DENTAL CEMENTS.

DENTAL CEMENTS

index Introduction Classification of dental cements
Characteristic properties of dental cements Cavity varnishes Cavity liners Cavity base Zinc phosphate cement Zinc polycarboxylate cement Zinc oxide eugenol Glass ionomer cement Compomers Resin cements Mineral trioxide cements Calcium phosphate cements

Dental cements A cement is a substance that hardens to act as a base,liner,filling material,or adhesive to bind devices and prosthesis to tooth structure or to each other. A variety of cements have been used in dentistry through the years . In addition cements can be used for specialized purposes in the restorative ,endodontic ,orthodontic,pedodontic and surgical fields of dentistry such as in high strength bases ,beneath direct restoration and endodontic sealers and to cement orthodontic bands and braces.

LIQUID POWDER Acidic solutions or protons donors
Most dental cements are supplied as :- 2 components ,a powder and a liquid (packaged in capsule form to be triturated) Some have been reformulated in 2 pastes . LIQUID Acidic solutions or protons donors POWDER Basic in nature,consisting of glass or metallic oxide particles. ACID BASE REACTION

REINFORCED ZINC OXIDE EUGENOL
ZINC PHOSPHATE POLYCARBOXYLATE WITH CAPSULE GLASS IONOMER CAPSULE RESIN CEMENT

UPON SETTING ,THESE CEMENTS GAIN SUFFICIENT STRENGTH FOR USE AS:-
Depending on the particle size and liquid powder ratio,these components when mixed yeilds a pastelike or flowable material ,which hardens(or sets) to a rigid solid within a reasonable time. UPON SETTING ,THESE CEMENTS GAIN SUFFICIENT STRENGTH FOR USE AS:- BASE RESTORATIVE MATERIAL LUTING AGENT PERMANENT TEMPORARY

BASE:- Layer of insulating ,sometimes medicated ,cement ,placed in the deep portion of the preparation to protect pulpal tissues from thermal and chemical injury. RESTORATION:- Filling material or prosthesis used to restore or replace a tooth ,a portion of tooth ,multiple teeth or other oral tissues. LUTING AGENT:- A viscous material placed between tooth structure and a prosthesis that hardens through chemical reactions to firmly attach the prosthesis to the tooth structure.

CLASSIFICATION OF DENTAL CEMENTS

GLASS AND RESIN MODIFIED GIC
DENTAL CEMENTS CLASSIFIED BY INGREDIENTS AND APPLICATION (12TH edition craigs) WATER BASED CEMENTS GLASS AND RESIN MODIFIED GIC ZINC POLYACRYLATE ZINC PHOSPHATE CLASS 5 RESTORATION RETENTION OF CONVENTIONAL ALLOY BASED RESTORATION. RETENTION OF ALUMINA OR ZIRCONIA-BASED ALL CERAMIC RESTORATION RETENTION OF ORTHODONTIC BANDS HIGH STRENGTH BASES LONG TERM PROVISIONAL RESTORATIONS RETENTION OF ALLOY RESTORATION RETENTION OF ORTHODONTIC BANDS RETENTION OF PEDIATRIC STAINLESS STEEL CROWNS HIGH-STRENGTH BASES LONG TERM PROVISIONAL RESTORATION RETENTION OF CONVENTIONAL RESTORATIONS RETENTION OF ORTHODONTIC BANDS HIGH STRENGTH BASES LONG TERM PROVISIONAL RESTORATION CRAIGS restorative dental material john m powers,ronals l sakaguchi

COMPOSITES AND ADHESIVE RESINS COMPOMERS
RESIN BASED CEMENTS COMPOSITES AND ADHESIVE RESINS COMPOMERS BONDED CONVENTIONAL ALLOY –BASED RESTORATIONS BONDED CERAMIC CROWNS,BRIDGES,VEENERS,INLAY,AND ONLAYS BONDED LABORATORY COMPOSITE CROWNS,BRIDGES,VENEERS,INLAYS AND ONLAYS BONDED POSTS AND CORES RETENTION OF PROVISIONAL RESTORATIONS RETENTION OF ORTHODONTIC BRACKETS BONDED CONVENTIONAL ALLOY –BASED RESTORATIONS RETENTION OF ALUMINA-OR ZIRCONIA-BASED ALL-CERAMIC RESTORATIONS RETENTION OF ORTHODONTIC BRACKETS HIGH STRENGTH BASES

NON EUGENOL –ZINC OXIDE
OIL BASED CEMENTS ZINC OXIDE EUGENOL NON EUGENOL –ZINC OXIDE HIGH STRENGTH BASES PROVISIONAL RESTORATIONS ROOT CANAL SEALERS GINGIVAL TISSUE PACKS SURGICAL DRESSINGS PROVISIONAL RESTORATION ROOT CANAL SEALERS GINGIVAL TISUE PACKS SURGICAL DRESSINGS

CLASSIFICATION ACCORDING TO MAJOR CHEMICAL REACTING COMPONENTS(phillips 12th edition)
MATERIALS FORMULATION AND REACTING COMPONENTS REACTION TYPE ZINC PHOSPHATE POWDER: ZINC OXIDE AND MAGNESIUM OXIDE LIQUID: PHOSPHORIC ACID AND WATER ACID-BASE REACTION ZINC OXIDE –EUGENOL POWDER: ZINC OXIDE LIQUID: EUGENOL ACID BASE REACTION ZINC OXIDE EUGENOL (EBA MODIFIED) LIQUID: EUGENOL AND ETHOXYBENZOIC ACID ZINC POLYCARBOXYLATE LIQUID: POLYACRYLIC ACID,WATER ACID –BASE REACTION

FORMULATION AND REACING COMPONENTS REACTION TYPE
MATERIALS FORMULATION AND REACING COMPONENTS REACTION TYPE GLASS IONOMER POWDER: FLUOROALUMINOSILICATE GLASS LIQUID:POLYACRYLIC ACID,POLYPROTIC CARBOXYLIC ACID,WATER ACID-BASE REACTION RESIN MODIFIED GLASS IONOMER PODWER: FLUOROALUMINOSILICATE GLASS,CHEMICALLY AND/ORLIGHT-ACTIVATED INITIATORS LIQUID: POLYACRYLIC ACID WATER-SOLUBLE METHACRYLATE MONOMER,WATER, ACTIVATOR LIGHT-OR CHEMICALLY ACTIVATED POLYMERIZATION AND ACID-BASE REACTION

MATERIALS FORMULATION AND REACING COMPONENTS REACTION TYPE POWDER: FLUOROALUMINOSILICATE GLASS,METALLIC OXIDES,SODIUM FLUORIDE,CHEMICALLY AND/ORLIGHT ACTIVATED INITIATORS LIQUID: DIMETHACRYLATE/ CARBOXYLIC MONOMERS,MULTIPLE FUNCTIONAL ACRYLATE MONOMERS WATER,ACTIVATOR LIGHT-OR CHEMICALLY ACTIVATED POLYMERIZATION AND ACID-BASE REACTION PASTE A: (NON AQUEOUS) FLUOROALUMINOSILICATE GLASS,NONREACTIVE FILLER REACTIVE MONOMERS PASTE B: (AQUEOUS)NONREACTIVE FILLER,METHACRYLATE MODIFIED POLYALKENOIC ACID,WATER-SOLUBLE METHACRYLATE MONOMER,WATER LIGHT-ACTIVATED POLYMERIZATION AND ACID BASE REACTION

