DENTAL CEMENTS

DR EMIL SANTHOSH MANI

In Dentistry the term cement has been applied traditionally to

powder / liquid materials which are mixed to a paste consistency, set to hardness and used clinically to restore teeth and attach preformed restorations in or on the teeth.

Dental cements, in the recent years has become restricted to those materials which are employed to bond inlays, crowns, bridges, posts and facings in or on the tooth and to retain orthodontic Bands and retainers, however secondary applications of these cements include cavity linings, bases and temporary fillings.

These different applications make varying demands on manipulative properties, working and setting time and resistance to mechanical breakdown and dissolution. Thus some materials are better suited to some application than others.

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The word `cement’ as used in this context, conveys the idea not only of a bonding agent but also the concept implied in the word `lute’ that is , the additional requirement of gap filling and sealing.

HISTORY

In the year 1858 zinc oxide eugenol was introduced. In the year 1880 silicate cement was used as a restorative cement for esthetic purpose for anterior teeth, it was also used for posterior tooth restoration.

• In the year 1902 zinc phosphate cement was used as temporary restorative cement as well as thermal insulating bases.
• In the year 1936 calcium hydroxide was used as a restorative cement as well as a pulp capping agent.
• In the year 1950 acrylic resin cement was introduced.

• In the year 1958 reinforced zinc oxide eugenol was introduced. This cement was used for temporary and permanent restorative purposes.
• In the year 1968 zinc poly carboxylate was introduced.

• The year 1969 saw the introduction of glass ionomer cement. After the introduction of this cement most of the other cements took a back seat on permanent restorative material. This cement had a capacity to remineralise dentine therefore it was used as a pit and fissure sealant as well.

In the year 1970 composite resin cement was introduced. This was visible light cured material, but, as technology advances different type of light cure composite material is available

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DEFINITION

Different definitions are given by different author. Some of the important definitions are:-

According to the text book by Anusavice

“Substance that hardens to act as a base, Liner, filling material or adhesive to bind devices and prosthesis to tooth structure to each other ”

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According to Karl. F. and Jack Mons

“A cement is commonly considered as a substance that holds 2 surfaces together, it also serves as an agent as esthetic restorative material, thermal insulator, temporary restorative material and medicament for pulpal protection under larger restorations.”

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According to the text book by CRAIG

"A non metallic material used for luting, filling permanent or temporary restorative purposes, made by mixing components into a plastic mass that sets or as an adherent sealer in attaching various dental restorations in or on the tooth"

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REQUIREMENTS OF A DENTAL CEMENTS:-�

• Should be non toxic, and non irritant to pulp and tissues.
• Should be insoluble in saliva and liquids taken into the mouth.
• Mechanical properties: these must meet the requirements for their particular applications e.g.: a cement base should develop sufficient strength rapidly to enable a filling material to be packed on it.

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• Protection of pulp from insults. Thermal insulation, a cement used under a large metallic restoration should protect the pulp from temperature changes. Chemical protection, should be able to prevent penetration into the pulp of harmful chemicals from the restorative material. Electrical insulation under a metallic restoration to minimize galvanic effects
• Optical properties, for cementation of a translucent restoration, eg: porcelain crown. The optical properties of the cement should stimulate those of tooth substance.

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• Cement should be ideally be adhesive to enamel and dentine, and to gold alloys, porcelain and acrylics, but not to dental instruments.
• Should be bacteriostatic in a cavity with residual caries.
• Should have an obtunding (soothing) effect on the pulp
• Rheological properties. A luting cement should have sufficiently low viscosity to give a low film thickness.

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CLASSIFICATION

I CLASSIFICATION OF DENTAL CEMENTS BASED ON THEIR FUNCTIONS – GIVEN BY CRAIG

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II CLASSIFICATION BASED ON USES OF DENTAL CEMENTS – SKINNER�

III CLASSIFICATION OF DENTAL CEMENTS GIVEN BY E.C. COMBE �

• Acid – base reaction cements:

Zinc oxide – this can react with a range of liquid

Ion leachable glasses – aluminosilicate, GIC, silicates

• Polymerising materials:

Cyanoacrylates

Dimethacrylate polymers

Polymer-ceramic composites

• Other materials:

Calcium hydroxide

Guttapercha

Varnishes

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IV CLASSIFICATION BASED ON COMPONENTS AND SETTING REACTION - KENNETH J.ANUSAVICE �

�ADA SPECIFICATION HAS FURTHER CLASSIFIED CEMENTS AS � �

Type 1: Fine grain for cementation, luting.

