FUNDAMENTAL CONCEPTS OF ENAMEL AND DENTIN ADHESION

Adhesion

the state in which two surfaces are held together by interfacial forces, which may consist of valence forces or interlocking forces or both

Adhesive

Material, frequently a viscous fluid, that joins two substrates together by solidifying and transferring a load from one surface to the other.

Adhesive strength

It is the measure of the load-bearing capacity of an adhesive joint.

FOUR DIFFERENT MECHANISMS OF ADHESION:

1. Mechanical adhesion

2. Adsorption adhesion

3. Diffusion adhesion

4. Electrostatic adhesion

interlocking of the adhesive with irregularities in the surface of the substrate, or adherend.

Mechanical Adhesion

chemical bonding between the adhesive and the adherend; the forces involved may be primary (ionic and covalent) or secondary (hydrogen bonds, dipole interaction, or van der Waals) valence force

Adsorption adhesion

interlocking between mobile molecules, such as the adhesion of two polymers through diffusion of polymer chain ends across an interface

Diffusion adhesion

an electrical double layer at the interface of a metal with a polymer that is part of the total bonding mechanism.

Electrostatic Adhesion

In dentistry, bonding of resin-based materials to tooth structure is a result of four possible mechanisms, as follows':

1. Mechanical—penetration of resin and formation of resin tags within the tooth surface.

2. Adsorption—chemical bonding to the inorganic component (hydroxyapatite) or organic components (mainly type I collagen) of tooth structure.

3. Diffusion—precipitation of substances on the tooth surfaces to which resin monomers can bond mechanically or chemically.

4. A combination of the previous three mechanisms

Failures of adhesive joints occur in three locations, which are generally combined when an actual failure occurs:

1. cohesive failure in the substrate;

2. cohesive failure within the adhesive; and

3. adhesive failure, or failure at the interface of substrate and adhesive.

Bonding techniques allow :

1. More Conservative tooth preparation

2. Less reliance on macromechanical retention

3. Less removal of unsupported enamel.

Adhesive restorative techniques currently are used to accomplish the following:

1. Restore Class I, II, III, IV, V, and VI carious lesions or traumatic defects.

2. Change the shape and the color of anterior teeth (c.g., with full or partial resin veneers).

3. Improve retention for porcelain-fused-to-metal

(ceramometal) or metallic crowns.

4. Bond all-ceramic restorations

5. Seal pits and fissures.

6. Bond orthodontic brackets.

7. Bond splints for tooth luxations and periodontally involved anterior teeth and conservative tooth-replacement prostheses.

8. Repair existing restorations (composite, amalgam, ceramic, or ceramometal).

9. Provide foundations for crowns.

10. Desensitize noncarious cervical lesions (NCCLs) and exposed root surfaces.

11. Impregnate enamel and dentin, making them less susceptible to caries.

12. Bond fractured fragments of anterior teeth.

13. Bond prefabricated fiber, metal, and cast posts.

14. Reinforce fragile endodontically treated roots internally.

15. Seal root canals during endodontic therapy.

16. Seal surgically resected root apices.

Buonocore [in 1955]

Inspiration behind enamel etching

• 85% phosphoric acid for industrial use was the inspiration behind enamel etching

• He introduced the acid-etch technique and

• Envisioned the use of acids to etch enamel for sealing pits and fissures.

● Most current phosphoric acid gels have concentrations of _% to _%.

● __% being the most common, although some studies using lower concentrations have reported similar adhesion values

● Most current phosphoric acid gels have concentrations of 30% to 40%.

● 37% being the most common, although some studies using lower concentrations have reported similar adhesion values

Etching time

● __ seconds originally was recommended for permanent enamel using _% to _% phosphoric acid.

● Although 40% of one study concluded that shorter etch times resulted in _________

● Other studies using scanning electron microscopy (SEM) showed that a -second etch resulted in a surface roughness ____ to that provided by a__ -second etch. Other in vitro studies have shown similar bond strengths and leakage for etching times of 15 and 60 seconds.

Etching time

● 60 seconds originally was recommended for permanent enamel using 30% to 40% phosphoric acid.

● Although 40% of one study concluded that shorter etch times resulted in lower bond strengths

● Other studies using scanning electron microscopy (SEM) showed that a 15-second etch resulted in a surface roughness similar to that provided by a 60-second etch. Other in vitro studies have shown similar bond strengths and leakage for etching times of 15 and 60 seconds.

Acid used for base metal alloy

Nitric acid

Acid or etchant used for feldspatic porcelain

Hydrofluoric acid

Shear bond strength

● Shear bond strengths of composite to phosphoric acid-etched enamel usually exceed ______________ (___) and can range up to _____ depending on the test method used.

● Such bond strengths provide adequate retention for a broad variety of procedures and prevent ________ around __________ of restorations.

Shear bond strength

● Shear bond strengths of composite to phosphoric acid-etched enamel usually exceed 20 megapascals (MPa) and can range up to 53 MPa, depending on the test method used.

● Such bond strengths provide adequate retention for a broad variety of procedures and prevent leakage around enamel margins of restorations.

What is the usual shear bond strength of composite to phosphoric acid-etched enamel

Usually greater than 20 MPa, with reported values reaching 53 MPa, depending on the testing method.

Enamel Adhesion:(Mechanism of enamel adhesion) AWMT

1. Acid etching transforms the smooth enamel into an irregular surface and increases its surface-free energy.

2. When a fluid resin-based material is applied to the irregular etched surface, the resin penetrates into the surface, aided by capillary action.

