1. Etching in dentistry
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2. What is adhesion?
The force that binds two dissimilar materials together when they are brought into intimate contact
In dentistry, bonding refers to the process of attaching a restorative material to tooth structure by adhesion
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3. Basic principles in the bonding process
Surface preparation to remove plaque & debris
Acid etching with phosphoric acid, to remove mineral, create porosity, wettability
Bonding agent applied and flows to fill the porosities and create resin tags (micromechanical retention)
Resin applied and bonds chemically to underlying bonding agent (primary bonding)
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4. Adhesion
For proper adhesion to occur, intimate contact between the adhesive and the substrate is needed. This intimate contact is affected by:
Wettability of the substrate surface
The viscosity of adhesive
The morphology or surface roughness,
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6. Etching
Preparation of TOOTH surfaces and DENTAL MATERIALS with etching agents, usually phosphoric acid, to roughen the surface to increase adhesion or osteointegration.
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8. Enamel etching Introduced by Michael Buonocore in 1950s
Etching time: seconds (around 15 seconds)
Primary teeth and fluoride treated teeth require more time
Etched enamel looks frosty white when dried
Etching produces a rough surface (pits) into which resin flows and forms resin tags = micromechanical retention
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9. Enamel etching
Resin tags may penetrate to a depth of microns in etched enamel
The depth of penetration depends on:
Etching time
Rinsing time
These two actors determine how effective etching was, and how well debris were removed from enamel surface
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10. Enamel etching
Liquid or gel (the gel is made by adding colloidal silica to the acid) phosphoric acid 30-50% (usually 37%).
Concentrations higher than 50% lead to deposition of phosphate monohydrate on surface preventing further dissolution
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11. Procedure Acid etch is applied, how ?
Etchant is applied for 15 seconds, or longer as mentioned previously
Rinsing for 20 seconds then drying. Appearance of enamel?
Enamel should be kept clean and contaminant free (saliva, blood, etc)
If contamination occurs? Re-etch.
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12. Enamel bonding
In the past, etching and bonding involved only enamel. Currently, total etch technique is done, and bonding agents are applied to both enamel and dentine.
Bonding agents used for enamel bonding were made from resin combined with diluents to lower viscosity. (Bis-GMA + TEGDMA)
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13. Dentine etching and bonding
What makes dentine a challenge when it comes to adhesive bonding:
Dentine is a living tissue (50% HA, 30% collagen, 20% fluid)
Tubular nature of dentine (dentinal fluid)
Branching patterns in tubules, may enhance retention
Possible side effects on the pulp
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14. Dentine etching
1979 etching was done for dentine as well as enamel using 37% phosphoric acid. Research proved enhanced bonding
Over etching, effects on dentine structure and pulp?
Over etching dentine leads to weaker bond and sensitivity
Over drying should be avoided to prevent collapse of collagen and occluding tubules
Exposed collagen will act as a barrier to dentine bonding agent coating
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