Zinc Phosphate Polycarboxylate

Zinc Phosphate and Zinc Polycarboxylate

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Zinc Phosphate Cement

CONTENTS

• Introduction• History• Composition : • Setting Reaction: • Working Time / Setting Time: • Control of Setting Time: • Manipulation: • Physical Properties: • Retention: • Biological Properties:

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Introduction

• Old ADA Specification no. 8- Dental zinc phosphate cement

• New ADA Specification no.96/ ISO Specification no. 9917 :1991- Dental water based cements

• It is also known as “Crown and Bridge Cement” and “Zinc Oxyphosphate”

• It is still used for cementing cast metal crowns and onlays.

• Formulation Components: Powder and Liquid• Reaction type: Acid-base reaction

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History• Zinc phosphate cement is one of the oldest and most reliable

dental materials. It has been used for last two hundred years.

• In 1870, Pierce introduced zinc oxide–phosphoric acid cement, which replaced oxychloride and oxysulfate cements, because it caused less irritation to the pulp and had greater durability.1

• The work of Ames and Fleck established the modern-day zinc phosphate cement.2,3

• By the turn of the century these cements were used to lute gold and porcelain crowns and inlays to teeth, in addition to serving as temporary filling materials and cavity bases.

1. Pierce CH. Discussion, Pennsylvania Association of Dental Surgery. Dent Cosmos 1879;21:696.2. Ames WVB. A new oxyphosphate for crown setting. Dent Cosmos 1892;34:392.3. Fleck DJ. The chemistry of oxyphosphates. Dent Items Int 1902;24:906.

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Composition Powder

• ZnO 90.2% Principal constituent • MgO 8.2% Reduce temperature in calcination

• SiO2 1.4% Aids In Calcination

• Bi2O3 0.1% Improves smoothness of mix

lengthen setting time

• Misc. BaO, Ba2SO4,Cao 0.2%

• Tannin fluoride source of fluoride ions

Liquid • H3PO4 38.2% Reacts with zinc oxide

• Water 36.0% Controls ionization of acid

• H3PO4 16.2% Buffers, to reduce rate of

(Al and Zn) reaction• Aluminium 2.5%• Zinc 7.1%.

Ronald L. Sakaguchi, John M. Powers, Craig’s Restorative Dental Materials, 11th Edition

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Powder • Zinc Oxide 90% Principal constituent • Magnesium Oxide 10%

Liquid • Phosphoric acid• Water• Aluminium phosphate• Zinc phosphate

Acid content of most liquids is 33+5 wt%

Phillips,Science of Dental Material 11th edition

Composition

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Manufacturing process:

• The powder is manufactured by sintering together the ingredient powders .

• Sintering is the process of heating closely packed particles to a specified temperature (below the melting point of the main component) to densify and strengthen a structure as a result of bonding, diffusion and flow phenomena.

• Sintering is done at 1000oC – 1400oC for 4-8 hours.• Mass is then ground and pulverised to fine powder, which is

seived to recover selected particle size.• The degree of calcination, fineness of particle size and

composition determine the reactivity of the powder and liquid. • The liquid is produced by adding aluminium and zinc or their

compounds to a solution of orthophosphoric acid.

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SETTING REACTION• When powder comes in contact with liquid wetting occurs• Alkaline powder dissolve in acidic liquid resulting in

exothermic reaction

• H3PO4 attacks ZnO Particles and releases zn ions in liquid.

• Al then reacts with zn to form zinc aluminophosphate gel on surface of remaining particles.

• Set cement is hydrated amorphous network of zinc phosphate surrounding unreacted ZnO particles

• Amorphous Phase is extremely porous

• Subsequent growth of crystalline hopeite Zn(PO4).4H2O (without Al )in presence of excess moisture is possible

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Working Time / Setting Time: • Working time is measured as the time from the start of mixing

to the maximum time at which the viscosity of the mix is still low enough to flow readily under pressure to form a thin film.

• Rate of matrix formation dictates the length of working time.Completion of the mix usually requires 1.5-2 min.

• Setting time is defined as the elapsed time from the start of mixing to the point at which the needle no longer makes a complete circular indentation in the cement. It can be measured with a 1 mm diameter needle indenter at a load of 400g, at a temperature of 37oC and relative humidity greater than 90o.

