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BDS4 EXAM STUDY > Dental Material Science Overview > Flashcards

Dental Material Science Overview Flashcards

1
Q

What are the desired properties of a dental adhesive?

A
  • provide high bond strength to tooth tissues
  • immediate high strength bond
  • durable bond
  • impermeable bond
  • easy to use & safe
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2
Q

Describe how the acid-etch technique works when preparing to bond to enamel:

A
  • long enamel prisms are filled with imperfectly packed hydroxyapetite crystals
  • application of 35% phosphoric acid roughens surface
  • roughened surface allows micromechanical interlocking of resin filling materials
  • surface energy also increased which increases wettability
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3
Q

What does the stress-strain ratio indicate about a dental material?

A

How rigid or elastic a material is

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4
Q

What is the meaning of ‘creep’ in relation to dental materials?

A

gradual dimensional change due to repetitive small forces

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5
Q

What is the meaning of ‘fatigue’ in relation to dental materials?

A

repetitive small stresses causes material fracture

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6
Q

What is the meaning of ‘deformation’ in relation to dental materials?

A

applied stress causes permanent change in materials dimensions
- but NOT fractured

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7
Q

What is the meaning of ‘elasticity’ in relation to dental materials?

A

the ability of a material to recover its dimensions after experiencing a stress

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8
Q

What is composite resin made up of?

A
  1. Filler particles
  2. Resin
  3. Camphorquinone
  4. Low weight dimethacrylates
  5. Silane coupling agent
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9
Q

What filler particles can be found in composite resins?

A

Glass
- microfine silica
- quartz
- lithium aluminium silicate
- borosilicate glass

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10
Q

What filler particle size is found in conventional composite resin?

A

10-40um

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11
Q

What filler particle size is found in microfine composite resin?

A

0.04-0.2um

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12
Q

What filler particle size is found in fine composite resin?

A

0.5-3um

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13
Q

What resin monomers are used in composite resins?

A
  • BIS-GMA
  • urethane dimethacrylates
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14
Q

What are the key characteristics of monomer found in composite resin?

A
  • difunctional molecule eg C=C bonds (facilitates crosslinking)
  • undergoes free radical addition polymerisation
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15
Q

How is camphorquinone activated?

A

Blue light (430-480nm)

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16
Q

Once activated how does camphorquinone cause composite to harden?

A
  • activated by blue light
  • radical molecules produced
  • initiation of free radical addition polymerisation of BIS-GMA
  • changes in resin properties
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17
Q

What is the function of low-weight dimethacrylates in composite?

A

adjusts viscosity & reactivity

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18
Q

What is TEGDMA an example of?

A

Low weight dimethacrylate found in comp resin

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19
Q

What is the function of silane coupling agents in composite?

A

Allows good bond between filler particle & resin

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20
Q

What type of composite is better suited to anterior restorations?

A
  • microfilled
  • submicron
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21
Q

What does the addition of filler particles contribute to composite resin?

A
  • improved mechanical properties
  • lower thermal expansion
  • lower polymerisation shrinkage
  • less heat of polymerisation
  • improved aesthetics
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22
Q

What is the estimated depth of cure of composite?

A

2mm increments

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23
Q

What is the average strength of composite resin?

A

350MPa

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24
Q

What clinical factors can affect the wear of composite resin?

A
  • cavity size & design
  • tooth position
  • occlusion
  • placement technique
  • cure efficiency
  • finishing methods
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25
Q

What is the typical bond strength between enamel/dentine & composite?

A

40MPa

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26
Q

How is stress transfer altered if composite is poorly bonded to tooth as opposed to well bonded?

A

Concentrates stress at the interface making failure more likely

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27
Q

Discuss the thermal properties of composite resin:

A

Thermal conductivity - low (good)

Thermal diffusivity - low (good)

Thermal expansion coefficient - high (bad… can cause microleakage)

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28
Q

What is the function of a lining material?

A
  • prevent gaps between restoration & tooth
  • acts as a pulpal protective barrier
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29
Q

How does a liner under a restoration protect the pulp?