Type 2: Medium grain for bases, orthodontic purpose.

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• OTHER CLASSIFICATION

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• ACCORDING TO Mc CABE

1. Cement based on phosphoric acid

a. zinc phosphate cements b. silicophosphate cement

c. copper phosphate cement

2. Cement based on organometallic chelate compounds

a. zinc oxide eugenol b. ortho- ethoxybenzoic acid (EBA) cements

c. calcium hydroxide cements

3. Cements based on polyalkenoic acids

a. polycarboxylate cement

b. glass ionomer/ polyalkenoate cements.

4. Resins

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ZINC PHOSPHATE CEMENT �

INTRODUCTION

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• Zinc phosphate is the oldest of the luting cements, and thus it serves as a standard with which newer cements can be compared.

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• The terms "Crown and Bridge" and "Zinc Oxyphosphate" have also been used for this cement.

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ZINC PHOSPHATE CEMENT �

CLASSIFICATION

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ADA Sp. No. 3 designates them as:

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Type - I : Fine grained for luting. Film thickness should be 25um or less.

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Type-II : Medium grain for luting and filling. Film thickness should not be more than 40 um.

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ZINC PHOSPHATE CEMENT �

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AVAILABLE AS

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• Powder and liquid system
• Capsules of pre proportioned powder and liquid.
• Available in shades of yellow, grey, golden brown, pink and white.

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ZINC PHOSPHATE CEMENT

COMPOSITION

Powder

• Zinc oxide - 90.2% — Principal constituent
• Magnesium oxide - 8.2% —Aids in sintering
• Other oxides (like bismuth trioxide,calcium oxide, barium oxide, etc.) - 0.2% —Improves smoothness of mix
• Silica - 1.4% —Filler, aids in sintering

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ZINC PHOSPHATE CEMENT

COMPOSITION

Liquid

• Phosphoric acid - 38.2% — Reacts with zinc oxide
• Water - 36.0% —Controls rate of reaction
• Aluminium phosphate -16.2% — Buffers, to reduce rate of reaction
• Aluminium - 2.5%
• Zinc - 7.1%.

ZINC PHOSPHATE CEMENT

MANUFACTURE

• The ingredients are mixed and heated at temperatures between 1000°C and 1400°C (sintering). The cake formed is then ground into a fine powder (fritting).
• The liquid is produced by adding aluminium and sometimes zinc or their compounds into orthophosphoric acid solution. The aluminium complexes with phosphoric acid to form a zinc aluminophosphate gel (with­out aluminium, a non-cohesive, crystalline structure matrix of hopeite, i.e. Zn3(PO4)2.4H2O, would be formed). The reaction is exothermic.

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���ZINC POLYCARBOXYLATE CEMENT ��

• INTRODUCTION
• In a quest for an adhesive luting agent that can bond strongly to tooth structure, Zn polycarboxylate cement was eveolved as the 1^st cement system that developed an adhesive bond to the tooth structure.
• It is also called as polycarboxylate or polyacrylate cement or ASPA [ aluminosilicate polyacrylic acid cement]

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• COMPOSITION
• POWDER
• Stannous oxide
• Silica, Alumina
• Bismuth
• Stannous fluoride – improves the manipulation,Chacteristics, strength – 4.5%
• Sodium fluoride - Anticariogenic property about 1%
• LIQUID
• Aqueous solution of Polyacrylic acid
• Co-polymer of acrylic And unsaturated carboxylic acid water.

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• MANIPULATION
• The cements supplied with the polyacrylic acid in the liquid an usually mixed at a powder liquid ratio of 1.5 parts of powder to 1 part of liquid. The consistency of the mixes is creamy compared with that of zinc phosphate cements. The mixed cement is thixotropic
• NOTE : Powder liquid reactions are accelerated by the presence of heat
• Liquid consists of partially centralized dilute Phosphoric acid.
• When this liquid is exposed to a humid atmosphere, it will absorb water.
• Whereas exposure to dry air tends to result in a loss of water which will alter the property of cement.
• Some manufactures supply the cement as a pre-capsulated powder liquid system for mixing in a mechanical mixer.
• The mixer cement should be used only as long as it still appears glossy on the surface. Once the surface becomes dull,
• the cement develops stringiness and the film thickness becomes too great to seat a casting completely.

