WETTABILITY
To minimise the irregularities on the investment & the casting a wetting agent can be used .

FUNCTIONS OF A WETTING AGENT

1 . Reduce contact angle between liquid & wax surface .
2 .Remove any oily film left on wax pattern .

SELECTION OF SPRUE 

1 . DIAMETER :
It should be approximately the same size of the thickest portion of the wax pattern .
Too small sprue diameter suck back porosity results .

2 . SPRUE FORMER ATTACHMENT :
Sprue should be attached to the thickest portion of the wax pattern .
It should be Flared for high density alloys & Restricted for low density alloys .

3 . SPRUE FORMER POSITION

Based on the
1. Individual judgement .
2. Shape & form of the wax pattern .

Patterns may be sprued directly or indirectly .
Indirect method is commonly used

CASTING: casting is the process by which the wax pattern of a restoration is converted to a replicate in a dental alloy. The casting process is used to make dental restorations such as inlays, onlays, crowns, bridges and removable partial dentures.

Objectives of casting

1) To heat the alloy as quickly as possible to a completely molten condition.
2) To prevent oxidation by heating the metal with awell adjusted torch .
3) To produce a casting with sharp details by having adequate pressure to the well melted metal to force into the mold.

STEPS IN MAKING A CAST RESTORATION
1. TOOTH PREPARATION
2. IMPRESSION
3. DIE PREPARATION
4. WAX PATTERN FABRICATION
5. SPRUING

ACRYLIC RESINS

Use. Acrylic (unfilled) resins are used as temporary crown material. Temporary crowns are placed to protect the crown preparation and provide patient comfort during the time the permanent crown is being constructed

Introduction

The science of dental materials involves a study of the composition and properties of materials and the way in which they interact with the environment in which they are placed

Selection of Dental materials

The process of materials selection should ideally follow a logical sequence involving

(1) analysis of the problem,

(2) consideration of requirements,

(3) consideration of available materials and their properties, leading to

(4) choice of material.

Evaluation of the success or failure of a material may be used to influence future decisions on materials selection.

Physical reaction-cooling causes reversible hardening

Chemical reaction-irreversible reaction during setting