A

Protection from:
- chemical stimuli (unreacted chemicals or pH of material)
- thermal stimuli (exothermic setting reaction)
- bacteria & endotoxins (microleakage)

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30
Q

What are the ideal properties of a lining material?

A
  • easy to use
  • good mechanical properties (eg strong)
  • radiopaque
  • marginal seal
  • low solubility
  • cariostatic
  • biocompatible
  • low thermal conductivity
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31
Q

Give examples of materials used as liners:

A
  • CaOH
  • RMGIC / GIC
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32
Q

What is the initial pH of setting CaOH liners? Why is this relevant?

A

initial pH of 12
- highly alkaline liner kills cariogenic bacteria that survive in acidic environment

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33
Q

What is the mode of action of a CaOH liner?

A
  • bacteriocidal to cariogenic bacteria (high pH)
  • causes irritation to odontoblast layer, necrosis followes which results in tertiary dentine production, calcified bridge walls the base of cavity off from pulp
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34
Q

What properties does CaOH have?

A
  • quick setting time
  • radiopaque
  • easy to use
  • low compressive strength (bad)
  • soluble (if cavity leaks lining will disappear)
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35
Q

What type of reaction results in Zinc Oxide Eugenol?

A

acid-base reaction

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36
Q

Why are ZOE materials unsuitable to be used with composite resin?

A

ZOE releases eugenol which inhibits the set of resin based filling materials
- softens them
- causes discolouration

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37
Q

What type of material is Kalzinol?

A

Resin modified ZOE

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38
Q

Why are glass ionomer lining materials good?

A
  • similar thermal expansion to dentine
  • high compressive strength
  • good marginal seal
  • fluoride release
  • cytotoxic to residual carious bacteria
  • GIC bonds directly to composite resin
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39
Q

What problem can be associated with RMGICs as liners?

A

Incomplete cure can cause unreacted HEMA to damage pulp

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40
Q

Why is RMGIC usually placed over CaOH when lining a cavity?

A

Prevents dissolution of CaOH beneath restoration (as CaOH soluble)

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41
Q

Explain the acid etch technique of bonding to enamel:

A
  • 35% phosphoric acid applied to enamel
  • roughens the surface of enamel & increases surface energy
  • roughened surface allows micromechanical interlocking of resin filling materials
  • increased surface energy leads to better wettability, allowing resin to flow and adapt better to rough surface
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42
Q

Why is bonding to dentine difficult?

A
  • permeable tubules so dentine is wet
  • smear layer present
  • inconsistent material (eg aged dentine more mineralised)
  • dentine is hydrophillic & bonding agents usually hydrophobic
  • low surface energy
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43
Q

What is the smear layer found on dentine?

A

layer of organic debris that remains on dentine surface after preparation of dentine
- generally contaminated with bacteria

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44
Q

How do dentine bonding agents alter the surface energy of dentine?

A

DBAs increase the surface energy of dentine surface to allow composite to flow & stick

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45
Q

What are the components of a Total Etch DBA?

A

Dentine conditioner: acid (usually 35% phosphoric)

Primer: the adhesive part of the agent with a hydrophilic/hydrophobic molecule

Adhesive: resin which penetrates into the surface of the dentine attaching to the primers hydrophobic surface

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46
Q

What is the purpose of a dentine conditioner when bonding to dentine?

A
  • removes smear layer
  • opens dentinal tubules by removing smear plugs
  • decalcifies upper layer of dentine
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47
Q

What is the function of primer in denting bonding agents?

A
  • contains bifunctional molecule with hydrophilic end & hydrophobic end
  • hydrophilic end bonds to the hydrophilic dentine surface
  • hydrophobic end (methacrylate) bonds to the resin (C=C bond opens and forms covalent bond)
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48
Q

What is an example of a coupling agent found in many dentine bonding agent primers?

A

HEMA

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49
Q

What is the function of the adhesive in dentine bonding agents?