• Setting time as specified by ANSI/ADA Specification no. 96 (ISO 9917) 2.5-8 min.


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Mixing Slab

• A properly cooled thick glass slab (21oC)will dissipate the heat of reaction .

• The temperature of the mixing should be low enough to effectively cool the cement mass but not be below the dew point unless the Frozen slab technique is used.

• A temperature between 18oC- 24oC is indicated when room humidity permits.

• The moisture condensation on slab cooled below the dew point contaminates the mix, diluting the liquid and shortening the setting time.

• The ability of the mixing slab to be cooled and yet be free of moisture greatly influences proper control of the reaction rate.


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Care of liquid

• The water content of the liquid is critical and must be carefully controlled to provide a satisfactory setting time.

• If the bottle of liquid is left unstoppered, the water content of the liquid is altered according to the vapor pressure of the atmosphere in relation to the vapor pressure of the liquid.

• If the humidity of the air is sufficiently high, i.e. when vapor pressure of the air is higher than that of liquid, water is absorbed by the liquid .

• Cement liquid stored over water gained 6.9% water while cement liquid exposed to dry air for one day lost 7.5% in weight due to evaporation of water.

• Changes in the water content within the range of + 10% does not have a marked effect on the setting time of the cement. However, any loss or gain in water has a comparable influence on compressive strength, tensile strength and abrasion resistence.


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Care of liquid

• Loss of liquid from the bottle is often indicated by precipitation of buffering salts on the walls of the bottle or a general cloudiness of the liquid.

• Unfortunately there is no change in appearance if water is absorbed by the liquid.

• Approximately last 1/5th of the liquid should be discarded. ADA Specification no. 8 includes a requirement that the manufacturer must supply 20% excess of liquid in proportion of the total amount of powder.

• Since the manufacture of zinc phosphate cement is a carefully controlled process, satisfactory results can seldom be achieved by mixing the powder of one brand of cement with the liquid of another


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Manipulation-1


• Measured quantity of powder is dispensed onto a cooled glass slab and divided into several portions.• The bottle is shaken gently to homogenise the contents and dispensed by holding it perpendicular to the slab to avoid air entrapment and ensuring a complete drop.• The liquid is dispensed just before mixing as the water content tends to evaporate degrading the composition of the liquid.

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Manipulation-1 • Loss of water lengthens the setting reaction whereas

its incorporation acclerates the reaction.• Powder is incorporated into the liquid in definite

proportions and spatulated thoroughly in a circular motion with a stiff bladed stainless steel spatula.

• As a rule each increment is spatulated for 15-20 seconds before adding another increment

• Large area of mixing should be used to dissipate the heat. Smaller increments are then added until the mix is complete.

• Powder-Liquid Ratio: 1.4 gm/O.5 ml


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Manipulation-2 •Measured quantity of powder is dispensed onto a properly cooled thick glass slab and divided into three portions.•The initial portion is small which easily dissipates the heat liberated. The heat of reaction is most effectively dissipated when the cement is mixed over a large area of the cooled slab.•The temperature of the mixing site is inversely proportional to the time consumed in mixing. If a large amount of powder is carried all at once, the temperature rise speeds the reaction and hinders control of consistency.•The middle portion is large, to saturate the liquid with the newly forming zinc phosphate complex.


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Manipulation-2

•The quantity of unreacted acid is less at this time because of the prior neutralization gained from initially adding small increments of powder. The amount of heat liberated will likewise be less.•Finally, smaller increments are incorporated so the desired consistency is not exceeded.•Depending on the product mixing time is 60-90 seconds to accomplish adequate mass.•If the mixing time is unduly long, the cementing mass may be weakened by the breaking down of the matrix because it tends to bind the undissolved powder particles together.


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Frozen Slab Technique-3

• The mixes used in normal mixing procedures have adequate working and setting time for the cementation of inlays and crowns.• However, in the cementaton of orthodontic bands, the short working time of normal mixes allows the cementation of only a few bands with one mix and the setting times are too long for clinical convenience.• Therefore the glass slab is cooled in a refrigerator at 6oC or a freezer at -10oC. No attempt is made to prevent moisture from condensing on the slab when it is brought to room conditions.


