bonding systems

Question 1

what are the properties of dental adhesive?

Answer 1

high bond strength to tooth tissues
immediate high strength bond
durable bond
impermeable bond
easy to use 
safe

Question 2

why is bonding to enamel easy?

Answer 2

the structure of enamel
heterogeneous structure
-densely packed prismatic
highly mineralised (95% organic)
-more like rock/stone than bio tissue
dry

Question 3

describe the acid etch technique

Answer 3

enamel prisms filled with imperfectly packed hydroxyapatite crystals
surface modified by application of acid
acid roughens surface producing etched pattern
roughened surface allows micromechanical interlocking of resin filling materials
etched surface increases surface energy of enamel surface by removing surface contaminants leading to better wettability of enamel
better wettability allows resin to adapt better to roughened enamel surface

Question 4

what is the requirement for enamel etch technique and why?

Answer 4

enamel must be dry

moisture contamination will prevent flow of resin into etched surface

Question 5

what is the acid normally used in etching?

Answer 5

30-50% phosphoric acid

Question 6

what are the 2 types of resin put on top of enamel etch?

Answer 6

low viscosity bis-GMA to penetrate into rough surface and light cured
higher viscosity composite resin filling material on top

Question 7

describe the composition of dentine

Answer 7

20% organic
70% inorganic (HA)
10% water
permeable tubules
fluid pumps from pulp floor of cavity making surface wet
inconsistent material
-aged more mineralised
low surface energy
hydrophilic, most bonding agent hydrophobic

Question 8

what are the requirements of a DBA?

Answer 8

ability to flow
potential for intimate contact w dentine surface
low viscosity
adhesion to substrace
-mechanical
-chemical
-van der waals

Question 9

describe mechanical dentine bonding

Answer 9

same as enamel

dentine bonding agent and dentine surface meshing and interlocking with minimum gaps

Question 10

what type of bond does mineralised dentine have?

Answer 10

ionic

Question 11

what type of bond does organic dentine have?

Answer 11

covalent

Question 12

what is van der waals adhesion based on?

Answer 12

electrostatic or dipole interaction between bonding agent and substrate

Question 13

what does the strength of a van der waals interaction depend on?

Answer 13

contact angle

-indicates wettability of a solid by a specific liquid

Question 14

what is critical surface energy?

Answer 14

surface tension of a liquid that will just spread on the surface of a solid

Question 15

what surface energy must a liquid have compared to the surface it is being placed on for it to flow and stick?

Answer 15

lower surface energy

Question 16

why will a low SA spread on a higher SA substrate?

Answer 16

leads to a lower SA of the material as a whole

Question 17

what SA does wet dentine have?

Answer 17

lower than composite filling materials

Question 18

how do you get composite resin to stick to dentine?

Answer 18

make the surface of the dentine have a higher critical energy than the composite

Question 19

how do dentine bonding agents work?

Answer 19

they increase the SA of the dentine surface and allow composite to flow and stick
-surface wetting agents

Question 20

what are the stages of bonding to dentine?

Answer 20

etching
wetting agent
molecular entanglement
adhesive

Question 21

describe adhesion through molecular entanglement?

Answer 21

adhesive is absorbed onto surface but can also penetrate into the surface of the dentine
due to good wetting of dentine by adhesive and appropriate SA’s
absorbed component can form long chain polymer
polymer meshes with substrate=molecular entanglement->high bond strength

Question 22

what is the smear layer?

Answer 22

an adherent layer of organic debris that remains on the dentine surface after the prep of the dentine during the restoration of a tooth
attached to dentine surface
contaminated with bacteria
interferes with adhesion

Question 23

what do you do with the smear layer?

Answer 23

remove it and bond to the clean dentine beneath

incorporate it by penetrating it, infiltrating it with the bonding agent and stick to the dentine below

Question 24

what are total etch bonding agents?

Answer 24

involve complete removal of the smear layer
eg. 
scotchbond multipurpose
clearfil photo bond
optibond FL

Question 25

what are the components of a total etch DBA?

