restorative resins
DESCRIPTION
MY SEMINAR HARD COPYTRANSCRIPT
1
RESTORATIVE RESINS
INDEX
Aesthetic restorative materials
Composite restorative materials
Curing of resin-based composites
Classification of resin based composites
Composites for posterior restorations
Use of composite for resin veneers
Finishing of composites
Biocompatibility of composites
Repair of composites
Survival probability of composites
HISTORY
20th century-silicates only tooth-colored aesthetic material.
Acrylic resins replaced silicates in1940’s because of their aesthetics
insolubility in oral fluids low cost and ease of manipulation
Excessive thermal expansion and contraction –stresses develop
Problem solved by addition of quartz
Early composites based on PMMA not successful
A major advancement made after introduction of bis-GMA by Dr ray
l. bowen in 1950,s
COMPOSITE RESTORATIVE MATERIALS
1
2
USES:
Restoration of anterior and posterior teeth
To veneer metal crowns and bridges
To build up cores
Cementation of orthodontic brackets, maryland bridges, ceramic
crowns, inlays , onlays, laminates.
Pit and fissure sealants
Repair of chipped porcelain restorations.
TYPES:
BASED ON CURING MECHANISM
o Chemically activated
o Light activated
BASED ON SIZE OF FILLER PARTICLES
o Conventional 8-12 um
o Small particle 1-5 um
o Microfilled 0.04-0.4 um
o Hybrid 0.6-1.0 um
DENTAL COMPOSITES
2
3
They are highly crosslinked polymeric materials reinforced by
a dispersion of glass, crystalline or resin filler particles or short fibres
bound to the matrix by silane coupling agents.
Composition -
o Resin matrix
o Filler particles
o Coupling agent
An activator-initiator system required to convert resin to soft
moldable filling material to hard durable restoration.
RESIN MATRIX:
Mostly blend of aromatic/aliphatic dimethacrylate monomers such
as BISGMA,TEGDMA,UDMA.
FILLER :
Based on the type of filler particles composites are currently
classified as micro hybrid and micro filled products.
BENEFITS OF FILLERS-
(1) Reinforcement of the matrix resin, resulting in increased hardness,
strength, and decreased wear
(2) Reduction in polymerization shrinkage
(3) Reduction in thermal expansion and contraction
(4) Improved workability by increasing viscosity
(5) Reduction in water sorption, softening, and staining
3
4
(6) Increased radiopacity
Important factors with regard to fillers that determine the properties
and clinical application-
o Amount of filler added
o Size of particles and distribution
o Index of refraction
o Radiopacity
o Hardness
TYPES OF FILLERS USED:
GROUND QUARTZ
Makes restoration difficult to polish and cause abrasion of
opposing teeth and restorations.
COLLOIDAL SILICA
o Used in microfilled composite
o Thicken the resin
o Glasses of ceramic containing heavy metals
o Radiopacity
o Barium
COUPLING AGENT:
4
5
o Bond filler particles to resin.
o Allows for transfer of stresses to stiffer filler particles.
FUNCTIONS:
o Improve physical and mechanical properties.
o Prevent water from penetrating the resin-filler surface.
o 3-methoxy-propyl-trimethoxy silane most commonly used
INHIBITORS
Inhibitors are added to the resin to minimise or prevent
spontaneous or accidental polymerization of monomers
A typical inhibitor is butylated hydroxytoluene (BHT) used in
concentration of 0.01 wt%.
OPTICAL MODIFIERS
o Dental composites must have visual shading and transluscency
for a natural appearance.
o Shading is achieved by adding pigments usually metal oxide
particles
o All optical modifiers affect light transmission through a
composite.
o Darker shades and greater opacities have a decreased depth of
light curing ability.
o Titanium dioxide and aluminum oxide most commonly used.
5
6
POLYMERIZATION MECHANISM
2 TYPES
Chemically activated
Light-activated
CHEMICALLY ACTIVATED COMPOSITE SYSTEM
TWO PASTE SYSTEM
o Base paste – benzoyl peroxide initiator
o Catalyst paste– tertiary amine activator (N,N-dimethyl-p-
toludine)
LIGHT ACTIVATED COMPOSITE RESINS
o Earliest system---Uv light activated system
o Limitations
Limited penetration of light into resin
Lack of penetration through tooth structure
VISIBLE LIGHT ACTIVATED SYSTEM
SINGLE PASTE SYSTEM
o Photoinitiator – Camphoroquinone
o Amine accelerator – diethyl-amino-ethyl-methacrylate
6
7
TYPES OF LAMPS USED FOR CURING
LED lamps.
Using a solid-state, electronic process, these light sources emit
radiation only in the blue part of the visible spectrum between 440
and 480 nm.