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Frozen Slab Technique-3•The amount of powder incorporated with this technique is 50%- 75% more than the normal procedures.• The compressive and tensile strengths are not significantly different from the normal mixes because condensed moisture incorporated in the mix counteracts the higher P/L ratio.• No differences exist in the solubility. The advantages include substantial increase in the working time (4- 11 minutes) and a shorter setting time (20% - 40% less) after placement in the mouth.• The method has also been advocated for cementation of bridges with multiple pins.


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Control of Setting Time: During Manufacturing Process

1. Sintering temperature: The higher the temperature, the more slowly the cement sets.

2. Particle size: Finer particles react more quickly as a greater surface area is exposed to the liquid.

3. Water content of liquid: Presence of excess water accelerates, whereas insufficient water retards the reaction.

4. Buffering agents: When added slow down the reaction.

Chairside Control of Setting Time:

• Reducing the P/L ratio produces a thinner mixture which has increased working and setting time. This change will adversely affect the physical properties and result in a lower initial pH of the cement. This is not an acceptable means of extending the setting time. The compressive strength as a function of decreasing P/L ratio is as follows.

20Phillips,Science of Dental Material 11th edition


• Mixing cements in increments and introducing smaller increments of powder for the first few increments has increased working and setting time and permits more incorporation of powder.

• Prolonged spatulation of the last increment will destroy the matrix as it is forming. Fragmentation of the matrix means that extra time is needed to rebuild the bulk of the matrix. This is different from the phenomenon observed for dental stones, in which a fragmented matrix represents new nuclei for crystallization that control the setting time and microstructure of the gypsum product.




• The reaction between the powder and liquid is exothermic. Cooling the glass slab markedly retards the chemical reaction eventually retarding matrix formation. This permits incorporation of optimum amount of powder in the liquid without the mix developing an unduly high viscosity.• For the same P/L ratio and mixing technique, the cement prepared on a cool glass slab is compared with the mix made on a slab at room temperature. The first mix is still fluid and suitable for cementation of cast restorations while the second mix may be too viscous for use in cementing precision castings

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Film thicknessAccording to ADA Specification no.8• Type I-Fine grained for luting

Film thickness 25 micron or less• Type II-Medium grained for luting and filling

Film thickness 40 micron or less

Test employed for film thickness :

A cement mix of standard consistency is placed over an area of approximately 2 cm2 between two glass plates, under a load of 15 kgs for 10 minutes

[Phillips,Science of Dental Material 7th edition]

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Consistencies1. Luting Consistency- final consistency will be

fluid, yet the cement will string about 2-3 cm as the

spatula is lifted from the mass.

2. Base Consistency- heavy putty like consistency which can be used for thermal and chemical insulating barrier over thin dentin

3. Band seating Consistency-midway between luting and base consistency

• The standard consistency as defined by ADA Specification no. 8 is determined by Modified Slump test. It is the consistency obtained when the proper amount of powder is mixed with 0.5 cubic cm of liquid so that a disk, 30 mm (1.8”) in diameter is formed from 0.5 cubic cm of the mixed unset cement when it is pressed between two glass plates under a load of 120gms (4.2 ounces)

[Phillips,Science of Dental Material 7th edition]• An appropriate consistency is attained by addition of more powder to

the liquid and not by allowing a thin mix to thicken.

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Properties of dental cements used for bonding applications

cement type setting time film thickness Solubility in water pulp response

ANSI/ADA 5.0(minimum) 25(maximm) 0.20wt%(max) see note*

specification 8

Zinc phosphate 5.5 20 0.06 moderate

ZOE type 1 4-10 25 0.04 mild

ZOE-EBA 9.5 25 0.05 mild

(Type 2)

