Resins in orthodon 2 /certified fixed orthodontic courses by Indian dental academy

Resins in
orthodontics
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Polymerization can be activated by
chemical,light or dual cure
Bis-GMA molecule:
2 reactive C=C grps
cross linking strength
-OH grp cross linking

Introduction
Dynamically growing science
Discovery of new techniques,materials
Improvement over older ones
Synthetic resins-single class of substances
that has influenced modern living

By def,non metallic compounds synthetically
produced that can be molded into various forms,used
for various purposes.
Chemical similarities-all are composed of polymers
Resin currently widely used-based on acrylic resins
called methyl methacrylic acid
Wide application-denture bases
removable appliances
impression trays
obturators

History
Goodyear(1840) :1st org polymers
rubber & vulcanite
Other polymers
J.W.Hyatt(1869) :cellulose
L. Baekland(1907) :bakelite
W.l. Semon :polyvinyl chloride
W.S. Carothers(1925) :synth. rubbers

Polymers truly adequate for dental
purpose(1930s)
O.rohn(1936):
Polymethyl methacrylate(plexiglass)
1946:- 98% of denture bases were of acrylic
1945:-Self cured resins 1st used in germany
1970:- fluid resin introduced

mid 1950s-direct bonding with epoxy resins
1955- Buonocore demonstrated acid etch
1958-Salder attempt to direct bond without
etch
Early 1960-epoxy acrylates
1962-bowen-bis-GMA,monomer consists of a
reaction product 4-4’isophylidine phenol and
glycidyl methacrylate
Mid 1960- use of bis-GMA resin composites

Newman(1965):1st to bond orthodontic attachments
to the teeth by means of epoxy resin,used low mol.
Wt epoxy resin liq with high mol. Wt solid epoxy &
polyamide curing agent,fast cure,reduced irritation
potential
Cueto(1966):used liq monomer methyl methacrylate
& silicate filler,working time-1mt
setting time-2 to 4mt
Mitchel(1966):failures with epoxy resin
Buonocore etal(1968):acid conditioning-prism tags
Retiel etal(1970):thich adhesive interface—more
imperfections,greater polymerization shrinkage
Miura etal(1971):modified tri alkyl borane
catalyst,useful for bonding plastic brackets,enhanced
adhesion in presence of moisture.

Reynolds(1975):maximum tensile bond strength of
5.9 to 7.9 Mpa adequate,in vitro tensile strength level
of 4.9Mpa clinically acceptable.
Keizer etal(1976):large standard deviation for bond
strength—speculation on reliability.
Zachrisson(1978):remnants of adhesive material
remained on the enamel surface after debonding &
all modalities of debonding abraded enamel to
varying degrees,thus none left a perfect surface.
Tavas etal(1979)light activated composites,significant
increase in bond st. of all materials after 24hr as
compared to values 5mts after bonding

Other polymers-
Polyurethane,polystyrene,vinyl acrylic
Recently-lass fibers,carbon fibre
graphite,polyaramide fibers added to acrylis
to improve mech. Properties
Rubber & butadine reinforced acrylics

Classification of resins
1) natural resins:complex of C,H,O
in paints,perfumes,medicine
dentistry-separating media,cavity liner
synthetic resins:non metallic
compounds,synthetically produced from org.
compounds,which can be molded into various
forms,hardened for commercial
use,commonly called plastics,bcz of their
plastic beh. under heat & pressure.

Synthetic resins are formed by a chemical
process ,polymerization
in which simple molecules with identical
structure link upto form a large molecule of
high molecular weight.
Poly=many
Mer=units
Compounds having Mol wt>5000-macromol.

Synthetic resins
A)thermoplastic:
Softens when heated above the glass transition temp
Tg,at which the molecular motion begins to force the
chains apart.resins shaped,molded,hardened on
cooling.
They are fusible I.e; they melt
They are soluble in organic solvents
Eg:
poly methyl methacrylates,polyvinyl
acrylics,polystyrenes

B)thermosetting resins:
Undergo chemical change & become permanently
hard when heated above the temp at which they
began to polymerize
Don’t soften again on reheating
Infusible,insoluble
Superior abrasion resistance,dimensional stability
Eg:
cross linked poly methyl methacrylate,silicones

Ideal requirements
1. Should be tasteless, odorless, non-
toxic and non-irritant to the oral tissues.
2. Aesthetically satisfactory, i.e. should
be transparent or translucent and easily
pigmented. The color should be permanent.
3. Should be dimensionally stable. It
should not expand, contract or warp during
processing and subsequent use by the
patient.
4. Have enough strength, resilience and
abrasion resistance.

 .
5. Be insoluble and impermeable to oral
fluids.
6. Have a low specific gravity (light in
weight)
7. Tolerate temperatures well above the
temperature of any hot foods or liquids taken
in the mouth without undue softening or
distortion.
8. Be easy to fabricate and repair.
9. Have good thermal conductivity.
10. Should be radio opaque
11. Thermal coefficient of exp should
match tooth

Uses of resins
1. Preparation of dentures
2. Artificial teeth
3. Tooth restoration
4. Cementation of crowns and bridges
5. Orthodontic and pedodontic appliances
6. Crown and bridge facings
7. Maxillofacial prostheses
8. Inlay and post core patterns

Temporary crowns and bridges
Dies
Implants
Endodontic and core filling materials
Athletic mouth protectors
Impression trays
Splints and stents
Models

Terms
Polymer:molecule made of many parts
composed of non metallic elements
bonded by covalent bonds
large molecular size,weight
Eg:polymerization of methyl methacrylate monomer(100g/mol)
into poly methyl methacrylate polymer(30,000g/mol)
Named accrd to mers
Eg:polymethyl methacrylate OR
by prefixing poly to the kind of monmer chemical links
eg:polyamide,polyester
commercial names:nylon,dacron,plexiglass,teflon

Monomer:
Molecules from which the polymer is
constructed;homopolymer or copolymer
Molecular weight:
Molecular weight of the various mers multiplied by
the no. of mers
Thousands to millions
Affects the physical property of resin

Chain length vs. mol wgt:
Longer the polymer chain—more the no. of
entanglements,more difficult to distort the
polymer
Increased rigidity,strength,melting temp
Mol wt of commercial dental resins 8,000-
39,000

Degree of polymerization:
Def as the total no. of mers in the polymer
The higher the mol wt of the polymer made from a
single monomer higher is the degree of
polymerization
Strength of resins increase with the degree of
polymerization
Avg degree of polymerization=
total no. of str units/total no. of molecules
Narrow mol wt distribution gives useful polymers
Higher the mol wt, high softening tmp,melting
pt,increased rigidity

Polymerization
The process of forming a poly mer from
identifiable subunits,monomers is
polymerization
2 main types:
condensation or step growth
addition polymerization

Condensation polymerization
Polymerzation acomplished by repeated
elimination of small molecules;byproducts-
water,halogen acids,ammonia
So there is a change in composition
Components are difunctional monomers
All cure or become reactive simultaneously
Reaction very slow
Stop before they form v high mol wt polymer

Addition polymerization
Most of the resins employed in dentistry
Starts from a active centre adding one
monomer mol at a time to rapidly form a
chain.theoritically this chain can grow
indefinitely
Monomers are activated one at a time ,add
together in sequence to form a growing chain
Process simple but control difficult
No change in composition

Inorder to be polymerized the monomer must
have a unsaturated grp its structural
formula.on activation of the monomer mol.
The bonds open up and collide with another
molecule,which inturn become activated and
covalent bonding takes place
Reaction exothermic

copolymerization
Two or more chemically different
monomers,each with some desirable property
can be combined to yeild a polymer with
specific property
Eg:ethyl acrylate copolymerized with methyl
methacrylate to alter the flexibility & fracture
resistance of a denture

Copolymer strc.
Three types:
1.random copolymer:no sequential order btw
two or more mer units
2.block copolymer:mer units occur in relatively
long sequences
3.graft/branched copolymer:
Sequence of one type of mer unit are attached
onto a backbone of second type of mer unit

Random copolymer:
ABBABABAAABAAABABBBBABAAABABB
BLOCK COPOLYMER
AAAAAABBBBBBBAAAAAABBBBBAAAAA
GRAFT OR BRANCHED COPOLYMER
AAAAAAAAAAAAAA
B
B
B
B

Polymers strc
1.linear:structural units are connected to one another in
linear sequence
2.nonlinear or branched polymers:
(Temporary connections)
3.cross linked polymers:
Form chemical bondage btw adjacent chain of
linear polymers giving rise to three dimensional
network-imp physical properties like,high strength,low
solubility and water sorption
permanent connections btw chains

Stages of polymerization
1.induction:
- two processes control induction:
activation & initiation
-for Add. Poly. to begin a source of free radical R*
is required.
Free radicals can be genrated by activation of the
radical producing molecule using:chemical
Heat
Visible light
Uv light
Energy transfer from another compound

Prerequisite for add.Poly.-
presence of unsaturated group(double bond).
when a free radical & its unpaired electron approach a
monomer with its high electron density double
bond,an electron is extracted & it pairs with R*
electron to form a bond b/t the radical & monomer
mol., leaving the other electron of the double bond
unpaired.thus the original free radical bonds to one
side of the monomer mol. & forms a new free radical
site at the other end.the reaction is now initiated.

