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PubMed2003

In vitro characterization of two laboratory-processed resin composites.

PURPOSE: To compare various characteristics of two new-generation laboratory-processed resin composites (BelleGlass HP/SDS-Kerr and Sinfony/3M-ESPE). The properties evaluated were degree of C=C conversion, microhardness, roughness, biaxial flexural strength and polymerization shrinkage-strain. MATERIALS AND METHODS: All specimens were subjected to a first and a second polymerization cycle according to the manufacturers' instructions. The degree of C=C conversion (DC) was recorded on rectangular (3 x 2 x 0.5mm(3)) specimens (n=3) by FT-IR micromultiple internal reflectance spectroscopy immediately after each of the two polymerization cycles. Twenty cylindrical specimens (10 x 2mm(2)) of each material were prepared for surface microhardness (n=10, VHN, 200 g load, 20s) and surface roughness (n=10, Ra) measurements. The biaxial flexural strength and stiffness were determined on disk-shaped (n=8, 15 x 0.7 mm(2)) specimens loaded to fracture at 1 mm/min crosshead speed. The polymerization shrinkage-strain was calculated with the bonded-disk method. All values were statistically analyzed by Student's unpaired t-test (p<0.05). RESULTS: The second polymerization cycle significantly increased the degree of C=C conversion for both materials (p<0.05). BelleGlass HP exhibited significantly higher degree of C=C conversion, surface microhardness, surface roughness, biaxial flexural strength and stiffness values compared to Sinfony (p<0.05). SIGNIFICANCE: Several differences exist between the materials although both products are recommended for the same clinical applications.

Composite Resins↗

PubMed2003

Irradiance effects on the mechanical properties of universal hybrid and flowable hybrid resin composites.

OBJECTIVES: A potential problem with high-intensity lights might be failure of polymer chains to grow and cross-link in a desired fashion, thereby affecting the structure and properties of the polymers formed. The purpose of this study was to evaluate mechanical properties of resin composites polymerized using four different light-curing units. METHODS: A conventional quartz-tungsten-halogen (QTH) light, a soft-start light, an argon-ion laser, and a plasma-arc curing light were used to polymerize disk-shaped (9.0mm diameter x 1.0 mm high) and cylinder-shaped (4mm diameter x 8 mm high) specimens of a universal hybrid and a flowable hybrid composite. Biaxial flexure strength, fracture toughness, hardness, compressive strength, and diametral tensile strength were determined for each composite. RESULTS: The use of the plasma-arc curing light, a high-intensity light, resulted in significantly lower hardness for the universal hybrid composite compared with the hardness obtained using the conventional QTH and the soft-start units. Hardness was the only mechanical property that was adversely affected by the use of a high-intensity light. SIGNIFICANCE: High-intensity lights might affect some resin composite mechanical properties, but this effect cannot be generalized to all resin composites and all properties.

Composite Resins↗

PubMed2003

Aspects of water sorption from the air, water and artificial saliva in resin composite restorative materials.

