Synthetic resins/ oral surgery courses

Seminar
on
Synthetic Resins
in
Prosthodontics
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Contents
Introduction
History
Classification
Preventive materials
Pit and fissure sealants
Restorative materials
Enamel and dentin bonding agents
Cements
Recent advances
Summary
References www.indiandentalacademy.com

INTRODUCTION
Synthetic resins are used in variety of dental
applications:
Dentures
Cavity filling materials (composites)
Sealants
Impression materials
Equipment (mixing bowls)
Cements (resin based)

HISTORY
Of the Direct Restorative materials, silicates
were developed first, followed by acrylic
resins, then resin composites.
Silicates- 1871 (anticariogenic, tooth colored)
Acrylic resins- unfilled.
Composites – 1960
Compomers – 1995 (improved handling and
fluoride release)

CLASSIFICATION
ISO 4049 for polymer based filling, restorative
and luting materials (ADA No. 27)
Type I: Polymer based materials suitable for
restorations involving occlusal surfaces
Type II: Other polymer based materials
Class I: Self- cured materials
Class II:Light- cured materials
Group 1: Energy applied intra-orally
Group 2: Energy applied extra-orally
Class III: Dual-cure materials

PREVENTIVE MATERIALS
PIT AND FISSURE SEALANTS
In 1965 a technique termed Occlusal sealing was
introduced where cyanoacrylate was used as a
sealant.
a.Resin sealants:Bis-GMA is the main resin. It is
mixed with diluent TEGDMA to decrease viscosity.
It can be light cured or self-cured.
b.Flowable composites: Low viscosity, high flow
composites. As their physical properties are low,
therefore, used for non-functional tooth surface
restorations.

c.Hybrid ionomers (resin modified glass
ionomers)- Used for restorations in low stress
areas and for patients with high caries risk.
Composition-
Powder similar to glass ionomer.
Liquid contains monomers, polyacids and water.
Setting-
Combined acid-base ionomer reaction and light-
cured resin polymerization.
Dentin bonding agent is contraindicated.

RESTORATIVE RESINS
COMPOSITES
It consists of atleast two distinct phases
formed by blending together components
having different structures and properties.
1. All purpose
2. Microfilled
3. Packable
4. Flowable
5. Laboratory

Composition:
Four major components: -
Organic polymer matrix
Inorganic filler particles
Coupling agent
Initiator-accelerator system

Organic polymer matrix
Two most common monomers:
1. Dimethacrylate (Bis-GMA)
formed by the reaction between Bis-phenol A
and Glycidyl methacrylate.
2. Urethane dimethacrylate (UDMA)
To decrease the viscosity of these monomers,
diluents must be added.e.g. low molecular
weight compounds with difunctional carbon
double bonds, triethylene
glycoldimethacrylate (TEGDMA).

Inorganic filler particles
Fillers are added to increase rigidity, hardness,
strength and to lower the value of coefficient
of thermal expansion.
It also lowers setting contraction depending on
its content.
Fillers commonly used include quartz, fused
silica and many types of glass including
aluminosilicates and borosilicates, some
containing barium oxide.

Dental composites are classified on the basis
of particle size, shape and distribution of
the filler.
Type of
composite
Particle
shape
Particle
size(μm)
Conventional spherical 20-30
Fine filled fine 0.4-3
Microfilled microfine 0.04-0.2
Microhybrid Fine+microfi
ne
-

•Composite filled
with course filler
•Composite filled
with finely ground
filler
•Heterogeneous
microfilled
composite

Coupling agent
It is used to bind the inorganic filler to the
organic monomer, so that when stress is
applied to a composite, the stress can be
transferred from one strong filler particle to
the other.
The most common coupling agents are organic
silicon compounds called silanes.
(γ-methacryloxypropyltrimethoxysilane)

Initiators and activators
Initiators :
a) Chemically activated
- Benzoyl peroxide
b) Light activated
UV cure- Benzoin methyl ether
Visible light cure- Diketone + tertiary
amines

Activators:
a) Chemically activated
- Dimethyl para toludine (DMPT)
- N,N Di hydroxy ethyl para toludine
b) Light activated
UV cure- 365 nm
Visible light cure- 460 nm
Pigments and other components:
Inorganic oxides are usually added in small
amounts to provide shades that match the
majority of tooth shades.