MATERIALS FORMULATION AND REACING COMPONENTS REACTION TYPE CALCIUM ALUMINATE /GLASS IONOMER HYBRID POWDER: CALCIUM ALUMINATE ,POLYACRYLIC ACID,TARTARIC ACID,STRONTIUM-FLUORO-ALUMINO-GLASS AND STRONTIUM FLUORIDE LIQUID: WATER ACID-BASE REACTION OF GLASS IONOMER AND HYDRATION OF CALCIUM ALUMINATE CEMENT COMPOMER ONE PASTE: METHACRYLATE MONOMER,ACIDIC MONOMER,FLUOROALUMINOSILICATE GLASS INITIATOR LIGHT ACTIVATED POLYMERIZATION POWDER: FLUOROALUMINOSILICATE GLASS,METALLIC OXIDES,SODIUM FLUORIDE,CHEMICALLY AND/OR LIGHT ACTIVATED INITIATORS LIQUID: DIMETHACRYLATE/CARBOXYLIC MONOMERS,MULTIPLE FUNCTIONAL ACRYLATE MONOMERS WATER,ACTIVATOR(FOR CHEMICAL CURE LIGHT OR CHEMICALLY ACTIVATED POLYMERIZATION AND ACID-BASE REACTION

MATERIALS FORMULATION AND REACING COMPONENTS REACTION TYPE RESIN CEMENT ONE PASTE: METHACRYLATE MONOMER ,INITIATOR LIGHT ACTIVATED POLYMERIZATION BASE PASTE: METHACRYLATE MONOMERS,FILLERS,CHEMICALLY AND /OR LIGHT –ACTIVATED INITIATORS CATALYST PASTE: METHACRYLATE MONOMERS,FILLERS ,ACTIVATORS LIGHT AND CHEMICALLY ACTIVATED POLYMERIZATION ,OR CHEMICALLY ACTIVATED POLYMERIZATION ONLY POWDER :POLYMETHYL METHACRYLATE BEADS(FOR THICKENING) LIQUID 1: METHACRYLATE MONOMERS LIQUID2:CATALYST CHEMICALLY ACTIVATED POLYMERIZATION

MATERIALS FORMULATION AND REACING COMPONENTS REACTION TYPE MINERAL TRIOXIDE AGGREGATE (MTA) POWDER: TRICALCIUM SILICATE,DICALCIUM SILICATE,RADIOPACIFIER(BISMUTH OXIDE,ZIRCONIA,OR TANTALUM OXIDE),CALCIUM ALUMINATE,GYPSUM LIQUID: WATER HYDRATION OF SILICATES

Classification by matrix bond (o’brein)
1)phosphate 2)phenolate 3)polycarboxylate 4)resin 5)resin-modified glass-ionomer Dental Cements for Definitive Luting: A Review and Practical Clinical Considerations Dent Clin N Am 51 (2007) 643–658 Edward E. Hill, DDS, MS Department of Care Planning and Restorative Sciences, University of Mississippi Medical Center School of Dentistry, 2500 North State Street, Jackson, MS 39116, USA

Based on knowledge and experience (donovan)
CONVENTIONAL CONTEMPORARY -ZINC PHOSPHATE -RESIN MODIFIED GIC -POLYCARBOXYLATE -GLASS IONOMER -RESIN Dental Cements for Definitive Luting: A Review and Practical Clinical Considerations Dent Clin N Am 51 (2007) 643–658 Edward E. Hill, DDS, MS Department of Care Planning and Restorative Sciences, University of Mississippi Medical Center School of Dentistry, 2500 North State Street, Jackson, MS 39116, USA

FLUORIDE RELEASING CEMENTS FOR DIRECT –FILLING RESTORATIONS
They have low strength hence used in low stress areas Beneficial when used for temporary and intermediate restoration as they are easy to remove . These cements are often used for restorations in patients at a high risk for caries. The use of dental cements as restorative material began with SILICATE CEMENT which is based on silicate glass and phosphoric acid.

The glass for silicate cement was made by fusing compounds of SILICA ,ALUMINA,FLUORIDE COMPOUND,and CALCIUM SALTS at approximately 1400 degree C. The impressive ANTICARIOGENIC potential of silicate cement confirms the ability OF FLUORIDE ION to inhibit demineralization and the role of fluoride releasing cements to serve as direct restorative materials.

ACID RESISTANCE OF ENAMEL
There are 3 major theories to explain the anticariogenic mechanism of fluoride ACID RESISTANCE OF ENAMEL REMINERALIZATION – DEMINERALIZATION BALANCE INHIBITION OF CARBOHYDRATE METABOLISM BY THE ACIDOGENIC PLAQUE MICROFLORA

ACID RESISTANCE OF ENAMEL
It suggests that fluoride ,when taken up in the apatite in the form of FLUORAPITITE.,reduces the solubility of apatite. Although the posteruptive fluoride uptake by enamel is minimal, the continuous release of fluorine ion from silicate cement provides a localized ,but high concentration of a fluoridated environment at the enamel/ restorative material interface.

Experiments performed with a silicate cement prepared with nonfluoride flux,had no appreciable change in the fluoride content of enamel,infact enamel solubility actually increased. Thus this theory implies that caries resistance,once obtained ,will last the lifetime of the tooth . However ,it has also been observed that caries protection by fluoride ceases when fluoride intake or its administration is terminated.

Remineralization –demineralization balance
The ionic fluorides are present in aqueous solution ,in plaque and within enamel and dentin . The remineralization –demineralization balance theory indicates that the presence of .02to1.0ppm of fluoride lowers the solubility of enamel ,and increased uptake in enamel results from an enhanced balance between remineralization and demineralization . Because fluoride in oral fluids is rinsed and swallowed ,a continuous supply is needed to maintain fluoride protection.

2 types of fluorides deposits on enamel after topical fluoride treatment or fluoride varnish application: BOUND FLUORIDE (FLUORAPATITE) UNBOUND FLUORIDE (CRYSTLE DEPOSISTS OF CALCIUM FLUORIDE) UNRELATED TO CARIES INHIBITION DISSOLVES IN RENSPONSE TO DECRESED pH IN ORAL CAVITY RELEASING FLUORINE IONS THAT SHIFT THE EQUILIBRIUM BALANCE TOWARDS REMINERALIZATION RATHER THAN TOWARDS DEMINERALIZATION

FLUORIDE AND PLAQUE METABOLISM
Fluoride accumulates in dental plaque . The sources of plaque fluoride include saliva, gingival fluid, diet, topically applied fluoride gel or fluoride varnish, and demineralising enamel. It is well established that fluoride inhibits carbohydrate metabolism by acidogenic plaque microflora. Fluoride enters microorganisms against a concentration gradient and accumulates intracellularly as the pH of extracellular fluid decreases. The transport of hydrogen fluoride (HF) into the extracellular fluid of cells leads to dissociation into H+ and F ions within the more alkaline intracellular fluid. Ionic fluoride then induces enzyme inhibition, leading to a slower rate of acid production . Meanwhile the fluoride increases cell permeability and it can rapidly diffuse out of the cariogenic bacterium, contributing again to the fluoride content within the plaque matrix.

CHARACTERISTIC PROPERTIES OF THE DENTAL CEMENTS

MAXIMUM FILM THICKNESS IS 25 µ m
FILM THICKNESS AND CONSISTENCY:- It greatly determines the adaptation of the restoration to the tooth. The retention may also be influenced by the film thickness ANSI/ADA specification no:96 has requirements for cement designed for seating of precision appliances:- MAXIMUM FILM THICKNESS IS 25 µ m

The heavier the consistency ,the greater the film thickness and the less complete the seating of the restoration. The ultimate film thickness that a well-mixed ,nonangular cement attains depends first on the particle size of the powder,the concentration of the powder in the liquid,the viscocity of the liquid,and the consistency of the cement. The film thickness also varies with the amount of force and the manner in which this force is applied to a restoration during cementation.

The consistency of the cement to be used in the cementation of a casting is critical.
Eg:-in a powder/liquid type of cement ,an increased amount of powder incorporated into the liquid will increased the consistency of the cement mass. Heavier than normal inlay seating consistencies of cement are more difficult to express from under a restoration,and incomplete seating of the inlay or crown may result from their use . The operator must frequently test each mass as the end of the mixing time is approached.

