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PRESENTED BY Dr. KUMAR .A I st Yr PG orthodontics, Guided by Dr.Rajasigamani MDS., vice principal, RMDCH
& H.O.D Department of orthodontics
Impression Materials and Orthodontic Cements
slide 2
Impression Materials used in orthodontics.
Contents
Definitions
Objectives
Ideal requirements
Classification of impression materials
Compositions and Reactions of Elastomeric materials.
Properties of Elastomeric materials.
Disinfection Of impressions.
Failures In impressions Making.
Conclusion
References
Impression
Definition :-
1) A negative likeness or copy in reverse of the surface or object.
2) An imprint of the teeth and adjacent structures for use in dentistry
Impression
Definition :
Impressions are negative reproduction of oral structures.
Impression material
Impression material:- Any substance or combination of
substances used for making an impression or negative reproduction.
Impression technique:- A method and manner used in
making a negative likeness.
Objectives
Provide general review of types of dental impression materials.
Provide general information on the physical and handling properties and indications for use of various types of impression materials.
Objectives of impression making
To provide
a. support , b. retention, c. stability, d. foundation of improved appearance of lips, e. maintain the health of tissues.
The impression should record all the potential denture-bearing surfaces available
The Ideal Impression Material
Easy to mix and handle.
Suitable working time.
Suitable setting time.
Compatible with die and stone
Not toxic or allergenic to the patient.
Dimensionally stable on setting.
Accurate to record the fine details of the prepared tooth
Has acceptable odor and taste.
Adequate strength.
Adequate shelf life.
The Ideal Impression Material cont.
Economical
Ready to disinfected without loss of accuracy.
Fluid or plastic when inserted into the mouth.
It must be an exact record of all the aspects of the prepared tooth and sufficient unprepared tooth structure immediately adjacent to margins, to allow the dentist and the technician to be certain of the location and configuration of the finish line.
Other teeth and tissue surrounding the abutment tooth must be accurately reproduced to permit proper articulation of the cast and contouring of the restoration.
It must be free from air bubbles especially in the finish line area.
• High accuracy Biocompatibility(very small contraction <0.5%)
• High dimensional stability Compatibility to stone
• High elastic recovery High tear strength• Ease of use Long shelf life• Hydrophilic Pleasant color &taste
and Hydrophobic• Proper setting time Cost
Classification of impression materialsImpression materials
Non elastic elastic
Hydrocolloids Synthetic elastomers
Reversible Irreversible Polysulphide
Polyether
Silicones
Addition silicone Condensation silicone
Zinc oxide eugenolZinc oxide eugenol
Impression CompoundImpression Compound
PlasterPlaster
Impression waxImpression wax
NonelasticNonelastic
Properties: Reaction: Set:Rigid:1. Impression Plaster Rigid Irrev (Chem)2. Impression Compound Rigid Rev (Phys)3. Zinc Oxide/ Eugenol Rigid Irrev (Chem)
CLASSIFICATION SYSTEMBased on Properties of Set Materials
Water-Based Gel:4. Alginate (Irreversible Hydrocolloid) Flexible Irrev (Chem)5. Agar-Agar (Reversible Hydrocolloid) FlexibleRev (Phys)
Elastomers:6. Polysulfide (Rubber Base, Thiokol) Flexible Irrev (Chem)7. Silicone (Conventional, Condensation) Flexible Irrev (Chem)8. Polyether Flexible Irrev (Chem)9. Polyvinyl Siloxane (Addition Silicone) Flexible Irrev (Chem)
Introduction
Elasto mers refer to a group of rubbery polymers, which are
chemically or physically cross-linked. They can be easily stretched and rapidly recover their original dimensions when applied stress is released.
Imp
ress
ion
M
ate
rials
Non-elastic
Elastic
Aqueous Hydrocolloids
Non-aqueous Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien, Dental Materials & their Selection 1997
Aqueous Hydrocolloids
Colloidal suspensions chains align to form fibrils traps water in interstices
Two forms sol
viscous liquid gel
elastic solid Placed intra-orally as sol
converts to gel thermal or chemical process
Phillip’s Science of Dental Materials 1996
Aqueous Hydrocolloids
Semi-permeable membranes poor dimensional stability
Evaporation Syneresis
fibril cross linking continues contracts with time exudes water
Imbibition water absorption
swells
Phillip’s Science of Dental Materials 1996
Hydrocolloids
Reversible and Irreversible
Introduced by Sears 1939 First elastic
Hydrocolloid impression materials
Reversible Agar Sets by cooling.