Benzoyl peroxide is the common initiator mol. Used.
At 50-100c it forms 2 free radicals
Chemical activation:2 reactants mixed,tertiary amine
(activator)+BPO(initiator)
Heat
Uv light:
adverse effect on retina & unpigmented oral
tissue,limited pentration,loss of intensity of the light
source over time
VLC:
Campharoquinone & an org
amine(dimethylaminoethylmethacrylate)
470nm wavelenght of light
One part system,stored unexposed to light

Initiation period is greatly influencved by the
purityof the monomer.impurities react with the
activated groups—increase in the induction
period.
Induction energy for activation of each
monomer mol-16,000-29,000cal/mol

Propagation:
less energy needed,5000-8000cal/mol
free radical-monomer complex acts
as a new free radical centre when it
approaches another monomer to form a
dimer,which also becomes a free radical

Chain transfer:
Active sites is transferred from an
activated radical to an inactive molecule
and a new nucleus for further growth is
created

Termination:
Takes place either by direct coupling or
exchange of hydrogen atom from one
growing chain to another

inhibitors
Inhibition of polymerization:
Impurity that can react with the free
radical will inb. the polymerization
Eg:hydroquinone(0.006% or less)
Oxygen inhibition

Acrylic resins
Derivatives of ethylene & contain a vinyl
group in their structural formula
2 acrylic resin series :
derived from acrylic acid
derived from methacrylic acid
both polyacids are hard & transperent but
their polarity rel to carboxly grp causes
imbibation of water.water tends to separate
the chains—softening & loss of strength.
H2C=CHR

Plasticizers
Added to resins to reduce their softening or fusion
temp.
Increase the solubility of the polymer in the monomer
& decrease the brittleness of the polymer
Action:
partial neutralization of the secondary bonds or
inter molecular forces-leading to-slipping of resin
molecules past one another under stress.
External:not part of polymer,penetrates b/t macromol
increasing the inter molecular spacing
Internal:by copolymerizationof suitable plasticizer
eg:butyi methacrylate add to methyl methacrylate

Esters of polyacids are of greater interest in
dentistry
Polymethyl methacrylate is the hardest resin
of the series with the highest softening
temperatures.

Methyl methacrylate:
monomer in liquid form
Clear transparent liquid at room temp
Physical prop:melt. Pt:-48c
Boiling pt-100.8c
density-0.945g/ml at20c
heat of polymerizatin-12.9kcals/mol
Exhibit high vapour pressure and is an
excellent organic solvent
Although heat,uv,vlc possible, chemical
initiator common

Degree of polymerization varies with the
conditons:temperature
method of activation
type of initiator conc;
purity of chemicals
Vol. Shrinkage of 21% occurs during the
polymerization of pure monomer

 Polymethyl methacrylate:
Linear polymer in powder form
Transparent resin,colored or tinted
Transmit light into the uv range to wavelenght of
0.25mcm
Hard resin-18-20khn
Tensile strength 8,500psi or 60Mpa
Modulous of elasticity:3,50,000psi or 2.4Gpa
Sp.gravity 1.19g/cm

Stable resin which will not discolor in uv light and
exhibit remarkable ageing prop
Chemically stable to heat,softens at 125c can be
molded as a thermoplastic material
Depolimerizes above 125-200c,at 450c 90%
depolymerization
Exhibit tendency to imbibe water.its non crystalline
structure posses a high internal energy.thus
molecular diffusion can occur in the resin bcz less
actvn energy reqd.
Greater the ml wt less the sorption
Sorption high in the 1st week,is reversible
Soluble in org solvents;chloroform,acetone
Adv:eas in processing,polymerizes readily under conditions
of use

COPOLYMERIZATION

Composition of acrylic resin(heat cure)
Monomer:pure methyl methacrylate
hydroquinone(.006%)-inhibitor
Polymer:polymethyl methacrylate
Ethylacrylate(co polymer)-increases the
solubility of the polymer in monomer
dibutyl phthalate-8-10%-plasticizer
initiator-BPO
pigments
cross linking agent-glycol dimethacrylate

Principal Ingredients of Acrylic Resins:
Powder and Liquid
Powder
Liquid
Poly (methyl methacrylate) and other co-
polymers (5%)
Initiator (benzoyl peroxide)
Pigments
Dyes
Opacifiers (Zn/Ti oxide)
Plasticizer (dibutyl phthalate)
Dyed organic fibers
Inorganic particles (glass fibres or beads)

Monomer (methyl methacrylate)
Inhibitor (hydroquinone)
Accelerator
Plasticizer (dibutyl phthalate)
Cross-linking agent (glycol
dimethacrylate)

Storage:tumble the powder in the container to restore uniform
distribution of the different particle sizes.
liquid kept in tightly sealed container to guard against
evaporation of the most volatile ingredient
Seperating media:tin foil,cellulose lacquer,sol of alginate
compounds,sodium silicate,starches
water sol alginates most popular-forming insoluble calcium
alginate film on gypsum
Polymer:monomer::3:1 by volume;2:1 by
weight

Monomer-polymer reaction
4 stages:
Stage1:wet sandy stage:polymer settles down
into monomer & incoherent mass formed
Stage2:sticky stage:monomer attacks the
polymer
stringiness if touched

Stage3:dough or gel stage
as polymer becomes saturated with the
monomer it gives dough like
consistency,doesn’t stick to jar walls
Stage4:rubbery stage
monomer disappears by more penetration into
the polymer,the mass more cohesive,rubber
like,cant be molded

Dough forming time:
The time required to reach stage3
Depends on the solubility of the polymer pearls in
monomer
Factors affecting:
Increase temp but not above 55c
Size of the polymer particles;smaller the particles
,faster the reaction,short DFT
ADA no.12 <40mt,but most reach with in 10mt
Working time:
Time elapsed b/t stage 2 & beginning of stage4.
Time during which material is in dough form
ADA no.12 dough should be moldable for 5mt min
Decreased temp longer working time

Curing procedure:
Packing:in dough stage acrylic introduced
30-60mt of bench curing- to allow equilibriation of
pressure
Polymerisation:the BPO in acrylic when heated
above 60c decomposes to give free radicals.
Curing cycle:denture flask placed immedeately in
water at 65c allowed to remain for 90mt to polymerize
thick areas without porosity,then boiled for 60mts to
cure the thin palate areas. OR 74c for 9hrs
Bench cooling :30mts,then cold tap water 15mts
ideally overnight
to reduce warpage
Deflask carefully

INJECTION MOLDING TECHNIQUE
It requires special equipment. The mold space is filled by
injecting the resin under pressure. A sprue hole and a vent
hole are formed in the gypsum mold. The soft resin is
contained in the injector and is forced into the mold space as
needed. It is kept under pressure until it has hardened. No trial
closure is required with this technique. There is no difference
in accuracy or physical properties as compared to
compression molding technique.
Advantages of this technique are
good dimensional accuracy,
low free monomer content
good impact strength.
Disadvantages are
high cost of the equipment, difficult mold design problems, less
craze resistance, less creep resistance and requirement of
special flask.

