Dentin Bonding Agents Flashcards
Why use a bonding agent?
- Retention of resin
- Offset polymerization shrinkage
- Prevent/reduce micro-leakage
- improve marginal adaptation
- Prevent marginal discoloration
- conserve tooth structure
Mechanism of adhesion?
-to replace hydroxyapatite with resin monomers using micromechanical retention
4 Factors affecting adhesion
- surface energy and wetting
- acid etching -removes enamel rods - roughens surface and increases surface area, decreasing surface tension and increasing wettability - 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
- micromechanical interlocking
- chemical bonding
How do you increase wettability?
Acid etching 37% Phosphoric acid
-removes smear layer, removes enamel rods, roughens surface, and increases surface area, thus decreasing surface tension and increasing wettability
Key concept of ENAMEL adhesion?
- 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
Key Concept DENTIN adhesion (x 3)
- 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
Problem with bonding to dentin?
Dentin is hydrophilic; hydrophilic environment
Bonding agents are hydrophobic
Factors affecting dentin adhesion
- 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
What is the smear layer? How thick is it?
- dentinal debris from cutting including blood and bacteria
- 1-5 ums thick
- protective function
what is the hybrid layer?
The area of the bond where polymerized resin has infiltrated within the collagen scaffold
- What’s is polymerization shrinkage?
- What is the bond strength required to resist stress caused by polymerization shrinkage in MPa?
- What can happen if bond fails?
- composites shrink as they polymerize: this creates stress
- 17-20 MPas
- Bond failure, marginal leakage, sensitivity
What is the C factor?
eqn?
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
Is the CTE of composite greater or less than that of the tooth?
By how much?
LTC of composite is greater than that of the tooth
4xs greater
What is microleakage?
How to best prevent?
- passage of bacteria/toxins between the restoration and the tooth preparation walls. ( happens at the margin)
- bond to enamel
What is nanoleakage?
What does it result in?
- 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??)
- cause sensitivity; can degrade bond or prevent complete polymerization
What are aging effects on dentin adhesion
- Collagen fibils in hybrid layer degrade leading to decreased bond strength
- MMPs degrade collagen- current dentin bonding research is focused on inhibiting MMPs
What is the type of etch used in dentin bonding?
Types of applications?
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
Function of the primer
Components of the primer?
- Function of the primer: wetting agent
- to keep the collagen fibrils expanded and exposed
- prevent collapse of collagen fibrils - Primers are solutions of monomers dissolved in solvents
- Common solvents: acetone, ethanol, water
- ideal is to remove solvent (air)
- Monomer- HEMA
What are the properties of the monomer HEMA and how does it work?
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
Function of the adhesive?
Examples of adhesive bonding agents?
- 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
4th Generation bonding system- explain?
components?
strength MPa?
Examples?
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
5th Generation bonding systems- explain?
components?
problems?
Examples?
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
What is the hybrid layer?
Goal of the hybrid layer?
-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
6th Generation bonding systems- explain?
components?
problems?
Examples?
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
7th Generation bonding systems- explain?
components?
problems?
Examples?
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
8th generation- Universal adhesives
- 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
Components of Scotchbond Universal
Shear bond strengths enamel and dentin for self etch and total etch options
- 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
T/F
- Literature supports 3 step total etch system? (generation?)
- Literature supports 2 step self etch systems? (generation?)
- T
4th gen
- T
6th gen
What possible advantage does Clearfill SE (6th gen) have over 4th gen?
Potenial problem and solution for Clearfil SE?
6th gen Clearfil SE contains 10-MDP
- 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
How many coats of adhesive have been shown to increase bond strengths?
2
What can you do to a prep to decrease sensitivity?
application of gluteraldehyde (Glumma) or HEMA - can disinfect and desensitize prep.
Example of a selective (and self) etch dentin bonding sequence
- RDI
- tooth preparation
- 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. - Cure 20 secs
- selective enamel etch: 37% H3PO4 15 secs/rinse (even if self-etch system)
- Gluma: scrub 30-60 secs - air dry and rinse (re-wets dentin)
- Scotchbond Universal- air to remove solvent
- Cure 10 secs
- place resin (Filtek Supreme- cure 20 secs per 2mm increment)
Example of Total etch technique
- RDI
- tooth preparation
- 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. - Cure 20 secs
- etch enamel first, then dentin: 37% H3PO4 15 secs/rinse
- Gluma: scrub 30-60 secs - air dry and rinse (re-wets dentin)
- Primer- light brushing motion 15 secs- air to remove solvent;
- Adhesive-light brushing motion 15 secs- air to remove solvent
- Cure 20 secs
- place resin (Filtek Supreme- cure 20 secs per 2mm increment)
example GI/RMIGC
tooth prep
conditioner (if necessary)
place GIC
(esthetics and moisture not a concern; no enamel at cavosurface margin)
