Lecture 8 Flashcards
Adhesive joint:
A layer of intermediate material (adhesive) with 2 surfaces (adherends) producing 2 adhesive interfaces
Tooth structure is generally hydro–
hydrophilic
composite is generally hydro–
hydrophobic
2 adhesive interfaces:
adhesive and composite, adhesive and tooth structure
Year acid etch was put into use, and by whom?
1955, Michael Buonocore
Ray Bowen discovered what, in what year?
Bis-GMA 1962
To understand the principles of adhesions we must talk about these parameters:
Substrate, adhesive system, mech of adhesion, clinical techniques
Enamel is hydro (philic/phobic) compared to composite
hydrophilic, bc of the water content
Enamel is hydro (philic/phobic) compared to dentin:
hydrophobic
Enamel is __% mineral by weight, __ % organic, and ___ % water.
95, 4, 1
What kind of shapes form enamel?
prisms
How many hyrdoxyapetite crystal form a prism of approx. 5-7 microns?
10,000
Comp of dentin:
70% inorganic, 20% organic (collagen), 10% water
What type of substrate is dentin?
dynamic substrate, subject to constant physiologic and pathologic changes in composition and microstructure
How does the dentin change with age?
the relative conc of organic vs. inorganic content, happens with repetitive trauma as well
Characteristics of dentin as a substrate:
permeable, wet, heterogenous, tubular, mineralized, collagen reinforced with inter and intra-fibrillar apatite
Dentinal tubules contain:
odontoblasts (1/3 into tubules), fluids, nerve fibers, other molecules in the intracellular matrix
2 types of dentin:
peritubular and intertubular
Peritubular dentin:
more mineralized than intertubular, lining of tubule, little organic matrix
intertubular:
rich in collagen fibers, ideal for hybridization, bulk of dentin
Adhesion to tooth structure is primarily:
micromechanical
T or F? Current adhesive system only employ bonding to hydrophilic substrates.
F. both hydrophilic and phobic
Adhesives used to be classified according to:
time of appearance into market: generation 1-7
Current classification of adhesives:
steps and adhesive strategy (1,2, or 3 steps)/ (etch-and-rinse, self-etch)
2 types of adhesive strategies:
etch-and-rinse AND self-etch
3 steps of dentin/enamel bonding:
etch, primer, adhesive
etch step is aka:
conditioner (typically acid)
Fxn of etch step:
cleans/preps surface, removes smear layer and mineral
What is primer?
amphipathic monomers + solvent carrier (has both hydrophilic and phobic carriers), connects philic and phobic
Fxn of primer:
infiltrates exposed collagen network, displaces moisture and links to hydrophobic adhesives
Adhesives are:
hydrophobic resin monomers
Fxn of adhesive:
link to resin composite
Most resin systems are based on:
high molecular weight hydrophobic monomers (UDMA, Bis-GMA)
The only true chemical bonding occurs with:
glass ionomers
What is the base for self-etching adhesives?
phosphate based acidic primers
How many steps are etch-and-rinse systems applied in?
either 3 or 2 (2: conditioner, then primer + adhesive, i.e. optibond solo plus)
How many steps are self-etching systems applied in?
either 2 or 1 (2: etch + primer no rinse, then adhesive), (1: all 3 in one bottle, shelf life and sensitivity make it undesirable)
How many steps are glass ionomer systems applied in?
2
What is the smear layer?
mineralization
What are you left with when you remove the smear layer?
demineralized dentin
What are you bringing into the interface when you add the primer and adhesive?
monomers
What does the final hybrid layer consist of?
Collagen + adhesive monomers
Fxn of etching:
to achieve adhesion to the restorative resin (i.e. acids, lasers, air abrasion), remove smear layer and open dentinal tubules, increase surface area of the enamel and create micro-porosities
With what systems is etching required?
All
ideal etch enamel:
phosphoric aced
How long to leave etchant on tooth:
15-20 sec depending on the acid pH and the substrate
Who was the first to talk about etchant?
Buonocore
T or F? Phosphoric acid is an organic acid.
F. inorganic
2 types of inorganic acid etches:
nitric acid, phosphoric acid
2 types of organic acid etches:
citric acid, malice acid (10% for either)
Acid-etch technique is aka:
hypertonic acids
How do different acids differ in terms of how they etch?
Leave different pattern in the tooth structure (circular holes for 37% phosphoric acid)
Effect of acid etch procedure depend on:
type of acid, conc (32-37), pH, (0.8-1.2%), etching time (10 vs 20s), form of etchant (gel vs. aqueous delivery system), rinse time (slightly longer than instructions, past when blue is gone), method of application, whether the enamel is instrumented prior, chemical composition and condition of enamel
active application:
rubbing with microbrush
Why is rubbing with a micro brush required with gel etchants?
to achieve better etching patterns
Different methods of application of etchant:
rubbing, agitation, and/or repeated application of fresh acid
Examples of how the condition of enamel can vary:
primary or permanent teeth, prism-strucuture or prismless, fluoridated, demineralized
Enamel etching
remove orgainic matieral, inc s.a, high bond stength, predictable bonding, about 20 MPa
Dentin etching
remove smear later, open tubules, remove mineral, inc s.a., create loose collagen network (5-10 microns in depth), variable substrate, less predictable bonding
Why is it important not to leave etchant longer than 15 sec on dentin?
leads to greater depth of demineralization, worse adhesion, we want 5-10 microns in depth
Prevent application technique for etchant depends upon:
type of dentin, i.e. superficial vs. deep dentin, young vs. old (more tertiary and reparative dentin)
high bond strength
20 MPa+
T or F. In todays adhesive systems the bonding to dentin is less predictable than to enamel.
