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Slide 1 : DENTAL MATERIALS

Slide 2 : “electron cloud” : The ease of giving up electrons make them malleable, lustrous, and conductors.

SOLIDIFICATION OF THE METAL: : SOLIDIFICATION OF THE METAL: When a liquid metal is cooled ot reaches a temperature below its fusion temperature that is called SUPERCOOLING. (during this crystallization begins) temperature rises due to the latent heat of fusion and reaches the fusion temperature or solidification temaprature and is maintained here (PLATEU) till all the metal is solidified

Nucleus formation: : Nucleus formation: EMBRYO: are numerous unstable structures in liquid state that tend to form the nuclei. When super cooled region is reached the embryo tend to convert into nuclei for solidification.

Slide 5 : Thus if homogenous solidification is needed melt must be cooled slowly this is called HOMOGENOUS NUCLEATION.

GRAINS: : GRAINS: Metal is made up of thousand crystals and each crystal is called grain. Smaller the grain size better the properteis Grain size can be decreased by Increasing nuclei of cystallisation rapid cooling of the metal to solid. Grain boundaries: are the regions of high energies and are the site of impurities. This is the region which is most commonly affected by chemicals and corrosion.

Slide 7 : Grain shape can be influenced by shape of the mould in which metal solidifies. Square mould: columnar grains Cylindrical mould: radial grains

CONSTITUTION OF THE ALLOY : CONSTITUTION OF THE ALLOY Alloys: Mixture of metal with one or more metal or non-metal . Solid solution: When two metals are mutually soluble in solid state the alloys are called as solid solutions

Solid solutions: : Solid solutions: When two metals are soluble, the solvent is the metal whose space lattice persists and the solute is the another metal . Based on the lattice configuration: Substitutional: Interstitial: Note : in interstitial type : the solute atom should be smaller in diameter than the solvent.

Conditions for solid solubility: : Conditions for solid solubility: Atom size :should not differ more than 15% in their size. Valence: metal of same valence are more likely to form solid solutions Chemical affinity: if metals have high degree of affinity they tend to form inter metallic compound rather than the solid solutions. Lattice type: only metals with same type of lattice tend to form the solid solutions.

Slide 11 :

Alloy constitution phase diagram: : Alloy constitution phase diagram: When the different compositions of the alloys are cooled and cooling curve plotted: Liquidus temperature: the temperature at which first solid forms. Solidus temperature: the temperature at which the last solid forms (or last liquid solidifies)

Slide 13 :

CORING: : CORING: Not both/ all the component metals of the alloy solidify together during cooling, this results in Coring. the core : composition with higher solidus temperature the matrix :composition of the lower solidus temperature.

HOMOGENISATION: : HOMOGENISATION: Elimination of coring The alloy is held near its solidus temperature to facilitate homogenization by solid state diffusion. Homogenization increases the ductility and corrosion resistance of the alloy

EUTECTIC ALLOY : EUTECTIC ALLOY The components in eutectic alloy exhibit complete liquid solubility but limited solid solubility. The composition where liquidus and solidus meet is the eutactic composition or simply eutectic.

Slide 17 :

Slide 18 : A eutectic alloy system occurs when two metals are soluble as liquids but nearly insoluble as solids. These systems have a single composition (the eutectic composition) with a melting point that is lower than either component metal

Slide 19 : Eutectic do not have solidification range they solidify at a constant temperature. The temperature at which eutectic occurs is lower than the fusion temperature of either metals Are inferior to the metals. They are usually brittle

PERITACTIC ALLOYS : PERITACTIC ALLOYS Limited solubility can result in the formation of peritectic. Eg (silver-tin system) Peritactic reaction (like eutectic reaction) is an invariant reaction ie it occurs at a particular composition and temperature.

Solid state reactions: : Solid state reactions: Strain hardening : Annealing Reducing the grain size Alloying Atomic diffusion by heat treatment in solid state.

Slide 22 : SOLUTION HEAT TREATMENT: gold alloy casting is heated slightly below solidus temp and held for a time it transforms into random solid –solution and if it is cooled rapidly to room temperature the structure is retained. (the alloy will be soft and ductile).

