Curing Shrinkage Research Articles

Trifunctional methacrylate monomers and their photocured composites with reduced curing shrinkage, water sorption, and water solubility

Novel trifunctional methacrylates, 1,1,1-tris[4-(2′-acetoxy-3′-methacryloyloxypropoxy)phenyl]ethane (Ac-THMPE) and 1,1,1-tris[4-(2′-acetoxy-3′-methacryloyloxypropoxy)phenyl]methane (Ac-THMPM), have been prepared by acetylation of the hydrophilic hydroxyl groups of 1,1,1-tris[4-(2′-hydroxy-3′-methacryloyloxypropoxy)phenyl]ethane (THMPE) and 1,1,1-tris[4-(2′-hydroxy-3′-methacryloyloxypropoxy)phenyl]methane (THMPM), respectively, for use as dental monomers. Decrease in monomer viscosity resulted from the acetylation. Unfilled resins and composites based on the four trimethacrylates were evaluated for photopolymerization conversion, water contact angle, and curing shrinkage. Water sorption, water solubility, and flexural strength of the composites prepared from the trimethacrylate were measured. Those data obtained for the trimethacrylate-containing materials were compared with control 2,2-bis[4-(2′-hydroxy-3′-methacryloyloxypropoxy)phenyl]propane (bis-GMA)-based materials in order to evaluate the applicability of the trimethacrylates as dental monomers. The acetylation of hydroxyl groups appeared to be an effective method to decrease curing shrinkage, water sorption, and water solubility of the dental composites. When compared with the bis-GMA composite, the composites based on Ac-THMPM and Ac-THMPM showed much lower curing shrinkage, water sorption, and water solubility, along with approximately equal conversion and flexural strength.

Synthesis and photopolymerization of trifunctional methacrylates and their application as dental monomers.

1,1,1-Tris[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]ethane (THMPE) and tris[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]methane (THMPM) were synthesized and evaluated as base monomers in a dental composite system. The photopolymerization reactivity of the trifunctional methacrylates was similar to that of conventional 2,2-bis[4-(2'-hydroxy-3'-methacryloyloxy-propoxy)phenyl]propane (bis-GMA). Of the three monomers (THMPE, THMPM, and bis-GMA), THMPE has the greatest molecular volume, and its composite showed the lowest photopolymerization shrinkage of the composites derived from the three monomers. The water-solubility values for the light-activated composite resins formulated with THMPE and THMPM were much lower than that for a control bis-GMA composite. The trimethacrylates were not leached out into water from their corresponding photo-cured composites whereas the difunctional bis-GMA was eluted from its composite. The water sorption and flexural strength of the composite resins based on THMPE and THMPM were comparable to those of the bis-GMA composite. THMPE is promising for application as a photocurable dental monomer because of its good polymerization reactivity along with relatively low curing shrinkage and water-solubility of its photo-cured composite.

Development of a new photocurable composite resin with reduced curing shrinkage

Objective: This study was conducted to evaluate the potential of a novel trifunctional methacrylate as a component of a photocurable composite resin with reduced curing shrinkage. Methods: Tris[4-(2′-hydroxy-3′-methacryloyloxypropoxy)phenyl]methane (TTEMA) was synthesized by reacting triphenylolmethane triglycidyl ether (TTE) with methacrylic acid in the presence of 4-(dimethylamino)pyridine. Photopolymerization reactivity and volumetric shrinkage of unfilled resins based on TTEMA were investigated by Fourier transform infrared spectroscopy and density measurements, respectively, and the results were compared with those for conventional dental monomers. A three-point bending test of the TTEMA-containing composite resin was carried out. Results: TTEMA was easily prepared in a good yield of 89%. Unfilled resins of TTEMA and bis-GMA, each containing 40% TEGDMA, showed similar photopolymerization reactivity. TTEMA exhibited a very low photopolymerization shrinkage of 2.09%, and 3:2 TTEMA–TEGDMA unfilled resin revealed 10% lower shrinkage than a conventional bis-GMA system containing the same amount of TEGDMA. The flexural strength of a light-activated composite resin formulated with TTEMA is comparable to that of a bis-GMA composite resin under the same conditions. Significance: TTEMA is promising for application as a photocurable dental monomer due to ease of synthesis, good polymerization reactivity, and relatively low curing shrinkage.