OBJECTIVE: Primarily to establish whether artificial saliva (AS) at 37 degrees C is essential as a clinically relevant environment for testing filled, resin composite restorative materials. The effect of other storage conditions was also investigated for comparison and controls: desiccation, exposure to the laboratory atmosphere, high humidity cabinet, saturated water vapor, and deionized water. METHODS: Two visible light-cured products were used: Heliomolar Radiopaque (HR) and Tetric Ceram (TC) (Ivoclar, Schaan, Liechtenstein). Bar specimens (26 x 1.5 x 1.0 mm(3)) were cured at five overlapping spots for 60s per spot and randomly distributed into groups of six. Trial 1: one group of each material was exposed first to atmospheric air at 24 degrees C, approximately 50% RH (24WV(50)), then to water vapor at 37 degrees C, approximately 97% RH (37WV(97)), and then immersed in deionized water at 37 degrees C (37DW). Trial 2 used three groups of each material, one first exposed to 37WV(97) followed by 37DW, the other two were immediately immersed in 37DW or artificial saliva (37AS). Trial 3: two groups of each material were vacuum desiccated at 37 degrees C, then exposed to 37 degrees C, approximately 100% RH (37WV(100)), then immersed in 37DW or 37AS. Trial 4: four groups of HR were treated similarly to Trial 3; one was left under desiccation, and another in 37WV(100) for the remaining period. Three-point bend tests for flexural strength (F), flexural modulus (E), and total energy to failure (W) were performed at the end of Trials 2-4. RESULTS: Environmental moisture absorption was substantial at 24WV(50)(c. 0.2%), at least 40% of that in 37DW (HR: c. 0.7%, TC: c. 0.5%). Saturation was achievable in 37WV(100). Mass loss on desiccation (HR: c. 0.4-0.5%, TC: c. 0.25%) was reversible in 37WV(100). There were some significant effects of exposure conditions on mechanical properties (e.g. F for HR: after desiccation, 85.7+/-1.4MPa; after 37WV(100), 73.2+/-3.6MPa; difference: p<0.0002), but overall the results were unclear. After a rapid gain in mass, there was a gradual loss in both 37DW and 37AS for both materials, slightly more in 37AS than 37DW. SIGNIFICANCE: Water vapor absorption is substantial, hence attention must be paid to the laboratory working environment and conditions of storage and testing, i.e. temperature and RH must be stated to assist interpretation of data and comparisons between studies. Test conditions need to be standardized and with reference to normal oral conditions, immediate immersion in artificial saliva at 37 degrees C is the preferred treatment for these materials, whatever time of testing is chosen.

Absorption↗

PubMed2003

Flexural fatigue behavior of resin composite dental restoratives.

OBJECTIVE: The aim of this study was to evaluate the mechanical properties of resin composite dental restoratives under quasi-static and cyclic loading. METHODS: Four-point-bending bars of 10 different resin composite materials were manufactured according to ISO standard and stored for two weeks in distilled water. The fracture strength (FS) was measured with the four-point-bending test in an universal testing machine. The flexural fatigue limits (FFL) for 10(5) cycles were determined under equivalent loading. All specimens were tested and fatigued in water at 37 degrees C. The data were analyzed using ANOVA, Weibull statistics of FS and the 'staircase' approach of FFL. Fractographic analysis was performed using SEM. RESULTS: The initial flexural strength values for the resin composite materials varied from 55.4 MPa for Solitaire up to 105.2 MPa for Filtek Z250. The mean flexural fatigue limit for 10(5) cycles ranged between 37 and 67% of the initial strength. SEM analysis of the fractured surfaces suggests two kinds of failure mechanisms for initial and fatigue fracture. SIGNIFICANCE: The fatigue behavior of resin composite materials does not correlate with initial strength values. Materials providing high initial strengths do not obviously reveal the best fatigue resistance. Flexural fatigue measurement of resin composite materials should be viewed as a useful tool to evaluate long term mechanical properties.

Analysis of Variance↗

PubMed2003

Continuous-fiber preform reinforcement of dental resin composite restorations.

OBJECTIVES: Direct-filling resin composites are used in relatively small restorations and are not recommended for large restorations with severe occlusal-stresses. The aim of this study was to reinforce composites with fiber preforms, and to investigate the effects of layer thickness and configurations on composite properties. It was hypothesized that fiber preforms would significantly increase the composite's flexural strength, work-of-fracture (toughness) and elastic modulus. METHODS: Glass fibers were silanized, impregnated with a resin, cured, and cut to form inserts for tooth cavity restorations. Also fabricated were three groups of specimens of 2mm x 2mm x 25 mm: a fiber preform rod in the center of a hybrid composite; a thin fiber layer on the tensile side of the specimens; and a thin fiber layer sandwiched in between layers of a hybrid composite. These specimens were tested in three-point flexure to measure strength, work-of-fracture and modulus. Optical and scanning electron microscopy were used to examine the restorations and the fiber distributions. RESULTS: Microscopic examinations of insert-filled tooth cavities showed that the fibers were relatively uniform in distribution within the preform, and the inserts were well bonded with the surrounding hybrid composite. Specimens consisting of a fiber preform rod in the center of a hybrid composite had a flexural strength (mean (SD); n=6) of 313 (19)MPa, significantly higher than 120 (16)MPa of the hybrid composite without fibers (Tukey's at family confidence of 0.95). The work-of-fracture was increased by nearly seven times, and the modulus was doubled, due to fiber preform reinforcement. Similar improvements were obtained for the other two groups of specimens. SIGNIFICANCE: Substantial improvements in flexural strength, toughness and stiffness were achieved for dental resin composites reinforced with fiber preforms. The method of embedding a fiber preform insert imparts superior reinforcement to restorations and should improve the performance of direct-filling resin composites in large restorations with high occlusal-loads.

