Post on 19-Jan-2016
transcript
IMPRESSION MATERIALS
Prof . Dr Amal EzzEl Din Dental Biomaterials ,Faculty of
Dentistry Alex _Univ.
o Uses Make an accurate replica of
tissues.o Impression
Single tooth.
Whole dentition.
Partially or
completely
edentulous mouth.
o Biocompatible: non toxic- non irritant.
o Acceptable to the patient: pleasant
odour, taste, esthetic colour.
o Ease of manipulation, reasonable
cost.
o Reasonable setting time.
o Adequate shelf life.
o Adequate strength: not tear or break
on removal from mouth.
o Compatible with model materials.
o Dimensionally stable: neither
expands nor contracts.
o Adequate flow properties: to
register fine details.
o Readily disinfected without loss
of accuracy.
Classification
1. According to the ability of a set material to be
withdrawn over undercuts.
Non Elastic
Elastic
According to the manner which they
harden(set):
Reversible
Sets by a physical
reaction due to temperature changes
Irreversible
Sets by a chemical reaction.
Impression materials
Impression materialImpression material
ElasticElastic
NonelasticNonelastic
HydrocolloidsHydrocolloids
Zinc oxide eugenolZinc oxide eugenol
Impression CompoundImpression Compound
PlasterPlaster
Non-aqueouselastomers
Non-aqueouselastomers
AgarAgar
AlginateAlginatePolyethersPolyethers
Additionsilicone
Additionsilicone
Condensationsilicone
Condensationsilicone
PolysulfidesPolysulfides
Impression waxImpression wax
Classification
By Setting Mechanism
By Application or Mechanical Properties
Non-elastic Elastic
Chemical reaction
(irreversible)
Plaster of ParisZOE
Alginate hydrocolloidElastomers
Temperature changes
(reversible)
CompoundWax
Agar hydrocolloid
o Thermoplastic material.
o Composition:
Natural resins e.g., shellac &
carnuba wax.
Fillers: soap or talc.
Lubricants: stearic acid.
Colouring agent: e.g., rouge.
Types (forms of Supply)
Type I: low fusing compound softens at
53-60°C
Supplied in the form of sheets, or cakes
used as: impression for edentulous
patients.
Or in the form of sticks or cones or
cylinders.
Used as: impression for a single tooth
preparation as in (crowns), known as
Copper Band Impression.
Impression Compound
Type II: High fusing compound softens at 70°°C.
Used as tray material to hold a secondary impression material
Heating: o In a water bath-soaking in water in cases
of sheets and cakes. o Over a flame in case of sticks.o Avoid over heating.o Kneading: with the fingers.o Importance: assures uniform heating
Increases the flow. Gives workability.
Manipulation The compound disc is completely immersed in a water
bath at 55-60 C for about 4-5 minutes to ensure complete softening. Gauze is placed at the bottom of the water bath to prevent adherence. However if it is left in too long some of the constituents may be leached out into the water bath, altering the properties of the material (it is often the plasticizer stearic acid that is leached out). If the compound is kneaded water will become incorporated and act as a plasticiser. Kneading of the compound will incorporate water into the mass and thus increase the flow in the material (water = plasticizer).
The compound is loaded on to the tray and firm pressure is used to seat the tray home in the mouth. After the impression has been taken it is carefully examined, a common mistake is not softening the compound enough. In this is the case the impression can be reheated in a separate bowl of water (cross infection control) and the impression is repeated.
Cooling:
oAssure uniform cooling by
spraying with water at 16-18°C
before removal from the mouth.
Flow type 1: 85% at 45°C
less than 6% at 37°C.
Type II: 70% at 45°C
less than 2% at 37°C.
Viscous material does not record fine
details.
• Low thermal conductivity.
• High expansion and contraction
coefficients.
• Linear contraction on cooling from
mouth temperature to room
temperature
(0.3%-0.4%).
o Dimensional Changes: due to relief of
internal stresses (relaxation) Warpage
distortion of the impression.
o Model should be poured as soon as
possible.
o No separating medium.
o Separation of model.
PROPERTIES
Poor surface detail High coefficient of thermal expansion
(contraction of up to 0.3% when removed from mouth to room temperature)
Distorts when removed over undercut areas
Poor dimensional stability Can be modified by re-heating Non toxic and non irritant Good shelf life
ADVANTAGES & DisADVANTAGES
ADVANTAGES 1. Non irritant and
non toxic2. Reusable (but with re-use the constituents are leached out)3. Can be reheated and readapted4. Can support other materials for wash impressions
DISADVANTAGES 1. Poor
dimensional stability2. Poor surface detail3. Expansion coefficient4. Will distort if removed from undercuts
THANK YOU