Irreversible Alginate Sets by chemical
reaction.
Elastic
Aqueous Hydrocolloids
Non-aqueous Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
O’Brien, Dental Materials & their Selection 1997
Irreversible Hydrocolloid (Alginate) Most widely used
impression material Indications
study models removable fixed partial dentures
framework Examples
Jeltrate (Dentsply/Caulk) Coe Alginate (GC America)
Phillip’s Science of Dental Materials 1996
Irreversible Hydrocolloid
Material that cannot return to a solution state after it becomes a gel.
Alginate is the irreversible hydrocolloid most widely used for preliminary impressions.
Alginate
Alginic acid;
Alginic acid, also called algin or alginate, is an anionic polysaccharide distributed widely in the cell walls of brown algae, where it, through binding water, forms a viscous gum.
In extracted form it absorbs water quickly; it is capable of absorbing 200-300 times
its own weight in water. Its colour ranges from white to yellowish-
brown. It is sold in filamentous, granular or
powdered forms.
Makeup of Alginate
Potassium alginate (Alginic Acid) (12-15%)Comes from seaweed; is also used in foods
such as ice cream as a thickening agent. Calcium sulfate (8-12%)
Reacts with the potassium alginate to form the gel.
Trisodium phosphateAdded to slow down the reaction time for
mixing.
Composition
Sodium alginate salt of alginic
acid mucous
extraction of seaweed (algae)
Calcium sulfate reactor
Sodium phosphate retarder
Filler Potassium
fluoride improves
gypsum surface2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4
Na alginate + CaSO4 Ca alginate + Na2SO4
(powder) (gel)
H2O
O’Brien Dental Materials & their Selection 1997
Makeup of Alginate- cont’d
Diatomaceous earth (70%)A filler that adds bulk to the material. Controls the stiffness of the set gel
Zinc oxideAdds bulk to the material.
Potassium titanium fluoride (~10%)Added so as not to interfere with the setting and
surface strength. Sodium Phosphate (retarder) (2%)
Coloring and flavouring agents (traces)
Physical Phases of Alginate
The first phase is a sol (as in solution). In the sol phase, the material is in a liquid or semiliquid form. (sol: resembles a solution, but is made up of colloidal particles dispersed in a liquid)
The second phase is a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.
“gel” entangled framework of solid colloidal particles in which liquid is trapped in the interstices and held by capillary forces (Jello)
Fig. 46-7 Examples of packaging for alginate.
Packaging and Storing of AlginateContainers about the size of a coffee
can are the most commonly used form of packaging.
Shelf life of alginate is approximately 1 year.
Manipulation
Weigh powder Powder added to water
rubber bowl vacuum mixer
Mixed for 45 sec to 1 min Place tray Remove 2 to 3 minutes
after gelation (loss of tackiness)
Caswell JADA 1986
Fig. 46-8 Scoop and water measure for alginate.
The mix of an alginate impression material is made by a vigorous stropping of the material against the side of the mixing bowl
Water-to-Powder Ratio
An adult mandibular impression generally requires two scoops of powder and two measures of water.
An adult maxillary impression generally requires three scoops of powder and three measures of water.
Manipulation
Weigh powder Powder added to water
rubber bowl vacuum mixer
Mixed for 45 sec to 1 min Place tray Remove 2 to 3 minutes
after gelation (loss of tackiness)
Caswell JADA 1986
Altering the Setting Times of AlginateCooler water can increase the setting
time if additional time is needed for the procedure.
Warmer water can reduce or shorten the setting time of the procedure.
Taking an Alginate Impression
Explain the procedure to the patient:The material will feel cold, there is no unpleasant
taste, and the material will set quickly.Breathe deeply through your nose to help you
relax and be more comfortable.Use hand signals to communicate any
discomfort.
Rinse and dry the patient's teeth, If teeth are too dry,
alginate will stick
An Acceptable Alginate Impression The impression tray is centered over the central and
lateral incisors. There is a complete "peripheral roll," which includes all
of the vestibular areas. The tray is not "overseated," which would result in
exposure of areas of the impression tray.The impression is free from tears or voids.There is sharp anatomic detail of all teeth and soft
tissues.The retromolar area, lingual frenum, tongue space,
and mylohyoid ridge are reproduced in the mandibular impression.
The hard palate and tuberosities are recorded in the maxillary impression.
