Dentin Bonding Agents

Question 1

Why use a bonding agent?

Answer 1

• Retention of resin
• Offset polymerization shrinkage
• Prevent/reduce micro-leakage
• improve marginal adaptation
• Prevent marginal discoloration
• conserve tooth structure

Question 2

Mechanism of adhesion?

Answer 2

-to replace hydroxyapatite with resin monomers using micromechanical retention

Question 3

4 Factors affecting adhesion

Answer 3

1. surface energy and wetting
   - acid etching -removes enamel rods - roughens surface and increases surface area, decreasing surface tension and increasing wettability
2. interpenetration (formation of hybrid zone)

Acid etch - removes smear layer from dentin, opening dentin tubules; dissolves Ca hydroxyapatite crystals around collagen fibrils, exposing them for interpenetration of primer monomer

3. micromechanical interlocking
4. chemical bonding

Question 4

How do you increase wettability?

Answer 4

Acid etching 37% Phosphoric acid

-removes smear layer, removes enamel rods, roughens surface, and increases surface area, thus decreasing surface tension and increasing wettability

Question 5

Key concept of ENAMEL adhesion?

Answer 5

• acid etching (15 seconds with 37% phosphoric acid) dissolves enamel rods creating a roughened surface (increase surface area/decreased surface tension/increase wettability)
• resin penetrates the roughened surface into micro-spaces and polymerization creates MICRO-TAGS within enamel

Question 6

Key Concept DENTIN adhesion (x 3)

Answer 6

• mechanism must allow resin monomers to penetrate collagen fibrils left exposed by acid etching
• when placing composite- ensure enamel bonding around periphery of preparation
• mechanical interlocking with etched dentin occurs by means of resin tags, adhesive lateral branches and hybrid layer formation and shows high bond strength values to dentin with marginal seal in enamel

Question 7

Problem with bonding to dentin?

Answer 7

Dentin is hydrophilic; hydrophilic environment

Bonding agents are hydrophobic

Question 8

Factors affecting dentin adhesion

Answer 8

• Smear layer
• Dentin moisture- dentin must be slightl moist to prevent collapsing of collagen fibrils
• pulpal dentin tubules- increase in number/diameter the closer to the pulp; intertubular collagen fibrils are less
• Hybrid layer
• Stresses
• Aging

Question 9

What is the smear layer? How thick is it?

Answer 9

• dentinal debris from cutting including blood and bacteria
• 1-5 ums thick
• protective function

Question 10

what is the hybrid layer?

Answer 10

The area of the bond where polymerized resin has infiltrated within the collagen scaffold

Question 11

1. What’s is polymerization shrinkage?
2. What is the bond strength required to resist stress caused by polymerization shrinkage in MPa?
3. What can happen if bond fails?

Answer 11

1. composites shrink as they polymerize: this creates stress
2. 17-20 MPas
3. Bond failure, marginal leakage, sensitivity

Question 12

What is the C factor?

eqn?

Answer 12

bonded surfaces

The cavity configuration

• restorations with a C-factor less than one are more likely to survive polymerization contraction stresses and remain bonded to the tooth.
• The higher the C factor, the greater the polymerization shrinkage; higher the stess on the bond

C factor= ________________

Class VI resin: 1/5= 0.2 stress

Class II: 4/2= 2.0 stress

Class V: 5/1= 5.o stress

ways to improve C factor: incremental placement of resin; bonding to enamel

Question 13

Is the CTE of composite greater or less than that of the tooth?

By how much?

Answer 13

LTC of composite is greater than that of the tooth

4xs greater

Question 14

What is microleakage?

How to best prevent?

Answer 14

1. passage of bacteria/toxins between the restoration and the tooth preparation walls. ( happens at the margin)
2. bond to enamel

Question 15

What is nanoleakage?

What does it result in?

Answer 15

1. where dentin is etched deeper than the bonding agent can infiltrate, creating small porosities in the hybrid layer and allowing fluid to pass from tubules around the hybrid layer (can be sealed at margin??)
2. cause sensitivity; can degrade bond or prevent complete polymerization

Question 16

What are aging effects on dentin adhesion

Answer 16

1. Collagen fibils in hybrid layer degrade leading to decreased bond strength
2. MMPs degrade collagen- current dentin bonding research is focused on inhibiting MMPs

Question 17

What is the type of etch used in dentin bonding?

Types of applications?

