Adhesives Flashcards
two primary methods used to measure bond strength
SBS
MBS
primary method of clinical testing for a dentin bonding
clinical evaluation in non-retentive, Class V , non-carious lesions
interaction of negatively charged phosphate or carboxylic acid groups is
chemical (ionic) adhesion.
Increasing the surface energy
improves adhesion
Roughening or etching a surface
- increases the surface’s surface energy
- creates micromechanical bonding
Removing surface contamination
improves surface adhesion.
Advantages of adhesion to tooth structure
1) conservation of tooth structure;
2) reduction of marginal leakage;
3) improved restoration retention;
4) makes possible esthetic restorations
Types of adhesion
1) mechanical;
2) chemical;
3) diffusional;
4) diffusive
Nature of enamel bonding
1) more homogeneous, regular structure; 2) high inorganic content; 3) higher surface energy - especially after acid etching; 4) surface rigidity and stability of bond strength over time.
Etching of enamel by acids:
Enamel can be etched to varying degrees by various acids (phosphoric acid, maleic acid, polyacrylic acid, etc.) and varying concentrations of those acids.
Etching of enamel by phosphoric acid was discovered
by Buonocore-1955.
Phosphoric acid gels ranging from____________ have been used to etch enamel.
10 - 50%
Preferred concentration of phosphoric acid for enamel etching is
35 - 40 %.
Preferred enamel etching time is minimum of
15 seconds if enamel minimum and dentin max
30 - 60 seconds (enamel only - not dentin).
Phosphoric acid is provided both in
liquid and gel form
Gel form of phosphoric acid is made of
Fumed silica (inorganic) or polymer thickening agents are used for phosphoric acid gels (~37% Phosphoric Acid).
Effects of phosphoric acid etching on enamel
1) creates micropores 5 – 50 microns deep; 2) increases surface energy; 3) increases wettability of the enamel surface.
Contamination on enamel:
saliva and enamel “pellicle” (surface layer of salivary proteins which forms rapidly).
Cleaning of both enamel and dentin involves use of
non-fluoridated pumise and a rubber cup in a low speed handpiece, following by thorough water rising and air drying.
Cleaning the surface increases
surface energy and decreases contact angle on the surface
Enamel bonding, after acid-etching, rinsing, and drying; involves the application of
unfilled resin bonding agent composed of low viscosity monomers (Bis-GMA. UDMA, TEGDMA,HEMA), and polymerization agents (initiators, accelerators, stabilizers).
Etched enamel shear bong strength
20 MPa
steps utilized in enamel bonding:
1- Phosphoric acid etch; 2- Rinse to remove acid + precipitate; 3- Apply hydrophobic bis-GMA monomer; 4- Light cure to polymerize; 5- Add composite resin against air-inhibited bonding agent surface and polymerize.
LED stands for
Light Emitting Diode.
density and morphology of dentinal tubules changes as dentin depth increases
as depth increases - density of tubules increases and tubule diameter increases
Dentin smear layer is produced by
Instrumentation
Smear layer composition
cut dentin debris & bacteria
Smear layer characteristics
- Reduces dentin permeability ~ 86%
- Weak adhesion to underlying dentin (2-3 MPa
- Thickness (0.5 - 5.0 microns);
- Will not wash off;
- very soluble
dentin is a hydrated/hydrophilic substrate, which makes it
difficult to bond to dentin.
basic components of contemporary dentin/enamel adhesive
1) AN ADHESIVE MONOMER (Carboxylic Acid or Acid Phosphate Methacrylate)
2) STRUCTURAL, CROSS-LINKING DIMETHACRYLATES – the “structural matrix
3) A SOLVENT, “WATER-CHASING” CARRIER – an ethanol or acetone
ethanol or acetone solvent characteristics
- solubilizes the adhesive and dimethacrylates of the adhesive
- reduces the viscosity to improve adhesive wetting, and (3) displaces (i.e. “chases”) water in the dentin
role and function of dentin primers as they were introduced in the 3rd and 4th generation adhesive
1) Contain Hydrophilic monomers dissolved in acetone, alcohol, and/or water;
2) Primer solvents (acetone/ethanol) serve to displace water in wet dentin;
3) Primer promotes infiltration into exposed collagen (hybrid zone) after etching;
4) Light air drying drive off solvents/ water ;
5) Primed dentin transforms hydrophilic surface to hydrophobic surface to bond more effectively to final hydrophobic resin adhesive component layer.
