Impression material

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Impression materials
‫أحمد عبد العزيز الحسين‬
‫أخصائي تركيبات سنيه في وزارة الصحة األردنية‬
‫محاضر غير متفرغ في جامعة العلوم والتكنولوجيا األردنية‬
Ahmad Abdul Aziz Alhussien
Prosthodontist at M.O.H
Part time lecturer at J.U.S.T
BSc , MSc, Jor. Board/ prosthodontics
1
• The function of an impression material is to make
a negative copy of the oral tissue … that is poured
to produce a positive replica for these tissues
2
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
“not too rigid” to be removed from the mouth without
becoming deformed.
• 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
3
Impression trays
• Used to carry the impression material into the oral cavity
• Can be
–
–
–
–
metal or plastic
Perforated or non perforated
for edentulous or dentate
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.
4
Variety of trays
5
• Cast
replica of dental arch
• Die
replica of a single tooth (cut from a cast)
6
Classification of dental impression
materials
• Inelastic / Elastic
• Mechanism of hardening
7
Impression material (rigid)
Inelastic materials
Setting mechanism
Impression
Cooling to mouth
temperature
compounds
‘Dental compounds’
Zinc-oxide
eugenol (ZOE) Chemical reaction
Impression
Chemical reaction
Cooling to mouth
temperature
plaster
Impression wax
8
Impression materials (aqueous)
Elastic material
(hydro-colloid)
Setting mechanism
Reversible
Cooling
(Agar)
Irreversible
(Alginate)
Chemical reaction
9
Impression materials (rubber)
Elastic material (non- Setting mechanism
aqueous)
Polysulfides
Polymerization reaction
Condensation
silicon Polymerization reaction
Polyether
Polymerization reaction
Addition
Polymerization reaction
silicon
10
Inelastic impression materials (rigid)
• Plaster of Paris (Type I gypsum)
• Dental compound/impression compounds
– Softened by heat and pressed against tissue before it hardens.
Thermoplastic softens at 60°C, remains plastic at 45°C and becomes
firm at mouth temperature. Used for primary impression
• ZOE (Zinc oxide eugenol)
– Other uses ???
• Impression wax
Elastic impression materials (non-rigid)
• Hydrocolloids
• Elastomers (Rubber)
11
Hydrocolloids
12
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
13
Agar
Composition of agar:
Material
Agar
(seaweed
extract)
Percentage purpose
12-15%
Colloidal particles as basis of
the gel
Potassium
sulfate
Borax
1%
0.2%
Ensures set of gypsum
materials
Strengthens gel
Alkyl
benzoate
water
0.1%
Antifungal agent
85%
Dispersing medium for the
colloidal suspension
14
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.
15
• 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.
16
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.
• Usually used in lab for cast duplication
• Agar is supplied in two viscosities, thick and thin
(depending on the amount of agar).
17
• Preparing the material for
impression:
– Gel heated to 71-100°C, 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 6066°C.
– 3rd camber kept at 45-47°C to temper agar
before use to prevent burns.
• Agar exhibits hysteresis, melting
at 85 °C and solidifying from 3240 °C
18
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
19
Composition/setting rxn/
working time
Material
Percentage purpose
Na, K alginate
15-20%
Basis of the gel
Ca sulfate
dihydrate
14-20%
Creates irreversible gel with
alginate
Potassium
sulfate
10%
ensures set of gypsum
Trisodium
sulfate
2%
Retarder to control setting
Diatomaceous
earth
55-60%
Filler to increase thickness and
strength
20
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
21
Setting rxn/working time
• Controlling water temperature shortens or
lengthens setting time
• Changing P:L has adverse effect on
materials property and strength
• Allow extra 1-2 minutes, tear strength
increases, and rebound from undercuts
w/out deformation improves
22
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
23
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)
24
• 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*
25
Alginate impression
26
Elastomers
27
Elastomers
• Often called rubber materials since they
have properties similar to rubber.
• Clinical uses:
– Bridges
– Implants
– Partial dentures complete dentures
– Indirect esthetic restorations
28
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
29
Polysulphides
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
30
Setting reaction
Mercaptan + lead dioxide
polysulfide+H2O
• The reaction is sensitive to temperature and
moisture so increase in any will accelerate the
setting.
• Also sensitive to correct mixing ratio
31
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
32
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
33
Silicon rubber
Addition (A) silicon
Condensation (C) silicon
34
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)
35
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
36
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.
37
Addition silicon (PVS)
• Desirable clinical qualities:
–
–
–
–
–
Dimensional stability
Accuracy
Clean
Easy to mix
No foul odor or taste
the most expensive
38
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-molecularweight silicon with silane hydrogens (putty) +
silica filler
– Catalyst: chloroplatinic acid
39
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
40
Impression making techniques
• Putty/wash technique
– One step
– Two step
41
Polyethers
• Also used for crown and
bridge work since they
are very accurate and also
more hydrophilic than
other silicons
42
Dispensing & composition
• Dispensing same as other rubber materials (2 tubes)
• In addition it’s 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.
43
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
44
Inelastic impression materials
45
Impression compound:
• Impression compound:
softens with heat, hardens
in the mouth.
• 2 main forms:
– Cakes (sheets) /low fusing
– Sticks /high fusing
• Clinical uses:
– Sheets:
• Primary impression in
metal trays
• To make custom trays
– Sticks are used for
border molding
46
Composition & properties
• Composition
–
–
–
–
–
Thermoplastic resin and waxes
Fillers to reduce flow
Plasticizers
Organic acids or oils
Pigments
• Properties
–
–
–
–
Softened at 60°C, remains plastic at 45°C, firm at 37°C
Heated in water not by flame
Should be poured ASAP to avoid distortion
Flame used to heat sticks
47
Impression plaster
• Impression plaster: seldom used
– Composed of plaster gypsum (Ca hemihydrae)
– Used for primary impression (high P:L)
– Scored with a knife in the mouth then removed and
reassembled in the lab (distortion?)
– Wash impression
– Easy to use
– Inexpensive
48
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 set:3-6 minutes, final set:10 minutes
• To accelerate the setting, a drop of water or zinc acetate
is added.
49
Properties
• Brittle, so not suitable for areas with
undercut
• Flows readily
• Accurate
• Eugenol can be irritant (burning sensation)
• Once set, dimensionally stable
50
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
51
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 or impression immersed in
disinfectant
• Protective gloves should be worn
• Rinse after disinfection is complete
52
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.
53
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
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