PubMed · 10405468
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J C Budden. 1999-06-12. Amalgam bonding.. https://pubmed.ncbi.nlm.nih.gov/10405468/
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OBJECTIVES: The aim of this study was to investigate whether a desensitizing agent (GLUMA Desensitizer) containing glutaraldehyde and HEMA improved the bond strength and bonding durability of a self-etching primer adhesive to Er:YAG-irradiated dentine. METHOD: Dentine of 120 human molars was exposed by wet grinding on SiC paper for bond strength testing. Thirty specimens each were allocated to the following treatment groups: (1) control; (2) Er:YAG laser irradiation; (3) Er:YAG laser irradiation followed by application of GLUMA Desensitizer; (4) Er:YAG laser irradiation followed by application of GLUMA Desensitizer and 10s rinsing with water. Composite cylinders were bonded to the dentine surfaces with a self-etching priming adhesive system. Tensile bond strengths (TBS) of 10 specimens of each treatment group were measured after 24-h water storage, 6 months water storage and 12 months water storage, respectively, and the failure modes were analyzed. TBS data were statistically treated by two-way ANOVA and Fisher's PLSD test at a significance level of p<0.05. RESULTS: TBSs for the GLUMA-non rinse and GLUMA-rinse groups were significantly higher than for the laser group at 24 h and 12 months. Specimens from the Er:YAG-irradiated dentine group had significantly lower bond strengths than the control group at each storage time. All control specimens showed cohesive fractures in resin close to the bonding interface whereas the Er:YAG laser-irradiated groups showed both dentine cohesive, resin cohesive and dentine-resin mixed failures. CONCLUSION: Application of GLUMA Desensitizer to Er:YAG-irradiated dentine increases the bond strength and durability of the self-etching priming adhesive used.
It has been shown that an increase in the content of nonsilanated submicron colloidal silica filler particles within dental composites resulted in the release of more bis-phenol-A diglycidyl dimethacrylate (bisGMA)-derived product, bis-hydroxy-propoxyphenyl propane, following incubation with cholesterol esterase (CE). This work further investigates the enzyme-catalyzed biodegradation of fine composite resin systems, containing silanated micron-size irregular glass fillers, commonly used in clinical restorations. Model composite resin samples (10 or 60% weight fraction silanated barium glass filler, 1 mum average particle size) based on bisGMA/triethylene glycol dimethacrylate (TEGDMA) were incubated in buffer or buffer with CE (pH = 7.0, 37 degrees C) solutions for 32 days. The incubation solutions were analyzed using high-performance liquid chromatography, UV spectroscopy, and mass spectrometry. Both groups were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. In contrast with previous findings for nonsilanated submicron filler systems, the higher filler containing composite showed an increase in its stability with time, following exposure to esterase and when compared to the lower filler content material. As well, the 60% filler composite leached less unreacted monomer TEGDMA. Since the model composite resins studied here were identical and only the filler content varied, the differences in biostability could be specifically associated with the relative amount of resin/filler distribution. The clinical use of different materials in varied dental applications (ranging from fissure sealant to tooth-colored highly filled materials) must consider the potential for different degradation profiles to occur as a function of filler content.
OBJECTIVE: The main purpose of this study was (1) to investigate the effects of cyclic loading and environmental aging on three dental resin composites with different filler compositions: a fiber filler, a hybrid filler, and a microfill; and (2) to predict fracture in dental resin composite under mixed-mode loading conditions. METHODS: Diametral disk specimens 25 mm in diameter and 2 mm in thickness were used in this study. Two methods were used for generating initial cracks in the specimen. The first method involved machining a 3-mm notch in the center of the disk specimens, and then the notch tips were sharpened with a 0.2-mm-diameter jeweler's saw blade. In the second method for obtaining sharper crack tips, a three-way wedge was forced into a 3.175-mm hole drilled in the center of the specimen, resulting in sharp cracks emanating from the notch tips. CYCLIC TESTS: The specimens were aged for 4 months in air, water, artificial saliva, and a 50/50 (by volume) mixture of ethanol and water at room temperature in sealed polyethylene containers. Both unaged and aged specimens (5 specimens for each variable) were subjected to cyclic loading at a frequency of 5 Hz with sinusoidal loads cycling for 1, 1000, and 100,000 cycles at a load level approximately 60% of the fracture load for noncycled specimens. Following load cycling, the specimens were tested in compression in a displacement-controlled loading mode at a loading rate of 1.27 mm/min. RESULTS: Test results show that aging in a 50/50 alcohol-water mixture lowered the fracture toughness of dental resin composite, which was further reduced by cyclic loading. MIXED-MODE TESTS: The maximum tensile stress (MTS) criterion was used to predict fracture in dental resin composite under mixed-mode loading conditions. The loads at failure were used as input into a finite element model. After obtaining the stress field in the specimens by the finite element method, the mixed-mode stress intensity factors were calculated using an interaction energy integral method. RESULTS: Good agreement was obtained between the fracture envelope predicted by the MTS criterion and the experimental fracture toughness data. Hence, it can be concluded that it is only necessary to characterize the mode I fracture toughness to fully characterize the mixed-mode behavior of the dental resin composites that were considered in the present study.