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Dental Material Science > Composites > Flashcards

Composites Flashcards

1
Q

Definition of composite restorative materials and indications for use

A
  • Class of materials that can replace biological tissue in both appearance and function
  • Largely successful but has certain limitations
  • Restoration of anterior and posterior teeth
  • Conservative class 1 or 2s
  • Pit and fissure sealants
  • Cementation of fixed prostheses
  • Bonding of ceramic veneers
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2
Q

Contraindications of dental composites

A
  • Very large posterior restorations
  • Bruxism??
  • Poor isolation
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3
Q

Dental Resin Composites definition

A

-Aesthetic, plastic adhesive restorative material consisting of co-polymerized methacrylate-based resin chains embedding inert filler particles and requiring a separative adhesive (bonding agent) to micro/nano-mechanically bond them to either enamel or dentine

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4
Q

Good properties of dental composites

A
  • Ability to withstand oral cavity environment
  • Easily shaped to the anatomy of the cavity
  • Match the natural tooth colour
  • Bonds directly to the tooth tissue
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5
Q

Recommended types of composites for each type of restoration

A

Class I and II: Multipurpose, nanocomposites, highly filled composites for posterior restorations

Class III and IV: Multipurpose, nanocomposites micro filled composites (hybrids)

Class V: Flowable composites

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6
Q

Dental composites constituents

A

Major constituents:

  • High molecular weight monomers (matrix phase)
  • Fillers (discontinuous phase)

Minor constituents:

  • Diluents or viscosity modifiers (dimethacrylate monomers with low molecular weight and viscosity)
  • Inhibitors, intiators, accelerators, radio-opacifiers and stabilizers
  • Silane coupling agent (filler is treated with the coupling agent)
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7
Q

Types of resin monomers in dental composite

A

-High molecular weight monomers are either aromatic or aliphatic dimethacrylates

  • Bis-GMA is very viscous
  • Aromatic
  • Difunctional methacrylate with two phenyl groups which provide rigidity
  • Hydroxyl groups present provide H bonding
  • UDMA is lower viscosity but still quite high viscosity
  • No phenyl groups
  • Non-aromatic
  • TEGDMA and EDMA added to reduce viscosity
  • Diluents
  • On polymerisation, the dimethacrylate monomers allow for extensive cross linking to occur
  • Cross linking renders them stronger, with an increased Tg and lowers fluid uptake
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8
Q

Inhibitors of dental composites

A

-Compounds added to prevent premature polymerization during storage, handling and placement
Examples of common inhibitors include hydroquinone, PMP and BHT

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9
Q

Accelerators in dental composites

A

-Dimethylaminobenzoates (DMAB) increase the reactivity of the photo-initiator, speeding up curing time

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10
Q

Photo stabilizers in dental composites

A

-HMBP provide colour stability by eliminating the UV action on amine initiators

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11
Q

Colour pigments in dental composites

A

-Various ferric and titanium oxides

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12
Q

Radio opacifiers in dental composites

A

-Aluminium, titanium or zirconium oxides

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13
Q

Filler Particles in Dental Composites role, constituent and affects

A
  • Inert filler particles made from barium, silica, quartz or strontium glass derivatives
  • Coated with an organo silane coupling agent to make the matrix and glassy phase compatible
  • Increased filler particles increases viscosity
  • Increased filler particles reduces volumetric shrinkage
  • Improves the coefficient of thermal expansion
  • More irregular shapes, larger, harder filler particles increases the wear resistance of the composite (surface hardness)
  • Improves mechanical properties such as modulus of elasticity, abrasion resistance and strength)
  • Finer, more spherical particles improve aesthetics
  • Decreases water sorption
  • More polishable
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14
Q

Silane Coupling agent role

A
  • Improves adhesion between filler and polymer matrix
  • Silane coupling agent has a polymerizable group along with a hydrophilic end which may have the ability to condense with hydroxyl groups present on the surface of the ceramics
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15
Q

Photo-Initiator definition, role and issues

A
  • Camphorquinone (a diketone) most common (yellow in colour)
  • Along with tertiary amine as an activator
  • Absorbs 480nm blue light
  • Forms free radicals
  • Initiation of addition polymerization

Camphorquinone is a bright yellow solid thus can be disadvantageous for obtaining different shades. TPO therefore currently being tested as an alternative and some composites are using mixture of the two

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16
Q

Recent development of photoinitiators

A
  • 1-phenyl-1,2 propanedione is a photosensitizer of potential value that helps in reducing colour problems associated with visible light cured dental resins
  • Acts synergistically to produce a more efficient photoinitiation reaction
  • Camphorquinone is a bright yellow solid thus can be disadvantageous for obtaining different shades. TPO therefore currently being tested as an alternative and some composites are using mixture of the two
17
Q

Setting reaction of dental resin composite

A
  • Free radical addition polymerisation reaction of methacrylates
  • Free radicals can be generated by heat, light or chemical activation