Answer 17

37% phosphoric acid

total etch: (etch both enamel and dentin)

selective etch: only etch enamel (used with 2-in one etch/primer, or all in one)

self-etch: no 37% phosphoric acid etch step

-only use the bonding adgent: either 2-in one etch/primer, or all in one

Question 18

Function of the primer

Components of the primer?

Answer 18

1. Function of the primer: wetting agent
   - to keep the collagen fibrils expanded and exposed
   - prevent collapse of collagen fibrils
2. Primers are solutions of monomers dissolved in solvents
   - Common solvents: acetone, ethanol, water
   - ideal is to remove solvent (air)
   - Monomer- HEMA

Question 19

What are the properties of the monomer HEMA and how does it work?

Answer 19

Bi-functional monomer and amphiphilic- both hydrophobic and hydrophilic

-hydrophilic end penetrates intertubular matrix and dentin tubules (have interfibilar water, collagen fibrils); hydrophobic layer is exposed to adhesive layer for bonding

Question 20

Function of the adhesive?

Examples of adhesive bonding agents?

Answer 20

• to fill the space betwen the collagen network and prevent fluid leakage by bonding to the hydrophobic ends of the monomer
• allow interaction and co-polymerization with the restorative material
• chemical bonding

bis-GMA

TEGDMA

UDMA

Question 21

4th Generation bonding system- explain?

components?

strength MPa?

Examples?

Answer 21

3-step etch and rinse- etch>primer>adhesive

Total etch system; moist dentinal bonding to avoid collagen collapse

~25 MPa

example: Opti-bond FL

etch: (37% H₃PO₄)

primer: HEMA + ethanol solvent

adhesive: Bis-GMA, GDMA, HEMA, Silica 48%

• gold standard for etch and rinse dentin bonding agents
• excellent enamel bonding
• hydrophilic primer is covered by a more hydrophobic resin, making it less susceptible to water sorption
• retention rates high 90s%

Examples: Optibond FL, Scotchbond Multi-purpose Plus, Amalgambond

Question 22

5th Generation bonding systems- explain?

components?

problems?

Examples?

Answer 22

2 step etch and rinse: etch> primer+adhesiveTotal etch system

problem: b/c primer and adhesive combined it is more hydrophylic and more susceptible to water sorption and hydolytic degradation over time
- the polymerized primer of the “one bottle system” tends to be hydrophilic in nature and not all 5th generation adhesives are compatible with dual and self-cured or core materials.
- are too acidic and thereby de-activate the tertiary amine in chemical-cured composites (dual cures)
- problems: post-sensitivity and marginal leakage

Components: Optibond Solo Plus

Solvent: Ethanol + HEMA monomer

15% resin filled + Fluoride

93% retention at 3 yrs

~25MPa

Ex: Optibond Solo Plus

Question 23

What is the hybrid layer?

Goal of the hybrid layer?

Answer 23

-The hybrid layer is formed by the monomer/resin infiltrated surface layer that penetrates the dentin and enamel.

The goal of ideal hybridization is to give high bond strengths and a dentin seal

Question 24

6th Generation bonding systems- explain?

components?

problems?

Examples?

Answer 24

self etch system

2 step: etch + primer> adhesive

Ex: Clearfil SE- gold standard of self etch systems

• contains 10-MDP- phosphate monomer (chemical and mechanical adhesion)
• better adhesion (higher bond strength) to enamel and dentin (PO₄ bonds chemically with Ca²⁺), metal and non-glass (Zr, Alumina)
  problem: Clearfil SE- pH is 2.0; 37% H₃PO₄ is 0.1-0.4;
• does not effectively remove the smear layer;
• ineffective etching of enamel and weaker enamel bond strength (25% less than 4th and 5th generations)
• recommend selective etching of enamel
• sufficiently bonds to dentin~40MPas
• 96% retention rate over 13 yrs

Question 25

7th Generation bonding systems- explain?

components?

problems?

Examples?

