Nanoleakage patterns of four dentin bonding systems

Abstract

Objectives: The purpose of this study was to evaluate the nanoleakage patterns of four dentin bonding systems.

Methods: The dentin bonding systems used in this study were: Single Bond, One Coat Bond, Prime & Bond NT/Non Rinse Conditioner (NRC), and PermaQuik. Flat occlusal dentin surfaces from extracted human molars were finished with wet 600-grit silicon carbide paper, and bonded with one of the dentin bonding systems. After 24 h storage at 37°C in water, margins were finished with polishing discs and the surrounding tooth surfaces coated with nail varnish. The samples were immersed in a 50% (w/v) solution of silver nitrate for 24 h, and exposed to photodeveloping solution for 8 h. The samples were cut longitudinally, polished, and mounted on stubs, carbon coated and observed in a Field Emission-SEM using backscattered electron mode.

Results: Different nanoleakage patterns were observed with the different adhesive systems. However, accumulations of silver particles were often noted at the base of the hybrid layer for all materials. Single Bond and One Coat Bond demonstrated uptake of silver particles both within the hybrid layer and the adhesive resin. Prime & Bond NT/NRC showed silver staining throughout almost the entire thickness of the hybrid layer. The leakage pattern of PermaQuik revealed loose silver deposition within the hybrid layer. The composition of each adhesive system may play a role in forming the different leakage patterns.

Significance: The current dentin bonding systems used in this study do not achieve perfect sealing at the restoration/dentin interface, which may influence the durability of the bond to dentin.

Introduction

The seal of a restorative material against the tooth structure, and the quality and durability of the seal, are major considerations for the longevity of restorations. This may influence the selection of restorative materials and can be a significant factor in preventing pulpal damage and secondary caries. Thus, the study of resistance to bacterial products and fluid penetration at the interface between the restoration and tooth structure, namely microleakage, has been of great concern in restorative dentistry. The term ‘microleakage’ may be defined as the passage of bacteria, fluids, molecules or ions between a cavity wall and the restorative material applied to it [1]. Consequently, it may result in discoloration [2], postoperative sensitivity, recurrent caries and pulp pathology [3], [4], [5].

The acid-etch technique proposed by Buonocore [6] has proved successful in enamel bonding and has effectively eliminated microleakage at the enamel/restoration interface [7], [8]. However, no satisfactory equivalent solution has been found for effectively inhibiting microleakage at dentin and cementum margins of cavities [9]. Dentin bonding is more challenging, since the dentine surface is a heterogeneous vital substrate with a low surface energy and outward dentinal fluid flow can occur onto the prepared surface [10]. Although gap-free margins at the dentin/restoration interface were achieved with some recent dentin bonding systems in which the ‘total-etch’ technique was applied [11], [12], [13], it was found by Fukushima et al. [14] cited by Sano et al. [15] that microleakage along the dentinal wall was still apparent even without gap formation between the filling and tooth structure.

Sano et al. [15], [16], [17] have described another pattern of leakage. By observing the penetration of silver nitrate along gap-free margins with several dentin bonding systems under scanning electron microscopy (SEM) or transmission electron microscopy (TEM), they described a leakage pattern occurring within the nanometer-sized spaces around the collagen fibrils within the hybrid layer, which they termed ‘nanoleakage’. It represents permeation laterally through the hybrid layer and may be the result of the incomplete infiltration of adhesive resin into the demineralized dentin [15]. This kind of leakage may allow the penetration of bacterial products and dentinal or oral fluid along the interface, which may result in hydrolytic breakdown of either the adhesive resin or collagen within the hybrid layer, thereby compromising the stability of the resin–dentin bond [18].

The development and marketing of new bonding agents continues to be rapid. The quality of the dentin bond was reported to be material dependent in certain situations [19] and associated with the chemistry of individual materials [20]. Although nanoleakage tests can provide much useful information on the sealing ability of restorations and the quality of the hybrid layer, current knowledge about this phenomenon is limited [15], [16], [17], [21]. Recently, a new group of dentin bonding systems has been developed, namely the ‘single-bottle’ systems. The original or conventional dentin bonding systems are applied in three consecutive steps: an etchant, to acid-etch the enamel and dentin surface; a primer, to wet the demineralized dentin and penetrate the exposed collagen network with resin; and an adhesive resin, to stabilize the hybrid layer and link the primer to the final composite [22]. In single-bottle systems, the primer and adhesive resin are combined into one bottle and achieve the functions previously accomplished by a separate primer and adhesive resin. However, the conditioning process remains unchanged [23].

The aim of this study was to determine whether differences occurred in the leakage patterns of four dentin bonding systems: Single Bond (3M Dental Products, St Paul, MN) and One Coat Bond (Coltène/Whaledent Inc., Altstätten, Switzerland), both single-bottle systems; Prime & Bond Nanotechnology/No Rinse Conditioner (NT/NRC) (Dentsply De Trey, Konstanz, Germany), a system combining a weak non-rinse etchant and a single-bottle adhesive; and PermaQuik (Ultradent, South Jordan, UT), a conventional three-step system.