TUTO | Casting technique for the transformation of a mandibular wax model into self-curing resin for the design of a partial removable prosthesis.
Copyright © 2021 Jimmy Darmon. All rights reserved.
Chapters :
00:00 Step 00 Introduction
00:04 Step 01 Silicone keys
01:24 Step 02 Positioning of the prosthetic elements
03:18 Step 03 Undercutting and varnishing
04:37 Step 04 Casting and curing the resin
Each removable prosthesis has an acrylic resin base that imitates the gum, serving as a support for artificial teeth that are made of resin. A distinction is made between a complete removable prosthesis and a partial removable prosthesis. The retention of this dental prosthesis is ensured by clasps that are inserted on natural teeth. Partial removable dentures (P.R.P.D.), restore a partial edentulism. These dentures rest on both the gums and the remaining teeth. The treatment of total or partial edentulism requires the realization of acrylic dental resin bases, the resin is used for the transformation of wax work bases to this material.
- They are a mixture of powdered polymer and liquid monomer. The basic chemical formula of acrylic resins is methyl polymethacrylate (PMMA). The mixture of these two components will harden under the action of a catalyst by heat (thermo-polymerizable) or a chemical element (chemo-polymerizable).
- Thermo-polymerizing resins: these are the resins used to make removable prostheses. They must be baked to polymerize/harden (the catalyst is heat).
- Chemo-polymerizable / self-polymerizing resins: the material is set with a chemical catalyst. They are mainly used for repairs, the polymerization can be done in the open air because the catalyst is chemical, but it is preferable to cook this resin in hot water in a pressurized polymerizer.
- Silicone key:
A wax assembly can be transformed into resin with silicone keys forming a negative impression (a mold) of the assembly created in wax. Example on the mandibular prosthesis: After mixing the silicone with the catalyst (to activate the hardening of the material in a period of about one minute), the silicone must enclose the entire wax part with the prosthetic teeth until it contacts the plaster, a hole is created on the posterior part for casting the resin later. The hardened key is removed, the wax can be removed from the model, the prosthetic teeth are cleaned with a steam jet. At this stage the model and the prosthetic teeth should be clean without wax residue. The prosthetic teeth are frosted at the foot of the tooth and grooves are created to facilitate the bonding to the resin. They are then placed in the key in their original position with a drop of cyanolite glue. The working model is isolated with a varnish, the key is positioned in the initial situation and glued with wax around the plaster to avoid possible resin leaks or a drop of the correct positioning. The self-curing resin is prepared by mixing the polymer (powder) and the monomer (liquid) in a cup and then poured inside the key. The model with the key and the resin are immersed in water at 50° in a vacuum polymerizer (2.5 bars) to avoid bubbles and accelerate the setting time. After the resin has hardened by polymerization in 20 minutes, the key can be removed, and the scraping and adjustment steps can be carried out to complete the prosthesis.
- The resin is obtained by mixing monomer (liquid) with polymer (powder) in the proportions indicated by the manufacturers. The mixing must be done in a suitable, thick, opaque and hermetically sealed container.
- Phase 1 of sedimentation, the resin will be spatulated for about 30 seconds.
- Phase 2 of dissolution, the resin will go from a stringy consistency to a sticky consistency, it takes a foamy aspect.
- Phase 3 of saturation, the plastic jelly phase will form a pasty mass no longer adhering to the walls of the container. It is at this point that the resin must be pressed.
- Phase 4 evaporation, the material left in the container loses its plasticity, all the monomer evaporates, the mixture begins to harden, it can no longer be molded, it must not be pressed.
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17 июн 2024