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• SETTING REACTION

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• When the powder & the liquids are mixed, the surface of the powder particles are attacked by the acid with subsequent release Zn magnesium & tin ions. They bind to the polymer chains via the carboxyl group. These ions react with carboxyl groups of adjacent polyacid chains so that a crosslinked di salt is formed & the cement sets.
• The hardened cement consists of an amorphous gel matrix in which residual powder particles are dispersed.
• Working time – approx 2.5mins
• Setting reaction – 6 to 10 mins

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• Working time – approx 2.5mins
• Setting reaction – 6 to 10 mins

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��GLASS IONOMER CEMENTS�

INTRODUCTION:

• GIC are adhesive tooth colored anticariogenic restorative materials.
• First usuable GIC system was formulated in 1972 by Wilson & Kent
• Glass ionomer is the generic name of a group materials based on the reaction of silicates glass powder & polyacrylic acid.

Synonyms

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• Polyalkenoate cement

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• ASPA (AluminoSilicate polyacrylic acid)

DEFINITION

• “Glass ionomer is a water- based material that hardens following an acid base reaction between fluroaluminosilicate glass particles and an aqueous solution of polyacid.”

- Davidson and Mjor

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CLASSIFICATIONS

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I. According to Wilson and McLean (1988) :

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1. Type I - Luting

2. Type II

a) Aesthetic filling material

b) Reinforced filling material

3. Type III – Lining, base and fissure sealant

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II. According to Sturdvent :

1) Traditional /Conventional

2) Metal modified GIC

a. Cermet

b. Miracle mix

3) Light cured GIC

4) Hybrid (Resin modified GIC)

5) Poly acid modified resin composite (or) compomer.

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According to clinical use as:

Type I - Luting

TYPE II - Restorative

Type III - Liner/ Base

Type IV - Pit & Fissure Sealant

Type V - Luting for Orthodontic Purpose

Type VI - Core build up material

Type VII - High fluoride releasing command set

Type VIII - ART

Type IX - Geriatric & Paediatric GIC

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• Availability:
• Powder/Liquid bottles
• Pre-proportioned Powder/Liquid in capsules
• Light cure system
• Powder /distlled water (water settable type)

CONVENTIONAL GLASS IONOMER CEMENT

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• According to G.J Mount “Glass ionomer refers to a material in which an acid-base reaction contributes to as setting process which takes place within a clinically acceptable time”.

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APPLICATION

1. Anterior esthetic restorative material for Class III cavities.

2. Restorative material for eroded areas and Class V restorations

3. As a luting agent for restorations and orthodontic brackets.

4. As liners and bases.

5. For core build up.

6. To a limited extent as pit and fissure sealants.

7. Intermediate restorative material.

8. Atraumatic restorative treatment (ART) technique.

COMPOSITION

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• The composition of glass ionomer cements is complex and varied. The basic component is a calcium aluminosilicate glass containing fluoride.
• The acid is a polyelectrolyte, which is a homo polymer or copolymer of unsaturated carboxylic acids known as alkenoic acids.

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POWDER

(Calcium Fluroaluminosilicate)

• Alumina (28.6%) Alumina: Silica --> 1:2
• Silica (41.9%)
• Fluoride
• Calcium fluoride (15.7%)
• Aluminium phosphate (3.8%)
• Cryolite
• Na⁺, K⁺, Ca²⁺

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LIQUID

• Polyacrylic acid (40 to 50%) polyacrylic: itaconic-- > 2:1
• Itaconic acid
• Maleic acid
• Tricarboxylic acid
• Tartaric acid(5-15%)
• Polyphosphates
• Metal oxides
• Water

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SETTING REACTION

• When the powder and liquid are mixed to form a paste, the acid attacks the surface of the glass ionomer particles. Calcium, aluminium, sodium and fluoride ions are leached into the aqueous medium.
• Polyacrylic acid chains are cross-linked by calcium ions and form a solid form.

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STAGES OF CEMENT -FORMING CHEMISTRY :

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STAGES DESCRIBED BY WILSON AND CRISP

1. Decomposition :

Decomposition of the glass and release of cement forming metal ions (Al+3 and Ca+2). 20-30%of the glass is attacked. As the cations are withdrawn the glass network breaks down into silicic acid, which polymerizes at the surface of the glass powder.

