Dental cement

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Dental cement

• Dent Mat. II

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Topic

• General requirements for dental cements
• Classification of dental cements
• Component and properties
• Setting reaction
• Mixing process
• The uses of dental cements

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Definition

• Dental cements materials made from two
  components, powder and liquid, mixed together.

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Uses of dental cements

• Luting agent
• Temporary cement
• Permanent cement
• Pulp protection or cavity sealer
• Cavity varnish
• Liner
• Base

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Uses of dental cement

• Filling
• Temporary filling
• Permanent filling
• Others
• Root canal sealer
• Calciumhydroxide cement
• Bite registration material

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Luting agent

• Luting the use of moldable substance to seal a
  space between two component.
• Most dental treatment necessitate attachment of
  prostheses to the teeth by means of luting agent.

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General requirements for luting agents

• Biocompatibility
• Retention
• High tensile strength, fracture toughness,
  fatique strength
• Good marginal seal

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General requirements for luting agents

• Low film thickness
• Ease of use
• Radiopacity
• Aesthetics

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Film thickness

• The thickness of film between two flat surface
• The maximum allowable thickness is 25 µm (ADA
  specification No. 96)
• Low film thickness value is preferred

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Cement base

• A thick layer of cement (gt0.75mm) is applied
  under restoration to protect pulp against
  injuries.
• The base should be strong enough to resist the
  condensation force during the placement of
  restoration.
• Well insulation ability
• Good sealing

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Classification of dental cements

• Conventional cement
• Zinc phosphate cement
• Zinc oxide-eugenol cement
• Polycarboxylate cement
• Glass ionomer cement
• Resin-base cement
• Resin cement
• Resin modified glass ionomer cement

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Conventional cement

• Typically powder/liquid system
• Liquid is an acid
• Powder is a base insoluble in oral fluid
• When mixed together ? Acid-base reaction

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Zinc Phosphate cement
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Zinc phosphate cement
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HEAT
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Unreacted ZnO
Unreacted ZnO
Unreacted ZnO
Unreacted ZnO
Zinc aluminophosphate matrix
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Setting reaction

• Exothermic reaction
• Adding of water can accerlate the reaction.
• Loss of water can lengthen the setting reaction.

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Working time and setting time

• Working time commonly is 3-6 minute
• Setting time is 2.5-8 minute(ADA specification
  No.96)
• Depending on the manufacturer instruction

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How to extend the setting time ?

• Reducing powder/ liquid ratio not recommended
• Mixing on the cool glass slap no moisture
• Mixing over a large area.
• Mixing cements in increments.

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Mixing procedure

• There are three steps
• First add the small amount of powder into the
  liquid
• To achieve the slow neutralization of the liquid.
• To control the reaction.

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Mixing procedure

• Second Larger amount of powder is added to
  liquid
• For further saturation of liquid to newly form
  zinc phosphate.
• This steps may not effect by heat released from
  the reaction.
• because of the less amount of unreacted acid

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Mixing procedure

• Finally the small amount of powder is added
  again
• To control the optimum consistency

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Characteristic properties
ADA specification NO.8 for Zinc phosphate cement
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Effects of manipulation on some properties.
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Biocompatibility

• Acid can penetrate into the dentinal tubule ?
  irritate pulp
• pH of cement
• Liquid 2.0
• 3 minutes after mixing 4.2
• 1 hour 6
• 48 hours 7

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Modified zinc phosphate cement

• Fluoride cement
• Add Stannous fluoride
• Higher solubility/ Lower strength
• Zinc silicophosphate
• Zinc phosphate Silicate
• Higher strength/ lower solubility
• Fluoride released
• Translucency

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Clinical applications

• Zinc phosphate cement
• Luting agent
• Base and temporary filling
• Modified zinc phosphate
• Luting prostheses
• Luting the orthodontics band

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Zinc oxide-eugenol cements

• Lower strength than Zinc phosphate cement.
• Sedative effect
• Usually used as temporary filling