Effect of co‐promoter and secondary monomer on shrinkage control of unsaturated polyester (UP)/styrene (St)/low‐profile additive (LPA) systems cured at low temperatures

AbstractThe shrinkage of unsaturated polyester (UP)/styrene (St) resins cured at low temperatures can be reduced by the presence of low‐profile additives (LPAs). It is believed that the reaction‐induced phase separation and the polymerization shrinkage in both the LPA‐rich and UP‐rich phases result in the formation of microvoids, which partially compensates the resin shrinkage. The relative reaction rate in the two phases plays an important role in shrinkage control. In this study, secondary monomers [such as divinylbenzene (DVB) and trimethylopropane trimethacrylate (TMPTMA)] and a co‐promoter, 2,4‐pentandione (2,4‐P), were added into the UP/St/LPA resin systems to investigate their effect on the shrinkage control of resins cured at low temperatures. Dilatometery results showed that the addition of both TMPTMA and 2,4‐P resulted in an earlier volume expansion during curing and better shrinkage control. The phase separation, reaction kinetics, and viscosity changes in the LPA‐rich and UP‐rich phases during curing were also investigated. The results confirmed that the increased reaction rate in the LPA‐rich phase led to an earlier formation of microvoids and, consequently, less volume shrinkage of the cured resin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 738–749, 2001

Bonding properties of epoxy resin containing mesogenic group

A liquid crystalline epoxy resin with a mesogenic group was synthesized and its adhesive bonding properties are compared to that of the bisphenol-A type epoxy resin. The bonding strength of the former resin system was higher than that of the latter. This suggested that the high bonding strength of the liquid crystalline epoxy system was due to the large deformation of this system along the stress direction. Bonding strength of all the cured systems had a maximum peak during curing, due to the increase in the internal stress which occurred during the curing shrinkage of the epoxy resins. To decrease the internal stress, we cured the epoxy resin with an excess amount of curing agents. Bonding strength of the system with the added excess amount of curing agent showed a higher value than that for the system with an equivalent amount of curing agent. It was considered that the high bonding strength of the former system was due to the low internal stress in this system.

The effect of the addition of a low profile additive on the curing shrinkage of an unsaturated polyester resin

Composites made of glass fibers and unsaturated polyester resins are widely applied for various products. The failure processes of such composites are insufficiently understood. Fracture of the resin often initiates bulk composite fracture. Residual stresses occur during the curing of the resin due to the resin volumetric shrinkage. These unfavorable stresses may enhance resin fracture. Moreover, resin shrinkage may decrease the surface quality of the product. The addition of Low Profile Additives (LPA) to the resin may decrease or even remove these problems. The shrinkage behavior of unsaturated polyester resin with varying amounts of LPA is investigated in this work. The emphasis is on the development of curing shrinkage occurring after the gel point of the resin and on accompanying shirnkage stresses. These stresses can be reduced and even reversed by the addition of LPA.

Influence of hydrogen bonding on properties of BIS-GMA analogues.

The influence of chemical structure on the important properties of composite matrix resins is being systematically investigated. This study addresses the relationships between pendent side chain structures, viscosity and curing shrinkage. In particular, viscosity is known to be greatly influenced by intermolecular interactions, such as hydrogen bonding, and free volume effects. In order to establish the relative importance of these factors, analogues of BIS-GMA were synthesized in which the pendent hydroxyl groups were replaced by trimethyl siloxyl, and by dimethyl, isopropyl siloxyl groups. The viscosities were determined with a cone and plate viscometer and curing shrinkages were determined gravimetrically. They were compared to previously determined values for BIS-GMA and its methyl and hydrogen substituted analogues. The high viscosity of BIS-GMA is drastically reduced by replacement of the hydroxyl group, or its substitution by silylation. The relatively smaller effects produced by varying the bulk of the substituted side chains indicates that the main effect on viscosity is due to the presence or absence of hydrogen bonding. Conversely, increasing the bulk of the side chain substituent has less effect on viscosity, but significantly reduces the curing shrinkage. Changes in curing shrinkages were explained in terms of effects of free volumes associated with the monomers.

