Bonding Flashcards
What are the properties of a dental adhesive?
- provide a high bond strength in dental tissues
- easy to use
- safe to use
- durable and impermeable bond.
How does the acid etch bond to enamel?
-long enamel prisms are imperfectly filled with hydroxyapatite crystals and when cid is applied the surface is roughened to produced a characteristic etch pattern.
-This roughened surface allows interlocking of materials (mechanical) of resin filling materials
The etching also increases the surface energy of the enamel surface by removing surface contaminants leading to better wettability of the enamel.
Better wettability allows the resin to adapt better to roughened enamel surface.
For this to work the enamel must be dry. Moisture contamination will prevent flow of the resin into the etched surface.
Enamel bonding is essentially Mechanical
What acid is most commonly present in acid etch and what strength is it?
-Phosphoric acid, 30-50%.
What happens when a lo viscosity Bis-GMA resin is applied to the etched dried enamel surface?
penetrate into the rough surface and light cured.
What is the composition of dentine?
- 20% organic (collagen)
- 70% inorganic (mostly hydroxyapatite)
- 10% water
What makes dentine a wet surface?
-The fluid from the pulp flows up to the dentine floor of any cavity.
Where in the dentine has more tubules?
The dentine near the pulp has more tubules and increased moisture content. LOW SURFACE ENERGY.
Why do most simple bonding agents not adhere to dentine?
Dentine is hydrophilic whereas most simple bonding agents are hydrophobic.
What is the smear layer of dentine?
The smear layer is a surface accumulation of debris formed on dentine during instrumentation. It is composed of organic and inorganic components and forms both a superficial, loosely adherent, layer and a deeper, tightly adherent, layer. This is a complicating factor when bonding to cut dentine.
It is 0.5 – 5 microns in thickness.
It is variably attached to the dentine surface.
It is generally contaminated with bacteria.
Originally it was thought of as a protective barrier reducing permeability of the dentine and protecting the pulp.
Now it is considered to interfere with adhesion.
What are the requirements of a dentine bonding agent?
- Ability to flow
- Potential for intimate contact with dentine surface
- Low viscosity
- Adhesion to substrate (mechanical, chemical and van Der Waals adhesion).
What is the chemical bonding of dentine at a molecular level?
Mineralised- Ionic.
Organic- Covalent.
Define critical surface energy.
The surface tension of a liquid that will just spread along the surface of a solid. A liquid must have a lower surface energy than the surface it is being placed on for it to flow onto it and stick.
A low surface energy liquid will spread on a higher surface energy substrate because this leads to a lower surface energy of the material as a whole.
What do dentine bonding agents do to dentine in relation to the critical surface energy?
Wet dentine has a low surface energy, lower than composite filling materials.
For composite resin to stick to dentine you must make the surface of the dentine have a higher critical energy than the composite.
Dentine bonding agents increase the surface energy of the dentine surface and allow composite to flow and stick to the surface.
They are SURFACE WETTING AGENTS.
Name examples of total etch.
Total etch completely removes the smear layer.
- Scotchbond multipurpose
- Clearfil photo bond
- Optibond FL
Name examples of total etch dentine bonding agent and what are the components of it?
Total etch completely removes the smear layer.
- Scotchbond multipurpose
- Clearfil photo bond
- Optibond FL
Dentine conditioner: An acid, usually 35% phosphoric.
Primer: Really the adhesive part of the agent with a hydrophilic/hydrophobic molecule
Adhesive: A resin which penetrates into the surface of the dentine attaching to the primers hydrophobic surface.