QTH lamps.
QTH lamps have a quartz bulb with a tungsten filament that
irradiates both LTV and white light that must be filtered to remove
heat and all wavelengths except those in the violet-blue range (400 to
500 nm).
PAC lamps.
PAC lamps use a xenon gas that is ionized to produce a plasma.
The high-intensity white light is filtered to remove heat and to
allow blue light (400 to 500 nm) to be emitted.
Argon laser lamps
Have the highest intensity and emit at a single wave
length.lamps currently avaialble emit 490 nm.
7
8
DEPTH OF CURE AND EXPOSURE TIME
Light absorption and scattering in resin composites reduces the power
density and degree of conversion (DC) with depth of penetration
Intensity can be reduced by a factor of 10 to 100 in a 2-mm thick
layer of composite which reduces monomer conversion to an
acceptable level.
The practical consequence is that curing depth is limited to 2- 3mm
Light attenuation vary from one type of composite to other depending
on opacity, filler size, filler concentration and pigment shade
Darker shades require long curing time
When polymerising resin through tooth structure exposure time
should be increased by a factor of 2 – 3 to compensate for reduction
in light intensity
For halogen lamps light intensity can decrease depending on quality
and age of light source,orientation of light tip,distance between light
tip and restoration and presence of contamination,such as composite
residue on light tip
Despite the many advantages of light cured resins,there is still need
for chemically cured composites for eg chemicaly cured materials can
be used with reliable results as luting agent under metallic
restorations.
8
9
DUAL CURING AND EXTRA ORAL CURING
o One way to overcome problems associated with light curing
combine chemical curing and light curing components in same
resin.
o Air inhibition and porosity are problems associated with dual-cure
resins
o Extra-oral heat or light can be used to promote a higher level of
cure
o For eg light cured or chemical cured composite for inlay can be
cured directly within the tooth or die and then transferred to oven
to receive additional heat or light curing
DEGREE OF CONVERSION
o DC is a measure of percentage of carbon-carbon double bonds that
have been converted to single bonds to form polymeric resin
o The higher the DC the better the strength,wear,resistance
o Conversion values of 50%-70% are achieved at room temperature
for both types of curing system
REDUCTION OF RESIDUAL STRESSES
2 APPROACHES-
Reduction in volume contraction by altering the chemistry of
resin system.
9
10
Clinical techniques designed to offset the effects of
polymerisation shrinkage.
INCREMENTAL BUILDUP AND CAVITY CONFIGURATION
o One technique is the attempt to reduce the so called C-
factor(configuration factor) which is related to the cavity
preparation geometry
o A layering technique in which restoration is built up in increments
reduces polymerisation stress by minimising the Cfactor.
o Incremental technique overcomes both limited depth of cure and
residual stress concentration.
SOFT STARTED,RAMPED CURING AND DELAYED CURING
o Variations on this technique include ramping and delayed cure.
o In ramping the intensity is gradually increased or ramped up during
the exposure which consists of either step wise,linear or
exponential modes.
o In delayed curing restoration is initialy cured at low intensity and
after contouring the resin to correct occlusion second exposure for
final cure is done.
o The longer the time available for relaxation,lower the residual
stress
HIGH INTENSITY CURING
o High intensity lamps could provide savings in chair time.
10
11
o However high intensity, short exposure times cause accelerated
rates of curing, which leads to substantial residual stress build up.
CONVENTIONAL / TRADITIONAL /MACROFILLED
COMPOSITE
COMPOSITION:
o Ground quartz most commonly used filler
o Average size : 8- 12 µm
o Filler loading - 70-80 weight % or 50 – 60 vol %
PROPERTIES :
o Compressive strength-
Four to five times greater than that of unfilled resins ( 250-300
Mpa)
o Tensile strength-
Double than of unfilled acrylic resins (50 – 65 Mpa)
o Elastic modulus-
Four to six times greater (8-15 Gpa)
o Hardness –
Considerably greater (55 KHN) than that of unfilled resins
o Coefficient of thermal expansion-
High filler –resin ratio reduces the CTE significantly.
o Esthetics –
Polishing result in rough surface.
Selective wear of softer resin matrix
Tendency to stain
11
12
o Radiopacity –
Composites using quartz as filler are radioluscent
Radiopacity less than dentin
CLINICAL CONSIDERATIONS
o Polishing was difficult
o Poor resistance to occlusal wear
o Tendency to discolor
o Rough surface tends to stain
o Inferior for posterior restorations
MICROFILLED COMPOSITES
Developed to overcome surface roughness of conventional composites
COMPOSITION
o Smoother surface is due to the incorporation of microfillers.
o Colloidal silica is used as the microfiller
o 200—300 times smaller than the average particle in traditional
composites
o Filler particles consists of pulverised composite filler particles
PROPERTIES :
12
13
o Inferior physical and mechanical properties to those of
traditional composites
o 40 – 80 % of the restorative material is made up of resin
o Increased surface smoothness
o Areas of proximal contact- Tooth drifting
o Compressive strength-
250- 350 Mpa.
o Tensile strength-
30- 50 Mpa.
