Dental Materials 221 - Spring 2025 - Practical Revision Notes

Dental Amalgam

Identification and Supply:
- Amalgam Capsule
- Tablet and mercury
- Powder and mercury
Proportioning
- Recommended techniques:
  - Wet technique: Mercury/alloy ratio is slightly more than 1:1.
  - Dry technique (Eam’s technique): Mercury/alloy ratio is 1:1.
- Consequences of wrong proportioning:
  - Excess mercury:
    - More formation of γ1 and γ2 phases at the expense of the stronger γ phase.
    - Results in decreased strength, decreased corrosion resistance, increased setting expansion, and increased creep.
  - Less mercury:
    - Incomplete wetting of powder particles.
    - Results in friable mix, increased voids, decreased strength, and decreased corrosion resistance.

Dental Amalgam - Trituration

Techniques:
- Mortar and Pestle (Hand trituration)
- Amalgamator (Mechanical trituration)
Advantages of Mechanical Trituration:
1. Less risk of mercury exposure.
2. Lower mercury/alloy ratio can be used.
3. More uniform and reproducible mix.
4. Saves time and effort.
Mix types and their properties
- Under-triturated:
  - Appearance: Grainy and friable, crumbles.
  - Properties: Difficult to condense, lower working time.
- Properly triturated:
  - Appearance: Shiny surface, soft consistency.
  - Properties: Good working time, best mechanical properties, best corrosion resistance.
- Over-triturated:
  - Appearance: Dull appearance, sticks to the capsule.
  - Properties: Lower working time, higher contraction and creep, poor properties (excess mercury).

Dental Amalgam - Condensation

Objectives:
1. Increase adaptation of the restoration to the cavity wall.
2. Decrease the mercury content by expressing excess mercury to the surface.
3. Reduce the porosity providing a strong compact mass.
Time Limit:
- 3 minutes after trituration.
Consequences of delayed condensation:
1. Reduced strength due to breaking up of partially formed matrix.
2. Partially set matrix contains excess mercury and excess porosities.
3. Decreased adaptation to the cavity wall due to decrease plasticity.
4. Decreased bonding between increments.

Dental Amalgam - Carving

Objectives:
1. Reproduce the anatomy of the tooth.
2. Removal of the top mercury-rich layer.

Dental Amalgam - Finishing and Polishing

Ideal Time:
- Conventional low copper amalgam: After 24 hours.
- High copper amalgam: Shortly after insertion.
Objectives:
1. Increase patient acceptance to the restoration.
2. Increase corrosion resistance by obtaining smooth surface.

Resin Composite

Classification by Mode of Curing:
1. Chemical cured resin composite (Two pastes)
2. Light cured resin composite (One paste)
3. Dual cured resin composite.
Chemical Cured Resin Composite - Modes of Supply:
1. Two jars: Pastes mixed over paper pad using plastic, Teflon, or gold-coated spatula.
2. Gun, cartridge (of two tubes), and mixing tip system.
Why not use stainless-steel spatula?
- Fillers may abrade the spatula resulting in discoloration of restoration.
Light Cured Resin Composite - Modes of Supply:
1. Screw-type syringe.
2. Compule (single dose) with special gun.
3. Syringe with dispensing tip for flowable resin composite.
Chemical vs. Light Cured:
- Light cured is better due to:
  1. No human variations as there is no mixing.
  2. No air bubbles incorporation during application.
  3. Command setting time.
  4. More color stability.
  5. Can be supplied in thicker viscosity (more fillers ==> better properties).
  6. Less polymerization shrinkage (incrementally cured).

Resin Composite Bonding to Tooth Structure

Bonding to Enamel - Steps and Roles:
1. Acid etching (37% phosphoric acid for 15-30 seconds):
  - Increases surface energy of the enamel.
  - Cleans enamel surface by removing surface debris.
  - Increases surface area of the exposed enamel to the resin.
  - Forms micro-pores that are penetrated by adhesive to form resin tags.
2. Adhesive application:
  - Fulfills the micro-pores formed over enamel surface.
  - Bonds with the resin composite.
Bonding to Dentine - Steps and Roles:
1. Acid conditioning:
  - Removes smear layer.
  - Demineralizes dentine collapses dentinal tubules decreases surface energy.
2. Primer application:
  - Hydrophilic group: interacts with moist dentine reopens collapsed dentinal tubules increases surface energy.
  - Hydrophobic group: interacts with adhesive.
3. Adhesive application:
  - Bonds primer and composite resin.