VISCOSITY The consistency of cements can be quantified by measuring viscosity . Increases in temperature and time have both been shown to increase the viscosity of some cements The rapid increase in viscosity with time demonstrates the need for prompt cementation after the completion of mixing to take advantage of the lower viscosity of the cement. Delays in cementation can result in considerably larger values of film thickness and insufficient seating of the restoration. For resin cements,viscosity can vary widely ,and in fact ,some products come with a choice of different viscosities.

Setting time Of equal importance to the viscosity of the cement is its setting time. A sufficient period of time must be available after mixing to seat and finally adapt the margins of a restoration or to properly contour a base or provisional restoration. Adequate working time is expressed by net setting time,which ,as ,determined by ANSI /ADA specification no.96 and based on a luting consistency ,is between 2.5 and 8 minutes at a body temperature of 37° C. The setting time test measures the time at which the cement is sufficiently hard to resist indentation by a standard indenter

The net setting time should occur within 2
The net setting time should occur within 2.5 to 8 minutes so that final finishing procedures associated with the restoration can occur. The first 60 to 90 seconds are consumed by mixing the cement,so the net setting time is the time elapsed between the end of mixing and the time of setting, as measured by resistance to a standard indenter. One advantage of light –cured resin cements is the fact that there is virtually an unlimited setting time with low ambient lightening prior to light –curing.

strength ANSI/ADA Specification no.96(ISO 9917)stipulates that the standard luting consistency of a dental cement must exhibit a minimum 24-hour compressive strength of 70MPa . SOLUBILITY Solubility in water and oral fluids is also an important consideration in cement properties. Water based cements are more soluble than resin-or- oil-based cements. ANSI/ADA Specification no 96 allows a maximum rate of acid erosion ,which is variable for the different types of cements,when a cement is subjected to lactic acid erosion by an impinging jet technique

CEMENTS AS LUTING AGENTS
Luting agents provides only mechanism adhesion ,such as those used for:- 1)fixed prostheses made of metal ,metal- ceramic,polymer ,or ceramic materials 2)temporary restoration 3)pins and posts used for retention of restorations

Microscopically the tooth and prosthesis surfaces are rough and the cement fills the irregular crevices between both surfaces to form a void-free continuum that microscopically locks one surface against another to resist shear stresses that might dislodge the appliance Mechanical retention may be sufficient . Chemical adhesion of the cement ,tooth and device improves retention

Mechanical retention Cement penetrates into the irregularities in the tooth structures abd the casting

GICs based on polyacrylic acids,bond to teeth by chelating acrylic acids to both organic and inorganic tooth components ,and continue to cure after the defined setting time. If glass ionomers are allowed to mature in an isolated environment ,the cements increase in strength and become more resistant to dissolution . Varnish coats applied at the margins of fresh GICs facilitates maturation .

Hydrophilic dentin bonding agents penetrate pores in dentin created by acid etching,these also have high bond strength through micromechanical retention. Resin cements based on NPG- GMA,polymerizable phosphates,and 4- META(methacrylethyl trimellitic anhydride)bond to calcium within dentin

Luting interface Luting cements are designed to fill the microscopic gaps between a prosthesis and a prepared tooth.

The first dental luting cements were not adhesive to the tooth or prostheses ,but they filled the microscopic space and created a strong physical attraction to both substrates that prevented dislodgement. The current approach for cementing prosthesis or appliances involves the use of an adhesive technique that forms a solid sealing layer within a few minutes to improve retention of the prosthesis. The cement should flow under pressure and wet the surfaces. A luting agent must form a continous film without forming voids,which are detrimental to retention and support of the prosthesis.

Procedure for luting a single crown
Luting of a single crown is in 3 steps:- 1)cement placement 2)seating of the crown 3)excess cement removal

Cement placement: The cement should coat the entire inner surface of the crown and extend slightly over the margin to ensure that the space between the crown and the tooth will be completely sealed. Cement should fill about half of the inner cavity volume of the crown and must be free of bubbles Air entrapments must be avoided in the critical occlusal region ;otherwise masticatory forces may fracture any ceramic prosthesis . Do not fill the entire crown cavity because this increases the risk of bubble entrapment .the time and pressure required for seating and the time and effort to remove excess cement.

Seating Use moderate finger pressure to displace excess cement and seat the crown on the prepared tooth Tapping or vibration of the crown or using ultrasonic device may also help to achieve complete seating of the crown Evaluate three points on the margins with an explorer to ensure that seating is adequate and ask the patient to bite on a soft substance such as cotton roll to ensure complete seating ,this will also expel excess cement Complete seating is essential Reevaluate at least 3 points of the margins and the occlusion before the cement has set

3 characteristics make seating a crown easier:
1)lower –viscosity cements 2)more taper of the prepared tooth 3)decreased height if the prepared tooth. HIGHER TAPER AND LOWER TOOTH HEIGHT COMPROMISE THE RETENTION

Removal of the excess cement:- Excess cement should be present at the margins of a crown just after seating ,but its removal depends on the properties of the cement used. Zinc phosphate cement and ZOE do not adhere to the surrounding surfaces,the tooth ,or the prosthesis, so the cement should set completely before the excess cement is removed. Glass ionomer,polycarboxylate,and resin cements adhere chemically and physically to the surrounding surfaces and should be removed as soon as the seating is completed to prevent adhesion to the exterior of the prosthesis or to the surrounding teeth.

A separating medium ,such as petroleum jelly,can be applied carefully to external and surrounding surfaces to inhibit cement adherence ,making cement removal easier when these cements are allowed to set completely. Some GICs and dual cure resin cements can be removed easily in about 1.5 to 3 minutes after mixing begins but before setting by an acid-base reaction or light curing is finished. At this point the cement has acquired some strength but is not strong enough to resist separation from the margin,which allows removal of larger pieces of the excess cement.

Zinc polycarboxylate cement transforms to a rubbery state before setting.
At this stage ,the cement is so thick that any attempt to remove the excess may inadvertently pull the cement away from the marginal area,or it may remove some of the cement from within the cemented prosthesis. Regardless of which cement the dentist may use ,it is always advisable to run a knotted dental floss through the interproximal regions towards the margins immediately after complete seating of the prosthesis . The knot removes excess cement and provides better access for cement removal required after the cement has set.

DISLODGEMENT OF PROSTHESES
Debonding may be caused by: Cement fracture Dissolution or erosion Secondary caries Excessive shear forces The cement layer is the weakest link of a prosthetic/tooth assembly.so cement with higher bond strength are preferred. In oral environment .luting agent may dissolve and erode,leaving a space in which plaque may accumulate and caries may recur Loss of cement at the marginal area resulting from exposure to oral fluid

Water based cements mature after they have reached the defined setting time.
If they are allowed to mature free of contamination from surrounding moisture and without loss of water,the cements increase in strength and become more resistant to dissolution. A coat of varnish should be applied or a bonding agent along the accessible marginal area of cemented restoration before discharging the patient. To maximize retention,the cement layer between the prosthesis and the abutment should be sufficiently thin to minimize pores in the cement. Thinner cement layers are created by applying a sufficient seating force such that excess cement is expressed out of the marginal space

The design of the prosthesis should allow the cement to flow and result in a uniform layer of cement between the prosthetic device and the tooth. When cement layers are thinner,plaque accumulation on the cement and microleakage are less likely. Cement should be insoluble in water and should not absorb water. The coefficient of thermal expansion between tooth ,prosthesis and cement should be similar over the range of temperature associated with consumed food and beverages. Cements having high compressive ,shear and flexural strengths are preferred. Dislodgement is minimized for cements with high shear bond strength

When chemical bonding occurs,failure may occur cohesively through the cement.
With a thin chemically bonded cement,the prosthesis may become dislodged when the luting cement fractures or dissolves. When a cement produces only mechanical retention ,failure begins at the interfaces. A low setting contraction is preferred to minimize interfacial stresses Cleavage through the cement layer Due to small thickness of cement Remnants of luting agent remain on opposing surface

Cements for pulp protection
Pulpal protection requires consideration of 1) chemical protection 2)electrical protection 3)thermal protection 4)pulpal medication 5)mechanical protection Metallic restorations are excellent thermal conductors,but they promote thermal sensitivity when hot and cold foods or beverages are consumed. Cements containing phosphoric acid ,direct filling resins, and some glass ionomer cements cause a chemical irritation.

