Adhesion on hard dental tissues 2 Flashcards
advantages of the adhesive techniques
- More retention & stability
- Reduce microleakage
– Reduce postoperative sensitivity
– Reduce marginal staining – Reduce recurrent caries – Reduce pulp pathology - Better transmition & distribution of the functional forces
– Have the potential to reinforce weakened tooth structure – Promote the material’s strength - More conservative (Conservative technique):Minimal loss of tooth material
- Desensitization: seal the dentinal tubules
- Expanded the range of possibilities for aesthetic restorative dentistry
Adhesion to the hard dental tissues
components
2 adherents(RC and HDT=hard dental tissue) • adhesive: adhesive system
Mechanisms of adhesion
- Chemical mech.:
• between adhesive and RC
• between adhesive and hard dental tissue - Micromechanical mech.: penetration of the adhesive into adherent’s surface and its fastening inside the hard dental tissue
- Inter-diffusion layer formation(the bond between long molecular chains):
between dentinal collagen fibers and adhesive polymer
Importance of the hybrid layer
Nakabayashi,1982…”Hybrid layer formation represents the main mechanism of adhesion to dentine”
• The hybrid layer has the role to:
- assure the bond between the RC – the hard dental tissue
- obturate the dentinal tubules, thus preventing the bacterial infiltration towards the dental pulp (microleakage)
Other names for the hybrid layer: ⇒Interdiffusion zone/layer
⇒Resin supported dentine
⇒Resin integrating dentine
Hybrid layer definition
replacement of removed
minerals after acid etching of dentine, with the monomers of the adhesive, and after their fastening, they’ll stay micromechanically attached inside the obtained porosities (micro crevices)
Factors affecting adhesion to hard dental tissues
- wettability of the adhesive
- composition and structure of the enamel and dentine
- the degree of the internal and external moisture of the dentine
- smear layer
- polymerisation shrinkage of the RC
- initial polymerization degree of the RC
- coefficient of shrinkage and coefficient of thermal expansion
- transmission of the polymerization stress towards the tooth-adhesive interface
Composition of enamel and dentine
Composition of enamel and dentine
enamel(more hydroxyapatite) dentine(more water and collagen)
Hydrophobic or hydrophilic monomers wet the same the enamel The dentin needs hydrophilic monomers
The enamel and the dentine need micromechanical retentions in order to obtain an intimate contact on a wider surface with the adhesive
The structure of the enamel
Almost homogeneous
– Low water content
– Low surface energy
– Enamel prism / rod=>Contain Hydroxyapatite crystal – is anisotropic(a)-depends on direction [isotropic(b)= same structure in all directions]
– is very hard, and it has a high compressive strength – it has a low tensile strength
The structure of the dentin
Vital and dynamic tissue
• Dentinal tubule:large near the pulp but small near the enamel
• More organic components and water content than enamel [more hydrophilic]
• Low surface energy
smear layer
Smear layer
= Poorly adherent layer of tooth debris, saliva and bacteria and other particles, produced by cutting the tooth surface with burs
• 0.5-5μmthickness
• Interferes with the bonding process(it has to be removed)
• Weak cohesion and adhesion(cannot be removed with air/water syringe)
• Newer dentin bonding systems(DBS
Requirements for an optimal bond
HARD DENTAL TISSUE - perfect clean surface, without any contaminants, with microcrevices - high surface energy – acid-etching ¤ ADHESIVE low viscosity - water/air removal from the microcrevices of the adherent before application of the fluid adhesive = the surface tension of the adhesive slightly
The components of adhesive/dentine bonding systems(DBS)
Acid
Acid-etch
Microrententions obtained within the hard dental substrate through etching/demineralization + increase of the surface energy through adsorption onto the surface of the tooth of a layer of phosphate groups highly polar, from the orthophosphoric acid 37%
Primer
Primer application
Premises for the hydrophobic adhesive application onto the dentin + physical adhesion with or without chemical adhesion with the demineralized dentin
Adhesive
Adhesive application (bonding)
Sealing of the demineralized zone + completion of the adhesive bond between the 2 adherents (the
hard dental substrate and RC) → hybrid layer
Acid-etching Content
orthophosphoric acid 37 % (35%, 10%)
- produces the most efficient acid-etching
- it has a content of cellulose filler which increases its viscosity (gel)
- 3% ferric chloride or 10% citric acid
- acid monomers (self-etch adhesive systems
acid etching Application
continuous brushing fluid - 30s on enamel -15s on dentin - water rinse – 10s - drying -good - enamel - light - dentin
I. a) Acid-etching patterns on enamel
The achievement of one or another etched model is not clinically predictable Type 1 (central) and 2 (peripheral) favorable – are found in the enamel area with a typical prismatic structure Type 3 (poorly structured) and 4 (fern structure) – are found especially at the premolars and to the unerupted teeth.
