Enamel and Dentin Bonding

Buonocore

"Father of operative dentistry", inspired by industries use of 85% phosphoric acid as adhesive of paints/resins to metal, he envisioned the use of acids to etch enamel for sealing pits & fissures

Gwinnet and Mitsui

identified the use of resin micro-tags on etched enamel adhesion

Fusayama

created total-etch technique to etch enamel and dentin at the same time (remove smear layer and open dentinal tubules)

Nakabayashi

He describes resin infiltration of dentin collagen to form "hybrid layer"

Kanca and Gwinnett

identified the wet bonding relationship that increases resin-dentin bond retention with slightly wetted tooth

Watanabe

created self-etch adhesives

Enamel

homogeneous structure, predictable bonding, and excellent long term bonding durability (96% mineral and 4% organic/water)

Dentin

heterogenous structure, tubular structure, and fair long term bonding durability (45% mineral, 33% organic, and 22% water)

Smear layer

thin layer of debris on newly prepared tooth that obstructs entrances of dentinal tubules and decreases dentin permeability

Etch-and-rinse (total-etch)

uses strong acid (phosphoric acid) to completely etch enamel/dentin and wash excess with water followed by adhesive application. It can come in 3-step or 2-step forms

Etch-and-dry (self-etch)

uses nourishing solutions of acidic monomers to dissolve smear layer (increase permeability but not removed) and demineralize dentin/enamel. It can come in 2-step or 1-step forms

Universal etch

can be used as self-etch, etch-and-rinse, or selective-etch. It can come in 2-step or 1-step forms

Etch-and-rinse 3-step

etchant: phosphoric acid gel

primer: solvent and bifunctional/amphiphilic monomers

adhesive: hydrophobic non-solvated film forming monomers

Etch-and-rinse 2-step

etchant: phosphoric acid gel

primer and adhesive: solvent and bifunctional/amphiphilic monomers (hydrophobic film forming monomers)

Self-etch 2-step

primer: acidic monomer, solvents, and bifunctional/amphiphilic monomers

adhesive: hydrophobic non-solvated film forming monomers

Self-etch 1-step

All in one: acidic monomers, solvents, bifunctional/amphiphilic monomers, hydrophobic film forming monomers

Enamel etching Type I

removes prism core

Enamel etching Type II

removes prism periphery

Enamel etching Type III

combination and not prism structure evident

hybrid layer

a resin/dentin layer formed by intermixing of the dentin bonding agent with collagen fibrils exposed by acid etching. It serves as an excellent resin rich layer onto which the restorative material, such as composite resin, can be bonded

Selective etching

technique where enamel is etched first with phosphoric acid prior to the application of self-etch acidic primers that lack sufficient acidity to produce a good etch of the enamel

Key differences between self-etch and total-etch (4)

1)self-etch occurs simultaneously and primes dental substrates while total-etch is separated out

2)Self-etch is less technique sensitive and does not require rinses

3)Self-etch has reduced steps

4)Self-etch has worse binding to intact enamel (does not etch it as well)

Challenges of enamel bonding with self-etching adhesives (4)

1)dentin and enamel are two different substances

2)Self-etching adhesive (pH 2) is not as acidic as phosphoric acid (pH 0.5)

3)Dentin bonding with self-etch adhesives is reliable but not with enamel (needs more etching)

4)Separate phosphoric etching of enamel enhances bonding (can damage dentin)

Selective enamel etch-technique (6)

1)Phosphoric acid etching of enamel only (15-30s)

2)Water rinse (30s)

3)Remove cotton pellet and air dry vigorously

4)Apply acidic primer (20s)

5)Gentle solvent evaporation (shiny surface)

6)Apply adhesive resin (20s)

Gold standard etches (2)

1)Optibond FL (3-step)

2)Clearfil SE Bond w/selective enamel etching (2-step)

Adhesion

An attraction between molecules of different substances

Cohesion

Attraction between molecules of the same substance

Ideal conditions for bonding

high substrate surface energy and low adhesive surface tension so that adhesives spread and bind well

Sclerotic dentin

A form of reparative dentin formed in response to trauma that requires increased etching time

Three main components of dental adhesins

etchant, primer, and bonding resin

Solvents

increase penetration and evaporation of water

Four classification methods for adhesives

1)generation

2)solvent type

3)mechanism of smear removal (etch-and-rinse or etch-and-dry)

4)number of clinical steps (3, 2, and 1 step)

Sound dentin etching

should not be etched for more than 15 seconds to avoid decreasing bond strength

Sclerotic dentin etching

should be etched for 30 seconds to increase bonding strength

Wet bonding technique

increase resin-dentin bind retention by having tooth slightly wetted (shiny/hydrated surface)

Viscosity

a liquid's resistance to flow

OptiBond FL application steps (6)

1)Apply phosphoric acid to dentin (15 sec) or enamel (30 sec) followed by 15 seconds of rinsing (leave surface moist)

2)Apply primer to moist surface with microbrush (30 sec)

3)Initially let primer air dry and then apply air pressure to evaporate solvents (shiny surface)

4)Apply adhesive in thin even layer with microbrush

5)Light cure long enough to apply 18 Joules of radiant energy

6)Apply resin composite and light cure long enough for 8 Joules of radiant energy

Why do you want the tooth surface to be wet before applying primer?

increases penetration of primer and hydration of dentin, which helps with adhesion

Why do you want the tooth surface to be shiny after primer application?

indicates that primer has been applied properly, and it is ready for adhesive/bonding