The inflammation caused by chemically irritating cements increases in the order of polycarboxylate cements,zinc phosphate cement,and GIC. The setting contraction of amalgam or composite can lead to marginal leakage as well as pulpal irritation. CAVITY VARNISH,LINERS,AND BASE MATERIALS have been used as adjuncts to restorative materials to protect the pulp from such injuries .

Schematic view of needs for pulpal protection below metallic restoration

Use of liners and bases for amalgam
Shallow depth Moderate depth Very deep preparations

Cavity varnish Varnishes are composed of natural gums- such as copal,resins or synthetic resins-dissolved in an organic solvent(acetone,chloroform or ether). The varnish forms a thin coating on the tooth as the solvent evaporates. Varnishes have a high solvent content and at least two thin layers should be applied to produce a continious coating;otherwise small pinholes may occur. A brush or a a small pledget of cotton may be used as an applicator.

Varnish reduces infiltration of irritating fluids through marginal crevices and lessens pulpal irritation. It prevent the penetration of corrosion products of amalgams into the dentinal tubules,thereby reducing the unsightly tooth discoloration often associated with amalgam restorations. High copper amalgam products,which are more corrosion resistant than their predecessors,have diminished the need for varnish . A varnish is not indicated when adhesive materials such as GICs or bonding agents serve the same purpose as varnish.

Cavity liners Calcium hydroxide is the chief ingredient in many cavity liners and cement base materials because calcium hydroxide is Antimicrobial Has an elevated Ph(basic,alkaline) Stimulates the formation of secondary dentin over an injured pulp to protect it over the long term. As a cavity liner ,the calcium hydroxide powder is suspended in a solvent carrier with a thickening agent. When it is placed on the pulpal floor,the solvent evaporates and leaves a thin film of calcium hydroxide .

The liner does not possess significant mechanical strength or thermal insulation capability but it can neutralize acids that migrate towards the pulp and in the process ,it can induce the formation of secondary dentin. Eventually the calcium hydroxide forms calcium carbonate and becomes inactive. Calcium hydroxide is soluble in water and must not be left on the margins of the prepared cavity or the margins will not be properly sealed. Many formulas that are available for cavity lining materials are based on adding calcium hydroxide to low – viscosity ZOE,GI,or resin cement. Some of these liners adhere to tooth –restoration interface,therefore the function of liners has been expanded to include the sealing of dentin from potential influx of microorganism and irritants from restorative procedures.

Calcium hydroxide liners are commonly used for direct and indirect pulp capping and as a dressing after vital pulpotomy procedures on primary teeth. MTA is a newer cavity liner that forms calcium hydroxide as it sets. Both MTA and calcium hydroxide undergo a transformation of hydroxide in the blood and oral fluids ,causing their antimicrobial effectiveness to diminish.

Cement bases Cements bases are applied in thicker layer (greater than 0.75mm)beneath restorative materials to protect pulp against thermal injury ,galvanic shock,and chemical irritation. Temperature changes have a more acute effect on the pulp when teeth containing large amalgam fillings are not insulated by a base. Zinc phosphate and ZOE cements are commonly used as well as some polycarboxylate and fast setting GICs .

Zinc phosphate and ZOE cements are better insulators than metals,although they have less insulating ability than portland cement corkboard or glass. The insulating abilities of polycarboxylate,glass ionomer, and calcium hydroxide materials also fall within this range . Their actual heat transfer is more complex and depends on the materials heat capacity ,thickness and density. Zinc phosphate cement is an effective base for thermal insulation,but its low pH (acidity)may require a cavity liner under the cement to protect the pulp.

However the risk of low pH in contact with the pulp is minimized if the zinc phosphate cement is mixed to a thick ,nontacky ,putty-like consistency ,which does not have excess acid. Calcium hydroxide,ZOE,polycarboxylate,and glass ionomer cement are effective barriers against the penetration of irritating constituents from restorative materials. When glass ionomer is used as a base, a calcium hydroxide liner should be applied 1st to protect the deep areas where pulp exposure is more likely to occur

Cement bases should be strong enough to withstand forces during the placement of fillings and mastication forces during service. Restorative materials should be placed after the initial set of the base cement has occurred. Their strength increases rapidly over the 1st 30minutes and continues to increase over 24 hours

The minimal strength required to resist masticatory forces has not been determined because of their complexity and the influence of the design of the prepared tooth cavity . For a class I tooth preparation where the base is supported on all the sides by tooth structure ,less strength is necessary than required for class II restorations A base cement should be selected after considering the design of the cavity ,the direct restorative material, and the proximity of the pulp chamber relative to the cavity floor of wall.

For amalgam restorations,calcium hydroxide and ZOE materials are more effective base cements.
For direct filling gold restoration,which are relatively ductile,a stronger base cement such as zinc phosphate ,polycarboxylate,or GIC is indicated. Where liners of calcium hydroxide or ZOE cement on the cavity floor is desired the liner should be overlaid with a strong base cement.

Neither microleakage nor acid penetration is prevented by using a base cement in conjunction with amalgam or direct-filling gold foil. When a cavity varnish or dentin bonding agent is indicated to seal a restoration,the base often governs the order of material application . If a zinc phosphate cement base is used, a sealing(varnish ) material should be applied to the cavity walls before placement of the base. For the more biocompatible cement base materials(eg calcium hydroxide,ZOE,polycarboxylate,and GIC),the base cement is placed ,followed by the cavity varnish after base has hardened.

For resin –based composites ,calcium hydroxide and GIC are satisfactory cements.
MTA is also used as a base because it is insulating ,antimicrobial and nonacid. However ,currently available products have slow setting characteristics. Thus MTA is primarily a specialty material.

Cements for restoratives
Cements can be employed for temporary or short-term periods(days to weeks) ,intermediate-term periods(weeks to month),or long –term periods (years)in the restoration of anterior teeth. In early 1990s ZOE,zinc phosphate ,and silicate cement were the major material system used for restorative. Silicate cement,based on silicate glass particles and phosphoric acid,was a translucent restorative material and it was the primary esthetic material before resin composites were introduced. In 1972,GICs based on new silicate glass formulas and polyacrylic acid ,were introduced .

ZINC PHOSPHATE CEMENTS

Zinc phosphate cement first appeared in the literature in 1879 and the chemistry of the modern –day cement was established in 1902. It is the oldest luting cement and its long clinical record of success serves as a standard by which newer cement are compared It has low film thickness and sufficient working time to allow complete seating of restoration. Initially on mixing it has low pH, which can irritate the pulp (less than 4) and gives rise to transient pain but reaches neutrality by 48 hours.