ZOE plus

Polymer(type 2) 6.0-10 32 0.08 mild

Silicophosphate 3.5-4.0 25 0.40 moderate

Resin 2.0-4.0 less than 25 0-0.01 moderate

Polycarboxylate 6.0 21 0.06 mild

GIC 7.0 24 1.25 mild to moderate

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Cement type 24hr compressive 24hr diametrical Elastic strength(Mpa) tensile strength modulus(GPaANSI\ADA 69 N\A N\A Specification 8(type 1)Zinc phosphate 104 5.5 13.5 ZOE(type 1) 6-28 - - ZOE-EBA(type 2) 55 4.1 5.0 ZOE plus POLYMER 48 4.1 2.5 (type2) Silicophosphate 145 7.6 - Resin 70-172 - 2.1-3.1 Polycarboxylate 55 6.2 5.1 GIC 86 6.2 7.3

Properties • Compressive Strength : Zinc phosphate

cement is stronger (103.5 MPa) than zinc oxide-eugenol cement but not as strong as silicophosphate. The set cement gains 75% of its maximum strength in the first hour. Maximum strength is attained in the first day. The minimum thickness required to attain this strength is 0.75mm.

• The strength of zinc phosphate cement is sufficient when used as a base or luting agent. However, when it is exposed to the oral environment its brittleness and low strength causes it to fracture and disintegrate.

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Modulus of Elasticity : 13.5 Gpa

It is comparatively high . This makes it stiff and resistant to elastic deformation. This is necessary when it is employed as a luting agent for restorations that are subjected to high masticatory stresses.

Solubility and Disintegration :

• This property is important for cements used for permanent cementation. It shows high solubility (0.06% Wt).

• ADA Specification no.96 describes the use of 0.1M lactic acid/ Sodium lactate (pH=2.74) to test the erosion of the cement. The maximum allowable loss in 24 hours is 0.2mm. (Philips 11th edi) Use of acetic acid, citric acid as well as ammonium hydroxide showed similar result. (Philips 7th edi)

• Previously , immersion in distilled water was accepted as a standard laboratory test method. ADA Specification no. 8 allows a maximum of 0.2% weight loss when a 40 mm disk is suspended in distilled water for 24 hours in water at 37oC. (Philips 7th edi)

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Solubility and Disintegration :• The pH and temperature inside the mouth fluctuate at

different intervals of time. This complexity of oral environment, coupled with the fact that different cements behave differently, has hindered the development of a standard laboratory test to measure solubility accurately.

• However, the relative disintegration rates apparently bear no resemblance to the data because no single in vitro test can duplicate all the oral conditions.

• Most reliable data is obtained in vivo by placing small specimens of the cements in intraoral appliances that can be removed from the mouth to measure the loss of material. In one study cements were inserted in tiny wells placed in the proximal surfaces of cast crown restorations cemented with temporary ZOE cement.

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Solubility and Disintegration : • They show greater disintegration over a period of time.

The increase in solubility with reduced pH is probably due to the greater solubility of the zinc oxide component than the solubility of the matrix. (Philips 11th edi)

• After seating of the prosthesis and setting of cement, excess cement should be removed. It is advisable to apply a layer of varnish or other nonpermeable coating to the margin to allow more time to the cement to mature and to develop an increased dissolution in oral fluids

• Maximum amount of powder should be incorporated in the liquid to ensure minimum solubility and maximum strength.

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• Thermal Properties: Zinc phosphate cements are good thermal insulators and may be effective in reducing galvanic effects. A thickness of 1-2 mm is used to provide thermal insulation. (Theodore M. Roberson, Sturdevant’s Art and science of Operative Dentistry, 5th edition, pg 175)

• Thermal Conductivity of set cement is 3.11 mcal.cm/cm2.secoK which is similar to standard insulators like asbestos (1.9 mcal.cm/cm2.secoK)

• Retention: The bonding occurs by mechanical interlocking at interfaces and not by chemical interactions. Therefore any coating for pulp protection reduces retention.

• Optical Properties :The set cement is opaque.

Biological Properties :• Pulp response is moderate. The acidity is high at the time of insertion. It

approaches neutrality in 24 to 48 hours.• There is concern to employ Zinc phosphate as thermal insulators in deep

cavities.• Radioactive phosphoric acid indicate that the acid from the cement can

penetrate a thickness of dentin as great as 1.5 mm.• If dentin is not protected against infiltration of this acid, pulpal injury may

occur, especially during the first few hours. Pulp protection in deep cavities is needed.