Chemical Reaction: Two paste system, initiators such as benzoyl peroxide and tertiary amine (N, N dimethyltoulidine) producing free radicals

or

Photoinitiation: One paste system, photoinitiators such as camphorquinone

Camphorquinone + amine activator produces free radicals

18
Q

What is the matrix and issues

A
  • Matrix is the phase formed on polymerisation of the methacrylate monomers
  • Weakest
  • Least wear resisistant
  • Can absorb fluids
  • Responsible for shrinkage
19
Q

Methods of curing a dental composite and pros/cons of each

A

Chemical activation

  • Gradual increase in viscosity
  • Limited working time
  • Mixing may incorporate air bubbles may inhibit polymerisation

Light activation (photoinitiation)

  • No mixing involved
  • Command set, light attenuation, limited depth of cure
  • Degree of cure: light intensity, exposure time and thermal energy
  • Incremental curing
20
Q

Process of photopolymerisation

A
  • Triggered by free radicals
  • Free-radicals generated on irridation of a light-sensitive initiator (initiation)
  • Free radical attacks the double bond of the methacrylate groups, creating monomer free radicals leading to the generation of a chain (propagation)
  • Extent of polymerisation is determined from the ratio of uncured monomer or remaining double bonds to the amount initially present ???
  • Degree of cure/conversion. Usually 40-78%

-Cross linked networks usually formed. Dimethacrylate monomers can form linear polymers, but in the presence of dilutent monomers such as EGDMA and TEGDMA, cross linking occurs. Crosslinked networks influence the resultant physical and mechanical properties

21
Q

Rate of reaction after initial set of composite

A
  • During polymerisation, there is a massive increase in the viscosity of the system
  • Results in restricting the mobility of the longer chains, thus formed thereby increasing the free radical concentration
  • Increases rate of reaction, often known as autoacceleration or the Tromsdorff Norish effect
  • Rapid vitrification
  • Limits the diffusion of monomers and leads to entrapped monomers/free radicals leading to less than 100% conversion
  • Predominant polymerisation occurs during irradiation, however, a very small amount of reaction may occur post setting due to the free volume relaxation
22
Q

Properties of dental composite

A

-Polymerisation leads to certain amount of shrinkage

Mechanical properties

  • Amount of filler
  • Type of filler
  • Filler-resin coupling

Surface Properties

  • Hardness
  • Roughness
  • Abrasion Resistance
  • Water sorption
  • Thermal Properties
  • Colour and Appearance
  • Adhesion
23
Q

What affects the elastic modulus, microhardness and compressive strength

A
  • Filler particles
  • But studies also show varying elastic modulus, microhardness and compressive strengths for lots of different types of composites with similiar filler weight content
  • Suggesting natuve resin matrix governs the properties as well
24
Q

Degree of conversion definition and affect on hardness

A
  • Effect on physical and mechanical properties
  • Determined by infrared spectroscopy
  • Often indirectly evaluated by determining microhardness with a reasonable correlation
  • Higher the degree of conversion, the higher the microhardness
  • But crosslinking also affects the hardness, so there are some exceptions to this rule
  • Mechanical properties usually improve with higher degree of conversion
  • Lowering in water uptake and monomer diffusion with increase DC
25
Q

Issues with undercuring

A
  • High residual monomer
  • Optimum properties of the polymer is not achieved
  • Higher residual monomer can lead to plasticization of the matrix
  • Release of residual monomer and higher fluid uptake
  • Ingress of oral fluids
26
Q

Crosslinking during polymerisation

A

-Network formation or the degree of crosslinking significantly affects the physical properties

  • Increase in crosslinking decreases fluid sorption
  • Reduces interaction with surrounding environments and solvents
  • Structural properties improve to an extent enhancing mechanical properties but a highly crosslinked network can become brittle
  • Increase in Tg also occurs
  • Crosslinked networks do not dissolve in solvent but can only exhibit swelling
27
Q

Effect of monomers and fillers on the degree of conversion

A
  • Viscosity of the resin monomers prior to polymerisation plays a role in DC
  • Mobility of monomers is important
  • Monomer types and the amount of filler both contribute to the viscosity of the matrix
  • Dilutents on their own such as TEGDMA have a much greater rate of conversion than BisGMA
  • Due to their molecular weight, viscosity and stiffness
  • However, use of low viscosity and low molecular monomers only would yield higher shrinkage and inferior mechanical properties

-Amount of filler, geometry of the filler particles and particle size all impact on polymerization efficiency

28
Q

Interactions with fluids and composites

A
  • Water sorption
  • Loss of ionic species from the fillers

Fluid uptake affects the fatigue life of polymers
Any species lost due to interaction of fluids has an effect on the long term performance of the restoration

