Care of Impressions and Making Casts

Study Notes

Care of Impressions and Making Casts

Removable Partial Dentures, 2020, Georges SAYEGH
Focuses on the care of impressions and making casts for removable partial dentures.

Content

Definitions: Explains key terms related to impression making, cast fabrication and procedures.
Impression Making: Describes the importance of impression-making skills for diagnostic casts required in patient treatment planning. An irreversible hydrocolloid material (alginate) is used for making impressions for diagnostic casts.
Preliminary Impression Materials: Lists alginate and impression compound as preliminary impression materials.
Alginate Impressions: Used to create diagnostic casts and removable partial dentures. Impressions should be poured soon after being taken.
Cast Fabrication: Details the Modified Two-Stage Technique for cast fabrication. This includes steps like weighing dental stone, zeroing out the weight of the bowl, mixing the stone and water, and achieving a creamy consistency.
Step 3: First Pour: Gently vibrates the dental stone into the impression, filling each tooth individually.
Step 4: Second Pour: Soaks the first pour, mixes stone, builds a "patty", and inverts the impression into the patty to completely fill.
Types of Casts: Covers diagnostic, working, and refractory casts, each with specific uses. Diagnostic casts are life-sized reproductions for study and treatment planning. Working casts form the basis of a prosthesis, while refractory casts withstand high temperatures without disintegration.
Diagnostic Casts: Detailed description of diagnostic casts. These are life-size reproductions of oral structures, used to assess hard and soft tissues of the maxillary and mandibular jaws for treatment planning. They're typically made from artificial dental stone type III.
Uses of Diagnostic Casts: Lists individual uses of diagnostic casts, including occlusal analysis, soft tissue assessment, hard tissue assessment, fabrication of splints, custom trays, provisional restorations and other.
Requisites for Casts: Outlines the critical qualities of casts for removable partial dentures. All surfaces contacted by the prosthesis should be accurate, free of voids and nodules. The surface of the cast should be hard and dense, free of any grinding sludge. The cast extensions need to extend for denture support.
Additional Cast Requirements: The peripheral roll should be complete and have a specified depth. The side walls of the cast are vertical (or slightly tapered outwards, but not undercut). The base needs a minimum thickness of 15 mm. The lingual region should be trimmed flat and show no signs of being wet or brushed.
Troubleshooting Guide (Problems & Solutions): Addresses issues like voids in the impression, impression separation, chalky cast surfaces, voids on cast surfaces, casts being too thin or thick or areas getting trimmed away or broken casts. Provides solutions for each issue. (e.g., voids in the impression require obtaining a new impression, while chalky cast surfaces require improvement of the water-powder ratio.)