Lowest among composites
o Hardness –
25- 30 KHN.
o Thermal Expansion Coefficient-
Highest among composite resins
CLINICAL CONSIDERATIONS
o Choice of restoration for anterior teeth.
o Greater potential for fracture in class 4 and class 2 restorations.
o Chipping occurs at margins.
SMALL PARTICLE COMPOSITE
13
14
Introduced in an attempt to have good surface smoothness and
to improve physical and mechanical properties of conventional
composites.
COMPOSITION –
o Smaller size fillers used-
o Colloidal silica - present in small amounts ( 5 wt % ) to adjust
paste viscosity
o Heavy metal glasses . Ground quartz also used
FILLER CONTENT
65 – 70 vol % or 80 – 90 %
PROPERTIES
o Due to higher filler content the best physical and mechanical
properties are observed
o Compressive strength
Highest compressive strength (350 – 400 Mpa )
o Tensile strength
Double that of microfilled and 1.5 times greater than that of
traditional composites ( 75- 90 Mpa )
o Hardness
Similar to conventional composites ( 50 – 60 KHN)
o Thermal expansion coefficient-
Twice that of tooth structure
o Esthetics
14
15
Better surface smoothness than conventional because of
small and highly packed fillers
o Radiopacity
Composites containing heavy metal glasses as fillers are
radio-opaque which is an important property in restoration of
posterior teeth
CLINICAL CONSIDERATIONS
o In stress bearing areas such as class 4 and class 2 restorations
o Resin of choice for aesthetic restoration of anterior teeth
o For restoring sub gingival areas
HYBRID COMPOSITE
Developed in an effort to obtain even better surface
smoothness than that provided by the small particle composite.
COMPOSITION
2 kinds of fillers-
o Colloidal silica – present in higher concentrations 10 – 20 wt %
o Heavy metal glasses – Constituting 75 %
o Average particle size 0.4 – 1.0 µm
PROPERTIES
o Range between conventional and small particle
15
16
o Superior to microfilled composites
o Compressive strength-
Slightly less than that of small particle composite(300 – 350
Mpa )
o Tensile strength-
Comparable to small particle (70 – 90 Mpa )
o Hardness –
Similar to small particle ( 50 – 60 KHN )
o Esthetics –
Competitive with microfilled composite for anterior
restoration
o Radiopacity –
Presence of heavy metal glasses makes the hybrid more
radio-opaque than enamel
CLINICAL CONSIDERATIONS
o Used for anterior restorations including class 4 because of its
smooth surface and good strength
o Widely employed for stress bearing restorations
FLOWABLE COMPOSITES
Modification of SPF and Hybrid composites.
Reduced filler level
CLINICAL CONSIDERATIONS-
16
17
Class 1 restorations in gingival areas.
Class 2 posterior restorations where acess is difficult.
Fissure sealants.
COMPOSITES FOR POSTERIOR RESTORATIONS
Amalgam choice of restoration for posterior teeth
Mercury toxicity and increased esthetic demand.
All types of composites except flowable composites
Conservative cavity preparation
Meticulous manipulation technique.
PACKABLE COMPOSITES
o 1990s
o Elongated fibrous,filler particles of about 100µm
o Time consumingInferior in stength when compared to amalgam
o Problems in use of composites for posterior restoration
o In class 5 restoration where gingival margin is located in
cementum or dentin.
o Marginal leakage
o Time consuming
o Composites wear faster than amalgam
INDICATIONS
o Esthetics
17
18
o Allergic to mercury
o To minimse thermal conduction
INDIRECT POSTERIOR COMPOSITES
o Introduced to overcome wear and leakage.
o Polymerised outside the oral cavity and luted with resin cement
o For fabrication of inlays and onlays.
DIFFERENT APPROACHES FOR RESIN INLAY CONSTUCTION-
o Use of both direct and indirect fabrication systems
o Application of heat,light,pressure or combination
o Combined use of hybrid and microfilled composites
USES OF COMPOSITES FOR RESIN VENEERS
These resins are polymerized by visible light in violet –blue
range or by combination of heat and pressure.
