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Setting reaction Mercaptan + lead dioxide polysulfide+H2O

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Setting reaction Mercaptan + lead dioxide polysulfide+H2O The reaction is sensitive to temperature and moisture so increase in any will accelerate the setting. – PowerPoint PPT presentation

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Title: Setting reaction Mercaptan + lead dioxide polysulfide+H2O


1
Impression material
2
  • The function of an impression material is to make
    a ve copy, which records the dimensions of the
    oral tissue and their relationships.
  • The impression must be accurate so that the
    model, cast, or die will be accurate. That is the
    positive copy of the oral structure will be
    accurate.

3
Initial requirement of an impression material
  • Must be a semi-liquid material that will flow and
    adapt itself around the structure of interest.
  • It must set and harden into a solid that is rigid
    enough to be removed from the mouth without
    becoming deformed.

4
Other characteristics of an impression material
  • Copy details accurately
  • Dimensional stability after removal from the
    mouth
  • Appropriate working time (from the start of mix)
  • Appropriate time to harden in the mouth (setting
    time)
  • Bio-compatibility/Aesthetic, odor/taste
  • Chemically compatible with material used to pour
    cast or dies

5
Impression trays
  • Used to carry the impression material into the
    oral cavity
  • Can be metal or plastic, for edentulous or for
    arches with teeth, pre-manufactured (stock trays)
    or custom-made (made in the lab. From resin).
  • Trays need to be rigid enough to support
    impression material.
  • For impression material to be retained in tray,
    tray maybe perforated, and adhesive spray can be
    used to enhance retention.

6
Variety of trays
7
  • Study model
  • a physical model of the oral tissue for study.
    Used in diagnosis and treatment planning.
  • Cast
  • a model requiring very exact replication of size
    and shape
  • Die
  • replica of a single tooth (cut from a cast)

8
Classification of dental impression materials
  • Inelastic / Elastic
  • Mechanism of hardening
  • Thermal behavior

9
Impression material (rigid)
10
Impression materials (aqueous)
11
Impression materials (rubber)
12
Inelastic impression materials (rigid)
  • Plaster of Paris (Type I gypsum)
  • Can not be removed over undercuts without
    impression being fractured
  • Dental compound/impression compounds
  • Softened by heat and pressed against tissue
    before it hardens. Thermoplastic softens at 60C,
    remains plastic at 45C and becomes firm at mouth
    temperature. Used for primary impression
  • ZOE (Zinc oxide eugenol)
  • Used as luting agent, temporary filling,
    secondary impression material.

13
Hydrocolloids
  • The colloid state represents a highly dispersed
    phase of fine particles within another phase,
    some where between solution and a suspension.
  • The colloid can exist as a viscous liquid known
    as a sol or a solid known as gel.
  • If the particles are suspended in water, the
    suspension is called a hydrocolloid (hydrosol,
    hydrogel
  • Hydrocolloids come in two forms
  • Reversible agar
  • Irreversible alginate

14
Composition of Agar
15
Properties
  • Flows well and adapts readily to hard and soft
    tissue contours
  • Accurate reproduction (hydrophilic nature),
    however, the impression need to be poured
    immediately.
  • Need to be stored in 100 humidity for short
    period of time if not poured immediately
  • Distortion is more likely to occur if impression
    not poured within an hour.

16
  • Tear strength is not high.
  • If compressed it might rebound if compression is
    not too sever otherwise deformation occurs.
  • Material suffers from loss or gain of water
  • Syneresis a process by which the gel contracts
    and some of the liquid is squeezed out, forming
    an exudate on the surface.
  • Evaporation loss of water which causes the
    material to shrink, and impression is distorted.
  • Imbibition uptake of water, this will swell and
    distort the impression.

17
Clinical application
  • The use of agar requires special equipment
    consisting of hydrocolloid conditioner (has 3
    water bath chambers) and water -cooled tray
    connected to a rubber hose that delivers water.
  • Agar is supplied in two viscosities, thick and
    thin (depending on the amount of agar).

18
  • Preparing the material for impression
  • Gel heated to 71-100C, becomes liquid (sol)
  • Tray and agar syringe are liquefied in 8-12
    minutes in boiling water in 1st chamber
  • 2nd chamber is used to store the agar at 60-66C.
  • 3rd camber kept at 45-47C to temper agar before
    use to prevent burns.
  • Tray is loaded and water hose attached and tray
    is seated on teeth.

