VARIOUS IMPRESSION MATERIALS USED IN ORTHODONTICS

1. UMAR MOHAMED

2. • Introduction
• History
• Ideal requirements
• Classification of impression materials
• Hydrocolloids
• Elastomers
• Causes for failure of impression
• Ora scanner
• Conclusion
• References

4. • A mould of the teeth used to make models of the
teeth.

5. • PHILIP PFAFFS (1756) was the first to
describe taking an impression of
the jaw .
• DELABARRE (1820) INTRODUCED THE
IMPRESSION TRAY
• E.C. Stanford, 1881 carried out the experimental
studies on the extraction of alginate from brown
seaweeds.
• 40 years later S. WILLIAM WILDING USED
ALGIN AS
DENTAL IMPRESSION MATERIAL

6. In orthodontics impression are primarily made to obtain
CASTS, which in turn are used for
1. STUDY PURPOSE
2. FABRICATION OF APPLIANCES
3. MAINTAINING RECORDS
In dentistry various types of materials are used for making an impression.
NO ONE MATERIAL will be used in all the scenarios rather based on the properties,
ease of use, accuracy and economy. Various material will be used according to the
particular need of the practitioner.

7. IDEAL REQUISITES OF AN IMPRESSION
MATERIAL
•They should be fluid enough to adapt to the oral tissue
•They should be viscous enough to be contained in the tray that seat in the
mouth
•While in the mouth they should transform in to rubbery or rigid solid in
reasonable amount of time
•The seat impression should not distort or tear when removed from the mouth
•They should dimensionally stable
•They should be biocompatible
Phillips .science of dental materials 11th
edition-Anusavice

8. No impression material fulfills all these requirements
And the selection of the material best suited for a
particular Clinical situation and technique rests with
Dentists.

9. SETTING
REACTION
THERMOPLASTIC THERMOSET
ELASTICITY ELASTIC INELASTIC OR
RIGID
NATURE OF
THE SETTING
REACTION
REVERSIBLE IRREVERSIBL
E
PRESSURE
EXERTED ON
THE TISSUE
MUCOCOMPRESSIVE MUCOSTATIC
DENTITION
STATUS
EDENTULOUS DENTULOUS

10. In orthodontics…
The most commonly employed materials include
I. Hydrocolloid – Agar Agar (reversible)
- Alginate (irreversible)
II. Elastomeric impression materials.

11. HYDROCOLLOIDS
Derived from two Greek words ’Kolla’ meaning glue and ‘oid’ meaning like. The
term was originally applied to substances that form solutions with properties that
fall between solution and suspension, Thomas Graham[1805-1869]
They are the fourth state of matter because of their differences in structure,
constitution, and reactions .
Particles size ranging from 1 to 200 nanometers.
Colloid: Suspension of 2 phases
Colloidal materials used for making impressions are either
algin or agar dissolved in water. Hence the name HYDROCOLLOIDS

12. Colloids , have two distinct phases
A dispersed phase + dispersion phase
LIQUID COLLOIDS ARE CALLED SOL
SOLID COLLOIDS ARE CALLED GEL

13. Sol to gel transformation
In the gel state, the dispersed phase
agglomerates, forming chains or fibrils called
“MICELLES”. The fibrils may branch and
intermesh to form a brush heap structure
Water being entrapped between the fibrils
SOL GEL
GELATION TEMPERATURE (370 – 500C)
Fibrils are held together by secondary
molecular forces

14. This process may also occur through a
chemical reaction the structure of the fibrils formed
is very similar but the process is very different and is
irreversible
The fibrils of the gel formed are chemically
bonded by primary forces and therefore they are
not affected by the temperature.

15. SYNERISIS
The process of synerisis may be explained as the
squeezing of water from between the polysaccharide
chains. As a result of which one may often observe a
small droplets of water on the surface of impression.
Which results in shrinkage of the impression.

16. IMBIBITION
In the presence of excess water the hydrocolloids may
absorb water by a process, which is opposite of synerisis
that will cause the separation of the polysaccharide
chains and thus the swelling of the impression.

