Adhesion to enamel Flashcards
What’s important when we bond something to enamel? In what do we have to focus?
mineral component - hydroxyapatite-
What is the smallest unit of enamel?
Crystallites
How are the submicron hydroxyapatite crystals orientated and what microscopic unit do we observe?
3 dimensions
rod or prism (about 100 crystallites)
How are the enamel rods connected and how do they appear like?
connected to one another,
appear like “keyholes”.
How are crystals called that surround each rod?
Interrod enamel.
Name the enamel composition:
- rod or prism
- enamel rods
- interrods
Where are the rods wider? Outside or inside?
wider on the outside than in the dental enamel junction
Describe the enamels surface:
smooth.
Prepared surfaces expose rods in tangential, oblique and longitudinal planes.
What can we obtain at the outer surface?
Aprismatic enamel
Crystallites run parallel to each other and perpendicular to the surface (20-200 μm thickness)
Where can we find a higher density of the rods?
The density of the rods is higher at the DEJ than at the enamel surface. The diameter of the enamel rod increases from the DEJ to the outer surface by a ratio of 1:2
Why is enamel a poor substrate to bond to?
cause its:
- Smooth
- Wet
- Organic pellicle
- Relatively low surface energy.
If we have a caries what do we have to remove in order to make a bevel?
if we have a caries, we have to remove the primatic layer, making a bevel
State the “Bonding to enamel” steps:
- Aprismatic layer removal
- Conditioning of the exposed tissue
- Priming/ bonding agent
How do we remove the aprismatic layer?
- Using a diamond bur and performing a roughening or a bevel.
- We expose prisms and so increase the surface energy.
- Clean and wash the teeth with water.
- Isolation.
How do we condition (aufbereiten) the exposed tissue?
We need to condition exposed tissue to obtain micro retention favouring adhesion
- Etching with phosphoric acid, increases surface energy, increases bonding area and roughness, slowing the hydrophobic resins to penetrate the porosities of the dried etched enamel
- selective dissolution (Auflösung) of the enamel prisms on its surface
Conditioning of the exposed tissue
a. Acid: Orthophosphoric acid.
b. Acid concentration: 37%.
c. Time: 15 sec
d. Enamel structure to etch: prism heads (ideally)
What type of bonding do we observe when the attack is paralell to the prism?
Type I (prism center etching)
- attack paralell to the prisms axes, removal of enamel prism cores (head of the prisms)
(like honey comb)
What type of bonding do we observe when the attack is perpendicular to the prism axes?
Type II (prism periphery etching)
Attack perpendicular to the prisms axes.
Whats a type II bonding attack?
Attack perpendicular to the prisms axes.
Whats a type I bonding attack?
Attack parallel to the prisms axes
What type of bonding to we observe when its attacked longitudinal and horizontal?
Type I and II
Whats a type I and II bonding?
Both can be present in the same tooth and the same zone simultaneously.
Can be due to structural characteristics of enamel mineralization
Which type of bond is the best?
Type U
Which type of bond is the worst?
Type III
What type of bonding do we observe when the etching time is longer than 25-30 sec?
Type III
mixed, no prism structures are evidenced
Includes areas resembling type I and type II patterns as well as regions in which the etching pattern appears prism-less as the prisms morphology is not well defined, appearing as a generalized rough surface.
What is type III bonding?
occurs with teaching times more than 25-30 sec
We get a decreased depth of microspores and a lower retention capacity
How do we have to put the acid etching properly?
After applying the acid etchant 37% during 15 sec, wash and dry the enamel.
(whitish appearance on drying)
What acid type do we have to use?
Acid type: orthophosphoric acid.
What concentration do we have to use?
Concentration: 37%
What form do we have to use?
gel
What performance time do we have to achieve?
15-20 sec
How long does the washing time has to be?
30-40 sec
How do we have to clean after washing?
Dry with clean air
What happens if we dont do the washing in a proper way?
If not done properly, calcium and phosphate precipitates will plug the microporosities created by the acid, not allowing micromechanical bond.
How do we have to dry properly?
The etched and washed enamel should be properly dried with cool, clean, dry air, free of contaminants, during a few seconds (aspect of chalk).
What are we adding to the priming/ bonding agent in order to decrease the viscosity?
Generally enamel bonding agents contain Bis-GMA or UDMA with TEGMA added to decrease the viscosity.
How does the priming/ bonding agent work?
They penetrate into the microporosities created by the conditioner due to a capillary process forming resin micro and macro tags when cured.
Whats less retentive, macro or microporosities?
Macro
no logic
Whats more retentive, macro or microporosities?
Micro
