Week 3- Tooth Bonding and Adhesives Flashcards
what is adhesion
the state in which two surfaces are held together by interfacial forces which may consist of valence or interlocking forces or both
what is adhesive
a material, frequently a viscous fluid that joins two substrates together by solidifying and transferring a load from one surface to the other
what is adhesive strength
the measure of the load bearing capacity of an adhesive joint
what is failure of adhesive joints caused by
- cohesive in substrate
- cohesive within the adhesive
- adhesive failure or at the substrate adhesive interface
what are the factors that affect adhesion
- clean substrate
- wetting ability of substrate
- adhesive viscosity
- surface roughness
what is wetting ability
ability to maintain intermolecule contact with dental surface
how does acid etching improve surface wetting
it increases surface free energuy
what does viscosity depend on
surface tension of the liquid (adhesive) and of the solid (substrate)
how does surface roughness affect the bonding ability
irregular surface increases the bonding ability
- increased area for bonding
- increased adhesive interlocking
how does acid etching affect surface roughness
increases the surface available for bonding and intermolecular contact with adhesive
what are the bonding mechanisms to tooth structure
- mechanical
- chemical/adsorption
- diffusion
- a combination of the 3
what does mechanical bonding do
- penetration of resin adhesive and formatino of hybrid layer/ or resin tags within the tooth surface after polymerization - entanglement
- resin tags
what do resin tags do
micromechanical interlocking within the tooth surface
what is chemical/adsorption bonding
chemical bonding to the inorganic component (hydroxyapatite) or organic components (mainly type I collagen) of tooth structure
what is the diffusion type of bonding
precipitation of substances on the tooth surfaces to which resin monomers can bond mechanically or chemically
what is the bond strength, origin, composition, structure, and type of substrate of ENAMEL
- 20MPa to 53MPa
- epithelial
- 97% mineral (hydroxyapatite), 1-2% organic (amelogenin and enamelin), 2% water
- prisms
- homogenous
what is the bond strength, origin, composition, structure, and type of substrate of DENTIN
- unpredictable
- conjunctive
- 55% mineral (hydroxyapatite), 30% organic (type I collagen), 15-20% water
- tubular
- very heterogenous
describe acid etching
- introduced by buonocore through the acid etch technique
- very predictable
- chemical drilling
- most effective for enamel retention (5-50 microns deep)
- 30-40% phosphoric acid (37% is most common)
- application 15-30 seconds, rinse for 10 seconds and 25 mL water is necessary
what is the role of acid etching
- clean surface for bonding
- increases wettability and SA for bonding
- increases surface free energy to EXCEED the surface tension of the adhesive
- micro retentions: adhesive penetration and resin tags
- mechanical interlocking after adhesive polymerization
- MICROMECHANICAL BOND
what is the fundamental mechansim of adhesion
micromechanical bond
what is the type 1 etching pattern on enamel
- honeycomb
- dissolutino of prism cores
what is the type 2 etching pattern on enamel
- cobblestone
- dissolutino of prism peripheries
what types are the best bonds achieved in enamel
type I and type II
where are type I and type II etching patterns of enamel location
occlusal and middel thirds of teeth
describe type III etching pattern of enamel
combination of type I and type II
describe type IV etching pattern
pitted
describe the type V etching pattern
-prismless
- flat and smooth
where is stronger retention and more predictable bonding performance of enamel located
incisal and middle third of the tooth
describe the bonding performance of the enamel in the cervical third of the tooth
prismless enamel -> fewer and shorter resin tags
why should you bevel the gingival floor in class II preps
reduce the microleakage at cervical and ascending walls
why is enamel prep with burs more efficient etching
it reveals underlying prismatic enamel
when do we not bevel enamel
-in deep class II preps where so little enamel remains that a bevel would remove it all
- gingival floor is on cementum or dentin
describe perpendicular prisms
-better performance (~25MPa)
- cavosurface margins class I prep
- bevels of class II prep
- ends of enamel rods
describe parallel oriented prisms
- lower performance
- 7-10 MPa
- internal walls occlusal prep
- gingival floor of box of class II prep
- sides of enamel rods
describe dentin tubules
-fluid filled
- enclose cellular extensions (odontoblasts)
- conntect pulp to DEJ
describe intertubular dentin
- higher organic content
- collagen rich zone
describe peritubular dentin
- surrounding the tubuels
- highly mineralized
describe the dentin structure
- tubules that connect the pulp with the DEJ
- tubules change in distribution and diameter through the dentin depth
how big are the dentin tubules near DEJ
20,000/mm^2
- 0.5 micrometer diameter
how big are the dentin tubules near the pulp
45,000/MM^22
- 2.5 micrometer in diameter
- more fluids
- less intertubular dentin
how is bond strength affected by dentin depth
better bonding at superficial dentin than deep dentin
what is the smear layer
- organic and inorganic residues left by burs or other instruments
- contaminated with saliva, blood, cells, and bacteria
what is it called when the smear layer is in the tubules
smear plus
how does the smear layer affect bonding
it decreases it to 7.0 MPa
how is smear layer removed
acid etch
how is the hybrid layer created
- after acid etching, collagen fibrils are exposed
- adhesive penetrates and encapsulates the collagen fibrils
- after polymerization creates an intermingled layer of collagen and resin called the hybrid layer
what is the hybrid layer key for
dentin bonding
- base for all composite restorations
what relies on the hybrid layer
stability/longevity of composite restorations
- stability of collagen and adhesive resin
what are the steps in forming the hybrid layer
- acid etch dentin for 15 sec: removes the smear layer and minerals surrounding collagen, rinse with water for 15 sec
- remove the excess of water but keep dentin moist: the space previously occupied by minerals is filled with water to support collagen fibrils