APPLICATIONS Luting of restorations High strength bases Temporary restorations Luting of orthodontic bands and brackets. CLASSIFICATION ADA specification No.8. Designates them as 1. Type I – Fine grained for luting Film thickness should be 25  or less 2. Type II - Medium grain for luting and filling Film thickness should not be more than 40 

MODE OF SUPPLY Available as Powder and liquid system. COMMERCIAL NAMES Confit Harvard Zinc cement improved Modern tenacin

COMPOSITION Powder Zinc oxide % - Principle constituent Magnesium oxide % - Aids in Sintering (reduce temperature) Other Oxides Bismuth trioxide, Calcium oxide, Barium oxide – 0.2% - Improves smoothness of mix. Silica – 1.4% - Filler Liquid Phosphoric Acid % - Reacts with zinc oxide Water % - Controls rate of reaction

CALCINATION PROCESS The ingredients of the powder are heated together at temperature ranging from 1000C to 1300C for approx 4 to 8 hours or longer depending on the temperature. This calcination results in a fused or sintered mass this mass is ground and pulverized to a fine powder, which is sieved to recover selective particle sizes. LIQUID Aluminum and zinc is added to liquid, partially it will neutralized the H3PO4 and temper the reactivity of the liquid and is described as buffering. WATER Presence of additional water shortens the setting time. Insufficient amount of water increases setting time

CHEMISTRY OF SETTING REACTION
When excess of zinc phosphate cement powder is brought in to contact with the liquid wetting occurs and a chemical reaction is initiated. The acid liquid resulting in an “exothermic reaction” dissolves the surface of the alkaline powder. The set zinc phosphate cement is essentially a hydrated amorphous network of zinc phosphate that surrounds incompletely dissolved particles of zinc oxide. The amorphous phase is extremely porus. The alumina of the liquid is essential to cement formation without its presence a non-cohesive crystalline structure matrix of tertiary zinc phosphate, Zn3 (PO4)2 4H20 (HOPEITE) would be formed. The alumina of the liquid complexes with phosphoric acid to form zinc alumino phosphate gel.

MIXING PROCEDURE INITIAL STAGE By the initial incorporation of small portions of the powder into the liquid minimal heat is liberated and easily dissipated the heat of the reaction is most effectively dissipated when the cement is mixed. Over a large area Over a cooled glass slab With a relatively long narrow bladed stainless steel spatula. During the neutralization of the liquid by the powder the temperature of the mixing site is inversely proportional to the time consumed in accomplishing the mix. If a large volume of powder is carried to the liquid all at once results in increase in temperature at reaction site and speeds the reaction and hinders control over consistency.

MIDDLE STAGE – II During this stage larger amount can be incorporated to further saturate the liquid with newly forming complex phosphate’s, the quantity of unreacted acid is less at this time because of the prior neutralization gained from adding small increments of the initial powder the amount of heat liberated will be less and can be dissipated adequately by the cooled glass slab. FINAL STAGE III Finally smaller increments of powder again are incorporated, so that the desired consistency is detained. The phosphoric acid attacks the outside of the powder particle forming a crystalline matrix of phosphate compounds, and traps the un-dissolved powder as the cement sets. Three critical factors must be considerer when working with zinc phosphate cement: Solubility Strength Setting time

Proper consistency(strung up about ½ to ¾ inch at separation
Strung up more than ¾ inch without seperation (too think for cementation) Spatulate each increment of powder for 15 to 20 seconds before adding another increment ,and all mixing should be completed within 1.5 to 2 minutes

All above factors are under control of dentist
Zinc phosphates are extremely water-soluble when used as a luting agents, it is important to keep the area of cement not to expose oral fluids or saliva during setting, if contact occurs with saliva or oral fluids surface of the cement will become dull, soft, easily dissolved. This can results in open margin, secondary caries Strength It is adversely effects by improper mixing of the cement. If mixes too rapidly, the crystalline formation will be disturbed. Control of setting time It is crucial in developing an optimal luting consistency for zinc phosphate cement factor governing the setting time is Mixing time Temperature Water content Powder liquid ratio Speculation of the powder in to the Liquid Concentration of H3PO4

Loss of water prolonged setting time
Even slight changes in concentration of H3PO4 can result in drastic changes in setting time. The liquid consist of partially neutralized diluted H3PO4, which, when exposed to humid atmosphere, will absorb water: when expose to dry air it will loose water. Water content of liquid H3PO4 effects the setting time the reason is weak H3PO4 in the presence of water will convert to less stable form of ortho phosphoric acid, which is easily dissociated, leads to decrease setting time because of increased dissociation so cap should always be replaced immediately after dispensing. The liquid contain should be discarded when 80% of the constant have been used because of possible absorption of water from repeated opening of the bottle. Loss of water prolonged setting time Addition of water shorted the setting time

WORKING AND SETTING TIME
Working time is the time measured from the start of mixing during which the viscosity (consistency) of the mix is low enough to flow readily under pressure to form a thin film. Setting time means that the matrix formation has reached a point were external physical disturbance will not cause permanent dimensional changes. It can be measured with a 4.5N (1 pound) Gilmore needle: A reasonable setting time for zinc phosphate cement is between 5 and 9 minutes (ADA NO 8) MIXING TIME Exceed the mixing time sec results in weakening of the cement mass by the breaking down of the matrix because it tends to form and bind the un-dissolved powder particle together.

FACTORS INFLUENCING WORKING TIME AND SETTING TIME
POWDER, LIQUID RATIO Working time and setting time can be increased by reducing the powder, liquid ratio if not it effects on physical properties and compressive strength of cement. RATE OF POWDER INCORPORATION Introduction of small quantity of powder in to the liquid for the first few increments increases working time and setting time by reducing the amount of heat generated and permits more powder to be incorporated in to the mix there fore it is the recommended procedure for zinc phosphate cement. SPATULATION TIME Operators who prolong the spatulation time are effectively destroying the matrix that was forming. TEMPERATURE OF MIXING SLAB If we use cool glass slab can increase working time and setting time.

MANIPULATION The proper amount of powder should be slowly incorporated in to the liquid on a cool glass slab (approximately 21C) to attain the desired consistency of cement. MIXING SLAB Most chemical reactions are accelerated by the presence of heat because of an increase in molecular actively of the reactants. When we mix powder, liquid result in liberation of heat in the immediate environment of the reaction, this heat must be dissipated readily or other wise the reaction will proceed too fast towards completion, so properly cool glass slab with sufficient thick enough. It should be sufficient thick. Glass slab should not influence by environment. The mixing slab temperature should be low enough to be effective in cooling the cement mass but not be below the dew point unless the frozen slab technique is used [a temperature of 18 to 24C is indicated when room humidity permits].

THERMAL PROPERTIES Primary use of zinc phosphate is an insulting base beneath the metallic restoration. These are good thermal insulators and may be effective in reducing galvanic effect. The premature contact of incompletely sets cement with water results in the dissolution and leaching of that surface, for this reason the use of the term hydraulic to describe any of the zinc phosphate cement is improper because they do not harden or set with desirable physical properties when submerged in water.

Compressive strength is as high as 104MPa Diametral tensile strength of 5.5MPa Elastic of modulus of 13GPa Making it relatively strong and stiff as compared with other cements It has low solubility in water Phosphoric acid in liquid makes mixture more acidic and therefore cytotoxic when a prostheis is luted with this cement,

ZINC POLYCARBOXYLATE

Developed by Dennis Smith 1968, in an effort to produce cement that could adhere to tooth structure
They adhere via chelation to dental surfaces are also reduce pulpal problems associated with low pH of the traditional cements Zinc poly carboxylate was the first cement system that develops an adhesive bond to the tooth structure these cements are first to have adhesive bond to the hard tooth structure. In liquid the Phosphoric acid is substituted by an acid functional polymer forming the matrix As they are less acidic hence they do not irritate pulp The strength is almost same as zinc phosphate cement They are used for Cementing cast metal restorations Directly cementing orthodontic brackets on the tooth They can also be used for temporary filling Cavity base, cavity liners

Generally supplied as a Type A powder liquid
COMMERCIAL NAMES Poly f (DENTSPLY) HARVARD CC DURELON CAROXYLON CARBCO (VOCO) CERMCO, ”P.C.A” SELFAST DISPENSING Generally supplied as a Type A powder liquid Type B water settable powder

2. To improve manipulative properties
COMPOSITION POWDER:- Consist mainly zinc oxide and magnesium oxide that have been sintered and ground to reduce the reactivity of the zinc oxide. Bismuth oxide, alumina is also added in small proportions. Stannous fluoride in very small quantity (It act as a flux) 1. To modify setting time 2. To improve manipulative properties The fluoride is released in negligible amount, hardly 15 to 20 % of the amount released from glass ionomer and silico phosphate cements. The water settable cements contain 15% to 18% poly acrylic acid coated on the powder particles

LIQUID:- SUPPLIED as a 32% to 42% solution of polyacrylic acid. ITACONIC AND TARTARIC ACID :-stabalize the liquid ,which can gel on extended storage Liquid should be kept in stoppered bottle, as loss of water the liquid will lower its pH and slow down the setting. Liquid that appears cloudy after water loss should be discarded

When we mix the powder and liquid Surface of the powder particles are dissolved by the acid present in the liquid Results in release of zinc, magnesium, strontium ions These binds and cross link the carboxyl groups. Result is a crosslinked polycarboxylate matrix phase encapsulating the unreacted portion of the particles

The hardened zinc polycarboxylate cement is an amorphous gel matrix in which unreacted powder particles are dispersed. The pH of the cement liquid is initially slightly less acidic than that of zinc phosphate cements but it is still very low The pH of the mix rises rapidly from 3 to 6 as the setting reaction proceeds. The setting time ranges from 6to9 minutes .

