Exam III Flashcards
(95 cards)
1
Q
adsorption
A
- the adhesion of atoms, ions, biomolecules or molecules of gas, liquid or dissolved solids to a surface
- physical adsorption –> where van der waals forces operate (more readily reversible)
2
Q
absorption
A
involves the incorporation of the molecules into the bulk of a material
3
Q
chemisorption
A
- chemical reaction (not usually reversible) has taken place
- desired for adhesives
4
Q
5 steps in forming good adhesion
A
- clean adherend
- good wetting
(hydrophilic materials do not wet hydrophobic surfaces very well. Enamel and dentin are hydrophilic while most composites are hydrophobic. The challenge for dental adhesives is to provide acceptable wetting for both materials) - intimate adaptation
- bonding
(the adheesive should interact in as many ways as possible with the substrate –> physical, chemical, and micromechanical bonding can develop) - good curing
5
Q
5 categories of factors affecting performance
A
- operator
(technical ability, eyesight, …) *most important - design
(smear layer, bevels, outline form, …) - materials
(composition, product age, temp, …) *least important - intraoral location
(A-P, Mx-Mn, Li-Fa, premolar-molar, tooth flexure, …) - Patient
(F-exposure, diet, oral hygiene IQ, caries risk, …)
6
Q
list 3 mechanisms for adhesion
A
one or more of these factors can contribute to bond strength
- chemical bonding
- micromechanical adhesion (*most important in bonding to enamel)
- hybridization bonding
7
Q
examples of where chemical adhesion is used in dentistry
A
- glass ionomer cements to tooth substance
- adhesive resins to alloys
- silane agents to ceramics
8
Q
what is micromechanical adhesion and what are examples of where it is used in dentistry
A
where a liquid flows into irregularities, pores or crevices in the adherend surface. Fluid sets producing micromechanical interlocking
- adhesion to etched enamel
- contributes to dentin bonding
- abraded alloy surfaces
- etched ceramics (HF)
9
Q
what is hybridization bonding and what ware examples of where it is used in dentistry
A
where one phase penetrates by diffusion into the surface of a second phase, forming a ‘hybrid’ layer
-bonding to dentin
10
Q
what type of mechanisms of adhesion are associated with enamel and dentin adhesion
A
- Enamel: mainly micromechanical (acid-etch), with sometimes chemical (only with polyelectrolyte)
- Dentin: all three mechanisms in combination
11
Q
composition of adhesive
A
- resin
- solvents
- filler
- adhesion promoters
- photo initiators
12
Q
2 step vs 3 step total etch (micromechanical bonding to enamel)
A
THREE STEP 1. Acid Etch H3PO4 (1* etch enamel, 2* rinse out etchant, 3* dry enamel surface) 2. Primer 3. Adhesive
TWO STEP
1. Acid Etch H3PO4
(1* etch enamel, 2* rinse out etchant, 3* dry enamel surface)
2. Primer + Adhesive
13
Q
principles for etching surface enamel
A
- clean surface
- roughen surface by selective decalcification (acid reacts with mineral and dissolves it heterogeneously)
- should have a chalky matte appearance
14
Q
surface energy of etched surfaces
A
- etched surface when clean and desiccated is chemically reactive
i. e. high surface energy and high critical surface tension
15
Q
what is the effect of etched enamel is unintentionally exposed to saliva or contaminated by microorganisms?
A
could possibly reduce bond strength and surface energy
16
Q
what does long-term durability depend on in regards to micromechanical bonding of enamel
A
- initial etching effectiveness (pH and time during etching)
- a fully integrated interface between polymer and etched enamel - micromechanical interlocking
- mechanical properties of the polymer and enamel
17
Q
what are resin-modified glass-ionomers used to bond to?
A
- used to bond to enamel
- add chemical bonding because positive charges in enamel strongly interact with negative charges in dental material
18
Q
what is self-etch
A
- a separate etching step along with washing and drying steps are not needed
- apply the material and it conditions and acts as bonding agent at the same time
19
Q
under what conditions do self etch systems perform best?
A
- only perform well when applied on cut enamel
- when applied to uncut enamel the etching effectiveness is not strong enough (pH is signigicantly higher than phosphoric acid based etchants)
- -> not rough enough to provide appropriate micromechanical bonding/retention
20
Q
how are sealants applied
A
- application after enamel etching with phosphoric acid agent
- light cured materials
- sealants are the most flowable of all dimethacrylate-based resin composites
21
Q
what are the two concerns with bonding ortho brackets with dimethacrylate-based resin adhesives after etching enamel?
