Degradation and Failure Phenomena at the Dentin Bonding Interface

Abstract

Damage in the bonding interface is a significant factor that leads to premature failure of dental bonded restorations. The imperfectly bonded dentin-adhesive interface is susceptible to hydrolytic degradation and bacterial and enzyme attack, severely jeopardizing restorations' longevity. Developing caries around previously made restorations, also called "recurrent or secondary caries," is a significant health problem. The replacement of restorations is the most prevailing treatment in dental clinics, leading to the so-called "tooth death spiral". In other words, every time a restoration is replaced, more tooth tissue is removed, increasing the size of the restorations until the tooth is eventually lost. This process leads to high financial costs and detriment to patients' quality of life. Since the complexity of the oral cavity makes prevention a challenging task, novel strategies in Dental Materials and Operative fields are required. This article briefly overviews the physiological dentin substrate, features of dentin bonding, challenges and clinical relevance. We discussed the anatomy of the dental bonding interface, aspects of the degradation at the resin-dentin interface, extrinsic and intrinsic factors affecting dental bonding longevity, perspectives on resin and collagen degradation and how these subjects are connected. In this narrative review, we also outlined the recent progress in overcoming dental bonding challenges through bioinspiration, nanotechnology and advanced techniques to reduce degradation and improve dental bonding longevity.

Keywords: collagen degrading enzymes; dental etching; dental restoration failure; smear layer.

Figure 1

A schematic illustration to show a defective bonded restoration (right). The image displays a restored tooth’s main components and illustrates secondary caries around the restoration. The blue line represents the bonding interface composite/tooth. At a greater zoom (left), the typical components of the dentin bonding interface are described.

Figure 2

Classification of dental adhesive systems based on their interaction with dentin substrate according to Van Meerbeek et al. (Top) The etch & rinse adhesives require the etching step. The primer and adhesive can be presented in separate bottles (3 steps) or combined in one bottle (2 steps). (Middle) The self-etch adhesives do not require the etching step with phosphoric acid since the acidic functional monomers present in the composition of these adhesives will treat the smear layer and provide micro-surface retention. The etching efficacy of functional monomers is commonly determined in terms of pH. The right column represents the acidity of the adhesives. The colors from yellow to red indicate a range of pH acidic solutions. Darker colors represent lower pH in the range of 1–3. (Bottom) Universal adhesives, the latest development in the field. This class of adhesives can be used as self-etch, etch-and-rinse or enamel selective-etch. The universal adhesives contain monomer blends of mild to moderate acidity. Note that greater acidity may contribute to the degradation process of the denting bonding interface.

Figure 3

A summary of influencing factors on the degradation at the resin-dentin interface.

Figure 4

Schematic drawing illustrates the influencing factors contributing most to resin and collagen degradation phenomena.