- apply adhesive or primer+ adhesive
- light cure
what are the factors affecting the hybrid laeyr formation
- clean dentin surface and free of smear layer
- poor adhesive infiltration
- incomplete adhesive polymerization
what does dentin over etching cause
denature dentin collaen matrix and premature bond failure
how does dentin moisuter affect hybrid layer formation
avoid over wetting or drying that impacts on adhesive penetration
how does poor adhesive infiltration affect the hybrid layer
collagen exposed is subjected to degradation by host derived enzymes (MMPs or CT) due to presence of water/hydrophobicity of adhesive
what would cause incomplete adhesive polymerization
- low density/energy light curing units
- lack of evaporation before polymerization
- premature faiure of bonding interface and premature loss of composite restorations
what are adhesive systems
agents that bond micromechanically and/or chemically the restorative material to tooth substrate through an interface
what are the current applications of adhesive systems
- direct restoration technique- class 1-5 and veneers
- indirect adhesive restorations- crowns or partial restorations to increase retention in metal crowns
- seals pits and fissues
- bond ortho brackets
- desensitize noncarious cervical lesions and exposed root surfaces
- repair existing restorations
- bond to root canal
what are the types of adhesive systems
- three step etch and rinse
- two step etch and rinse
- two step self etch
- one step self etch
- two step etch and rinse
- one step self etch
what are the components of the three step etch and rinse
-phosphoric acid
- hydrophilic primer
- bonding resin
what are the components of the two step etch and rinse
- phosphoric acid
- adhesive(hydrophilic primer and bonding resin)
what are the components of the two step self etch
-self etching primer
- bonding resin
what are the components of the one step self etch
all in one (self etch hydrophilic primer and bonding resin)
what are the components of the two step etch and rinse/ one step self etch
- phosphoric acid and hydrophilic bonding resin
- self etch hydrophilic primer/ bonding resin
what are the components of the adhesive systems
- acid etchant: phosphoric acid gel 30-40%
- primer: hydrophilic monomers in HEMA, solvent (acetone, ethanol/water, water)
- adhesive bonding resin/agent: hydrophobic dimethacrylate monomers, initiators and activators, camphorquinone, or benzoyl peroxide tertiary amine, filler
describe the polymerization process
-adhesive/primer: monomers to be converted into polymers- chemical reaction
- reaction: activator converts initiator into a free radical and free radical starts polymerization reaction
- light activator: blue light and initiatory- camphorquinone and DMAEMA
- chemical: tertiary amine and benzoyl peroxide-> free radical -> polymerization reaction
describe the dentin bonding mechanism of micromechanical interlocking
- acid etched, demineralized collagen fibrils, adhesive to form hybrid layer
describe dentin bonding mechanism chemically
phosphate acidic monomers, phosphate monomer chemically interacts via ionic bonding to calcium in hydroxyapatite
what is the bonding procedure at UMKC SOD
- step 1: acid etch: enamel for 15-30 sec and dentin for 15 sec or SELECTIVE ETCH (enamel only)
-step 2: rinse 10 seconds at least. air dry gently- enamel should be dry and dentin slightly moist - step 3: click the viva pen and apply adhesive, agitate for 20 sec, air dry until glossy immobile film layer
- step 4: light cure for 10 s
- step 5: place composite resin
what are the steps in three step etch and rise
- step 1: acid etch enamel for 15-30 sec and dentin 15 sec
- step 2: rinse 15 sec and air dry
- step 3: primer application and agitation only on dentin and air dry
- step 4: adhesive bond application and agitation and air dry
- step 5: polymerization for 10 sec
- step 6: place composite
what are the steps in two step etch and rinse
- step 1: acid etch enamel 15-30 seconds and dentin 15 sec
- step 2: rinse 15 sec and air dry
- step 3: adhesive application and agitation and air dry
- step 4: polymerization for 10 sec
- step 5: place composite resin
what are the steps to two step self etch
step 1: acidic primer application agitation and air dry
- step 2: adhesive application agitation and air dry
- step 3: polymerization for 10 sec
- step 4: place composite resin
what are the steps to one step self etch
- step 1: adhesive (all in one) application and agitation and air dry
- step 2: polymerization for 10 sec
- step 3: place composite resin
what are the factors affecting bond to dentin
- cavity depth
- caries affected dentin
- C factor
- adhesive system used
- thickness of increment of composite resin
- operator error
- moisture of dentin
what are the advantages and disadvantages to etch and rinse
-advantages: more predictable in enamel, stronger bond in enamel, less marginal staining and marginal openings overtime. HL with more robust resin tags
- disadvantages: more clinical steps, longer tx time, hard to control dentin moisture, collagen collapse is possible, etched zone is often deeper than adhesive penetration
- post operative sensitivity
what are the advantages and disadvantages of self etch
- advantages: less clinical steps, shorter clinical time, control dentin moisture, simultaneous deminerlization and adhesive infiltration, reduced the difference between adhesive penetration and etched dentin depth, post op sensitivity, good for dentin
- disadvantages: in enamel- weaker bond strength, more marginal staining and marginal openings overtime. not compatible with self cure, dual cure composite
what can increased hydrophilic content affect
- polymerization of adhesive
- more susceptible to hydrolysis of adhesive
- more degradation of the bonding interface
- lower bond strength
- incompatibility with chemically activated composites
what did the presence of 10-MDP do
increased clinical performance of universal adhesives through retention rate, marginal staining and adaptation overtime
why does a perfect hybrid layer not exist
all HL are subject to degradation overtime
to reduce degradation in attempt to prolong the lifespan of composite restorations:
-increase the adhesive properties
- reduce the collagen degradation