2. Migration :

Migration of these metal ions into the aqueous phase of the cement. The acid attack occurs preferentially at Ca- rich sites and thus the concentration of these ions increases. The ph and the viscosity of the paste also increases.

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3. Gelation :

Gelatin of the polyacid by the metal ions leading to set. At a critical ph and ionic concentration, precipitation of insoluble polyacrylates begins to take place. When this process reaches a certain stage, the cement sets. Calcium polyacylate is responsible for the initial set.

Gelation may simply be caused by the multivalent Al+ and Ca+ ions displacing or partly displacing the various spheres of hydration that interpose themselves between the cation-anion pairs. Chain entanglement, weak ionic cross-linking and hydrogen bonds are all involved in matrix formation.

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4. Maturation :

Even after 24 hours a further slow maturation takes place and in the first few days translucency develops further as does resistance to desiccation and acid attack.

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FACTORS AFFECTING THE RATE OF SETTING :

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The rate of setting depends on a number of manufacture-controlled variables such as:

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1)Glass composition :

Especially the alumina: silica ratio and fluoride content. Up to a limiting value, the higher this ratio, the faster the set and shorter the working time.

2)Particle size of the glass powder :

The finer the powder the faster the set and shorter the working time.

3)Addition of tartaric acid :

Sharpens the set without shortening the working time.

4)Relative proportions of the constituents :

The greater the proportion of the glass and lower the proportion of the water, the faster the set and shorter the working time.

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5)Temperature of mixing :

The higher the temperature the faster the set and shorter the working time. The setting will be faster when the powder is finer, the amount of water in the mix is lower, the proportion of powder in the mix is greater and the temperature of mixing is higher.

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PROPERTIES

1) Mechanical properties

a) Compressive strength

Because of differences in the powder-liquid ratio GIC used for different applications show variations in their physical properties. Restorative GIC has a compressive strength of 150 MPa. The luting GIC has a lower compressive strength of about 85 MPa.

b) Tensile strength Luting type—6.2 MPa Restorative type—6.6 MPa

c) Hardness (49 KHN) Less harder than silicates. The hardness is also far lower when compared to composites. Fracture toughness A measure of energy required to produce fracture. Type II GIC’s are far inferior to composites in this respect.

d) Elastic modulus (7.3 GPa) It is a measure of their stiffness. The MOE is half that of zinc phosphate cement. Wear resistance They are more susceptible to tooth brush abrasion and occlusal wear when compared to composites.

2) Solubility and disintegration

The initial solubility is high due to leaching of intermediate products. The complete setting reaction takes place in 24 hours; therefore, the cement should be protected from saliva in the mouth during this period. Glass ionomer cements are more resistant to attack by organic acids. � Solubility in water for Luting type—1.25% wt. � Solubility in water for Restorative type—0.4% wt.

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3) Adhesion

It adheres well to enamel and dentin. Shear bond strength ranges from 3–5 MPa. Mechanism of adhesion Glass ionomer bonds chemically to tooth structure. The exact mechanism has not been fully understood. The bonding is due to the reaction between the carboxyl groups of the polyacids and the calcium in the enamel and dentin. The bond to enamel is always higher than that to dentin, probably due to the greater inorganic content of enamel and its greater homogeneity.

4) Esthetics

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Esthetically they are inferior to silicates and composites. They lack translucency and have a rough surface texture. They may stain with time. The restorative GICs are available in different shades. The esthetics are sufficient for restoring cervical lesions and minor defects in nonesthetic zones. The luting cement is more opaque than the restorative cement.

5) Biocompatibility

Pulpal response to GIC is classified as mild. Type II glass ionomers are relatively biocompatible. The pulpal reaction is greater than that from zinc oxide eugenol cements but less than that produced by zinc phosphate cement. Polyacids are relatively weak acids. The water settable cements show higher acidity. Luting type GIC is more acidic than Restorative type because of the lower powder/liquid ratio. Occasionally sensitive patients show a painful response to GIC luting cement.

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Pulp protection In deep cavities, the smear layer should not be removed as it acts as a barrier to acid penetration. Deep areas are protected by a thin layer of calcium hydroxide cement.

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6) Anticariogenic properties

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Type II glass ionomer releases fluoride in amounts comparable to silicate cements initially and continue to do so over an extended period of time. In addition, due to its adhesive effect they have the potential for reducing infiltration of oral fluids at the cement-tooth interface, thereby preventing secondary caries.

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