33Ronald L. Sakaguchi, John M. Powers, Craig’s Restorative Dental Materials, 11th Edition

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Uses

• Luting of inlays and crowns• Luting of posts• High strength bases • Temporary restorations • Luting of orthodontic bands and brackets.

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Commercial names• Confit• Harvard

A mixing device that can be used for mixing dental cements. Mixing is achieved by rapid shaking of a capsule.

• Zinc Cement Improved• Modern Tenacin

An encapsulated type zinc phosphate cement. The capsule contains powder and liquid. The mixed material can then beextruded from the syringe type capsule.

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Mohammad Saleem, Ikramul Ul Haq, Comparison of solubility of zinc phosphate and glass Ionomer cement in artificial saliva of varying ph values - in vitro study, Pakistan Oral & Dental Journal, Vol 31, No. 1 (June 2011) pg 231-4,

• Factors which govern the dissolution of the material are the particle size, powder/ liquid ratio, mixing technique, contamination, medium pH, exposure time to pH medium and status of oral hygiene

• The aim of this study was to compare the solubility of Zinc Phosphate and Glass Ionomer cements (conventional) in artificial saliva of different pH values.

• Both cements were mixed as per manufacturer’s directives to achieve excellent properties while using these as luting materials.

• In this study Zinc phosphate cement presented higher solubility at high pH medium but the solubility of glass ionomer cement was higher at low pH values after 96 hours immersion in artificial saliva adjusted to different pH values of 2.46, 3.15, 3.56, 4.96 and 6.57.

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Aleisa, Khalil Ibrahim ,Bond strengths of custom cast and prefabricated posts luted with two cements. Quintessence International. 2011, Vol. 42 Issue 2, pe31-38.

• This in vitro study evaluated the bond strength of custom cast and prefabricated posts luted with resin or zinc phosphate cements into unobturated canals of extracted teeth.

• Two of the groups were then luted with resin cement, while the other two groups were luted with zinc phosphate cement.

• A pull-out bond strength evaluation was performed using a universal testing machine.

• For both luting agents, the prefabricated posts group exhibited significantly less bond strength than the custom cast posts group.

• There were statistically significant differences in mean bond strength for the prefabricated posts group luted with resin cement vs the group cemented with zinc phosphate cement .

• However, there was no significant difference between the mean bond strength values of custom cast posts luted with resin cement or zinc phosphate cement.

• For Custom cast posts zinc phosphate cement showed equal bond strength as compared to resin.

http://web.ebscohost.com/ehost/viewarticle?data=dGJyMPPp44rp2/dV0+njisfk5Ie45PFKr6azT7ek63nn5Kx95uXxjL6urUmupbBIr6ieSrimtFKyr55oy5zyit/k8Xnh6ueH7N/iVa+ttUizprdNsqekhN/k5VXj5KR84LPifOac8nnls79mpNfsVbOvtk23prZRpNztiuvX8lXk6+qE8tv2jAAA&hid=108





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Behr, Michael; Rosentritt, Martin; Wimmer, Jutta; Lang, Reinhold; Kolbeck et al Self-adhesive resin cement versus zinc phosphate luting material: A prospective clinical trial begun 2003, Dental Materials. May2009, Vol. 25 Issue 5, p601-604.

• The literature demonstrates that conventional luting of metal-based restorations using zinc phosphate cements is clinically successful.

• This study compared the clinical outcomes of metal-based fixed partial dentures luted conventionally with zinc phosphate and self-adhesive resin cement.

• Forty-nine patients (mean age 54±13 years) received 49 metal-based fixed partial dentures randomly luted using zinc phosphate or self-adhesive resin cement at the University Medical Center Regensburg.

• At study end, resin cement and zinc phosphate scores showed no statistically significant difference.

• The zinc phosphate cement performed clinically as well as self-adhesive resin cement and can be used as easily as to retain metal-based restorations over a 38-month observation period.