Assessment of residual stresses during cure and cooling of epoxy resins

AbstractA new stress monitoring technique, a stress‐tracking device, is described here. It has been used to study some important properties of epoxy resin. Residual stresses, including a curing shrinkage stress and a cooling shrinkage stress, were measured automatically and continuously during curing and cooling. Simultaneously, information such as an apparent gelation time and glass transition temperature were obtained directly during the experiment. These epoxy resin properties were related to the extent of cure. Varying cure temperature produced changes of cure behavior, which resulted in different residual stresses.

Curing shrinkage and volumetric changes of resin-modified glass ionomer restorative materials

Objectives. The objective of the study was to evaluate initial curing shrinkage and volumetric change during water storage of six resin-modified glass ionomer cements (Dyract, DeTrey Dentsply; Fuji II LC, GC Dental Int.; Ionosit Fil, DMG; VariGlass VLC, DeTrey Dentsply; Vitremer, 3M Dental Products; Photac-Fil, ESPE), a hybrid composite (blend-a-lux, Blendax) and a chemical-cured glass ionomer cement (ChemFil Superior, DeTrey Dentsply). Methods. The curing shrinkage was determined 5 min and 24 h after polymerization and mixing, respectively. Volumetric changes were examined after 14 d and 28 d water storage. Curing shrinkage and volumetric changes were evaluated using the hydrostatic principle. In addition, the total water content of the materials was measured after 28 d water storage. Results. Curing shrinkage of most of the resin-modified glass ionomers was greater than the hybrid composite and the chemical-cured glass ionomer cement. After a 28 d water storage, the resin-modified glass ionomers showed volumetric expansion and the chemical-cured glass ionomer showed volumetric loss. All of the examined glass ionomer materials had a higher total water content than the composite. Significance. The large curing shrinkage of the resin-modified glass ionomer materials measured in this in vitro study could affect the marginal integrity of glass ionomer restorations.

Matrix Cracking In Brittle-Matrix Composites with Tailored Interfaces

ABSTRACTMatrix cracking from controlled through cracks with bridging filaments was studied in a model unidirectional composite of SiC filaments in an epoxy-bonded alumina matrix. An unbonded, frictional interface was produced by moderating the curing shrinkage of the epoxy with the alumina filler and coating the filaments with a releasing agent. Uniaxial tension test specimens (2.5 × 25 × 125 mm) with filament-bridged through cracks were fabricated by a novel two-step casting technique involving casting, precracking and joining of cracked and uncracked sections. Distinct matrix-cracking stresses, corresponding to the extension of the filamentbridged cracks, were measured in uniaxial tension tests using a high-sensitivity extensometer. The crack-length dependence of the matrix-cracking stress was found to be in good agreement with the prediction of a fracture-mechanics analysis that employed a new crack-closure force - crack-opening displacement relation in the calculation of the stress intensity for fiber-bridged cracks. The prediction was based on independent experimental measurements of the matrix fracture toughness (Kcm), the interfacial sliding friction stress (τ) and the residual stress in the matrix (σmI). The matrix-cracking stress for crack lengths (2a) greater than 3 mm was independent of the crack length and agreed with the prediction of the steady-state theory of Budiansky, Hutchinson and Evans[2]. Tests on specimens without the deliberately introduced cracks indicated a matrix-cracking stress significantly higher than the steady-state stress.

