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BDS2 CLINICAL Dental Materials > Bonding to Tooth > Flashcards

Bonding to Tooth Flashcards

1
Q

what are the properties of a dental adhesive

A

 Provide a high bond strength to tooth tissues
 Immediate high strength bond
 Durable bond
 Impermeable bond (doesn’t allow fluid to pass through)
 Easy to use
 Safe

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2
Q

what are the factors that govern the ability of the adhesive to make intimate contact with substrate

A

 The wettability of the substrate by the adhesive
 The viscosity of the adhesive
 The morphology or surface roughness of the substrate

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3
Q

describe the structure of enamel

A

heterogenous structure
densely packed prisms
95% mineralized
made up of tiny crystals of hydroxyapatite which are packed together to form prisms, held together by organic matrix

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4
Q

describe the structure of the prisms in enamel

A

long, rod like shapes having a key hole cross section - aligned perpendicular to the tooth surface

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5
Q

describe the structure of hydroxyapatite crystals

A

flattened hexagonals

spaces left between crystals is occupied by water and organic material

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6
Q

enamel does have water in it, so why does it remain dry?

A

much of the water is bound within enamel structure and not easily removed on drying

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7
Q

What is the acid etch technique

A

surface modification through the application of acid

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8
Q

what does the acid etch do to the enamel

A

roughens the surface of the enamel

this allows micro mechanical interlocking of resin filling material

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9
Q

what does the acid etch do to enamel in terms of surface energy

A

increases the surface energy of the enamel surface

increases wettability of the enamel

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10
Q

what does an increased wettability allow

A

wettability allows resin to adapt better to roughened enamel surface

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11
Q

why must enamel be dry after acid etch

A

Moisture contamination will prevent flow of the resin into the etched surface.

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12
Q

what is enamel bonding essentially

A

mechanical

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13
Q

what is usually used for enamel etching

A

35% phosphoric acid

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14
Q

what happens after the enamel is etched

A

 Generally a low viscosity bis-GMA resin or any one of a number of dentine bonding agent resins (often phosphorylated Bis-GMA) is applied to the etched and dried enamel surface to penetrate into the rough surface and light cured
 The higher viscosity composite resin filling material is then applied on top

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15
Q

what happens to the resin after it flows into the ‘roughness’

A

 It polymerises which creates a strong bond greater than 20MPa which is more than enough to keep it in the mouth when chewing

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16
Q

describe the structure of dentine

A

permeable tubules
70% inorganic - mostly HA
20% organic - mostly collagen

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17
Q

what is the issue with the dentinal tubules being permeable

A

Fluid pumps up from the pulp to the dentine floor of any cavity making the surface wet

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18
Q

describe how dentine is an inconsistent material

A

o Dentine near the pulp has more tubules and increased moisture content
o Aged dentine is more mineralized

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19
Q

why does dentine have a low surface energy

A

because it is wet

dentine is hydrophilic but most bonding agents are hydrophobic

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20
Q

what is the smear layer

A

cadherent layer of organic debris that remains on the dentine surface after the preparation of the dentine during the restoration of a tooth
generally contaminated with bacteria
variably attached to dentine surface
0.5-5 microns thick

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21
Q

what are the requirements of a dentine bonding agent

A

ability to flow
Potential for intimate contact with dentine surface
low viscosity
adhesion to substrate mechanically, chemically and through van der waals

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22
Q

describe mechanical bonding in dentine

A

achieved by dentine bonding agent and the dentine surface meshing and interlocking with minimum gaps

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23
Q

describe what the etch does to the dentine surface

A

demineralizes the dentine surface so exposing the network of collagen in the dentine matrix and resin infiltrates the tubules

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24
Q

describe chemical adhesion in dentine

A

bonding at a molecular level

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25
Q

what type of bond does mineralized dentine have

A

ionic bond type

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26
Q

what type of bond does organic dentine have

A

covalent bond type

27
Q

describe van der waals adhesion

A

based on electrostatic or dipole interaction between bonding agent and substrate

28
Q

what does the strength of van der waals adhesion depend on

A

contact angle which is a good indication of wettability of a solid by a specific liquid

29
Q

what is the contact angle which means the solid surface is hydrophilic

A

90 degrees

30
Q

what is the critical surface tension

A

The critical surface tension of a liquid is the surface energy that will just spread on the surface of a solid

31
Q

what is the rule for critical surface energy

A

Whatever you put onto a substrate should have a lower surface energy than the substrate

32
Q

why will a low energy liquid spread on a higher surface energy substrate

A

this leads to a lower surface energy of the material as a whole

33
Q

what needs to be done to dentine for composite resin to stick in terms of energy

A

Dentine bonding agents increase the surface energy of the dentine surface an allow composite to flow and stick to the surface
they are called surface wetting agents and have a non polar and polar group

34
Q

what is molecular entanglement

A

Adhesive is absorbed onto the surface but can also penetrate into the surface of dentine
This is due to good wetting of the dentine by the adhesive and appropriate surface energies of the two
The absorbed component can form a long chain polymer
This polymer meshes with the substrate in whats known as molecular entanglement leading to a high bond strength

35
Q

what do we do with the smear layer?