Other sources of heat
(1) Steam
(2) Dry air oven
(3) Dry heat (electrical)
(4) Infrared heating
(5) Induction or dielectric heating
(6) Microwave radiation
Microwave energy can be used for the polymerization of acrylic
resin. Microwaves are used to generate heat inside the resin by
a generator called magnetron.
Advantage:
Faster than heat cure technique
Less prone to porosity
Initiator used is benzoyl peroxide

Chemically cured acrylics
Self curing or auto polymerizing or cold curing
Instead of using heat to activate BPO, a
tertiary amine(chemical activation),NN-
dimethyl para toludine added to monomer
before mixing
Toludine conc-0.75%,BPO 2%
Smaller the particle size more rapid is the
polymerization

Heat cure vs cold cure
Degree of polymerization is less than heat
cured,inferior properties
Color stability poorer bcz of tertiary amine
oxidation,minimized by adding stabilizing
agent
For repair cold cure used as heat cure warps
Better initial fit,as curing at room temp

Mixing techniques for self cure resins
(a) Salt and pepper method
(b) Knead – on method
(c) Compression molding technique
(d) Injection molding technique
(e) Fluid resin technique

Salt and pepper method (sprinkle on
technique)
After application of separating media the
polymer is uniformly sprinkled over the cast.
Then the monomer is introduced form a
dropper so that no excess monomer is
splashed over the powder. This process is
continued until the entire powder reacts with
the liquid to form the
acrylic resin with the metallic components
incorporated in the resin
mass for retention. Soon after acrylization the
acrylic resin is immersed in a bowl of water to
prevent monomer evaporation and thus
preventing granular porosity.

Knead - on Method
The powder and the liquid are mixed and
when dough stage is reached the mix is
molded on to the surface of the cast and
shaped accordingly.
 Disadvantages:
(1) Fit of the base to the cast is not as
good as that obtained with salt and pepper
method.
(2) The finger of the operator should be
protected as it comes into more contact with
the monomer.

Fluid resin technique (pour-type acrylic
resins)
The chemical composition of this type of resins is
the same as that of polymethyl methacrylate resins.
The principal difference is that the pour-type of
denture resins have high molecular weight powder
particles that are much smaller and when they are
mixed with monomer, the resulting mix is very fluid.
They are used with significantly lower powder-liquid
ratio, i.e. it ranges from 2:1 to 2.5:1.
Agar hydrocolloid is used for the mold
preparation in place of usual gypsum. The fluid mix is
quickly poured into the mold and allowed to
polymerize under pressure at 0.14 M Pa.

The advantages:
better tissue fit
fewer open bites
less fracture of porcelain teeth during deflasking
reduced material cost and simple laboratory
procedure.
The disadvantages:
air inclusion (bubbles)
shifting of teeth during processing, closed bites
(infraocclusion)
occlusal imbalance due to shifting of teeth,
incomplete flow of the material over neck of anteriorwww.indiandentalacademy.com

Some acrylic resins instead of the amine
peroxide system utilize the sulfonate or
sulfinic acid system for polymerization. The
colour stability has improved over the amine
peroxide system. The sulfinic acid and its
salts are unstable in the presence of
moisture.

LIGHT ACTIVATED DENTURE BASE RESINS
Douglas etal
. The first light activated system utilized u.v. light to
initiate free radicals.
Subsequently visible light activating systems were
developed with a greatly improved ability to
polymerize thicker increments. They have totally
displaced the u.v. light systems.
It consists of a urethane dimethacrylate matrix
acrylic copolymer, microfine silica fillers, and a
camphoroquinone- amine photo-initiator system.

The amine accelerator used is DEAEMA (Diethyl-
amino-ethyl methacrylate) at a concentration
of about 0.15% or less.
It is supplied in premixed sheets having clay
like consistency. It is provided in opaque light
tight packages to avoid premature
polymerization.
with blue light of 400 – 500 nm from high
intensity quartz halogen bulbs.

PHYSICAL PROPERTIES OF ACRYLIC
(a) Strength
The strength of the acrylic resin denture base
materials may fluctuate considerably depending on:
the composition of the resin.
the technique of processing.
the subsequent environment of the denture.
The lower the degree of polymerization of a given
solid polymer the lower will be its strength.

The stress properties of the resin are generally
measured by means of a transverse test described by the ADA
sp no. 12 Transverse strength is a combination of tensile
strength and compressive strength.
strength varies from 78 to 92 MPa.
Owing to the lower degree of polymerization, the
maximal strength and stiffness of the self cure resins
are lower than that of the heat cured type.
The mean flexural modulus for heat cured resin
is 2500 MPa and that for self cured resin is about
2200 MPa.

The modulus of elasticity, the proportional
limit and tensile strength of heat cure acrylic
resin is about 2350 Mpa, 27 Mpa, 52 Mpa,
respectively.
The properties of the resin are reduced by the
heat generated from polishing with abrasive
and polishing agents. The excess heat
generated may cause partial
depolymerization with resulting decrease in
strength and rigidity.
.

The bulkier portion of the denture
may show greater strength than the
thinner portion because of more degree
of polymerization.

(b) Impact strength
It is a measure of the energy absorbed by a
material when it is broken by sudden blow.
The plasticizing ingredients may increase the impact
strength of acrylic resin but they decrease the
hardness, proportional limit, elastic modulus and
compressive strength.
The charpy impact strength of heat cured acrylic
resin is 0.98-1.27 joules and that of self cured resin is
0.78 joules. The Hounsfield impact strength of heat
cured acrylic is 455 Nmx10-4

(c) Hardness
The knoop hardness no
- for self cure resin is approximately 16-18
-for a resin cured under heat may be as high as 20.
-The low hardness no. of acrylic resin indicates that
these materials may be scratched easily and
abraded.
(d)Modulus of elasticity
They have sufficient stiffness (2400 MPa) for
use in complete and partial dentures. Self cured
acrylic resins have slightly lower values.

(e) Abrasion Resistance
This has been evaluated by abrading
specimens against 600 grit silicon carbide
paper for 1 hour under a stress of 0.76 MPa
in water at 37 c and measuring loss of
material. For Heat cure it is 530 mmx10-3 and
self cure it is 611mmx 10-3.
(f) Density: The acrylic resin has densities
ranging from 1.16 to 1.36g/cc.

(g) Polymerization shrinkage
When methyl methacrylate monomer is polymerized
the density changes from 0.94 gm/cm2 to 1.19
gm/cm3. This change in density results in a
volumetric shrinkage of 21% usually called
polymerization shrinkage. But this shrinkage is
distributed uniformly throughout the surfaces so that
the fit of the denture to the tissues is not seriously
affected.
Another shrinkage called linear shrinkage varies from
0.2% to 0.69% for acrylic resins heat cure.

The processing shrinkage has been measured
as 0.53% for heat cured acrylic resin as
compared with only 0.26% for a self cured
resin.
The fit of the acrylic resin produced from heat
cure resin is lower than that of self cure
resin.

(h) Porosity
There are a number of causes of porosity
that can occur during the processing of the
acrylic resin.
If the porosity appears on the surface of the
resin cleansing will be difficult.
If the porosity is internal the cured resin will
be weakened.
More over such area of internal pore or bleb
is an area of stress concentration; the resin
may warp as the stresses relax.

Internal porosity of the resin occurs as a
result of the vaporization of the monomer or of the
low molecular weight polymers when the temperature
of the resin increases above the boiling point of the
monomer (100.8º C).
It is confined to the thick portions of the denture base
and it may not occur uniformly.
It can be avoided by curing dentures with excessive
thickness using long , low temperature curing cycle.

Second type of porosity (external porosity)
is due a lack of homogeneity in the dough at
the time of the polymerization.
It is seen that some regions will contain more
monomer than other and these regions will
shrink more during polymerization than the
adjacent regions & such a localised shrinkage
will lead to void formtn.

It is avoided by using
(a) Proper P:L ratio
(b) Favorable mixing procedures
(c) Pack during the dough stage
External porosity can also occur due to lack of
adequate pressure during polymerization
by a definite lack of dough or gel at the time of
final closure. It is avoided by using the
required amount of dough.

(i) Water absorption
Poly methyl methacrylate absorbs water
slowly over a period of time.
The absorption is undoubtedly due to the
polar properties of the resin molecules.
The diffusion coefficient of a heat cured
denture acrylic resin is 1.08 to 10-12 m2/sec at
35 C ,when the temperature drops to 23 c it
is reduced by one half.
For self curing resin D is 2.34 x 10-12 m2/sec.

The diffusion presumably occurs
between the macro molecules which are
forced slightly apart.
For each 1% increase in the weight due
to the water absorbed the acrylic resin
expands linearly 0.23%.

The water sorption of acrylic can be
measured by -an increase in the weight of the
resin per unit of surface area exposed to the
water.
According to ADA sp. No. 12 a disc of
material with specified dimensions is
prepared,the disk is first dried to constant
weight and then it is stored in water for seven
days. According to the specification the gain
in weight by the resin during this treatment
must not be greater than 0.8mg/cm2.