17. IRREVERSIBLE HYDROCOLLOID
ALGINATE (ADA no 18)
At the end of 19th century the chemist from Scotland noticed that certain
brown seaweed produced a mucous extraction that he termed as ‘ALGIN’. Later S
William wilding used this algin as dental impression. This became the chief
ingredient in our popularly used dental ALGINATE, which is
A SODIUM SALT ANHYDRO-ß-D-MANURONIC ACID/ ALGINIC ACID

18. Structural formula of alginic acid with molecular wt of 32000-200000

19. The factors causing its successful use as an impression
material include:
• Ease of manipulation
• Comfortable to the patients
• Relatively inexpensive not requiring elaborate
armamentarium.
TYPES
TYPE I – RAPID SETTING
TYPE II – NORMAL SETTING

20. NO COMPOSITION FUNCTION %
I. Salt of Alginic acid Dissolves in water & reacts
with calcium ions
15%
II. Calcium sulphate Reacts with pottasium
alginate to form calcium
alginate
16%
III. sodium phosphate Reacts in preference with
calcium sulphate - retarder
2%
IV. Pottasium Titanium
fluoride
Gypsum hardener and
accelarator
3%
V. Zinc oxide Filler 4%
VI. Diatomaceous earth Filler 60%
VII. Flavouring &
coloring agents
Makes the material more
palatable
traces
Dental materials 8th edition Robert G
Craig

21. SETTING REACTION.
Soluble alginate reacts with the calcium sulphate resulting in the formation of an
insoluble calcium alginate.
This process occurs quite rapidly and thus would not allow sufficient working time, so
to compensate for this problem a water soluble salt namely Tri-sodium phosphate is
added to prolong the working time.
The basic idea behind adding this salt is to allow calcium sulphate to initially react with
tri-sodium phosphate in preference to the soluble alginate
K2nAlg + CaSO4 nK2SO4 + CanAlg

22. Working time-for fast setting materials-1.25-2 min (mixing time-45 sec)
for regular set-3-4.5 min (m.t.-60 sec)
Setting time-1-4.5min(regular) 1-2min(fast set)
Permanent deformation- The A D A specification requires that the
recovery from deformation be more than 95% when material is
compressed 20% for 5sec

23. Flexibility
A D A specification permits a range of 5% to 20% at a stress
of 1000 gms/cm2 and most alginate have a typical value of 14%.
Strength
The compressive strengths range from 5000 – 9000 gms/cm².
The Tear strength vary from 380- 700 gms/cm.

24. DIMENSIONAL STABILITY
For maximum accuracy the model material must
should be poured into alginate impression as soon as
possible.
If it is delayed , the impression should be stored in
100% relative humidity in a plastic bag or wrapped in a
damp paper towel
It is satisfactory for some materials for periods up to 2
hours
BIOCOMPATIBILITY
Inhaling fine airborne particles from alginate impression
materials Can cause SILICOSIS and PULMONARY
HYPERSENSITIVITY

25. Crosslinking of Na alginate molecules to form Ca alginate

26. STEPS IN MAKING IMPRESSION
• Selection of the tray
• Preparation of the patient
• Seating of the tray
• Disinfection of the impression

27. • Practice the placement of the empty tray into the patient’s mouth
• Assume the correct operator positioning
 Maxillary impression - 11 o’ clock
 Mandibular impression - 7 o’ clock

28. MANIPULATION
The recommended water powder ratio should be used. In general it is 38 ml
of water per 16 gms of powder but slight variation can be present depending
on the manufacturer. The weighed power is incorporated into the water by
carefully mixing with the spatula. Care should be taken to ensure that air is
not incorporated into the mix by spatulating the mix against the side of the
bowl while using the vigorous figure of 8 motion till a smooth creamy
homogeneous mix is obtained.

29. IMPRESSION MAKING
Manipulation

30. Maxillary tuberosity
Palate
Rolled round & thick borders
Maxillary impression
IMPRESSION MAKING

31. Mandibular retromolar area
Detailed along gingival anatomyPosterior lingual areas
Rolled round & thick borders
Mandibular impression
IMPRESSION MAKING

32. SEQUENCES OF IMPRESSION MAKING
It is advisable to make mandibular
impression first as there is less chance of the
patient to gag .This allows the patient to become
accustomed to the taste and the feeling of the
material in the mouth which in turn reduces the
chances of gagging while making an impression of
the maxillary arch.

33. DISINFECTING THE IMPRESSION
Disinfection of impression is a concern due to viral diseases such as
Hepatitis B,A I D S and herpes simplex
• Gently rinse the impression under the tap water to remove any
debris that may be retained in the impression.
• May immerse the impression in a disinfectant such as :
gluteraldehyde solution
iodophors
1:10 dilution of sodium hypochlorite
synthetic phenols
for less than <10 min

34. CRITERIA FOR ACCESSING THE IMPRESSION
• Lack of voids.
• No distortion , clear and distinct impression
• Adequately extended.
• Free of debris and extraneous material.
• Adequate details and all structure must be recorded.
• Stable material which is sufficiently attached to the tray.