Linear dimensional variability of three denture base resins after processing and in water storage

It has been shown that denture base resins shrink during curing and expand during storage in water. This investigation measured and compared linear dimensional changes of three denture base resins that occurred during processing and after storage in water for 30, 60, and 90 days. Triad, Accelar 20, and Lucitone 199 long and short-cured resins were studied, and it was found that Accelar 20 resin exhibited the least curing shrinkage and Lucitone 199 resin short-cured exhibited the most. However, no significant differences occurred between the groups. After 90 days of water storage, the only resin that exhibited a shrinkage from the processed state was Accelar 20. All of the expansion or shrinkage changes were so small that they were not statistically significant and should not be clinically detectable.

The mechanism for occurrence of internal stress during curing epoxide resins

AbstractThe mechanism for the occurrence of internal stress in the curing cycle of four‐functional epoxide resins was investigated in detail. The internal stress in this system was generated at the vitrification point in the course of curing, because the modulus of samples was rapidly increased at this point. After the vitrification point, the internal stress was increased with an increase of the shrinkage in the curing and cooling processes.Moreover, the magnitude of the internal stress in the four‐functional resin systems depended on the chemical structure of aromatic diamines used as curing agents. This was explained by the difference of curing shrinkage after vitrification in each system.

支台築造用コンポジットレジンの熱膨張係数，重合収縮率および辺縁封鎖性について

Linear coefficient of thermal expansion (LCTE), linear curing shrinkage (LCS), and marginal sealing of eight commercial core composite materials and one posterior composite resin were investigated in this study.Micro filler type core composite had a largest LCTE and submicron filler type core composite had smallest LCTE. Nevertheless, exception of micro filler type, there were no remarkable differences of LCTE in composite resins tested.Posterior composite resin had a largest LCS, following micro filler type core composite, and photo-cured type core composite had a smallest LCS.Significant inverse correlation existed between filler content and LCTE. No significant correlation observed between filler content and LCS. However, core composites containing a large amount of filler tended to reveal a small LCS.Micro filler type core composite, had a largest LCTE and LCS, demonstrated high degree of marginal leakage. Submicron filler or photo-cured type core composites, had small LCTE or LCS, revealed low degree of marginal leakage.

Significance of property mismatch in the patch repair of structural concrete Part 1: Properties of repair systems

Approximately £500 m is spent in the UK each year on the repair of concrete members. Despite the existence of this large and expanding market, little fundamental attention has been paid to the structural implications of property mismatch between patch repair materials and the substrate reinforced concrete. To pursue this question, it was necessary to identify the desirable characteristics of repair systems for satisfactory structural performance, and then to measure the relevant mechanical and physical properties of the various systems currently on the market. It was found that these repair systems could be conveniently categorized in nine generic types; a representative system from each was selected. Properties measured included strength, modulus, Poisson's ratio, coefficient of thermal expansion, tensile adhesion, early curing shrinkage, long-term creep and shrinkage. Where deemed appropriate, standard test methods have been utilized; otherwise techniques have been developed specifically for the purpose. These techniques, some of which now form the drafts of revisions to British Standards, are described. The range of property values determined are discussed in relation to patch repairs in typical reinforced concrete members and the desirable characteristics previously identified.

Physical and mechanical properties of the thermosetting resin for crown and bridge cured by micro-wave heating

A heating method using micro-waves was utilized to obtain strong thermosetting resin for crown and bridge. The physical and mechanical properties of the thermosetting resin were examined. The resin was cured in a shorter time by the micro-waves heating method than by the conventional heat curing method and the working time was reduced markedly. The base resins of the thermosetting resin for crown and bridge for the micro-waves heating method were 2 PA and diluent 3 G. A compounding volume of 30 wt% for diluent 3 G was considered good the results of compressive strength, bending strength and diametral tensile strength. Grams of 200-230 of the filler compounded to the base resins of 2 PA-3 G system provided optimal compressive strength, bending strength and diametral tensile strength. A filler gram of 230 provided optimal hardness and curing shrinkage rate, the coefficient of thermal expansion became smaller with the increase of the compounding volume of the filler. The trial thermosetting resin for crown and bridge formed by the micro-waves heating method was not inferior to the conventional resin by the heat curing method or the light curing method.