A
- formation of white spot lesions (cause and solution of them still under research)
- debonding of the well bonded bracket might be challenging because damage of enamel can occur
22
Q
what is the smear layer?
A
- dentin affected by instrumentation (cavity prep)
- partially denatured collagen and mineral
- penetrates into tubules to form smear plugs
23
Q
what are the effects of dentin conditioning?
A
- removes smear layer
- demineralizes most superficial hydroxyapatite crystals leaving collagen fibers
- result –> conditioned dentin can be readily infiltrated by monomers and ready to form hybrid layer
24
Q
how are primers used on dentin?
A
- applied to conditioned dentin to aid adhesion
- hydrophilic to better interact with dentin (to penetrate/diffuse into collagen and flow into dentinal tubules)
- will adhere to dentin and to bonding agent
- usually light cured (should be light cured before composite)
- forms hybrid layer
25
what are the consequences of conditioning and priming dentin?
- infiltration of monomers into treated dentin (absorption: diffusion effect)
- monomers polymerized in situ to form a hybrid layer composed of resin, collagen, residual hydroxyapatite and a small quantity of water
- resultant tensile bond strength was 18 MPa (similar to enamel)
- hybrid layer reported to be about 10 microns in depth, following etching with 20% H3PO4
26
method of total etch on dentin
- uses 37.5% phosphoric acid
- rinsed then dried
- smear layer removed, tubules are exposed
- technique sensitive
- risk of post operative sensitivity
- time consuming
27
nature and function of dimethacrylate monomers
- react with monomers of restoration --> covalent bonds formed
28
nature and function of polyalkenoic acids or methacrylates with carboxylate groups
- try to mimic chemical adhesive effect of zinc polycarboxylate and glass-ionomer cements
- aim to specifically interact with mineral in dentin
- most used functional groups present at the end of the functional molecules are carboxylic (-COOH) and phosphate (-H2PO4)
29
nature and function of inorganic fillers
- mechanical toughening, analogous to resin composites
30
nature and function of initiators
- similar to those for resin composites
- *adhesive is cured BEFORE application of composite restorative material
- -> otherwise may not cure properly by light shining through composite; potential severe problems if unset fluid left near pulp
31
clinical outcome of enamel/dentin bonding
- three-step etch and rinse adhesives still result in best clinical outcome of all resin-based adhesives
- one-step self-etch adhesives have not yet matched the clinical reliability provided by other types of adhesives
32
effects of water and time (nanoleakage) with self etch systems
- self-etch resins exhibit fairly severe water-sorption (from dentin) --> compromising mechanical properties
- fluid mvmnt within hybrid layers created by self-etch systems has been shown (compromises adhesion to composite --> critical to work quickly)
33
what are the functions of primer (dentin)
- penetrates dentinal tubules and obtain micromechanical bonding
- diffusing/absorbing into layer of demineralized dentin obtained after etching, forming the hybridization layer
34
nature and function of adhesive (bonding agent)
- incorporates ampiphilic molecules (ex. NTG-GMA)
| - should be light cured before curing the composite
35
ethanol as a solvent in adhesive systems
- mixture of water and ethanol
- used as fluids to transport molecules to interact with tissues
- have an intermediate time of evaporation, ideal for drying the adhesive not too fast and not too slow
36
what is nanoleakage and what does it do to a restoration?
- nanoleakage: passage of water from dentin into the interface between the tissue and adhesive
- happens due to high hydrophilicity of systems used for bonding to dentin
- may compromise: biocompatibility of dental materials and mechanical properties at the interface (water acts as plasticizer)
37
what is the "gold standard" system for bonding to dentin?
- 3-step total etch system
| - self-etch systems are not as clinically reliable
38
what are the main factors that limit long term durability of bonding to dentin?
- microleakage
- water/nanoleakage
- adhesive systems are hydrophilic and all degradative agents are water or water borne
- degradative agents plasticize, hydrolyze and/or catalyze breakdown of methacrylate-based resin that composes adhesives
39
what are the 4 essential components to a composite
- organic polymer matrix
- inorganic filler particles
- coupling agent
- initiator/accelerator system
40
what is the function of composite composition being based on resin matrix (consisting of dimethyacrylates)?