35. MODIFIED ALGINATE
• Dust free alginate – GLYCOL COATED particles
•A new system in which the SOL contains water but not calcium ion
so that the second component added is actually Plaster of Paris.
• A two component paste system
(I) Alginate Sol
(II) calcium reactor
• Chromatic alginate actually changes the color once set.
• Alginates modified with silicon/polymers for fine detail but these
have the disadvantage of having a very poor dimensional stability.

36. 1. Grainy material •Improper mixing
•Prolong mixing
•Undue gelation
•Water : powder ratio too low
2. Tearing •Inadequate bulk
•Moisture contamination
•Premature removal from mouth
•Prolong mixing
3. External bubbles •Undue gelation, preventing flow
•Air incorporated during mixing

37. 4. Irregularly shaped voids •Moisture or debris on tissue
5. Rough and chalky stone
model
•Inadequate cleansing of
impression
•Excess water or potassium
sulfate solution left in
impression
•Premature removal of model
6. Distortion •Impression not poured
immediately
•Movement of tray during
gelation
•Premature removal from mouth

38. REVERSIBILE HYDROCOLLOIDS
AGAR-AGAR
This is a organic , hydrophilic colloid (polysaccharide)
extracted from certain type of sea weed. It is a sulfuric ester of
a linear polymer of galactose
The temperature at which the
LIQUIFACATION TEMPERATURE (700 – 1000C)
GEL SOL
GELATION TEMPERATURE (370 – 500C)

39. INGREDIENTS FUNCTION COMPOSITION %
1. AGAR BASIC CONSTITUENT 13-17
2. BORATES STRENGTH 0.2-0.5
3. SULPHATES GYPSUM HARDNER 1.0-2.0
4. WAX FILLER 0.5-1.0
5. THIXOTROPHIC
MATERIAL
THICKNERS 0.3-0.5
6. WATER REACTION MEDIUM BALANCE
7. ALKYL BENZOATE PRESERVATIVE 0.1%

40. THE MATERIAL
TYPES AVILABLE
The hydrocolloid is supplied in two forms:-
The more fluid “cartridge form” available for use in syringes.
the more viscous type used in trays
Special water cooled trays are used to rapidly cool the material in the
patients mouth

41. AGAR

42. At 1000C – rapidly converts Gel to Sol and the contents of the tube
become very fluid.
At 650c- transfer the material to second bath, this temperature will maintain
the material in its SOL form leave the material in this temperature until the material
is required for use
At 450c a few minutes prior to the use the material is cooled to this
temperature before placing in the patients mouth.

43. CONDITIONING UNIT

44. The cooling of the material in the mouth to promote rapid gel
formation may be achieved by circulating cold water on the tray or by using
special water cooling impression trays. These trays are stock trays with a
narrow bore metal tube attached to the outer surface, the tube is connected
to the cold water supply and circulatory water reduces the temperature of the
tray.

45. WATER COOLED TRAYS

46. DUPLICATING MATERIAL
Alginate and Agar –Agar may be used successfully as a duplicating
material. In this way multiple casts can be duplicated from a single master cast,
which may have been formed using some other material. This process is essential
in ones orthodontic practice as it enables the use of one master cast to form several
casts subsequently.

47. NON AQUEOUS ELASTOMERIC IMPRESSION
MATERIAL (ADA no 19)
These materials are classified as synthetic rubbers,
developed to mimic natural rubber when it became difficult to
obtain during WORLD WAR II .They are liquid polymers and can be
converted to rubber at room temperature by mixing with a suitable

48. polymerization and or cross linking by
condensation/addition reactions to produce a firm
elastic solid.
CLASSIFICATION
• POLYSULFIDES
• SILICON POLYSILOXANES
CONDENSATION POLYSILICON
ADDITION POLYSILICON
(POLYVINYL SILOXANE)
• POLYETHER

49. THEY ARE SUPPLIED IN FOUR VISCOSITY
• LIGHT BODY
• MEDIUM /REGULAR)
• HEAVY BODY
• PUTTY (VERY HIGH)

50. HIGH, MEDIUM AND LOW CONSISTENCIES ARE SUPPLIED IN TWO
FORMS
• BASE
• ACCELARATOR / CATALYST
CATALYST SOME TIMES AS LIQUID
PASTES ARE SUPPLIED IN COLLAPSABLE TUBE.

