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Biomaterials[21]

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Dental cements are materials produced by mixing a powdered oxide with a liquid
(except resin cement) allowing it to be a hard brittle material.
Uses:
1) Cementation (luting - joining two substances together);
 Permanent cements (used with permanent restorative materials)
 Temporary cements (with temporary restorations)
2) Liners: thin coatings used for chemical insulation.
 thin film liners which is subdivided to solution liners (2-5 μm ) and
suspension liners(20-25 μm)
 the thick film liners (0.2-1 mm)
3) Bases:
 Used for chemical and thermal insulation.
 Capable of being reshaped and contoured.
 Used as pulp capping in case of pulp exposure during dental procedure
 Also used as root canal treatment sealer.
Requirements:







Nontoxic and non- corrodible
Insoluble
Antibacterial
Allow adhesion between the tissue and the restoration
Obtundent (pain relievers)
Provide chemical, electrical and thermal insulation to protect the pulp.
High modulus of elasticity (to avoid fracture).
Classification:
 Oil based (Zinc-oxide Eugenol)
 Water based (Zinc Phosphate – Zinc polycarboxylate – Glass Ionomer)
 Resin based (Compomer – Resin cement)
Zinc Phosphate cement:
It is the oldest luting agent.
Applications:
1)
2)
3)
4)
Cementation of cast restorations.
Base under metallic restorations.
Cementation of orthodontic bands.
Temporary filling material.
Composition:
 Powder:
 Zinc Oxide: 90%
 Magnesium Oxide: 10%
 Small Quantities of Silicon Dioxide & Bismuth trioxide
(Sintered at 1000-1400 °C for 4 to 8 hours – this slows down the setting reaction
and increases working time. Small particles lead to short setting time). .
 Liquid:
 Phosphoric acid: 40%
 Water: 33% (Affects rate of reaction with powder by ionizing the
acid)
 Metal salts; ex: aluminum phosphate, zinc phosphate
Metallic salts work as a buffering agent and decrease the rate of the
reaction with the powder.
Care of liquid:
The zinc phosphate liquid bottle (consisting of partially neutralized diluted
phosphoric acid) should always be closed after use to prevent:
 Loss of water in case exposed to dry air
 Absorbance of water if exposed to humid atmosphere.
Setting Reaction:
Zinc Oxide + Phosphoric Acid
(Exothermic reation)
Zinc aluminophosphate + Heat
Factors Influencing Working and Setting Times:
1) Rate of Powder Incorporation
Powder should be added slowly to the liquid
Mixing with a spatula on a large surface area so that the heat released will
dissipate; thus, increasing setting reaction.
2) Powder/Liquid Ratio
Increasing the ratio will decrease working and setting time resulting in
thinner mix
Affects the physical properties lowering the initial pH of the cement and
decreases compressive strength.
3) Temperature of Mixing Slab
Cooling down the mixing slab extends the working and setting time.
4) Water Content of the Liquid
Setting reaction increases when adding high water content.
 Consistency: depends on the powder/liquid ratio:
 Low P/L ratio
thin consistency (used for luting)
 Higher P/L ratio
thick consistency (used as a base)
 Film thickness:
 For luting: should not exceed 25 micrometers. Consistency should be
fluid and follow the spatula 2-3 cm (string test).
 The smaller the powder particles
the thinner is the film.
 P/L ratio: when the amount of the powder increases,
consistency increases.
 The lower the initial viscosity, the thinner is the film and the better is
the retention.
 The greater the pressure applied during the restoration placement,
the better is the flow of the cement and the thinner is the film.
 Cement base: due to the thick consistency, it:
 Provides thermal and chemical insulation over the thin dentin
 Has high strength (less soluble and stronger than the thin
consistency)
 May serve as a temporary filling material
*It doesn’t flow the spatula.
 Mechanical properties:
Depend on the Powder/Liquid ratio.
