Permanent soft bases
Introduction :
The use of these materials, often very controversial in the profession, must respond exclusively to a clinical situation where the use of a thermopolymerizable resin in contact with the fibromucosa is considered unfavorable, or even contraindicated.
The intrados of a complete prosthesis using a soft material is an idea that seems judicious in the face of certain delicate clinical situations of the totally edentulous. Indeed, it seems logical not to compress the mucosa between two hard structures, the prosthesis and the bone.
Principle :
The principle is to remove about 2 mm of thickness from the base to replace it with a flexible material.
This replacement involves all or part of the support surface and the edges.
Indications:
The major indication for the use of “permanent” flexible bases is represented by a whole category of partially or totally edentulous patients in whom any surgery is contraindicated or refused either temporarily or permanently.
•Surgery will be contraindicated with
: – the major risks of osteoradionecrosis;
– specific pathological conditions in development;
– too much senescence;
-psychological refusal (phobia or trauma).
•For these patients, for whom no surgery is an option, the following problems will however have to be addressed:
-thin and fragile mucous membranes that cannot withstand contact with a hard resin: the soft base will provide better tolerance of removable prostheses and comfort;
– irregular ridges on which it is very difficult, in the absence of surgical correction, to correctly distribute the pressures: the prosthesis lined with a flexible base will minimize the excess pressures ensuring a better distribution of the constraints;
– significant resorption in the mandible, with emergence of the mental nerve: the cushioning provided by the flexible material will improve comfort and preserve the residual bone support;
– reduced bone support compared to natural teeth, aggravated by an Angle class II: the flexible base will allow the patient to have few concentrated contacts to support and to protect the support tissues;
-after fracture, the installation of an osteosynthesis system makes it difficult to wear the prosthesis. The use of a flexible base leads to a reduction in painful phenomena as well as the stresses transmitted to the bone, while achieving a “gentle” functioning of the bone tissue;
– loss of substance with skin grafts is mainly the result of operated cancers, but also due to ballistic trauma (more favorable biological context, because healthy and stable). In these cases, a prosthesis with a flexible base is the only possible alternative.
There are other indications for the use of soft bases in removable prosthetics:
-in pedodontics: in young edentulous patients, the removable prosthesis lined with a flexible base allows a certain adaptation to tissue remodeling and growth;
-In partial removable prosthesis when there is persistence of the incisor-canine block and very significant resorption of the lateral and posterior sectors, the flexible base provides non-traumatic support on the deficient osteomucosal support;
– In maxillofacial prosthesis: in the transitional phases, this type of prosthesis promotes the acquisition of compensatory reflexes before the definitive prosthesis;
-In cases of psychological refusal following a phobia or, more often, trauma linked to numerous interventions: the flexible base then provides an alternative (and the only one) which is non-aggressive and therefore accepted by the patient.
Properties required for the use of permanent flexible materials:
•Ease of use.
•Permanent adhesion with the hard material used to allow proper cleaning and to avoid any infiltration giving the prosthesis a foul odor.
•Any porosity must be excluded for easy maintenance.
•The permanence of its degree of resilience (abandon all products which harden from the first months)
•Fidelity of form and dimension.
•An absence of subsequent chemical or physical modification.
•Great resistance to chewing efforts.
Disadvantages
– Difficulty in gripping with the rigid base
– Change of coloring of the soft material
-Surface porosity inducing proliferation of candidal bacterial strains
-Difficulties in retouching by milling;
– Bad smell from the prosthesis
Materials:
The materials used are mainly acrylic resins and silicones.
Acrylic resins : These are “classic” polymethyl methacrylates made flexible by the addition of a plasticizer, these resins bond very well to the rigid resin of the prosthetic base since they are of the same chemical nature. Implementation in the laboratory is easy. In this family, we find thermopolymerizable and photopolymerizable.
Silicones: They are flexible by their chemical nature. They have non-stick properties towards microorganisms, but it is necessary to use an adhesive to connect this flexible material to the base resin: this silicone is either pressed and vulcanized at high temperature (practically 200 ° C), or pressed and crosslinked at around 100 ° C.
Practical Realization
The creation of a flexible base requires that all corrections and modifications allowing the adaptation of the intrados and the edges of the prosthesis have been carried out beforehand.
The implementation will always be done by indirect techniques, never by direct techniques.
First, after the prosthesis has been formed, plaster is poured into the intrados. To get around the problem of undercuts on the intrados, casting is done in 1 step if there are no undercuts or in 2 or
3 times if they are numerous and accentuated.
In a second step, the flexible base is made using techniques that involve putting in a muffle or using a bridle.
Permanent soft bases
Soft base and mittening:
The mittening is carried out according to the usual sequences.
The mitten opens easily thanks to the split model.
The intrados is hollowed out, the edges shortened by approximately 2 mm. To ensure a perfect junction between the two materials, the surface of the base resin is treated.
This is placed on the treated intrados, the muffle is closed under
press to avoid any occlusion errors . After polymerization, the muffle is opened and the prosthesis removed. Burrs are removed with a scalpel blade and polished with a suitable silicone mounted tip.
Conclusion
Permanent soft materials should be considered as a provisional and evolving therapeutic weapon . This is in order to provide a non-traumatic and comfortable response in situations where the conventional prosthesis with rigid base is very unfavorable.
The soft base is a way, in some cases, to reduce the discomfort caused by a prosthesis. It is an addition of material under the complete lower prosthesis. This addition is made of a more porous material, therefore more adherent than the acrylic prosthesis but, at the same time, more difficult to maintain. It remains important to visit the professional who made your prosthesis annually. He will be able to advise you and help you keep your prosthesis clean and comfortable for longer.
Permanent soft bases
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.