A
  • mixture of resins usually BIS-GMA and HEMA
  • predominantly hydrophobic
  • penetrates the primed dentine (which now has a hydrophobic surface)
  • forms a micromechanical bond within tubules known as the HYBRID LAYER
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50
Q

What problems are associated with the total etch technique when bonding to dentine?

A
  • over etching of dentine causes collapse of collagen fibres & resin cannot penetrate
  • over etching causes too deep of an etch and primer cannot penetrate to full depth
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51
Q

When might amalgam be contraindicated?

A
  • if aesthetics are paramount to pt
  • pt has history of sensitivity to mercury or other amalgam components
  • loss of tooth substance is such that a retentive cavity cannot be produced
  • where excessive removal of sound tooth tissue would be required to create retentive cavity
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52
Q

What are some advantages of using amalgam?

A
  • durable
  • long lasting if placed properly
  • short placement time
  • radiopaque
  • cheap
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53
Q

What are some disadvantages of using amalgam?

A
  • poor aesthetic qualities
  • no bond to tooth surface
  • high thermal diffusivity
  • cavity prep may require destruction of sound tooth tissue
  • marginal breakdown common
  • local sensitivity reactions eg lichenoid lesions (type IV)
  • tooth discolouration
  • amalgam tattoo
  • mercury toxicity ?
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54
Q

Why does amalgam cause tooth discolouration?

A

corrosion products migrate into porous tooth surfaces
- darkened tooth

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55
Q

Why does an amalgam tattoo occur?

A

fine amalgam particles migrate into the soft tissue causing discolouration

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56
Q

What is this likely to be?

A

Amalgam tattoo

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57
Q

Describe the cavity design requirements of amalgam?

A

Retention form:
- cavity floor should be parallel to occlusal surface
- approx. 1.5-2mm deep
- gingival floor of interprox. box should be approx. 90 degrees to axial wall
- undercuts to prevent losing restoration

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58
Q

What cavity designs are available to treat interproximal caries when restoring with amalgam?

A
  • self retentive box preparation (minimal prep box)
  • proximo-occlusal prep
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59
Q

What is the consequence of moisture contamination during placement of amalgam?

A
  • reduces strength
  • increases creep
  • increases corrosion
  • increases porosity
60
Q

What are the functions of a matrix band?

A
  • recreates walls of cavity
  • allows adequate condensation of materials
  • creates contact point with adjacent tooth
  • confines filling material to cavity (reduces overhangs)
61
Q

Why are wedges essential when placing matrix bands?

A
  • produces adaptation of matrix at cervical margin
  • prevents overhangs
  • aids contour of restoration
  • holds matrix in place
62
Q

How is amalgam placed into cavities?

A

Placed via amalgam carrier and then condensed down with large plugger

63
Q

What occurs if amalgam is not properly condensed into cavity?

A
  • lack of adaptation to cavity/more likely to fall out
  • poor bonding between layers
  • inferior mechanical properties
64
Q

What phase of amalgam is corrosion associated with?

A

Gamma 2 phase
(most amalgam is now non-gamma 2, high copper, so less of a problem)

65
Q

What is creep in reference to amalgam?

A

slow internal stressing and deformation of amalgam under stress

66
Q

What helps to prevent creep formation in amalgam?

A

copper incorporated to decrease creep (Ag-Sn-Cu phase stronger)

67
Q

When is mercury release from amalgam at its greatest?

A

During insertion and removal

68
Q

What is the purpose of the Minimata Convention on Mercury treaty?

A

Aim is to protect human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds

69
Q

Who should amalgam not be used in as per Minimata Treaty?

A
  • children under 15
  • pregnant women
  • breastfeeding women
70
Q

What are some uses of glass ionomer cement?

A
  • restorative
  • core build ups
  • linings
  • luting cements
71
Q

What is GI composed of?

A

Acid (liquid)
- polyacrylic acid
- tartaric acid
Base (powder)
- silica SiO2
- alumina
- calcium fluoride
- aluminium fluoride
- aluminium phosphate
- sodium fluoride

72
Q

What alters the translucency of Glass Ionomer?

A

Ratio of alumina/silica
- more silica = more translucent

73
Q

What particle size of power in GI is required to use it for luting purposes?