A

Most dentine bonding agents take off the smear layer and bond to the clean dentine beneath
Some incorporate it by penetrating it, infiltrating it with the bonding agent and stick it to the dentine below

36
Q

what are the two ways we remove or modify the smear layer

A

total etch

self etch

37
Q

what are examples of total etch

A

o Scotchbond multipurpose
o Clearfil photo bond
o Optibond FL

38
Q

what are the components of a total etch DBA

A

dentine conditioner
primer
adhesive

39
Q

what is a dentine conditioner

A

an acid, usually 35% phosphoric

40
Q

what is a primer

A

really adhesive part of the agent with a hydrophilic/hydrophobic molecule – it is bifunctional and it changes the surface from a low energy to a high energy one and it allows a hydrophobic material to stick to a hydrophilic one

41
Q

what is an adhesive

A

a resin which penetrates into the surface of the dentine attaching to the primers hydrophobic surface – it attaches to the bipolar molecule and the molecular entanglement occurs

42
Q

what does the dentine conditioner do

A

o Removes the smear layer
o Opens dentinal tubules by removing smear plugs
o Decalcifies the uppermost layer of dentine
o The etchant is washed off with water
o The collagen network in this top ten nanometers of dentine is exposed and subsequently penetrated by the next 2 components

43
Q

what does the primer do

A

the coupling agent
the C=C bond opens and forms a strong covalent bond within the next resin layer
the hydroxyl group can combine with similar polar groups on the HA and can react with amine groups on the collagen proteins
it gives dentine a hydrophobic surface into which the next layer of resin will follow

44
Q

why must the molecule or group of molecules be dissolved in a solvent in the primer

A

allows the primer to be carried into the moist collagen fibrillar network and displace the water molecules from the collagen permitting the primer to enter into the micro and nano spaces created around the collagen fibrils after the etching process

45
Q

give two examples of chemicals used as primers

A

HEMA (scotch bond, gluma, optibond)

4-META (hybrid bond, G bond)

46
Q

what is the adhesive

A

mixture of resin
usually bis-Gm or HEMA
hydrophobic
may contain filler particles to make it stronger
contains camphorquinone to allow it to light cure
penetrates primed dentine
forms micro mechanical bond within the tubules and exposed dentinal collagen fibres
molecular entanglement forms the hybrid layer

47
Q

what are problems with total etch

A

overetching causes collapse of collagen fibres so no penetration can occur
over etching causes a deep etch so primer cannot penetrate to full depth of the etch and can result in sensitivity
process is moisture dependent

48
Q

what happens if the tooth is overdried

A

collapsed dentine
decreased porosity
poor penetration by primer
poor bond

49
Q

what does moist dentine allow

A

a good bone

expanded dentine surface is porous and will absorb the primer and give a good bond

50
Q

what are the two reduced stage systems

A

separate etchant with primer and sealer combined

51
Q

describe the separate etchant with primer and sealer combined

A

still total etch technique
etchant still phosphoric acid
primer and sealer combined in a single bottle and applied to etched, washed dentine and light cured

52
Q

what are examples of total etch two stage bonding agents

A 
scotch bond One
Prime and bond
optibond solo 
I-bond TE
XP bond
53
Q

what is the general procedure for total etch two stage bonding agents

A
  1. Application of etchant and washed off to create demineralized dentine layer
  2. Application of primer and sealer in a single solution
54
Q

why are self etching primers different

A

 They do not attempt to remove the smear layer. They infiltrate it and incorporate themselves into it
 The acid monomers etch and incorporate themselves into the surface of the smear layer and dentine at the same time
 It is not washed off this removes the problem of how dry to make the dentine however it is still possible to contaminate from saliva

55
Q

what is present in self etching primers that allows them to work the way they do

A

contain acidic methacrylate monomers

56
Q

how do the acid monomers work in self etching primers

A

very complex bifunctional monomers etch and infiltrate the dentine surface with their hydrophilic end while polymerizing like a simpler bis-GMA material at the hydrophobic end.

57
Q

what does the acid group in the acid monomer react with

A

calcium ions in the tooth bonding to the surface and also creates an amorphous calcium chelate on the surface

58
Q

what is the fundamental mechanism of all bonding

A

Fundamental mechanism of all bonding is mineral exchange where minerals removed from the dental hard tissues are replaced by resin which once mineralized mechanically interlock in these porosities – MOLECULAR ENTANGLEMENT

59
Q

what does the self etch primer remaining bonded depend on

A

stability of the HA monomer bond
monomers with a lower pKa do not form a stable bond as they continue to dissolve HA which leads to a hybrid layer with unstable calcium phosphates incorporated

60
Q

why is a strong self etch not best for dentine

A

o Etching by-products are not washed away as in total etch
o These are soluble and weaken the integrity of the bond
o If too much hydroxyapatite is dissolved away the exposed collagen is vulnerable to breakdown and the bond will fail

61
Q

why is a mild self etch better for dentine

A

only partially demineralizes dentine
o The HA crystals remain around the collagen and are protective against hydrolytic breakdown and the remaining calcium ions allow ionic bonding
o MDP and 4-META agent are better than HEMA containing materials
o HEMA materials are more aci ic and absorb more water resulting in a less durable bond

62
Q

what are the advantages of self-etching bonding agents

A

 Less technique sensitive as there is no rinsing, no excessive drying, no dentine collapse leading to low bond strength
 Simultaneous demineralization and resin infiltration meaning there is less chance of post operative sensitivity

63
Q

what are the disadvantages of self etching bonding agents

A

 There is great variability between products with regard to the initial pH of the solution
 The different in pH results in different etch and different penetration of resin
 Those materials with a lower initial pH may not etch enamel efficiently
 There is little evidence of a stronger bond to dentine than with total etch

BDS2 CLINICAL Dental Materials (15 decks)

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