MECHANISM OF ADHESION outstanding characteristic is the chemical bond to the tooth structure. The polyacrylic acid bonds to calcium ions on the surface of the enamel or dentin. The bond to enamel is greater that that to the dentin as enamel has higher concentration of calcium.

Clinical manipulation
The inner surface of the crown must be cleaned to improve wettability and the mechanical bond at the cement-metal interface. The surface can be carefully abraded with a stone or sandblasted with alumina abrasive. Crowns should be thoroughly rinsed to remove debris and dried. The outer surface of the prosthesis should be coated carefully with a separating medium,such as petroleum jelly to prevent excess polycarboxylate cement form adhering to its surface

A clean tooth is necessary to achieve adhesion and ensure intimate contact between the polycarboxylate cement from adhering to its surface. Prepared tooth should be isolated to prevent contamination by oral fluids and blotted dry.

Mixing of the cement The powder liquid ratio is about 1.5 by weight.
It should be mixed on a nonabsorbent surface(glass slab) Liquid component should not be refrigerated (as its is viscous) The liquid should be dispensed just before use because the water in the liquid evaporates quickly,which raises its viscosity . The powder should be rapidly incorporated with liquid. A cement must be used before it looses its glossy appearance as it indicates free carboxylic acid groups are still present for good bonding to the tooth . A dull looking mixture means insufficient carboxyl group are present for bonding to the calcium in the tooth

CONTROL OF WORKING TIME
The working time is much shorter than that for zinc phosphate cement ,2.5versus 5 minutes. A cool slab lengthens the working time for zinc carboxylate cement,although it causes the polyacrylic acid to thicken,which hinders mixing. Refrigerating the powder is useful because it retards the reaction without raising the viscosity of the liquid. Rapid spatulation and fast seating will reduce the viscosity of the polycarboxylate cement to ensure complete seating.

Mechanical and biological properties
COMPRESSIVE STRENGTH is 55MPa It is more elastic which makes it more difficult to remove excess cement after seating. It produce minimal irritation to the pulp. The larger size of polyacrylic acid molecules compared with those of phosphoric acid limits acid penetration into the dentinal tubules ,contributing to the excellent biocompatibilty and lack of postoperative sensitivity of this cement.

ZINC OXIDE EUGENOL CEMENT

Zinc oxide eugenol cement is used for luting and intermediate restorations because of its medicament quality and neutral pH. Certain types of Zinc oxide eugenol cement, when mixed with eugenol sets to hard cement that are compatible with the hard and soft tissues of the mouth. These cements have been used extensively in dentistry since 1980’s. They are cements of low strength, and are known to have an obtundant (sedative) effect on exposed dentin. Recently, non-eugenol cements have become available. Suitable for patients sensitive to eugenol

Eugenol, a phenol derivative is known to be toxic, and it is capable of producing thrombosis of blood vessels when applied directly to pulp tissue. It has also aesthetic properties and is used as an anodyne in relieving the symptoms of painful pulpitis. This presumably results from its ability to block the transmission of action potentials in nerve fibers.

classification ADA SPECIFICATION NO: 30 It has listed 4 types of Zinc oxide eugenol Restorative materials. TYPE APPLICATION TYPE I TEMPORARY CEMENTATION TYPE II PERMANENT CEMENTATION TYPE III TEMPORARY FILLING MATERIAL AND THERMAL INSULATION TYPE IV CAVITY LINER Craig restorative dental materials john m powers,ronald l salaguchi 12th edition

COMMERCIAL NAMES 1. Unmodified - Tempac - - Cavitic - - Tempbond - 2
COMMERCIAL NAMES 1. Unmodified - Tempac - - Cavitic - - Tempbond - 2. EBA alumina Modified Opoton alumina - EBA 3. Polymer Modified Fynal - - IRM 4. Non-eugenol -Neogenol - - Freegenol -

COMPOSITION ZINC OXIDE EUGENOL: Powder:
Zinc oxide: 69.0% - Principal ingredient White rosin: 29.3% - To reduce the brittleness to set cement. Zinc stearate: 1.0% - Accelerator, Plasticizer. Zinc Acetate: 0.7% - Accelerator improves strength. Magnesium oxide: Added in some powders, acts with eugenol in a similar manner as Zinc oxide. Liquid: Eugenol: 85.0% - Reacts with Zinc oxide Olive oil – 15.0% - Plasticizer

MODIFIED ZINC OXIDE EUGENOL CEMENTS:
EBA – Alumina modified cements: Powder: Zinc oxide : 70% Alumina: 30% Liquid: EBA – 62.5% Eugenol – 37.5% POLYMER RE-INFORCED ZINC OXIDE EUGENOL CEMENT: Zinc oxide; Finely divided natural or synthetic resins. Eugenol: Acetic acid: accelerator Thymol: Antimicrobial agent

SETTING REACTION It involves chelation of two eugenol molecules, with one zinc ion to form Zinc eugenolate. The reaction is as follows: 1st reaction Hydrolysis of Zinc oxide to its hydroxide. Zinc oxide + H2O  Zn (OH) 2 2nd reaction Chelation: Zn (OH) 2 + 2HE  ZnE2 + 2H2O (Base) (Acid) (Salt) Zinc Hydroxide Eugenol Zinc Eugenolate

The chelate forms an amorphous gel that tends to crystallize imparting strength to the set mass.
This reaction proceeds very slowly in the absence of the moisture. When the mixed material contacts water, however, setting is often completed within a few seconds. Setting time: 4 – 10 minutes.

MANIPULATION :DISPENSING AND MIXING PROCEDURE
For temporary cementation or for provisional restoration ,powder is often incorporated into a dispensed amount of liquid until a suitable consistency is achieved for the operation at hand. A considerable amount of powder can be incorporated into the liquid by heavy spatulation with a stiff spatula. More powder incorporated,the stronger the cement and the more viscous the mixed cement

CHARACTERISTIC PROPERTIES:-
ANSI/ADA specification no.30(ISO 3107) FILM THICKNESS :- Its is an important factor in the complete seating of restoration at the time of cementation . The film thickness should be not more than 25µm for cement used for permanent cementation and not more than 40µm for cement used for temporary cementation.

SETTING TIME A range of setting time 4 to 10 minutes is required
SETTING TIME A range of setting time 4 to 10 minutes is required. For cements intended for filling materials and bases,the preference of some operators for a faster setting cement is recognized in the specification by extending the lower end of range to 2 minutes. COMPRESSIVE STRENGTH A maximum value of 35MPa is required for cements intended for temporary cementation. A minimum of 35MPa is required for cements intended for permanent cementation . 25MPa for filling materials and bases. Lining materials are required to have a minimum compressive strength of 5MPa

DISINTEGRATION It is regarded as less critical for cements used for provisional restorations or for temporary cementation. Maximum specification value for disintegration in 24 hours. A maximum value of 2.5% is acceptable for provisional cementing materials,but a value of 1.5% is required for the other cements.

