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