USE OF SYNTHETIC STONE IN BUILDING CONSERVATION

A report on tests carried out by the australian mineral development laboratories (amdel) on an epoxy resin based synthetic limestone (both mortar and pre-cast) used for repairs and replacement of stone at melbourne university. The advantages of this synthetic over the more traditional cement based synthetics include lower curing shrinkage and superior adhesion to substrates, lower, bulk density, and superior strength and durability. Its disadvantages include colour and dimensional instability and higher costs. Table references. -- ICCROM

Composite Restorative Resins

Physical and mechanical properties of 18 commercial light-activated composite resins were measured and the correlation between their properties was discussed. Hardness of the material, which was polymerized in accordance with the manufacturer's recommendation, increased considerably after exposure to light and reached approximately constant values after 24 hours. Hardness and elastic modulus were strongly dependent upon the filler fraction. On the other hand, there was no significant correlation between filler fraction and compressive strength. Most of the curing shrinkage was brought together at the bottom part of the cavity, as the light-activated composite resins polymerized from the surface exposed to light.The resistance to toothbrush abrasion increased according to the increase of inorganic filler content level.

Dimensional change of acrylic resin tray materials

Twelve commonly used acrylic resin tray materials were compared for linear curing shrinkage. Three of the 12 were found to expand slightly during the first few hours, which had the effect of reducing the net shrinkage. All trays, however, exhibited shrinkage during the 24-hour test period. Therefore, autopolymerizing acrylic resin tray materials should not be used for an impression the same day that they are made unless the tray is boiled as suggested by Pagniano et al. 5 This agrees with research already completed even though the magnitude of shrinkage was considerably less than that reported in previous studies.

Physical aging in particulate‐filled composites with an amorphous glassy matrix

AbstractPhysical aging was studied on particulate ‐filled glassy network polymers by means of mechanical ‐dilatational, differential scanning calorimetry (DSC) and density measurements on specimens that were aged at room temperature. The composites aged for 0.5 day fractured in a brittle manner at a constant ultimate stress, which is close to the tensile strength of the unfilled material, regardless of the filler content and the presence of a coupling agent. This type of mechanical behavior is caused by the compressive residual stresses that are present due to curing and differential thermal shrinkage. As aging takes place, the compressive residual stresses are relieved; as a result the ultimate tensile strengths of the composites decrease. The 120 ‐day ‐old untreated glass bead containing composites exhibited dilatation and yield in mechanical ‐dilatational testing. This type of behavior is described as “having no adhesion” between the filler and the matrix. The 120 ‐day ‐old composites with coupling agent ‐treated glass beads fractured at a tensile stress which is equal to 1/1.6 the tensile strength of the unfilled material. These materials did not exhibit dilatation and yield in mechanical ‐dilatational testing. Density and DSC data indicate densification and enthalpy relaxation upon again and support the hypothesis presented for the observed change in the mechanical ‐dilatational behavior.

Clinical Placement and Performance of Composite Resin Restorations

The most frequent complaints registered against composite restorations are stained margins and a rough surface. The stained margins have many causes such as (1) fracturing or crazing of enamel during preparation of the cavity, (2) using a composite having an excessive curing shrinkage, (3) manipulating too slowly, which permits a loss of plasticity during placement, (4) maintaining inadequate pressure during setting or curing of the composite, and (5) using finishing instruments which cause defects in the margin area of the tooth and/or composite. All of these the operator can control, and if not, the defect will be built into the restoration. The roughness of composites can be reduced by polishing with the finest grit available in disks and by coating with a glaze. Today's composite restorations placed with care will provide long lasting esthetic restorations providing they are not placed in areas subjected to load bearing abrasion.