19
Hydrocolloid conditioner, water cooled tray with
hose, impression materials
20
Alginate
  • Inexpensive
  • Easy to manipulate
  • Requires no special equipment
  • Reasonably accurate
  • Common uses
  • Diagnostic cast (study model)
  • Preliminary impression for complete denture
  • Partial denture framework
  • Custom trays for fluoride or bleaching

21
Composition/setting rxn/working time
22
Setting rxn/working time
  • Setting rxn occurs when the powder is mixed with
    water
  • Ca sulfate dihydrate NaAlginate Ca
    alginate
  • Working time total time from start of mixing to
    the final time at which an impression tray can be
    fully seated without distortion
  • Regular set 2-3 minutes
  • Fast-set 1.25-2 minutes
  • Setting time elapsed time from the start of
    mixing until impression material becomes firm
    enough to resist permanent deformation.
  • Regular set 2-5 minutes, Fast set 1-2 minutes

23
Setting rxn/working time
  • Controlling water temperature shortens or
    lengthens setting time
  • Changing PL has adverse effect on materials
    property and strength
  • Allow extra 1-2 minutes, tear strength increases,
    and rebound from undercuts w/out deformation
    improves

24
Important considerations to ensure accurate
impression
  • 2-4 mm bulk material in tray
  • Snap action removal from mouth
  • Allow extra 1-2 minutes after setting to improve
    tear strength
  • Stored in a moist environment to avoid loss of
    water and deformation
  • Disinfect in less than 10 minutes to avoid
    dimensional instability

25
Impression making
  • Fluff powder, wait 30 seconds for the dust to
    settle
  • Measure powder and water according to
    manufacturer instruction
  • Use spatula to stir water into powder to mix
  • Stir vigorously to create homogenous mix (45
    seconds for regular, 30 seconds for fast setting
    alginate)

26
  • Tray should cover all anatomical features
  • Utility wax can be added on tray borders to
    extend its coverage
  • Adhesive spray is used to prevent separation of
    alginate from tray.
  • Tray is loaded from posterior towards anterior
  • Moisten and smooth alginate
  • Posterior part of tray is seated first then
    anterior.
  • tips to control gag reflex

27
Alginate impression
28
Troubleshooting alginate impression
  • Premature set
  • Slow set
  • Voids
  • Distortion
  • Excess alginate at back of tray
  • cause solution

29
Criteria for acceptable alginate impression
  • All teeth and relevant soft tissue recorded
  • No large voids
  • Free of debris
  • No distortion
  • Etc etc etc (refer to text book)

30
Elastomers
  • Often called rubber materials since they have
    properties similar to rubber.
  • Clinical uses
  • Bridges
  • Implants
  • Partial dentures complete dentures
  • Indirect esthetic restorations

31
Polymerization reaction
  • Involves formation of long-chain polymers and
    cross-linking of chains
  • General properties
  • Not as sensitive to water as hydrocolloids
  • Have a certain amount of rebound, the highest is
    for addition silicon and polyethers, medium for
    condensation silicon and poorest for Polysulfides
  • Not wet well by water (hydrophobic) possible
    solution surfactants

32
Polysulfides
33
Dispensing Composition
  • Supplied in two tubes as base and catalyst, equal
    lengths are mixed. Light, regular, heavy
    viscosities
  • Chemical composition of base
  • 80 low-molecular-weight organic polymer
    containing mercaptan reactive groups (-SH), and
    20 reinforcing agents titanium dioxide, silica,
    zinc sulfide
  • Chemical composition of catalyst
  • Lead dioxide or copper hydroxide

34
Setting reaction
  • Mercaptan lead dioxide polysulfideH2O
  • The reaction is sensitive to temperature and
    moisture so increase in any will accelerate the
    setting.
  • Also sensitive to correct mixing ratio

35
Manipulation and dispensing
36
Uses
  • Crown and bridge impressions
  • Partial and complete denture impressions
  • Clinical considerations when used
  • Used with custom trays
  • Allow 2mm thickness
  • Use tray adhesive
  • Dry field

37
Properties of clinical interest
  • Setting time 8-14 minutes
  • Higher tear strength than hydrocolloids
  • Accuracy improves if impression is poured within
    30 minutes
  • very unpleasant taste and odor
  • Messy (orange solvent to remove stains)
  • Can be irritant to oral mucosa
  • For all these reasons, Polysulfides have been
    largely replaced by other rubber materials

38
Silicon rubber
39
Classification according to polymerization rxn
Condensation silicon
Addition silicon
40
Condensation silicon
  • Developed as alternative to Polysulfides
  • Has more desirable qualities in comparison
  • Easy mix
  • Better taste and odorless
  • Shorter setting time (5-7 minutes)

41
Dispensing Composition
  • Two pastes, base and catalyst.
  • Comes as light, medium, or heavy viscosity
  • Base dimethylsiloxane filler (silica)
  • Catalyst suspension of stannous octoate alkyl
    silicate

42
Setting rxn
  • Condensation reaction that produces ethyl alcohol
    as by product. The alcohol evaporates which
    causes dimensional instability.
  • The material continues to contract with time, so
    needs to be poured within minutes.