Slide 23 : AGE HARDENING HEAT TREATMENT: If the same casting is heated to a temperature slightly below the temperature required to form the ordered structure and maintained for sometime stronger, harder AuCu3 phase is formed

CORROSION : CORROSION TARNISH: surface discoloration CORROSION: actual deterioration

Classification of corrosion : Classification of corrosion Chemical Corrosion (Dry corrosion) Electro Chemical Corrosion (wet corrosion) galvanic corrosion : dissimilar metals in contact in presence of saliva. The metal with low EMF (electric potential or electromagnetic force) acts as anode (gets corroded) eg Amalgam and metal with high EMF acts as cathode.

AMALGAM ALLOYS : AMALGAM ALLOYS

stress corrosion : stress corrosion Metal at the site of maximum stress becomes more reactive than the unstressed metal. The stressed metal undergoes corrosion.

concentration cell corrosion/ crevice corrosion: : concentration cell corrosion/ crevice corrosion: Corrosion of pits which are covered by food debris and depth of the pit suffers from the lack of oxygen thus acts as anode. The pit periphery acts as cathode.

Slide 29 : Protection against corrosion Coating of Nobel metal " Passivation" : Chromium, aluminum and titanium form strong adherent oxide films on their surface to protect from corrosion

AMALGAM ALLOYS : AMALGAM ALLOYS Dental amalgam alloy : alloy of silver, copper, tin that is processes to form a powder (this term is applied before mixing with mercury) Dental amalgam: alloy of mercury, silver, copper and tin (after mixing with mercury)

Slide 31 : Alloy containing zinc in excess of 0.01% are designated zinc containing. High copper alloy:> 6% wt by wt copper Admixed - 9 - 20% Single composition - 13 - 30%

Slide 32 : Based on alloy particle shape amalgam is classified as: Lathe cut - Irregular shape Spherical Admixed - Contain both lathe cut and spherical alloys.

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Slide 36 :

Slide 37 : © AimMDS Here the Undesirable ?2 phase is eliminated

DIMENTIONAL STABILITY : © AimMDS DIMENTIONAL STABILITY During setting amalgam undergoes initial contraction :due to dissolution of alloys particles in mercury and growth of Y1phase. Expansion:impingement of Y1 crystals this happens till the sufficient mercury is present. Thus according to the above model is sufficient mercury is present expansion occurs otherwise contraction is seen According to ADA specification 1, amalgam should not expand or contract more than 20µm/ cm measured at 37°C,between 5 minutes to 24 hrs after beginning of trituration.

Effect of moisture contamination : © AimMDS Effect of moisture contamination Zn containing high or low copper alloy : Delayed expansion It starts after 3-5 days and may continue for months, reaching value greater than 400 micro meter (4%) This is due to production of hydrogen by reaction of Zn and water.

Strength: : © AimMDS Strength: Mercury content : increasing mercury content increases the volume of the matrix phase in cost of alloy particle thus decreasing the strength.

Slide 41 : © AimMDS Creep is defined as the time dependant plastic deformation. The higher the creep, the greater is the marginal deterioration. • Low copper 0.8 - 8% • High copper 0.4 - 0.1% According to ADA specification no 1 creep should be lower than 3%

Technical consideration: : © AimMDS Technical consideration: Trituration: Mercury alloy ratio according to EAMES or Minimum mercury technique is 1:1 or 50% mercury. The mercury content of the finished restoration should be approximately 50Wt.% while for spherical alloys it should be approximately 42 Wt. %. Objective of trituration is to wet the alloy particles with mercury. Increased trituration time or speed shortens the working and setting times. Mulling??

Strength: : © AimMDS Strength: high compressive strength and low tensile strength.. THUS Cavosurface angle should be 90° (butt type) to prevent fracture of the marginal material

Condensation and carving: : Condensation and carving: started at the center and condenser point is stepped by little towards the cavity wallls. Normally condensation force is 3-4lbs (2- 3 kg.) per increment. Larger condensers should be used for condensing spherical amalgams, as their resistance to condensation forces is less.

Polishing: : © AimMDS Polishing: Finishing and polishing should be done 24hrs. after insertion Mercury hazard: The maximum level of occupational exposure considered safe is 50 µgm of mercury / m3 of air.