(j) Solubility
The acrylic resins are soluble in many
solvents but they are virtually insoluble in
most fluids with which they will come in
contact in the oral cavity.
They are soluble in ketones, esters, and
aromatic and chlorinated hydrocarbons
eg:chloroform and acetone.
Alcohol cause crazing in some resins.

(k) Creep:
Acrylic resins are viscoelastic when they are
subjected to a constant load so that strain can
be observed as a function of time
they show primary and secondary creep.
Creep rate increases with increase in
temperature, stress, residual monomer,
plasticizers and cross linking agents.
The creep rate for self cure resins is more
than heat cure resins.

(l) Colour stability
The colour stability is usually tested by
exposure to u.v. light.
The colour stability of heat cure acrylic resin
is more when compared to self cure acrylic
resin.
According ADA sp. No. 12 when a specimen
is exposed for 24 hours to an u.v. light source
shall not show more than a slight change in
colour when compared with an original
specimen.

(m) Dimensional stability and accuracy
The dimensional stability of the resin during
processing and in service is important in the
fit of the denture and the satisfaction of the
patient.
If the denture is properly processed the
original fit and dimensional stability of the
various denture base plastics is good.
However excess heat generated during
finishing can easily distort a denture base by
releasing residual stresses.

(n) Processing stresses
Whenever a natural dimensional change is
inhibited the structure involved will be
stressed with the result that a distortion or
warpage may occur if such stresses are
relaxed.
During polymerization shrinkage tensile
stresses are actually induced in acrylic resin.
The total dimensional change that occurs in a
typical resin denture during processing and in
service is in the range of only 0.1 to 0.2 mm.

(o) Crazing
after processing, relaxation of surface stresses may
result in the formation of cracks or crazing.
Crazing of the resin actually consists of small cracks
that may vary in size from microscopic dimensions to
a size that is readily visible.
Crazing may occur under mechanical stress or as a
result of an attack by a solvent.
Crazing occurs only when a tensile stress is present.
The cracks appear at right angles to the direction of
the tensile stress.
.

The modern concept is that crazing is an
actual mechanical separation of the polymer
chains or groups of chains under tensile stress.
Crazing can be avoided by using cross linked
acrylics, tin foil separating medium and metal molds.

Stability to heat
Polymethyl methacrylate is chemically
stable to heat.
It softens at 125ºC. However above this
temperature it begins to depolymerize.
At 450º C, 90 % of the polymer will
depolymerize to monomer.

(q) Thermal conductivity
Acrylic resins are poor thermal and electrical
conductors.
The coefficient of thermal conductivity for
acrylic resin is 5.7x10-4 compared to 1.3x10-3
for dentin.
Low thermal conductivity results in plastic
resin bases serving as an insulator between
the oral tissues and hot or cold materials
placed in the mouth.

(r) Coefficient of thermal expansion
They have high co-efficient of thermal
expansion of the range of 81x10-6 when
compared to tooth having only 11.4 x 10-6
. Thermal expansion is important for the fit of
the acrylic bases–
an acrylic base that fits a cast accurately at
room temperature will not fit the same at
mouth temperature.

(s) Toxicology
There is no indication that these dental resins could
produce any systemic effects upon the patient.
The quantity of methyl methacrylate monomer that
might enter the circulation by passing through the
oral mucosa would be extremely low.
The half life of methyl methacrylate in blood at 37 c is
said to range between 20-40 minutes.
Clearance being by hydrolysis to methacryclic acid.

(t)Tissue compatibility and allergic
reactions
Possible allergic reactions to poly methyl
methacrylate have been postulated.
Chemical irritation can occur either from the
polymer, the residual monomer, the benzoyl
peroxide, the Hydroquinone, the pigment or
some reaction product.
One such product is formaldehyde. Self cure
resins release more formaldehyde than heat
cure acrylics. Increasing polymer monomer
ratio will reduce formaldehyde release.

The residual monomer content of0.5%
is the component singled out as an irritant. But
it is found that the free monomer of the
surface of the denture is leached out within
17 hours. The remainder of the monomer is
not readily extracted even if so it washes
away very rapidly.
So if residual monomer were the cause its
effect is expected to appear rapidly. But most
of the cases reported occur after months or
years. Careful clinical evaluation revealed
that either unhygienic conditions under the
denture or ill fitting denture that is
traumatizing the tissue are the causative
factors.

A true allergy to acrylic resin can be carried
out by a patch test.
The residual monomer can be reduced by
processing heat cured acrylic for 7 hours at
70 c followed by boiling for 1 hour.
Direct contact of the monomer over a
continuing period can cause dermatitis. So
dentist or dental technicians should refrain
from handling the acrylic resin dough with the
hands.

Inhalation of the monomer vapor can produce
toxic reaction. So use of the monomer should
be restricted to well ventilated areas.
The plasticizer phthalates can produce
dermatitis

Growth of Candida albicans on the surfaces
of acrylic resin is a concern for patients. This
can be avoided by treating with nystatin or
chlorhexidine gluconate.
In addition to Candida other microorganisms
such as streptococcus oralis, Bacteriodes
gingivalis, Bacteriodes intermedius and
streptococcus sanguis also adhere to acrylic
resin bases especially on rough surfaces

BARDAY S.C and FORSYTH. A
published a case report on BDJ 1999
October in which they have seen that
the colouring agents added to acrylic
resin can cause hypersensitivity
reactions.

Infection control
Care should be taken to prevent cross
contamination between patients and dental
personnel.
They should be disinfected after
constructed,after adjustments and before
leaving the clinic.
Appliances can be sprayed before they leave
the operatory. Ethylene oxide gas is a
suitable method for sterilization. Other
materials such as glutaraldehyde 2% and 5%
phenol can also be used. As these materials
absorb liquids their use is not widely
recommended.

SHENEE and JAVID conducted a study to
find out the effect of disinfectants on acrylic
resins and they concluded that
Glutaraldehyde does not affect the flexural
strength and surface morphology of acrylic
resins.
But if acrylic resins were immersed in
phenolic compounds for more than 12 hours
pitting on the surface of acrylic resin may
occur.

In an another study conducted by
Watkinson A.C which appeared on
J. PROST DENT 1992 July he found
that transverse strength of acrylic resin
is affected by alcohol based
disinfectants.

Acrylic Resin Cleansers
The most common cleansers used are the
immersion type which includes, alkaline
compounds, detergents flavouring agents,
and sodium per borate.
Sodium hypochlorite can effectively remove
certain type of stains. But they are not
preferred to use with metals.
Tooth brush has very little effect on the
surface of the resin. Salt, soap, soda and
most common dentifrices can also be used.
But their prolonged use may affect the fit and
makes the surface rough which is difficult to
maintain clean.

Property Poly(methyl
methacrylates)
Density (g/cc)
Polymerization shrinkage
(% by volume)
Dimensional stability
Water sorption (mg/cm2; ADA Test)
Water solubility (mg/cm2)
Resistance to weak acids
Resistance to weak bases
Effect of organic solvents
Processing ease
Adhesion to metal and porcelain
Adhesion to acrylics
Colorability
Color stability
Taste or odor
Tissue compatibility
Shelf life
1.16-1.18
6
Good
0.69
0.02
Good
Good
Soluble in ketones, esters,
and aromatic and chlorinated
hydrocarbons
Good
Poor
Good
Good
Yellows very slightly
None
Good
Powder and liquid, good;
gel, fair

USES IN ORTHODONTICS
Chemically activated acrylic resins are mainly used in
orthodontics. The accuracy of fit and convenience of
molding without the necessity of flasking make this
material is useful to the specialty of orthodontics.
For the construction of removable and
functional appliances.
For making impression trays.
For the fabrication of occlusal splints
temporary space maintainers
For the fabrication of extraoral chin caps.
Bonding materials
In Stereolithography

Acrylics for bonding
Acrylic resins were the first material to be
used as orthodontic adhesive. The acrylic
resins used for bonding can be classified as:
(a) Acrylic based systems – PMMA systems
(b) Diacrylate systems – BISGMA systems

The Acrylic resins are (e.g., Orthomite, Genie) are
based on self curing acrylics and consists of methyl
methacrylate monomer and ultra fine powder. This
was introduced into orthodontics by Miura et al in
1970 when he described an acrylic resin orthomite
using a modified trialkyl borane catalyst that proved
to be particularly successful for bonding plastic
brackets and for enhanced adhesion in the presence
of moisture.
Acrylic resins possess good flow and wettability
but lack sufficient bond strength. High degree of
polymerization shrinkage and great difference in
linear coefficient of thermal expansion between tooth
and resin further affect bond strength.

