Impression materials in orthodontics
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Transcript of Impression materials in orthodontics
IMPRESSION MATERIALS IN ORTHODONTICS
UMAR MOHAMED
CONTENTS• Introduction• History• Ideal requirements
• Classification of impression materials
• Hydrocolloids
• Elastomers
• Causes for failure of impression
• Ora scanner
• Conclusion
• References
INTRODUCTION
Impression
• A mould of the teeth used to make models of the teeth.
HISTORY
• 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
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.
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
•Cost effective
Phillips .science of dental materials 11th edition-Anusavice
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.
CLASSIFICATION OF THE IMPRESSION MATERIALS BASED ON:
SETTING REACTION
THERMOPLASTIC THERMOSET
ELASTICITY ELASTIC INELASTIC OR RIGID
NATURE OF THE SETTING REACTION
REVERSIBLE IRREVERSIBLE
PRESSURE EXERTED ON THE TISSUE
MUCOCOMPRESSIVE MUCOSTATIC
DENTITION STATUS
EDENTULOUS DENTULOUS
In orthodontics…
The most commonly employed materials include
I. Hydrocolloid – Agar Agar (reversible)
- Alginate (irreversible)
II. Elastomeric impression materials.
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
Colloids , have two distinct phases
A dispersed phase + dispersion phase
LIQUID COLLOIDS ARE CALLED SOL
SOLID COLLOIDS ARE CALLED GEL
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 GELGELATION TEMPERATURE (370 – 500C)
Fibrils are held together by secondary molecular forces
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.
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.
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.
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
Structural formula of alginic acid with molecular wt of 32000-200000
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
COMPOSITIONNO 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
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
Properties
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
Flexibility A D A specification permits a range of 5% to 20% at a stressof 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.
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
Crosslinking of Na alginate molecules to form Ca alginate
STEPS IN MAKING IMPRESSION
• Selection of the tray
• Preparation of the patient
• Seating of the tray
• Disinfection of the impression
• 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
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.
IMPRESSION MAKING
Manipulation
Maxillary tuberosity
Palate
Rolled round & thick borders
Maxillary impression
IMPRESSION MAKING
Mandibular retromolar area
Detailed along gingival anatomyPosterior lingual areas
Rolled round & thick borders
Mandibular impression
IMPRESSION MAKING
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.
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
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.
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.
CAUSES OF FAILURE
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
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
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)
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%
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
AGAR
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.
CONDITIONING UNIT
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.
WATER COOLED TRAYS
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.
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 catalyst they
undergo
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
THEY ARE SUPPLIED IN FOUR VISCOSITY
• LIGHT BODY
• MEDIUM /REGULAR)
• HEAVY BODY
• PUTTY (VERY HIGH)
HIGH, MEDIUM AND LOW CONSISTENCIES ARE SUPPLIED IN
TWO FORMS
• BASE
• ACCELARATOR / CATALYST
CATALYST SOME TIMES AS LIQUID
PASTES ARE SUPPLIED IN COLLAPSABLE TUBE.
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 silicatesor it may be supplied as paste by addition of thickening agent
The reaction proceeds producing 3 dimensional network rubber withethyl alcohol as a byproduct Stock trays are generally used
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
Polyether
Supplied as base and catalyst systemBase- 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
Better mechanical propertiesLess dimensional changesGood wetting properties
limitationsShort working timeHigh stiffness
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
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
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.
FOR MAKING DIGITAL ORTHODONTIC STUDY MODELS
The impression can be taken in a high quality ALGINATE orPOLYVINYL SILICONE or POLYETHER material
High quality alginate such as ORTHOPRINT taken in a rigid plastic impression tray The alginate impressions are sanitized, wrapped in a damp paper towel and Packaged in seal able plastic bags This ensures that impression will remain stable for 5 daysIf the impression will not be delivered by the 5 days then we considerUsing a polyether such as IMPREGUM
Orthodontic Products update :Impression materials by B.Doubleday British journal of orthodontics Vol 25 No2 may 1998
Impression of dentate archesAlginate No benefit using putty or heavy body silicon Xantalgin(bayer) Ideal(GAC) Blend a print
Impression for neonates and cleft patientsCatridge delivery systems of silicon materials perfexil Elite H-D
Bite registrationDedicated bite registration materials
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
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.
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
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)