unit, and also showed reduced water solubility values. These results suggest that the metal halide light source is effective in curing composite materials within a shorter period of time and with improved conversion.

THFMA in dental monomer systems

This study investigates the physical properties of a range of dental resins containing up to 30% by weight of tetrahydrofurfuryl methacrylate (THFMA). The principal monomer was 2,2-bis-(4(2-hydroxy-3-methacryloyloxypropoxy)-phenyl)-propane (bis-GMA) or 1,6-bis-(methacryloxy-2-ethoxycarbony lamino)-2,4,4-trimethyl-hexane (UDMA). Heat-cured resins were tested for Young's modulus, flexural strength, refractive index, polymerization shrinkage and degree of conversion. The results indicated that THFMA has negligible effects on the mechanical properties of bis-GMA and UDMA and on the refractive index of UDMA, whilst the other measured properties present a strong relationship with the concentration of the additive. The dental relevance of the results is discussed and it is concluded that there is scope for further research on the use of THFMA as a comonomer in resin-based materials for dental applications.

Hardness and fracture toughness of four commercial visible light-cured composite resin veneering materials

Four commercial visible light (VL)-cured composite resin veneering materials with a dentine shade were examined for their Knoop hardness and fracture toughness. Composite specimens were classified into three groups. The first group was cured by VL only, the second group was cured by VL and post-cured by VL and the third group was cured by VL and post-cured by heat. It became evident that one composite containing four-functional urethane monomer had both hardness and fracture toughness greater than those of the other three composites containing two-functional urethane monomer. The filler content (vol%) in the composite tended to be linearly proportional to both hardness and fracture toughness. Post-curing by VL and heat were proven to effectively increase both hardness and fracture toughness of once light-cured composites. These results suggest that the clinical performance (e.g. wear resistance and colour stability) of VL-cured composite resin veneering materials might be improved with the aid of post-curing.

Effect of unfilled resins and a silane primer on bonding between layers of a light-activated composite resin veneering material

This investigation evaluated the effect of unfilled resins and a silane primer on bonding between layers of a urethane-based composite resin veneering material. Shear bond strengths between the layers were determined with a two-liquid silane primer and three unfilled resin bonding agents. The silane primers and unfilled resins enhanced the bond between layers of the veneering material. Durability of the bond, however, was influenced by the composition of the bonding agent. Among the systems investigated, combined use of the silane primer with triethyleneglycol dimethacrylate-based unfilled resin exhibited durable and consistent bond strength.

Three-body wear of light-activated composite veneering materials

The in vitro wear of two types of composite resin veneering materials was determined by use of a three-body wear testing device. The wear of a microfilled high-filler content composite resin (Dentacolor) was less than that of a hybrid low-filler content one (Visio-Gem). The worn surface of Dentacolor material was smoother than that of Visio-Gem material. The wear-testing results and scanning electron micrographs demonstrated that the findings obtained by this wear-testing device correlated well with clinical findings.

Effect of photoinitiator on degree of conversion of unfilled light-cured resin

In general, the concentrations of photosensitizer and reducing agent in light-cured dental polymers are fixed by manufacturers for a specific product. These concentrations vary from product to product and the effect of photoinitiator concentration on the final network structures is not clear. Accordingly, the influence of varying concentrations of camphorquinone (CQ) and amine reducing agent, 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA), on the degree of conversion (DC) of an unfilled light-cured resin was investigated. The resin consisted of 50 wt% triethyleneglycol dimethacrylate (TEGDMA) and 50 wt% 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylhexane (UDMA) activated with varying concentrations of CQ (0.25-5 mol.%) and DMAEMA (0.125-5 mol.%). At low CQ concentrations, the DC measured by a Fourier Transform Infrared (FTIR) spectrometer increased rapidly with increasing concentration of DMAEMA and reached a plateau. At CQ concentrations of 0.5 mol.% and above, the plateau DC values were approximately 75-77%. On the basis of the systematic variations of CQ and DMAEMA, a contour representing the optimal combination of photoinitiator concentration from the standpoint of DC was established.

