Stresses in adhesive restorations / dental courses

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CONTENTS….
• Basic polymer chemistry
• The fundamentals of polymerization
• Reaction kinetics in photopolymerised networks
• The effects of polymerization shrinkage
• Factors influencing shrinkage and stress
• Measurement of shrinkage and stress
• Counteracting polymerization shrinkage and stress
• Conclusion

BASIC POLYMER CHEMISTRY
Inter atomic induction forces
Chain configuration

POLYMERISATION
• A repetitive intermolecular reaction……
• Types……
• Addition and Condensation Polymerization
• Co polymerization….

R – R
External energy
2 R ¤
C = C
R C – C ¤
C = C R C – C – C – C ¤
R C – (C – C) n – C ¤
C = C
R C – (C – C) n = C +
HC – C ¤
R C – (C – C) m – C ¤
R C – (C – C) n – C –C – (C – C) m – C R (or)
R C – (C – C )n – CH3 + R C – (C – C) m – CH3
INDUCTION
PROPAGATION
CHAIN TRANSFER
TERMINATION

Inducing and inhibiting polymerization
Chemicals
 peroxide - amine
 peroxide – sulfinic acid
 xylidine – diethanolamine
 Ascorbic acid – peroxide
 Sulfinic acid – lauryl mercaptan
 Tri alkyl boranes
Light
 Ultraviolet light
 visible light
Thermal systems
 peroxides
 azo compounds
Inhibitors of polymerization
• methyl ether of hydroquinone
• oxygen
(Chandler – 1973 ; Bowen – 1974;
Stansbury and Ge – 2003; Watts
– 2005)www.indiandentalacademy.com

CONDENSATION POLYMERISATION
• Production of a “non macromolecular structure”
• Formation of by products…..
• STEP GROWTH polymerization…….
• Vs addition polymerization :
 Simultaneous activation
 Non macro molecular product
 By products
 Kinetics of the reaction

CO POLYMERISATION
• What is a co polymer????
• The need for copolymeric structures…..
• n H2C = CHA + m H2C = CHB --(H2C – CHA – H2C – CHB) m+n
• n H2C = CHA + m H2C = CHB - (H2C – CHA)n + (H2C – CHB)m
• Types :
• Random - ABBAABBAAABBBBAAB
• Block - AAAABBBBAAAABBBB
• Graft / Branched – AAAAAAAA
B B

WHAT EXACTLY HAPPENS ??
• Why does volumetric shrinkage
occur ?
• Monomeric factors
 Bis GMA – 5.2 %
 TEGDMA – 12.5 %
(Thompson – 1979 ; Versluis – 1996 ;
Ferracane – 2005 ;Braga – 2005)

Kinetic landmarks…..
• Gel point – formation of a continuous network
structure - conversion dependent
• Visco elastic flow
• Auto acceleration : viscosity – macroradical
termination – inhibition of monomer mobility
• Vitrefication stage : glass transition temperature
reaches cure temperature
• Residual unsaturation : mixture of pendant reactive
groups and free monomers
(Carvalho – 1996 ; Russo – 1999; Ferracane – 2005, 2006 ; Pereira – 2005)

Effects of shrinkage and stress….
(York and Arthur – 1973;
Hancox – 1998)
(Sekiya – 1989; Sano – 2000)
(Willems – 1990; Tanaka – 2001)
Cuspal deflection;
cusp crack ;
enamel fracture
Adhesive failure -
Secondary caries
Micro cracks

Factors influencing shrinkage and
stress…..
Cavity Technique
Material
Reaction kinetics

Cavity configuration
C=C=
BONDED WALLSBONDED WALLS
UNBONDED WALLSUNBONDED WALLS
C-FACTORC-FACTOR
(Feilzer, Davidson and De Gee – 1987)

(Davidson‘ s
modification)

Curing LightCuring Light
0 mm0 mm
11
22
33
44
DEPTH OF CUREDEPTH OF CURE
DEGREE OFDEGREE OF
CONVERSIONCONVERSION
65%65%
25%25%
45%45%