METALLURGY : © AimMDS METALLURGY CLASSIFICATION OF DENTAL CASTING ALLOYS

Slide 47 : © AimMDS Alloy classification by ADA (1984)

Slide 48 : © AimMDS Karat: is a part of the pure gold in 24 parts of the alloy. Fineness: describes gold alloys by the number of parts per 1000 of the gold. Eg : pure gold has fineness of 1000. while 650 fine gold has 65% of the gold content.

Casting gold alloys : © AimMDS Casting gold alloys Type I and II alloys are called as Inlay alloys. Type III and IV are called as crown and bridge alloys. Type III and IV gold alloys usually can be age hardened especially those containing at least 8 wt % of copper.

HEAT TREATMENT : © AimMDS HEAT TREATMENT Softening heat treatment: 10 minutes at the temperature of 700oC (1292oF) then it is quashed in the water. The tensile strength, hardness and proportional limit are reduced by such treatment but ductility and malleability is increased.

Slide 51 : © AimMDS Hardening heat treatment (Age hardening) aging the casting for 15-30minutes at temperature between 200-450°C. Proportional limit, hardness and yield strength are increased but ductility is reduced

Casting shrinkage: : © AimMDS Casting shrinkage: Liquid metal (hot) Liquid metal (till liquidus temperature) Solid solidus tempearture Solid room temperature This contraction is of no consequence as the metal is still liquid and more metal flows into the mold after the contraction the metals starts contracting on solidification, the adhesion to the walls prevent contraction till adequate contraction has taken place This contraction dominates the casting shrinkage. The shrinkage is maximum for high melting alloys that is why base metal alloys have higher casting shrinkage (2.3%) than gold alloys (1.5%).

METAL CERAMIC RESTORATION: : © AimMDS METAL CERAMIC RESTORATION: Alloys used for metal ceramic restoration should have High fusing temperature to resist sag deformation. Coefficient of thermal expansion closer to Porcelain. Potential to bond with porcelain

Slide 54 : © AimMDS GREENING: Greenish discoloration of porcelain due to silver vapour escaping from the surface of the Palladium silver alloy.

Slide 55 : © AimMDS METALS FOR PARTIAL DENTURE: Type IV gold alloys are rarely used now a days and base metal alloys have replaced them. base metal alloys: alloys containing < 25wt% of noble metal. Eg: Co-Cr, Ni- Cr, Ni-Cr-Be, Ni- Co- Cr, Ti-Al-V.

Slide 56 : © AimMDS Tarnish corrosion:’ Base metal alloys resist corrosion: not because they are not reactive but because of the passivity.

Slide 57 : © AimMDS The metals well known for passivation: Aluminium Chromium Titanium (most resistant to corrosion) For alloys to be protected they should have at least 12% of chromium.

Slide 58 : © AimMDS Castability: Base metals were inferior in castability to gold alloys: Beryllium improves castability of fine details in BMA Modulus of elasticity: BMA have modulus of elasticity (measure of stiffness) twice that of cast gold alloy, thus can be made thinner than the latter. They are harder, stronger than gld alloy Nickel is the most common cause of allery to BMA. Titanium can be alternative to patients with known nickel allergy.

WROUGHT BASE METAL AND GOLD: : © AimMDS WROUGHT BASE METAL AND GOLD: When the casting is plastically deformed it is considered as wrought metal. "Cold working" / Strain hardening / Work hardening increases hardness, strength but decreases ductility. The effects of cold working can be reversed by simply heating the metal. It is called as "Annealing"

CARBON STEELS: : © AimMDS CARBON STEELS: Carbon Steels are iron based alloys that usually contain less than 1.2%carbon. Cutting efficiency high but more brittle They are superior at higher speed used for cutting enamel.

The different classes of steel : © AimMDS The different classes of steel

STAINLESS STEEL : © AimMDS STAINLESS STEEL When 12 -30% chromium is added to the steel it becomes stainless steel due to passivating effect. Cutting efficiency low and becomes dull rapidly Hardness is less than carbon steel but is not brittle Superior at low speed and used for cutting dentin

STAINLESS STEEL : © AimMDS STAINLESS STEEL

Corrosion resistance : © AimMDS Corrosion resistance Stainless steel may loose corrosion resistance when heated between 400-900 oC due to precipitation of chromium carbide. This can be prevented by addin titatnium that precipitated carbide in preference to chromium.