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Zinc oxide-eugenol cement

• Simple ZOE
• Reinforced ZOE
• EBA cement

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Compositions of simple ZOE

• Powder
• Zinc oxide
• Rosin reduce the brittleness of the set cement
• Zinc stearate plastcizer
• Zinc acetate improve strength
• Liquid
• Eugenol and olive oil

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Setting reaction

• First
• ZnO Eugenol -- water? Zn(OH)2
• Second
• Zn(OH)22HE ? ZnE2H2O

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Setting reaction

• Water accelerates the reaction
• Zinc eugenolate is easily hydrolized by moisture

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Manipulation

• Paste/paste
• Mix two equal pastes together until it obtains
  the homogeneous color.
• Powder/liquid
• Usually 4/1 for maximum strength
• Mix the large increment, firstly
• Not require cool glass slap

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Classification

• Type I
• Temporary luting cement
• Type II
• Permanent cementation
• Type III
• Temporary restoration for a few days
• Type IV
• Cavity liner

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ZOE
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Specification requirements
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Reinforced ZOE

• Used as the intermediate restorative materials
  (IRMTM)
• Add 10-40 resin polymer in the powder for
  strengthening the set cement
• Compressive strength 35-55 MPa

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EBA cement

• Powder
• Add 20-30 of aluminium oxide
• Liquid
• Add 50-60 ethoxybenzoic acid in eugenol
• Compressive strength 55-75 MPa

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Clinical applications

• Base
• Temporary cementation
• Permanent cementation
• If cement contains eugenol, it is not to use with
  resin restorative material.

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Zinc polycarboxylate cement

• Or called Zinc polyacrylate cement
• The first adhesive cement
• Bond to tooth structure and metal
• More biocompatibility than zinc phosphate cement
• Polyacrylic acid have more molecular weigth
• Moderate strength/ moderate solubility

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Composition

• Powder the same as zinc phosphate cement
• Zinc oxide
• Magnesium oxide
• Stannous fluoride
• Liquid
• Aqueous solution of polyacrylic acid
• Other carboxylic acid

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Manipulation

• Mix first half of powder to liquid to obtain the
  maximum length of working time.
• The reaction is thixotropic
• The viscosity decreases when the shear rate
  increases

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Setting reaction

• Like zinc phosphate cement
• Retarded by cool environment

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Bonding to tooth structure

• The polyacrylic acid is believed to react with
  calcium ion via the carboxyl group.
• The adhesion depends on the unreacted carboxyl
  group.

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Specification requirements

• Setting time at 37OC 9 minutes
• Maximum film thickness 25µm
• Minimum compressive strength 50 MPa
• Maximum solubility 0.2

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Applications

• Cement inlays or crowns
• Used as base
• Temporary filling
• Lute the stainless steel crown

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Glass ionomer cement

• Or called Polyalkynoate cements
• Conventional glass ionomercement
• Resin-modified glass ionomer cement RMGICs
• Powder Liquid/ Powder water/ Encapsulated

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Composition

• Powder
• Calcium aluminum fluorosilicate glass
• Liquid
• Polyacid
• Copolymer of polyacrylic / itaconic acid
• Copolymer of polyacrylic / maleic acid
• Add tartaric accelerator

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Setting reaction

• There are three stages
• Dissolution
• Gelation
• Hardening.
• Water hardening or water setting

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Dissolution
Polyacid liquid
Hydrogen ions
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Gelation
Polyacid liquid
-COOH
Ca2
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Gelation

• Calcium ions have more reactivity than aluminium
  ions.
• This is critical phase of contamination.

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Hardening
Polyacid liquid
-COOH
Al3
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Hardening

• Last as long as 7 days.
• The reaction of aluminium ions provides the final
  strength of set cement.

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Glass core
Cross-linked polyacid
Silica gel
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Properties

• Film thickness is similar or less than zinc
  phosphate cement.
• Setting time 6 to 8 minutes from start of mixing.
• Less pulpal irritation.
• Bacteriocidal or bacteriostatic.
• Prevent caries.

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Strength

• The 24-hour compressive strength is greater than
  zinc phosphate cement.
• The compressive strength increase to 280MPa
  between 24 hours to 1 year after initial setting.

