Transcript DH 104 Chapter 05

Principles of Bonding
Chapter 5
Basic Principles of Bonding
 In dentistry, the term bond, or bonding, is
used to describe the process of attaching
restorative materials to the tooth by
adhesion.
 When describing cosmetic restorations such
as porcelain or composite veneers, patients
often use the term bonding.
Bonding
 The basic principles of the bonding process
involve preparing the surface of the tooth or
restoration.
 Preparing the tooth surface includes
removing decay, plaque, and debris.
 The tooth then is etched or conditioned with
a 10% to 38% solution of phosphoric acid.
 This conditioning removes microns of tooth
to provide a rough surface to which bonding
can occur.
Bonding to an Etched Surface
 When a resin bonding agent or primer is
flowed over the etched surface, it penetrates
into the microscopic pores.
 When a resin bonding agent cures, it forms
resin tags that adhere to the etched surface of
the tooth.
 The resin bonding agent then will chemically
bond to other resins placed over it, such as
composite resin.
Primary and Secondary Bonds
 The primary or chemical bond occurs
through adhesion when the bonding agent
and the composite resin material adhere to
each other.
 The chemical bond is stronger than a
secondary or physical bond.

Example: adhesion of paint to a metal surface
Surface Wetting
 Etching increases the ability of the bonding
material to wet the tooth surface by creating
a high surface energy.
 Good wetting increases the contact of the
material and the tooth; poor wetting
prevents complete contact.
 For this reason, bonding agents are typically
made of a low-viscosity material.
Bond Strength
 The strength of the bond is determined by
the amount of force needed to break the two
materials apart.
 This is accomplished by pulling the two
materials apart or by applying force until the
bond fails.
 An enamel bond is typically stronger than a
dentinal bond.
Enamel Etching
 Etching of the enamel removes a small
portion of the surface, reduces enamel rods,
and opens porosities among the rods.
 Etching also removes the smear layer, which
is made up of debris on the enamel or
dentinal surface that results from the cutting
of tooth structure during the cavity
preparation.
 The smear layer comprises bacteria, salivary
components, and tooth dust.
Etching
 Etching should take approximately 20 to 60
seconds, depending on the manufacturer’s
instructions and the type of procedure to be
completed.
 Some teeth are more dense and must be
etched for a longer time; others respond well
in as little as 10 seconds.
 Etch materials are available in liquid or gel.
 The area is rinsed for approximately 10
seconds to remove the etch material.
Smear Layer
 The dentin has a higher water content because of
its organic makeup. It also contains collagen and
other fluids from the pulp chamber.
 The smear layer, which is made up of debris on the
enamel or dentinal surface resulting from the
cutting of tooth structure during cavity
preparation, must be removed before the bonding
procedure is performed.
 The smear layer comprises bacteria, salivary
components, and tooth dust.
Dentin Etching
 Etching dentin with phosphoric acid dissolves the
smear layer first, then portions of the
hydroxyapatite crystals from the surface of the
dentin, creating a porous surface and exposing
collagen fibrils that are part of the dentin matrix.
 This opens the dentinal tubules, which leaves a
rough, porous surface.
 Dentin has a lower mineral content and needs to
be etched for only about 10 seconds. Over-etching
leaves a weaker bond.
Bonding Agents
 Bonding agents are low-viscosity resins
dissolved in solvents, typically acetone or
ethyl alcohol, that penetrate porosities in the
tooth surface created by etching.
 Bonding of agents for enamel requires only a
single component—low-viscosity liquid.
 Bonding agents for dentin are viewed as two
types:


Primer
Bond
Preparing to Bond
 If only the enamel is etched, the surface is
dried to a frosty finish.
 When dentin is bonded, it is left moist to
keep the collagen fibrils from collapsing,
which could prevent penetration of the
bonding material.
 The primer is placed first and is dried before
curing, to remove the solvent and the
remaining water.
Oxygen-Inhibited Layer
 On the surface of the polymerized bonding resin is
a very thin coating of uncured resin.
 The resins used for composites and sealants also
form this layer of uncured resin on their surfaces.
 Polymerization is inhibited when the surface is
exposed to oxygen in the air.
 Once the composite resin is placed over the
bonding resin, the uncured layer on the bonding
resin will cure when the composite is cured.
Types of Bonding Agents
 Self-etching: Some two-component bonding
agents have incorporated acidic groups in the
primer that will etch enamel and dentin and
allow penetration of the resin without the
need for rinsing and drying.

These are called self-etching primers.
 These materials work well on prepared
surfaces but are not as effective on
unprepared surfaces.

Sealants and veneers
Modes of Cure
 Three modes of curing are used for resin
bonding agents:

Self cure


Light cure


Chemical reaction occurs between two resins (base
and catalyst) are mixed together
Light in the blue wave range activates a chemical
(photoinitiator) that sets off the polymerization
reaction or curing process
Dual cure

Uses a combination of self-cure and light-cure
ingredients
Microleakage
 When restorations are not completely sealed
at the margins, they can leak.
 This permits fluids, bacteria, and other
contaminants to enter the cavity preparation.
 This microleakage can result in recurrent
decay and failure of the existing restoration.
Tooth Hypersensitivity
 Some patients may experience transient
tooth sensitivity after a bonded restoration.

Usually lasts only a short time
 Common causes of tooth hypersensitivity
include the following:



Tooth is over-dried during the bonding process
(desiccation).
Tooth has been over-etched and not properly sealed.
Composite resin is cured in too large segments.
Clinical Application of Bonding
 Porcelain: stronger retention if bonded
rather than cemented
 Metal: used to create a stronger bond before
cementation of a crown or bridge
 Amalgam: helps seal out microleakage
Orthodontic Bonding
 Brackets have replaced bands for orthodontic
treatment.
 Conventional cements cannot be used, so the
brackets must be bonded.
 Conventional cements are difficult to cure
through brackets, so a dual cure material is
used.
Endodontic Posts
 A post is placed within the roots of
endodontically treated teeth to retain dental
materials used to build up missing tooth
structure.
 Posts may be metal or nonmetal.
 Posts are bonded with the use of bonding
agents and resin cements.
Summary
 Bonding of resins permits restorative
materials to stick to tooth structure by way of
micromechanical retention or chemical
bonds.
 Phosphoric acid is used on both enamel and
dentin to remove the smear layer and
provide a rough surface to which to bond.
 Tooth sensitivity may occur but should be
minimal when correct techniques are used.