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Keywords:

thermo-cycling, adhesion, dental adhesive, enamel, dentin, bond strength, 4-year water degradation, self-etching primer, resin, restorations, system, configuration, storage, 2-step, vivo, sem, Science & Technology, Life Sciences & Biomedicine, Technology, Dentistry, Oral Surgery & Medicine, Materials Science, Biomaterials, Materials Science, 4-YEAR WATER DEGRADATION, SELF-ETCHING PRIMER, RESIN, RESTORATIONS, SYSTEM, CONFIGURATION, STORAGE, 2-STEP, VIVO, SEM, Analysis of Variance, Composite Resins, Dental Bonding, Dental Cavity Preparation, Dental Stress Analysis, Dentin, Dentin-Bonding Agents, Humans, Hydrolysis, Materials Testing, Phase Transition, Random Allocation, Resin Cements, Silicon Dioxide, Statistics, Nonparametric, Tensile Strength, Zirconium, 09 Engineering, 11 Medical and Health Sciences, Dentistry, 3203 Dentistry

Abstract:

A widely used artificial aging methodology is thermo-cycling. The ISO TR 11450 standard (1994) recommends 500 cycles in water between 5 and 55 degrees C. Recent literature revealed that more cycles are needed to mimic long-term bonding effectiveness. Furthermore, the artificial aging effect induced by thermo-cycling is not clearly established. Two underlying mechanisms can be advanced: (1) hot water may accelerate hydrolysis and elution of interface components and (2) repetitive contraction/expansion stress can be generated. OBJECTIVES: The purpose of this study was to evaluate the relative contribution of both chemical (hydrolysis and elution of interface components) and mechanical (repetitive contraction/expansion stress) degradation pathways on the thermo-cycling-induced artificial aging of dentin-adhesive interfaces at the bottom of class-I cavities. METHODS: The micro-tensile bond strength (muTBS) of contemporary adhesives (a three-step etch and rinse, a two-step and a one-step self-etch adhesive) bonded to class-I cavity-bottom dentin was determined after 20,000 cycles as well as after 20 days of water storage (control). Restored class-I cavities (repetitive contraction/expansion stress) as well as prepared micro-specimens (diffusion-dependent hydrolysis and elution) were subjected to the thermo-cycling regimen. RESULTS: Thermo-cycling did not enhance chemical or mechanical degradation of the bonds produced by a two-step self-etch and a three-step etch and rinse adhesive to dentin. The one-step self-etch adhesive tested was, however, not able to withstand polymerization shrinkage stress, nor thermo-cycling, when applied in class-I cavities. SIGNIFICANCE: Thermo-cycling results in combined contraction/expansion stress and accelerated chemical degradation. However, the relative contribution of each is strongly dependent on the specific test set-up and the adhesive used.