Curing EquipmentCuring Equipment
FactorsFactors
ProceduralProcedural
FactorsFactors
RestorationRestoration
FactorsFactors
• Bulb frosting or degradationBulb frosting or degradation
• Light reflector degradationLight reflector degradation
• Optical filter degradationOptical filter degradation
• Fiber-optic bundle breakageFiber-optic bundle breakage
• Light-guide fractureLight-guide fracture
• Tip contamination by resin buildupTip contamination by resin buildup
• Line voltage inconsistenciesLine voltage inconsistencies
• Infection control barriersInfection control barriers
• Light tip directionLight tip direction
• Access to restorationAccess to restoration
• DISTANCE from surfaceDISTANCE from surface
• Size of tipSize of tip
• Tip movementTip movement
• TIME of exposureTIME of exposure
• Restoration thicknessRestoration thickness
• Cavity designCavity design
• Filler - amount and sizeFiller - amount and size
• Restoration shadeRestoration shade
• Monomer ratiosMonomer ratios
FACTORS AFFECTING CUREFACTORS AFFECTING CURE

0 25 50 75 100
0
2
3
4
5
CONVERSION (%)
SHRINKAGE(%)
1
65%65%
ConversionConversion
15-25% =15-25% =
GelationGelation
50% Filler
25% Bis-GMA
25% TEGDMA
Flow
Bond Stretching
(External Contraction)
Micro cracks
(Internal Contraction)
The Shrinkage – Conversion RelationshipThe Shrinkage – Conversion Relationship
Revisited….Revisited…. A physico chemical explanation
(Fogleman – 2002 ;Boutry and Deveaux – 2006)

Post-gel Phase
Possibility No. 1Possibility No. 1
Gap FormationGap Formation
If stress exceeds bond strengthIf stress exceeds bond strength
Post Curing
High C factor restoration

Possibility No. 2Possibility No. 2
DistortionDistortion
If bond strength exceeds stressIf bond strength exceeds stress
(Davidson, Feilzer and De Gee – 1984)(Davidson, Feilzer and De Gee – 1984)
Post-gel Phase

C -FACTOR IN THE ROOT CANAL….
• The advent of resin based sealers….
• The importance of canal geometry and resin film thickness
• The lack of shrinkage stress relief in narrow canals….
• Possible parameters influencing stress relief
– Resin sealer volumetric shrinkage
– Voids in sealer
– Polymerization rate
• The monobloc concept…..mission impossible????
(Tay and Pashley – 2005)

MATERIAL BASED FACTORS
- Theoretical Considerations
• Filler content : shrinkage α polymer matrix
• Filler size – relationship between surface are – volume
ratio …. (Spahl et al – 1994)
• Filler distribution / dispersion…… (Stansbury – 1999)
• CTE mismatch…..
FILLERS

Elastic modulus
• Higher the elastic modulus and
shrinkage, higher the
contraction stress
• Hooke’s Law……

• Conversion kinetics of dimethacrylate monomers….
• Influence of co monomer concentrations….
(Cook et al – 1992 ; Lovell et al – 1999)
• Role of TEGDMA and its stereochemistry….
(Krejsci – 2000 ; Truffier –
2001;Ferracane – 2001; Braga – 2003)
• Reaction diffusion termination….
• The role of inhibitor (BHT)…..
Chemistry of Co monomers

Self cure Vs Light cure
• The magnitude of polymerization….
(Kato – 1993 ; Kinomoto – 1999)
• Marginal adaptation….
• Manipulation – voids – porosity….
(De Gee – 1979 ; Alster – 1992 ; Feilzer – 1993)
• Layer thickness Vs stress generation

ADHESIVE THICKNESS….
• Importance of bond strength…
• The reason behind…..stress absorption
• Low stiffness of adhesive….
• Drawbacks……
(Asmussen – 1975; Ferracane et al – 2000 ; Davidson et al – 1990)

PRE HEATED COMPOSITES
– Pre heating to 54 – 60 º C ; 45 – 60 seconds - rapid
photo polymerization
– Increased molecular mobility and collision
frequency….
– Increased degree of conversion and physico
mechanical properties….yet…..
(Daronch and Rueggeberg – 2005, 2006)

