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Flashcards in adhesion to hard dental tissues 3 Deck (24):
1

Primer content

A bi-functional molecule
• HEMA(hydroxyethylmethacrylate)
• MEP-P(dimethacryloxyethylphenolphosphate) • NPG-GMA
• ethanol
• water

– solvent(helpstheprimertohaveabetterinfiltrationinsidedentin) • acetone
is very important for the primer to penetrate the demineralized dentinal structure, in order to obtain complete re-hydration (saturation) of the collagen fibers after their drying, otherwise there’ll remain some collagen fibers exposed and uncovered by the bonding agent, and this may be a weak interfacial zone.
in order to obtain a good infiltration of the primer, one may use an efficient solvent to replace the water from the demineralized dentin with the primer and may also create the favorable imposed requirements of the hydrophobic adhesive agent’s application.

2

primer role

acts as a dentin adhesive agent, ensuring the bonding of the hydrophobic monomer with the hydrophilic dentin
– HEMA – it has a hydrophilic (1) functional group (polar group: hydroxyl, aminic, carboxylic, aldehydic) + intermediary group (2)
+ hydrophobic (3) (methacrylate group)
– Assures the bond with the wet dentin (1)(sometimes only through physical adhesion, but in certain situations there may be also chemical bonds)
– Assures the flexibility of the molecule (2)
– Assurestheoptimalconditionsoftheadhesive’sapplication (3)(hydrophobic) in order to obtain a good adhesive bond with the dentin

The dentin primers try to form bonds with dentinal collagen or with left hydroxyapatite or with both of them
• The collagen has as reactive groups: hydroxyl and aminic groups
• Hydroxyapatite has as reactive group the Ca (calcium)
• Thus it helps for the hybrid layer formation

3

Application of the dentin primer

is very important to do a proper demineralization, thus the dentin won’t be too much acid-etched (in depth) and the primer will be able to infiltrate it
- in order to have a good infiltration of the primer at the collagen level it is necessary a sufficient application time of the primer and attention the way how it’s applied
- it must be applied in multi-layers, through continuous and dynamic brushing (20s) followed by a very light drying (2s)
- otherwise, at the base of the demineralized dentin it will remain a thin layer of demineralized collagen uncovered by the adhesive resin, because there the primer didn’t action at all
- The way how the primer is applied is crucial for the presence or the absence of the microleakage

4

Adhesive content

BisGMA (monomer) TEGDMA (dilution monomer ) - hydrophobic monomers
– HEMA - dilution monomer
– CQ - activator of the light-curing
– +/- inorganic filler (0.5 to 40 wt%) – gives strength to the adhesive bond

5

adhesive role

it fills the etched dentin zone after the primer’s action (the primer transforms the dentin in to a hydrophobic surface)
– after its light-curing it seals the dentinal tubules
– with the help of the primer the adhesive bonds to dentin and the 2nd light-curing group chemically bonds to the composite
– it results an interpenetrated layer between the dentin and the adhesive agent, the hybrid layer

6

Application of adhesive

20 sec through continuous brushing
– light drying (it eliminates the excess of water) – light-curing (20 s)

7

Mechanism of adhesion to enamel

Orthophosphoric acid application- 30sec
– A dull appearance after drying means a good demineralization
– SEM shows 2 favorable types of demineralization of enamel rods
• Adhesive application which
infiltrates the microcrevices, achieving after its
polymerisation, micromechanical adhesion,
with macrotags (intraprisms) and microtags (interprisms)

8

adhesive bond strength to enamel :factors

the length of tags hasn’t a significant importance
-moisture presence may interfere with tag formation – it is necessary a good drying and isolation
- the degree of polymerisation of the adhesive may influence the adhesion strength

9

mechanism of adhesion to dentin

Acid-etching for 15sec with orthophosphoric acid produces:
• Excessive drying produces
– Collapse of the collagen fibers =>!!! A light drying will prevent
this phenomenon
– It re-hydrates the collagen fibers
– It transforms the hydrophilic dentinal substrate into one which is hydrophobic
• Adhesive penetration into dentinal intratubules (macrotag) and intertubules (microtag) assures
– Micromechanical adhesion after polymerization – Dentinal tubules sealing

10

adhesive bond strength to dentin(critical) factors

excessive drying of the dentin produces the collapse of the collagen fibers and loss of micro- crevices
- it is necessary a reduced degree of moisture
- the tags’ length hasn’t any significant importance - very important is the perfect sealing of the whole demineralized dentinal tubules

11

Adhesive systems used nowadays
Classification according to mechanism of action(mechanism of HL formation)

1. Etch and rinse adhesive systems
2. Self-etch adhesive systems
3. Resin modified glass-ionomer adhesives
+/- inorganic filler

12

Etch and rinse adhesives

They have a separate step of acid-etching (conditioning), followed by rinsing
1.a.Classical – 3 steps:
– Acid-etching (rinse + drying)
– Primer (light drying)
– Adhesive (light-curing)
• Disadvantage:
– Difficult technique (each step has to be rigorously
followed) (technique sensitive

