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Yr 2 DM > DM L1 Composites pt 3 > Flashcards

DM L1 Composites pt 3 Flashcards

1
Q

why are adhesives used in dentistry

A

tooth tissue is hydrophilic + restorative materials are hydrophobic -> no chemical bonding between them
- adhesives used to retain restoration in cavity, + bond the 2 for longevity

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2
Q

what can types of adhesive bonding are there

A

micromechanical
molecular entanglement
chemical

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3
Q

what are the 6 advantages of adhesives

A
  • better aesthetics
  • conservation of tooth tissue
  • reinforcement of weak tooth structure
  • range of techniques
  • ↓ marginal leakage
  • ↓potential for pulp sensitivity
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4
Q

what are the ideal requirements of adhesives

A
  • provide high bond strength to enamel + dentine
  • immediate + durable bond
  • prevent ingress of bacteria
  • safe + simple to use
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5
Q

what is the acid-etch technique which is the gold standard adhesive

A

bonding resin to enamel + used in placing anterior + posterior composites

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6
Q

describe enamel structure

A
  • most dense calcified tissue
  • heterogenous structure
  • crystals of hydroxyapatite (Ca10(PO4)6(OH)2)
    forming prisms
  • organic matrix/water holds prisms together
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7
Q

when would you need to bond composite restoratives to enamel

A

orthodontic appliances

bridges

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8
Q

what are the problems of bonding composite restoratives to enamel

A
  • composites have no intrinsic adhesive qualities to tooth tissues
  • composite resins = non-polar (hydrophobic)
    + enamel = hydrophilic
  • Surface tension of enamel < adhesive resin (~34-38mJ/m2)-> ↓ wetting (resin won’t cover enamel surface properly)
  • Enamel has pellicle layer = ↓ surface energy ~ 28mJ/m2 prevents wetting
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9
Q

how is the pellicle layer removed + enamel is etched for restorative bonding?

A

acid-etch - 30-50% phosphoric acid added to enamel -> rough enamel results in micro-mechanical retention - good bonding between enamel + resin

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10
Q

what are the main reasons of using acid-etch technique for restorative bonding

A

removal of pellicle layer + contaminants allows:

  • ↑ surface roughness of enamel -> ↑ bonding area
  • ↑ surface energy
  • ↑ wettability (resin runs into enamel rods)
  • opens inner prism areas for interlocking tag formation
  • ↑ contact area + micro-mechanical bonding for adhesion
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11
Q

what acid is used for acid etching and how does it work

A
  • usual 37% phosphoric acid
  • acid-base reaction starts
  • acid dissolves enamel surface hydroxyapatite -> loss of enamel prism structure
  • enamel = frosty look, etching is achieved
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12
Q

how do you apply the unfilled resin to the tooth + what to remember when applying

A
  • apply low viscous resin ( unfilled Bis GMA)
  • unfilled resin applied to dry/well etched enamel surface
  • resin flows into etched enamel prisms + forms resin tags which penetrate to 30μm depth
  • the filled resin applied on top of unfilled resin
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13
Q

how does microfilled resin bond to the unfilled resin in etched enamel + how does resin bond to etched enamel prisms

A

mech for adhesion for microfilled restorative resin bonding to unfilled resin = chemical bonding (methacrylate groups)
mech for adhesion into enamel prsims = molecular entanglement

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14
Q

what are the properties of enamel/resin

A
  • Bond strength ~20MPa
    -↑surface area
    -Long-term efficacy
  • Failure of adhesive bond due to: poor clinical technique, failure of
    bond along adhesive interface (due to contamination)
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15
Q

what 6 things is acid etch enamel technique can be used for

A
  • fissure sealing
  • direct composite/compomer restorations
  • ceramic veneers
  • resin bonded bridges
  • orthodontic brackets
  • periodontal splinting
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16
Q

why does a restorative resin have to be adhesively bonded to dentine

A

retain the restoration in cavity + eliminate marginal/internal gaps to prevent bacterial micro-leakage

17
Q

why is it more difficult to bond restorative resin to dentine than enamel

A
  • most resins = hydrophobic, but dentine = hydrophilic
  • bonding agent needed to enhance bonding + retain restoration
  • bonding agent = added strength to restored tooth
  • prevent dentine hypersensitivity (dentinal tubules are sealed)
18
Q

properties of dentine

A

Heterogeneous structure (70% mineral, 20% organic material, 10% water)
o Hydrophilic
o Vital (living tissue)
o Dentinal tubules communicate w/ pulp

19
Q

what are the difficulties in bonding to dentine

A

when dentine cut:

  • fluid is pumped through dentine tubules -> wet surface
  • inorganic hydroxyapatite crystals broken + collage stretched, torn + smeared over cut surface
20
Q

Cut dentine is covered by a smear layer. what is a smear layer

A

▸ composed of layer of denatured collagen + debris covering surface - weakly bound to dentine (0.5-5um thick)
▸ contaminated with bacteria (caries) + cutting debris

21
Q

what are smear plugs

A

smear layer covers dentine tubules + can form smear plugs

22
Q

how does the smear layer affect bonding to dentine

A

cut dentine results in wet surface - covered by smear layer –> acts as contaminant
so more difficult to bond to dentine

23
Q

how do you achieve strong bonding to dentine + what happens to the dentine tubules

A
  • strengthen in situ
  • or remove smear layer completely
  • when smear layer removed, dentine tubules are open + exposed to bacteria + irritants
24
Q

why must the adhesive resin be effective seal that will seal dentine tubules ( why dentine bonding agents needed)

A
  • when smear layer removed, tubules are open + exposed to bacteria + irritants
  • adhesive resin must seal them so no contamination in the tubules
25
Q

what agent is necessary when bonding to dentine

A

dentine bonding agent

26
Q

What are the 3 essential components of dentine bonding agents + briefly describe their functions

A
  1. Conditioner (acid-modifies/ clears smear layer)
  2. Coupling/bonding agent/primer (adhesive)
  3. Sealer ( bond, adhesive, seals dentine tubules)
27
Q

what is the dentine conditioner and what does it do ( dentine bonding agent)

A

etch
▸ acid solution , stronger acid, ↑ effect (EDTA, maleic, oxalic, phosphoric + nitric)
▸ remove or modify smear layer ( acid/base reaction with hydroxyapatite - dissolves)
▸ rinsed with water
▸demineralised dentine surface left

28
Q

what is the dentine bonding agent/primer and what does it do (dentine bonding agent)

A

prime
▸ acts as adhesive in dentine bonding agents
▸ bonds hydrophilic dentine to hydrophobic resin
▸ consists of bi-functional molecule (HEMA) - philic + phobic end (coupling agent) . Hema dissolved in solvent

Yr 2 DM (5 decks)

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