Most diacrylate resins are based on the
acrylic modified BISGMA or Bowen’s resin.
A fundamental difference is that the resins of
the acrylic system form linear polymers only
those of the diacrylate system can be
polymerized by cross linking into a 3-D
network.

The diacrylate resins have the best physical
properties and are the strongest adhesives for metal
brackets.
Buzzitta et al found that a highly filled diacrylate
resins with large filler particles gave the highest
values of in vitro bond strength for metal brackets.
The clinical implication is that adhesives with large
particle fillers are recommended for extra bond
strength but careful removal of the excess is
mandatory because such adhesives accumulate
plaque more easily.

Diacrylate resins do not bond with plastic
brackets. Either an acrylic monomer as a
primer to enhance bonding between the
diacrylate resin and the polycarbonate
bracket is necessary or an acrylic resin
adhesive must be used.
Acrylic or combination resins have been most
successful with plastic brackets.

Other alternatives to chemically
autopolymerizing paste-paste systems.:
No-mix adhesives: These materials set (e.g.,
Rely a bond) when paste under light
pressure is brought together with a primer
fluid on the etched enamel or bracket backing
or when another paste on the tooth is to be
bonded. Curing occurs within 30 - 60
seconds.

Visible light polymerized adhesives
These materials (e.g., Transbond) may be
cured by transmitting light through tooth
structure and ceramic brackets.
Light activated resins are now preferred in
some cases because of the ease of
processing and elimination of methyl
methacrylate monomers.

Stereolithography
This technology uses a laser to cross link
specific areas as a pool of acrylic is being
filled.
Polymerization occurs only in the areas the
laser activates.
This technology has been used to produce
copies of dental models and models of
craniofacial complex to visualize and plan
difficult surgeries.

Newer advances in acrylic Resin
(1) High impact strength materials
These materials are butadiene-styrene rubber
– reinforced poly methyl methacrylate.
The rubber particles are grafted to methyl
methacrylate so that they will bond to the heat
polymerized acrylic matrix. These materials
are supplied in a powder – liquid form and are
processed in the same way as other heat-
accelerated methyl methacrylate materials.

Indicated for patients who drop their
dentures repeatedly, e.g. senility,
parkinsonism

(2) Vacuum adapted plates
A quick and easy method of making a usable
base plate is to vaccum mold a sheet of
thermoplastic resin (eg: acrylic,
polycarbonate, polyvinyl acetate
thickness control and good adaption to the
cast particularly when using thinner sheets.
More intimate adaptation is obtained
compared to manual adaptation.

(3) Rapid heat polymerized Resin
These are hybrid acrylics that are
polymerized in boiling water immediately after
being packed into the flask.
After being placed in boiling water, the water
is brought back to full boil for 20 min. (reverse
cure). After the usual bench cooling to room
temperature the denture is deflasked.
The initiation is formulated from both
chemical and heat activated initiators to allow
rapid polymerization without porosity.

(4) Carbon Fiber and polyaramid reinforcement of
acrylic resins
Early experiments with glass fiber have resulted in
failure because of the irritant nature of the fibers
.Carbon fibers have no such irritancy and greatly
increased impact strength and flexural stiffness of the
denture base.
But the black colour of carbon fiber and the potential
toxicity at coupling agents silane 174 prevent their
use for reinforcement of acrylic resins. Their use is
restricted only to lingual aspects of denture.
Eg: Polyethylene, Graphite

Polyaramid or Kevlar fibres (poly p Phenylene
terephthalmide) have stiffness of 90 GPa
straw coloured and greatly enhance the
mechanical properties of the denture.
They do not require treatment with coupling
agent. Their soft yellow colour is masked by
the pink resin.

ACRYLIC RESIN introduced into Dentistry about
70 years back. After its introduction into dentistry
it has revolutionized the way we are practicing
Dentistry. Many new materials were introduced
into Dental profession after that like epoxy resin,
poly styrene and poly urethane etc. to name a few
. It has some disadvantages in the form of water
absorption, low abrasion resistance low colour
stability etc. But it still remains as one of the main
stay materials used in dentistry for making bases,
removable appliances, obturators crown and
bridge material etc.

Bonding adhesive
Ideal requirement
1.nontoxic
2.polymerize at or near body temperature with
minimal shrinkage
3.minimal expansion & water sorption
4.produce lasting bond

5.strong-resist masticatory forces and
forces applied during orthodontic
treatment
6.Strain resistant
7.easy to use ,less time consuming
8.sufficient working time

9.no additional equipment
10.option of bonding directly or indirectly
11.easy correction of shy spot
12.easy replacement of base bond

Types/classification
A.based on the bonding system type:
acrylic base system-
poly methyl methacrylate
diacrylate system-
bis-gma system
glass inomer systems-chemical cure
light cure
dual cure

Based on flouride content:
Flouride realising system
Non flouride releasing systems

Based on curing system:
Self curing system
Light curing system
Dual curing system

Based on the filler content:
Lowly filled bonding systems
Highly filled bonding systems

Composites
Mixture of 2 or more components
Hard inorganic filler particle
+
Soft organic dimethacrylate polymer
Bone a natural composite

Dr.Raphel Bowen:1960
Have the following major components:
organic resin matrix
inorganic filler
coupling agent
initiator-accelerator system
pigments

Composition & strct
Resin matrix
Composed of mainly monomers & comonomer
Monomers of mol wt 100-1000g/mol
bis-GMA & UDEMA common monomers
TEGDMA- comonomer,diluent to control viscosity
C=C functional grp(difunctional monomer)

Polymerization activated by
chemical,light,dual cure
Bis-GMA molecule:
2 reactive C=C grps
crosslinking strength
-OH grps cross linking

Properties of bis-GMA:
Higher mol wtg than MMA
polymerization shrinkage
High mol wtg viscosity
TEGDMA,EDMA,MMA viscosity

TEGDMA= DILUENTS
Viscosity
So delicate balance maintained

Clinical significance:
High conc of acrylate/MA grps remain
unreacted after setting as:
1.large size
2.rapid increase in viscosity
during setting

Benificial properties contributed by the resin:
1.molded at ambient temperature
2.sets by polymerization in short time
Drawbacks of matrix:
Weakest phase
Least wear resistant
Water sorption
Stain,discolor

Disadvantages of resins without filler:
Low MOE Flexibility marginal
breakdown
Low compressive strength & hardness
poor durability
Setting contarction 6% by vol
wear resistance
High COTE marginal breakdown

Biological properties
Residual monomer MMA-irritant to pulp
Temperature rise –exothermic setting

Filler:
Inorganic content(ceramic)
Advantages:
COTE closer to that of tooth
Water absorption
Abrasion resistance
Mech. Prop.-tensile st.compressive
st,MOE,rigidity,hardness

Uses:
Quartz filler:natural,inert(chemically
stable),strong,hardness
difficult polish
abrasion of opposite tooth

Glass –fine sized particles
-barium,lithium aluminium silicate
-borosilicate glasses,strontium,zinc
glasses
Colloidal silica particles:
in microfine composites

Physical properties of the composite depend
on the filler quantity.maximum amt of filler
incorporated by:
1.selecting filler particles of different sizes
2.irregular shaped particles(less dislodge)
3.filler with large surface area
eg:colloidal silica
But viscosity so small amt added
4.limit to the filler added,all filler should be
wetted by monomer,else voids stress conc.