Advantages
Inexpensive Easy to use Hydrophilic
displace moisture, blood, fluids Stock trays
Phillip’s Science of Dental Materials 1996
Disadvantages
Tears easily Dimensionally unstable
immediate pour single cast
Lower detail reproduction unacceptable for fixed pros
High permanent deformation Difficult to disinfect
Phillip’s Science of Dental Materials 1996
Uses of alginate impression and its applications
Irreversible hydrocolloid (alginate) : Alginate is the most widely used impression
material in dentistry. They are used to take impressions for:1. Diagnostic casts.2. Partial dentures with clasps.3. Preliminary impressions for CD.4. Occlusal analysis
5. Orthodontic treatment planning & ort. retainers 6. Crown, bridge and implant planning 7. Mouthguards 8. Occlusal splints 9. Inlays & onlaysslide 42
Elastic
Aqueous Hydrocolloids
Non-aqueous Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Condensation Silicone
Indications complete dentures crown and bridge
Examples Speedex (Coltene/Whaledent) Primasil (TISS Dental)
Composition
Base poly(dimethylsiloxane) tetraethylorthosilicate filler
Catalyst metal organic ester
By-product ethyl alcohol
Phillip’s 1996
Manipulation
Mix thoroughly paste - paste paste - liquid
Putty-wash technique reduces effect of polymerization shrinkage stock tray
putty placed thin plastic sheet spacer preliminary impression
intraoral custom tray inject wash material
Advantages
Better elastic properties Clean, pleasant Stock tray
putty-wash Good working and setting time
Disadvantages
Poor dimensional stability high shrinkage
polymerization evaporation of ethanol
pour immediately within 30 minutes
Hydrophobic poor wettability
Elastic
Aqueous Hydrocolloids
Non-aqueous Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Addition Silicones
AKA: Vinyl polysiloxane Indications
crown and bridge denture bite registration
Examples Extrude (Kerr) Express (3M/ESPE) Aquasil (Dentsply Caulk) Genie (Sultan Chemists) Virtual (Ivoclar Vivadent)
Composition
Improvement over condensation silicones no by-product
First paste vinyl poly(dimethylsiloxane)
prepolymer Second paste
siloxane prepolymer Catalyst
chloroplatinic acidPhillip’s 1996
Phillip’s Science of Dental Materials 1996
Manipulation
Adhesive to tray Double mix
custom tray heavy-body
light-body to prep Putty-wash
stock tray
Craig Adv Dent Res 1988
Advantages
Highly accurate High dimensional stability
pour up to one week Stock or custom trays Multiple casts Easy to mix Pleasant odor
Phillip’s Science of Dental Materials 1996
Disadvantages
Expensive Sulfur inhibits set
latex gloves ferric and Al sulfate
retraction solution Pumice teeth before
impressing Short working time Lower tear strength Possible hydrogen gas release
bubbles on die palladium added to absorb
Manikos Aust Dent J 1998
Addition Silicones
Surfactants added reduce contact angle improved
castability gypsum
wettability?? still need dry field clinically
Elastic
Aqueous Hydrocolloids
Non-aqueous Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Composition
Base difunctional epimine-terminated prepolymer fillers plasticizers
Catalyst aromatic sulfonic acid ester fillers
Cationic polymerization ring opening and chain extension
Manipulation
Adhesive to tray stock or custom tray
very stiff Paste-paste mix Auto-mixing
hand-held low viscosity
mechanical dispenser high viscosity
Advantages
Highly accurate Good dimensional stability Stock or dual-arch trays Good surface detail Pour within one week
kept dry Multiple casts Good wettability
Disadvantages
Expensive Short working time Rigid
difficult to remove from undercuts Bitter taste Low tear strength Absorbs water
changes dimension
Phillip’s Science of Dental Materials 1996
Impression Material Usage*Civilian General Dentists
Crown & Bridge vinylpolysiloxane 81% alginate 38% polyether 28%
Inlays and Onlays vinylpolysiloxane 71% polyether 22% alginate 20%
*Multiple responses DPR 2001
Handling Properties
Agar Alginate Polysulfide Condensation Silicone
Addition Silicone
Polyether
PreparationBoil,
temper, store
Powder, water
2 pastes 2 pastes or paste/liquid
2 pastes 2 pastes
Ease of Use Technique sensitive
Good Fair Fair Excellent Good
Patient Reaction
Thermal Shock
Pleasant, clean
Unpleasant, stains
Pleasant, clean Pleasant
Unpleasant clean
Ease of removal
Very easy
Very easy
Easy Moderate Moderate Moderate to difficult
Disinfection Poor Poor Fair Fair Excellent Fair
Handling Properties
Agar Alginate Polysulfide Condensation Silicone
Addition Silicone
Polyether
Working Time (min) 7 – 15 2.5 5 – 7 3 2 –4.5 2.5
Setting Time(min)
5 3.5 8 – 12 6 – 8 3 – 7 4.5
Stability 1 hour 100% RH
Immediate pour 1 hour
Immediate pour 1 week
1 week kept dry
Wettability and
castabilityExcellent Excellent Fair Fair Fair to
goodGood
Cost Low Very low Low Moderate High to very high
Very high
Comparison of Properties
Working time longest to shortest
agar > polysulfide > silicones > alginate = polyether
Setting time shortest to longest
alginate < polyether < agar < silicones < polysulfide
Comparison of Properties
Stiffness most to least
polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids
Tear strength greatest to least
polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids
Summary
Study models Alginate most widely used
inexpensive displaces moisture lower detail reproduction dimensionally unstable
Impression
Impression Tray
IMPRESSION MATERIALSKey Properties
Accuracy
a. Accuracy = ability to replicate the intraoral surface details.