F. Not if you follow instructions
Appearance of etched enamel:
chalky (not true for dentin)
Deep vs superficial dentin:
Deep: large tubules, closer spaced, more peritubular dentin (66%) than interlobular (12%), lower bond strength
T or F? Peritubular is less ideal for bonding than intertubular dentin.
T
Superficial dentin:
small tubules, (0.8um at DEJ), space further apart, PD (3%)/ ID (96%), higher bond strength
Which is more ideal for bonding, peritubular or interlobular dentin?
intertubular
T or F? Primers are required in both dentin and enamel.
F. Dentin only
Fxn of primer:
adhesion promoter, increases surface tension of the collagen
Is adhesive resin hydrophobic or hydrophilic?
hydrophobic
What would happen if we accidentally used primer on enamel?
Nothing
What type of monomers does primer contain?
bifunctional monomer (HEMA) dissolve in solvents (acetone, ethanol, and/or water)
What solvents are primers dissolved in?
acetone, ethanol, and/or water
Are the solvents of primers volatile?
Yes
From where does the primer displace water?
the dentin surface and the moist collagen network
How does water displacement aid in adhesion?
promotes infiltration of monomers through the nano spaces of the exposed collagen network.
What does wetting the surface do?
increases the surface tension
What are bifunctional monomers:
HEMA dissolved in solvents
Is the adhesive filler or unfilled resin?
either
RBC aka:
resin composites
T or F? most adhesives are filled.
F. unfilled. those that are filled have very little
T or F? Bonding is chemical.
F. micromechanical
Fxn of adhesive resin;
stabilize hybrid layer and forms resin tags
What are formed when resin monomers penetrate micro-porosities created by etching?
tag-like resin extensions
How are the tag-like extension connected?
micro-mechanically interlocked with partially demineralized enamel (entangled w the enamel)
hydrophobic, more viscous adhesive resins:
Bis-GMA, UDMA
higher hydrophilicity, less viscosity adhesive resins:
TEG-DMA, HEMA (as a wetting agent)
2 types of monomer used to make adhesive resins:
hydrophobic and higher hydrophilicity monomers
What happens to the collagen fibers when they are dried?
they collapse
Why do the collagen fibers collapse when they are dried?
bc it is supported b inorganic material, demineralization causes the collapse
What type fo bonding in requried for adhesion to dentin?
wet bonding
Fxn of wetting:
to get the collagen fibers to raise again
Composition of demineralized dentin:
70% resin, 30% collagen
What forms the hybrid layer?
the infiltration of the demineralized dentin layer by resin monomer
Composition of dentin before etching:
50% inorganic mineral, 30% organic, 20% water
T or F. The mineral and water are pretty much gone after etching.
T
Layers of the hybrid layer:
composite resin, adhesive resin, dentin
What is the hybrid zone made of?
adhesive resin and collagen fibrils, and partially demineralized dentin
Resin tags are aka:
microtags (lateral branches) or macrotags (larger ones)
Fxn of acid:
remove inorganic phase and expose rods and collagen
What promotes the effective link bw hydrophilic substrate and hydrophobic resin?
bi-functional monomers
What raises collapsed dentin?
primer
What is responsible for wetting the collagen?
primers
The solvents in the primer acts as:
water chaser
Which is more hydrophilic, dentin or enamel?
dentin
Fxn of resin:
penetrates collagen matrix, interlocks collagen, forms hybrid layer
T or F? Etchant can be used on both enamel and dentin.
T
How far past the margins do we apply the etchant?
1mm beyond
Why do we apply etchant 1mm beyond the margins of the prep?
bc there is a bevel
Excess etching leads to:
further decalcification/ demineralization, area at bottom of hybrid layer that is weak, decreasing longevity of restoration
T or F? The over-etching of enamel would be critical.
F
After etching the surface should appear:
damp
Challenge when bonding:
working with 2 different tissues, enamel must be dry, dentin must be slightly damp
How to dampen detntin if we dried to much:
damp microbrush
T or F? Primer requires only 1 coat.
F. Multiple
The suface should appear ___ after solvent evaporation.
shiny
Goal of air-drying primer vs adhesive
evaporate solvent vs. thin, even layer
What are we doing if we over dry at the solvent evaporation stage:
collapsing the collagen mesh
When does the adhesive work best?
in thin, even layers
Which step do we go back to if contamination occurs at any step?
etching
What type of adhesive system do we use?
2 step etch and rinse system, ethanol solvent, 15% filled (adhesive a little more viscous) with 0=.4 icon barium glass filler (reinforces hybrid zone and penetrates dentin tubule), can be bottle or unidose
What do the 2 steps of Optioned Solo Plus consist of
etching + primer/adhesive
Ethanol based systems work best in:
fewer coatings
Acetone based systems work best in:
multiple layers
When should we use the less preferred, indirect vision?
when direct vision would result in improper operator positioning
The center of focus on the hand mirror should be:
the bur contacting the tooth
What should you do before using indirect vision?
check orientation of handpiece and bur relative to tooth with direct vision.
With which visual field should you be monitoring the positioning of the handpiece during the prep?
both central and peripheral
Pt of origin of Class III caries:
interproximal enamel, generally gingival to the contact pt
Acid etch allows for:
Selective demineralization of enamel
