SEM evaluation of resin-carious dentin interfaces formed by two dentin adhesive systems

Abstract

Objectives-We investigated the influence of dentin tubule direction and identifiable zone of carious dentin on the microstructure and the thickness of the hybrid-like layer (HL) formed by selfetch and etch-rinse adhesive systems.Methods-An etch-rinse and a self-etching adhesive were bonded to dentin carious zones divided into groups with parallel or perpendicular orientation relative to the dentin tubules at the resin-carious dentin interface (N = 5/variable). Bonds were prepared to each of the four zones of carious dentin apparent after staining with Caries Detector: pink, light pink, transparent and apparently normal Six non-carious third molars were controls. The microstructure and thickness of the HL were determined by SEM.and compared using three-way ANOVA and Tukey's multiple comparisons (p<0.05).Results-Etch-rinse controls gave thicker HLs than self-etching systems; ; orientation did not affect thickness for the self-etch system. Perpendicular orientations gave thicker HLs than parallel for the pink zone bonded with the etch-rinse system. For both adhesives, HL thickness in the pink zone were significantly greater than in light pink for the perpendicular group, but no significant differences were found among other variables. HL microstructure was more granular and rougher for the etch rinse than for the self etching system. Pores and cracks were obvious in the more demineralized zones, Resin tags were shorter and irregular in the transparent zone and often were completely absent in the outer demineralized zones (pink, light pink).Significance-Microstructure of bonded interfaces varies markedly depending on adhesive system, tubule orientation and carious zone.

Molecular and Structural Evaluation of Dentin Caries-Like Lesions Produced by Different Artificial Models

“…However, this method cannot simulate all factors involved in the natural process, such as biofilm, saliva and collagen degradation. In addition, caries-like lesions produced by pH-cycling showed similarity with the natural ones concerning only hardness (13) and morphology (7,11).…”

“…These approaches used acidic gels (7), buffered solutions (10) and microbiological models (7). Some studies (5,11) used them as a useful parameter for the assessment and comparison of de-or remineralization mechanism and obtaining information of these two correlated processes during caries lesion formation, mineral loss and caries progression (5,11).…”

Dentin as a bonding substrate

“…Bond strengths tend to be even lower when bonding to caries-infected dentin (133,134). Caries-affected and caries-infected dentin are more porous (31,135), contain significantly more water (136), and the hybrid layers tend to be much thicker, but not necessarily well-infiltrated in caries-altered dentin, irrespective of the bonding strategy (131,137,138).…”

Contemporary research findings on dentine remineralization

“…Dentine bonding is a unique form of tissue engineering in which a demineralized collagen matrix continuous with the underlying mineralized dentine is created via acid‐etching or acidic self‐etching adhesives, and this is used as the scaffold for resin infiltration (Tay and Pashley, ). The most compelling problem associated with resin–dentine bonds is their limited durability (De Munck et al , ), which is the result of several factors, including: water sorption‐induced hydrolysis of the hydrophilic resin components present in the adhesives (Ito et al , ); degeneration of collagen fibrils via endogenous matrix metalloproteinases (MMPs) derived from the demineralized dentine (Pashley et al , ); and the presence of acid‐resistant mineral deposits, which are composed of whitlockite in tubule lumens of caries‐affected dentine that restrict the penetration of bonding agents (Arrais et al , ; Doi et al , ; Erhardt et al , ; Hsu et al , ; Marshall et al , ; Nakajima et al , ; Yoshiyama et al , , ; Zavgorodniy et al , ). Remineralization of the exposed collagen in the incompletely infiltrated areas in the hybrid layer can effectively improve bonding durability.…”