Bonding Systems

Question 1

What makes enamel good for bonding and how does bonding occur?

What type of bonding?

Answer 1

highly mineralised, dry prisms

acid etching with phosphoric acid creates microporosities on enamel surface

this roughened etched pattern allows micromechanical interlocking of resin materials

etching also increases surface energy for better wetting by resin

bonding to etched, dry enamel is essentially a micromechanical process

Question 2

What is the surface energy of a material?

Answer 2

A measure of the disrupted intermolecular bonds that exist at the surface of a material. Surfaces with high surface energy attract other materials to reduce this energy.

Question 3

Why do impurities reduce the surface energy?

Answer 3

surface atoms become attracted to impurities and bond

Question 4

What is the wetability of a material?

Answer 4

ability of a liquid to spread out and maintain contact with a solid surface.

Question 5

Why must enamel be dry for bonding?

Answer 5

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

Question 6

What is the bond strength of enamel to composite ?

Answer 6

> 20MPa
usually between 20-30

Question 7

What is the composition of dentine?

What are the characteristics and why does this affect bonding?

Answer 7

20% organic (mostly collagen) 70% inorganic (HA) 10% water
Full of permeable tubules (increased water contimation)
Less mineralisation
Low surface energy (due to water and weaker forces due to collagen

Question 8

What water quality are most bonding agents and what water quality is dentine?

Answer 8

Hydrophobic (plastic is oil)

Question 9

What is an added complicating factor when bonding dentine?

Why is this not present in enamel?

Answer 9

smear layer - an adherent layer of organic debris that remains on the dentine surface after the preparation of the dentine during the restoration of a tooth

does not occur in enamel as enamel is more mineralised (more resistance than collagen) and debris can penetrate less due to lack of tubules

Question 10

What bonds does the adhesion of dentine include?

Answer 10

Mechanical
Chemical
Van der waals

Question 11

How does mechanical bonding in dentine occur?

Answer 11

Same as enamel bonding. DBA and dentine surface mesh together and interlock with minimum gaps.

Question 12

At the molecular level, what bonds do the mineralised and organic components of dentine make?

Answer 12

Mineralised = ionic
Organic = covalent

Question 13

What does a contact angle of less than 90 mean?

Answer 13

Solid surface is hydrophilic and has good wetability (better adhesion to surface)

smaller contact angle = better wetting

Question 14

What is a critical surface energy?

Answer 14

the surface tension of the liquid needed to just spread on solid (in that case the contact angle of solid is zero)

Question 15

For a liquid to flow onto a surface and stick, what must happen?

Answer 15

Liquid must have a lower surface energy than the surface it is being placed on

Question 16

What is the surface energy of wet dentine?

Answer 16

Low surface energy - lower than composite filling materials

Question 17

For composite resin to stick to dentine, what must be done?

Answer 17

The surface energy of dentine must be increased higher than the composite so that the composite is able to flow over and adhere

Question 18

What agents increase the surface energy of dentine?

Answer 18

Dentine bonding agents (surface wetting agents)

Question 19

What is molecular entanglement?

Is it the same as mechanical bonding

Answer 19

Absorbed adhesive forms a long chain polymer which meshes with substrate (dentine) leading to high strength bond after there is good wetting of the dentine by adhesive and appropriate surface energies of the two

mineral exchange where some minerals from the dental hard tissue are removed and are replaced by the resin which once mineralised can mechanically interlock in these porosities.

It is specific to polymers unlike mechanical bond which is general

Question 20

What are the options of what to do with the smear layer?

Answer 20

Remove it and bond to the ‘clean’ dentine beneath
Incorporate it by penetrating it, infiltrating it with the bonding agent and stick it to the dentine below

Question 21

Why is it not a good idea to incorporate the smear layer?

Answer 21

the smear layer is not tightly bound to dentine and was affected by moisture
therefore saliva or dentinal fluid caused hydrolysis of the bond and it would break down resulting in leakage of the filling

Question 22

What do todays materials rely on that previous generations of DBAs didn’t?

Answer 22

Total etch or self etch
To modify/ remove the smear layer

Question 23

What is the gold standard DBA?

Answer 23

Total etch bonding agents

Question 24

What are examples of total etch DBAs?

Answer 24

Scotchbond multipurpose
Clearfil photo bond
Optibond FL

Question 25

What are the components of a total etch dentine bonding agent?

Answer 25

Dentine conditioner (etch) - acid usually 35% phosphoric acid Primer - really the true adhesive part of the agent with a hydrophobic/hydrophilic molecule Adhesive - resin which penetrates into the surface of the dentine attaching to the primer’s adhesive surface

Question 26

What does the dentine conditioner do in DBAs?

