Role of the smear layer in adhesive dentistry and the clinical applications to improve bonding performance

Abstract

Currently, dental adhesives can be divided into two systems; a smear layer-removal approach with etch-and-rinse adhesives or a smear layer-modified approach with self-etching adhesives. After phosphoric acid etching, the smear layer is completely removed. More attention is, however, required when using self-etching adhesives. The smear layer is partially demineralized by the weak acidic monomer and subsequently incorporated into the hybrid layer. Therefore, the characteristics of the smear layer play an important role on the bonding performance of self-etching adhesives. Such characteristics, for instance, smear layer thickness and smear layer density, are influenced by many factors, e.g. , instruments used for dentin surface preparation, cutting speed, and the abrasive particle size of the cutting instruments. This review discusses the contributing factors that affect the smear layer characteristics, and the influence of the smear layer on the bonding performance of dental adhesives. Also, the application techniques regarding how to improve the bonding performance of self-etching adhesives – the smear layer removal by using chemical agents, or the modification of the adhesive application procedures – are provided.

Hardness and indentation modulus of human enamel and dentin

“…Acid etching can cause in decrease of mechanical properties due to release of phospate ions from the enamel crystallites to the enamel pores and flushing organic matters from the crystallites surface 31–33,37–41 . Furthermore, acid etching could create voids between the collagen fibres of dentin due to loss of HAP crystals 42 .…”

Physicochemical Properties of Dentine Subjected to Microabrasive Blasting and Its Influence on Bonding to Self-Adhesive Prosthetic Cement in Shear Bond Strength Test: An In Vitro Study

“…As a result, the dentin connection might be weakened by dissolved mineral remains that must be incorporated into the resin layer. The mild (pH ~2) and ultra-mild self-etching adhesives (pH ≥ 2.5), conversely, demineralize the dentin surface just superficially; if the smear layer is dense, they cannot penetrate it [59,92]. Lastly, as shown by Breschi et al self-etch adhesives often infiltrate no further than the smear layer and smear plugs, revealing a more homogenous morphology that is devoid of long resin tags.…”

“…They theorized that the adverse effect was caused by the smear layer's compaction after alumina blasting, which could prevent the adhesive resin from penetrating [55]. Nevertheless, the effect of APA on the formation, compaction, or removal of the dentin smear layer is still the subject of many studies, which have often produced contradictory conclusions [47,[56][57][58][59][60].…”

Effect of desensitizing dentifrices on eroded dentin wettability

“…Restorative treatments are effective when the adhesive material adheres satisfactorily to the dental substrate [12][13][14][15]. Close contact between the adhesive material and the dental substrate is necessary for adhesion to occur [13][14][15][16][17].…”

“…Restorative treatments are effective when the adhesive material adheres satisfactorily to the dental substrate [12][13][14][15]. Close contact between the adhesive material and the dental substrate is necessary for adhesion to occur [13][14][15][16][17]. The surface contact area between a liquid (adhesive) and a solid (dental surface) increases when substrate wettability by the liquid adhesive is good [18][19][20].…”