A

<20um

74
Q

What are the 3 phases of the glass ionomer setting reaction?

A
  • dissolution
  • gelation
  • hardening
75
Q

Describe dissolution in relation to the glass ionomer setting reaction:

A
  • acid into solution
  • H+ ions attack the glass surface
  • Ca, Al, Na & F ions are released
  • Leaves silica gel around unreacted glass
76
Q

Describe gelation in relation to the glass ionomer setting reaction:

A
  • calcium ion crosslinking with the polyacid by chelation with the carboxyl groups
  • formation of calcium polyacrylate
    (initial hard set of the material)
77
Q

Describe hardening in relation to the glass ionomer setting reaction:

A

Formation of aluminium polyacrylate due to crosslinking of trivalent aluminium
(does not start for at least 30 mins)

78
Q

What happens if there is contamination of GIC during setting?

A
  • aluminium ions diffuse out of material
  • water absorption
    ALL LEAD TO A WEAK MATERIAL
79
Q

What has been added to GICs to improve ease of use?

A

Tartaric acid
- shortened setting time

80
Q

What is the bonding mechanism between GIC and tooth?

A

Chelation between carboxyl groups in the cement & Ca on the tooth surface

81
Q

What are some negatives of GIC when compared with composite resins?

A
  • poor tensile strength
  • lower compressive strength
  • poor wear resistance
  • lower hardness
  • higher solubility
82
Q

Give some uses of GICs:

A
  • dressing
  • fissure sealants
  • temporary filling
  • luting cement
  • restorations
  • base / lining
83
Q

Give the constituents of the powder of RMGIC:

A
  • fluoro-alumino-silicate glass
  • barium glass
  • polyacrylic acid (vacuum dried)
  • potassium persulphate (redox catalyst to provide resin cure in dark)
  • ascorbic acid
  • pigments
84
Q

Give the constituents of the liquid component of RMGIC:

A
  • HEMA (resin)
  • Polyacrylic acid with pendant methacrylate groups
  • Tartaric acid
  • Water
  • Photo-intitiators
85
Q

What are the cons of using RMGIC as opposed to regular GIC?

A
  • polymerisation contraction
  • swelling due to water uptake of HEMA
  • HEMA is toxic to pulp if left unpolymerised
86
Q

What is the composition of traditional amalgam?

A

Powder:
Ag (70%)
Sn (25%)
Cu (3%)
Zn (1%)
Hg (1%)

Liquid:
Hg

87
Q

What is the γ phase of amalgam?

A

Ag3Sn (reacts with Hg liquid to form amalgam)

88
Q

What is the function of copper and zinc in amalgam?

A

Copper
- increased strength & hardness
- corrosion resistance

Zinc
- scavenger during production
- oxidises

89
Q

What is the setting reaction of amalgam?

A
90
Q

What amalgam phase is weak and has poor corrosion resistance?

A

γ2 phase (Sn7Hg9)

91
Q

What effect could occur in a freshly placed amalgam restoration as a result of the presence of zinc in the amalgam alloy?

Explain the mechanism.

A

Expansion of material
- interaction of zinc with saliva/blood
- bubbles of H2 formed within amalgam
- pressure buildup causes expansion
- downward pressure cause pulpal pain

92
Q

What handling factors are the properties of amalgam dependent on?

A
  • proportioning & trituration (composition and how it is mixed)
  • condensation
  • carving & polishing
93
Q

Give examples of some factors that can decrease strength of amalgam:

A
  • undermixed
  • low condensation pressure
  • slow packing rate (increments do not bond)
  • corrosion
94
Q

Explain how ditching can occur around an amalgam restoration. What can this lead to?

A
  • an amalgam placed in cavity experiences repeated & prolonged low level stresses
  • amalgam “flows” and changes shape
  • amalgam now sitting proud of tooth surface
  • ditched margins present
  • amalgam now vulnerable to microleakage or fracture at margins
95
Q

What are the thermal properties of amalgam like? How is this relevant to patients?