Resin Composite - Polymerization

Types of Light Curing Units:
- Blue visible light curing unit is better due to:
  - More depth of curing.
  - No health hazards like ultra-violet curing units (skin cancer and eye damage).
Factors Affecting Depth of Curing:
1. Type of curing unit.
2. Shade of resin composite.
3. Distance between light source and restoration.
4. Restoration thickness.
5. Exposure time.
6. Initiator system absorption characteristics.

Dental Cements - Zinc Oxide-Eugenol

Modes of Supply:
1. Powder and liquid.
2. Ready-made single paste.
3. Two pastes.
Modifications:
1. Polymer reinforced cement.
2. EBA (ethoxy-benzoic acid).
3. Rapid set form.
4. Eugenol free cement.
Uses:
1. Temporary cement.
2. Temporary filling.
3. Permanent cement (modified types).
4. Base under amalgam (modified types).
5. Surgical and periodontal pack.
6. Root canal sealer.

Dental Cements - Zinc Phosphate

Ways to Avoid Loss of Water from the Liquid:
1. Keep the bottle tightly closed.
2. Dispense the cement just before use.
3. Dispense the powder followed by the liquid.
Ways to Increase Working Time:
1. Mix over a wide area.
2. Mix incrementally.
3. Use thick glass slab.
4. Use cool glass slab.
- Reason: To dissipate the heat evolved during setting.
Why mix over wide area and incrementally?
- To dissipate heat and increase working time.
Why use a thick, cooled glass slab?
- To dissipate heat and increase working time.
Why cool the mixing glass slab above dew point?
- To prevent water condensation from the atmosphere, as excess water alters the cement properties.
Why precede with calcium hydroxide sub-base in deep cavities?
- To protect the pulp from chemical irritation due to high acidity of zinc phosphate cement.
Why not use under resin composite or ceramic restorations?
- Because zinc phosphate is an opaque material.
Uses:
1. Permanent cement for metallic and metal-ceramic restorations.
2. Base under amalgam.

Dental Cements - Zinc Polycarboxylate

Modes of Supply:
1. Powder and liquid.
2. Water settable cement.
Recommended Mixing Spatula:
- Plastic spatula.
- Stainless steel spatula can react chemically with the cement.
When to Discard the Mix:
- If it loses its surface gloss.
- Indicates initial setting and absence of free carboxylic groups essential for chemical bond.
When to Remove Excess Cement During Crown Cementation:
- Just after cementation process or after the cement becomes hard.
- Avoid removing during the rubbery stage as it may pull out some cement from beneath the margins leaving voids.
Uses:
- Permanent cement for metallic and metal-ceramic restorations.
- Base under amalgam.

Dental Cements - Glass Ionomer

Modes of Supply:
1. Powder and liquid.
2. Water settable cement.
3. Pre-proportioned capsule.
4. Paste-Paste dispenser.
Advantages and Disadvantages of Glass Ionomer Cement Capsule:
- Advantages:
  1. Requires no mixing, so the restoration has fewer voids.
  2. Saves time.
  3. Easy to use.
- Disadvantage:
  - High cost.
Recommended Mixing Spatula:
- Plastic spatula.
- Stainless steel spatula can react chemically with the cement, and the glass particles may abrade the stainless steel spatula, leading to incorporation of metals into the mix, resulting in bad esthetics.
How to Prepare Tooth Surface Before Placement:
- Condition the tooth surface with 20% polyacrylic acid.
- To clean it from debris.
- Phosphoric acid should not be used because it will remove the minerals from tooth structure that is necessary for bonding with GIC.
Precaution After Placement:
- The restoration should be covered with a coat or varnish after its initial setting in order to protect the restoration from early moisture or dryness to achieve the desired properties.
Uses:
1. Restoration of deciduous teeth.
2. Abrasion and erosion lesions, especially root lesion.
3. Long-term intermediate restoration.
4. Core buildup.
5. Fissure sealants.
6. Cavity base (under amalgam, composite, or ceramics) or liner.
7. Luting cement for crowns, bridges, and orthodontic brackets.
Modifications:
1. Metal modified glass ionomer cement.
2. Resin modified glass ionomer cement.
3. Highly viscous glass ionomer cement (packable glass ionomer cement).
4. Zinc reinforced glass ionomer cement.
5. Nanoionomer.
6. Zirconia modified glass ionomer cement.
7. Poly-acid modified composite resin (compomer).