Setting reaction:
Self cured composite is chemically initiated with
a peroxide initiator and an amine accelerator.
Light cured composites is initiated by visible
blue light.
Dual cured products use a combination of
chemical and light activation.

Packing of composites
Light cured composites-
Supplied in various
shades in spills, syringes
and compules.
Self cured/ dual cured
composites-
Packaged in syringes or
tubs of paste and catalyst
and require mixing.

Properties
Property class1 class2 class3
Working time (min.,
sec)
90 - 90
Setting time (max., sec) 5 - 10
Depth of cure ( max.) - 1.5 -
Water sorption (max.,
µg/mm³)
40 40 40
solubility (max.,
µg/mm³)
7.5 7.5 7.5

Property All
purpose
Microfil
led
Packabl
e
Flowa
ble
Flexural
strength
(MPa)
80-160 60-120 85-110 70-120
Compress
ive
strength
(MPa)
240-290 240-300 220-300 210-
300
Polymeri
zation
shrinkage
(%)
0.7-1.4 2-3 0.6-0.9 -
Laborat
ory
90-150
210-280
-

Manipulation of composites
PULPAL PROTECTION
If deep cavity exists after preparation, protect the
pulp with a calcium hydroxide cavity liner.
ETCHING AND BONDING
- Etch the enamel and dentin for 30 sec with an
etchant i.e. 37% phosphoric acid solution or gel.
- Flush the acid away with water and gently dry
the surface.
- Bonding agent applied which penetrates the
etched enamel and dentin.

INSERTION
Composite can be inserted into the cavity
directly with a plastic instrument or through
the compule which reduces the chances of
incorporating voids.
POLYMERIZATION
Light cured composites
-Time may vary from 20-60 sec for a restoration
2 mm thick depending on the type of curing
unit and the type, depth and shade of the
composite.

Self and dual cured composites
- The self cured composite has a working time of 1 to
11/2
minutes.
- Setting time of about 4 to 5 minutes from the start of
the mix.
FINISHING AND POLISHING
- For gross reduction diamonds, carbide finishing burs,
finishing strips of alumina.
- For final finishing, rubber cup with various polishing
pastes can be used. Final finishing can be started
immediately after light curing.
- Polishing is done with aluminium oxide abrasives
with progressively finer grit sizes.

MICROFILLED COMPOSITES
Used in class III and class V restorations, where
a high polish and esthetics are important.
Because they are less heavily filled, higher
values of polymerization shrinkage , water
sorption and thermal expansion are present.
PACKABLE COMPOSITES
Used in classes I,II and VI (MOD) cavity
preparation. They have high depth of cure, low
polymerization shrinkage, radiopacity and low
wear rate.

FLOWABLE COMPOSITES
These are low viscosity composites used for cervical
lesions, pediatric restorations and other small, low
stress bearing restorations.
LABORATORY COMPOSITES
Crowns, inlays, veneers bonded to metal substructures
and metal free bridges are prepared indirectly on dies
from composites processed in the laboratory using
various combinations of light, heat, pressure and
vacuum to increase the degree of polymerization and
the wear resistance.

CORE COMPOSITES
These are typically two paste, self cured
composites although light cured and dual cured
products are available.
PROVISIONAL COMPOSITES
Temporary inlays, crowns and long span bridges
are usually fabricated from composite or
acrylic resins.
REPAIR OF CERAMIC OR COMPOSITE
Repair is achieved by abrading the surface of the
remaining composite and then treating with
primer and adding new composite.

