DM- Ch 4 Adhesive Materials Pt 1

Adhesion/bonding

the joining together of two objects, using glue or cement (adhesion and bonding used interchangeably)

Adhesive

glue

Adherend

surface attached to

The oral environment is wet and hostile

this limits the types of adhesives used in dentistry

A molecular attraction between two contacting surfaces

can be a chemical bond, mechanical adhesion, or a combination of both

Not all adhesion or bonding to tooth structures

is truly adhesive

Adhesive

A material that can bond two surfaces together, particularly smooth surfaces

True adhesion

is through chemical bonds between materials being joined

Adhesives in dentistry

can be chemical bonds or mechanical bonds

Most dental materials that are adhesive

involve micromechanical adhesion

Micromechanical bonding (retention)

Most dental materials use this type of bond

Bonding using small surface irregularities

smaller than the eye can see or can be felt with explorer

Mechanical/structural interlocking of materials during micromechanical bonding is

NOT a chemical reaction bond

Glue or cement flows into the irregularities during micromechanical bonding

and hardens/sets, objects are joined

Micromechanical bonding is

STRONGER than Macro due to greater number of surface irregularities involved

Macromechanical bonding

• Surface roughness can be seen and felt

• Mechanical/structural interlocking of materials

• NOT a chemical reaction bond

In dentistry, macromechanical bonding

is used for cementing (luting) crowns and bridges to

teeth

Macromechanical bonding involves

undercuts in hard tissue

Adhesion/bonding helps retention of restorations

• Adhesion is used to keep restorations in place

• Undercuts and other mechanical locks are not necessary when adhesive materials are used

• Also used to attach orthodontic brackets and other appliances to teeth

Adhesion/bonding reduces

microleakage of restorations

Microleakage

seeping/leaking of fluids & bacteria between tooth/restoration interface (space between tooth and restoration)

Adhesion/bonding can also

reduce postoperative sensitivity

• sensitivity caused by fluids & bacteria moving in/out of interface between restoration and tooth and irritating pulp from microleakage

Restorative material

MUST have similar Coefficient of Thermal Expansion (CTE)

Percolation

when teeth are heated/cooled and the material and tooth surface don't have the same CTE, they expand/contract at different rates causing microleakage

Adhesion/bonding reduces staining

at margins of esthetic restorations

• keeps margins sealed to prevent microleakage and staining

Adhesion/bonding caries

reduction of recurrent caries

• the blocking of microleakage reduces secondary decay (recurrent decay) at margins of restorations, no space exists at interface

Development of Dental Adhesives

Acid etching of enamel to create a rough surface, allows low-viscosity adhesive to flow into irregularities to cure/set

The purpose of acid etching

is to open pores of tooth surface and create a rough

surface to improve adhesion

• this is a MICROmechanical bond

1950's

pit and fissure sealants

1960's

composite restorations

1970's-1980's other uses

• Orthodontic brackets bonded to labial surfaces

• Pit and fissure sealants

• Maryland bridges

• Veneers

Chemical adhesion examples in dentistry

- Polycarboxylate cements

- Glass ionomer cements

Polycarboxylate cements

1970's this first chemically adhesive cement enabled materials to be bonded to dentin

• Uses polyacrylic acid & zinc oxide powder

Glass ionomer cements

Use polyacrylic acid & glass powder to chemically bond to dentin and enamel

• Not as esthetic or mechanically tough as composites

Dentinal bonding agents

1990's composites bonded to dentin via acid etching

• Dentinal bonding systems now used to bond ceramic & cast metal to dentin and enamel

Surface factors

Cleanliness and biofilms

Cleanliness surface factor

Must bond to a clean surface, if surface is dirty adhesive (glue) bonds to debris and not surface irregularities of the adherend (surface)

If tooth surface becomes contaminated by oral fluids (saliva, blood, crevicular

fluid)

it becomes covered by layer of biofilm, so adhesive won't bond to surface now

When adhesive won't bond to the surface

using a rubber dam helps prevent contamination

• Tooth surface must be isolated to prevent contamination and failure

• Isolating tooth surface also protects soft tissue from chemical burn from etch

Testing adhesion

Adhesive and cohesive failure

Adhesive failure

When the bond breaks cleanly at the interface with tooth

• Adhesive material remains on the restoration/appliance

Cohesive failure

When the bond breaks within the bonding material

• Adhesive material remains on the tooth surface and restoration/appliance

Acid etching process (Steps 1-3)

1. Enamel surface cleaned with pumice or other abrasive

2. Cleaned surface is rinsed

3. Cleaned surface is dried

Acid etching process (Steps 4-6)

4. Acid or etchant is applied for 15-30 seconds, rinsed, dried

• Typically, 37% (+-) orthophosphoric acid

5. Etched surface is rinsed with water

6. Etched surface is dried

• If acid etching is successful, it causes enamel to become "chalky" or "frosty", bonding occurs at ends of enamel rods

Acid etching process (Step 7)

7. Liquid bonding resin (polymer system) applied, polymer chemically reacts, cures

• Layers of restorative materials are chemically bonded to this initial layer to reach the depth/size of restoration desired

Unetched enamel

Etched enamel

Adhesive applied

Composite applied

Etched enamel

Acid etching causes micropores at ends of enamel rods, surface is rough

• Enamel looks "frosty" when dried