Fundamental Concepts of Enamel and Dentin Adhesion (Chapter 5)

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

1. mechanical adhesion

2. adsorption

3. diffusion

4. combination of the mentioned mechanisms

Mechanical Adhesion

penetration of material within the tooth surface

Adsorption

chemical bonding to inorganic component (hydroxyapatite) or organic component (collagen)

Diffusion

flow of material from high to low concentration on the tooth surface

What is used to acid etch enamel?

30 - 40% phosphoric acid

What is the maximum amount of time to etch enamel?

15 seconds

What is the purpose of etching enamel?

Transforming enamel from a smooth to rough surface

What is the fundamental mechanism of resin-enamel adhesion?

formation of resin tags in dentin

True / False: bonding to dentin is easier than bonding to enamel

False - bonding to dentin is more difficult

What does etching of dentin rely on?

Penetration of material into open collagen fibers that are exposed via acid etching

Why is bonding to dentin more difficult than bonding to enamel?

Dentin contains more organic material (collagen type 1 fibers) and water

Are there more dentin tubules near the DEJ or the pulp?

pulp = dentin tubules decrease from pulp to DEJ

Does material bond to interlobular dentin or peritubular dentin?

Intertubular dentin

Why does material bond to intertubular dentin instead of peritubular dentin?

intertubular dentin has a higher concentration of collagen fibrils

peritubular dentin is more mineralized/crystalized

Why do bonding materials not bond well to peritubular dentin?

composed of densely packed mineralized crystals

Is bonding strength greater in superficial or deep dentin?

superficial

Smear layer

Very thin layer of debris on newly prepared dentin

The smear layer acts as a --- barrier

diffusion

Do smear plugs increase or decrease dentin permeability?

decrease

What other factors decrease dentin permeability, besides smear plugs?

Vasoconstrictors in local anesthetics = decrease fluid flow in tubules

radius /length of the tubules

bonding molecule size

Composites --- as they polymerize, creating considerable stress within the preparation

shrink

What happens when a composite is bonded to one surface?

stress is relieved by the unbonded surface

C factor stands for

configuration factor

What is a C factor (configuration factor)?

ratio of bonded / unboned surface area

How many surfaces is composite or amalgam bonded to in an facial preparation?

1

How many surfaces is composite or amalgam bonded to in an occlusal preparation?

5 =

mesial

distal

buccal

lingual

pulpal

What is the C factor in an occlusal restoration

5 bonded surface (mesial/distal/buccal/lingual/pulpa) / 1 unbounded surface (occlusal)

c factor = 5

Why is stress relief minimal in an occlusal restoration?

stress can only be released from the occlusal surface

What does polymerization depend on?

- C factor

- Rate of polymerization

- Stiffness of composite

- What monomers are used in the composite

- Composite technique

- Opacity of the composite

What kind of monomers undergo hygroscopic expansion?

hydrophilic materials = larger net expansion

True / False: each time a restoration is exposed to wide temperature changes in the mouth it undergoes volumetric changes

true

CTE

coefficient of thermal expansion

how much a material expands per one degree temperature increase

True / False: cyclic loading weakens a restoration

true

Smear layer is removed using --- agents

chelating

Chelating agents

EDTA and citric acid

Why does a restoration undergo volumetric changes when exposed to wide temperature changes in the mouth

CTE is different from the tooth structure

Should materials be bonded to moist or dry dentin surface?

Slightly moist = prevents collagen collapse

What was added into etch and rinse adhesives to keep dentin open?

Acetone = displaces water from dentin tubules and allows infiltration of materials

How should dentin be dried if too moist?

cotton swab, brush, tissue

if an air syringe is used then dentin has to be remoistened after to open the collagen matrix

True / False: phosphoric acid from etching significantly damages dentininal collagen

false

Microleakage

Microscopic leakage at the interface of the tooth structure and the sealant or restoration

True / False: pulpal response correlates to degree of marginal micro leakage

true

True / False: adverse pulpal reactions are caused by the material used in the restoration

false - caused by bacterial invasion

What causes adverse pulpal reactions in a restoration?

- Bacterial invasion

- Pressure gradient due to desiccation or excess pressure during restoration

-Trauma

True / False: sclerotin dentin is less resistant to acid etching

false - more resistant

Does bonding to sclerotic dentin cause high or low bond strength?

low

What explains dentin sensitivity?

Hydrodynamic theory

What is the most common area of tooth hypersensitivity?

Cervical area

Composite is composed of ---- embedded into a ----

glass particles embedded into an organic matrix

What is used for porcelain veneers, inlays/onlays, and single crowns

glass matrix ceramics

What coupling agent is needed to bond glass matrix ceramics?

Silane

What affects the polymerization, shrinkage, stability, and fluidity in composite

the organic matrix

Types of filler particles in composite

Macrofilled

Microfilled

Hybrid

Nano

---- volume affects properties of composite

% filler volume

Where does bonding strength of dentin come from?

Intertubular dentin

Intertubular dentin

large surface area of dentin between the tubules

As you move from the DEJ down towards the pulp there is ---- intertubular dentin

less

What happens when enamel is etched for > 30 seconds

deposition of crystals

decreases strength of bonding to enamel

The smear layer has to be either -- or --

modified or removed

Carious strength has a --- bond strength than normal dentin

lower

Composites shrink between --- to ---%

3 - 17%

Self etch / total etch / etch and rinse technique

a bonding system that does not use a separate etching procedure with phosphoric acid.

The acid is contained in the resin primer and no rinsing is needed

Multiple step etch and rinse technique

a clinical technique that includes etching of both enamel and dentin as a separate step from the application of bonding agents