Strategies to stabilise dentine-bonded interfaces through remineralising operative approaches – State of The Art

Dental adhesive systems have improved considerably over the last ten years, although shortcomings such as post-operative sensitivity, premature reductions in bond strength, interface and marginal degradation, and biocompatibility are still considered important issues with such materials. Enzymatic degradation of collagen fibrils within the hybrid layer and hydrolysis of polymers are the major factors thought to destabilise the resin-dentine interface. However, “smart” resin-based materials that can interact therapeutically with dental hard tissues and reduce the degradation of the resin-dentine interface via remineralisation of the mineral-depleted dental hard tissues can improve the durability of resin-dentine bonds. Moreover, as the resin-dentine interfaces produced by contemporary adhesives are characterised by low mechanical properties, therapeutic remineralising bonding approaches may also contribute to strengthening of hybrid layers, producing more gradual gradients of stiffness that prevents localised stress concentrations. This review attempted to bring together a number of seemingly unrelated events, to show how they may contribute to improvements in the durability of resin-dentine bonds. Innovative new approaches to remineralise the resin-dentine interface may protect hybrid layers from different types of degradations over time, and have a therapeutic role in caries prevention. Recent investigations have revealed that the air-abrasion technique performed with bioactive glass 45S5 (BAG) is capable of creating a therapeutic bioactive smear-layer-covered surface for bonding procedures. BAG can react with body fluids, evoking hydroxyapatite (HAP) precipitation and remineralisation of dentine at the bonded interface, especially when used in combination with fluoride-releasing materials such as glass ionomer cements (GIC) and resin-modified glass ionomer cements (RMGIC). The remineralising potential of these therapeutic approaches is potentiated in the presence of a calcium-sequestering agent such as poly(acrylic acid). However, GIC-based materials as well as calcium silicate cements are not able to restore the mechanical properties of dentine. Thus, experimental adhesive systems containing (30–50 wt%) ion-releasing fillers with advanced remineralising properties and matrix metallo-proteinases (MMP) inhibitors have been developed and used in combination with resin primers containing Ca-sequestering polyanion acids such as poly(aspartic acid) (PASA) or poly(acrylic acid) (PAA) and biomimetic analogues of collagen phosphoproteins such as sodium trimetaphosphate to remineralise resin-dentine interfaces. This biomimetic approach is able to evoke a “bottom-up” remineralisation that restores the original stiffness (i.e. Young׳s Modulus) of water-rich/resin-poor dentine-bonded interfaces. The next step will be the commercialisation of resin-based materials such as flowable composites and “smart” adhesive systems containing biomimetic reagents that can remineralise and prevent degradation of resin-dentine bonds to enhance their clinical longevity.