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Dental materials > direct aesthetic restorative material > Flashcards

direct aesthetic restorative material Flashcards

1
Q

What are the requirements of fillings that are used to restore anterior teeth?

A
  • it should match the tooth in color, and not discolor by time
  • it should be non irritant to the pulp or to the gingiva
  • it should not dissolve in saliva or in fluids taken into the mouth
  • it should have adequate mechanical properties to withstand the forces of mastication
  • It should have a coefficient of thermal expansion similar to that of enamel and dentin to prevent marginal percolation
  • it should undergo minimal dimensional changes on setting to prevent marginal leakage
  • it should be radio-opaque to enable the detection of secondary caries
  • ideally, it should adhere chemically to enamel and dentine
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2
Q

What are the mechanical properties required for a filling for anterior teeth?

A
  • it should have strength and modulus of elasticity similar to those of enamel and dentin
  • good abrasion resistance to dentifrices and food
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3
Q

What are the direct aesthetic restorative materias developed?

A
  • silicate cements
  • unfilled acrylic polymers
  • filled acrylic plymers (composites)
  • glass ionomer restoration
  • resin-modified glass ionomer
  • compomers
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4
Q

What are the characteristics of silicate cements?

A
  • introduced in the late 1800s and were used extensively until about 1950
  • initially, silicate restorations have excellent aesthetic properties and can match the tooth color well
  • however, after a short period of time, silicates become stained because a gap is formed between the restoration and cavity margin due to their high solubility
  • main disadvantage of silicate cements is their high solubility in the oral fluids
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5
Q

What are the factors that cause silicate cements to have color matched with the tooth?

A
  • the refractive index of silicates is similar to that of enamel and dentine
  • the silicates are translucent due to the fact that the core is unreacted glass
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6
Q

Why was the unfilled acrylic resin introduced?

A

to overcome high solubility of silicates

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7
Q

What is the composition of unfilled acrylic resin?

A
  • polymer (polymethyl methacrylate) + benzoyl peroxide (initiator)
  • monomer (methyl methacrylate) + tertiary amine (activator)
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8
Q

What are the disadvantages of unfilld acrylic resin?

A
  • low compressive strength i.e. easily fractured
  • low modulus of elasticity i.e. easily deformed
  • low hardness (15 B.H.N.) i.e. easily abraded
  • aesthetics: initially, excellent aesthetics can be achieved; however, over a period of time staining is evident at the cavity margins due to their thermal properties
  • high heat and residual monomer i.e. affect tooth pulp
  • high polymerization shrinkage i.e. marginal leakage
  • high coefficient of thermal expansion
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9
Q

Which restorative material has the highest coefficient of thermal expansion and what is its effect?

A
  • acrylics have the highest coefficient of thermal expansion than all other filling materials
  • with temperature changes in the mouth, acrylic may expand and contract at least seven to eight times more than enamel and dentine
  • thus on cooling the restoration, a gap may be opened up between the tooth and cavity, into which fluids can penetrate
  • on subsequent warming up, the fluids can be excluded from the gap
  • this process is termed marginal percolation that causes staining at the cavity margin and recurrent caries
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10
Q

Why was composite fillings introduced?

A

to overcome the disadvantages of silicate cement and unfilled acrylic resin filling materials, composite restorative materials were introduced in the early 1970

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11
Q

What are the uses of composite filling?

A
  • most common filling for anterior teeth
  • great increase in the application of composites as posterior filling material as a substitutes for amalgam
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12
Q

What is the definition of composite?

A

a combination of two chemically different materials with an interface separating them and having properties which could not be obtained by any of the components alone

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13
Q

What is the composition of composite fillings?

A
  • inorganic fillers
  • inorganic resin mix
  • coupling agent
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14
Q

What is organic resin matrix?

A

in early composites, it was polymethyl methacrylate, but recently it is either BIS-GMA (Bown’s resin or UDMA (urethane dimethacrylate))

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15
Q

How is BIS-GMA superior to PMMA?

A
  • lower volatility
  • lower polymerisation shrinkage
  • production of stronger and stiffer resin matrix
  • higher mechanical properties
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16
Q

What is the disadvantage of BIS-GMA?

A

high viscous liquids which limit amount of fillers added

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17
Q

How to achieve a suitable viscosity of organic resin matrix that allows incorporation of more fillers?

