Preclinics of Conservative Dental Medicine · MU Sofia
13. Adhesive systems – classification according to clinical steps, mechanism of action and characteristics.
Explains how adhesive systems bond resin composite to enamel and dentin, starting with the differences between enamel and dentin and the smear layer. It then covers the etch, prime and bond steps, the hybrid layer, and the classification by clinical steps including the generation numbering. A comparison table of etch-and-rinse against self-etch systems, a list of typical bonding mistakes and a set of key points close the note.
Topic 13 of 53 in the MU Sofia syllabus for Preclinics of Conservative Dental Medicine (Dental Medicine, Year 3). The free AceMed note covers it in 6 sections, about 910 words (7 min of reading), with 17 flashcards.
In this note
Introduction
Enamel, dentin and the smear layer
Mechanism of action: etch, prime, bond
Classification by clinical steps
Typical mistakes
Key points
Introduction
Adhesive systems (bonding agents) join resin composite to enamel and dentin, mainly by micromechanical interlocking of resin in the etched tooth surface, in some systems helped by a chemical bond. They allow minimally invasive cavities without retentive undercuts and seal the margins against microleakage, secondary caries and postoperative sensitivity.
Enamel, dentin and the smear layer
Enamel is about 96 % mineral by weight, dry and homogeneous, and bonds reliably. Dentin is only about 70 % mineral, with about 20 % organic matter (mainly type I collagen) and 10 % water; its tubules carry outward fluid and become wider and denser towards the pulp. Dentin is therefore wet and variable, and much harder to bond to.
The smear layer is a 1–5 µm layer of cutting debris (hydroxyapatite, denatured collagen, bacteria) left on every prepared surface; it also plugs the tubule openings as smear plugs. It lowers dentin permeability but is loosely attached, so a bond made on top of it is weak. Every adhesive therefore either removes it (etch-and-rinse) or dissolves and incorporates it (self-etch).
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