- provide setting mechanism: undergoes addition polymerization reaction initiated by free radicals
- cross-linked for serving as the binder for optimal mechanical and optical properties
41
what are the limitations of composite composition being based on resin matrix (consisting of dimethacrylates)?
- shrinkage on polymerization (stresses at bonded interfaces, lack of marginal adaptation, and microleakage)
42
what are the main functions of inorganic fillers in composites and how do the materials differ?
- main function: reinforcement, radiopacity, control of shrinkage
- variety of inorganic fillers with materials that differ significantly:
> chemistry of filler
> size and distribution of particle size of filler
> mixture of fillers
> quantity of fillers
*the last three are important for 'flowing' properties/handling before curing
43
what is the function of coupling agents in composites
- silane compounds
- ensure binding between inorganic fillers and resin matrix
- essential for mechanical reinforcement that inorganic particles provide
44
what is the function of initiators and accelerators in composites?
- generate free radicals upon activation by visible light
- initiate polymerization (setting) across the double bond of the resin monomers
- also bind resin to filler via coupling agent
45
what are minor constituents of composites
- pigments: to ensure good aesthetics
- polymerization stabilizers: to prevent premature polymerization of material on storage
- UV absorbers: to prevent discoloration in sunlight
46
pros and cons of bis-GMA
PROS
- optimum combination of rigid and cross-linkable agents
- aromatic unit allows good match of refractive index with strong and radiopaque filler
- good optical properties
- easily synthesized
CONS
- extremely viscous resin: almost impossible to manipulate
- difficult to incorporate filler
47
what are the approaches to low shrinkage resin systems?
Low-Shrink Methacrylate Monomers
- increased distance between the methacrylate
Silorane Chemistry
- non-methacrylate resin
- ring-opening polymerization give less shrinkage
- need special bonding agent
Photocleavable Monomers
- incorporation of photocleavable monomers that can relieve stresses during shrinkage of resin
48
what are the effects of (particulate) ceramic fillers on polymer properties (dental composites)
- increase strength in compression
- increase surface hardness and wear resistance
- decrease shrinkage on polymerization
- possible contribution to aesthetics/translucency
- increase control of exothermic heat
- may confer radiopacity (Ba, Sr, Yb, Zr, La) (increased)
49
effect of fillers on stress-strain properties on dental composites
- principle of combined action:
> ceramic is load bearing if: ceramic is more rigid and stronger than polymer; and ceramic and polymer are well bonded to each other (use coupling agent)
50
inorganic filler composition: Crystalline Silica / Quartz mineral
- rough surface; difficult to obtain and maintain a smooth surface
- very hard -- could abrade enamel
- used in early composites
- prepared by grinding process (0.1-100 um)
- not opaque to x-rays
51
inorganic filler composition:
| Glasses e.g. Barium or Strontium glass
- ground to desired particle size
- limitation on how fine the grind can be (>0.4 um)
- obtained by glass melting process
- can be radiopaque
52
inorganic filler composition:
| Sol-gel filler ex. Zirconia-Silica
- approximately spherical particles
- good polishability (preparation and retention)
- sol-gel production process
- continuum in sizes
- high packing density (85 weight %)
53
inorganic filler composition: Microfill
- very poor handling if filler used alone
- modified with pre-polymerized resin
- excellent polishability
- derived from amorphous fumed silica filler
- low filler content (35 vol%)
- not radiopaque
- low mechanical properties -- cannot be used for stress-bearing areas
54
what are the critical roles of silane coupling agent?
- forms an interfacial bridge that strongly bonds filler to resin matrix
- enhances mechanical properties; minimizes pluking of filler during wear process
- interfacial phase provides medium for stress distribution
- provides a hyprophobic environment that minimizes water absorption of composite
55
list classifications of composites based on flow properties (increasing viscosity)
lowest viscosity
- sealants (based on dimethacrylate resins with pigment added)
- flowable (can be injected though syringe needle. multipurpose use for small restorations)
- anterior (microfilled)
- universal (hybrid, continuum, and nano)
- packable X --> now changed to bulk-filled
highest viscosity
56
parameters for ability of a material to be syringed
- material of low viscosity
- material that will show shear thinning (pseudoplasticity)
- reversible structural breakdown -- this ensures that the material will not slump/the material will stay in place
57
define pseudoplasticity
- shear thinning
| - a material has lower viscosity at faster rates of shearing
58
why are composites places incrementally?