29
Q

Depth of cure definition and what it depends on

A
  • Maximum thickness of composite that can be adequately cured
  • Incremental curing to enhance depth of cure
  • Concentration of photoinitiatior
  • Translucency of composite
  • Light type
  • Light source
  • Time
30
Q

Polymerisation shrinkage of composites

A
  • Significant role in restoration failure
  • Gap formation
  • Secondary caries formation
  • Marginal leakage
  • Post operative sensitivity
  • Counteracted with incremental placement and lower shrinkage composite
  • Reducing the C factor to prevent shrinkage stress
31
Q

Shrinkage Stress of composites and relation to dc

A
  • Volumetric shrinkage has a significant correlation to degree of conversion
  • Greater the degree of conversion, the greater the volumetric shrinkage
  • Reduction or minimizing shrinkage stress important
  • Decreasing C factor
32
Q

Compomers definition, composition and issues

A

Aluminifluorosilicate glass particles
Resin such as UDMA
Multifunctional carboxylic acid with polymerisable double bonds
Photo initiator
Monomer with free double bonds
Light activated free radical polymerisation
Water uptake post curing can cause secondary acid-base reaction which further cross links

33
Q

Chemistry and setting of compomers

A
  • Hydrophobic resins, containing polyacid side chains which are attracted to one or more of their methacrylate monomers
  • For example, Dyract has TCB, the reaction product of butane tetracarboxylic acid and hydroxy-methyl-methacrylate, and contains 2 methacrylate groups and 2 carboxylate grousp per molecule
  • Primarily undergoes a light initiated free radical polymerization mechanism
  • Filler is a barium and reactive fluoroaluminosilicate glass containing fluoride
  • Monomer ionizes following water uptake: hydrogen ions that are released then act with the glass filler to initiate an acid base reaction
  • Ionic cross linking occurs and fluroide is released
34
Q

Compomers advantages and disadvantages

A

Advantages

  • Ease of placement
  • No mixing
  • Easy to polish
  • Good aesthetics
  • Excellent handling
  • Less susceptible to dehydration
  • Radioopaque

Disadvantages

  • Bonding agent required
  • More marginal staining and chipping
  • Wears more than composites
  • Variation of products makes longevity difficult to predict
  • Weaker physical properties than composites that decrease over time
  • Clinical signifcance of fluoride release undetermined

Phased out because no advantages over composites/GICs/RMGICs

35
Q

Nanocomposites, why discovered, details and properties

A
  • Polymerization shrinkage major drawback of composites
  • Modern day dentistry revolves around prevention so smaller cavity size is advocated
  • Low shrinkage composites ideal
  • Nanocomposites (3M-ESPE) has very small filler particles
  • Easy handling, good aesthetics
  • Flexural strength, abrasion and polymerisation shrinkage similiar to regular composites
  • INCREASED POLISH RETENTION
  • Allowing long lasting perfect aesthetics
  • Reduced plaque adhesion
  • Reduced risk of secondary decay
  • Reduced risk of gingival inflammation in class Vs
  • No external discolouration
  • Reduced antagonistic wear
  • High oral comfort
  • Reduction of the interstitial spacing between filler particles
  • Better physical properties
  • Increased filler loading
36
Q

Flowable composite definition

A
  • Contraction stresses during the polymerisation of composites are transferred to the tooth due to reduced fillers
  • Post operative pain, marginal discolouration, recurrent caries and loss of restoration
  • 20-25% lower filler content
  • Lower rigidity
  • Modulus of elasticity is considerably lower
  • Greater flexibility
  • Liners, fissure sealants and small restorations only
  • Low viscosity good for clinical placement
37
Q

Pre-Warming of composites. Why?

A
  • Recently advocated to lower the viscosity during placment
  • Higher temperatures enhance flow of resins
  • Used as an alternative to a flowable composite
  • Thermal vibration of monomers resulting in increased entropy
  • Pre heating prior to light curing lowers the film thickness of the composites that suggests a decrease in the viscosity
  • Calset is a heating device design that is used to warm composites before placement
  • Eases clinical placement and allows better marginal adaptation
  • Some studies suggest DC is not affected, but some have resported higher DCs
  • No changes in flexural strength and DC with prewarming according to Sanjukta
38
Q

Prewarming and fit of ceramic restoration

A
  • Properties of luting cement can affect the fit of a cemented restoration
  • Prewarming showed significant differences in composite thickness, but microleakage studies did not exhibit any significant advantages
39
Q

Bulk-Filling Composites

A
  • Do not require incremental curing
  • Depths of 4-5mm
  • New photoinitiator systems
  • Ivocerin used in Tetric Evo Ceramic is more reactive than conventional initiators and allows large increments to be polymerised
  • Sonic bulk fill composites can be used that respond to sonic energy, applied through a handpiece during placement
  • Lowers viscosity of material and improves adaptation
  • Higher translucency
  • LOOK AT STUDIES ON SLIDES FOR MORE

Dental Material Science (13 decks)

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