Flashcards in Dental Bonding Deck (51)
What does Adhesion mean?
Force which binds 2 differing materials together when they are in intimate contact with one another
What does Dental bonding mean?
Process of attaching a resin composite based material to the underlying tooth tissue using some form of intermediate material
What does Sealing mean?
Achievement of an impermeable barrier between the cavity wall and the restorative material to prevent the passage of bacteria
Give 6 advantages of bonding?
- No preparation of any mechanical retentive features necessary so tooth tissue is preserved
- Enhanced retention of the restoration to tooth tissue
- Seals the margins of the restoration with the tooth so reducing or eliminating microleakage
- Polymerisation shrinkage may be reduced
- Bonding to the tooth tissue may have a reinforcing effect on the weakened tooth structure
- Permits tooth coloured restorative materials to be used
What are the characteristics of Bonding?
- Solid-liquid interface is commonly encountered i.e intervening layer (adhesive) is generally applied as a liquid
- More readily wets the surface to be bonded
- Easier with a liquid and solid surfaces rather than solid-solid
- Needs good wetting for good bonding
- Viscosity of the liquid will limit the degree to which it wets the surface - less viscous the better
What is wetting?
Ability of a material to achieve an intimate microscopic contact with another
What's surface Tension?
The elastic tendency of the a fluid surface which makes it acquire the least surface area possible
Ability of the surface of a liquid to resist an external force
- Higher the surface tension, the lower is the ability of bonding to it
(Oil doesn't bond to/stays on top of water due to having a greater surface tension)
How many types of adhesion are possible at the interface?
What's Mechanical Adhesion?
- Utilises the rough aspect of all surfaces at a microscopic level
If both surfaces are uncontaminated, the irregularities in surface can connect and an attempt to slide one against the other is resisted by friction
What's Physical Adhesion?
- Due to molecular charges
- Dipolar molecule is attracted to an opposing charge on the other substrate
- Substrates orientate themselves so that the oppositely charged ends of the molecules are adjacent to eachother - relatively weak
- Increasing the surface area increases the forces to attract
What's Chemical Adhesion?
- Dissociation of a substrate structure after the application onto the surface of other
- Bonding process enhanced when the fluid contains a chemical which interacts with the substrate surface
- Failure is due to substrates rather than interface
What's the aim of Dental Bonding?
Use a combination of adhesion methods to bind the restoration to the tooth
1. Tooth surface is usually rough and intervening layer of resin fills these micro/macroscopic irregularities
2. Restorative surface has a relatively rough surface due to the filler causing irregularities
- Liquid resin (bonding agent) flows into the irregularities produced by the surface modification of the enamel (created by etching)
Resin solidifcation on polymerisation and the 2 materials become mechanically and chemically bound together
What are the essential prerequisities of a substrate (tooth) surface?
2. Large surface area
3. Good wetting properties
4. High surface energy
5. Free from debris and organic material
How do you ensure the tooth surface is free from debris and organic material?
- Surface should be cleaned thoroughly to remove AEP and plaque
- Use a pumice slurry and make sure a rubber dam is used
Why do we need to acid etch enamel?
- Outer layer is amorphous and has very little means of retention
- Very smooth and poor for micro-mechanical bonding
-> To enhance irregularities
What is Acid Etch?
Partially demineralise the crystalline structure of enamel to create a pitted surface for resin infiltration
- Critical requirement or any bonding process - substrate (tooth) prep
- Removes interprismatic enamel creating pits/clefts
What will etching of the enamel do?
1. Increase surface area for bonding
2. increase surface roughness
3. Decrease surface tension
4. Increase wettability
5. Increase the surface energy
What's the appearance of enamel after etching?
Why does bevelling enamel improving the quality of etching?
- Removes the outer amorphous enamel exposing fresh enamel for bonding and roughening its surface
- Alters the angulation of the enamel prisms and ensures that no unsupported prisms remain
- Higher bond strength may be achieved
What should you take into consideration when etching?
- Etching time should be extended for unprepared enamel to achieve a successful etch
- Same with older enamel due to increased fluoride content
- Primary enamel contains more prismless enamel surface so etching time needs to be increased to penetrate deep into the underlying prismatic enamel
- Bond strength is generally low though
- Leaving the etch on for too long
Causing decalicifation of the substrate to too great a depth so losing the etch pattern and decreased ability of the resin to form tags to penetrate into the etched pattern
- LOWER BOND STRENGTH AND INCREASED SENSITIVITY
What acid is typically used to etch enamel?
- 35-37% conc applied for 15-30 secs (30-50% optimum range)
- Most be strong enough to etch but not too concentrated so that the small amount of water present doesn't get saturated as this would slow dissolution rate
- Read manufacturers instructions
What forms can etching agents be found in?
Liquid and gel
What's liquid etching agent?
Typically a low viscousity liquid; flows easily - aids localisation of the acid solution = more precision
- But difficult to control
- Viscosity can be increased via the addition of fine particles
of collodial silica
What's gel etching agent?
- More viscous than liquid and stays in place
- A balance is needed in terms of viscosity - should be viscous enough to be placed precisely + remain there
- Not too viscous where it doesn't penetrate into the smallest fissures
WE USE: SCOTCHBOND ETCHANT (3M) (35% PHOSPHORIC ACID GEL)
What should you do after apply etch (either liquid or gel)?
- Newly etched surface and exposed crystallites are friable and may breakdown
- Acid should be gently agitated during application - removes etch solution at the surface of the tooth which has been contaminated with products of dissolution
- Movement introduces fresh acid to the surface so enhancing the efficacy and effectiveness of the etch process
What do you do to the enamel after applying and washing off the etch?