USES :
o Veneers for masking tooth discoloration
o Used as performed laminate veneers
ADVANTAGES
o Ease of fabrication
o Predictable intra-oral reparability
o Less wear of opposing teeth or restorations
DISADVANTAGES
18
19
o Leakage of oral fluids
o Staining below veneers
o Susceptible to wear during tooth brushing
TECHNIQUES OF INSERTION
o Chemically activated resin
o Correct proportions dispensed
o Rapid spatulation with plastic instrument for 30 sec
o Avoid metal instruments
o Inserted with syringe or plastic instrument
o Cavity slightly overfilled
o Matrix strip placed to apply pressure and to avoid air inhibition
LIGHT ACTIVATED RESINS
o Single component pastes
o Working time under control of operator
o Hardens rapidly once exposed to curing lights
o Limited depth of cure
o Incremental build up
o High intensity light used
o Exposure time not less than 40 – 60 sec
o Resin thickness not greater than 2.0-2.5mm
o Caution – High intensity light causes retinal damage
ACID ETCH TECHNIQUE
19
20
Most effective way of improving marginal seal between resin
and enamel
MODE OF ACTION-
o Creates microporosities by discrete etching of enamel
o Etching increases surface area
o Etched enamel allow resin to wet the tooth surface better
o When polymerised forms resin tags
ACID USED-
o 37% phosphoric acid
DENTIN BONDING AGENTS
Supplied as - kit containing primers/conditioners and the
bonding liquid.
PRIMERS/CONDITIONERS
o Remove the smear layer and provides opening of dentinal
tubules.
o Provides modest etching of inter-tubular dentin.
CLASSIFICATION :
FIRST GENERATION
o Use glycerophosphoric acid dimethacrylate.
o Main disadvantage-low bond strenghth.
SECOND GENERATION –
o Developed as adhesive agents for composites.
20
21
o Bond strength 3 times more.
o Disadvantage – short term adhesion.
bond hydrolysed eventually.
Eg Prisma,Universal bond,Mirage bond.
THIRD GENERATION –
o Had bond strengths comparable to that of resin to etched enamel.
o Complex use-requires 2-3 application steps.
o Eg Tenure,Scotch Bond 2,Prisma.
FOURTH GENERATION –
o All bond – 2 systems.
o Consists of 2 primers (NPG-GMA and BPDM).
o An unfilled resin adhesive(40%BIS-
GMA,30%UDMA,30%HEMA).
o Bonds composite not oly to dentin but to most surfaces like
enamel,casting alloys,amalgam,porcelain and composite.
FIFTH GENERATION –
o Most recent product.
o More simple to use.
o Only single step application.
o Eg 3M Single Bond,Prime and Bond(Dentsply).
INDICATIONS FOR USE
o For bonding composite to tooth structure.
o Bonding composite to porcelain and various metals like
amalgam,base metal and noble metal alloys.
21
22
o Desensitization of exposed dentin or root surfaces.
o Bonding of porcelain veneers.
SANDWICH TECHNIQUE
o Composite does not bond adequately to dentin.
o Bond to dentin improved by placing GIC liner between
composite and dentin.
INDICATIONS :
o Lesions where one or more margins are in dentin.
eg cervical lesions.
o Class II composite restorations.
CORES
o If half or more of clinical crown is destroyed.
o Must be anchored firmly to tooth.
o Pin-retained cores mostly used.
o Amalgam and composite resins .
o Composited more favored.
ADVANTAGES-
o Easily molded into large cavities.
o Polymerise quickly.
o Crown preparation done at same appointment.
DISADVANTAGE –
o Dimensionaly not stable
22
23
o Greater microleakage
FINISHING AND POLISHING
o Started 5 min after curing
o Initial contouring with knife or diamond stone
o Final finishing with rubber impregnated abrasives or aluminum
oxide discs
o Best finish obtained on setting against matrix strip
BIOCOMPATIBILITY
o Relatively biocompatible.
o Inadequately cured composites serve as reservoir that can induce
pulpal inflammation
o Shrinkage of composite leading to marginal leakage and
secondary caries
o Bisphenol A precursor of bis-GMA – Xenoestrogen –
Reproductive anomalies
SURVIVAL PROBABILITY OF COMPOSITES
o Judged on long term clinical trials
23
24
o Survival rates of composites after 7yrs was 67.4%
o Amalgam 94.5%
o Glass ionomer was 64% after 5 yrs.
o Glass ionomer/composites avoided in class II restorations
SUMMARY
Amalgam continues to be the best posterior restorative material :--
o Ease of use.
o Low cost.
o Wear resistance.
o Freedom from shrinkage during setting.
o High survival probabilities
REFERENCES
o Anusavice K.J Phillips’science of dental materials ,11th Edition
Saunders publication.
o Craig.R.G, Dental Materials, 8th edition, Elsevier publications.
o O’Brien.W.J, Dental materials and their selection, 3rd edition,
Quintessence publications.
24
25
25