Applications:- A range of ZOE and modified ZOE cements are suitable for many uses in restorative dentistry. 1)temporary cementation:- Unmodified ZOE cements are also used as luting materials for provisional crowns and temporary cementation of metal restoration in crown and bridge prosthodontics. A cement with the compressive strength of 15 to 24 Mpa is the most appropriate cement based on 1)retention 2)taste 3)ease of removal 4)ease of cleaning

Provisional restorations:-
Ethoxybenzoic acid –alumina-modified cements have been tried as provisional restoration based in their physical properties. These cements are handled easily and have improved carvability,which prevented chipping during trimming . The EBA –alumina –modified cements despite their low solubility in water ,disintegrated and wore excessively in the mouth. A thick mix,2.6g/0.4mL of polymer-modified ZOE is more serviceable than the EBA –alumina- modified type.

BASE:- Materials having a compressive strength of 5.5 to 39MPa are used as a cement base. And the strength reaches a maximum in about 12 to 15 minutes. The zoe cement have the advantage that the thermal insulating properties of the cements are excellent and are the same as those for human dentin.

These sealers have a long history of successful use, and have been the standard against which many newer sealers have been measured. Based on zinc oxide powder mixed with eugenol, numerous proprietary variations have been applied to these basic components to enhance various qualities of the sealer, such as dentin adhesion, reducing inflammation, or antibacterial action. ENDODONTIC SEALERS:-

ANSI/ADA SPECIFICATION NUMBER 57 (ISO 6876)
PROPERTIES:- VISCOSITY:- The ability of a sealer to penetrate into irregularities and accessory canals has been viscosity. SETTING TIME:- ranges from 15 minutes to 12 hours FILM THICKNESS:- Influenced by viscosity ,setting time and the size of filler particles in the cement. Ranges from 80 to 500µm ANSI/ADA SPECIFICATION NUMBER 57 (ISO 6876)

Compressive strength:- The strength if a sealer is an indication of its ability to support tooth structure weakened by the cleaning of the canal and its durability . Value ranges from 8to 50MPa Solubility:- It is an undesirable characteristic in a root canal sealer ,because the process of dissolution can cause sealer to release components that may be biologically incompatible . It has been measured in water and typically value ranges from 0.1%to 3.5%

Radiopacity:- It is desirable and minimum value has been establised at the equivalent of 3mm of aluminum. Value of radiolucency range from 0.10 to among various sealers and 0.78 for gutta percha. Dimensional change:- Shrink as a result of setting This shrinkage affects the integrity of the bond between the sealer and the tooth or core material Value of volume loss after 90 days in a capilary tune range from 0.7% to 5%

GLASS IONOMER CEMENT(GIC)

GIC is the generic name for materials based on the reaction of glass powder and polyacrylic acid.
The cements were developed in the 1970s to improve clinical performance compared with silicate cements and to reduce the risk of pulp damage. The use of polyacrylic acid makes GIC capable of bonding to tooth structure. GIC is considered superior to many types of cements because it is adherent and translucent . Various formulas are available depending on the intended clinical application.

Water –soluble polymers and polymerizable monomers have been replacing part of the liquid content .
Particles of metal,metal-ceramic and ceramic have been added to some products to enhance mechanical properties. GICs have been used for the esthetic restoration of anterior teeth eg,class III and V sites,as luting cements and intermediate restoration,as pit and fissure sealants,liners and bases and as a core buildup materials.

The GICs are classified :-
TYPE 1 : luting crown ,bridges and orthodontic brackets. TYPE IIa : esthetic restorative cements TYPE IIb : reinforced restorative cements TYPE III : lining cements,base

CHEMISTRY AND SETTING:
It is essentially the same for all three types,with variations in powder composition and particle size to achieve the desired function. The consistency of the mixed GIC varies widely among manufacturers ,from low to very high viscosity as influenced .by their use of various particle size distributions and the P/L ratio. Larger particles(50µm) are used for the various restorative indications and finer glass particles (15µm)are used for cementing.

GLASS COMPOSITION:- It contains silica ,calcia,alumina and fluoride
COMPONENT COMPOSITION A B C SiO2 41.9 35.2 20-30 Al2O3 28.6 20.1 10-20 AlF3 1.6 2.4 CaF2 15.7 NaF 9.3 3.6 AlPO4 3.8 12.0 F - 10-15 Na2O 1-5 BaO CaO P2O5

The ratio of alumina to silica is the key to their reactivity with polyacrylic acid. Barium,strontium,or other higher atomic number metal oxides are added to the glass to increase the radiopacity . The silica glass is melted at temperature between 1100°C and 1500°C ,depending on the raw materials and overall composition. The glass is ground into a powder with particles ranging from less than 15µm to about 50µ ,depending on the indication.

Liquid composition Aqueous solution of polyacrylic acid(above 40% to 50%) were used,but such liquids were viscous and had a short shelf life because of gelation. The liquids are copolymers of itaconic ,maleic or tricarboxylic acids. Tartaric acid is a rate controlling additive in the GIC liquid that allows a wider range of glasses to be used ,improves handling properties ,decreases viscosity ,lengthens shelf like before gelling of the liquid occurs ,increases working time ,and shortens the setting time.

A specialized GIC known as water soluble GIC is formulated with freeze-dried polyacrylic acid solid powder,which is mixed with water or an aqueous solution containing tartaric acid. This type of GIC has an extended working time because additional time is needed to dissolve the dried polyacrylic acid in water and start the acid- base reaction.

Setting reaction When the powder and the liquid are mixed for a GIC ,the acid starts t dissolve the glass, releasing calcium ,aluminum sodium and fluoride ions. Water serves as reaction medium. The polyacrylic acid chains are then cross linked by calcium ions are replaced by aluminum ions. Sodium and fluorine ions from the glass do not participate in the cross linking of the cement. Some of the sodium ion may replace the hydroden ions of carboxylic groups,and fluorine ions are dispersed within the cross linked(matrix) phase of the set cement.

The cross linked phase becomes hydrated over time as it matures.
The undissolved portion of glass particles is sheathed by a silica rich gel that is formed on the surface of the glass particles. This the set cement consists of undissolved glass particles with a silica gel coating embedded in an amorphous matrix of hydrated calcium aluminum polysalts containing fluoride.

Structure of gic

Photmicrograph of a set GIC showing unreacted particles surrounded by the continous matrix

Clinical manupilation
Conditions for GIC that must be satisfied for cementing fixed prosthesis: 1)the surface of the prepared tooth must be clean and blotted dry. 2)the entire intaglio of the prosthesis must be coated with luting cement and seated completely 3)excess cement must be removed at the appropriate time. For restorative indications,the GIC surface must be protected to prevent dehydration or premature exposure to saliva. Surface finishing of GIC restorations must be carried out without excessive drying to ensure their survival

Surface preparation Clean tooth surface is essential for sustained adhesion. A pumice slurry can be used to remove the smear layer produced by prepared cavity. Alternatively the tooth may be etched (conditioned) with phosphoric acid or an organic acid like polyacrylic acid for 10 to 20 seconds water rinse After conditioning and rinsing the preparation ,the surface should be dried but not desiccated and it must remain uncontaminated by saliva or blood.

Material preparation The P/L ratio recommended by the manufacturer should be followed . A paper pad or cool ,dry glass slab should be used. Normally half of the powder is mixed into the liquid for 5 to 15 seconds ,the rest of the powder is then quickly added and mixed by folding the cement on itself until a uniform ,glossy appearance is achieved. Mixing time should not exceed 45 seconds Glossy appearance indicates presence of unreacted particles. Dull appearance indicates that the acid has reacted too much with glass particles for good bonding

They are supplied in 2 bottles or capsules containing preproportioned powder and liquid .
A triturator is used to mix the powder and liquid after the seal between the powder and liquid has been broken. Capsule contains a dispensation tip that facilitates direct injection of the mix into the prepared tooth cavity or onto a fixed prosthesis for bonding .