For best mechanical properties, we use the highest P/L ratio possible that
can give the desired rheology (for either luting or the base).
 Solubility:
When used as luting cement, solubility leads to marginal leakage resulting
in:
 Loosening of the restoration
 Recurrent caries
 Retention:
Depends on:
 The flow of the cement to the tooth and restoration irregularities.
 Strength of the cement to resist forces.
 Biocompatibility:
 Irritant to the pulp: the low pH induces pulpal inflammation in deep
cavities (the thinner the mix, the lower the pH)
 May induce pain during cementation due to the low pH and the
osmotic pressure by the fluid movement through the dentinal
tubules.
 Advantages:
 Easy to mix
 High compressive strength
 Disadvantages:
 Irritant to the pulp (low pH)
 Not antibacterial
 Brittle
 Not adhesive
 Vulnerable to acid attack
Zinc Oxide Eugenol (ZOE):
Zinc Oxide Eugenol cements are known for their sedative effects on the pulp and
their neutral pH.
 Types:
- Unmodified ZOE
- Resin Modified ZOE
- Ortho EthoxyBenzoic Acid Alumina ZOE
 Applications:
- Temporary cementation of cast restoration
- Temporary filling material of teeth
- Cavity liner
- Root canal sealer
- Periodontal and surgical dressing
- Gingival tissue packing
 Composition:
- Powder:
 Pure zinc oxide 69% (main reactant)
 Rosin 30% (increases toughness)
 Zinc acetate 1% (accelerator)
- Liquid:
 Purified Eugenol 85% (main reactant)
 Olive oil 15% (improve handling)
 Setting reaction:
Zinc oxide + water
Zinc hydroxide
Zinc hydroxide + Eugenol
Zinc eugenolate
 Solubility:
ZOE is very soluble in the oral environment, which is considered a disadvantage.
Eugenol is constantly released, and as it dissolves, the cement disintegrates.
 Film thickness:
Value is about 40 micrometers
The particle size along with the viscosity of the mix govern it.
 Biocompatibility:
pH: 6.6-8 (no effect on the pulp in deep cavities)
 Advantages:
1) Obtundent effect on the pulp (presence of eugenol)
2) Good sealing ability and resistance to marginal penetration
 Disadvantages:
Low strength and abrasion resistance, solubility, and disintegration in oral fluids
Type 2: Resin –modified zinc oxide eugenol: (zinc oxide with basic additives and
major bulk resin).
Resins are added to the powder and/or the liquids.
Applications:
 permanent cementing agents for restorations
 Cavity liner and base materials
 Temporary filling materials
 Properties:
 Addition of polymer:
 increases compressive strength
 Decreases brittleness
 Reduces solubility
 Film thickness: 35-75 micrometer
Type 3: Ortho-Ethoxybenzoic Acid-Alumina Modified Zinc Oxide-Eugenol (EBAZOE)
Polymeric components such as polymethyl methacrylate may be present
Liquid: 50-66% ethoxybenzoic acid
*highly resistant to solubility (less eugenol)
Applications:
 Permanent cementation of crowns ad bridges
 Temporary fillings
 Base or lining materials
 Film thickness: 40-70 micrometer
 Compressive strength similar to zinc phosphate cement
 Solubility similar to resin modified ZOE and greater than zinc phosphate
cement
Subtitles:
P/L ratio of Zinc phosphate:
- Luting: 2 scoops of the powder to 5 drops of the liquid
- Base: 2 scoops of the powder to 3 drops of the liquid
 Luting:
Mixing time: 60 – 90 seconds
Working time: 3 – 4 minutes (from the start of mixing to the start of
setting)
Setting time: 6 – 8 minutes (from the start of mixing to complete setting)
 Base:
Mixing time: 2 – 2.5 minutes
Working time: 4 – 4.5 minutes
Setting time: 6 – 7 minutes
P/L ratio of ZOE:
Mixing time:
Working time:
Setting time:
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