In vitro abrasion of two acrylic veneers

OBJECTIVES

The purpose of this investigation was to compare the degree of abrasion in vitro of two acrylic veneers and dental enamel using a dentifrice with and without fluoride.

METHODS

Ten specimens of each of the two acrylics and enamel were embedded in resin, and eventually polished to 1 micron with diamond paste. Specimens were brushed in a brushing machine with 10,000 double strokes using a dentifrice (Solidox, A/S Denofa) with and without fluoride. The abrasion was evaluated by the naked eye, by photographs and measured by means of profilometer.

RESULTS

One of the polymer materials (Dentacolor, Kulzer) showed a significantly higher resistance to abrasion than the other (Biodent, DeTrey), irrespective of fluoride treatment. Brushing with or without fluoride revealed no significant difference in degree of abrasion between the two acrylic materials. Dentacolor showed significantly higher abrasion resistance than enamel, whereas Biodent did not. There was no significant difference in the degree of abrasion of enamel using dentifrice with or without fluoride.

SIGNIFICANCE

Abrasion of acrylic veneering material differed greatly between brands, but did not seem to be influenced by the fluoride in toothpaste.

Evaluating interfacial gaps for esthetic inlays

Because of some inadequacies associated with the direct fill posterior composite resin, the inlay/onlay form of the same material or ceramic agents has been introduced. This clinical investigation measured the wear rate of several types of luting agents with both resin and ceramic restorative systems and identified several factors related to wear of the cementing agent.

Effect of an adhesive primer on the integrity of occlusal veneer-metal interface and wear of composite resin veneered restorations

This study examines the influence of a metal-resin bonding agent on the wear rate of composite resin veneer. The specimens were prepared with a silver-based casting alloy and a light-cured composite veneering material. After application of repeated loading through a three-body wear testing device, the amount of wear was measured. The results showed no significant difference in wear between bonded and nonbonded specimens on the 1.5 mm areas of the veneer-metal interface. However, the bonded specimens exhibited significantly lower wear values at the veneer-metal interface. The use of an adhesive primer effectively enhanced the integrity of the occlusal veneer-metal junction.

Localized three-body wear of six types of composite resin veneering materials

The wear resistance of six types of composite resin veneering materials was determined in vitro by use of a three-body wear-testing device. This investigation examined the wear characteristics of the veneering composite resins in heavy occlusal contact areas. After repeated cyclic loading, wear values were measured with a profilometer, and surface textures were evaluated with a scanning electron microscope. All of the composite resin veneering materials were significantly more wear resistant than unfilled acrylic resin; but the composite resin materials demonstrated rougher surfaces than unfilled resin. Three of the composite resins exhibited fractures in the contact areas.

Effects of two amine reducing agents on the degree of conversion and physical properties of an unfilled light-cured resin

The influence of varying concentrations of two amine reducing agents commonly used in commercial light-cured composites, N,N-dimethyl-p-toluidine (DMPT) and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), on the degree of conversion (DC), Knoop hardness, and compressive and transverse strengths of an unfilled light-cured resin was investigated. The DC obtained from employing two different internal standard peaks, carbonyl (C=O) at 1730 cm-1 and urethane (N-H) at 3350 cm-1, was compared. The resin consisted of 50 wt% triethyleneglycol dimethacrylate (TEGDMA) and 50 wt% 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylhexane (UDMA) activated with 0.5 mol% camphorquinone (CQ) and varying concentrations of either DMPT or DMAEMA. The DC calculated by use of either C=O or N-H absorption peak as an internal reference showed similar values. For both amines, the physical properties were directly related to DC and appeared to reach maximal values at an amine/CQ molar ratio of 4.0. The DC, however, appeared to reach a maximum at an amine/CQ molar ratio of 3.0. Generally, for the same amine/CQ molar ratios, the polymers formulated with DMAEMA, had greater DCs and better physical properties than those formulated with DMPT.