Influence of Photo activation methods….
• Achieving adequate polymerization….
• Increase in temperature – increased shrinkage
• Increased light intensity – increase in
temperature – increased shrinkage strain
• Why ???? (Contraction stress = Power Density x Time)
(Rueggeberg – 1994 ; Bennett – 2004 ; Elhejazi- 2006)

Contraction stress relaxation by
hygroscopic expansion
• Main cause for mechanical stress in adhesive
restorations…..
• Expansion by water diffusion up to equilibrium….
• Relaxation of shear stresses parallel to adhesive
interface.
• Influencing factors…..
– Cavity configuration
– Chemistry of the monomer
– Nature of fillers
(Feilzer, Gee and Davidson – 1990)

C-Factor 0.5
HOW DOES IT SHRINK ?????
(Hansen – 1982; Versluis and Douglas – 1998 ; Sagakuchi – 1998)
Challenging the
traditional
view….

Measuring shrinkage and stress -
A review of literature….

• Direct measurement
– Tensilometer (Bowen – 1967; Feilzer – 1987 ; Ferracane – 1998)
– Strain gauge (Kinomoto – 1998; Torii – 1999)
– Force transducer (Bowen – 1967; Shono – 1999; Manahart – 2001)
– Ring slitting method (Ferracane – 2003)
– Dilatometry (Cash – 1991 ; Braga – 2002)
– Interferometry (Davidson – 1984; Hoffman – 2003)
• Finite Element Analysis (Versluis -1999; Ausiello – 2002)
• Photoelastic analysis (Kinomoto – 1998 ; Torii – 1999)
• Indirect measurements
– Microleakage analysis (Anseth – 1996; Morgan – 1998)
– Cuspal deflection measurement by LVDT (Linear Variable Displacement
Transducer) – WATT’S METHOD (Rueggeberg – 1989; Braga – 1999)
– Degree of conversion
• Direct chemical analysis (Sagakuchi – 1999; Ferracane – 2002; Chen –
2004)
• Mid IR spectroscopy (Dusek – 2004)
• FTIR spectroscopy (Elliott – 2002; Hilton – 2003)
• Photo differential scanning calorimetry (Labella – 1999; Lovell – 2002)

Strategies To Counteract
Shrinkage And Stress….
Controlled stress
reduction
Natural
mechanisms

Incremental layering
Weaver and Blank technique /
Deliperi and Bardwell
technique (1988)
(Wedge layering / oblique
stratification)
Bertolotti technique (1991)
(The Three site layering
technique / Directed Shrinkage
technique)

• Vertical layering / facio lingual layering
• Horizontal layering / gingivo occlusal layering
• Centripetal build up / Bichacho tecnique (1994)
• Successive Cusp Build up / Axial bevel technique / Liebenberg
technique (1996)
Other stratification techniques……..

 The conventional view….
 If each increment were to shrink
and exhibit stress….
(Morin – 1988 ; Sakaguchi – 1991;
Hassan – 2005)
 Hypothesis – cavity deformation Vs
no deformation
The incremental layering approach…..
Controversies exist !!!!

Split increment horizontal layering / Hassan
Technique (2005)
Uncured increment
Diagonal increment
3
4

Stress absorbers….
• Low elastic modulus liners….
(Alster – 1992; Ferracane – 1999; Ausiello – 2002)
• Parameters :
– Elastic modulus
– Thickness
• Flowable composites as liners….
(Braga – 2003)

Bi Layered restoration
• Mc Lean and Prosser (1985)
• The advantages of using glass
ionomer….
• Types
– Open
– Closed
– Centripetal approach

Auto-cure
GIC
Fuji 2 LCFuji 2 LC
LiningLining
consistencyconsistency
Pack composite alongPack composite along
the fissure patternthe fissure pattern
Melichez technique – modified sandwich approach

CURING PROTOCOLS…..
Initial low radiant exposure (290 mW/cm2 for 2 seconds) ; delay of 5
minutes ; radiant exposure of 330mW/cm2 for 60 second
Vs
Single continuous exposure ( 330 mW/cm2 for 60 seconds)
(Lim et al – 2002)Pulse
Delay
Stepped
Ramped
Standard Intensity
Pulsed
High Intensity
Time (seconds)
Irradiance
The duty cycles
• Full power
• Two staged
• Ramped
• Custom
• oscillating