COMPOMERS
Compomers or poly acid modified composites
are used for restorations in low stress bearing
areas.
Composition:
Contains poly acid modified monomers with
fluoride releasing silicate glasses and are
formulated without water.
Average filler particle size – 0.8-0.5µm

Dispensing:
Single paste formulations in compules and
syringes.
Setting reaction:
Light cured polymerization, but an acid-base
reaction also occurs as the compomer absorbs
water after placement and upon contact with
saliva.
Properties:
Release fluoride similar to glass and hybrid
ionomers.

LIGHT CURING UNITS
Most common light curing source used in
dentistry is the quartz-tungsten-halogen light.
In the mid 1990s, high intensity, plasma-arc
lights were introduced. In 2000, blue light-
emitting diodes became available.

QUARTZ-TUNGSTEN-HALOGEN
LIGHT CURING UNITS
-The peak wavelength varies from 450 nm to
490 nm.
-The intensity ranges from 400-800 megaW/cm2
.
-The output from the various lamps decreases
with the continuous use and the intensity is not
uniform for all areas of the light tip, being
greatest at the center.
- The intensity of light decreases with the
distance from the source.
- Bulb life ranges from 50 to 75 hours.

PLASMA ARC LIGHT CURING
UNITS
- High intensity light curing units
- Light is obtained from an electrically
conductive gas (plasma) that forms between
tungsten electrodes under pressure.
- Energy transmitted – 380-500 nm.
- It saves time, an exposure of 10 sec from PAC
light is equivalent to 40 sec from a QTH light.

LIGHT EMITTING DIODES
- Solid state light emitting diodes
(LEDs) use junctions of doped
semiconductors (p-n junctions)
based on gallium nitride to emit
blue light.
- Spectral output ranges- 450-490
nm
- LED units do not require a filter,
have a long life span and do not
emit significant heat.
- Depth of cure with LED units is
higher.

ENAMEL AND DENTIN BONDING
AGENTS
Modern bonding agents
contain three major
ingredients: -
1. Etchant
2. Primer
3. Adhesive
These may be packaged
separately or
combined.

ETCHANTS
- Organic (maleic, tartaric, citric, EDTA, acidic
monomers)
- Polymeric (Polyacrylic acid)
- Mineral (hydrochloric, nitric, hydrofluoric)
Phosphoric acid solutions and gels
(37%,35%,10%) are the most widely used
etchants.
Acid etchants are also called conditioners.
Gel etchants were developed by adding small
amounts of microfiller or cellulose thickening
agents.

PRIMERS
It contains hydrophilic monomers to produce
good wetting.
They are carried in solvents (acetone, ethanol,
water).
ADHESIVES
They are generally hydrophobic, dimethacrylate
monomers that are compatible with monomers
used in primer and composite.

Component Composition of major
components
4TH
GENERATION
Etchant
Primer
Adhesive
Solvent
Phosphoric acid
HEMA/GPDM,
4-META/MMA
Bis-GMA/TEGMA
Acetone, ethanol/water
5TH
GENERATION
Etchant
Primer-Adhesive
Solvent
Phosphoric acid
PENTA,
methacrylated phosphonates
Acetone, ethanol/water,
solvent free
6TH
GENERATION
Acidic Primer-Adhesive
Solvent
methacrylated phosphonates
Water

MANIPULATION
ENAMEL BONDING:
• Bonding to enamel occurs
primarily by micro
mechanical retention.
• 15 sec etch with 37%
phosphoric acid is
sufficient to produce
microtags.
• Acid etching is used to
remove smear layer and
dissolve hydroxyapatite
crystals.

•After etching, enamel surface
is washed with copious
amounts of water for 60 sec.
•Then the etched surface is
thoroughly dried.
•Adhesive penetrates into
surface irregularities and
become locked into place after
polymerization of the adhesive.
•The composite filling material
is applied directly to the
surface of bonding resin.www.indiandentalacademy.com

DENTIN BONDING:
Involves three distinct processes:
1. Conditioning
2. Priming
3. Bonding

SMEAR LAYER
•It is formed during cavity preparation and
extends over the whole prepared surface of dentin
and into the dentinal tubules (smear plugs).
•It is a loosely bound layer of cutting debris
including dentin chips, micro-organisms, salivary
proteins and collagen from the dentin.
•It is 3-15µ thick and prevents formation of any
durable bond.