43
Addition silicon (PVS)
  • Desirable clinical qualities
  • Dimensional stability
  • Accuracy
  • Clean
  • Easy to mix
  • No foul odor or taste
  • However, they are among the most expensive

44
Dispensing composition
  • Light, regular and heavy viscosities and also
    putty
  • Dispensed as cartridge with 2 chambers (pastes),
    or two putty- system
  • Base low-molecular-weight silicon with vinyl
    groups (paste system), or low-molecular-weight
    silicon with silane hydrogens (putty) silica
    filler
  • Catalyst chloroplatinic acid

45
Setting rxn
  • Polymerization rxn of chain lengthening and
    cross-linking with reactive vinyl groups,
    producing a stable silicon rubber.
  • No ethyl-alcohol by product
  • Some addition silicons produce hydrogen as by
    product, manufacturers incorporated palladium
    powder that absorbs hydrogen
  • setting time 3-7 minutes

46
Impression making techniques
  • Putty/wash technique
  • One step
  • Two step
  • Pros and cons for each technique and possible
    solution

47
Clinical use
  • Crown and bridge work
  • Bite registration (rapid setting 1-2 minutes)
  • Indirect composite inlays (silicon die technique)

48
Polyethers
  • Also used for crown and bridge work since they
    are very accurate and also more hydrophilic than
    other silicons

49
Dispensing composition
  • Dispensing same as other rubber materials (2
    tubes)
  • In addition its supplied in pouches of base and
    catalyst placed in mechanical mixer.
  • Composition
  • Base low- molecular-weight polyether with cation
    reactive group
  • Catalyst aromatic sulfonic acid
  • clinical tip mix well to avoid irritation from
    unmixed catalyst.

50
Properties
  • Stiff, difficult to remove from undercuts
  • Short working and setting times
  • Setting time 3-5 minutes
  • Sensitive to moisture and temperature
  • More hydrophilic (must not be stored in water or
    disinfectant)
  • accurate

51
Inelastic impression materials
  • Impression compound softens with heat, hardens
    in the mouth.
  • Cakes (sheets) and sticks
  • Clinical uses
  • Sheets
  • Primary impression in metal trays
  • To make custom trays
  • Sticks are used for border molding

52
Composition properties
  • Thermoplastic resin and waxes
  • Fillers to reduce flow
  • Plasticizers
  • Organic acids or oils
  • Pigments
  • Properties
  • Softened at 60C, remains plastic at 45C, firm
    at 37C
  • Heated in water not by flame
  • Should be poured ASAP to avoid distortion

53
Other impression materials
  • Impression plaster seldom used
  • Composed of plaster gypsum (Ca hemihydrae)
  • Used for primary impression (high PL)
  • Scored with a knife in the mouth then removed and
    reassembled in the lab (distortion?)
  • Wash impression
  • Easy to use
  • inexpensive

54
ZNO eugenol
  • Secondary impression for complete dentures, or
    wash impression (mucostatic impression)
  • 2 tube paste system, different colors
  • Zinc oxide (80) and fillers, eugenol (15) with
    oils, resin, fillers. In addition to chemical
    accelerator (zinc acetate)
  • Dispensed in 2 equal lengths and mixed to
    homogenous color forming zinc eugenolate
  • Initial set3-6 minutes, final set10 minutes
  • To accelerate the setting, a drop of water or
    zinc acetate is added.

55
Properties
  • Brittle, so not suitable for areas with undercut
  • Flows readily
  • Accurate
  • Eugenol can be irritant (burning sensation)
  • Once set, dimensionally stable

56
Impression wax
  • Clinical uses
  • Preliminary impression for edentulous patients
  • Bite registration
  • Baseplate wax used to be used for provisional
    crown and bridge work
  • Melted to correct voids in gypsum casts

57
Disinfection of impressions
  • The disinfectant should be compatible with the
    impression materials.
  • After taking the impression, it should be rinsed
    with water, excess water shaken off, and
    disinfectant sprayed (2 disadvantages?) or
    impression immersed in disinfectant
  • Protective gloves should be worn
  • Rinse after disinfection is complete

58
Disinfecting casts
  • Maybe necessary if impression was not properly
    disinfected, or if immersion of impression
    adversely affects the impression
  • Casts should be set and stored for 24 hours
    before disinfection.
  • Solution used Na hypochlorite, iodophors.

59
Sterilizing trays
  • Trays should be properly sterilized before use
  • Disposable trays are recommended if appropriate
  • Sterilization can be achieved by heated steam,
    dry heat, chemical vapors

60
Reference dental materials, clinical
applications for dental assistants and dental
hygienists
THANK YOU
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