RINGLESS INVESTMENT TECHNIQUE
Used for phosphate bonded investments .
This method uses paper or plastic casting ring .
It is designed to allow urestricted expansion .
Useful for high melting alloys .

Cement Bases

Applications

•    Thermal insulation below a restoration
•    Mechanical protection where there is inadequate dentin to support amalgam condensation pressures

Types

•    Zinc phosphate cement bases
•    Polycarboxylate cement bases
•    Glass ionomer cement bases (self-curing and light-curing)

Components

o    Reactive powder (chemically basic)
o    Reactive liquid (chemically acidic)

Reaction

o    Acid-base reaction that forms salts or cross linked matrix
o    Reaction may be exothermic

Manipulation-consistency for basing includes more powders, which improves all of the cement properties

Properties

Physical-excellent thermal and electrical insulation

Chemical-much more resistant to dissolution than cement liners

    Polycarboxylate and glass ionomer cements are mechanically and chemically adhesive to tooth structure

    Solubility of all cement bases is lower than cement liners if they are mixed at higher powder- to-liquid ratios

Mechanical- much higher compressive strengths (12,000 to 30,000 psi)
    Light-cured hybrid glass ionomer cements are the strongest
    Zinc oxide-eugenol cements are the weakest

Biologic (see section on luting cements for details)

    Zinc oxide-eugenol cements are obtundent to the pulp
    Polycarboxylate and glass ionomer cements are kind to the pulp
 

Solution Liners (Varnishes)

Applications 

o    Enamel and dentin lining for amalgam restorations
o    Enamel and dentin lining for cast restorations that are used with non adhesive cements
o    Coating over materials that are moisture sensitive during setting

Components of copal resin varnish

o    90% solvent mixture (e.g., chloroform, acetone, and alcohol)
o    10% dissolved copal resin

Reaction
 
Varnish sets physically by drying → Solvent loss occurs in 5 to 15 seconds (a film forms the same way as drying fingernail polish)

Manipulation

Apply thin coat over dentin. enamel. And margins of the cavity preparation → Dry lightly with air for 5 seconds Apply a second thin coat → Final thickness is 1 to 5 µ.m

Properties

o    Physical 

Electrically insulating barrier that prevents shocks. Too thin to be thermally insulating. Decreases degree of percolation attributable to thermal expansion

o    Chemical

Forms temporary barrier that prevents microleakage into dentinal tubules until secondary dentin formation occurs. Decreases initial tendency for electrochemical corrosion

o     Mechanical

Very weak and brittle film that has limited lifetime 
Film adheres to smear layer

Denture Teeth

Use-complete or partial dentures

Type

a. Porcelain teeth
b. Acrylic resin teeth
c. Abrasion-resistant teeth (microfilled composite)

Structure and properties

1. Porcelain teeth (high-fusing porcelain)
Only bonded into denture base mechanically. Harder than natural teeth or other restorations and abrades those surfaces. Good aesthetics.Used when patients have good ridge support and sufficient room between the arches

2. Acrylic resin teeth (PMMA  [polymethyl methacrylate])

Bonded pseudochemically into the denture base. Soft and easily worn by abrasive foods . Good initial aesthetics
Used with patients with poor ridges and in cases where they oppose natural teeth

3. Abrasion-resistant teeth (microfilled resins)
Bonded pseudochemically into the denture base.Better abrasion resistance then  acrylic resin teeth
 

Solution Liners (Varnishes)

Applications 

o    Enamel and dentin lining for amalgam restorations
o    Enamel and dentin lining for cast restorations that are used with non adhesive cements
o    Coating over materials that are moisture sensitive during setting

Components of copal resin varnish

o    90% solvent mixture (e.g., chloroform, acetone, and alcohol)
o    10% dissolved copal resin

 Reaction
 
Varnish sets physically by drying Solvent loss occurs in 5 to 15 seconds (a film forms the same way as drying fingernail polish)

Manipulation

Apply thin coat over dentin. enamel. And margins of the cavity preparation  Dry lightly with air for 5 seconds Apply a second thin coat Final thickness is 1 to 5 µ.m

Properties

o    Physical 

Electrically insulating barrier that prevents shocks. Too thin to be thermally insulating. Decreases degree of percolation attributable to thermal expansion

o    Chemical

Forms temporary barrier that prevents microleakage into dentinal tubules until secondary dentin formation occurs. Decreases initial tendency for electrochemical corrosion

o     Mechanical

Very weak and brittle film that has limited lifetime 
Film adheres to smear layer
 

Mercury bioactivity

• Metallic mercury is the least toxic from and is absorbed primarily through the lungs rather than the GI tract or skin
• Mercury in the body may come from air, water, food. dental (a low amount). Or medical sources
•  Half life for mercury elimination from body is 55 days .-
• mercury toxicity is <50 µm / m³ on average per 40-hour work week.
• Mercury hypersensitivity is estimated as less than 1 per 100,000,000 persons
• Indium-containing amalgams can have lower Hg vapor pressures than conventional dental amalgam