Abstract
Composite resins may undergo wear by the action of chemical substances (e.g., saliva, alcohol, bacterial acids) of the oral environment, which may affect the material's structure and surface properties. This study evaluated the effect of acidic substances on the surface properties of a micro-hybrid composite resin (Filtek Z-250). Eighty specimens were prepared, and baseline hardness and surface roughness (KMN0 and Ra0, respectively) were measured. The specimens were subjected to sorption (SO) and solubility (SL) tests according to ISO 4049:2009, but using different storage solutions: deionized water; 75/25 vol% ethanol/water solution; lactic acid; propionic acid; and acetic acid. The acids were used in two concentrations: PA and 0.02 N. pH was measured for all solutions and final hardness (KMN1) and surface roughness (Ra1) were measured. Data were analyzed with paired t-tests and one-way ANOVA and Tukey's test (a=5%). All solutions decreased hardness and increased the Ra values, except for the specimens stored in water and 0.02 N lactic acid, which maintained the hardness. All solutions produced similar SO and SL phenomena, except for the 0.02 N lactic acid, which caused lower solubility than the other solutions. Ethanol showed the highest pH (6.6) and the 0.02 N lactic acid the lowest one (2.5). The solutions affected negatively the surface properties of the composite resin; in addition, an acidic pH did not seem to be a significant factor that intensifies the surface degradation phenomena.
Highlights
Dental composite resins had their properties and characteristics substantially improved since they were introduced in dentistry [1], leading to an excellent acceptance by the dentists who can use them for a variety of clinical procedures
Regarding the organic matrix, which is mostly formulated with dimethacrylate monomers such as 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropyl)phenyl]propane (Bis-GMA), triethyleneglycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA), it constitutes the body of the composite and may influence the handling ability and properties of the material; on the other hand, silica and glass fillers are commonly used to modify esthetic, physical and mechanical characteristics of composites [1]
With regard to these acidic substances, the lactic, propionic and acetic acids are commonly found in the oral environment and they are used as storage solutions for screening accelerated hydrolysis phenomena of composite resins [6] and increase of hygroscopic expansion of Bis-GMA-based materials
Summary
Dental composite resins had their properties and characteristics substantially improved since they were introduced in dentistry [1], leading to an excellent acceptance by the dentists who can use them for a variety of clinical procedures They are basically constituted by an organic matrix and inorganic fillers chemically connected by a silane substance. The biofilm accumulated over the restoration can produce acidic substances that may imply surface degradation, leading to the material’s softening and surface roughening [4,5] With regard to these acidic substances, the lactic, propionic and acetic acids are commonly found in the oral environment and they are used as storage solutions for screening accelerated hydrolysis phenomena of composite resins [6] and increase of hygroscopic expansion of Bis-GMA-based materials
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