Composite Resins↗

PubMed2003

Polymerization contraction stress in light-cured compomer restorative materials.

OBJECTIVE: The magnitude and kinetics of polymerization contraction stress build-up may be potential predictors of bond failure of adhesive restorations. The present study determined these properties of seven commercial compomers (Dyract, Dyract AP, F2000 Rasant, Hytac, Compoglass F, Luxat, Glasiosite). METHODS: Polymerization shrinkage was generated by 40 s light curing the test materials (800 mW/cm2). The contraction force induced was recorded for 300 s at room temperature (23-24 degrees C) by means of a Stress-Strain-Analyzer (C factor=0.33). Maximum contraction stress (MPa), coefficient of near linear fit of contraction force/time (gradient) and relative force rate (%/s) of each material were compared with that of two hybrid composites (Tetric Ceram, Prodigy). The statistical analysis was conducted by ANOVA (alpha=0.05) and post hoc Tukey's test. RESULTS: No statistically significant differences in the maximum stress between Glasiosite (2.27+/-0.06 MPa), Hytac (2.31+/-0.07 MPa) and Tetric Ceram (2.21+/-0.11 MPa), and between Compoglass F (2.60+/-0.18 MPa) and Prodigy (2.70+/-0.06 MPa) were found. The contraction stress of F2000 Rasant (3.41+/-0.09 MPa) and Luxat (3.33+/-0.08 MPa) were significantly highest, whilst Dyract exhibited the significantly lowest shrinkage stress (1.27+/-0.08 MPa) among the tested materials. SIGNIFICANCE: High contraction stress, early start of stress build-up and rapid contraction force development may lead to failure of bond to tooth structure. This study suggested that the contraction stress and kinetic behavior of compomers are generally similar to those of hybrid composites in a dry condition. Dyract might be superior in maintaining the bond with cavity walls compared to conventional hybrid composites in view of its low shrinkage stress.

Analysis of Variance↗

PubMed2003

The effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation.

OBJECTIVE: The objective of this study is to evaluate the effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation. METHODS: Strain gages were bonded to maxillary premolars. The rigidity was tested by applying a load to a sequence of sound, prepared and restored teeth as follows: sound tooth, MOD preparation, amalgam restoration, amalgam removed recovering the MOD preparation, bonded amalgam restoration, bonded amalgam removed recovering the MOD preparation, bonded composite restoration. The relative stiffness (RS) and relative deformation (RD) of each condition for each cusp to that of the sound tooth was determined. RESULTS: The premolar cusps were deformed 1.80, 2.14, and 2.32 times more than the cusps of the sound tooth for the three succeeding MOD preparations. For these three preparations, the stiffness of the premolar cusps was 0.58, 0.48, and 0.46 relative to a stiffness of 1.00 for the sound tooth. The deformation was 1.77, 1.27, and 1.16 for the non-bonded amalgam, the bonded amalgam, and the bonded composite, respectively, corresponding to a mean RS of 0.59, 0.80, and 0.88. The calculated mean stiffness parameter C (standard deviation) was 2.6% (6.9) for the amalgam restoration, 62.5% (12.8) for the bonded amalgam restoration, and 77.8% (15.8) for the bonded composite restoration. The stiffness parameter C measured the extent to which the procedure returned the stiffness of the restored tooth to the original stiffness of the intact tooth (100%). SIGNIFICANCE: Cavity preparation reduced the stiffness and weakened the tooth. Restoring the prepared tooth with unbonded amalgam did not restore the lost tooth stiffness. Restoring the prepared tooth with bonded amalgam or with bonded composite recovered a significant portion of the lost tooth stiffness. It was concluded that bonding amalgam to tooth structure could partly restore the strength and rigidity lost by the cavity preparation. This might lead to a reduction in cuspal flexure and the incidence of tooth fracture due to fatigue.

