Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biomaterials > Exam II > Flashcards

Exam II Flashcards

1
Q

define the words cast and die

A
  • Cast: replica of the teeth and/or associated supporting bony tissues of one jaw (prepared from an impression)
  • Die: model of a single tooth prepared from an impression
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the desirable properties of cast and die materials

A
  • mechanical: bulk properties (strength) and surface properties (hardness; resistance to abrasion)
  • detail reproduction
  • dimensional accuracy and stability
  • compatibility with impression materials
  • color contrast
  • economical
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the dihydrate of calcium sulfate?

A

Gypsum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

how are hydrates of calcium sulfate dihydrate (gypsum) made?

A

heating

when gypsum is heated, it loses water of crystallization creating a hemihydrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how do you reverse the creation of a hemihydrate from a dihydrate (gypsum)

A

mix with water

reforms the dihydrate form causing setting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

classifications of dental gypsum products

A
  • Type I: impression plaster
  • Type II: model plaster
  • Type III: dental stone
  • Type IV: high strength dental stone
  • Type V: high strength, high expansion dental stone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

describe the chemical setting reaction of calcium sulfate hemihydrate with water

A
  • dissolution of some of the hemihydrate –> dihydrate formed in solution/diffusion of Ca2+ and SO42- ions
  • crystal growth of dihydrate from crystal nuclei
  • more hemihydrate dissolves
  • interlocking crystals give rigidity and strength
  • porosity because of excess water
  • set material is almost entirely calcium sulfate dihydrate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

why is water required for setting reactions

A
  • hydration

- give smooth workable mix

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe the setting process of gypsum product

A
  • initial fluid mix
  • then becomes rigid, not hard (initial set)
  • exothermic heat
  • dimensional changes - expansion
  • hygroscopic expansion
  • hard set material (final set)
  • porosity (due to excess water that doesnt react and finally evaporates)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

describe the mechanism of setting expansion of gypsum products

A
  • crystals growing from nuclei

- volumetric expansion caused by thrust of growing crystals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what are the two main forms of calcium sulfate hemihydrate

A
  • Calcined (beta) –>plaster
  • Autoclaved (alpha) –>stone
  • the initial form of hemihydrate influences the application of set gypsum
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

differences in manufacturing and particle size/shape in beta in alpha hemihydrates

A
  • manufacturing process influences size and shape of supplied hemihydrate crystals
  • Calcined (beta): irregular crystals
  • Autoclaved (alpha): smaller prismatic crystals
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

water-powder ratio and set material denstiy in beta and alpha hemihydrates

A
  • beta is mixed with more water than alpha
  • result of the difference in water excess = difference in porosity of set gypsum
  • dental plaster is more porous than set dental stone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

difference in set material mechanical properties and applications - dental plaster vs stone

A
  • plaster is more brittle and weaker than stone
  • set dental plaster used for mounting study casts (type II gypsum)
  • set dental stone used for working casts (type III) and dyes (type IV and V)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what are the effects of additives to gypsum

A 
- effect on setting time
     > accelerators - gypsum, potassium sulfate
     > retarders - borax, potassium citrate
- effect of setting expansion 
     > increase - calcium acetate
     > decrease - potassium sulfate 
- effect of mechanical properties
     > usually weakening
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

correct manipulation of setting materials to obtain optimum properties

A
  • select correct material
  • use correct water/powder ratio
  • smooth mix
  • eliminate air bubbles (vacuum mixing/vibration on pouring)
  • dry set material
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is setting time dependent on

A
  • not greatly affected by temp

- depends on: type of material, water/powder ratio, and mixing time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what are critiques of gypsum products

A
  • mechanical: brittleness; abrasion resistance
  • fine detail, sharp margins: good reproduction
  • accuracy and stability: good
  • compatibility with impression materials
  • color contrast
  • cost - inexpensive
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is working time

A

measurement of working begins with start of mixing and ends just before impression material has developed elastic properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is working time dependent on