- limited depth of cure - particularly darker and more opaque shades
- management of polymerization shrinkage and associated stresses
- more precise manipulation to ensure adaptation to cavity especially at cavosurfaces
- less void in restoration
- reduction of incidence of postoperative sensitivity
- better ability to produce multishade restorations
59
what are the disadvantages of incremental placement of composites?
- time consuming, especially in posterior teeth
- potential of gaps/voids between layers of composites
- dry field requirements for longer time
- risk of contamination is greater
60
what are new approaches toward bulk-fill composites?
- decrease of viscosity during placement to provide good adaptation
- deep cure initiator
- polymerization modulator to relieve stresses
- addition-fragmentation monomer inclusion
61
how is the setting mechanism of composites activated by light?
- free radicals formed in some chemicals when shinned with a light and start the polymerization of resin monomers and link with inorganic particles by reacting with the coupling agent (silane)
62
what is bis-GMA?
- most dental resin composites contain this as a basic monomer
- one methacrylate (double bond) at each end (dimethacrylate) to polymerize and crosslink with other molecules
- rigid central part to provide additional good mechanical properties
63
the composite gets an intermediate balanced combination of the mechanical properties of its main constituents (resin and inorganic fillers) if _________
- the filler is stronger and more rigid than the resin
| - silane is properly used
64
sealants
- based in dimethacrylates resins and contain none or small amounts of inorganic fillers
- incorporate inorganic pigments
65
flowable composites
- low viscosity
- display shear thinning
- do not suffer from structural break down
- might be used as sealants
- mostly used for anterior teeth restorations as microfilled composites
66
hybrids, continuum and nano composites (universal)
- good handling properties
- very good mechanical properties
- most common choice for filling cavities in posterior teeth in occlusal positions
67
packable composites
- almost completely out of the market bc they didn't match the desired initial handling properties
68
how is shrinkage strain measured?
- dilatometry (volumetric)
- bonded-disk method (linear)
- strain gauge method (post-gel, linear)
- digital image correlation (DIC, 2D)
69
what is a consequence of low shrinkage composite?
shallow depth of cure
70
does low shrinkage strain equate to low shrinkage stress?
- not necessarily
| - -> need to measure stress directly
71
how is shrinkage stress measured
- tensometer (compliant)
| - MTS (rigid)
72
what does stress level depend on apart from material properties (shrinkage, flow, stiffness)?
- cavity size and shape
- restraints (stiffness of surrounding tissues)
- placement technique (bulk or incremental)
73
is shrinkage stress high enough to cause damage?
- whether debonding would occur depends on whether the shrinkage stress exceeds the bond strength
- *need to know bond strength
- generation of shrinkage stress/strain is highly dynamic process but so is bond strength
- "race" between bond formation and shrinkage stress development
74
how does composite thickness effect rate of bond formation
rate of bond formation reduced with composite thickness
75
how is final bond strength affected by irradiance (light intensity)
final bond strength was independent of irradiance
76
what is rate of bond strength controlled by and limited by?
- rate is controlled by the developing cohesive strength of composite
- max bond strength limited by the pre-cured dentin-adhesive bond strength
77
how is evidence of debonding proven?
- in vitro microleakage measurement can provide evidence that debonding has occurred
- but...its destructive, time consuming and only qualitative
- micro-CT imaging
- acoustic emission (measurement of micro tremors)
78
what are suggested measures to reduce shrinkage stress or debonding?
MATERIALS
- use resins with longer monomers
- increase amount of filler particles
- use "ring-opening" silorane-based resin
- use bond-breaking and -reforming resin
- use dual-cure materials
CAVITIES
- avoid deep cavities
- avoid large C-factors (ratio of bonded to unbonded surfaces
- minimize dentine surface
TECHNIQUES
- use low-modulus lining material
- use incremental filling
79
what is cement (in relation to dentistry)?
- non-metallic material that is mixed to a plastic consistency (capable of permanent deformation), followed by setting
- many different cement types used for many different applications
80
what are 5 dental applications of cements?
- restorative materials
- provisional restorative materials
- for cementing metal castings and ceramic restorations, veneers, etc
- for bonding orthodontic appliances
- in conjunction with restorative materials, as cavity linings, for example
81
what caution is needed when choosing dental cements?