Answer 25

one step (All in one etch + primer+ adhesive) self etch system

• mixed chemistries of components make solution hydrophilic and attract water- leads to hydolysis and chemical breakdown
• once placed and polymerized, they are generally more hydrophilic- makes them more prone to water sorption, limits the depth of resin infiltration into the tooth and creates some voids

Examples: I-bond, Clearfil S3, Optibond All-in-one

research: meta-analysis (2010) Class V lesions- performed the worst of all dentin adhesive systems; sigificantly higher annual failure rates

Question 26

8th generation- Universal adhesives

Answer 26

- can be total, selective or self etching (1 or 2 steps)

• selective etching of enamel is recommended
• hydrophylic in nature- important to evaporate solvent (reduce water sorption and hydrolysis)
• can be used with direct or indirect restorations

Components: may contain 10-MDP

some have nano-fillers -increases the penetration of resin monomers and the hybrid layer thickness, which in turn improves the mechanical properties of the bonding systems

-Nano-bonding agents are solutions of nano-fillers, which produce better enamel and dentin bond strength, stress absorption, and longer shelf life

Scotchbond universal bond strength: ~29 MPa (self etch), 40 MPa (total etch)???

Ex: All-Bond Universal, Scotchbond Universal, Clearfil Universal, Optibond XTR

Question 27

Components of Scotchbond Universal

Shear bond strengths enamel and dentin for self etch and total etch options

Answer 27

• MDP phosphate monomer
• better adhesion (higher bond strength) to enamel, metal and non-glass (Zr, Alumina)
• Dimethacrylate resins (UDMA, GDMA)
• Vitrebond copolymer (to decrease effects of varying humidity)
• Monomer: HEMA
• Solvent: Ethanol/Water
• Silane- adhesion to glass based restorations ( no need for separate primer)

Shear bond strengths MPas:

Self-etch: cut enamel: 26 cut Dentin: 30

Total etch: cut enamel: 33 cut Dentin: 27

Question 28

T/F

1. Literature supports 3 step total etch system? (generation?)
2. Literature supports 2 step self etch systems? (generation?)

Answer 28

1. T

4th gen

2. T

6th gen

Question 29

What possible advantage does Clearfill SE (6th gen) have over 4th gen?

Potenial problem and solution for Clearfil SE?

Answer 29

6th gen Clearfil SE contains 10-MDP

1. contains 10-MDP- phosphate monomer (chemical and mechanical adhesion)
   - better adhesion (higher bond strength) to enamel and dentin (PO₄ bonds chemically with Ca²⁺), metal and non-glass (Zr, Alumina)
2. problem: Clearfil SE- pH is 2.0; 37% H₃PO₄ is 0.1-0.4;
   - does not effectively remove the smear layer;
   - ineffective etching of enamel and weaker enamel bond strength (25% less than 4th and 5th generations)
   - recommend selective etching of enamel

Question 30

How many coats of adhesive have been shown to increase bond strengths?

Answer 30

2

Question 31

What can you do to a prep to decrease sensitivity?

Answer 31

application of gluteraldehyde (Glumma) or HEMA - can disinfect and desensitize prep.

Question 32

Example of a selective (and self) etch dentin bonding sequence

Answer 32

1. RDI
2. tooth preparation
3. VitreBond (RMIGC) deepest dentin part as required -
   - Placement on dentin prior to etch so dentinal tubules are more easily sealed and are protected from etch
   - Dentin pretreatment is not recommended. The use of smear layer cleansers such as polyacrylic acid based solutions results in decreased adhesion of Vitrebond Plus liner/base.
4. Cure 20 secs
5. selective enamel etch: 37% H₃PO₄ 15 secs/rinse (even if self-etch system)
6. Gluma: scrub 30-60 secs - air dry and rinse (re-wets dentin)
7. Scotchbond Universal- air to remove solvent
8. Cure 10 secs
9. place resin (Filtek Supreme- cure 20 secs per 2mm increment)

Question 33

Example of Total etch technique

Answer 33

1. RDI
2. tooth preparation
3. VitreBond (RMIGC) deepest dentin part as required -
   - Placement on dentin prior to etch so dentinal tubules are more easily sealed and are protected from etch
   - Dentin pretreatment is not recommended. The use of smear layer cleansers such as polyacrylic acid based solutions results in decreased adhesion of Vitrebond Plus liner/base.
4. Cure 20 secs
5. etch enamel first, then dentin: 37% H3PO4 15 secs/rinse
6. Gluma: scrub 30-60 secs - air dry and rinse (re-wets dentin)
7. Primer- light brushing motion 15 secs- air to remove solvent;
8. Adhesive-light brushing motion 15 secs- air to remove solvent
9. Cure 20 secs
10. place resin (Filtek Supreme- cure 20 secs per 2mm increment)

Question 34

example GI/RMIGC

Answer 34

tooth prep

conditioner (if necessary)

place GIC

(esthetics and moisture not a concern; no enamel at cavosurface margin)