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References • Kenneth J. Anusavice, Phillips’

Science of Dental Materials, 11th edition

• Kenneth J. Anusavice, Phillips’ Science of Dental Materials, 7th edition

• Ronald L. Sakaguchi, John M. Powers, Craig’s Restorative Dental Materials, 11th Edition

• Theodore M. Roberson, Sturdevant’s Art and science of Operative Dentistry, 5th edition

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Zinc Polycarboxylate CementCONTENTS

• Introduction• Composition : • Setting Reaction: • Working Time / Setting Time: • Physical Properties: • Adhesion• Manipulation: • References

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Zinc Polycarboxylate Cement

• Old ADA Specification no. 51- Zinc Polycarboxylate Cement

• New ADA Specification no.96/ ISO Specification no. 9917 :1991- Dental water based cements

• ISO Specification no. 9917-2 :1998- Dental water based cements- part 2: Light activated cements

• ISO Specification no. 4049 :2000- Polymer based filling, restorative and lutings materials

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Introduction

• Zinc Polycarboxylate cement is also known as Zinc Polyacrylate cement

• In 1963, Dennis Smith, a British researcher, developed the first polyelectrolyte cement that set by the reaction of metal oxides and acidic water-soluble polymers.

• First cement to have the property of adhesion to tooth structure.

• Primarily used for cementation of restoration • Also used as thermal insulating bases• Formulation Components: Powder and Liquid• Reaction type: Acid-base reaction

SMITH, D.C.: A New Dental Cement, Br Dent J 125: 381-384, 1968. Smith DC. A new dental cement. Br Dent J 1967;123:540–1.

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Composition Powder

• ZnO Principal constituent • MgO/ Stannic oxide Reduce temperature in calcination• Bismuth oxide/ Aluminiun oxide• Stannous Fluoride Increases strength

Liquid • Aqueous solution of Polyacrylic acid or• Coploymer of acrylic acid with other carboxylic acids such as Itaconic and

tartaric acids• Sodium hydroxide to control the pH which in turn controls viscosity• Acid concentration varies from 32%-42%.• Molecular weight of polyacids ranges from 30,000-50,000

Kenneth J. Anusavice, Phillips’ Science of Dental Materials, 11th edition

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Water Settable Cements

• Polyacrylic acid is freeze dried and powdered to be mixed with the powder component

• The liquid component contains water • When the powder is mixed with the liquid,

polyacrylic acid reacts in the same way as conventional polycarboxylate cement.

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Manufacturing process:

• The powder is manufactured by sintering together the ingredient powders to reduce the reactivity. Sintering is done at 1000oC – 1400oC for 4-8 hours.

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Setting Reaction:

• The setting reaction of this cement involves particle surface dissolution by acid that releases zinc ,magnesium ions and tin ions.

• These ions bind to the polymer chain via the crosslinked carboxyl groups.

• The set cement is zinc polyacrylate ionic amorphous gel matrix,surrounded by unreacted powder particles.

• The gel is bound by electrostatic interactions rather than by stronger specific ion binding.

• The setting reaction is accelerated by warm atmosphere and vice-versa.


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Bonding to tooth structure

• The cement bonds to the tooth chemically

• The mechanism is thought to be analogous to the setting reaction of this cement

• The polyacrylic acid is believed to react with calcium ions via the carboxyl groups on the surface of enamel or dentin.

• Thus the bond strength to enamel is greater than to dentin.


48

Film thickness

• When zinc polycarboxylate cements are mixed at the recommended P/L ratio they appear to be much more viscous than a comparable mix of zinc phosphate cement.

• However, zinc polycarboxylate mix is classified as pseudoplastic and it undergoes thinning at an increased shear rate.

• This means that the action of spatulation and seating reduces the viscosity of the cement and the procedure can yield a film thickness of 25 mm or less

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Working time/Setting Time: • Working time is much shorter

than zinc phosphate (ie. Approximately 2.5 min)

• Setting time is 7-9 min from the start of mixing.

• Lowering the temperature of the reaction can increase the working time which is achieved by cooling the powder

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Manipulation• The cement supplied with the polyacrylic acid in the

liquid are usually mixed at a P/L ratio of 1:1 to 2:1• The mixed cement is pseudoplastic ie the viscosity

decreases as the shear rate increases or the flow increases as the spatulation increases or as the force is placed on the material.

• The correct consistency is found in the mix that is viscous but that will flow back under its own weight when drawn up with a spatula.

• Dispense the liquid immediately before the mixing to prevent evaporation of water and subsequent thickening.