Corrosion resistance : © AimMDS Corrosion resistance

SOLDERING : © AimMDS SOLDERING Brazing: Joining metal parts together by melting a filler metal between them at a temperature below the solidus temperature of the metal being joined.Here the fusion temperature of filler material is greater than 450°C.

Soldering : © AimMDS Soldering Joining metal parts together by melting a filler metal between them at a temperature below the solidus temperature of the metal being joined. Here the fusion temperature of filler material is less than 450°C.

Welding : © AimMDS Welding Joining two or more metal pieces by applying pressure (cold welding) or heat (hot welding) or both. .Spot welding is used to join orthodontic components.

Post-soldering : © AimMDS Post-soldering joining of metals after porcelain veneering is called POSTSOLDERING. FLUX: Word flux means flow Flux is to remove any oxide coating on the substrate metal surface when the filler meal is fluid.

Types of fluxes : © AimMDS Types of fluxes Surface protection: covers the surface and prevents the oxide formation Reducing agents: reduces the oxides formed and exposes the clean metal Solvent: dissolves the oxide present. Fluxes have temperature range for the optimum activity: Eg : Borax flux designed for post-soldering is too fluid for preordering temperatures Fluoride flux may not have sufficient chemical activity at lower post soldering temperatures.

Slide 71 : © AimMDS for noble metals: fluxes are usually based on Boric or borate compounds For base metal alloys: Fluoride fluxes are used to dissolve chromium, nickel and cobalt oxides. Heat source: Or it may be fused on the surface of the filler metal strip. Also , Fluoride containing flux may attack the porcelain if they are used post soldering.

Application method: for flux : © AimMDS Application method: for flux Flux may be painted on substrate metals. But the flux amount should be minimum as excess flux may cause weakening of the joint.

Soldering (brazing ) or filler metal : © AimMDS Soldering (brazing ) or filler metal Should have appropriate flow temperature. Should have the ability to wet the substrate metal. Should have sufficient fluidity at the flow temperature.

INVESTMENT AND CASTING : © AimMDS INVESTMENT AND CASTING INVESTMENT FOR THE SMALL CASTINGS Two types of investment: gypsum bonded phosphate bonded GYPSUM BONDED: Investment for the Dental Gold Alloy

GYPSUM BONDED : © AimMDS GYPSUM BONDED Three type Type I: for casting of inlays and crown, alloy shrinkage compensated only by thermal expansion Type II: for casting of inlays and crown, alloy shrinkage compensated mainly by hygroscopic expansion.’ Type III: for the construction of the partial dentures.

Composition : © AimMDS Composition

Thermal expansion of gypsum : © AimMDS Thermal expansion of gypsum

Slide 78 : © AimMDS Finer the particles of the silica, greater the hygroscopic expansion. a-hemihydrate produces greater expansion than ß-hemihydrate. At least 15% binder is necessary to prevent drying shrinkage. 75% of quartz content entirely balances the contraction of the gypsum. More hygroscopic expansion if immersion is before the initial set.

PHOSPHATE BONDED : © AimMDS PHOSPHATE BONDED Composition

PHOSPHATE BONDED : © AimMDS PHOSPHATE BONDED phosphate bonded investment show slight expansion, which can be considerably increased by adding colloidal silica solution instead of water. The early thermal shrinkage of the phosphate bonded investment id due to the decomposition of the binder, magnesium ammonium phosphate and liberation of ammonia.

ETHYL SILICATE BODED INVESTMENT : © AimMDS ETHYL SILICATE BODED INVESTMENT Silica is the binder which may be derived from ethyl silicate or silica gel Used for high fusing base metal partial denture alloys In addition to setting shrinkage" green shrinkage" occurs due to loss of alcohol and water from the gel. The investment can be heated upto 12000C

THE CASTING PROCEDURE : © AimMDS THE CASTING PROCEDURE The compensation for casting shrinkage: By hygroscopic/thermal expansion. Ringless casting system can be used to provide maximum expansion.