Type
Concentration
Particle size
Particle size distribution
-of the filler decide the properties
of composite
Trend of filler particle selection from strongest
to softer

Coupling agent:
To improve properties filler(inorg. Phase)
should be bonded to resin matrix(organic
phase)
This bond achieved by a silane coupling
agent-methacryloxypropyl trimethoxysilane

Functions of coupling agent:
1. To physical,mechanical prop.
2. To retention of filler particles
abrasion resistance
3. Stress distribution under function
4. Prevents water penetration b/t resin matrix
& filler

Mode of action of the coupling agent:
Silane molecule has reactive grps at
both ends
Reacts with the resin matrix at one end
ceramic filler at the other end

SCOTHBOND
Coupling agent that is not a silane
Composed of halophosphorus ester of bis-
GMA,TEGDMA,benzoyl peroxide and an aryl
sulfinate salt
Long chain of molecules- one end bond to
tooth ,other to resin
Shear bond strength of etched enamel
by 86%

Initiator & activator:
1.chemical cure-amine+BPO R*
BPO-initiator
tertiary amine-activator
2.visible light cure:
photoinitiator+activator
campharoquinone+amine
(0.2-1%)
3.inhibitors:hydroquinone(0.1%)

Pigments----for shades
Uv light absorber---to minimize color
change by oxidation

Classification of
composites
Based on ADA specification no.27
Based on filler
Based on the method of polymerization

1.As per the ADA specification no.27
classified into 2 types and 3 classes:
type 1-polymer based materials
suitable for restoration involving
occlusal surface
type 2-other polymer based materials

3 classes:
class1 - self cure materials
class 2 – light cure material
class 3 – dual cure material

Classifacation based on fillers:
Macrofilled composite
Microfilled composite
Small particle composite
Hybrid composite

A.Macrofilled( traditional) composites:
first type of dental composite(1960)
quartz /glass filler(10-50um)
60-80% by weight
Since fillers are denser than the resin
phase,the vol % is 10-15% lower than
weight%

Disadvantages:
1. Polishability
2. Poor surface finish(dull appearance)
3. Rough finish-plaque retention
4. Staining
Precaution-mix of chemical cure-no metal
spatula

Uses:
1. Some orthodontists still prefer,as
rough feel allows easy detection after
debonding
2. Class lll,lV
3. Class v
4. Limited in class l & ll (wear)

Microfilled resins(late 1970s):
Enhanced polishability & esthetics over
traditional composites
Submicron particles(colloidal silica)-
0.03-0.5um
20-50 wt%
35-60 vol%

Limitation:
Small particle size high surface
area(100-300m²/g) so not possible to
incorporate very high filler loading
detrimental effect on strength &
stiffness

Advantage:
Smooth,lustrous surface finish
Disadvantage:
High resin content COTE
High resin content strength

Uses of microfilled composites:
1. Where esthetics is dominant concern
2. Class lV
3. Veneers,to add translucency to core
buildup
4. Class V

SMALL PARTICLE COPMOSITES:
1980s
Filler size:avg-1-5um(range;0.5-10um)
80-85 wt%
60-77 vol%
Advantage:
Best physical properties
Surface is not rough as macro filled but not as
smooth as microfilled
Uses:
Classl, class ll

Hybrid or blend composites(late1980s):
Esthetics + durability
Blend of conventional glass & quartz
particles(75%)(1-50u)
+
submicron silica(8%)(0.04u)
Advantage:
Strong
Polishable
Use:
Small- medium class l, ll
Class lll,lV

Method of activation
A.Chemical cure
Tertiary amine(0.5%)+BPO(1%)
Early self cures –2pastes
Short working time:inhibitor destroys R* for a
short period of time
Other systems:
Paste/paste system
Powder/liquid system-powder containing filler
&peroxide initiator,liq containg
monomer,activator
Paste/liquid system,encapsulated materials

Disadvantage:
air entrapment during mixing
Limited working time
Setting characteristics:
Begins immedeately after mixing
Gradual in viscosity
Setting time 3-5mt
Rate of setting uniform through out the
material thickness

Material should not be disrupted once
the initial setting period start /working
time is over
disrupts polymerization
Desirable to place plastic matix strips
during cure to prevent o2 inhibition

Light cured composites
visible light cure
uv light (blue light cure)
Supplied as a sinlge paste
Contain monomer,comonomers,filler,initiator
which is unstable in presence of uv/visible light
of high intensity

Uv light cure:
360-400nm wavelength
Initiator-benzoyl methyl ether
Advantage:
Unlimited working time
Set on comand
Disadvantage:
Retinal damage,unpigmented oral tissue
Limited depth of cure
Intensity of the uv light cure system with
time

Visible light cure:
400-500nm;greatest intensity arnd 480nm
Initiator system=diketone+amine
(campharoquinone)
Advantage:
1. No chair side mix,so no air entrapment
2. Paste is thicker with more filler ,less matrix
so stronger than CC
3. Working time under dentist control
4. Intensity of VL remains same over time
5. Safe for operator

Setting characteristics:
75% of polymerization takes place in 1st 10mt
,though curing continues for >24hr
Longer working time
Very little in viscosity before exposure to
light
High rate of polymerization
Command setting:10-40sec exposure
Setting first achieved in the surface layer
where light intensity greatest

Depth of cure-2-3mm(VLC)
1.5-2mm(UVLC)
Factors affecting depth of cure:
1. Type of composite:
with darker shade penetration
Microfilled composites-longer
exposure time(smaller & more numerous
filler particles ,scatter more light than hybrid
composite with larger & fewer glass
particles)

2.Quanlity of light source:
480 nm
check quality at regular intervals
3.Method used:
Distance:light intensity on unit surface area
drops off with the inverse square of the
distance b/t light source & resin
distance kept minimum.
light tip should not be contaminated with
composites
Exposure time(20-60s) recommended
Light conducting wedges & transperent
matrices(MOD) restoration

Avoid curing to >2mm fundamental
rule
Cure for atleast 40sec
Compatibility of light source:
Polymerization reaction of composite materials
in exothermic in nature
Pulpal damage
Rise in temp for VLC>CC

1.heat of polymerization in VLC is liberated over a
small period of time
2.heating effect of the light activation unit.
To reduce the effect of light cure units, filters are
added which remove the hotter parts (red part of the
spectrum), so the light appears blue

Light safety & protection:
1. avoid unnecessary exposure
2. Avoid direct exposure,don’t look direct
3. Use protective eye wear

Light curing units:
2 types presently:
Quartz-tungsten-halogen light
Plasma arc lights
Quartz tungsten halogen light:
Peak wavelenght-450-490nm
Intensity not uniform for all area of the light tip
Intensity with distance from light source
Intensity with continuous use
Avg life span-50-100hr

Most units have light source & intraroal tip
together & are held by a gun type device with
a trigger.separate power source attached to
gun by an electrical cord.
large amt of heat generated from the bulb
during use.for cooling a fan in mounted within
the gun.
when the bulb overheats, the unit will shut
down & be inoperable till bulb cools.

Plasma arc lights:
High intensity curing units 380-
500nm,480nm(peak)
Light obtained from the electrically conducive
gas filled b/t the tungsten electrodes.
Advantages:
Reduces exposure 10sec
Saves time of curing
Disadvantge:
polymerization shrinkage
expensive

Disadvantage:
Requires special equipment
Precaution:
Storage of material away from sunlight
Lid replaced immediately

Superiority of VLC over UVLC
Faster cure
Greater depth of cure
Cures through tooth structure and into
undercuts
No warm up time needed
Energy output reasonable constant until
bulb burnout
Light bulb is rel. inexpensive & simple to
replace
Safety appears to be less of an issue

Difference b/t CC & LC
Light cured
Polymerization is
always at the
surface close to the
light source
Less wastage of
material
Curing is done in
increments
Chemical cured
Polymerization is
uniform
More wastage
Curing in one phase

Finish always better
Strength is higher
Command sets
Working time is more
No mixing required
More color stable
More resistant to wear
Finish poor
Strength lower
Sets within 1mt
Working time is less
mixing is required
Less color stable
Less resistant to
wear

New composites
Flowable composites:
1. For cervical lesions,pediatric use
2. <45% filler by vol
3. Low viscosity
4. Easily displaced froma very smalll gauge
needle into the cavity directly
Advantge:
1. Easy dispensing
Disadvantage:weak, wear resistance,low
MOE,high polymerization shrinkage

CONDENSABLE COMPOSITE:
Filler % similar to hybrid composite
Heavy consistency produced by using
modified fillers/altering the distribution of
particles so that it inb. the sliding of filler
particles over one another thicke ,stiffer
material
Unit dose compules
Advantage:
Easy to place in cavity
Low polymerizatiom shrinkage
Radioopacity & wear rate3.5um/yr

Properties
Physical properties
1.polymerization shrinkage:
is a direct function of the amt of resin present in
the composite
Composite setting concn-1.5%
Effects:
marginal adaptation,polymerizaton
stresses(10-15Mpa) strain the
interfacial bond,postoperative pain

Greater the diluent monomer, greater
the ploymerization shrinkage
Greater the unpolymerized
monomer,greater is the shrinkage
Higher the proportion of fillers lower is
the shrinkage

Water absorption:
Reasons:
Glass may be partially dissolved
Hydrolytic breakdown of the bond b/t filler and
resin
Incomplete cure of resin
Amt of water absorption depends on:
Resin content of composite
Quality of the bond b/t resin & composite

Effects of water absorption:
1. Detrimental on color stability
2. Discoloration by oral fluid absorption
3. Poor wear resistance
4. Decrease in surface hardness

3.solubility:
0.01-0.0mg/cm²
Increased if incomplete polymerization
Manifested clinically as color instability

4.coefficient of thermal expansion:
Has to be as close to tooth as possible
Filler has low COTE
Resin has HIGH COTE
Mismatch in COTE :
1. Marginal leakage
2. Bond strain
3. Material fatiguewww.indiandentalacademy.com

Mechanical properties
1.Compressive strength:
Higher than tensile strength
Indicates brittleness
VLC=260Mpa
CC=210Mpa
CC strength is lower because air
entrapment during mixing

Microfilled composite have comp. St
similar to conventional, but
Lower yield stg(point of irretrievable
breakdown)
Low MOE-will deform under stress

Porosity –incorporated in 2 stages:
During incorporation of filler particles
into resin
During mixing two components

Tensile strength
Composites tend to fail under tension
But measurement of t.s of brittle materails
difficult.
As the brittle materials tend to develop
internal flaws,surface cracks,t.s judged from
surface finish

Modulus of elasticity
Measure of stiffness
Microfine composites have E ¼-½ of
highly filled fine composite,so tend to
flex under stress.