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Bonding

• It can be chemically bonded to the tooth
  structure.
• The mechanism of bonding is the same as
  polyacrylate cement.
• The dentine bond strength may be lower than
  polyacrylate because of technique sensitivity.

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Modified GI

• Cermet
• Combination of glass and metal
• No significantly improve the strength
• More wear resistance and short setting time
• Resin-modified GI

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Resin-modified glass ionomer cement

• Add polymerizable function groups
• Both chemical light curing
• Overcome moisture sensitive low early strength
• Names Ligth cured GICs, Dual-cured GICs,
  Tri-cured GICs, Hybrid ionomer, Compomers,
  Resin-ionomers

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• Setting reaction
• Polymerization
• initial setting
• Acid-base reaction
• maturing process final strength
• Heat released from the polymerization reaction.

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Properties

• Higher strength than conventional GI
• Higher adhesion to resin material
• Less water sensitivity
• Can be polished after curing

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Relative properties of a glass ionomer and a
resin-modified GI cements
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Applications

• Type I Luting agent
• Type II Filling material
• Type III Base and liner

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Conventional GI for cementation
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GI filling material
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Adhesive resin cement

• Occur later from the direct filling resin
• Become popular because of the improved
  properties, high bond strength.
• Resin cement is flowable composite resin.

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Composite resin cement

• Composite
• Resin matrix inorganic filler

Silane coated
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Composition

• Filler
• Silica
• Matrix
• Bis-GMA (polymer)
• The fillers binds with matrix by
• silane coupling agent

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Setting reaction

• Polymerization
• Chemical activation
• Light activation
• Dual activation chemical and light

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Preparations

• Powder / liquid
• Chemical, light, or dual cure
• 2 paste system base / catalyst
• Chemical, light, or dual cure
• Single paste
• Light cure

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Bonding system

• Bond with the tooth surface by enamel an dentine
  bonding system.
• Bond with metal by using metal primer.
• Bond with ceramic restoration by treating the
  surface of porcelain with silane coupling agent

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Properties

• Very good bond strength
• High compressive strength
• Water sensitive
• Might irritate pulpal tissues

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Applications

• Tooth color filling materials
• Luting cements

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Calcium hydroxide cement

• Used as base and liner
• High pH value
• Good biocompatibility

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Composition

• 2 Pastes system
• Base
• Salicylate ? reaction
• Calcium tungstate and barium sulfate
• ? radiopacity
• Catalyst
• Calcium hydroxide

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Properties

• Lower compressive strength than others
• Resist to the condensation force of amalgam
  filling
• High pH 9.2-11.7 Alkaline
• Bactericidal
• High solubility

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Properties

• Stimulate the secondary dentine formation in the
  area of thin dentine lt0.5mm
• Stimulate the dentine formation in the
  exposed-pulp lesion Direct pulp capping

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Comparable properties of cements
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Compressive strength MPa
Zhen Chun Li and Shane N. White, 1999
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Bond strength
Separation forces MPa
Sule Ergin and Deniz Gemalmaz, 2002
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Film thickness µm
Shane N. White, Zhaokun Yu, 1992
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Others

• Solubility
• ZOE gt Polycarboxylate gt Zinc phosphateGIC gt
  Resin cement
• Irritation to pulp tissues
• ResinZinc phosphate gt GIC gt Polycarboxylate gt
  ZOECalcium hydroxide

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References

• Textbooks
• Kenneth J. Anusavice
• Phillips science of dental materials
• 11th edition
• W.B. Saunders company 2003

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References

• Textbook
• Robert G. Craig
• Restorative dental materials
• 9th edition
• Mosby company 1993

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References

• Textbook
• Richard van Noort
• Introduction to dental materials
• 2nd edition
• Mosby company 2002

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References

• Journals
• Li ZC, White SN. Mechanical properties of dental
  luting cements. J Prosthet Dent
  199981(5)597-609
• White SN, Yu Z. Film thickness of new adhesive
  luting agents. J Prosthet Dent 199267(6)782-90
• Ergin S, Gemalmaz D. Retentive properties of five
  luting cements on base and noble metal copings. J
  Prosthet Dent 2002885491-97