BONDING AND ADHESION

Dr.linda Maher

The modern dental practice uses bonding for a wide variety of dental procedure. the dental assistant and dental hygienist must be familiar with the terms and processes used in bonding of various restorative and preventive materials.

BONDING It is the process of attaching

restorative materials to the tooth structure by adhesion

TYPES OF BONDING: 1\mechanical bonding 2\chemical bonding 3\combination of two

1\mechanical bonding: Adhesive materials fill the voids or

pores of the surfaces and hold surfaces together by interlocking

2\chemical bonding: chemical adhesion (true adhesion) occurs

when the surface atoms of two separate surfaces form chemical bonds to each others

USES OF BONDING IN DENTISTRY1\RESTORATIVE MATERIALS

(COMPOSITE-COMPOMER-GIC-PORCELAIN )

2\ORTHODONTIC PRACITS3\ENDODONTIC POSTS

BASIC PRINCIPLES OF BONDING1\PREPARATION FOR BONDINGThe first step in bonding involves

preparation of the surface of tooth or the restoration or both to receive the material that will be bonded to it.

Preparing the tooth structure includes: 1\removing debris and caries,

2\etching or conditioning the enamel or dentine or both with an acid.

acid etchant :Commonly used acid is phosphoric acid in concentration of( 10-38 %)Can be in two forms: Liquid or gelPurpose of etching:1\The acid removes mineral from the surface to create roughness or microscopic

porosity2\remove smear layer3\increases surface wetting

smear layer: -The layer of cutting debris that forms

on the surface of the tooth after a cavity is prepared.

-It may also contain: plaque, bacteria , pellicle.

-Mainly formed in dentin layer -It interferes with the formation of a

bond to dentin and needs to be removed - Dissolved with acid etch

surface wettingAcid etching of enamel increases its

ability to be wet by a resin bonding agent resulting in a stronger bond

Preparation of a metal surface: roughening the metal surface

by( sandblasting) creates mechanical retention in the same way that acid etch roughens the enamel surface

Sandblasting system

2\BONDING TO THE ETCHED SURFACE

-A bonding agent(resin material) is applied to the etched tooth surface

-It penetrates into the microscopic pores.

-When it hardens (polymerized) it creates projections called resin tags that lock into the tooth

This creates micromechanical retention

ENAMEL ETCHING 1\apply acid etchant(for 20-30 sec) 2\wash with water 3\dry with air Etched enamel appears frosty white

when dried

DENTINE ETCHINGEtching time: 10 sec (less than enamel)Keep the surface moist (but not with

saliva) Because dentin contains more

collagen fibers than enamel and when dried they will collapse and occlude the porosities created by etching

THE HYBRID LAYERThe layer that is formed by the dentin

bonding resin , the collagen fibrils of dentin , and the etched dentin surface

It forms the bond that links the dentin to the restorative material

BONDING AGENTS1\ENAMEL BONDING RESINS:Bonding to enamel alone is much

simpler than bonding to dentinRequires only a low viscosity liquid

resin monomer that will penetrate into enamel tags created by etching(BONDING AGENT)

2\DENTIN BONDING RESINS:Two components are required for

better adhesion of the restorative material to the wet surfaced dentin.

1\primer :hydrophilic monomer that penetrates etched dentin and lay down a resin layer

2\adhesive resin: applied over the primer and chemically bond to it

TYPES OF BONDING SYSTEMS:1\TOTAL-ETCH BONDING SYSTEM:composed of:1\separated phosphoric acid etchant for both

enamel and dentine 2\bonding agent which is applied either in: A\two-bottles system (primer-bonding

resin) B\one bottle system (primer and bonding

resin in one step)

Total etch bonding system

2\SELF-ETCHING BONDING SYSTEMS:

bonding agents that do not require the use of acid etching step separately

1\two bottle system (acid and prime-adhesive)2\one bottle system (all in one bottle )

Bond strengthThis is measured by determining the

force needed to separate the two joined materials.

The value for the bond strength is reported as Mpa (mega Pascal).

Bonding to enamel usually gives around 30 Mpa (high bond strength)

The bond strength to dentin is usually less than to enamel

Choosing materials with high bond strength is important for:

1\enhance the longevity of the restoration

2\potentially allow for more conservative preparation (does not require excessive removal of the tooth structure to increase retention )

FACTORS THAT INTERFERES WITH GOOD BONDING1\remaining caries in the surface of

dentin2\sclerotic dentine(physical process

occur with aging and leading to narrowing of the dentinal tubules)

3\contamination of the cavity by saliva

4\the presence of smear layer

THANK YOU.