Fundamental Concepts of Enamel and Dentin Adhesion (Chapter 5)

Mechanical Adhesion

the interlocking of adhesive with adherend

Adsorption Adhesion

chemical bonding between the adhesive and the adherend

Diffusion adhesion

interlocking between mobile molecules

Electrostatic adhesion

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

The surface energy of the adhesive must be ---- than the surface energy of the adherand

less than / lower

Adhesive failure occurs in one of 3 locations:

1. Failure in substrate

2. Failure in adhesive

3. Failure in bonding between substrate and adhesive

What is a major problem with bonding resin?

Methacrylate based resins shrink during polymerization

True / False: dental adhesives must provide a strong bond to resist the stresses of shrinkage

true

Bonding techniques allow for more ----- tooth preparations and less reliance on -----

more conservative tooth preparation

less reliance on macromechnical features

Enamel adhesion involves ---- technique

phosphoric acid etch

Most phosphoric acid etch gels for enamel are --- to --- %

30-40%

How does acid etching affect surface energy of enamel?

Increases surface energy

True / False: enamel adhesion is easier than dentin adhesion

true

Dentin adhesion relies on penetration of adhesive into ---- exposed by ----

collagen fibrils exposed by acid etching

Why is bonding to dentin harder than bonding to enamel?

Enamel is mineralized

Dentin has water and organic material = type 1 collagen

Small tubule radius

Less tubules at DEJ for absorption

Where are there more dentinal tubules: at the DEJ or pulp

Pulp

What is the composition of the smear layer?

Hydroxyapatite and denatured collagen

What happens when smear layer is removed from dentin?

Adhesion is compromised because a hydrophilic layer forms

True / False: composites shrink as they polymerize

True

What happens to the stress of composites as it is bonded to more tooth surfaces?

The more surfaces composite is bonded to, the higher the stress

C factor

Configuration factor

Number of surfaces a composite is bonded to

True / False: unrelieved stress in composites results in internal bond disruption and marginal gaps in respirations that lead to increased microleakage and post op sensitivity

True

What is very important to consider with composites?

Stress relief

What happens each time a restoration is exposed to wide temperature variations in the oral cavity?

Restoration undergoes volumetric changes

Effect of cyclic loading on bond strength

significantly reduces bond strength

What chemically modifies / removes the smear layer?

chelating agents = EDTA

Smear layer acts as a ---- that reduces the permeability of dentin

diffusion barrier

Total etch is also called the

etch and rinse technique

How does total etch work?

Simultaneous application of acid to enamel and dentin

How does the three step etch and rinse system work?

1. acid etching

2. primer

3. adhesive

How does acid etching affect surface energy of dentin?

Decreases surface energy of dentin = opposite of what is needed for adequate binding

SEA

self etch adhesive

True / False: the elimination of rinsing and drying steps reduces the possibility of overwetting or overdrying dentin, either of which can affect adhesion adversely

true

True / False: smear layer remnants do not interfere with bond strength

false

What can be used to induce remineralization of exposed dentin collagen fibrils?

Calcium phosphate

Vital dentin is inherently ---

wet

What is an obstacle in attacking effective adhesion of resins to dentins

water

What displaces the water from the dentin surface / collagen network and promotes infiltration of monomers though dentinal tubules?

Acetone or ethanol

What happens when dentin is dried? How does it affect penetration of monomers?

Collagen collapses and prevents penetration of monomers

What happens when demineralized dentin is restored with an adhesive system

It may undergo remineralization

What is a normal etch time?

15 sec

What is the main organic component of dentin?

type 1 collagen

What happens to the tension and compressive strength of dentin after acid etching?

Tension / compressive strength decreases

True / False: collagen fibrils break more easily with dehydration

true

True / False: with dentin bonding collagen should be demineralized as minimally as possible, kept hydrated, and infiltrate with a hydrophilic adhesive

true

What kind of adhesive is needed for dentin bonding: hydrophilic or hydrophobic?

hydrophilic

Ideally a dentin bonding agent should have both ---- and ---- ends

Hydrophilic and hydrophobic ends

Hydrophilic end displaces the dentinal fluid, to wet the surface. Hydrophobic end bonds to the composite resin.

What non collagen proteins are in dentin?

proteoglycans and MMPS

The most characterized dentin mineral nucleator is

dentin phosphoprotein (DPP)

dentin phosphoprotein (DPP) is highly ---- and binds to ----

acidic and binds to calcium

Function of MMPs

degrade extracellular matrix components

Micro-leakage

passage of bacteria between restoration margins and tooth preparation walls

Pulpal response is often a response to the degree of marginal ---

leakage

True / False: micro leakage does not necessarily cause de-bonding of the restoration

True / False: acid is directly responsible for injury to the pulp

False - it is very unlikely for acid to penetrate to the pulp

Does acid etching rate increase with higher or lower pH?

Lower pH = more acidic

To prevent bacterial infections restorations must be ---- sealed

heretically - airtight

True / False: Adverse pulpal reactions after a restorative procedure are not caused by the material used in that procedure but by bacteria remaining in, or penetrating, the preparation.

True

What type of dentin is resistant to acid etching?

Sclerotic dentin

What contributes to failure of class V restorations?

masticatory forces

What happens to materials with higher modulus in response to stress?

Unable to relieve stress

What is the most common site of hypersensitivity?

Cervical area

True / False: dentin desensitization agents affect bonding

False

Zirconia

a nonglass polycrystalline ceramic that is the strongest ceramic used in dentistry

What is a luting material?

an adhesive material