DimensionalStability
b. Dimensional Stability = ability to retain its absolute dimensional size over time.
TearResistance
c. Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.
Trouble Shooting
Inadequate working or setting time:
temperature of the water, incomplete spatulation W/P too low improper storage of alginate powder
Distortion: Tray movement during gelation or removed from mouth prematurely weight of tray compressing or distorting alginate
impression not poured up immediately
Tearing: removing impression from mouth before adequately set thin mixes (high W/P ratio) presence of undercuts (blocking out these areas before an impression may help) inadequate amount of impression material in tray (avoided by minimum 3 mm of
impression material between tray and oral tissues)
• Loss of detail: removed from mouth prematurely
Consistency: preset mix is too thin or thick The W/P ratio is incorrect (avoid by fluffing powder before measuring; do not
overfill powder dispenser) inadequate mixing (avoided by vigorous spatulation and mixing for recommended
time) using hot water: grainy and prematurely thick mix
• Dimensional change: delay in pouring alginate impression stored in air: results in distorted, undersized cast due to
alginate impressions losing water when stored in air
Porosity: whipping air into the mix during spatulation (proper mixing: after initial wetting of powder by the water, mix alginate so as to squeeze the material
between the spatula blade and the side of the rubber bowl)
• Poor stone surface (of cast) set gypsum remaining in contact with the alginate for too long a period of time
Disinfection of Impression Materials
Irreversible Hydrocolloids (Alginate) Diagnostic Casts:
Soak 10 min in Gluteraldehyde
Final Impressions: Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under
damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under
damp gauze 10 min
Reversible Hydrocolloid Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under
damp gauze 10 min Spray with Sodium Hypochlorite rinse, spray again & let stand under
damp gauze 10 min
Addition –reaction Silicones In Gluteraldehyde 1 hr., Rinse sterile water Soak in fresh solution Gluteraldehyde 10 min
Disinfection for impression materials
Formulated with isopropyl alcohol, Septodont's Dimenol isdesigned specifically to disinfect impression materials – alginates and silicones – to protect patients, practice professionals,laboratory professionals and the prosthesis itself.
Spray sufficient bactericidal, fungicidal and virucidalDimenol evenly onto the impression materials to moisten, leave for 15 minutes and rinse carefully to effectively decontaminatethe blood, saliva and proteins that can harbor pathogens. Supplied in 200ml spray bottles,
Dimenol disinfects without altering the surface accuracy and without producing any dimensional variation
References
Phillips’ Science of Dental Materials, edited by K Anusavice, 11th ed., 2008, Saunders Publishing.
RG Craig, Review of Impression Materials, Advance in Dental Research, Aug 1988, 2,51-64.
ORTHODONTICCEMENTS
CONTENTS
INTRODUCTION CLASSIFICATION OF CEMENTS ZINC PHOSPHATE CEMENT ZINC POLYCARBOXYLATE CEMENT GLASS IONOMER CEMENT RESIN IONOMER HYBRID CEMENTS IN BANDING CEMENTS IN BONDING NEWER PRODUCTS
INTRODUCTION Cements are routinely used for orthodontic purposes.
Proper cementation of the bands and bonding of the brackets plays an important role for the betterment of treatment and for reducing the duration.
Problems like failure of the bands and brackets and demineralisation were often faced by the practitioner.
These problems can be due to poor seal between
cement ,bracket or band material and enamel surface; inadequate structural and bonding strength;solubility of cements in oral fluids and so on.
