Dental Cements Flashcards
Uses of dental cements
1- luting or cementing agent
2.Cavity liners (materials that placed as thin coating layer to
provide a barrier against chemical irritation), and bases to
protect the pulp from thermal, chemical and irritation.
Requirements of Dental Cements
- Non-toxic and non-irritant + obtudent
- Antibacterial effect.
- Adhesion to the tooth
4.Optical properties - Protect the pulp
- Insoluble in saliva
7- used as filling materials
Classification Of Dental Cements
Are generally classified according to their chemical ingredient
- Cements based on zinc oxide.
- Cements based on aluimino-silicate glasses.
- Resin cements.
- Calcium hydroxide (liner and pulp capping)
- Cavity varnishes.
Zinc Oxide-Eugenol Cement characteristics
PH approximately 7 , also they are characterized by their sedative (obtundent)
Zinc Oxide-Eugenol Cement types
- Unmodified zinc oxide-eugenol cement.
- Resin-modified zinc oxide-eugenol cement.
- Ortho-ethoxy benzoic acid alumina-modified zinc oxide-
eugenol (EBA- ZOE).
for patients sensitive to eugenol use
carboxylic acid
Applications of Zinc Oxide-Eugenol
Cements
1- Temporary cementation of cast restorations.
2-Temporary filling materials.
3- Cavity liner in deep cavities preparation.
4- Root canal sealer.
5- Periodontal and surgical dressing.
6- Gingival tissue pack.
Zinc oxide-eugenol cement is contra-indicated to be used under
composite resins because
it interferes with their polymerization and causes discoloration of the composites
Main disadvantage of Unmodified Zinc Oxide-Eugenol
Low strength, and high solubility
Biocompatibility of Unmodified Zinc Oxide-Eugenol
has a pH of 7 and has little or no effect on the pulp
when placed in deep cavities. The presence of free-eugenol has an
obtundent effect on the pulp and reduces pain. It is irritant when in
direct contact with the pulp .
Resin-modified zinc oxide-eugenol applications
- Cementing (luting) agents.
- Cavity liner and base materials.
3.Temporary filling materia
Ethoxy Benzoic acid Alumina-modified Cement
(EBA- ZOE) applications
- Permanent cementation of crown and bridges
- Temporary filling
- Base and lining materials.
(EBA- ZOE) solubility
Similar to that of the polymer-reinforced zinc oxide-eugenol.
*The resistance to solubility is greater than that of the zinc
phosphate cements.
Zinc phosphate cements composition
Powder :
(Magnesium oxide is added to maintain the white color)
silica and alumina (improve mechanical properties).
Liquid:
Is aqueous solution of phosphoric acid buffered by adding
metallic salts such as aluminium 2%-3% phosphate and zinc phosphate
(buffering agents)
Zinc phosphate cements Setting reaction is
exothermic
Zinc phosphate cements manipulation
Setting time…. , time increased by
3-6min
• Reducing P/L ratio
• Prolonging the spatulation of last increment.
• Cooling the glass slab
Zinc phosphate cements should be incorporated into the liquid slowly on a
cool slab
In Zinc phosphate cement’s manipulation, Film thickness depends on
A. Particle size of the powder
B. P/L ratio
C. Viscosity of the cement: the lower initial viscosity of the cement the
thinner is the film
D. Pressure applied
• Film thickness of zinc phosphate cement is 25µ
Zinc phosphate cement Biological properties
Irritant to pulp when used as cavity lining, PH of the freshly
mixed cements 1.3-3.6, at the end of one hour PH reach 6
a sub-lining should be used under zinc phosphate
cements.
Zinc phosphate cement Thermal and electrical conductivity
Has thermal insulating properties when used as a deep cavities
under metallic restoration to protect pulp .
Zinc phosphate cement advantages and disadvantages
Advantage
1. It is easy to mix
2. It has a sharp well-defined set.
3. It has a sufficiently high compressive strength to resist the forces of amalgam
condensation.
Disadvantage
1. Acidic – possible pulpal irritation
2. Lack of antibacterial action
3. Brittle (Low tensile strength)
4. Lack of adhesion
5. Provides only mechanical bond
6. Exothermic during set
7. High solubility (in oral fluids)
8. Low hardness
Zinc phosphate cement applications
• Permanent cementation.
• Temporary filing.
• Base.
Zinc poly-carboxylate cements applications
• Cementation of cast alloys, and orthodontic bands.
• Cavity liner or base material
• Temporary filling materials.
Zinc poly-carboxylate cements composition
Powder:
• The powder contains mainly zinc oxide (ZnO) with some magnesium oxide , may also contain small quantities of stannous fluoride.
Liquid:
• The liquid is approximately 30-40% aqueous solution of poly acrylic acid with other organic acids such as itaconic acid to prevent gelation upon storage and tartaric acid to control the setting reaction. Sodium hydroxide is added to control the pH and control the viscosity of the liquid.