3. Monomers in the material polymerize, and the material becomes interlocked with the enamel surface.

4. The formation of resin microtags within the enamel surface is the fundamental mechanism of resin-enamel adhesion

fundamental mechanism of resin-enamel adhesion

formation of resin microtags within the enamel surface

THREE DIFFERENT MICROMORPHOLOGIC PATTERNS OF ENAMEL ETCHING

● Type I - involves the dissolution of prism cores without dissolution of prism peripheries (honeycomb appearance)

● Type II—the peripheral enamel is dissolved, but the cores are left intact. (Cobblestone appearance)

● Type III—less distinct than the other two patterns. It includes areas that resemble the other patterns and areas whose topography is not related to enamel prism morphology.

Adhesive materials can interact with dentin in different ways:

○ Mechanically,

○ chemically, or

○ Both

Dentin adhesion relies primarily on?

Dentin adhesion relies primarily on the penetration of adhesive monomers into the network of collagen fibrils left exposed by acid etching

Dentin Adhesion

adhesive materials that do not require etching, such as ____________ and some _________________ , chemical bonding between _________or ___________ and _________has been shown to be an important part of the ________ mechanism.

Dentin Adhesion

adhesive materials that do not require etching, such as glass ionomer cements and some phosphate-based self-etch adhesives, chemical bonding between polycarboxylic or phosphate monomers and hydroxyapatite has been shown to be an important part of the bonding mechanism.

CHALLENGES IN DENTIN BONDING SUBSTRATE

● Bonding to dentin presents a much greater challenge. Several factors account for this difference between _____ and _________

● Enamel is a highly mineralized tissue composed of more than __% (by volume) hydroxyapatite, whereas dentin contains a ___________ and __________, primarily ______.

● Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ). A cuff of hypermineralized dentin called ___________ lines the tubules.

● The less mineralized ________ dentin contains _____________ with the characteristic ___________

● Intertubular dentin is penetrated by submicron channels, which allow the passage of tubular liquid and fibrils between neighboring tubules, forming _________

CHALLENGES IN DENTIN BONDING SUBSTRATE

● Bonding to dentin presents a much greater challenge. Several factors account for this difference between enamel and dentin bonding.

● Enamel is a highly mineralized tissue composed of more than 90% (by volume) hydroxyapatite, whereas dentin contains a substantial proportion of water and organic material, primarily type I collagen.

● Dentin also contains a dense network of tubules that connect the pulp with the dentinoenamel junction (DEJ). A cuff of hypermineralized dentin called peritubular dentin lines the tubules.

● The less mineralized intertubular dentin contains collagen fibrils with the characteristic collagen banding.

● Intertubular dentin is penetrated by submicron channels, which allow the passage of tubular liquid and fibrils between neighboring tubules, forming intertubular anastomoses.

CHALLENGES IN DENTIN BONDING

• Dentin is an intrinsically _________ tissue, penetrated by a maze of _____________

• Adhesion can be affected by the remaining dentin thickness after tooth preparation. Bond strengths are generally less in ______ than in ___________

• Dentin is an intrinsically hydrated tissue, penetrated by a maze of fluid-filled tubules.

• Adhesion can be affected by the remaining dentin thickness after tooth preparation. Bond strengths are generally less in deep dentin than in superficial dentin.

Known to negatively affect the bonded interface.

Degradation of collagen by dentin proteinases

How to remove whitish appearance on the prepared surface known as “smear layer”

Use wet cotton on a cotton plier

What is a smear layer?

Residual organic and Inorganic components Compose of hydroxyapatite and altered denatured collagen.

What is a smear plug?

When the smear layer fills the orifices of dentin tubules, it will form "smear plugs", and decreases dentin permeability by nearly 90% in vitro.

Composition of smear layer

• Hydroxyapatite

• Altered Denature collagen

Mentioned by doc:

• Bacteria

• Saliva and Blood

• Smear Plugs

Removal of the smear layer and smear plugs with acidic solutions results in an__________ onto the exposed dentin surface and interfere with adhesion because ________ resins do not adhere to ________ substrates, even if resin tags are formed in the dentin tubules

Removal of the smear layer and smear plugs with acidic solutions results in an increase of the fluid flow onto the exposed dentin surface and interfere with adhesion because hydrophobic resins do not adhere to hydrophilic substrates, even if resin tags are formed in the dentin tubules

Composition of Hybrid layer

1. Demineralized Collagen matrix

2. Polymerized Resin

3. Residual Hydroxyapatite

4. Water

Several additional factors that affect dentin permeability:(UR V4 MR)

● Use of vasoconstrictors in local anesthetics (decrease pulpal pressure and fluid flow in the tubules)

● Radius and length of the tubules,

● Vscosity of dentin fluid

● 4 pressure gradients

● Molecular size of the substances dissolved in the tubular fluid

● Rate of removal of substances by the blood vessels in the pulp

What is a hybrid layer?

The hybrid layer forms when adhesive resin infiltrates the demineralized dentin

What is C-factor?

Configuration factor(c-factor) is the ratio of the bonded surfaces to the unbonded surfaces in a tooth cavity preparation when composite resin is placed

Example: A Typical Class V cavity has 5 bonded surfaces and 1 unbonded surface, this means the cavity has high C factor and greater potential for polymerization shrinkage stress

In addition to the C-factor, the magnitude of the polymerization shrinkage stress depends on several other variables, including the:

1. Rate of the polymerization reaction(control curing light irradiance)

2. Degree of conversion

3. Composite stiffness

4. Nature and relative volume of the inorganic filler and the type of monomers in the composite

5. The composite insertion technique

   • Incremental Insertion Technique

   • Bulk-fill Technique

6. The opacity of the composite

Effects of polymerization shrinkage stress:

● Cuspal deflection

● Tooth cracking

● Marginal leakage and gap formation

● Reduction of adhesive bond strength

● Decrease physical properties of the resin