- choice of several materials for each application
- many materials have multiple potential applications
- potential for overlap
82
list dental cement materials (1-9) by increasing strength, increasing durability, and decreasing solubility
calcium hydroxide
1. zinc oxide non-eugenol
2. zinc oxide eugenol
3. zinc polycarboxylate
4. zinc phosphate
5. glass-ionomer
6. resin-modified glass-ionomer
7. compmer
8. resin cement
9. adhesive resin cement
this list is in order of increasing strength/durability and decreasing solubility
83
categorize the list of dental cements by the type of setting reaction: acid-base materials (AB) or polymerizing materials (P)
AB (calcium hydroxide)
1. AB (zinc oxide non-eugenol)
2. AB (zinc oxide eugenol)
3. AB (zinc polycarboxylate)
4. AB zinc phosphate
5. AB glass ionomer
6. AB & P (resin-modified glass-ionomer)
7. P (compomer)
8. P (resin cement)
9. P (adhesive resin cement)
84
for acid-base material cements, what is included as an "acid" and "base"
```
ACIDS
- phosphoric acid (PHA)
> aqueous acid
- poly(acrylic acid) and related materials (PAA)
> aqueous acid
- eugenol (EUG)
> non-aqueous, oil
```
```
BASES
- zinc oxide (ZnO)
> powder
- fluoro-aluminosilicate glass (FAS)
> powder
```
85
what are the similarities between acid-base cements
- all powder-liquid materials
- cement liquids are acids
> proton donors or electron acceptors
- cement powders are bases
> proton acceptors or electron donors
- on mixing, an acid-base reaction occurs
- but, not all of powder reacts -- ~80% remains unreacted bc the "acidic" liquid attacks the outside of the powder particles
> thus the set structure is heterogeneous (unset powder + reaction product)
> this is called a cored structure
86
ZnO characteristics and consequences
| dental cements
- powder type
- optically opaque; since 80% is usually unreacted, the set cement is opaque
- generally is weaker than FAS glass, so gives weaker cements
- consequences:
>ZPH, ZOE and ZPC are all yellow/opaque
> ZPC not as strong as GIC
87
FAS glass characteristics and consequences
| dental cements
- powder type
- can be translucent, so set material can be aesthetic
- stronger than ZnO
- contains fluoride, with possibility of delivering fluoride
- consequences:
> more aesthetic than ZPH, ZOE and ZPC
- G-IC stronger than ZPC
- therapeutic? - bioactive
88
PHA (phosphoric acid) characteristics
| dental cements
- H3PO4
- aqueous
- very acidic
- might be irritant bc of low pH
- no chemical adhesion with tissues
89
PAA (poly acrylic acid) characteristics
| dental cements
- aqueous
- water soluble
- adhesive -- can react chemically with calcium in tooth substance
> this is why PAA-containing cements (mostly GICs) are used as restorative materials
- non-irritant
90
EUG (eugenol) characteristic (dental cements)
- oil from cloves
- forms eugenolate salts which slowly disintegrate in water
> this is why eugenol-based cements are never used in permanent luting applications
- powerful scavenger of free radicals --> much weaker composite --> eugenol-containing cements should never be used in contact with resin-based composites (which are set by free radical addition polymerization)
- obtundent (numbing, anesthetic) and bacteriostatic
> this is why eugenol-based cements are used as base and liner in endodontics
- interferes with setting of composites
91
cement materials 1 and 2 (zinc oxide non-eugenol and zinc oxide eugenol) characteristics and applications
- opaque
- weak
- short-term disintegration in water
- interfere with setting of restorative composite
- applications:
> NEVER for permanent luting
> NEVER in conjunction with composites
92
cement material 3 (zinc polycarboxylate) characteristics and applications
- opaque
- weak
- adhesive
- non-irritant
- applications:
> developed as an adhesive cement
> tends to be superceded by G-IC
93
cement material 4 (zinc phosphate) characteristics and applications
- opaque
- weak
- more resistant to water degradation than eugenol-containing
- irritant?
- applications:
> has been widely used as a luting agent
94
cement material 5 (glass ionomer cement) characteristics and applications
- translucent
- stronger
- adhesive
- non-irritant
- fluoride-releasing
- applications:
> permanent luting and restorations (permanent and temporary)
95
advantages of cement material 6 (resin-modified glass-ionomers)
- translucency
- potential for fluoride release
- better mechanical properties
- set by acid-base reaction & polymerization
