Bonding to Tooth

Question 1

what are the properties of a dental adhesive

Answer 1

 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

Question 2

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

Answer 2

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

Question 3

describe the structure of enamel

Answer 3

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

Question 4

describe the structure of the prisms in enamel

Answer 4

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

Question 5

describe the structure of hydroxyapatite crystals

Answer 5

flattened hexagonals

spaces left between crystals is occupied by water and organic material

Question 6

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

Answer 6

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

Question 7

What is the acid etch technique

Answer 7

surface modification through the application of acid

Question 8

what does the acid etch do to the enamel

Answer 8

roughens the surface of the enamel

this allows micro mechanical interlocking of resin filling material

Question 9

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

Answer 9

increases the surface energy of the enamel surface

increases wettability of the enamel

Question 10

what does an increased wettability allow

Answer 10

wettability allows resin to adapt better to roughened enamel surface

Question 11

why must enamel be dry after acid etch

Answer 11

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

Question 12

what is enamel bonding essentially

Answer 12

mechanical

Question 13

what is usually used for enamel etching

Answer 13

35% phosphoric acid

Question 14

what happens after the enamel is etched

Answer 14

 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

Question 15

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

Answer 15

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

Question 16

describe the structure of dentine

Answer 16

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

Question 17

what is the issue with the dentinal tubules being permeable

Answer 17

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

Question 18

describe how dentine is an inconsistent material

Answer 18

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

Question 19

why does dentine have a low surface energy

Answer 19

because it is wet

dentine is hydrophilic but most bonding agents are hydrophobic

Question 20

what is the smear layer

Answer 20

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

Question 21

what are the requirements of a dentine bonding agent

Answer 21

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

Question 22

describe mechanical bonding in dentine

Answer 22

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

Question 23

describe what the etch does to the dentine surface

Answer 23

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

Question 24

describe chemical adhesion in dentine

Answer 24

bonding at a molecular level

Question 25

what type of bond does mineralized dentine have

Answer 25

ionic bond type

Question 26

what type of bond does organic dentine have

Answer 26

covalent bond type

Question 27

describe van der waals adhesion

Answer 27

based on electrostatic or dipole interaction between bonding agent and substrate

Question 28

what does the strength of van der waals adhesion depend on

Answer 28

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

Question 29

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

Answer 29

90 degrees

Question 30

what is the critical surface tension

Answer 30

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

Question 31

what is the rule for critical surface energy

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

what is molecular entanglement

Answer 34

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

Question 35

what do we do with the smear layer?

Answer 35

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

Question 36

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

Answer 36

total etch | self etch

Question 37

what are examples of total etch

Answer 37

o Scotchbond multipurpose o Clearfil photo bond o Optibond FL

Question 38

what are the components of a total etch DBA

Answer 38

dentine conditioner primer adhesive

Question 39

what is a dentine conditioner

Answer 39

an acid, usually 35% phosphoric

Question 40

what is a primer

Answer 40

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

Question 41

what is an adhesive

Answer 41

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

Question 42

what does the dentine conditioner do

Answer 42

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

Question 43

what does the primer do

Answer 43

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

Question 44

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

Answer 44

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

Question 45

give two examples of chemicals used as primers

Answer 45

HEMA (scotch bond, gluma, optibond) | 4-META (hybrid bond, G bond)

Question 46

what is the adhesive

Answer 46

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

Question 47

what are problems with total etch

Answer 47

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

Question 48

what happens if the tooth is overdried

Answer 48

collapsed dentine decreased porosity poor penetration by primer poor bond

Question 49

what does moist dentine allow

Answer 49

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

Question 50

what are the two reduced stage systems

Answer 50

separate etchant with primer and sealer combined

Question 51

describe the separate etchant with primer and sealer combined

Answer 51

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

Question 52

what are examples of total etch two stage bonding agents

Answer 52

``` scotch bond One Prime and bond optibond solo I-bond TE XP bond ```

Question 53

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

Answer 53

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

Question 54

why are self etching primers different

Answer 54

 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

Question 55

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

Answer 55

contain acidic methacrylate monomers

Question 56

how do the acid monomers work in self etching primers

Answer 56

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.

Question 57

what does the acid group in the acid monomer react with

Answer 57

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

Question 58

what is the fundamental mechanism of all bonding

Answer 58

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

Question 59

what does the self etch primer remaining bonded depend on

Answer 59

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

Question 60

why is a strong self etch not best for dentine

Answer 60

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

Question 61

why is a mild self etch better for dentine

Answer 61

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

Question 62

what are the advantages of self-etching bonding agents

Answer 62

 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

Question 63

what are the disadvantages of self etching bonding agents

Answer 63

 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