1. Conditioning:
• They are generally acid solutions which are
capable of dissolving the smear layer, thus
exposing the underlying dentin to the bonding
agent.
• Rinsing is done to remove the smear layer
completely, leaving patent dentinal tubules.

2. Priming and Bonding:
•After rinsing, dentin is slightly air dried to
remove excess of water.
•Priming agent is applied to overcome the normal
repulsion between the hydrophilic dentine and the
hydrophobic resin.The most commonly used agent
is HEMA.
•Bonding agent is applied which wets the primed
surface and cured.

HYBRID LAYER:
•Efficient dentine conditioning also causes
decalcification of the intertubular dentine. This
process leaves a collagenous network which can
be infiltrated by primer and resin to form a resin
infiltrated layer or hybrid layer.
•2-10µ thick layer.

BONDING SYSTEMS FOR OTHER
SUBSTRATES
AMALGAM: The objective is to cause the unset
bonding agent and unset amalgam to
intermingle before they set. Amalgam bonding
simply seals the cavity against fluid flow and
microleakage providing little retention for set
amalgams.
LABORATORY COMPOSITES: Resin cements
are used. Monomer from bonding agent
penetrates the space between existing polymer
chains, intertwine and forms strong bond.

CERAMIC:
• The undersurface of all ceramic inlay, onlay,
crown, bridge or veneer is treated with 5% to 9%
hydrofluoric acid gel (which removes the smear
layer) or sandblast with 50µ aluminium oxide
particles.
• Then a Silane coupling agent is applied.
•Resin cements are used for bonding.
CAST ALLOYS:
A silicone oxide coating or “Silicoating” is
generated to achieve chemical bonding. This
technique is applied to gold, cobalt-chromium,
silver-palladium and titanium alloys.

CEMENTS
HYBRID IONOMER CEMENT
Drawbacks of GICs:
- Moisture sensitivity and low early strength are
the result of slow acid-base setting reactions.
To overcome these drawbacks polymerizable
functional groups are added.
Applications:
Permanent cementation of porcelain fused to metal
crowns, bridges, metal inlays or onlays and
crowns, post cementation and luting of
orthodontic appliances.

Compomers
Fluoride releasing capability of conventional
glass ionomers and durability of composites has
led to the introduction of it.
Applications:
Cementation of cast alloys crowns and bridges,
porcelain fused to metal crowns and bridges and
gold cast inlays and onlays.

Resin cements
Flowable composites of low
viscosity with improved properties.
Composition:
Resin matrix with Silane treated
inorganic fillers.
Applications :
Cementation of thin ceramic
prostheses, resin based prostheses
and direct bonding of plastic.

RECENT ADVANCES
Fiber reinforced composites

Summary and conclusion
It is apparent that no single type of luting
or restorative material satisfies all the ideal
characteristics.

References
Anusavice Kenneth J.: Phillips Science of Dental
Materials. 10th
edition, W.B. Saunders, 1999.
Combe E.C.: Notes on dental materials: 6th
ed.
Churchill Livingstone, 1992.
Craig Robert G. and Powers J.M.: Restorative
dental materials. 11th
ed. Mosby Inc. 2002.
Gladwin Marcia, Bagby Michael: Clinical aspects
of dental materials, Lippincott, 2000.

O’Brien W.J.: Dental material and their selection,
2nd
ed. Quintessence, 1997.
Van Noort Richard: Introduction to dental
materials, Mosby 1994.
McCabe J.F. and Walls A.W.G.: Applied dental
materials, 8th
ed. Blackwell Science Limited, 1998.

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