Classification

Rigid impression materials

(1) Plaster
(2) Compound
(3) Zinc oxide-eugenol

Flexible hydrocolloid impression materials

(I) Agar-agar (reversible hydrocolloid)
(2) Alginate (irreversible hydrocolloid)

Flexible, elastomeric, or rubber impression materials

(1) Polysulfide rubber (mercaptan rubber)
(2) Silicone rubber (condensation silicone)
(3) Polyether rubber
(4) Polyvinyl siloxane (addition silicone)
 

Dental Solders

Applications-bridges and orthodontic appliances

Terms

Soldering -joining operation using filler metal that melts below 500° C

Brazing -joining operation using filler metal that melts above 500°C

Welding-melting and alloying of pieces to be joined

Fluxing
 -Oxidative cleaning of area to be soldered
 - Oxygen scavenging to prevent oxidation of alloy being soldered
16- 650 -- 650 fineness solder to be used with 16-karat alloys; fineness refers to the gold content

Classification

a. Gold solders-bridges
b. Silver solders-gold-substitute bridges and orthodontic alloys

Structure of gold solders

Composition-lower gold content than of alloys being soldered

Manipulation-solder must melt below melting temperature of alloy

Properties

1. Physical-similar to alloys being joined
2. Chemical-more prone to chemical and electrochemical corrosion
3. Mechanical-similar to alloy  being joined
4. Biologic-similar to alloys being joined
 

Properties of Amalgam.

The most important physical properties of amalgam are

• Coefficient of thermal expansion = 25-1 >ppm/ C (thus amalgams allow percolation during temperature changes)

• Thermal conductivity-high (therefore, amalgams need insulating liner or base in deep restorations)
• Flow and creep. Flow and creep are characteristics that deal with an amalgam undergoing deformation when stressed. The lower the creep value of an amalgam, the better the marginal integrity of the restoration. Alloys with high copper content usually have lower creep values than the conventional silver-tin alloys.

 Dimensional change. An amalgam can expand or contract depending upon its usage. Dimensional change can be minimized by proper usage of alloy and mercury. Dimensional change on setting, less than ± 20 (excessive expansion can produce post operative pain)

•  Compression strength. Sufficient strength to resist fracture is an important requirement for any restorative material. At a 50 percent mercury content, the compression strength is approximately 52,000 psi. In comparison, the compressive strength of dentin and enamel is 30,000 psi and 100,000 psi, respectively. The strength of an amalgam is determined primarily by the composition of the alloy, the amount of residual mercury remaining after condensation, and the degree of porosity in the amalgam restoration.
• Electrochemical corrosion produces penetrating corrosion of low-copper amalgams but only produces superficial corrosion of high copper amalgams, so they last longer

• Because of low tensile strength, enamel support is needed at margins

• Spherical high-copper alloys develop high tensile strength faster and can be polished sooner
• Excessive creep is associated with silver mercury phase of low-copper amalgams and contributes to early marginal fracture
• Marginal fracture correlated with creep and electrochemical corrosion in low-copper amalgams
• Bulk fracture (isthmus fracture) occurs across thinnest portions of amalgam restorations because  of high stresses during traumatic occlusion and/or the accumulated effects of fatigue
• Dental amalgam is very resistant to abrasion

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
 

Denture Cleansers

Use -  for removal of soft debris by light brushing and then rinsing of denture; hard deposits require professional repolishing

a. Alkaline perborates-do not remove bad stains; may harm liners .
b. Alkaline peroxides-harmful to denture liners
c. Alkaline hypochlorites-may cause bleaching, corrode base-metal alloys, and leave residual taste on appliance
d. Dilute acids-may corrode base-metal alloys
e. Abrasive powders and creams-can abrade denture surfaces

Denture cleaning Method

a. Full dentures without soft liners-immerse denture in solution of one part 5% sodium hypochlorite in three parts of water
b. Full or partial dentures without soft-liners immerse denture in solution of  1 teaspoon of hypochlorite with 2 teaspoons of  glassy phosphate  in a half of a glass of water
c. Lined dentures -- clean any soft liner with a cotton swab and cold water while cleaning the denture with a soft brush

Properties

1. Chemical-can swell plastic surfaces or corrode metal frameworks
2. Mechanical-can scratch the surfaces of denture bases or denture teeth
 

ZINC OXIDE AND EUGENOL 

This material is used for many dental purposes ranging from temporary restorative material to pulp capping. The material is composed of a powder that is basically zinc oxide and a liquid that is called eugenol.

Chemical Composition.

The powder must contain between 70 and 100 percent zinc oxide. The manufacturer may add hydrogenated resins to increase strength and zinc acetate to hasten the set. 

Eugenol is usually derived from oil of cloves. The oil of cloves contains more eugenol (82 percent) Eugenol is an obtundent (pain-relieving agent). It is a clear liquid that gradually changes to amber when exposed to light. 

Physical Properties. 
This material relieves pain, makes tissue less sensitive to pain, is slightly antiseptic, and is low in thermal conductivity. It provides a good marginal seal when placed in tooth cavities. The crushing strength (compression strength) of pure zinc oxide and eugenol is about 2,000 psi, which is low in comparison to other cements. The addition of hydrogenated resin increases the crushing strength to 5,000 psi. 

CLINICAL USES OF ZINC OXIDE AND EUGENOL 

Treatment Restoration. It helps prevent pulpal irritation in carious teeth, lost restorations, advanced caries, or pulpitis. This dental material also exerts a palliative effect on the pulp. 

Temporary Cementing Medium. Zinc oxide and eugenol is used as a temporary cementing medium for crowns, inlays, and fixed partial dentures. 

Intermediate Base. Zinc oxide and eugenol is used as an intermediate base. This material provides insulation between metallic restorations and vital tooth structure. Because of the low crushing strength, its use is sometimes contraindicated. 

Surgical Packing or Dressing. The surgical dressing applied and adapted over the gingival area after a gingivectomy. This dressing protects the area and makes the tissue less sensitive.