Dental Cements - Resin Cement

Modes of Supply:
- Paste system.
- Capsules.
How to Cure Light (Dual) Cured Resin Cement:
- Apply light for 3 seconds, then remove the excess cement, then complete the light application.

Dental Cements - Cavity Varnish

Uses:
1. Seal dentinal tubules against chemical irritants as zinc phosphate cement.
2. Seal dentinal tubules against dental amalgam corrosion products.
3. Protect glass ionomer restoration from early moisture sensitivity.

Dental Cements - Calcium Hydroxide

Modes of Supply:
1. Two pastes (chemical cured).
2. One paste (Light cured).
Uses:
1. Sub-base under highly irritant zinc phosphate cement.
2. Indirect pulp capping material.
3. Direct pulp capping material.

Dental Ceramics

Steps of Dental Porcelain Restorations Fabrication:
1. Porcelain paste formation
2. Compaction (Condensation).
3. Firing.
4. Glazing.
5. Cooling.
Methods of Compaction:
a. Mild vibration to pack the porcelain, excess water removed with a clean tissue.
b. Spatula is used to compress and smooth the surface, removing excess water.
c. Dry powder is applied to absorb excess water from the wet porcelain.

Non-metallic Denture Base Material - Acrylic Resin

Proportioning (Powder/Liquid Ratio):
- P/L is 3:1 by volume or 2.5:1 by weight.
- High P/L: Incomplete wetting of the powder with liquid leading to granular mix.
- Low P/L: Increase shrinkage and porosity of the denture.
Mixing:
- Mixing is done by a stainless-steel spatula inside a glass jar.
- Mixing stages: sandy, sticky, dough, rubbery, and stiff.
- Packing stage: Dough stage.
Role of Separating Medium Before Packing:
1. Prevent passage of water from gypsum to resin to avoid resin crazing.
2. Prevent passage of monomer from resin to gypsum to prevent porosity.
3. Decrease surface porosity.
4. Facilitate separation of the two parts of the flask.
Packing Stage:
*Dough Stage.
- Early packing at sandy or sticky stages leads to: a) Flow of the mix outside the flask due to their lower viscosity. b) Denture porosity as a result of monomer evaporation.
- Delayed packing at rubbery stage leads to: a) The two parts of the flask will not contact due to high viscosity of the mix. b) Movement or fracture of the artificial teeth.
Processing (Curing Cycles):
- a) Long cycle: Constant temperature is applied at $74^{\circ}C$ for 8 hours.
- b) Short cycle: Heat is applied at $74^{\circ}C$ for 2 hours, then increase the temperature until water boiling ( $100^{\circ}C$ ) for an additional 1 hour.
Consequences:
- Decrease curing time (under curing) leads to high residual monomers.
- Increase curing temperature (over curing) will result in gaseous porosity.
Delivery:
- Why the denture should be stored in water until delivery?
  - Because water sorption will compensate the thermal shrinkage. Get rid of some residual monomers before the patient wears the denture.
Maintenance:
*Why the denture should be kept wet all the time? Why the patient should keep the denture under water when it is outside its mouth?
*Because continuous wetting and drying the denture results in its crazing.
Cleaning:
*Why the patient should not clean the denture with bleaching materials or other chemicals? To avoid its crazing by chemicals.
Uses of Chemical Cured Acrylic Resin:
1. Special tray making
2. Repair of denture base.
3. Some orthodontic appliances

Impression Material

Impression Compound:
- Material: Sheets, cakes, and sticks impression compound.
- Manipulative Process: Kneading.
- Setting Reaction: Physical reaction (soften by heat).
- Sheets and cakes are heated in a water bath, while sticks are heated over a direct flame.
- Why knead? Due to its lower thermal conductivity, it should be immersed for sufficient time and kneaded to obtain a homogenous soft mass.
- Why knead sheet outside water? To avoid water incorporation, which acts as a plasticizer and increases the flow.
- Why not overheat sticks? Because it will cause volatilization of some ingredients, which will affect its properties.
Zinc Oxide and Eugenol Impression:
*Mode of Supply Two pastes.
*Mixed How Mixed using a stainless steel spatula over a glass slab or oil-resistant pad.
*Adherence How to overcome adherence to patient’s skin and lips? Coat the extra-oral tissues with Vaseline before impression making.
Agar Impression Material
Agar impression material
*Identify the tray, State the impression used with it?
* tray with water cooling system, Agar impression