Shear strength of laboratory-processed composite resins bonded to a silane-coated nickel-chromium-beryllium alloy

The shear bond strengths of three commercial laboratory curing composite resin veneers bonded to a nickel-chromium-beryllium alloy treated with the Silicoater system were evaluated. Two light-cured resins and one heat- and pressure-cured resin were evaluated. No statistically significant difference in bond strengths among the three resins was found. Microscopic analysis of the fracture surfaces indicated that all failures were complex and cohesive in nature within the resin and composite. On the basis of the shear bond strengths measured, any of the composite resin veneers tested appear to be clinically acceptable.

The relationship between monomer composition and physical properties of light-cured opaque resin

Light-cured opaque resins were prepared using four types of monomer liquids and titanium dioxide powder. This study investigated the relationship between the monomer composition and the physical properties of light-cured opaque resin. Depth of cure, KHN, residual monomer eluent, and bond strength between the opaque resin and cobalt-chromium alloy were measured. The physical properties of triethyleneglycol dimethacrylate (TEGDMA)-based compositions were superior to those of methyl methacrylate (MMA)-based compositions. Viscosity of the opaque resin's liquid monomer was enhanced by 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylhexane (UDMA). The TEGDMA-based light-cured opaque resins showed excellent physical properties and may be clinically acceptable in bonding prosthodontic composite to metal frameworks.

Monomer composition and bond strength of light-cured 4-META opaque resin

A light-cured opaque resin was prepared with 4-(2-methacryloxyethoxycarbonyl) phthalic anhydride (4-META), bifunctional methacrylates, and titanium dioxide (TiO2). The relation between monomer composition and bond strength was examined with seven methacrylate monomers. Methyl methacrylate (MMA) was useful as a solvent of 4-META. However, it was not sufficiently cured by photo-initiator. The bond strength of a triethyleneglycol dimethacrylate (TEGDMA)-based composition was superior to other monomer-based compositions after repeated thermocycles. 1,6-bis(methacryloxy-2-ethoxycarbonyl-amino)-2,4,4-trimethylhex ane (UDMA) effectively provided viscosity to the composition. The prepared opaque resin consisted of 4-META/MMA-TEGDMA primer, TEGDMA-UDMA-based monomer, and titanium dioxide. This opaque resin bonded strongly to alumina-blasted cobalt-chromium alloy. The light-cured 4-META opaque resin may be useful for bonding prosthodontic composite to metal frameworks.

Adhesion of resins to Ag-Pd alloys by means of the silicoating technique

The purpose of the investigation was to study the effect of water storage on the bond strengths between silanized, silicoated Ag-Pd alloys and veneered composites, in comparison with the bond strengths of systems with conventional retention beads. Furthermore, the mechanism of the bonding was examined. The bond strength of silanized, silicoated dry specimens and similar specimens stored in water was measured by four-point bending. Water storage for 90 days at 37 degrees C reduced the bond strength by approximately 30% to about 15-20 MPa. Mechanical retention beads caused bond strengths of approximately 16-18 MPa which were unaffected by water storage. SEM and microprobe investigations showed that sandblasting with AI2O3 prior to silanization caused substantial numbers of cracks and porosities in the surface layer of the alloy, partly filled with Al2O3. Some particles of silicon oxide in these surface defects were produced by the flame-spraying of the so-called silicoating technique. Further painting of the surface with a silane adhesion primer provided chemical bonding to the composite at the densely spaced Si-O-H-containing silica particles. Many cracks were observed in the interfaces between these particles; thus, water is likely to penetrate the interface with time. The bond strength is most likely reduced by reaction between water and the composite/Si-O structure. The silicon oxide particles are probably attached to the alloy substrate by mechanical retention. Without sandblasting, no bonding was obtained by means of the silicoating technique.