POLYMERIZATION OF PROSTHESES
The functional test was carried out satisfactorily, the models are stable, responsive, they simultaneously restore aesthetics and functions
The last sequence in the lab “polymerization” can be approached
The transformation of the wax model into a resin prosthesis is a fundamental step in prosthetic construction.
It is therefore necessary to clearly define the objectives:
- compliance with clinical records,
- research into the optimal mechanical, aesthetic and biological qualities of resins.
Currently, there are many resin casting and polymerization processes, mostly based on methyl methacrylate, that meet these criteria.
Each process is briefly presented to highlight its advantages and disadvantages.
2 )-Preparation of MODELS:
- Edge widening:
- Improvement of the sublingual and retromolar seal
- Materialization of landfills.
3)-Rehabilitation of waxes:
- Checking the thickness of each model: must be uniform at all points 1.5 mm in the center and 2.5 mm at the periphery.
- Secure the models: pour the wax over the entire periphery of the support surface, thus creating a flawless seal.
- Wax finishing: in order to considerably reduce the time spent in the laboratory after polymerization and especially to avoid having to touch up the surface of the extrados of the prosthesis, the superficial layer of which is the most compressed, the most homogeneous and the best polymerized .
4) DIFFERENT METHODS OF POLYMERIZATION:
1. “Conventional” or classic method:
The protocol is generally similar to the polymerization of the removable partial prosthesis.
We propose to illustrate the sequences of the technique
The mittening
- After cleaning the artificial teeth, finishing the wax, isolating the base of the model with varnish and lubricating the base of the muffle; the model is tried in the part of the muffle in such a way that the walls of the latter are located at least 1 cm from the vestibular faces of the teeth.
- The muffle part is filled with plaster and the model, with the chassis and wax mount, are placed on it. The plaster is smoothed so as to fill all the peripheral undercuts.
Note : Instead of plaster, an elastomer (silicone) can be used by placing it on the prosthetic teeth and taking care to clear the occlusal surfaces to allow intimate contact between these and the plaster of the counterpart of the muffle.
This will allow easier separation of the two parts of the muffle, less plaster-resin reaction and faithful reproduction of the false gums while ensuring good immobilization of the prosthetic teeth when pressing the resin.
- Finally, the muffle is closed and the counterpart is filled with plaster.
Scalding
After the plaster has completely set, the muffle is placed in boiling water for 5 minutes, then gently opened vertically. The softened wax is removed using a spatula and is completed by quickly passing the parts of the muffle through boiling water and by cleaning the wax and prosthetic teeth with a brush.
POLYMERIZATION OF PROSTHESES
Resin preparation and stuffing
When the teeth are made of resin, their retention is improved by milling carried out at the heels of the resin prosthetic teeth. Then a varnish is delicately spread around the artificial teeth.
The preparation of the resin itself is done by mixing the liquid and powder of the resin in a glass container, following the manufacturer’s instructions. When the resin reaches the plastic phase, a quantity is applied to the stool by digital pressure and another quantity to the teeth.
The muffle is closed and then put under pressure, gradually increasing, until the excess resin is reduced to the maximum and the muffle is completely closed. This protocol reduces the subsequent risks of vertical dimension over-elevation
The muffle is pressed at 1.4 bar for 20 minutes, then immersed in water for polymerization.
Demoulding and finishing of the resin
After gradual cooling of the muffle, the demoulding process is carried out.
The prosthesis is separated from the broken model, the excess resin that has flowed to the periphery is eliminated, then the extrados is carefully polished. The intrados is examined and, unlike the extrados, it is not polished; only the protruding roughness is softened.
2- MICROWAVE POLYMERIZATION METHOD
EXP; Acron Mc® : This is a “press” molding and microwave-induced polymerization system.
This is a pressed resin method whose polymerization is carried out in a microwave oven, instead of a thermostatic bath. The polymerization protocol is substantially identical to that of the classic method. The necessary equipment is:
- A microwave-permeable muffle with screws for closure
- A microwave oven with a turntable; (an AW-42 R continental oven with 2,450hz frequency and 900W power).
- A special thermo-polymerizable resin for microwave-induced polymerization and a microwave-compatible plaster.
The muffle is done in the classic way. The microwave is placed for one minute on high power to begin the process of removing the wax. Then, the wax is removed, the surface of the plaster is left to cool for about 5 minutes. This allows the steam to escape.
After the preparation and placement of the resin, the special microwave muffle is closed.
The closing tests are repeated two or three times in a row to remove excess resin. To close the muffle, the screws (provided by the manufacturer) are inserted into the holes, pressure is applied with the muffle press and the screws are tightened under constant pressure using a wrench (also provided by the manufacturer).
Then the resin polymerizes in the oven by applying the Compatible cooking and cooling cycle.
Demolding and polishing are carried out in the conventional manner.
Benefits
- – allows a short cycle,
- – requires little equipment,
- – gives a chemically very stable resin,
- – gives a resin with an excellent surface condition.
- Disadvantages
- – induces, like any “pressing” method, slight occlusal modifications,
- – induces, like any “high temperature” protocol, shrinkage phenomena,
- – does not allow deep coloring.
POLYMERIZATION OF PROSTHESES
3- CASTING RESIN METHOD
Exp; SR-Ivocap® System: This is a resin injection molding system and there is high temperature polymerization. The resin (presented in the form of pre-dosed cartridges) is injected into the muffle under a pressure of 6 bars using a pneumatic piston. The assembly is placed in boiling water for 30 minutes then in cold water, the pressure being maintained
Benefits
- allows a short cycle,
- induces, like any injection system, few occlusal disturbances,
- has a packaging and preparation of the resin which avoids any approximate dosage and any untimely handling,
- gives a chemically stable resin with an excellent surface finish.
Disadvantages
- requires a significant investment,
- induces, like any “high temperature” protocol, shrinkage phenomena,
- does not allow deep coloring.
- 8)-Manipulation errors:
– Wrong orientation of model and its mock-up in the muffle
– Presence of traces of humidity before stuffing or poor quality insulation,
– Failure to respect the powder/liquid ratio,
-The presence of impurities,
-Water and liquid absorption = dimensional variations,
– Too rapid or too sudden rise in temperature during polymerization as well as rapid cooling after polymerization,
-Opening the muffle before cooling,
These errors are the cause of either deformations of the prosthesis or porosities.
POLYMERIZATION OF PROSTHESES
Wisdom teeth can cause infections if not removed.
Dental crowns restore the function and appearance of damaged teeth.
Swollen gums are often a sign of periodontal disease.
Orthodontic treatments can be performed at any age.
Composite fillings are discreet and durable.
Composite fillings are discreet and durable.
Interdental brushes effectively clean tight spaces.
Visiting the dentist every six months prevents dental problems.