A

temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is setting time

A

time measured from when mixing the impression material begins until complete reaction occurs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is viscosity of a fluid

A

measure of its resistance to gradual deformation by shear stress or tensile stress
(informal concept of “thickness” of a liquid)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

viscosity depends on:

A
  • composition: (molecular weight, filler content,…)
  • rate of deformation (shearing): (Newtonian and non-newtonian liquids)
  • temperature: (viscosity decreases with temp)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

distinguish between direct and indirect restorations

A
  • Direct: where material is placed directly into the mouth, where it sets (amalgam, resin composite)
  • Indirect: where a restoration or prosthesis is prepared in a lab (dentures, cast gold, ceramics)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what are the applications of dental impression materials

A

to produce cast/models for:

  • pros and ortho treatment planning
  • occlusal analysis
  • fabrication of provisional restoration
  • fabrication of definitive indirect restoration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what are the requirements for impression materials

A

General: BICMEP

  • B: non-toxic, non-irritant
  • I: good wetting
  • C: long shelf life
  • M: good resistance to tearing
  • E: acceptable odor and taste
  • P: appropriate working and setting time

Specific:
C, M, P: dimensional accuracy and stability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what are the 7 stages of impression taking that needs to be considered (for most accurate dimensions)

A
  1. insertion
  2. setting
  3. removal
  4. cooling to room temp
  5. disinfection
  6. storage
  7. compatibility with gypsum (cast/die materials)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what are the classifications of dental impression materials

A 
- Non-elastic materials
     >impression plaster/paste/compound
- Elastic Materials
     >Hydrocolloids
          \+reversible (agar)
          \+irreversible (alginate)
     >Elastomers
          \+polysulfides, condensation silicones, polyethers, addition silicones
29
Q

non-elastic materials as dental impression material

A
  • not used in dentistry anymore

- rigid when set, will deform/fracture when displaced from tissue

30
Q

distinguish between hydrocolloids and non-aqueous elastomers

A
  • both are elastic impression materials
  • Hydrocolloids: aqueous materials with poor strength and stability
  • Elastomers: non-aueous synthetic rubbers which are more stable and stronger than hydrocolloids
31
Q

define colloid and hydrocolloid

A
  • Colloid: a suspension of finely divided particles as a continuous medium in a dispersion medium from which the particles do not settle out rapidly and cannot readily be filtered
  • Hydrocolloid: dispersion medium is water
32
Q

difference between a sol and a gel

A
  • sol: fluid

- gel: elastic

33
Q

dental application of sols and gels

A
  • convert sol to gel (setting mechanism)
  • two ways to do this:
    > reversibly: by cooling material (agar)
    > irreversibly: by chemical reaction (alginate)
34
Q

physical structure of a irreversible hydrocolloid gel and the consequences of this structure

A
  • Set material of irreversible hydrocolloid gel consists of bonded chains of the particles entrapping a significant amount of water

Consequences:

  • set materials are elastic (good)
  • poor strength properties –> may tear easily when withdrawn from undercuts (water acts as plasticizer)
  • water may be lost or taken up by material at different steps of the process –> Compromises stability of the dimensions and mechanical properties of the impression (impression can expand and shrink)
35
Q

define syneresis and imbibition - then explain the significance of these factors in relation to dimensional stability

A
  • syneresis: loss of fluids by the material
  • imbibition: uptake of fluids by the material

CONSEQUENCE:

  • syneresis results in the colloid molecules being drawn closer together–> substantial shrinkage
  • inbibition results in expansion

*syneresis and imbibition must be avoided

36
Q

what are the main constituents of alginates

A

POWDER:
- soluble salt of alginic acid (polysaccharide)
> sodium alginate
- calcium salt
- trisodium phosphate
> setting retarder
- about 70% filler to increase gel strength