FILLERS
• Non bonded silica nanofillers :
• size of the filler….
• why NON bonded ?????
• High density polyethylene spheres
• size of the filler….
• how does it reduce stress ??
www.indiandentalacademy.comwww.indiandentalacademy.com

OTHER REINFORCING FILLERS……OTHER REINFORCING FILLERS……
 Silicate glass and glass ceramic fillers
(Antonucci – 1991 ; Bowen – 1992 ; Bayne – 1999)
 Chopped glass fillers (glass inserts) and
branched fiber fillers
(Bayne and Thompson – 1996)
 Nano porous fillers ; cooled composite inserts
(Luo – 1999)
 Ceramic whiskers….
(Antonucci and Eichmiller – 1999)

Fiber reinforcementFiber reinforcement
 Reinforcing mechanisms….Reinforcing mechanisms….
 Transitional boundary layer (the crack shieldingTransitional boundary layer (the crack shielding
effect)effect)
 Load – crack formation – crack deflection – absorbedLoad – crack formation – crack deflection – absorbed
by layer - tougheningby layer - toughening
 Silane coupling agentSilane coupling agent – increases particle / matrix bond– increases particle / matrix bond
 Rod like particlesRod like particles – bridges across the advancing crack– bridges across the advancing crack
( the crack blocking effect)( the crack blocking effect)
(Bausch et al – 1997; Breschi – 1999)

Alternative monomer formulations….

CYCLOPOLYMERIZABLE MONOMERS
• Monofunctional acrylate monomers + paraformaldehyde = difunctional
monomers (Stansbury – 1990)
• Chemistry : oxy bis – methacrylate + α hydroxy methyl acrylate +
Isobutyronitrile initiator
• Expanding monomer + diepoxide monomer + PTHF (polyol) (Krenkel et al
– 1999)
• Polymer backbone with cyclic ether structure
• High degree of conversion (30 % more that conventional dimethacrylate
monomers) (Stansbury – 1990, 1992; Ruyter – 1996)
• Yet………….decreased shrinkage….????? ( 40% decrease ) (BUTLER’S
HYPOTHESIS – 1975)
• Disadvantage….

OXASPIRO MONOMERS
• Chemistry : 2,3- Bis (methylene) Spiro orthocarbonates
• “Double ring opening” polymerization….. (Zindan – 1987; Feilzer – 1990)
• Shrinkage values 50 % lesser than conventional dimethacrylates….
(Thompson – 1990; Stansbury and Bailey – 1991)
• Requirements…….difficulties not addressed so far:
 reactivity with dimethacrylates
 effective utilization of “ring opening” mechanism
 glass transition temperature
 drawbacks of symmetrical orthocarbonates….

THIOL ENE OLIGOMERS
• Posner – 1905 ; Bowman - 1990
• Step growth addition reaction with free radical chain transfer (Jacobine –
1993 ; Cramer – 2002)
• Drawbacks of spiro orthocarbonates… (Carioscia – 2005)
• Chemistry : Triallyl- 1,3,5 – Triazine- 2,4,6 – trione + Pentaerythritol tetra
( 3- mercaptopropionate) + CQ + ethyl 4-dimethylaminobenzoate.
• Stepwise, yet rapid….
• Not inhibited by oxygen…. (Cramer – 2002)
• Increased depth of cure.
• Complete conversion…….no longer a dream.
• Shrinkage 3.3 % as compared to 5 % of Bis GMA/TEGDMA
• STRESS 0.3 MPa ( 2.8 Mpa for BisGMA/TEGDMA)
(Bowman – 2003, 2005 ; Stansbury – 2005)

Also tried…….and forgotten !!
• Vinyl Cyclo Propanes (VCP) – replaces TEGDMA
(Miyazaki et al – 1997)
• Poly butadiene rubber polymer (20 µm aggregates) + fumed silica + Bis
GMA – TEGDMA
(Lee et al – 1999; Mozner - 1999)
• Liquid crystal monomers - 1,4 [4,6 – acryloyloxy hexane – 1, oxy]
benzoyloxy – 2 t butyl benzene + silica - OX 50
(Rawls – 1997; Norling et al – 1999)
• Methacrylated derivative of styrene allyl alcohol (MSAA)….
(Culbertson et al – 1997; Ferracane – 2000)
• Reaction between branches of Bis GMA
(Holter and Frey – 1997; Mulhaupt – 1997)

EPOXY RESIN BASED COMPOSITES
• Chemistry : 3,4 – epoxy cyclo hexyl methyl – (3,4 – epoxy)
cyclohexane carboxylate + nanosilica fillers (55 %) + photo initiator
( 4 – octyl phenyl) phenlidonium hexafluoroantimonate (OPIA) +CQ
• Surface treatment of fillers – γ glycidoxy propyl trimethoxysilane
• Light absorption at 240 – 250 nm… UV light…disadvantage…..
• 75 % degree of conversion
• Shrinkage 35 % less than conventional monomers……WHY??
• Shrinkage stress of 0.8 Mpa
(Craig – 1998;Chen – 2006; Brinker – 2006)

SILORANES
• Chemistry : Siloxanes + Oxiranes (ethylene oxide – an epoxide)
• Siloxane – hydrophobic
• Cationic ring opening polymerization – acidic carbo cation based
• Weinman and Christopher – 2005 : Shrinkage values
 Silorane (3M ESPE) – 1 %
 Tetric Ceram – 2.5 %
 Spectrum TPH – 3%
 Solitaire – 4 %

Resins with enhanced cure….Resins with enhanced cure….
 Multi ethylene glycol dimethacrylates– diethylene glycolMulti ethylene glycol dimethacrylates– diethylene glycol
dimethacrylate + polyethylene glycoldimethacrylate + polyethylene glycol (Anseth – 1996)(Anseth – 1996)
 Esterified multi methacrylate oligomers of poly isopropylideneEsterified multi methacrylate oligomers of poly isopropylidene
diphenoldiphenol (Wan and Culbertson – 1997)(Wan and Culbertson – 1997)
 DiBenzylidene Sorbitol in bioactive composites withDiBenzylidene Sorbitol in bioactive composites with
ethoxylated Bis GMA - decreased shrinkage; enhancedethoxylated Bis GMA - decreased shrinkage; enhanced
propertiesproperties (Antonucci, Wilson and Wilder – 2005)(Antonucci, Wilson and Wilder – 2005)

 Ormocers…..multifunctional urethane + thioether
methacrylate alkoxysilanes (Wolter and Storch – 1994)
 Organosilsesquioxane (RSi01.5)n – condensation reaction of
siloxanes and silanes (Antonucci – 1997; Laine – 1998)
ORGANIC – INORGANIC HYBRIDS

Indirect composites
• The need for indirect composite restorations…..
• Microfilled, small particle, hybrid and Ceromer (CERamic
Optimized polyMER)
• Main differences :
– Increased filler loading ( > 60 %)
– Multi functional methacrylates and bi functional
monomers
– Shrinkage < 1.2 %
(Braga – 2004; Rueggeberg – 2005)www.indiandentalacademy.com

Modes Of Curing Indirect Composites
• Superficial - temperature and pressure
Eg., SR Isosit, Coltene Brilliant, Visio Gem, Clearfil CR
• Conventional – only light curing
Eg., EOS
• Secondary curing – initial light curing, additional heat and light
curing
Eg., True Vitality, Dentacolor, Adoro, Herculite XRV, ArtGlass,
BelleGlass)

TECHNIQUE MATERIAL
• Forget GV Black for
adhesive restorations !
• Stratification technique (?)
• Stress absorbers;
Bilayered restorations ;
Melichez approach
• Modified curing protocol
• Indirect composite
restorations
• Reinforcing fillers
• Increasing inhibitor
concentration
• Alternative monomer
formulations (SOC; thiol ene;
siloranes; epoxy resins)
• Ormocers

To conclude…..To conclude…..
• Understanding the physics of polymerization – notUnderstanding the physics of polymerization – not
just a theoretical expanse of knowledge……just a theoretical expanse of knowledge……
• The target …..The target …..

THANK YOU !!THANK YOU !!

Stresses in adhesive restorations / dental courses

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