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Manipulation• A nonabsorptive surface such as glass slab or a treated paper

will keep all the liquid available for the reaction and facilitate spatulation.

• Mix cement within 30-60 seconds with half to all of the powder incorporated at once to provide maximum working time (2.5-6 minutes)

• Extend the working time to 10-15 minutes by mixing on a glass slab chilled to 4oC

• The strength of the mix is not compromised by this technique

• Some manufacturers supply the cement as a capsulated Powder Liquid System for mixing in a mechanical mixer


52

Manipulation• The cement liquids for zinc polycarboxylate are quite viscous. The

viscosity of the liquids vary from one brand to another .• Generally 1.5 parts of powder to 1 part of liquid by weight is

considered .• The glass slab affords an additional advantage over paper pads

because once cooled the slab maintains the temperature over a longer time

• Under no circumstances should the liquid be stored in refrigerator • The liquid should not be dispensed at a very early stage since it

loses water to the atmosphere.• The powder is rapidly incorporated into the liquid in large

quantities


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Manipulation• The figure shows a consistency of cement

immediately after completion of 30 seconds mix as compared to a consistency after a longer mixing time

• If good bond to tooth structure is to be achieved the cement must be adapted to the tooth structure

• Cement to be used should be glossy in appearance.

• Loss of surface shine and stringiness indicates progressed working time where proper wetting of the tooth surface is not possible hence should not be used.


• The excess should be removed only on hardening since an attempt to remove in rubbery stage lifts the cement.• It is important that the outer surface of the prosthesis be coated carefully with a thin layer of separating medium such as petroleum jelly to prevent excess cement from adhering to its surface.

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Properties of dental cements used for bonding applications

ANSI/ADA specification 8

1. Setting time - 5.0 min (minimum)

2. Film thickness – 25 micron (maximm)

3. 24hr compressive strength -69 Mpa

4. 24hr diametrical tensile strength N\A

5. Elastic Modulus N\A

6. Solubility in water- 0.20 wt%(max)

7. Pulp response- should not be irritant

Zinc Polycarboxylate

1. Setting time - 6.0 min

2. Film thickness– 21 micron

3. 24hr compressive strength -55 Mpa

4. 24hr diametrical tensile strength 6.2 Mpa

5. Elastic Modulus 5.1 Gpa

6. Solubility in water- 0.06 wt%

7. Pulp response- mild


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Strength

• The 24 hour compressive strength is lower than that of zinc phosphate, however the tensile strength is about 40% higher than that of zinc phosphate.

• The modulus of elasticity of zinc polycarboxylate cement is about 1/3rd that of zinc phosphate cements mixed to a luting consistency

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Solubility• The solubility of Zinc Polycarboxylate cement in

water is low but in organic acids of less than 4.5 pH, the solubility increases.

• Also, a reduction in the P/L ratio results in a significantly higher solubility and disintegration rate in the oral cavity

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Biological Considerations

• pH of the liquid is approximately 1.7.• That of set cement is also higher than zinc phosphate• Despite this Polycarboxylate cement is less irritant to

the pulp• This might be because the pH rises more rapidly.• Also, larger size of polyacrylic acid molecule compared

to that of phosphoric acid molecule may limit its diffusion through the dentinal tubules.

• Polycarboxylate cement has excellent biocompatibility with the pulp.

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Adhesion• The cement bonds chemically to the tooth structure.• This is due to the carboxyl group in the polymer molecules to

chelate with calcium ions in the tooth structure.

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Adhesion• Thus the bond strength is is greater to enamel than to dentin

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Adhesion• The bond strength to enamel ranges from 3.4 to

13.1 MPa while to dentin is 2.07MPa.• Clean dry surface of tooth is a prerequisite since

saliva reduces bond strength• Since the bonding is with tooth structure there

should not be any remnant of previous restoration• Also, adhesion to stainless steel is good which is

why it is used in cementation of fixed appliances in orthodontics

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Surface Preparation and Retention

• Despite the adhesion property polycarboxylate cement is not superior to zinc phosphate cement in the retention of cast noble metal restorations.

• The cement does not bond to the noble metal when chemically contaminated as cast or pickled condition.

• Examination of the fractured surface shows that failure occurs at cement-metal interface rather than at cement-tooth interface.