Alginate Material
*Identify the impression, State the problem State the problem. How can it be avoided
*Alginate impression, Synersis, Store in $100\%$ relative humidity

Alginate Material

Alginate Material
*Identify the impression, Why should its surface be smoothed with moistened fingertip? To prevent formation of air bubbles.'
Elastomers
Elastomers
*Identify *Why should it knead by finger tips not palm of the hand?, Elastomeric impression (Putty consistency), Because the hand temperature may accelerate the setting reaction
Elastomers
**Elastomers
Identify. Mention other mixing techniques?
*Dynamic mixer for elastomers, Hand mixing and static mixing
Elastomers
**Elastomers *
Why addition silicon impression should not be mixed with latex gloves? Because Sulfur contamination from natural latex and some vinyl gloves inhibits its polymerization reaction

Selection of impression material

Selection of impression material
*
What are the impression materials that can be used for making primary impression for completely edentulous patient? State the tray used?
Impression compound (sheets and cakes) == non-perforated stock tray., Alginate == perforated stock tray.

Selection of impression material

*Selection of impression materialWhat are the impression materials that can be used for making primary impression for dentulous patient? State the type of used tray?
*Alginate == perforated stock tray.

Selection of impression material

**Selection of impression material *
What are the impression materials that can be used for making secondary impression for edentulous patient? State the type of used tray?
*Plaster impression (historical) == non-perforated special tray.
*Zinc oxide-eugenol ==non-perforated special tray.
*Agar == water cooled tray perforated or with adhesive.
*Elastomers == special tray with adhesive

Selection of impression material

Selection of impression material
*
What are the impression materials that can be used for making secondary impression for dentulous patient? State the type of used tray?
*Agar == water cooled tray perforated or with adhesive.
*Elastomers == special tray with adhesive

Gypsum Products

**Gypsum Products
Identify the type of gypsum. Mention other uses?
*Plaster of Paris.1. Primary cast for completely edentulous patient.2. Mounting casts at articulator.3. Making base of the cast.
Gypsum Products
**Gypsum Products
Identify the type of gypsum. Mention other usesPlaster of Paris. Primary cast for completely edentulous patient. Mounting casts at articulator. Making base of the cast
Gypsum Products
**Gypsum Products
Identify the type of gypsum.Mention other uses Plaster of Paris. Primary cast for completely edentulous patient. Mounting casts at articulator. Making base of the cast
Gypsum Products
**Gypsum Products
Identify the type of gypsum. Mention other uses?
*Dental Stone.1. Secondary casts for completely edentulous patient2. Primary cast for completely dentulous patient.3. Secondary cast for removable partial denture.
Gypsum Products
**Gypsum Products
Identify the type of gypsum. Mention other uses Dental Stone. Secondary casts for completely edentulous patient Primary cast for completely dentulous patient. Secondary cast for removable partial denture
Gypsum Products
**Gypsum Products
Identify the type of gypsum. Mention other uses Dental Stone.1. Secondary casts for completely edentulous patient 2. Primary cast for completely dentulous patient.3. Secondary cast for removable partial denture..
Gypsum Products
**Gypsum Products
Identify the type of gypsum. Why this type is used?
*Improved Stone.It used due to High hardness to avoid scratching during wax pattern construction,High strength due to small size of the die

Investment Material

**Investment Material
Mention the types of investment materials. State their uses:
*Gypsum bonded investment (casting of gold alloy)Phosphate bonded investment (casting of gold alloy if mixed with water, casting of base metal alloy if mixed with silica sol).Silicate bonded investment (casting of base metal alloy

Dental Casting Alloys

Dental Casting Alloys
*Identify the alloy. How can they be polished?
*Gold alloy (acid pickling). Base metal alloy (sand blasting)  pickling not used to avoid removal of passive layer

Dental Casting Alloys

Dental Casting Alloys
*Identify the alloy.How can they resist corrosion?
*Gold alloy (resist corrosion due to its nobility Base metal alloy (resist corrosion due to passive layer formation