Thermocycling effect on mechanical and tribological characterization of two indirect dental restorative materials

Abstract

The purpose of this study is to evaluate the effects of aging by thermocycling on the mechanical and tribological properties of two indirect filling commercial resin-based restorative composite materials. The studied composites are referenced by the capital letters: A and B. The commercial trade names are omitted, to avoid commercial references. Forty specimens of each material were produced and divided into three groups: a control group not subjected to aging, and two groups, T 1 and T 2 submitted to different thermocycling conditions. The studied properties were surface roughness, elastic modulus (determined dynamically by impulse excitation of vibration, and statically by four-point bending test), flexural strength and work of fracture (four-point bending test), micro-hardness (Vickers micro-indentation) and coefficient of friction (scratch test). From this study, it was possible to conclude that Composite A, in addition to having better mechanical properties, is less affected by thermocycling than Composite B, which suggests that it will better withstand the stresses, both mechanical and thermal, which it is subjected to. It is also possible to infer that the thermocycling regimen proposed by Standard ISO 11405 (Dental materialstesting of adhesion to tooth structure, 2003) is not sufficient to adequately simulate the degradation caused by the oral Technical Editor: Estevam Las Casas.

Effect of Simplified Bonding on Shear Bond Strength between Ceramic Brackets and Dental Zirconia

“…The surface was observed before and after the sandblasting on three samples, each under a confocal laser scanning microscope (CLSM; LSM 800-MAT, Carl Zeiss MicroImaging GmbH, Jena, Germany). The roughness parameters evaluated were average surface roughness ( R a ), root mean square roughness ( R q ), roughness depth ( R z ) and roughness skewness ( R sk ) [23].…”

Mechanical and Tribological Characterization of a Dental Ceromer

“…The coefficient of friction increased after thermocycling, and a variation of the frictional force between the test group and the control group was identified. This has been observed in materials that have hard reinforcing particles [6] and therefore resist the advancement of the indenter, causing a decrease in their roughness. The larger the size of the reinforcing particles, the higher the coefficient of friction and consequently the higher the contact forces, which can increase the volume of material removed by wear [6].…”

“…The maximum roughness parameter (Rmax) provides data on the deterioration of the vertical surface of the specimens. Thus, its increase is associated with an increase in peaks and roughness on the surface of the restoring material [6]. The total roughness depth parameter (Rt) measures the distance between the highest peak and the deepest valley, within the total evaluation length, which also supports a significant increase in Rmax.…”

“…The degradation that takes place in the restorations, whether these are composite resins or composite resins reinforced with ceramic particles, is because, when in contact with water (and, in the case of the oral cavity, with saliva), the diffusion of water molecules occurs in the polymer matrix, which degrades the siloxane bonds, compromising the physical and mechanical properties of the material. This produces a decrease in the hardness and modulus of elasticity of the restorations over time [6,28].…”

“…Both teeth and restorative materials are subject to oral cavity conditions such as humidity, load cycles, temperature variation, bacteria, external agents and contact geometry [5], which makes it challenging to find a material that can withstand the mechanical, thermal and chemical stresses [6] without damaging the structures of the oral cavity while maintaining high longevity. The degradation and erosion of resin composites occur more easily when incomplete polymerizated and/or when the teeth isolation during treatments is not achieved, due to degradation processes caused by oxidation [7].…”