A

low molecular weight monomers added as thinners or diluents

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18
Q

What is the use of methyl-methacrylate?

A

can be added to BISGMA as a thinning polymer

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19
Q

What is the use of ethylene glycol dimethacrylate?

A
  • preferred as a thinning polymer than methyl methacrylate (MMA)
  • this is because it gives a more cross linked polymer in addition to its diluting action
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20
Q

What are the types of fillers in the past?

A
  • silica
  • alumina
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21
Q

What are the types of fillers recently?

A
  • lithium
  • alumino silicate glass fillers with barium or strontium (to make composite radio-opaque)
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22
Q

What are the functions of fillers?

A
  • increase strength of composite
  • increase hardness of composite
  • increase stiffness of composite
  • produce good aesthetic (glass reflect color of tooth structure)
  • decrease polymerization shrinkage
  • decrease heat of polymerization
  • decrease coefficient of thermal expansion
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23
Q

Why is the size of fillers important?

A

it determines the amount of fillers that can be added to the resin and its effect on the mechanical properties as well as surface smoothness (esthetic properties)

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24
Q

What are the characteristics of large particle fillers (conventional composites)?

A
  • particle size: 10-35µm
  • weight/volume: 78%
  • superior mechanical properties
  • surface roughness may occur that attracts plaque and hence causes discloration
  • not used nowadays
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25
Q

What are the characteristics of fine particle fillers (small particles composites)?

A
  • particle size: 1-8µm
  • weight/volume: 70-85%
  • good mechanical properties
  • superior finishing and polishing than conventional composite fillers
26
Q

What are the characteristics of micro-fine filled (small particles composites)?

A
  • particle size: 0.04-0.2µm
  • weight/volume: 25-60%
  • easy to obtain and maintain smooth surface which does not attract plaque and stains
  • poor mechanical properties
  • greater shrinkage on setting and more water sorption owing to the lower filler content
27
Q

What are the characteristics of hybrid or posterior composite?

A
  • particle size: 0.04 and 1.8µm
  • weight/volume: 77-80%
  • developed to obtain the advantages of both types of fine & micro fine
28
Q

What are the characteristics of nao-composite (nanomers and nanoclusters)?

A
  • particle size: 2-5nm (nanomers) and 5-20nm (nanoclsuters)
  • weight/volume: 78.5%
  • highly translucent
  • increased mechanical propoerties
  • reduced polymerization shrinkage
  • restorations have and maintain a smoother surface
29
Q

What is the problem of micro-filled composite and how is it overcome?

A
  • microfilled composite have very small fillers (0.04 µm) and hence they have very high surface area
  • therefore only 25% can be used otherwise; very viscous material is produced which is not accepted clinically
  • to overcome this, maximum amount of fine fillers is incorporated into the resin then polymerized and ground into large particles (10-40 µm)
  • these pre-polymerized polymer particles are then added to the polymer matrix as an organic filler which is already containing microfine particles
  • by this method, the amount of fillers are increased from 25% to 60% in recent types
30
Q

What is vinyl silane coupling agent?

A

this compound has inorganic terminal group that react with the inorganic fillers and organic terminal group that react with the organic polymer matrix, thus the filler and resin matrix are bonded

31
Q

What are the functions of vinyl silane coupling agent?

A
  • bonds fillers to the matrix
  • improves the mechanical properties of composite by transferring the stresses from the weak resin matrix to the stronger fillers
  • reduces loss of fillers caused by penetration of water between the resin and filler
32
Q

Why are pigments added to composite filling materials?

A

so that the color of the composite matches the tooth structure

33
Q

Why is a inhibitor added to composite filling materials?

A

since monomers may polymerize on storage, an inhibitor (hydroquinone) is added to increase the shelf life of composite during storage

34
Q

What is the initiator of composite?

A

benzoyl peroxide

35
Q

What is composite classified ino according to method of activation?

A
  • chemical or self activated composite
  • light activated composite
36
Q

How is self activated composite supplied as?

A

two pastes, one contain tertiary amine activator and the other contain benzoyl peroxide initator

37
Q

What are the disadvantages of self activated composite?

A
  • need mixing that incorporate air bubbles, decreasing strength
  • uncontrolled setting time
  • discoloration by time
38
Q

How is light activated composite supplied as?