- Apply Bonding material
- Low viscosity dilute dimethacrylate resin (bis-GMA + TEGDMA)
- Add after etching - flows into the crevices formed - monomer is then polymerised to form a solid polymer
up to 30μm deep into enamel surface
- The resin composite is then added to this
Should you treat Dentine differently?
- It's a living tissue and heterogeneous
- More problematic for bonding:
+ always wet
+ surface is difficult to clean
+ frequently contaminated with smear (debris from cutting process)
What considerations should be applied to dentine?
- Smear layer must be removed or else the restoration won't be viable
- Dentinal fluids flow out of the tubules which can contaminate the surface
What 3 chemical processes must occur to bond to dentine?
1. (Priming) Removal of the smear layer and the etching of the dentine
2. (Coupling agent) impregnation of the dentine by a water miscible fluid or one which will substitute for the water
3. (Sealer) Application of a fluid which will bond to both the impregnated material and the overlying restorative or cast restoration
What is used to remove the smear layer and dentine etching?
- Phosphoric acid
- Nitric acid
Ethylene diamine tetra-acetic acid (EDTA)
What happens during Dentine Etching (priming)?
Modifies/removes the smear layer
Followed by partly demineralisation of the intertubular dentine and the periphery of the dentinal tubules
- Extends to depths of 10μm
What's the end result of dentine etching (priming)
Collagen matrix is left and uncollapsed (like dried spaghetti sticking up)
- Acts as a scaffolding which may be impregnated with the primer
(TOO MUCH ETCHING OR DRYING MAY COLLAPSE THE COLLAGEN MATRIX SCAFFOLDING)
What's the coupling and sealing process?
- Bifunctional monomer has the role of ionically linking to the hydrophobic methacrylate groups in the sealer to the collagen and hydroxyapatite in the hydrophilic dentine
- Called AMPHIPHILIC (has a polar, water-soluble group attached to a non-polar, water-insoluble hydrocarbon chain)
- Has a inert backbone
How is the bonding agent carried?
- Chemicals for bonding are dissolved in some form of solvent (hydrophilic chemicals which rapidly pass through the conditioned dentine carrying the coupling agent with them)
- Infiltrates the partly demineralised layers as well as passing into the dentinal tubules
What are the benefits of using a solvent as a carrier?
It displaces water in the dentine and are removed after they have served their function
What are the features of alcohol-based carriers?
- Evaporates less quickly
- Less sensitive to dentinal moisture
- Not as good at water chasing as acetone
- Decreased postoperative sensitivity
- May increase shelf-life of product containing acetone
What are the features of acetone-based carriers?
- Evaporation may be too fast; limiting penetration of the solute into the dentine
- More sensitive to dentinal moisture so more technique sensitive if the tooth is overdried
- Aggressive water chasing (removal of water of dentinal tubules)
- Bad odour
- Multiple coats may be require
What are the features of water-based carriers?
- Hydrophilic so better for substrate (dentine)
- Does not need to evaporate but has a long drying time
- Rehydrates demineralised collagen after drying of the primer
- Water may interfere with adhesion
- Difficult to remove
Why should you keep the caps of carrier bottles on?
- Solvent will evaporate without it
- Thickens the carrier solution
What's hybridisation and why is it important?
- The infiltration of partly demineralised dentine with the conditioning agent
Forms the hybrid layer
- Failure to achieve hybridisation results in voids leading to microleakage in the long term
What's wet bonding and why is it important?
Dentine the must be kept moist
- Over-drying the dentine or the collagen causes it to collapse which will decrease compromise bond strength
- CAN BE SAVED
- Remoistening with water will rehydrate the collagen and the fibrils stiffen slightly but not to their normal amount
- After air-drying the dentine should be left moist with glassy appearance
Why should you air-thin the bonding agent?
- Increase evaporation of residual solvent
- Strong blast will blow bond off the surface =
+ incomplete covering of the cavity
+ Formation of voids
+ Bond failure
+ Postoperative sensitivity
What's the Total Etch technique?
- Etches both enamel and dentine in one application
- Controlled acid penetration (less than 15μm) - minimal pulp risk
- Less time consuming
- Higher bond strengths gained
What should you do after using total etch?
- Wash and Dry BUT not over dry
- Apply bond and lightly dry
- Light cure and apply resin composite
What's a Selective Etch technique?
- Selectively etching just Enamel (or a substrate) at a different time to Dentine
- Etch the Enamel for an appropriate amount of time then etch the dentine
- Less potential to over etch the dentine
What are Self-Etching Systems?
- Self-conditioning etch adhesive system attempting to combine conditioning, priming and bonding in a single step
- Reduces working time
- No-post-conditioning rinsing = less technique sensitive
- Less sensitive to the degree of wetness/dryness of the dentine surface
What are some of the features of the Self-etch systems?
- Smear-layer adhering to dentine is dissolved then incorporated into the hybrid layer
- Simultaneous demineralisation and resin-infiltration means it's impossible to over-etch dentine so reduced post-operative sensitivity
- Reduced leakage due to better sealing ability
How does Self-etch Systems work?
Passenger Train & Tunnel:
- Train locomotive (etch part of the molecule) enters the tunnel (dentine tubule) pulling its carriages behind it (primer/bonding component)
- When the train (etch) gets some way into the tunnel it may stop (etching depth) but the carriages are still attached
- Penetration depth of the acid and the bonding agent are the same = no void where leakage or incomplete curing may result
What does a Self-Etch System compose?
- Acidic etchant to demineralise the tooth
- Linking molecule or primer and the bonding agent
- Solvent to carry the mixture to the sites of action (acetone or alcohol)