The sprue former : © AimMDS The sprue former Provides channel through which molten alloy can reach the mold after' the wax has been eliminated. Its diameter should be the same as the thickest area of the wax pattern and it should be attached to the thickest portion of the wax pattern to prevent turbulence. Its length should be within 6mm of the trailing end and yet short enough so the metal does not solidify before reaching the mould. It should be sprued at 45° angles to the proximal area.

The sprue former : © AimMDS The sprue former Direct spruing: sprue procides the direct connection between the pattern and the base. Indirect sprue: a reservoir bar is placed between the pattern and the crucible former. The reservoir prevents localized shrinkage porosity

Casting ring liner: : © AimMDS Casting ring liner: To permit investment expansion: an aluminum silicate ceramic liner or a cellulose paper strip used. Thickness should be at least 1mm Expansion is more in longitudinal direction than the lateral direction, to reduce longitudinal direction liner should be placed short (3.25 mm) of the ends of the ring. CASTING PROCEDURE Wax elimination Temperature for wax eliminatio

Gypsum : © AimMDS Gypsum 468oC for hygroscopic tech 650 oC for thermal expansion technique. Phosphate 700 to 870 oC The burn out procedure should start when the mold is still wet, because the water in the pores reduces the adsorption of the wax to the wall and flushes the wax. To rapid heating of gypsum investment causes cracking of investment (radial cracks) that results in

FIN FORMATION : © AimMDS FIN FORMATION of the casting. This is especially seen with crystobalite investment If gypsum is heated above 700 oC sulfur dioxide is formed that contaminates the gold casting making them brittle. Pickling: heating the discolored casting in the acid for gypsum bonded the best acid is 50% hydrochloric acid. ( the casting is kept in the test tube and the acid is poured it can be heated but should never be boiled.)

Melting the alloy : © AimMDS Melting the alloy Alloy placed on the inner sidewall of the crucible. The dim blue reducing zone of the flame should be used for melting the alloy Cleaning the casting Gold-based and palladium based metal ceramic alloys and base metal alloys are generally not pickled

CAUSES OF THE DEFECTIVE CASTING : © AimMDS CAUSES OF THE DEFECTIVE CASTING

POROSITIES : © AimMDS POROSITIES Solidification defect Localized shrinkage porosity Due to incomplete feeding of the molten metal. Due to premature termination of the flow of the metal Generally occur near sprue casting junction. If sprue freezes before feeding is complete, the porosity develops in the last portion of casting that solidifies. Can be prevented by attaching one or more small guage sprues to the surface distant from the main sprue attachment.

POROSITIES : © AimMDS POROSITIES Suck back porosity: if a hot spot is created due to impingment of the hot metal on the mold wall this area solidifies last causing Suck back porosity usually occurs at line angles.

Pin hole and gas inclusion porosity : © AimMDS Pin hole and gas inclusion porosity Due to entrapment of gas during solidification. Gas inclusion (caused by mechanically trapped gas) > pin hole (due to release of adsorbed gases) Prevented by pre-melting the alloy on graphite crucible.

subsurface porosity : © AimMDS subsurface porosity simultaneous nucleation of the solid grains and the gas bubbles at the first moment that metal freezes at the mold walls prevented by controlling the rate of the metal entry into the mold.

entrapped air or back pressure porosit : © AimMDS entrapped air or back pressure porosit caused by inability of the air to escape from the mold prevented by proper technique and the distance between the tip of the pattern and the end of the ring should not be greater than 6mm and by Sufficient casting pressure.