Placement of material A tooth cavity should be slightly overfilled with GIC restorative. A freshly prepared GIC mixture is hygroscopic that is it absorbs water from the surrounding environment. After placement ,GIC surface should be covered with plastic matrix for 5minutes to protect the material from gaining or losing water during the initial set. Water dilutes the matrix –forming cations and anions, destroying the ability to form the hydrated matrix. When matrix is removed ,the surface must be protected with varnish supplied with the GIC.

For luting application ,the GIC is applied by a plastic instrument to the prosthesis device.
The excess cement can be removed immediately upon setting or after a length of time as prescribed in the manufacturer’s instructions. Coating of the margin of the cemented prosthesis with a varnish after complete removal of the excess will allow proper maturation of the GIC cement.

Release of fluoride After setting GIC release fluoride in amounts comparable to those released initially from silicate cement.

Biological and mechanical preparation
It elicit greater pulpal reaction than ZOE cement but less than zinc phosphate cement. GIC luting agents pose a greater pulpal hazard than GIC restorations when the GIC is mixed with a low P/L ratio because the pH remains acidic longer. With any GIC a protective liner should be used eg calcium hydroxide if preparation is closer than 0.5mm to the pulp chamber.

Properties of restorative GIC

Fracture toughness of gic and selected materials

Metal-reinforced GIC Metallic fillers have been incorporated in the GIC to improve their fracture toughness and stress bearing capacity . The metallic fillers are derived from silver alloy powder or particles of silver sintered to glass that make the cement grayish and more radiopaque,these metal reinforced GIC are called alloy admixture and CERMET. The adhesion and fluoride release from the metal reinforced GICs are very useful for core builups of teeth to be restored with cast crowns and for restoratives on occlusal surfaces of primary molars. These are limited in use as an alternative to amalgam or composite for posterior restorations.

High viscosity GIC ART is a preventive and restorative caries management concept developed for dentistry in regions of the world that do not have an infrastructure with electricity or piped water system. GIC which releases fluoride and bonds chemically to tooth structure ,is the natural choice of material for these situations. Initial results of using conventional GIC have proven the feasibility for ART ,which has led to the development of HIGH VISCOSITY GIC. These have smaller glass particles size and use higher p/l ratio

They exhibits excellent packability for better handling characteristics .
They are also used for core buildups ,primary tooth fillings,non-stress-bearing restorations.and intermediate restoration in general practices. Encapsulated packaging of the high –viscosity GICs is convenient

Clinical manupilation
Clinical steps in the ART procedure with high- viscosity GICs are as follows: 1)isolating the tooth with cotton rolls 2)accessing the carious lesion with hand intrument. 3)removing the soft tissue with an excavator. 4)using weak acid to prepare the tooth and enhance chemical bonding 5)placing the high viscosity GIC using finger pressure.

Resin –modified GIC(hybrid ionomer)
Water –souble methacrylate –based monomers have been used to replace part of liquid components of conventional GIC results in a group of materials called resin –modified glass ionomer cement/hybrid ionomer cement

The monomers can be polymerized by a chemical or light activation or both and the GIC acid base reaction will occur along with the polymerization. Some hybrid ionomer cements also contain nonreactive filler particles,which lengthens the working time,improves early strength ,and makes the cement less sensitive to moisture during setting. CHEMISTRY AND SETTING:- Liq contains a water solution of polyacrylic acid,HEMA, and polyacrylic acid modified with methacrylate. The powder component contains fluoroaluminosilicate glass particles of conventional GIC plus initiators such as camphorquinone,for light curing or chemical curing.

The acid –base reaction begins upon mixing and continues after polymerization at much a slower rate than for conventional GICs because less water is present and the reaction is much slower in the solid phase than in the liquid phase. The bonding mechanism is same as the conventional GIC The clinical manipulation includes liners,fissure sealants,base materials,core buildups,restorative,adhesives for orthodontic brackets,repair materials for damaged amalgam cores or cusps and retrograde root filling materials. For any indications ,surface conditioning of the tooth with mild acid is essential for bond formation.

Calcium aluminate GIC A hybrid with a composition
between that of calcium aluminate and GIC for luting fixed prosthesis is new addition to family of GIC. It is made by sintering the mixture of high-purity aluminum oxide and calcium oxide (1:1molar ratio)to create monocalcium aluminate. The powder acts as base and water as a weak acid. It is also known as hydraulic cement

Powder: calcium aluminate ,polyacrylic acid,tartaric acid,strontium-fluoro-alumino- glass,and strontium fluoride. liquid: 99.6%water and 0.4% additives for controlling setting.

COMPOMERS

compomers

Compomer is polyacid-modified composite made by incorporating glass particles of GIC in water free polyacid liquid monomer with appropriate initiator. The rationale for using these material is the integration of the fluoride –releasing capabilty of glass ionomer with the durability of resin composites. Compomers possess properties distinctly different from those of resin composites and glass ionomers.

Chemistry and setting Compomers are one paste ,light cure materials for restorative applications,although liquid powder system for luting application are available . These water free material contain nonreactive inorganic filler particles ,reactive silicate particles ,sodium fluoride ,and polyacid modified monomers such as diester of 2-hydroxyl methacrylate with butane carboxylic acid and photoactivators. Setting is initiated by photopolymerixation of the acidic monomer. Compomer cements are sensitive to moisture and are packaged to protect against moisture absorption ,even though their acid base reaction is slow.

For powder liquid product compomer producs,the powder contains strontia-alumina-fluorosilicate glass,metallic oxides,and initiators. The liquid contains polymerizable methacrylate /carboxylic monomers,multifunctional acrylate monomers and water. Depending on the initiators the material can be chemically cured,light cured,or dual –cured to augment the slower acid –base reaction.

Bonding mechanism It requires a dentin bonding agent prior to their placement as the do not contain water which could make them self adhesive. Bond strength of one paste is similar to or higher that hybrid ionomer. The p/l compomer cements for luting are self adhesive ,as water in the liquid makes the mixture acidic like hybrid ionomer.

Clinical manpulation Mainly used in low-stress-bearing areas such as class III and V prepared cavity,or as an alternative to GIC or resin based composites. The tooth structure should be etched trior to the application of the dentin bonding agent and the compomer . Compomers are finished just like resin composites. Compomers luting system are indicated for cementing prosthesis with metallic substrate. The cement mixture is placed only on the prostheses with metallic substrate

Water uptake Water absorption which is high as 3.5% by weight ,is desired process to complete the acid base reaction and fluoride release. It releases less fluoride than that from conventional and hybrid GIC Compressive strength and flexural strength decreases on storage in saline solution. Surface hardness and microtensile stength appears to be unchanged.

RESIN CEMENT

The success of attaching unfilled resin to etched enamel gave rise to the concept of using resins to bond fixed prosthesis to abutments. CHEMISTRY AND SETTING:- RESIN CEMENTS are low –viscosity version of restorative composites . These cements are virtually insoluble in oral fluids,but the brands widely vary in physical properties because of the variety and proportions of resin and fillers in the formulas. A dentin bonding agent is needed to promote the adhesion of resin cement to dentin.

The adhesive monomers incorporated in the bonding agent and the resin cements includeHEMA ,4-META ,carboxylic acids and organophosphate,such as MDP. MANIPULATION Liner is important when the thickness of the remaining dentin is less than .5mm as the monomeric component is irritating to the pulp. Chemically cured resin cements are suitable for all types of restorations. They are supplied as powder liquid or 2 paste which are mixed on paper pas for 20 to 30 seconds. Chemical activation is slow and provides extended working time and strength increases as the chemical process continues.

Dual cure cements require mixing similar to that for the chemical cure system
Static mixing and trituration of capsules have largely replaced the need for hand mixing. Curing proceeds slowly until the cement is exposed to the curing light at which point the cement hardens rapidly. They should not be used with light transmitting prosthesis thicker than 2.5 mm.anything thicker than 2.5 should be bonded with chemical cure cement Removal of excess cement may be done after seating of prosthesis.

DENTAL CEMENTS.

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