4.Hardness:
Good indicator of wear resistance
hardness with filler content
+
degree of polymerization
VHN :unfilled resins-18
microfill -30
hybrid -100
KHN:22-80kg/mm²

5.Wear:
Loss of material by interfacial forces when 2
surfaces rub against eash other
Types:
Abrasive wear
Fatigue wear
Corrosion wear:
hydrolytic breakdown of the resin
Breakdown of the resin filler interface
Chemical wear-solvents in food,acids
LC . Wear resistant ,as porosity
CC2-5% porosity,polymerization inhibition

Factors affecting:
filler content
Small particle wear
polymerization
Coupling agent
Porosity
Finish with diamond burs
Posterior tooth
Wear reduced by:
High filler load
Smooth surface finish
Hydrolytically stable resin,
Strong bond b/t filler & resin

6.Radio opacity:
by adding Barium,strontium
Color stability:
Oxidation of tertiary amine

Biocompatibility
The ability of a material to elicit an
appropriate biological response in a given
application in the body.
When closely seen this def includes
interaction b/t host,material and an expected
function of the material.

2 key factors relevant when discussing
biological effect of a material:
1.Whether material releases any of its
components
2.Whether the released components have
any relevant biological effect

In practice polymerization is not complete and small
amt of starting products are released.
There is no doubt that the cured dental resin
releases components into the body.
Early test showed a short lived release(48hr)
By HPLC several week to months of release was seen.
There is a large reservoir of uncured monomer inside
the cured bulk

Dental resin releases bis-GMA,
TEG-DMA and others
Controversy regarding the estrogenicity of dental resin
started froma single article by Olea etal 1996-some
dental sealants released at a signf. Conc. In saliva
Bisphenol A was a plausible Xenoestrogen in the body
Xenoestrogen-a chemical,not indigenous to the body
that acts in the body in a manner similar to that of
estrogen.

Relevance:
Release of components a necessary factor,but
not sufficient event to cause adverse effect
Biological effect depends on form,conc.,
location
BPA is weakly estrogenic in a culture of
sensitised cells but invivo action not clear

First generation bonding adhesives
Unfilled acrylic resins & epoxy resins
1st bonding adhesives used in
orthodontics unfilled poly(methyl
methacrylate)
Powder/liquid OR paste/paste

2 types of induction mechanism:
A)benzoyl-peroxide—tertiary amine
B)sulfinate system:
p-toulene sulfinic acid(accelerator or co-
catalyst) as salts incorporated in powder.
sulfinate salts
sulfinic acid
R*

DISADVANTAGE OF UNFILLED RESINS:
Low hardness & strength
High co-efficient of thermal expansion
Lack of adhesion to tooth structure
High polymerization shrinkage
Eg:Bracket bond
Genei

EPOXY RESINS
Large no. of dental products that were epoxy
resins were developed esp
bis-GMA,an aromatic ester of a
dimethacrylate,synthesized from an epoxy
resin(ethlene glycol of bis-phenolA) & methyl
methacrylate
Disadvantages:
Lack color stability
Water absorption
Patient sensitivity

b)second generation:
Uv light activated resins
Provided greater bond strength
Used bowen’s hybrid molecule-the back
bone similar to epoxy resin,but
functional reactive grps are acrylic
Esters of alkyl benzoin to facilitate UVL
activation

Advantages:
Higher bond strength then 1st gen
Low polymerization shrinkage
Greater hardness
Low water absorption
Disadvantage:
Uv light
In indirect technique,a tray carrier neede to
position the brackets,this interfered with
access to the resin beneath the brackets &
made cleaning difficult

Third generation(filled resins)
Late (1970s)
Filled resins with high % of inert filler,2 paste
system
Improved thermal expansion property
Macrofilled(10-30um)eg:Consice
Microfilled(0.20.3um)
eg:Endure,DynaBond

COMPOSITION :
David Russel Barn etal combination of six-
stranded wire & concise will provide optimum
performance in bonded fixed retainers.1mm
thickness gives optimum strength with min.
bulk
Advantage over NO-MIX adhesives:
High bond strength
More homogeneous & perdictable mix
Short snap time-possible to ligate archwires
sooner(4 handed approach to bonding
recommended to help mix 2 paste system)

1 to 1 bonding:
2 paste self cure adhesive system
Extra small quartz particles-smooth mix,no
stick to spatula
Simple 1:1 mixing ratio of sealant paste &
bonding paste
Work time-1½mt, by cooling paste/slab

Eliminates bracket drift
Reduces decalcification due to feather edge
on the tooth surface
Recommended when close adaptation b/t
tooth surfaces & bonding pads is not
possible,in lingual bonding brackets,retainer

EXTEND-a-BOND:
Highly filled ,self polymerizing 2 pase system
Low viscosity psate,small particle fillers
Longer working time
Use:
With bondable retainers
Indirect bonding

4th generation:
No –mix adhesives(1980s)
Composite placed on the tooth surface in
unpolymerized form
Polymerization catalyst on back of brackets
Artun & zachrison-mutagenic potential of
unreacted monomer?;;arch wire cant be
engaged with min of delay
Eg:Monolok,Unite
Ching etal-static load like tying archwire can
be placed without significant In bond strg

―Right-on‖ No mix adhesives:
Most advanced self curing bonding system
available
Superior bond strength
Drift proof bracket placement
2yr shelf life without refrigeration
Adhesive paste preloaded in syringes
Thin coat of activator/sealant liq is brushed
on bracket base & prepared tooth
surface.place small amt paste on bracket
base,bracket pressed on tooth
Arch wire 7min after last bond

5th generation:
Visible light cure orthodontic adhesive
Douglas etal
Single paste system:ketone+amine
470nm λof light
TRANSBOND,HELIOSIT
Wang &Meng-VLC for metal bracket(0.75-
2.1mm) suggested cure for 40-60sec, bond
strength( cross linking)

Hugo.R.Armas Galindo etal:
Failure rates with VLC=11.3%
CC=12%
Trans Bond XT:
Leading light cured orthodontic adhesive
Instruction to cure both mesial & distal of
incisal or gingival surfaces of metal brackets
for 10sec each,total 20s
Immedeate arch wire insertion
For ceramic brackets,the light guide placed
approx. 2mm away from from the bracket
face & shine through the ceramic bracket for
10s

Greenlaw etal:
1hr bond strength of VLC system 26% of 30hr
bond strg
Enamel loss with debonding & cleanup ½ of
with CC heavy fill resin.
Helvatjoglou & colleagues:
Continued hardening progressive cross-
linking or polymerization (10mt-12 months)
Larry colleagues:
By extending setting time 5mt 20%
increase in bond strength,20-30 mt additional
7-8% additional,so wait for 5mt befor archwire
placement.40s curing time,20 for mesial, 20
for distal for Max. shear strg.