51. Condensation silicones
Supplied in a low and putty type consistency.
The base contains poly dimethyl siloxane
which have reactive terminal hydroxyl groups.
The accelerator maybe liquid that consists of stannous
octoate suspension and alkyl silicates
or it may be supplied as paste by addition of thickening agent
The reaction proceeds producing 3 dimensional network
rubber with
ethyl alcohol as a byproduct
Stock trays are generally used

52. Addition silicones
It is available in low,medium,heavy and putty
consistencies and is also
Poly siloxane.
No by product.
Pinpoint voids
Base contains low molecular wt polymer with
silane group and filler.
The accelerator contains a moderately low
molecular wt polymer with vinyl terminal groups
and filler

54. Polyether
Supplied as base and catalyst system
Base- low molecular weight polyether
Polyether + sulfonic ester- cross-linked rubber
Base paste- polyether polymer, colloidal silica as
filler and plasticizer such glycolether or pthalate
Accelator paste-alkyl aromatic sulfonate, filler
and plasticizer

55. Better mechanical properties
Less dimensional changes
Good wetting properties
limitations
Short working time
High stiffness

56. Biocompatibility
Comparing the cell cytotoxicity for different
impression materials reveals that polysulfide
results in the lowest cell count and set polyether
impression material produces the highest cell
cytotoxicity
Foreign body of impression material can cause
severe gingival inflammation if it is left in a
gingival sulcus
Contact dermatitis from polyether especially to
the dental assistant has been reported due to
polyether catalyst

57. MANIPULATION
Equal lengths of two pastes are dispensed on a paper pad
for normal mixes. Initial mixing is accomplished with circular motion
and final mixing to produce a mix free from streaks is done with
broad stroke of spatula.
Mixing is readily accomplished in 45 seconds.
When catalyst is supplied in liquid form a specific number of drops
per unit length is indicated in the instructions and mixing is
accomplished in the manner similar to the two paste system

58. The putty system use scoops supplied by the manufactures for
dispensing and may be mixed with heavy spatula or kneaded with hand until
free from streaks.

59. FOR MAKING DIGITAL ORTHODONTIC STUDY MODE
The impression can be taken in a high quality ALGINATE or
POLYVINYL SILICONE or POLYETHER material
High quality alginate such as ORTHOPRINT taken in a rigid plas
impression tray
The alginate impressions are sanitized, wrapped in a damp pap
towel and Packaged in seal able plastic bags
This ensures that impression will remain stable for 5 days
If the impression will not be delivered by the 5 days then we cons
Using a polyether such as IMPREGUM

60. Orthodontic Products update :Impression materials by B.Doubleday
British journal of orthodontics Vol 25 No2 may 1998
Impression of dentate arches
Alginate
No benefit using putty or heavy body silicon
Xantalgin(bayer)
Ideal(GAC)
Blend a print
Impression for neonates and cleft patients
Catridge delivery systems of silicon materials
perfexil
Elite H-D
Bite registration
Dedicated bite registration materials

61. ORASCANER
It is a revolutionary new process. The orthodontist uses 3-D
images taken by the OraScanner™ to build a computer model of the
teeth. The OraScanner functions much like a video camera, taking
pictures of the teeth and sending them to the computer to build a
complete 3-D model

62. CONCLUSION
One must not depend on a material to provide good
impressions.
Any material is as good as the dentist using it and
any material must be used for sometime before the
operator is familiar with its characteristics
Selecting the impression material depends on the
convenience of the dentist
ALL NEED IS AN ACCURATE IMPRESSION.

63. REFERENCES
I Anusavice
Philips science of dental materials XI Edition
2 Restorative dental materials X EDITION
By Robert G. Craig
3 Contemporary Orthodontics III Edition
By William R. Proffit
4 Removable appliance Fabrication
By Emil Witt, Dr Med. Dent
5 Hand book of Orthodontics IV Edition
By Robert E. Moyers

64. 6 Cleft lip and palate Persectives in Management
Vol II By SAMUEL BERKOVITZ
7 Orthodontics for dental students
By T.C. White and J.H. Gardiner
8 Journal of Orthodontics Vol 31 Nov 4 Dec 2004 ISSN 1465-3125
(AJODO)