1.b.Simplification–2steps:
– Acid-etching (rinse + drying)
– Primer + adhesive (light-curing) (1 bottle)
• Disadvantage:
– Simultaneous application of the primer and adhesive; in fact it needs successive applications of some layers, thus ensuring a saturation of the collagen fibers
– A mixture of the primer with hydrophilic group and of hydrophobic adhesive, frequently leads to phase separation – the bottle needs to be shaked before usage

Etch and rinse techniques involve:
smear layer removal, HL with thicker macrotag formation

13

Self-etch adhesives

Acid monomers within primer, which aren’t rinsed from the dentinal surface and make a simultaneous etching (conditioning) + primer application
• Dissolve only partially the smear-layer (dentin) including it, into HL
• They do a much less depth of demineralization, depending on the pH of the acid monomers

Strong –self-etch adhesives – the pH

14

Classification of the adhesive systems according to their steps

3 steps
Type 1 (E&R0
1. Acid application, rinse, produces demineralized HL
2. Primer application
3. Adhesive application

2 steps
Type 2 (E&R)
1. Acid application, rinse, produces demineralized HL
2. Application of the primer and adhesive into single solution
Type 3 (SE)
1. Self-etch primer application
2. Adhesive application

1 step
Type 4 (SE)
1. Application of the self-etch primer and of the adhesive into single solution

15

which adhesive system should be used in daily practice according
to the clinical situation ?

Nowadays, optimal results obtained with:
– Etch and rinse - 3 steps => enamel
– Self-etch mild - 2 steps => dentin
– If there are mixed cavities => self-etch mild -2 steps onto the dentin, with extra acid-etching (15sec orthophosphoric acid 37%) only onto the enamel

16

is the adhesive bond reliable ?

the bond between hard dental tissue – adhesive is subjected to mechanical and chemical stresses which may lead to its degradation in time -!!more susceptible to degradation is the dentinal HL

17

mechanical stresses of adhesive bond

Mechanical stresses (break of the newly formed adhesive bond):
– polymerization shrinkage of the RC
– the way how the filling is applied and polished - finished
– high coefficient of thermal expansion of the RC
– eccentric occlusal stress

18

Chemical stress– chemical degradation of the components from the newly adhesive bond

Chemical stress– chemical degradation of the components from the newly adhesive bond
Biodegradation of the dentinal collagen matrix with or without the adhesive components (so degradation of the hybrid layer – the studies show its degradation mostly after 1-3 years)
Acid-etching of the dentin in order to remove the smear layer determines the collagen matrix exposure (after that the adhesive should infiltrate all the formed spaces, sealing in this way the collagen fibers)

19

causes od enzymatic attack

the resin (the adhesive) doesn’t completely infiltrate the
demineralized zone (wrong application of the primer) - the residual water from the dentinal tubules wasn’t
replaced by the resin (wrong application of the primer) - the distribution of the adhesive wasn’t homogeneous
(wrong application of the adhesive)

20

enzymatic attack definition and mechanism

Enzymatic attack (MMP = matrix metaloproteinases from the non-acid-etched dentin or bacterial) over the exposed collagen fibers (uncovered by the hydroxyapatite or by the adhesive)
determines
2. slowly hydrolysis of the fibers from the HL, finally depletion of the collagen fibers from the HL, gap formation inside the HL

21

incomplete polymerization

If
- the polymerization of the adhesive is not complete => residual monomers, susceptible to hydrolysis
- Takes place:
1. Extraction of the residual monomer resin (through hydrolysis and dissolution) which has infiltrated the dentinal matrix
2. exposure of the collagen fibers from the HL, followed by the previous mechanism

22

Nanoleakage

Nanoleakage – the term is first introduced by Sano et al, in 1995, to describe a specific type of leakage, which exists even in the absence of the marginal gaps
-takes place in the submicron porosities of 20-100nm, at the base of the HL in those zones where the adhesive resin didn’t infiltrate or which have been left poorly polimerized
- There are too small spaces in order to allow the bacterial penetration (0.5-1.0 μm) BUT
- Big enough to allow the penetration of the MMP
- This type of leakage is seen only microscopically and with Ag nitrate solution tracer (tree formation)
!!!! Nanoleakage is independent
from microleakage

23

Microleakage

Microleakage – clinically undetectable passage of bacteria, fluids, molecules or ions between a cavity wall and the restorative material
- There are spaces between 20 - 100 μm which allow the bacterial infiltration visible with an optic microscope
This it will have in time, visible microscopic effects : – marginal staining
- secondary caries
- adhesion loss

24

how to avoid micro and nano leakage

Complete infiltration into demineralized dentin and complete polymerization of the adhesive
- Side-effects locking of the MMPs at the dentin – adhesive interface (new ideas of using clorhexidine - within adhesives composition, which inhibits the activity of dentinal MMPs)
- Chemical adhesion between left hydroxyapatite among the dentin collagen fibers and the primer (self-etch mild, 2 steps)