Waxes

Many different waxes are used in dentistry. The composition, form, and color of each wax are designed to facilitate its use and to produce the best possible results.

Applications

o    Making impressions
o    Registering of tooth or soft tissue positions
o    Creating restorative patterns for lab fabrication
o    Aiding in laboratory procedures

Classification

a. Pattern waxes-inlay, casting, and baseplate waxes
b. Impression waxes-corrective and biteplate waxes
c. Processing waxes-boxing, utility, and sticky waxes

Types

1) Inlay wax-used to create a pattern for inlay, onlay or crown for subsequent investing and casting in a metal alloy.
2) Casting wax-used to create a pattern for metallic framework for a removable partial denture
3) Baseplate wax-used to establish the vertical dimension. plane of occlusion. and  initial arch form of a complete denture
4) Corrective impression wax-used to form a registry pattern of soft tissues on an impression
5) Bite registration wax-used to form a registry pattern for the occlusion of opposing models or casts
6) Boxing wax-used to form a box around an impression before pouring a  model or cast
7) Utility wax -soft pliable adhesive wax for modifying appliances, such as alginate impression trays
8) Sticky  wax-sticky when melted and used to temporarily adhere pieces of metal or resin in laboratory procedures

Components

a. Base waxes-hydrocarbon (paraffin) ester waxes    
b. Modifier waxes-carnauba, ceresin, bees wax, rosin, gum dammar, or microcrystalline waxes
c. Additives-colorants

Reaction-waxes are thermoplastic

Properties

Physical

a. High coefficients of thermal expansion and contraction
b. Insulators and so, cool unevenly; should be waxed in increments to allow heat dissipation

Chemical

a. Degrade prematurely if overheated
b. Designed to degrade into CO2and H2Oduring burnout

Mechanical-stiffness, hardness, and strength depend on modifier waxes used
 

Manipulation

1. Selection-based on strength for models, casts, or dies

2. Mixing
(1)Proportion the water and powder 
(2) Sift powder into water in rubber mixing bowl
(3) Use stiff blade spatula to mix mass on side of bowl
(4) Complete mixing in 60 seconds

3. Placement

(1) Use vibration to remove air bubbles acquired through mixing
(2) Use vibration during placement to help mixture wet and flow into the impression

COMPOSITE RESINS

Components

• Filler particles-colloidal silica, crystalline silica (quartz), or silicates of various particle sizes (containing Li, AI, Zn, Yr)
• Matrix-BIS-GMA (or UDMA) with lower molecular weight diluents (e.g., TEGDMA) that correct during polymerization
• Coupling agent- silane that chemically bonds the surfaces of the filter particles to the polymer matrix

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 .

Spruing Technique:

Direct Spruing:

The flow of the molten metal is straight(direct) from the casting crucible to pattern area in the ring. Even with the ball reservoir, the Spruing method is still direct. A basic weakness of direct Spruing is the potential for suck-back porosity at the junction of restoration and the Sprue.

Indirect Spruing:

Molten alloy does not flow directly from the casting crucible into the pattern area, instead the alloy takes a circuitous (indirect) route. The connector (or runner) bar is often used to which the wax pattern Sprue formers area attached. Indirect Spruing offers advantages such as greater reliability & predictability in casting plus enhanced control of solidification shrinkage .The Connector bar is often referred to as a “reservoir .

Armamentarium :
1 . Sprue
2 . Sticky wax
3 . Rubber crucible former
4 . Casting ring 
5 . Pattern cleaner 
6 . Scalpel blade & Forceps 
7 . Bunsen burner

Suspension liners

Applications

o    Dentin lining under amalgam restorations
o    Stimulation of reparative dentin formation

Components

-Calcium hydroxide powder
-Water
-Modifiers

Manipulation

Used as W/P or pastes Paint thin film on dentin → Use forced air for 15 to 30 seconds to dry → Film is thicker (15 µm) than varnishes → Do not use on enamel or cavosurface margins

Properties

Physical

-Electrically insulating barrier
-Too thin to be thermally insulating

Chemical

-High basicity for calcium hydroxide (pH is II)
-Dissolves readily in water and should not be used at exposed cavosurface margins or gaps may form

Mechanical - weak film

Biologic - calcium hydroxide dissolves, diffuses, and stimulates odontoblasts to occlude dentin tubules below cavity preparation