• Thus cleaning with 10% polyacrylic or maleic acid for 10-15 seconds is recommended.

• Surface of tooth should be isolated, cleaned and blotted dry before placement of cement. Blottin gis considered sufficient as adrying procedure

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Optical properties

• Radio opaque • This is due to unreacted zinc oxide particles

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Uses

1. Primarily for luting permanent restorations.

2. As bases and liners.

3. Used in orthodontics for cementation of bands.

4. Also used as root canal filling in endodontics

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Frederick M. Mclntyre, Soren f, Sorensen, I. Malcolm Carter, Robert R. lohnson, The Effect of Film Thickness on the Bond Strength of Polycarboxylate Cement, Int J Prosthodont 1994:7:461-467.

• This study examined the bond strength ot polycarboxylate cement when used to cement gold alloy specimens to dentin. The film thickness was controlled and varied over a range of 10 to 150 μm.

• Tensile and shear bond strengths were measured and, contrary to anticipated results, there was an increase in bond strength as the film thickness increased.

• In this study, the bond strength of polycarboxylate cement as it relates to film thickness is evaluated in relationship to the clinically significant value of 50 μm over the thickness range of 150 μm.

• Polycarboxylate cement exhibited lower bond strengths for film thickness less than 50 μm as compared with film thickness greater than 50 μm.

• Porosities had a significant effect on the bond strength of polycarboxylate with cement film thickness of less than 50 μm as compared with cement film thickness greater than 50 μm over the cement film range of 150 μm

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Dorothy McComb, Dennis C. Smith, Comparison of physical properties of polycarboxylate-based and conventional root canal sealers, Journal of Endodontics,Volume 2, Issue 8 , Pages 228-235, August 1976

• Several physical properties of nine commercial root canal sealers were evaluated in vitro and were compared with those of two experimental endodontic materials based on polycarboxylate formulations.

• Flow, setting time, compressive strength, radiopacity, adhesion to root dentin, and solubility were evaluated.

• The zinc oxide eugenol root canal sealers were typically of low strength and high solubility. These sealers and the Diaket polyvinyl resin sealer showed no adhesion to dentin. The epoxy resin AH26 showed superior properties with respect to strength, flow, radiopacity, and adhesion; solubility of this material was high.

• The polycarboxylate formulation showed significantly higher values over the commercial sealers in properties of strength, adhesion, and reduced solubility. The tensile adhesive bond strength of the polycarboxylate to root dentin was twice that of AH26

http://www.jendodon.com/article/S0099-2399(76)80162-8/abstract



http://www.jendodon.com/issues?issue_key=S0099-2399(76)X8151-8

http://www.jendodon.com/issues?issue_key=S0099-2399(76)X8151-8

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Berrin Ors Orug, PhDa/Mehmet Baysallar, Deniz Cetiner, Ayten Kucukkaraaslan, Berna Dogan , Increased Antibacterial Activity of Zinc Polycarboxylate Cement by the Addition of Chlorhexidine Gluconate inFixed Prosthodontics, Int J Prosthodont 2005;18:377–382.

• This study evaluated the antibacterial activity of water-activated zinc polycarboxylate cement with adjunctive 0.12% chlorhexidine gluconate on the subgingival microbiota in fixed partial dentures

• In the control group, the subgingival microbiota altered to closely resemble the flora of chronic gingivitis (increased proportions of gram-negative anaerobes such as Prevotella intermedia, Fusobacterium nucleatum) by 13 weeks.

• In contrast, the microflora at test sites comprised predominantly gram-positive facultative cocci and rods at 13 weeks.

• This study demonstrated that the addition of 0.12% chlorhexidine gluconate may enhance the antimicrobial action of polycarboxylate cements to ensure the maintenance of a microflora compatible with periodontal health, at least up to 13 weeks post-cementation

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References • Kenneth J. Anusavice, Phillips’

Science of Dental Materials, 11th edition


• Ronald L. Sakaguchi, John M. Powers, Craig’s Restorative Dental Materials, 11th Edition

• Theodore M. Roberson, Sturdevant’s Art and science of Operative Dentistry, 5th edition

Documents

Zinc Phosphate Polycarboxylate