Properties of Zinc poly-carboxylate
cements
Biological properties
Poly-carboxylate cements are acidic but not as irritant as
phosphate cements for the following reasons:
1. Polyacrylic acid is a weaker acid than phosphoric acid.
2. Polyacid chains are too large and lack mobility required to
penetrate dentinal tubules.
3. Rapid rise of PH of mixed cements on setting to approach
5.5-6.
Zinc poly-carboxylate
cements bonding
One of the most important advantage of polycarboxylate cements is their ability to bond chemically (ionic bond)
- It doesn’t adhere to porcelain or gold.
Zinc poly-carboxylate cements main disadvantage
Lower compressive strength than zinc phosphate cements
Glasses for the
glass ionomer cements contain three main component…
silica and Alumina mixed in a flux of sodium and calcium fluorides.
Barium glass added to give radiopacity.
Glass Ionomer cement Setting reaction
Is acid base reaction undergo the following stages on mixing
powder with liquid :
1. Dissolution.
2. Migration.
3. Reaction and precipitation.
Glass Ionomer cement , The precipitation process of carboxylic gel salt is a continuous process and take
24 hours. Therefore, the setting material
should be protected against premature exposure to saliva
Types of glass ionomer cements
Type I: Luting applications.
Type II: as a restorative materials.
Type III :liner and base .
Biological properties of glass ionomer cements
Have a mild affect on the pulp, in case of deep cavities
calcium hydroxide lining must be used under glass ionomer
cements.
Anti-carcinogenic affect
glass ionomer cements , its necessary to coat the restoration
immediately by varnish to
its necessary to coat the restoration
immediately by varnish to protect the cement from premature
exposure to saliva.
glass ionomer cements Adhere…
chemically to the tooth structure
glass ionomer cements , Optical properties
Translucent, so used in anterior restoration
Advantage & disadvantage of GIC
Advantages:
Adhesion to tooth structure (chemical adhesion)
Long term fluoride release.
Biocompatibility (due to large molecules of weak polyacrylic acid weak acid, will
restrict its passage through dentinal tubules).
High compressive strength.
Low solubility
Disadvantages:
Technique-sensitive to water contamination and dehydration.
Short working time, and long setting time.
Brittleness
Metal modified glass ionomer :
- Miracle mixture:
Incorporation of amalgam alloy powder with in glass powder
in order to increase wear resistance - Cermets glass ionomers:
Fine precious metals such as silver, gold and have lower
fluoride release than conventional glass ionomers
Uses of Metal-Reinforced Glass-Ionomer Cements:
- Core build-up material.
- Filling material for posterior deciduous teeth.
Double cure
free radical reaction when light is applied to the cement.
Triple cure
Three reactions
• Conventional acid base reaction.
• Light cured polymerization of the resin.
• Chemical cured polymerization.
Giomer is
hybird of glass ionomer and resin composite having the properties of
fluoride release, resists solubility, high bond strength to tooth structure,
no coating is needed and minimal post operative sensitivity.
Resin cements have …. And used specific uses for …
have high aesthetic and high bond strength.
of orthodontic brackets or resin-bonded bridges
Resin cements composition
The resin may be bis-GMA or Urethane dimethacrylates
The fillers usually are barium glasses filler may make up 30% to 60% by weight
Resin cements Biological properties
are irritating to the pulp. Thus, pulp protection via a calcium hydroxide base
Resin cement applications
Applications:
1. For bonding of orthodontic brackets to acid-etched enamel.
2. Cementation of porcelain laminates and inlays.
3. Cementation of all porcelain crowns.
4. Cementation of etched-cast restorations.
Calcium hydroxide Ca(OH)2 is a
relative weak cement employed as direct or indirect pulp capping agents. Due to it s alkaline nature
Calcium hydroxide cements applications
Applications:
1. Direct and indirect pulp capping.
2. Low-strength bases beneath
restorations for pulp protection.
(Cavity liner)
3. Root canal sealing pastes.
Calcium hydroxide cements properties
- It has low compressive strength.
- Thermal properties , thickness greater than 0.5 mm is not
recommended - High water solubility.
- Calcium hydroxide is radiopaque
- Biological properties:
- Effect on pulp
- Formation of secondary dentine
- They can neutralize the free phosphoric acid of zinc phosphate
cement.
- Adhesion
Cavity varnishes are
natural resins or synthetic resins dissolved in a solvent such as ether or chloroform.
Varnishes Functions
Reduce microleakage that occurs in conjunction with amalgam
restoration.
Reduce sensitivity
Varnish is used under amalgam restorations and contraindicated under? And why
composite restoration. The resin in the varnish comes in contact with
composite and may be inhibited the polymerization
A minimum of two thin layers should be applied for the varnishes , why?
As initial layer dries it
leaves small pinholes and the second coating fills in the voids and produce
more continuous coating.