A
  • High thermal expansion (may lead to marginal gaps)
  • High thermal conductivity (may need to use a liner in deep cavities to prevent pulp damage)
  • High thermal diffusivity (amalgams temp rises quickly also a risk to pulp)
96
Q

How can corrosion of amalgam be reduced?

A
  • use copper enriched amalgams
  • ensure well polished margins
97
Q

How do copper enriched amalgams differ from conventional amalgams?

A
  • Non γ2 phase (Sn7Hg9)
  • high copper content (MUST BE > 6%)
98
Q

What are the benefits of NON- γ2 phase Amalgams?

A
  • higher early strength
  • less creep
  • higher corrosion resistance
  • increased durability of margins
99
Q

Explain the difference between mucostatic and mucocompressive materials:

A

Mucostatic = fluid materials that displace the soft tissues slighty (eg tissues dont move)

Mucocompressive = viscous materials that record an impression of the mucosa under load

100
Q

How can the load time of an impression material be reduced in clinical practise?

A

Impression tray removed with a sharp pull

101
Q

Why are non-elastic impression materials not suitable for impressions of bulbous crowns?

A

Impression will:
- be deformed
- fracture/tear

102
Q

What are the ideal properties of an impression material?

A
  • low viscosity so able to flow
  • no dimensional change on setting
  • low thermal expansion (to cope with mouth to room temp change)
  • elastic
  • high tear strength
  • non-toxic
  • acceptable taste & smell
103
Q

Give an example of a non-elastic impression material:

A

impression compound

104
Q

What type of material is alginate?

A

irreversible hydrocolloid impression material

105
Q

What is the composition of alginate?

A
  • sodium alginate
  • calcium sulphate
  • trisodium phosphate
  • filler
106
Q

Give some pros and cons of alginate as an impression material?

A

Pros:
- easy to use
- good setting time
- nearly elastic
- cheap

Cons:
- poor tear strength
- will uptake water if too dry/will release water if too moist LEADS TO DIMENSION CHANGES

107
Q

Why do we sometimes bond porcelain to metal for restorations?

A
  • helps eliminate defects/cracks on porcelain surface
  • aloy acts as a support & limits the strain that porcelain experiences
108
Q

Describe the meaning of the statement of “elastic limit” in relation to endodontic files:

A

The set value representing the maximal strain that can be applied to a file before permanent deformation occurs

109
Q

What is the meaning of the “plastic limit” of endodontic files?

A

The point at which a plastic deformed file breaks
- permanent bond displacement when elastic limit exceeded

110
Q

How can you prevent endodontic instrument fracture?

A
  • creation of a manual glide path to prevent torsional fatigue
  • ensure files are in constant motion
  • avoid use of files in abruptly curved or dilacerated canals
111
Q

What is work hardening?

A

Strengthening of a metal by plastic deformation
- crystal structure dislocation
- dislocations interact and create obstructions in crystal lattice
- resistance to dislocation formation develops
- stronger metal

112
Q

What is the role of irrigants in endodontic treatment?

A
  • facilitation of debris removal
  • lubrication
  • dissolution of organic & inorganic matter
  • biofilm disruption
  • kills microbes
113
Q

What is typically used to irrigate canals in endodontic treatment?

A

2.5 or 3% Sodium Hypochlorite (NaOCl)

114
Q

What is used to remove the smear layer?

A

17% EDTA

115
Q

What is the function of sealers in endodontic treatment?

A
  • seals space between dentinal wall & core
  • fills voids & irregularities in canal
  • lubricates during obturation
116
Q

What are the properties of an ideal endodontic sealer material?

A
  • exhibits tackiness to provide good adhesion
  • establishes a hermetic seal
  • radiopacity
  • easily mixed
  • no shrinkage on setting
  • non-staining
117
Q

Why might a GI sealer be a better option rather than a ZOE sealer?

A
  • Eugenol in ZOE reacts with resin and prevents setting of composites
  • glass ionomer bonds directly to dentine
118
Q

What type of sealers can be used in endodontic treatment?

