Abstract
Roughness and hardness are among the most important variables in the wear (resistance) performance of dental resin composites. In this study, silica nanoparticles and nanoclusters of silica and silica-zirconia nanoparticles were evaluated for use as reinforcement agents in dental resin composites. Nanoclusters with spherical morphology were obtained from aqueous dispersions of nanoparticles by spray drying. Roughness was measured through atomic force microscopy (AFM) while nanohardness was evaluated by nanoindentation. The roughness values obtained with silica nanoparticles were lower (22.6 ± 6.6 nm) than those obtained with silica and silica-zirconia nanoclusters (138.1 ± 36.6 nm, 116.2 ± 32.2 nm, resp.), while the hardness values of all composites were similar (nanoparticles = 0.24 ± 0.01 GPa, silica nanoclusters = 0.25 ± 0.04 GPa, and silica-zirconia nanoclusters = 0.22 ± 0.02 GPa). Based on this study, it can be established that particle size is a determining factor in the roughness of the final material, while the key variable for nanohardness was the concentration of the reinforcement materials.
Highlights
Composite dental materials are widely used to repair anterior and posterior teeth due to their ability to replicate natural dental structure, workability, mechanical properties, and clinical performance [1,2,3]
E monomers were bisphenol A glycidyl methacrylate (Bis-GMA) (90%), bisphenol A polyethylene glycol diether dimethacrylate (Bis-EMA) (90%), urethane dimethylacrylate (UDMA) (90%), and triethylene glycol dimethacrylate (TEGDMA) (90%). ese were acquired from Esstech (USA)
The lack of chemical bond between the nanoparticles could be modified by submitting the aggregates to sintering with temperature, obtaining a higher level of cross-linking of the particles, leading to an increase in the bond strength and higher rigidity [43]. e above may explain why the results found in this study with nanoclusters are different to those reported for Filtek Supreme Body and Filtek Supreme Translucent resins (3M) [5, 20], where the aggregates were subjected to a sinterization process that caused a chemical bond of the individual particles [20], allowing lower roughness values to be obtained, as well as improved surface property values such as gloss and wear resistance [5, 6, 20, 24, 44]
Summary
Composite dental materials are widely used to repair anterior and posterior teeth due to their ability to replicate natural dental structure, workability, mechanical properties, and clinical performance [1,2,3]. Wear resistance is an important property in the performance of dental composites because lack of wear resistance will produce an excessive reduction in structure, resulting in the loss of posterior tooth support, vertical dimension of occlusion, masticatory efficiency and esthetics, as well as alterations in the functional path of masticatory movement, fatigue of masticatory muscles, and faulty tooth relationship [4]. Finer particles for a fixed-volume-fraction have been shown to result in decreased interparticle spacing and thereby reduced wear of dental composites [12]. Wear resistance tends to increase with increasing hardness, but quantitative relationships between wear resistance and hardness have not been established, with some studies finding a direct correlation and others not [4]. is may be due to the fact that hardness is an intrinsic property of the material, which depends only on composition and microstructure, while abrasion resistance is not an intrinsic property, since it may depend
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