CERAMICS : © AimMDS CERAMICS Ceramic is a compound of metallic and non-metallic compounds. Porcelains are glass ceramics. CLASSIFICATION According To Firing Temperature High fusing - 1290-1370oC Medium fusing - 1095-1260oC Low fusing - 870-10650C ultralow fusing < 850oC

CERAMICS : © AimMDS CERAMICS According to the processing method sintering casting machining According to the use denture teeth metal ceramic veneers crowns inlays

CERAMICS : © AimMDS CERAMICS According to type felspathic porcelain leucite reinforced porcelain aluminous porcelain glass sintered alumina

Composition : © AimMDS Composition

Strengthening ceramic : © AimMDS Strengthening ceramic Development of residual compressive stresses (by selecting an alloy that contracts more than porcelain on cooling putting porcelain in compression.) By ion exchange (exchange of large potassium with small sodium ion) Thermal tempering (heating and quenching in silicon oil) interrupting crack propogation Adding particulate alumia that interrups the crack propogation. Eg dicor glass ceramic: Incorporating crystalline material that changescrystal structure under stress (eg partially stabilize zirconia)

The color of the ceramic : © AimMDS The color of the ceramic Metallic oxides are added to obtain various shades simulating natural teeth.

THE METAL CERAMIC RESTORATIONS : © AimMDS THE METAL CERAMIC RESTORATIONS Porcelain powders are mixed with liquid to form a plastic mass and is condensed to form the porcelain restoration. Then it is fired in the furnace for sintering. Condensation is achieved by vibration, spatulation and brush technique.

Stages in firing Changes in porcelain : © AimMDS Stages in firing Changes in porcelain

DENTAL CEMENTS : © AimMDS DENTAL CEMENTS DENTAL CEMENTS Restorative cements can be classified as temporary or short-term (for days to weeks), intermediate term (for weeks to months) and permanent or long term (for years). Most cement set by acid base reaction except calcium hydroxide and resins

SILICATE CEMENTS : © AimMDS SILICATE CEMENTS Composition

SILICATE CEMENTS : © AimMDS SILICATE CEMENTS Properties Silicones strong in compression but weak in tension (brittle) Anticariogenic (due to fluoride) pH less than 3 at insertion and remain below 7 for even a month. (severe irritant) Silicate has high solubility and disintegrates readily in oral fluids. They become stained over a period of time. It is contraindicated in mouth breathers, as its surface becomes rough and opaque when allowed to dry.

GLASS IONOMER CEMENT : © AimMDS GLASS IONOMER CEMENT Also called as Polyalkenoate cement, Man made dentin, Dentin substitute, Alumino silicate poly acrylic cement (ASPA) GI group of material use silicate powder and an aquous solution of polyacrylic acid. Bonds to tooth: The bond of enamel is always higher than that of dentin.

GLASS IONOMER CEMENT : © AimMDS GLASS IONOMER CEMENT Three types Type I = luting Type II= restorative material Type III =liner or the base. Type IV =Fissure sealant Type V =Orthodontic cement Type VI =Core build up cement Type VIII and Type IX= Posterior packable GIC for atraumatic restorations

Slide 108 : © AimMDS Properties low fracture toughness and wear resistance. Very sensitive to moisture (causes weakening) over drying causes cracks in the cement. (surface of cement should be protected by coating with varnish or cocoa butter during setting.) Relatively biocompatible - The pulpal reaction is greater than ZOEbut less than zinc phosphate/silicates cement. Anticariogenic property is due to fluoride release.

Manipulation : © AimMDS Manipulation Powder liquid ratio is 3:1 by weight. Mixing should be done by agate or plastic spatula. Cool dry glass slab may be used to slow down the reaction. Conditioning of the cavity surface done by 10% polyacrylic acid Polishing done after 24 hours.

MODIFIED GICs : © AimMDS MODIFIED GICs Metal modified Silver alloy mix: spherical silver alloy particles mixed with class II GIC powder Cermet: fusing of glass powder to silver powder by sintering.

Resin modified : © AimMDS Resin modified Resin modified: the initiators of light or chemical curing are added to the powder and the liquid contains polyacrylic acid with carboxylic group modified with methacrylate and HEMA. Initial setting Is by polymerization and the ultimate setting by the acid base reaction.

ZINC OXIDE EUGENO : © AimMDS ZINC OXIDE EUGENO Classification Type I - For temporary cementation Type II - For permanent cementation Type III - Temporary filling material and base Cavity liners Type IV:- cavity liners.

Composition : © AimMDS Composition

Setting reaction : © AimMDS Setting reaction Sets by chelation. Addition of drop of water, alcohol and acetic acid accelerates the setting reaction while addition of a drop of glycerin retards the reaction. Substitution of eugenol with orthoethoxybenzoic acid results in appropriate increase in the strength. Smaller particle size increase the strength.