A

supplied as one paste as light is the activator

39
Q

What is the advantage of light activated composite?

A

harden on demand (controlled working time)

40
Q

What are the types of light activated composite?

A
  • UV activation
  • visible light activation
41
Q

What are the characteristics of UV activated composite?

A

replaced by visible or blue light because of its limited depth of cure (2 mm) and the harmful effects such as skin cancer and eye damage

42
Q

What are the characteristics of visible light activated composite?

A
  • the visible (blue) light having wave length around 470nm is absorbed by α-diketon which in presence of the initiator starts the polymerization reaction
  • little is known about the blue light hazards ( harmful effects), therefore we have to use eye protectors (special glasses) for safety
43
Q

What are the advantages of visible light activated composite?

A
  • deep curing (3-4 mm)
  • controlled setting time (on demand)
  • less harmful effects on eye & skin
44
Q

What does degree of activation depend on?

A
  • intensity of the light source
  • distance between light source and composite surface
  • exposure time (range from 10-40 seconds)
45
Q

What are the advantages of LED curing method?

A
  • low power consumption
  • have a long life span
  • they do not produce much heat, thus they have no fan
  • they do not require a filter
46
Q

What is the addition polymerisation reaction?

A

BIS-GMA (polymer) + benzoyl peroxide (initiator) + BIS-GMA (monomer) + glass particles (fillers) coated with silane coupling agent —(activation by either light or chemical)—> composite

47
Q

What are the biological properties of composite?

A
  • all composites undergo polymerization shrinkage away from cavity walls on setting leading to marginal leakage, recurrent caries and pulp irritation (main disadvantage of composite)
  • polymerization shrinkage depends on the amount of resin polymer matrix therefore, conventional composite shrink less than microfilled composite
48
Q

How to decrease polymerisation shrinkage

A
  • using composites with more filler %
  • using composites with low shrinkage polymer matrix
  • incremental addition of composite
  • using composite inlay
  • using adhesive material to bond composite with tooth
49
Q

What is the effect of coefficient of thermal expansion on composites?

A

The higher the amount of polymer matrix, the higher the coefficient of thermal expansion. As a result, microfilled composites have higher values for thermal expansion and will have more marginal percolation than conventional composites. Moreover, thermal stresses are more which may cause fatigue of the material and bond failure

50
Q

Which composite has the best smoothsurface finish ability?

A

microfilled composites

51
Q

What are the aesthetics of composite?

A

initially good but discolor by time

52
Q

What are the mechaical properties of composites?

A

brittle (high compresssive strength and low tensile strength)

53
Q

How is bonding to enamel done?

A

acid etch technique

54
Q

How is acid etching technique done for enamel bonding?

A
  • done by using 30 to 50% phosphoric acid for 1 to 2 minutes to remove 5 µm of the surface enamel
  • enamel adhesive which is a diluted BIS-GMA liquid is then applied to flow and fill the produced irregularities to bond with enamel by mechanical interlocking then composite is applied to bonds chemically with the cured BIS-GMA
55
Q

How does acid etching help bonding to enamel?

A
  • removal of surface debris
  • producing pores in the surface into which enamel adhesive penetrates
  • increasing the surface energy of enamel and hence wetting by adhesive
  • increasing the surface area of enamel
56
Q

What are the 3 parts of bonding to dentin (dentin adhesives)?

A
  • etchant or conditioner
  • primer
  • adhesive
57
Q

Wha happens during conditioning or etching for dentin?

A

phosphoric acid 10-15% is applied to dentin for 10-15 seconds only to:
* remove the smear layer
* demineralize the surface that produce porous dentin
* open the dentinal tubules.

58
Q

can the same etchant be used on enamel and dentin?

A

yes

59
Q

What happens during priming of dentin?

A
  • HEMA is applied to etched dentin
  • because the most inorganic material (Ca) has been removed by the acid, the primer penetrates into the organic material (collagen fibers) leading to its expansion and interlock mechanically with it
  • this will form the (collagen-resin) hybrid layer
60
Q

What adhesive is used and what does it do during dentin bonding?

A
  • low viscosity resin that contains hydrophilic molecules can penetrate into the porous dentin and the hybrid layer to bond with the primer and the collagen fibers by mechanical interlocking
  • composite is then applied to bond with the adhesive chemically

Dental materials (9 decks)

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