A
  • ZOE sealers
  • GI sealers
  • resin sealers (best option)
119
Q

Why are ZOEs good options as endo sealers?

A
  • Zinc Oxide antimicrobial
120
Q

Why are Glass Ionomer endodontic sealers good?

A

dentine bonding properties

121
Q

What are the downsides of using glass ionomer endodontic sealers?

A
  • removal for re-treatment difficult
  • minimal antimicrobial activity
122
Q

How long do resin endo sealers take to set?

A

8 hours

123
Q

What are the ideal properties of a luting agent?

A
  • easy to use
  • radiopaque
  • good marginal seal
  • not soluble
  • biocompatible
  • cariostatic
124
Q

Explain the ideal viscosity and thickness of luting agents:

A
  • low viscosity to allow seating of restoration without interference
  • film thickness should be as thin as possible 25um or less
125
Q

Explain how a glass ionomer cement bonds to the tooth surface:

A
  • ion exchange with calcium in enamel and dentine
  • hydrogen bonding with collagen in dentine
126
Q

Give an example of a Glass Ionomer luting cement material:

A

AquaCem

127
Q

Give an example of a composite luting agent:

A

NX3 (nexus)

128
Q

If you don’t light cure a dual cure composite, what happens?

A

25% reduction in physical properties

129
Q

What would you use to bond a composite resin inlay to a tooth? How does it bond?

A

Dual cure composite cement with a dentine bonding agent. Bonds via:
- micromechanical bond to rough internal surface of inlay
- chemical bond to remaining C=C bonds on fitting surface of inlay

130
Q

Why does porcelain need to be bonded to teeth?

A

Because it is brittle so needs to be bonded to tooth to prevent fracture

131
Q

How does porcelain bond to teeth?

A

dentine bonding agent + composite luting resin + silane coupling agent [applied to porcelain]

132
Q

Explain how porcelain is prepared to be bonded to a tooth as a veneer:

A
  • Porcelain etched with Hydrofluoric acid [produces rough retentive surface]
  • Silane coupling agent applied to etched porcelain surface [strong bonds between oxide groups on porcelain & the silane]
  • Other end of silane molecule has C=C bond which reacts with composite rein luting agent
133
Q

Although required, what is the disadvantage of using a dual cure composite (eg RelyX) to bond a porcelain veneer?

A

can cause discolouration

134
Q

How are metals prepared to be bonded to teeth?

A
  • sandblasted
  • electrolytic etching
135
Q

How are non-precious metals (eg MCC) bonded to tooth surfaces?

A
  • dentine bonding agent
  • composite luting resin
  • metal bond agent is applied to the metal [eg 4-META, which has an acidic end and a C=C end, the acidic end reacts with the metal oxide and renders surface hydrophobic to allow for bonding]
136
Q

What kind of composite luting resin should be used when bonding metal restorations to teeth?

A

Dual cure material
[can be used to cement most crowns, bridges & posts]

137
Q

What luting agents can be used to cement MCCs?

A
  • GIC [AquaCem]
  • RMGIC

[Dual cure composite + DBA]
[anaerobic cure composite]
[self adhesive composite]

138
Q

What luting agent is used to bond a metal post?

A

GIC [AquaCem]

139
Q

What luting agent is used to bond a fibre post?

A

NX3 [dual cure composite + DBA]
or Self Adhesive Composite

140
Q

What luting agent is used to bond a veneer?

A
  • NX3
  • RelyX [although can discolour]
141
Q

What luting agent is used to bond a RRB?

A

Panavia 21 [anaerobic cure composite]

142
Q

What luting agent is used to bond a zirconia crown?

A
  • GIC [aquacem]***
  • RMGIC
  • Dual Cure Composite + DBA [RelyX]***
  • Anaerobic Cure Composite
  • Self Adhesive Composite
143
Q

What luting agent is used to bond a composite inlay?

A
  • NX3
  • RelyX
144
Q

What luting agent is used to bond a gold restoration?

A
  • GIC [AquaCem]
  • RMGIC
145
Q
A

BDS4 EXAM STUDY (39 decks)

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