bonding Flashcards
what are the 3 conditions of true adhesion of restorative materials to tooth structure?
- Conservation of tooth structure
- Achievement of optimal retention
- Prevention of microleakage
What are 4 factors affecting adhesive bonding ?
- Wetting
- Interpenetration (forming a hybrid zone)
- Micromechanical interlocking
- Establishment of a chemical bond
what is the acid-etch technique?
First introduced in 1955 by Michael Buonocore.
He micromechanically roughened the surface of interest, etched it with acid, then applied an acrylic restorative material.
The acrylic monomers wet the etched surface, flowed into the etched micropits, and created retentive resin tags that penetrated as deep as 10 – 20 microns into the porous enamel.
(The acid you are etching with is a gel so you can control the area, you don’t want acid flowing all over the mouth. )
Phosphoric acid is most widely used to etch dentin and enamel
Acid etching is key to a strong bond between resin and enamel
Provided the basis of innovative procedures such as: porcelain laminated veneers and bonded orthodontic brackets
Also solved the problems associated with interfacial leakage
what is the acidic agents and things about it?
Phosphoric acid with a concentration of 30 to 50 % is used to produce microporosity. The preferred agent has a 37% concentration.
Concentrations above 50% forms a monocalcium phosphate monohydrate layer on the etched surface, inhibiting further dissolution of the structure.
Generally the etchant is provided in gel form for accurate application.
Etching time of 15 seconds is enough, followed by a water rinse for 20 sec.
Drying with warm air or ethanol improves the bond strength
how does the died etch surface appear and what does the acid etch do to the surface energy of the enamel?
The dried etch surface appears frosted or white.
The acid etch raises the surface energy of the enamel
The etched surface should remain uncontaminated.
Bond strength of etched enamel ranges between 15 to 25 MPa depending on the resin and testing method used.
(By changing the surface energy you change the surface tension and therefore wettability increases. )
what does dentin have to do with bonding agents?
Dentin poses greater obstacles to adhesive bonding because it is live tissue made of 50 vol% hydroxyapatite (inorganic), 30 vol% Type I collagen (organic), and 20 vol% water.
Dentin adhesives should be hydrophilic to wet the surface
Dentin bonding could be achieved by establishing a chemical bond between the resin and either of the organic or inorganic components of the dentin.
Hydrophilic means the angle is as low as possible.
what was the development of dental adhesives in the past?
Generally, different products were developed to act as:
Conditioner (acid etchant)
Primer (dentin bonding agent)
Adhesive
(They were able to combine the conditioner and the primer and the primer and adhesive together but it is very difficult to do all three together. )
what are current dentin bonding agents like?
They are based on micromechanical retention through:
- Penetrating into the partially opened dentinal tubules.
- Forming a hybrid layer where hydrophilic monomers penetrate and polymerize to create an interpenetrating network with the demineralized collagen fibril network.
- Chemical interactions involving first- and second-order bonds.
(Don’t go too into detail about what are the first and second order bonds. )
The interpenetrating network formed by the polymerization of the dentin bonding agent monomers within the demineralized collagen fibril network plays a major role. However, similar bonding strengths can be accomplished by treating the conditioned surface with sodium hypochlorite which removes the demineralized collagen.
Self-etching primer (conditioner plus primer).
Self-priming adhesive (primer plus adhesive).
what can the bond strength be effected by?
The bond strength can be affected by several variables inherent to the dentin’s surface such as: water content, dentin permeability, and the orientation of the tubules to the surface.
Achieving 20 MPa minimal bond strength is an acceptable target.
In microtensile tests, the failure of the bond occurs at the adhesive interface, and not within the dentin.
how can microleakage be measured?
Microleakage at the restoration/tooth interface can be monitored using tracers and staining agents.
No good correlation between bond strength and microleakage.
How is amalgam bonding achieved?
In one scenario, 4-META is used.
Predominantly mechanical in nature.
Produced by condensing the amalgam into a plastic resin layer.
Produces macroretentive areas within the resin after polymerization of the resin.
what is good about pit and fissure sealants and what is the most popular ones?
Responsible for an Impressive reduction of occlusal caries
Applying a resin to penetrate through pits and fissures to seal them against bacteria and debris
Most popular sealants are polyurethanes and bis-GMA
Unfilled resins are colorless or tinted transparent
Filled resins are opaque and available in tooth color
To improve wetting, a conditioner is applied to the surface before the sealant