ZINC PHOSPHATE CEMENT : © AimMDS ZINC PHOSPHATE CEMENT Composition

Setting reaction : © AimMDS Setting reaction Phosphoric acid attacks the powder and releases zinc, the aluminium complexes with the phosphoric acid and reacts with the released zinc to form Zn aluminophosphate gel on the surface of the remaining particle. Manipulation Cool glass slab to prolong the setting time. Liquid should be dispensed just before mixing to avoid loss of water.

Slide 117 : © AimMDS Small increments of the powder is added to the liquid each speculate for 15 secs before adding the second completeion of mix requires 1min 30 secs. ( recommended to dissipate heat because the reaction is exothermic permits more powder to be incorporated into the mix.)

Slide 118 : © AimMDS P:L ratio = 1.4 gm to 0.5 ml Prolonged spatulation retards the setting reaction as the formed matrix is effectively destroyed Biocompatibility Fresh mix has a pH of 2 and then increases rapidly in 24-48 hours, thus damage occurs during early insertion period

ZINC POLYCARBOXYLATE CEMENT : © AimMDS ZINC POLYCARBOXYLATE CEMENT Composition

Slide 120 : © AimMDS Properties Chemically binds to the tooth; adhesion is better to smooth surface than rough surface. Pseudoplastic (spatulation reduces viscosity) Less brittle than Zn phosphate Manipulation 1.5 parts of powder and 1 part liquid by weight Powder incorporated in liquid rapidly (opp to ZnPO4)

Slide 121 : © AimMDS Removal of excess cement is difficult due to rubbery less brittle consistency on setting, Biocompatibility The pH of liquid is 1.7 and that of freshly mixed cement is 3-4. After 24 hours, pH of the cement is 5-6. Cooling the slab increases viscosity thus to increases the setting time the powder is refrigerated before mixing

CALCIUM HYDROXIDE CEMENT : © AimMDS CALCIUM HYDROXIDE CEMENT The cement is alkaline in nature. It has a pH of 11. The high alkalinity and its consequent antibacterial and protein-lysing effect helps in formation of "Reparative dentin" . It is an effective antibacterial agent.

CAVITY VARNISHES : © AimMDS CAVITY VARNISHES Natural gum such as copal, resin or synthetic resin dissolved in organic solvent such as alcohol,acetone or ether. Cavity varnish is a solution of one or more resins which when applied onto the cavity walls, evaporates leaving a thin resin film, that prevent infiltration of irritating fluid from restoration and the dentinal tubules. it decreases the micro leakage due to margin sealing and prevents discoloration It may be used as a surface coating over GIC, silicate restorations to protect from dehydration. It prevents galvanic shock if applied over metallic restorations.

Slide 124 : © AimMDS THE CAVITY LINER The main purpose of the cavity liners is to use the beneficial effect of the reparative agents like CaOH in the formation of reparative dentin.. The liners are volatile or aqueous suspensions of zinc oxide or calcium hydroxide that can be applied to a cavity surface in a relatively thin film. Varnishes are Contraindicated in: Composite resins - Varnish interferes with polymerization. GIC& Polycarboxylate -Varnish interferes with the potential for adhesion

Slide 125 : © AimMDS THE CEMENT BASES A base is a thicker layer of cement placed under permanent restoration to encourage recovery of the injured pulp and to protect the pulP. from thermal, chemical and galvanic insults. for effective thermal protection the base should have a minimal thickness of 0.75 mm Calcium hydroxide (or) GIC liner should be used under composite restorations. ZOE liner is contraindicated under composite as the eugenol in the cement may interfere with polymerization of composite.

THE CEMENT BASES : © AimMDS THE CEMENT BASES The base must have sufficient strength to withstand forces of condensation and masticatory stresses. Base does not prevent micro leakage and acid penetration A varnish or dentin-bonding agent is used to assist sealing of the restoration. With ZnP04 as a base, the sealant should be applied first followed by base. If the base is Ca(OH}z, ZOE, GIC or polycarboxylate, the base should be placed first followed by the sealant.