basic composition of the primer component in two bottle, 4th generation adhesive system
1) Contains a bifunctional monomer that links hydrophilic collagen to hydrophobic resin; 2) Chemical Structure contains: HEMA/Could also contain either: Phophate/Phosphoric acid ester-based monomer and/or Carboxylic Acid -based monomer.
Composition of adhesive components
Unfilled or lightly-filled monomers equivalent to enamel bonding Bis-GMA, UDMA, TEGDMA;
Function of adhesive components
- Stabilizes the hybrid layer by filling up remaining pores/gaps and creating resin tags in tubules/intertubular dentin
- Links primer to composite resin.
What is the hybrid layer
Conditioner (37% Phosphoric Acid/15 seconds max.) demineralizes dentin, removing mineral component and leaving hydrated collagen “sponge” layer;
Effect of primer and solvent on hybrid layer
- displaces water in the collagen “hybrid” zone with bifunctional monomers;
- interdiffuse this collagen-rich layer with low-viscosity monomers and resin component
Hybrid layer forms from
Polymerization which causes resin component mechanically to interlock with collagen
Why keep moisten dentin before bonding
Overdrying collapses the hybrid layer of collagen, preventing penetration of the open collagen matrix to create an adequate hybrid layer.
role of solvents
- displace remaining water in collagen (hyrbid zone) and dentin
- carry monomers into collagen
- upon gentle but prolonged air-drying, solvents are removed, leaving monomers behind to polymerized into cured adhesive.
Self-etch adhesives, composition:
1) Acidic monomers
2) Structural, crosslinking monomers - both hydrohphilic and hydrophobic;
3) Solvents which include water to lower the pH sufficiently to achieve etching of enamel.
Self etch function
1) Simultaneously etch enamel and dentin; 2) Bond to dentin is usually stronger than enamel. 3) Can be used with separate enamel etch of phosphoric acid as first step - but avoid separate dentin etch. 4) Dissolve the smear layer and create a thinner hybrid zone than total etch adhesive systems
Clinical efficacy for self etch
- increased staining of enamel margins over time compared to total etch.
- best clinical performance
Seventh Generation Self-etch adhesives
- All-in-one” adhesive
- combine conditioner, primer and adhesive in one bottle; one-step - no mixing
All in one adhesive characteristics
Low bond strengths; clinical performance thus far is not encouraging.
components of a contemporary dentin-enamel adhesiv
1) AN ADHESIVE MONOMER
2) STRUCTURAL, CROSS-LINKING DIMETHACRYLATES
3) A SOLVENT, “WATER-CHASING” CARRIER
Light curing initiator: Camphorquinone (CQ) is the
primary viable light initiator also used in dental composite resin restoratives and dental cements.
470nm is peak absorption
Light curing accelerator
tertiary amines that transfer free electrons to methacrylate groups and initiate free radical polymerization.
Self-cure initiator:
Benzoyl Peroxide (BPO) is the most commonly used chemical-cure initiator.
Self-cure co-initiator/accelerator
BPO reacts with certain tertiary amine compounds to form free radicals that cause the polymerization reaction to occur.
How do you convert light cured to light and chemical cured
by adding a drop of a second bottle (self-cure activator), which provides a chemical initiator to the first bottle.
Issues in dentin bonding:
1) Metalloproteases in dentin (collagen degradation in the hydrid zone); 2) Hydrolysis of the adhesive (water trees); 3) Degradation of the adhesive resin by natural and bacteria esterases; 4) Colonization by bacteria and biofilm formation in marginal gap areas.
Methods to avoid issues in dentin bonding
1) Chlorhexidine to inactivate metalloproteases; 2) Gluma (5% glutaraldehyde/35% HEMA/60% Water) to also inactivate metalloproteases and crosslink collagen - prevent degradation.