What are cements? In the Oxford dictionary
A material which ”glues“ various things together e.g.
embedded particles in minerals are glued in a compact
body sand, particles of rocks are ”glued“ using Portland cement in a concrete
2007/2008
Powder + Liquid
Pastelike or flowable material
Hardens to a rigid solid
In dentistry
Materials used for: Luting, fixation, cementation - i.e. luting
inlays crowns, bridges, veneers on the prepared tooth To protect pulp from heat (”thermal
insulation“) and from chemical irritation (liners and bases) - to stimulate secondary dentin formation Temporary filling material
2007/2008
Applications of Dental Cements:
Cementing agent for permanent restorations.
Temporary restorations. Liners and bases. Cementing agents for orthodontic
appliances. Periodontal dressing. Root canal fillers and sealers. Pulp capping agents. Anterior restorations.
2007/2008
Requirement of Dental Cements Adequate mechanical properties. Non-irritating & non-toxic. Insoluble. Insulating the pulp from thermal,
electrical and chemical irritants. Adhesive properties. Esthetic properties. Easy to manipulate.
2007/2008
CLASSIFICATION OF DENTAL CEMENTS
The cements may be classified by composition into four categories
a. Phosphates; which includes the zinc phosphate and silicophosphate cement.
b. Phenolates; which includes the zinc oxide eugenol and calcium hydroxide cements
c. Polycarboxylate; which includes the zinc polycarboxylate and glass ionomer cements.
d.Resin cements.
Types of Dental Cements:
1- Cements based on Zinc Oxide. 2- Cements based on Alumino Silicate
Glasses ( Ion leachable glasses ). 3- Other cements:
Resin cements. Calcium – Hydroxide cements. Cavity liners and Varnishes.
2007/2008
1- Cements based on Zinc Oxide
2007/2008
Zinc Oxide
Eugenol Phosphoric acid Polyacrylic acid
Zinc oxide eugenol cement
Zinc phosphate cement
Zinc polycarboxylatecement
2- Cements based on Alumino Silicate Glasses.
2007/2008
Phosphoric acid Polyacrylic acid
Alumino-Slicate Glass
Slicate cements Glass-ionomer cements
GLASS IONOMER CEMENTS HISTORY
Development of glass ionomer cements was first announced by Wilson and kent in 1972.
It is referred to as polyalkenoate cement.
The first commercial glass ionomer was made by the De Trey company and distributed by the amalgamated Dental company in England and by Caulk in the United States.
Known as ASPA(Alumino-silicate poly acrylate) it consisted of an ion leachable alumino silicate glass and an aqueous solution of a copolymer of acrylic acid.
Glass ionomers are hybrids of silicate cements and polycarboxylate cements.
The intention was to produce a cement with characteristics of both the silicate cements (flouride release and translucency) with those of the polycarboxylate cements(ability to chemically bond to tooth structure and kindness to pulp).
Glass ionomer cement was introduced to orthodontics in 1986.
Glass Ionomer Cement
2007/2008
Composition
Powder Liquid
-Calcium fluoroalumino silicate glass .
-Barium glass or zinc oxide.
-Polyacrylic acid copolymer with itaconic, maleic, or tricarboxylic acid.
- Tartaric acid.
Setting Reaction of Glass Ionomer Cement:
2007/2008
Dissolution .
Gelation
Hydration
SETTING REACTION AND STRUCTURE The setting reaction of conventional glass ionomer
cement can be represented as an acid base reaction leading to the formation of polycarboxylate salts that comprise the cement matrix.
Dissolution : The carboxyl(COOH)groups are dissociated to carboxylate groups(COO-)and hydrogen(H+)ions.
The positively charged hydrogen ions attack the surface layer of glass particles,releasing calcium and aluminium ions in the form of flouride complexes.
The calcium ion concentration rises more rapidly.As the ionisation reaction continues, the polyacrylic chains assume a more linear format, allowing the commencement of gelation.
Gelation : The more readily available calcium ions are complexed with the carboxyl groups and a weak ionic cross linking is formed,which corresponds to the initial setting of the cement that is observed.
Final Hardening : As the setting reaction continues,Al3+ ions are increasingly deposited in the matrix,leading to calcium-aluminium carboxylate gel that corresponds to the final stage of cement hardening.
2007/2008
Unreacted glass particles.
Silica hydrogel sheath .
Amorphous matrix of cross- Linked polysalt hydrogel of Ca++&Al+++.