Rashid Ahmed Chamda-compared bond
strength achieved with LC bonding system &
CC over 24hr at 10mt,60mt,24hr found no
sign diff in bond strg
Advantages of TransBond XT LC ADHESIVE
Extended working time allows precise bracket
placement
Immediate bond strength,allowing immediate
archwire placement
Saves time for rebonds
Efficient bonding of ceramic & metal brackets
Excellent handling properties:
No bracket drift
Easy flash clean up

Adhesion
boosters/hydrophilic
bonding systems
Failure of orthodontic bonded
attachments & brackets is mainly due to
contamination..moisture..saliva
To overcome this
PRIMERS/COUPLING
AGENTS/DENTINE CONDITIONERS
were introduced

Primers
Hydrophilic monomers carried in a
solvent,acetone,ethanol water or water
Solvents displace the water in the dentinal
tubules and in the process pull the resin
adhesive into the dentin

Coupling agents make the dentin
surface more hydrophobic
wetting by momomer
No shrinkage of resin tags away from
the dentin

Bonding agents
1st generation
Late 1956-Buonocore-GPDM containing
resin(glycerophosphoric acid-dimethacrylate)
1965-Bowen-NPG-GMA(N-phenyl glycine) &
glycidyl methacrylate
Bifunctional molecule
i.e, one end bonds to dentin,other end bonds to
composite resin

Bonding mechanism:
chelation to Ca++ in the hydroxyapatite
Ignored the smear layer
Bond strength- 1-3Mpa
Drawbacks:
Debonding
Postopterative sensitivity
Eg:Cervident(S.S White)

2nd generation
Late 1970,early 80’s
1978 1st product-Clearfil bond system
Bonding mechanism:
surface wetting phenomenon
Ion interaction of phosphate grp & ca++
Smear layer intact

Content :
Polymerizable phosphates added to
bis-GMA resins(phosphate bonding systems)
3 types:
Phosphate ester based
Poly urethane based
Etched tubule type
Bond strength 2-8Mpa
Examples-scotch
Bond,Clearfil,Bondlite,Creation Bond,Prisma
universal bond

3rd generation(late1980)
Smear layer either modified/partially
removed
2 imp changes:
Use of dentin conditioning
Use of hydrophilic monomer
Multistep procedure

Clinical steps:
Selective etching of enamel conditioner
10%H3PO4
Dentine conditioning 2% NITRIC
EDTA,maleic
Intermediate primer application-
HEMA,4-META
Bonding agent/adhesive-unfilled/partially fill-
HEMA
bond st=8-9Mpa
Eg:Mirage Bond,Scotch Bond 2,Prima universal bond 2&4

4th generation:early1980
Transformed dentistry
total smear layer removal
Total etch concept-
Takao fusayama(1979)
(40% H3PO4 both E & D)
1991,accepted in US- KANACA-Moist
Dentine bonding-10% H3PO4

HYBRIDIZATION-replacement of HA & H2O
in the surface dentine by resin)
Resin +remaining dentine=hybrid layer
Bond strength:17-25Mpa
Also called-
total etch multi bottle adhesives
3 step etch & rinse adhesive
3 clinical steps:etching-phosphoric acid
priming-hydrophilic monomer
bonding-unfilled resin

4-META product:
ORTHOMITE SUPERBOND
4META/MMA-TBB System:
10-3 Etch-10%citric acid
3% Fe3Cl
META-MMA:
methacryloyloxyethyl trimellitate anhydride
Methylmethacrylate
TBB:tri-n-butyl borane

Bond strength:17-25Mpa
Eg:All bond2(Bisco)
Scotch Bond Multipurpose(3M)
Prime & bond

5th generation
TOTAL SMEAR LAYER REMOVAL
TOTAL ETCH CONCEPT
2 STEP system:
etching
priming+bonding

As primer + bonding adhesive together in 1
bottle=ONE BOTTLE ADHESIVES
2STEP ETCH & RINSE ADHESIVES
Rely on hybridization to achieve bond
strength
BOND STRENGTH:25-28Mpa
Window of oppurtunity for optimal
adhesiondepends on keeping the
demineralized collegen intact

Contents=PHOSHORIC ACID+PENTA
EG:One step,Single Bond(3M)

PENTA
Multifunctional phosphate based molecule
Dipentaerythrytol pente acrylate phosphoric
acid ester
Weakly acidic
Per molecule contains:
Phosphate grp-etch enamel & dentin
5 acrylate grps- reactivity,cross linking
ability

Prime & bond NT
Etchant-34% or 36%H3PO4
Primer adhesive:PENTA,UDMA
elastomeric resins
T-resis(cross linkin)
D resins(hydrophilic)
photoinitiator-
4 ethyldimethylamonibenzoate,
Silane nanofiller,acetone,butylate
hydroxytoulene,stabilizers

6th generation
One step bonding
No etch , no rinse,no cure
Self etching primer+bonding adhesive
2 types-mix(etchant & primer mixed)
no mix

2 clinical steps clubbed--- etching + priming
By the use of acidic primer(self etching
primer)these are not rinsed off
Less technique sensitive.no problem rel to
dentine wetness or dryness+depth of etching
does not exceed the depth of the primer
infiltration,no nanoleakage
Acid treatment of dentin is self limiting & the
etch by-products are incorporated into the
dental-restorative interface pemanently

Eg:
Promt-L-Pop(ESPE,Germany)
Unit dose system in blister pack
Etchant,primer,adhesive,microbrush
sealed in a triple lollipop shaped
aluminium package

Red blister-initiator,stabilizer,MA phosphate
esters
Yellow blister-stabilizer,H2O,Flouride complex
Green blister –microbrush tip

7th generation
ALL IN ONE ADHESIVE
Etchant+primer+adhesive in one solution
Also called:All in one self priming
adhesive/Single solution/Self etching
Adhesive
Xeno lll,i bond

Resin modified
glass ionomer

Hybrid materials have been developed to over
come some shortcomings in GICs:
Short working time
Long setting time,not command set
Cracking on desiccation
Poor resistance to acid attack
Low fracture toughness
Low abrasion resistance
Initial sensitivity to moisture
Low early mechanical strength

Resin modified GIC
light activated chemical cure
Advantages:
Bond to E & D
Flouride release
Prolonged working time
Command set
Improved resistance to dessication
Enhanced strength
eliminate dry field need

Composition:
Ceramic powder:ion leachable powder
70-75% by weight
organic matrix-forming molecules
Most imp changes :
Replacement of water byHEMA-water mixture
Incorporation of photoinitiator/chemical
initiator
Set by acid-base reaction and by free radical
addition polymerization which may be light or
chemically activated

Powder:fluoro aluminium silicate glass
Liquid-copolymer of acrylic acid &
nueclic acid
HEMA
Water
Campharoquinone
P/L:3:1
Fuji ortho LC

Amount of demineralization adjacent to
the bracket is reduced
Reduction in strep.mutans & lactobacilli
around the brackets

Compomer
Composite +ionomer
Anhydrous single paste
Contents:
Powder:aluminium fluorosilicate glass,
sodium flouride
chemical or light cure initiators

Liquid:polymerizable methacrylate
carboxylic acid monomer
diacrylate monomer
No water,ensures that initial setting accurs by
polymerization & this prevents premature
settign in container
Contain carboylic grp molecule,can undergo
acid-base setting reaction
Setting mainly by light

Advantages:
Excellent esthetics
Low solubility
High bond strength
High fracture toughness
Drawbacks:
Require bonding agent
Flouride release less than GI

Reliance quick cure
orthodontic paste
Light curing of metal bracket in 6 sec
Unique chemistry provides a broader area of
sensitivity to blue light for a faster & more
complete cure
Ideal viscosity,no bracket floatation,easy
cleaning,no stringing
Flouride release protection

Flouride releasing
adhesives
Flouride reservoir that does not depend on
the patient co-operation
Light cure/chemical cure
Steck etal - bond strength-flouride
incorporated in the resin phase altered the
surface tension of the liquid wetting

Flouride release:
Most of it in 1st few days /wk
with ph
Recharging
Mark.L.Underwood etal:FR2.5 ortho
adhesive:
Flouride ion –anion exchange process
instead of material dissolution,structural
integrity of resin maitained
FLOUREVER OBA-85wk;LIGHT BOND-2wk

DUAL CURE RESINS
1980S
LIGHT CURE+CHEMICAL CURE
Eg:Vivadent Thick,Viva Dent Thin
Advantage:
Reduced bonding time
20 brackets-6.5mt
Completely polymerized in 30s

Allow set by CHEMICAL CURE
Visble light cure 30s
10s VLC chemical cure:allows
proper placement of bracket

Cyanoacrylate
Smart Bond
1991-ethyl cyanoacrylate tested for
orthodontic bracket adhesive
High tensile strength
Polymerization starts only in presence
of moisture & pressure

Imp that surfaces to be bonded are close to
each other ,as material can’t flow,fill gaps
Wilner & Oliver-unsuitable for routine
orthodontic practise as bond strength
deteriorated after few wks
Used to adhere to wet surface where less
force is required for short time
eg:impacted canine

Thank you
For more details please visit

Resins in orthodon 2 /certified fixed orthodontic courses by Indian dental academy

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