Applications/Use

• Load -bearing restorations for posterior  teeth  (class I, II)
• Pinned restorations
• Buildups or cores for cast restorations
• Retrograde canal filling material

 (1) Alloy. An alloy is a solid mixture of two or more metals. It is possible to produce a material in which the desirable properties of each constituent are retained or even enhanced, while the less desirable properties are reduced or eliminated.

(2) Amalgam. When one of the metals in an alloy mixture is mercury, an amalgam is formed. A dental amalgam is a combination of mercury with a specially prepared silver alloy, which is used as a restorative material.

(3) Mercury. Mercury is a silver-white, poisonous, metallic element that is liquid at room temperature

Temporary Filling Materials

Applications / Use

While waiting for lab fabrication of cast restoration
While observing reaction of pulp tissues

Objectives

Provide pulpal protection
Provide medication to reduce pulpal inflammation
Maintain the tooth position with an aesthetic restoration

Classification

Temporary filling cements
Temporary filling resins

Components

Temporary filling cements

1. Zinc oxide-eugenol cement with cotton fibers added
2. Polyme r powder-reinforced zinc oxide eugenol cement

Temporary filling resins

•    MMA / PMMA filling materials
•    Polyamide filling materials
•    BIS-GMA filling materials
 

Acrylic Appliances

Use - space maintenance  or tooth movement for orthodontics and pediatric dentistry

1. Components

a. Powder-PMMA powder. peroxide initiator, and pigments

b. Liquid-MMA monomer, hydroquinone inhibitor, cross-linking agents, and chemical accelerators (N, N-dimethyl-p-toluidine)

2. Reaction

 PMMA powder makes mixture viscous for manipulation before curing . Chemical accelerators cause decomposition of benzoyl peroxide into free radicals that initiate polymerization of monomer .  New PMMA is formed into a matrix that surrounds PMMA powder. Linear shrinkage of 5% to 7% during setting. but dimensions of appliances are not critical

Principles of cutting, polishing, and surface cleaning

• Surface mechanics for materials

Cutting-requires highest possible hardness materials to produce cutting

Finishing-requires highest possible hardness materials to produce finishing, except at margins of restorations where tooth structure may be inadvertently affected

Polishing- requires materials with Mohs ./ hardness that is 1 to 2 units above that of substrate

 Debriding-requires materials with Mohs hardness that is less than or equal to that of substrate to prevent scratching

•    Factors affecting cutting, polishing. and surface cleaning
  • Applied pressure
  • Particle size of abrasive
  •  Hardness of abrasive
  •  Hardness of substrate
•      Precautions
  • During cutting heat will build up and change the mechanical behavior of the substrate from brittle to ductile and encourage smearing
  • Instruments may transfer debris onto the cut surface from their own surfaces during cutting, polishing, or cleaning operations (this is important for cleaning implant surfaces)

Composition of Acrylic Resins.

·        Powder. The powder is composed of a polymethyl methacrylate (PMMA), peroxide initiator, and pigments

·        Liquid. The liquid is a monomethyl methacrylate (MMA), hydroquinone inhibitor, cross-linking agents, and chemical accelerators (N, N-dimethyl-p-toluidine)

Classification of Dental amalgam

1. By powder particle shape .

• Irregular (comminuted, filing, or lathecut)
• Spherical (spherodized)
• Blends (e.g., irregular-irregular, irregularspherical, or spherical-spherical)

2. By total amount of copper

• Low-copper alloys (e.g., conventional, traditional); <5% copper
• High-copper alloys (e,g.  corrosion resistant); 12% to 28% copper

3.By presence of zinc

Examples

• Low-copper, irregular-particle alloy-silver (70%)-tin (26%)-copper (4%)
• High-copper, blended-particles alloy-irregular particles, silver (70%) –tin (26%) -Copper (4%); spherical particles, silver (72%)-copper (28%)
• High-copper, spherical-particles alloy-silver (60%) - tin (27%)-copper (13%)