Answer 25

dentine conditioner -35% phosphoric acid primer -adhesive part with hydrophilic/hydrophobic molecule adhesive -resin which penetrates into surface of dentine attaching to the primers hydrophobic surface

Question 26

what does the dentine conditioner do?

Answer 26

``` removes smear layer opens dentinal by removing smear plugs decalcifies uppermost layer of dentine etchant washed off with water collagen network exposed so penetrated by next 2 components ```

Question 27

describe the primer

Answer 27

adhesive element coupling agent bifunctional molecule with a hydrophilic end to bond to the hydrophilic dentine surface and a hydrophobic, methacrylate end to bond to resin also has spacer group to make it long enough to be flexible when bonding dissolved in suitable solvent

Question 28

what coupling agent is commonly found in primers?

Answer 28

HEMA

Question 29

how does bonding to dentine occur?

Answer 29

C=C bond opens and forms strong covalent bond with next resin layer hydroxyl group can combine w/ similar polar groups on the HA and react with amine groups on the collagen protein

Question 30

give another example of a chemical used as a primer

Answer 30

MDP -clearfil

Question 31

describe the adhesive

Answer 31

``` mixture of resins -bis-GMA & HEMA predominantly hydrophobic filler particles make it stronger camphorquinone makes it light cure ```

Question 32

describe how the adhesive works

Answer 32

penetrates primed dentine which now has a hydrophobic surface forms micromechanical bond within tubules and exposed dentinal collagen fibres molecular entanglement forms hybrid layer of collagen plus resin

Question 33

what problems can occur with total etch?

Answer 33

technique sensitive over etching-collapse of collagen fibres no resin can penetrate over etching-too deep an etch and the primer cannot penetrate to the full depth of the etch moisture dependent -too dry surface collapse -too wet primer diluted

Question 34

how does self etch work?

Answer 34

dont remove smear layer infiltrate and incorporate themselves into it not washed off creates hybrid layer

Question 35

advantages/disadvantage of self etch

Answer 35

not as technique sensitive | bond not as strong

Question 36

what component allows self etch to work?

Answer 36

acidic methacrylate monomers eg methacryloyloxyalkyl acid phosphatase

Question 37

how do the bifunctional monomers work?

Answer 37

etch and infiltrate the dentine surface with their hydrophilic end while polymerising like a simpler bis-GMA material acidic groups react with Ca2+ ions bonding to the surface and creating an amorphous ca chelate smear layer dissolved then incorporated in hybrid layer penetrates 2um into surface but gives good bond strength no evidence for reduced sensitivity

Question 38

what is the chemistry of molecular entanglement?

Answer 38

minerals removed from dental hard tissue replaced by resin which once mineralized mechanically interlock in these porosites all acid monomers bond to ca in HA whether they stay bonded depends on stability of HA monomer bond hybrid layer with unstable CaPO incorporated

Question 39

where is strong self etch best used?

Answer 39

enamel | less bond to dentine

Question 40

why does self etch not work well with dentine?

Answer 40

etching by products not washed away they are soluble so weaken integrity of bond if too much HA dissolved exposed collagen is vulnerable to breakdown and bond will fail

Question 41

describe mild self etch

Answer 41

only patrially demineralises dentine HA crystals remain around collagen MDP and 4-META agent are better than HEMA -more acidic absorb more water=less durable

Question 42

what are the problems with the smear layer?

Answer 42

if its too thick mild self etch may not penetrate challenge=penetrate without decalcifying tooth surface and removing HA HA required for durable bond and protects dentine from hydrolytic breakdown

Question 43

advantages of self etch

Answer 43

less technique sensitive -no rinsing -no excessive drying -no dentine collapse leading to low bond strength simultaneous demineralisation and resin infiltration less change of post-op sensitivity

Question 44

disadvantages of self etch

Answer 44

great variability between products initial pH dif in pH results in dif etch and dif penetration of resin materials with lower pH may not etch efficiently little evidence of stronger bond to dentine than total etch

Question 45

how is the best bond achieved with self etch?

Answer 45

etch the enamel with phosphoric acid