WATER

37
Q

what are the two sequential reactions of alginates

A
  1. formation of calcium phosphate (precipitate)
    >retarder
    >reaction 2 cannot take place until reaction 1 is substantially complete
  2. formation of calcium alginate (gel)
38
Q

list the factors that are important in correct manipulation of alginate material

A
  • shake powder container
  • correct powder to water ratio
  • ensure retention to tray
  • vigorous mixing
  • don’t move material during impression taking
  • recognize when material has fully gelled
  • displace sharply from the tissues
  • wash, remove saliva, disinfect (disinfection by immersion is not recommended, spray preferred)
  • keep material moist and prepare cast as soon as possible
39
Q

critiques of alginates

A

POSITIVE:

  • well-defined working time
  • elastic
  • records fine detail
  • comparatively inexpensive

NEGATIVE:

  • dimensionally unstable
  • tear easily
40
Q

dental applications of alginates

A
  • used for cast models: pros and ortho impressions

- generally considered to be insufficiently accurate and stable for inlay, crown and bridge impressions

41
Q

define amalgam and amalgamation

A
  • Amalgam: alloy of mercury with another metal

- Amalgamation: reaction of mercury with other metallic materials - this can occur at room temperature

42
Q

list the practical stages in the preparation of an amalgam restoration

A
  • mix powdered alloy with liquid mercury
  • metallic paste is formed
  • paste is packed (condensed) into tooth cavity
  • material is carved to correct anatomy
  • amalgamation reaction occurs
  • material sets and hardens
  • restoration is polished
43
Q

Ag3Sn (gamma-phase)

A

Alloy powder is based in the intermetallic alloy Ag3Sn (a silver tin alloy) this is the metallic alloy that will react with mercury during amalgamation –> this intermetallic compound is called gamma-phase

44
Q

what is the structure of set material resulting from the reaction of Ag3Sn (gamma phase) with mercury

A
  • silver-tin reacts with mercury to form:
    >silver-mercury compound (gamma1)
    >tin-mercury compound (gamma2)
    -also unreacted Ag3Sn present

STRUCTURE:
-core of unreacted powder surrounded by reaction products from powder-liquid reaction (like a brick wall)

45
Q

traditional low copper amalgams

A
  • older material
  • less than 6% Cu
  • added Cu to increase strength and hardness and to reduce excess contraction (Sn) and expansion (Ag) on setting
  • low copper amalgams have limited durability because they corrode
  • now make amalgams with higher copper concentrations
46
Q

limitations of low copper amalgam

A
  • gamma 2 phase is weakest and softest phase and is most liable to electrolytic corrosion
  • gamma 2 phase acts as anode and corrodes
  • products of gamma 2 corrosion:
    > tin salts: weak amalgam
    > amalgamation from free mercury released: expansion (mercuroscopic expansion)
47
Q

why is gamma2 phase not formed in high copper amalgams

A
  1. Powder in high Cu amalgams contains silver-copper particles in addition to silver-tin particles
    1. Gamma2 phase initially forms, as in low Cu amalgams
    2. The initially formed gamma2 phase further reacts with added silver-copper particles and form new phase made of copper-tin, n-phase (eta phase) that doesn’t corrode
    3. All the initially formed gamma2 phase reacts to form eta phase = final amalgam is free of gamma2
      Eta phase located around silver-copper particles forming a halo in the final set
48
Q

classify contemporary high copper amalgams

A
  1. Blended Alloys (dispersalloy or admixed alloys)
    - 2 parts irregular shaped lathe cut silver-tin particles
    - 1 part spherical silver-copper
  2. Single Composition
    - Contains only one type of spherical silver-tin-copper particles
49
Q

what does excess Hg in the final set amalgam result in

A

weaker restoration

50
Q

what happens with overtrituration and overtrituration of amalgam

A

Overtrituration:

  • may give unworkable mix
  • dry and brittle: grainy/crumbly mix

Undertrituration:

  • shiny, too soft, sticks to capsule
  • decreases working time
  • may result in excessive contraction during setting
51
Q

toxicity of mercury depends on:

A
  • form in which mercury is present (vapor is most toxic)
  • quantity of exposure
  • frequency of exposure
52
Q

what are the forms of mercury

A
  • liquid
  • vapor
  • intermetallic compound
  • organometallic compound

*must consider each separately

53
Q

mercury as a liquid

A
  • high vapor pressure at room temp
  • if swallowed, poor absorption by gut –> rapidly and easily excreted
  • two main problems: skin contact may result in absorption and a few people have allergy to Hg
54
Q

mercury as an intermetallic compound

A
  • formed in set amalgam
  • comparatively insoluble and harmless
  • if in dissolved salts, much more toxic
55
Q

mercury as a vapor

A
  • very toxic
  • Hg can rapidly cross alveolar membranes and directly into bloodstream
  • small quantities in expired air from patients (1-2 micrograms/day) less than environmental level (10-20 micrograms/day)
  • acute toxicity is rare
56
Q

mercury as an organo-metallic compound

A
  • methyl mercury is very toxic

- sources: in food chain (fish) and other environmental sources

57
Q

mechanical strength of dental amalgam

A

strength increases with time

58
Q

weak amalgam restoration results from:

A
  • undertrituration
  • too much mercury in set material
  • too low condensation pressure
  • slow rate of packing
  • corrosion
  • contamination with blood or saliva during placement
59
Q

dental amalgam creep

A
  • amalgam shows phenomenon of dynamic creep (material slowly deforms during mastication and bruxing)
  • modern high Cu alloys show much less creep than older materials
60
Q

thermal conduction of dental amalgam

A
  • enamel and dentin are good thermal insulators
  • amalgam conducts heat
  • consideration must be given to pulpal protection if large amalgam restoration placed
61
Q

what are the types of demineralization

A
  1. surface demineralization (surface softening)
    • no white patches, but surface is rough and looks matte (not opaque)
    • beverages, stomach acid, various acids
    • dental erosion
  2. sub-surface demineralization (lesions)
    • white, opaque lesions
    • surface less mineralized
    • main demineralization is sub surface
  3. etched enamel demineralization
    • similar to #1 but part of surface is removed…can be more advanced stage of #1

*remineralization looking at mostly for subsurface, surface one still being researched

62
Q

what leads to surface opacity in enamel demineralization

A

Ca and PO4 redeposit during remineralizaiton leads to opaque color (pH there is higher…further down pH is lower and diffusing)

63
Q

what is needed for enamel remineralization

A
  • need bioavailable calcium and phosphate
  • need partically demineralized crystals
  • remineralization no possible after mineral phase if its nucleation sites are lost completely
64
Q

definition of remineralization

A
  • process of ion deposition, sourced from the surrounding environment into voids in demineralized enamel to produce net mineral gaini
  • void: any intercrystal and interrod spaces caused by dissolution
  • includes crystal repair
  • does not include precipitation of solid phases onto enamel surfaces
  • needs bioavailable calcium phosphate
65
Q

what is needed for fluoride to be effective

A

Ca and PO4 from saliva

low salivary flow, fluoride does not help

66
Q

what does fluoride do in oral cavity

A
  • fluoride increases deposition rate by factor of 2-3
  • fluoride is incorporated into mineral as fluorohydroxyapatite
  • results in: reduced acid solubility of remineralized enamel, and development of fluoride gradients if repeated remineralization occurs
67
Q

where on the tooth is fluoride most effective

A
  • highly effective on smooth surface caries

- less so on pit and fissure caries

68
Q

what are ideal properties of remineralizing materials

A
  • diffuses into the subsurface and delivers calcium and phosphate onto body of lesion
  • does not deliver an excess of calcium
  • works at acidic, neutral, and basic pHs (fluoride better at slightly acidic)
  • works in xerostomic patients
  • enhances or maintains the remineralizing effect of saliva
  • for novel materials, shows a benefit over fluoride, or establishes a synergistic effect with fluoride to promote remineralization
69
Q

what are 5 therapeutic options for remineralization

A
  1. fluoride
  2. compounds that increase mineral saturation
  3. biofilm modifiers
  4. self-assembling peptides
  5. diffusion barriers (like sealants)

Biomaterials (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions