Interfacial fracture toughness of universal adhesive systems treated with an antioxidant

Abstract

Background: Secondary caries, degradation of the dentin-resin interface and fracture of the restoration are the most common forms of failure. The aim of this study was to assess the interfacial fracture toughness of three different adhesive approaches and to compare their fracture toughness after surface treatment with antioxidant.

Material and methods: Seventy two dentin blocks with 3×4mm dimension and 3mm thickness were prepared and attached to precured 3×4×12mm composite blocks from both sides. Six adhesive groups (N=12), All-bond universal, Scotchbond universal and Clearfil SE bond with or without antioxidant treatment (Sodium Ascorbate 10% )were applied to dentin surfaces, a 160µ polyethylene paper formed the chevron in adhesive-dentin interfaces. Chevron-notched beam fracture toughness was measured following a modified ISO 24370 standard. The uniform composite-dentin-composite block was subjected to a 4-point test in universal machine. Data were analyzed by Kruskal-Wallis, Wilcoxon signed-rank and Mann-Whitney tests (α =0.05).

Results: Different adhesive approaches yielded different significant in fracture toughness rates. A significant increase of fracture toughness was observed between adhesive groups after antioxidant surface treatment. The difference in fracture toughness between Scotchbond universal and All-bond universal were significant.

Conclusions: The highest value of fracture toughness was reported for Clearfil SE bond and the lowest value was found for All-bond universal. Sodium ascorbate as antioxidant surface treatment had a significant effect in increasing the fracture toughness. Key words:Chevron-notched beam fracture toughness, fracture toughness, dentin, adhesive, antioxidant.

Figure 1

Specimen preparation: 1.cutting the third of the crown 2.preparation of dentin blocks 3×4×3 3.precured composite blocks 4.attached dentin to composite 5.fixing the chevron with polyetheln barrier 6.the uniform 3-part composite-dentin-composite. 7. 4-point test loading.

Figure 2

A. Overview of the fractured surface of a Clearfil SE Bond specimen. At the chevron tip, the specimen failed very close to the resin–dentin interface, while further away, fracture deviated into the adhesive resin and composite. A1. After antioxidant surface treatment at the chevron tip, failure occurred at resin dentin interface and the crack deviated toward the resin composite. B. Overview of the fractured surface of a ScotchbondUniversal specimen. At the chevron tip, the specimen fractured at the adhesive–dentin interface and the crack deviated toward the adhesive resin and composite at the end of the fracture surface. B1.With antioxidant treatment, the pattern of fracture changed and failure occurred at the resin–dentin interface. Although the flaw (tip of the chevron notch) was positioned at the interface, the crack deviated toward the resin composite. C. Overview of a fractured surface of an All-bond Universal specimen. The entire surface failed at the resin–dentin interface. C1. After antioxidant treatment, the initiation of crack was at the chevron tip located in the hybrid layer. Higher magnification of the chevron tip area showed the specimen failed at the interface exposing the hybrid layer, and some resin tags were observed at the tip of chevron, but it propagated almost completely along the resin–dentin interface.

Figure 3

All-bond Universal before and after antioxidant treatment: 1: see the shallow interaction of ultra-mild adhesive with dentin surface. 2: after antioxidant treatment, more resin tags were formed and the zone of interaction became wider.