The structure of the set GIC
TYPES OF GIC
Type-I Luting applicationsType-II Restorative materialType-III Liner or Base Type-IV Pit and Fissure SealantType-V Orthodontic BracketType-VI Core build up
Manipulation:
The proper powder/liquid ratio is dispensed onto paper pad or glass slab,mixed for30-60 sec.
Encapsulated products are mixed for 10 sec.in mechanical mixer.
An extension of the working time to 9 minutes can be achieved by mixing on a cold slab.
The cement should not be used once a “skin” forms on the surface or when the viscosity increases noticeably.
2007/2008
Manipulation:
Once the cement has achieved its initial set (about 7 minutes), the cement should be coated with the coating agent supplied with the cement.
2007/2008
Working time-range is 3-5 min Setting time- 5-9 min Manipulation- The powder is introduced into the
liquid in large increments and spatulated rapidly for 30 to 45 seconds
Recommended P:L ratio is 1.25 to 1.5 g of powder per 1ml of liquid
Glass Ionomer Cement
Adhesion to tooth structure.
Biocompatibility. High compressive
strength. Low solubility.
Technique sensetive
Moisture sensitivity.
Short working time and long setting time.
Low abrasion resistance.
Brittlness. 2007/2008
Advantages Disadvantages
Modification of GIC :
A. Metal Reinforced GIC .1. Silver alloy admix.2. Cermet cement.
B. Hybrid Ionomer (Resin-Modified GIC)
Dual cure . Tricure .
C. Compomer (Polyacid modified resin composite materials ).
2007/2008
RESIN MODIFIED GLASS IONOMERS
COMPOSITION
The powder of resin modified glass ionomer cements,consists of either the glass composition used for conventional glass ionomer cements or strontiumaluminoflourosilicate glass; a barium aluminosilicate glass is also incorporated in some products.
Significant alteration have been made in the liquid component of RMGIC's.
Applications of Resin-Modified GIC :
1) Restoration.2) Liners and bases.3) Fissure sealants.4) Core buld up.5) Cementation of orthodontic
brackets.6) Retrograde root filling material.
2007/2008
CEMENTS IN BONDING When used for bonding GIC requires no more etching
other than cleaning with pumice and moderate drying with a cotton roll.
The absolute dryness required for composites have been found to be unnecessary and even harmful for GIC bonding.
It acts as a reservoir of fluoride ions preventing decalcification that occurs around brackets.Also it offers a longer working time.
Light forces must be used first,because gelation continues and full bond strength is not reached for 24 hours.
However, the bond strength of GIC to enamel(2 to 6 MPa) is approximately one-half that of Composite resin(5 to 25 MPa) bonding after etching.No enamel is damaged during debonding.
Compomers in Bonding
Robert A.Miller describes a compomer (Dyract Ortho) that consists of a radiopaque flourosilicate glass in a matrix of acid polymerisable monomers and other light cured polymers.
It is dispersed in single unit 'no mix'capsules.
The 'no mix' feature is made possible by an acid polymerisable monomer that cross links after exposure to light and cross links further after uptake from saliva.
This saves time when bonding in difficult,wet fields,or with impacted canines or second molars.
Although Dyract is self adhesive,it is most retentive to enamel when used after Prime&Bond, a light cured, single component direct bonding agent.
Prime&Bond provides an active adhesion monomer that forms ionic interactions with the inorganic portions of the enamel.
This yields a bond strength that is adequate for brackets and other attachments under wet conditions in most impaction cases.
The impacted tooth is pumiced shortly after surgical exposure.
Prime&Bond is applied followed by Dyract to bracket base and placed firmly to remove excess adhesive since this material is considerably viscous.
Composite resin cement Composite :
Resin matrix + inorganic filler
Silane coated
Composition
Filler Silica
Matrix Bis-GMA (polymer)
The fillers binds with matrix by
silane coupling agent
Setting reaction
Polymerization Chemical activation Light activation Dual activation [chemical and light]
Preparations
Powder / liquid Chemical, light, or dual cure
2 paste system [base / catalyst]Chemical, light, or dual cure
Single paste
Light cure
Bonding system
Bond with the tooth surface by enamel an dentine bonding system.
Bond with metal by using metal primer.
Bond with ceramic restoration by treating the surface of porcelain with silane coupling agent
Properties
Very good bond strength High compressive strength Water sensitive Might irritate pulpal tissues
Applications
Tooth color filling materials Luting cements
References
Textbooks Kenneth J. Anusavice
Phillips’ science of dental materials 11th edition W.B. Saunders company 2003
Thanks