Classification of Dentine

Dentine adhesives

• bond composite to dentin

• are critical for durable resin–

tooth bonds.

• They work by micromechanical and chemical adhesion to dentine

Structure of Dentine

• hydrated composite of hydroxyapatite (50%), collagen (30%), water (20%)

*Presence of dentinal tubules and smear layer affects bonding.

Resin

is an organic polymer material made of small molecules (monomers) that chemically link together (polymerize) to form a hard, solid structure.

• dental resins:

  • Monomers: Bis-GMA, UDMA, TEGDMA

  • Photoinitiator system: camphorquinone + amine

  • (In composites) filler particles like glass or silica

Dentine Adhesive: Mechanism of Action

Micromechanical interlocking via resin tags in demineralized dentine.

• Chemical bonding via functional monomers (e.g., 10-MDP) with hydroxyapatite.

• Hybrid layer: zone of resin infiltration into collagen network.

Etching Patterns

Type I: Preferential dissolution of the prism core (honeycomb appearance); *most ideal the periphery is intact

Type II: Preferential dissolution of prism peripheries (core intact)

Type III: Mixed or Irregular pattern

Components of Adhesives: primer

Composition

• Hydrophilic monomers (e.g., HEMA, MDP)

• Solvent: acetone / ethanol / water

function:

• rehydrates collagen fibers to allow penetration to demineralized dentin

• Displaces water & maintains collagen expansion

• carries monomer into demineralized dentin, keeps collgen fibers from collapsing to form hybrid layer thru penetration

Components of Adhesives - Adhesive

Composition

• Hydrophobic resin monomers (e.g., Bis-GMA most viscous, UDMA, TEGDMA flowy)

• Initiators & accelerators

Function:

• Infiltrates primed dentin

• Polymerizes to form resin tags

• Bonds dentin to restorative material

primer vs adhesive

primer conditions the dentin vs adhesive provides strength of bond

purpose of air drying after dentin adhesive application?

Air thinning evaporates solvents and creates a uniform, well-penetrated adhesive layer that cures completely and forms a stronger bond.

First Generation bonding

(1950s–1960s):

• Relied on ionic bonding to calcium in hydroxyapatite.

• Used phosphate ester-based resins.

• Weak adhesion (<3 MPa) and rapid

Second Generation

(1970s)

• Bonded to the smear layer, not actual dentine.

• Used glycidyl methacrylate derivatives.

• Slightly improved bond (~5 MPa) but no

Third Generation

• Introduced conditioning agents (e.g., maleic or citric acid).

• Partially removed or modified the smear layer.

• Combined hydrophilic primers with hydrophobic resins for better penetration.

• Bond strength: 8–12 MPa.

Fourth Generation (Total Etch, 3 Step)

*Key innovation: formation of the hybrid layer

Steps:

1. Etch (35–37% phosphoric acid): removes smear layer, demineralizes dentine (~5 µm).

2. Primer (HEMA-based): improves wetting of collagen fibrils.

3. Adhesive resin (Bis-GMA, UDMA): infiltrates and polymerizes in the collagen network.

• Bond strength: 15–25 MPa; gold standard in durability.

5th Generation (2 Step Etch and Rinse)

• Combines primer and adhesive into one bottle. (primer + adhesive)

• Simplifies application but increases sensitivity to moisture control.

• Dentine must be moist but not overwet ('wet bonding').

• Typical monomers: HEMA, Bis-GMA.

• Bond strength: 18–25 MPa; hydrolytic degradation over time.

6th Generation: acidic monomers etch and primer at once

(2-step self-etch):

• Mild self-etch primer + separate bonding resin.

• Smear layer modified, not removed.

• Example: Clearfil SE Bond (Kuraray),

7th generation

(1-step self-etch):

• All-in-one adhesive; includes acid, primer, and resin.

• Very simple, but may suffer from water sorption and phase separation.

• Bond strength: 12–20 MPa.

8th Generation (Universal Adhesives *what we use)

• Introduced 2010s – true multi- mode systems (universal meaning)

• Can be used as total-etch, self-etch, or selective-etch.

Key ingredients:

• Functional monomers (10-MDP) for chemical bonding to Ca²⁺

• Silane coupling agents for indirect restorations.

• Nanofillers for mechanical reinforcement.

• Mild self-etching effect (pH ~2.5).

• Excellent versatility for enamel, dentine, zirconia, and metal.

Self-Etch Adhesives - Classification by pH

1) Strong self-etch (pH ≤ 1.0)

• Very aggressive etch

• Complete smear layer removal

• Deep dentin demineralization

2) Moderate self-etch (pH ≈ 1.5)

• Controlled etching

• Partial smear layer dissolution

• Good hybrid layer formation

3) Mild self-etch (pH ≈ 2.0)

• Gentle etching

• Smear layer modified, not removed

• Preserves hydroxyapatite (chemical bonding)

• what we use

4) Ultra-mild self-etch (pH ≥ 2.5)

• Minimal etching

• Smear layer largely intact

• Bonding mainly via functional monomers

Classification According to Etching Strategy (4)

• Etch-and-Rinse: phosphoric acid removes smear layer. (completely- highest bond strength)

• Self-Etch: acidic monomers condition and prime dentine.

• Universal: flexible use depending on clinical indication. (mix of both)

• Selective Etching: Only enamel is etched, dentin is left untouched

Classification by Number of Steps

• Three-Step: Etch → Primer → Bond (4th gen) gold standard

• Two-Step: Etch + combined primer/adhesive (5th gen) OR self-etch + bond (6th gen)

• One-Step: All-in-one (7th/8th gen). *least sensitive but weakest

Clinical considerations

• Moisture control: crucial for resin infiltration.

• Hybrid layer quality determines longevity.

• Compatibility with composites and curing systems must be verified.

• Simplification vs. durability trade-offs.

enzyme that can cause hydrolysis (breaks polymers to monomers) and degradation of dentin bonding?

MMP (Matrix Metalloproteinases)

Dental Adhesive Systems (4):

• Self Etch-2 step, 1 step

• Etch & Rinse - 3 step, 2 step

• Multi Mode Universal

• selective etching

* Self Adhesive (for cementing ex: GIC)

main inhibitor of photo polymerization

butylated hydroxytoluene (BHT)

*oxygen during curing though