Analysis of Variance↗

PubMed2004

Marginal and flexural integrity of three classes of luting cement, with early finishing and water storage.

OBJECTIVES: The aims of this investigation were to clarify the effects of finishing-time and 24 h water-storage on mechanical properties and marginal adaptation to dentin of seven modern luting cements, representing three chemical types. METHODS: Bistite II, Chemiace II, Compolute, XenoCem, PermaCem, Fuji Cem and Fuji Plus were investigated with specimen sub-groups (N=10) for each property measured. The principal series of experiments was conducted in dentin cavities with interfacial polishing either immediately (3 min) after setting or after 24 h water-storage. After the finishing procedure, the maximum marginal gap width and the opposing width (if any) per cavity were measured microscopically, and summed. Then the overall sum of gap-widths (per group; N=10) was calculated. Marginal gaps were similarly measured in Teflon cavities, together with shear-bond-strengths to dentin and early flexural strengths, moduli and swelling data. RESULTS: For specimen-sets polished immediately after setting, summed marginal gaps of 23-121 microm were observed, for all luting cements except Compolute. A significantly different (p<0.05) result of either no gap or 6-28 microm summed gap-widths occurred in specimens polished after 24 h. For all materials, their shear-bond-strengths, flexural strength and moduli significantly increased after 24 h storage. SIGNIFICANCE: The marginal behavior can be interpreted in terms of the contributions of bonding, shrinkage, swelling and compliance of components, along with compositional features of the cements. With these types of cement it is generally inadvisable to polish the interfacial luting surface immediately after cementing. The polishing procedures should be carried out not less than 24 h later. One resin-cement was able to withstand immediate finishing.

Bicuspid↗

PubMed2004

Polymerization shrinkage: effects of constraint and filling technique in composite restorations.

OBJECTIVES: To evaluate the linear polymerization shrinkage (LPS) and its effect upon mean gap width, bond strength and cohesive strength of a composite placed under different constraints (C-factors--CF) and filling techniques. METHODS: Composite was placed in cavities sized 4 x 4 x 2 mm3 (CF = 3) or on flat dentin surfaces (CF = 0.3) of bovine incisors, after adhesive application. They were inserted in one or three increments, and light cured (600 mW/cm2) for 80 s. The LPS was measured by placing a probe on the top surface of the composite in order to measure its dislodgment in the top-bottom direction. Half of the sample was sectioned to obtain composite resin sticks subjecting them to tensile forces at 0.5 mm/min. The other half of the sample was sectioned and the mean gap width was measured in both sides of the sections. Then the sections were sliced again to obtain composite/dentin sticks. The mean gap width in the sticks was performed before subjecting them to tensile forces at 0.5 mm/min. Data was analyzed by a two-way ANOVA and the correlation between the bond strength and gap width was analyzed by simple linear regression. RESULTS: (1) Linear polymerization shrinkage: significant differences were observed for the interaction (p < 0.05). Under the low constraint, the LPS were similar for both filling techniques. Under higher constraint, polymerization shrinkage was lower for the incremental technique. (2) Gap width and bond strength: no difference was detected either for interaction, or for technique (p > 0.05). Under higher constraint, the gap width was higher and the bond strength lower. (3) The cohesive strength of composite resin was similar for all groups (p > 0.05). No correlation between bond strength and gap width was found (p = 0.17). SIGNIFICANCE: The effects of polymerization shrinkage were not reduced by the filling technique under the different cavity constraints tested.

Analysis of Variance↗

PubMed1990

Measurement and analysis of clinical abrasion--a modified approach.

The abrasion of three posterior composites, after three years' clinical service, was measured by use of a calibrated stone step-wedge. The enamel exposure by each cusp was measured, so that the maximum and overall abrasion could be calculated. The results indicated uneven abrasion around the margin, signifying that local factors, acting by each cusp, had a significant effect on abrasion. This differs from the behavior of the earlier composites, where there was uniform abrasion around the margins. The overall abrasion had a nonparametric distribution, and frequency distribution diagrams proved to be the best way of comparing the performances of the individual materials.

Composite Resins↗

PubMed1987