Answer 26

Removes smear layer Opens dentinal tubules by removing smear plugs Decalcifies the uppermost layer of dentine Increases surface area Exposes collagen network and subsequently penetrated by the next two components (primer + bond)

Question 27

What does the primer do?

Answer 27

Coupling agent Bifunctional molecule with a hydrophilic end to bond to the dentine surface and a hydrophobic methacrylate end to bond to the resin maintains expanded collagen network while removing residual water off dentine, helps bond infiltrate into collagen network

Question 28

What must the primer have to ensure flexibility?

Answer 28

The molecule must have a spacer group to make it long enough to be flexible when bonding. Lack of flexibility reduces bonding sites and bond strength

Question 29

What solvent dissolve primer?

Answer 29

water acetone ethanol

Question 30

What is a common coupling agent found in many primers?

Answer 30

HEMA (water absorbing plastic)

Question 31

What does the C=C bond in HEMA form?

Answer 31

Strong covalent bond with next resin layer

Question 32

What does the hydrophilic hydroxyl COOC2H4-OH group combine/react with? | What does this create?

Answer 32

Similar polar heads in dentine HA and reacts with amine groups on the collagen protein gives the dentine a hydrophobic high energy surface that the bond will flow into

Question 33

What is the adhesive usually a mix of and what do adhesives have that improve bond strength?

Answer 33

Mix of resins. Usually Bis-GMA and HEMA May contain some filler particles to make it stronger

Question 34

What does the adhesive have that allows it to light cure?

Answer 34

camphorquinone

Question 35

How does the adhesive bond?

Answer 35

Penetrates the primed dentine which now has a hydrophobic surface Forms a micro-mechanical bond within the tubules and exposed dentinal collagen fibres Carries out molecular entanglement Forms the hybrid layer of collagen and resin

Question 36

What are the problems with total etch? | not a simple technique

Answer 36

Over etching leads to collapse of the collagen fibres so no resin can penetrate Over etching creates too deep an etch and the primer cannot penetrate to the full depth of the etch. Too dry and the dentine surface collapses Too wet and the primer is diluted leads to reduced strength

Question 37

How have the bonding steps been combined?

Answer 37

Separate etchant with primer and sealer combined. Self etching primer and sealer all combined and applied together as a single solution.

Question 38

What type of technique is the separate etchant with primer and sealer combined?

Answer 38

Total etch technique

Question 39

What are examples of total etch two-stage bonding agents?

Answer 39

Scotchbond One Prime and Bond Optibond Solo i-Bond TE XP Bond

Question 40

How do self-etching primers work?

Answer 40

They do not attempt to remove the smear layer. They infiltrate it and incorporated themselves into it. They are not washed off. 1 bottle system

Question 41

Advantages VS Disadvantages of self etch

Answer 41

Advantages Less technique sensitive No rinsing and no excessive drying Simultaneous demineralisation and resin infiltration Disadvantages Difference in pH results in different etch and different penetration of resin. Those materials with a lower initial pH may not etch enamel efficiently.

Question 42

Why does pH affect self-etch?

Answer 42

acid monomers with a lower pKa do not form a stable bond as they continue to dissolve HA

Question 43

What allows self etch DBAS to etch the dentine? | What else do they contain?

Answer 43

Bifunctional complex acidic methacrylate monomers, which infiltrate the dentine surface with their hydrophilic end and then they polymerise a simpler bis-GMA material at the hydrophobic end. contain same chemicals as total and bonds via molecular entanglement and mechanical bonding

Question 44

What reacts with Ca+ ions at the tooth surface in self-etch? | What type of bond

Answer 44

acidic groups to form amphorous chelate | ionic

Question 45

Strong self etch VS Mild self etch

Answer 45

Strong Soluble byproducts are formed that weaken the integrity of the bond and are not washed away If too much hydroxyapatite is dissolved away the exposed collagen is vulnerable to breakdown and the bond will fail Mild Partially demineralises the dentine - HA crystals remain around the collagen Protective against hydrolytic breakdown Remaining Ca ions allow ionic bonding

Question 46

Why must HA not be completely demineralised?

Answer 46

The HA is required for strong durable bonding The HA protects the dentine from hydrolytic breakdown

Question 47

Which direct restorative material relies on chelation between carboxyl groups and the calcium in the tooth as a major component of the bonding mechanism?

Answer 47

Glass ionomer cements