Support, Stabilization and Retention in Complete Removable Prosthesis
Housset’s triad conditions the principle of respect for tissue integrity: “It is more important to maintain what remains rather than to replace what is missing.”
Roles:
- Ensure the prosthesis is held in place, prevents it from coming loose.
- Preserve tissue integrity.
- Enable functional efficiency.
- Contribute to aesthetic credibility.
- Promote the psychological integration of the prosthesis.
Sustenance:
Favorable reaction which opposes the forces exerted on the prosthesis perpendicular to the support surface, thus avoiding the sinking of the base plate into the supporting tissues.
Sustainability factors:
- Support surface
Any increase in the support surface improves the lift (ratio between force and application surface) P = F/S
It is therefore necessary to seek maximum extension of the base, while allowing free play of the paraprosthetic organs.
2. Shape of the jaws
Support is conditioned by the shape of the bony infrastructure: thus a flat palate is more favorable than an ogival palate, a flat crest than a knife-edge crest.
3. Supportive fabrics
Sustenance is influenced by the quality of the supporting tissues at the bone level as well as at the mucosal level: thus a fragile bone (osteoporotic) or a damaged mucosa (hypertrophied) cannot ensure good sustenance.
The viscoelastic character of the fibromucosa:
The application of a force F on the mucosa (F compression force)
- First there is compression, then progressive deformation of the tissues gradually
🡪 When the pressure is removed, there is an instantaneous elastic decompression followed by a gradual and slow return to normal thickness.
Stabilization
Favorable reaction which opposes the forces (transverse or anteroposterior) exerted on the prosthesis parallel to the support surface.
It is related to the wedging of the prosthesis and prevents the mobilization of the base plate by translation or rotation under the effect of muscular forces in eccentric movements.
Factors of stabilization :
1. Shape of the jaws
Stabilization depends on the shape of the jaws; a U-shaped palatine vault is more favorable than a perfectly flat palate.
2. The occlusal scheme: bilaterally balanced occlusion
Generalized contact in eccentric movements and an occlusal plane parallel to the crest stabilize the prosthesis.
Accentuated cusp reliefs are unbalancing, hence the interest in fitting flat teeth when the crests are very resorbed.
3. Extensions
Extensions that increase sustenance also significantly increase stabilization; retromylohyoid fins (niches). Ampullary pockets.
Retention
Favorable reaction which opposes the forces exerted on the prosthesis to move it away from the support surface.
Physical factors of retention
1. Atmospheric pressure:
this is the pressure difference between two places that the peripheral seal creates.
It is said to be responsible for the “suction cup effect”.
2. Interface phenomena
* Membership:
It corresponds to the physical force that attracts the molecules of two bodies
Different.
In total prosthesis it is the force of attraction between the surface
supporting mucosa and the prosthetic intrados between which the
salivary film, So the thinner the salivary film, the more adhesion increases.
* Wettability:
is defined as the ability of a liquid to spread on the surface of a solid.
characterized by the angle of connection of the liquid with the solid.
Support, Stabilization and Retention in Complete Removable Prosthesis
* Capillarity
Ascent, with a concave meniscus surface, of a liquid in a capillary tube made of a material that it wets.
Corresponds to the force established between two parallel surfaces between which a layer of liquid is interposed.
Support, Stabilization and Retention in Complete Removable Prosthesis
Physiological factors of retention
1. Contact intimacy: To achieve retention by direct adhesion of the prosthesis/mucosa, a plate fitted to the palate to less than 0.007 mµ would be required.
2. Saliva:
The thickness of the film is inversely proportional to the detachment force of the prostheses. It is necessary to strive to obtain as thin a salivary layer as possible between the prosthesis and the mucosa.
The lower retention of mandibular prostheses can be explained by a much greater salivary flow than in the maxilla, which opposes the formation of an effective meniscus.
3. Peripheral sealing
Peripheral sealing prevents loss of adhesion due to air penetration or increase in fluid volume under the prosthesis.
The salivary film should be as thin as possible at the edges.
A seal is only achieved if the edges of the prosthesis are smooth, thick and rounded and rest on soft, depressible tissues.
Support, Stabilization and Retention in Complete Removable Prosthesis
Mechanical factors
1. Anatomical factors
The elements favorable to retention are
- a dense fibromucosa adherent to the underlying bone
- sufficient vestibular depth (at least 4 mm)
- wide, high, parallel-sided ridges
– a U-shaped palatine vault
– well-formed tuberosities without undercut;
– a horizontal soft palate allowing posterior extension
- pronounced and hard retromolar tubercles
- an internal oblique line not too prominent
- a sublingual region allowing the creation of an effective seal
2. Occlusal factors
Accuracy of intermaxillary relationship and fully balanced occlusion provide maximum adhesion during function.
Psychological factors:
They are essential and determine the integration of the prosthesis because if the patient does not accept his handicap, he will always have complaints to express.
An active effort of participation facilitates the integration of the prosthesis, allowing a more rapid adaptation of the musculature.
Surgical factors:
1. Pre-prosthetic surgery : can restore anatomical conditions necessary for proper retention and stability: -remodeling of bone hypertrophies, resection of fibrous hypertrophies.
2. Contribution of oral implantology
Implants greatly improve retention and stabilization, especially in the mandible.
Thus, two implants in the mandible and four in the maxilla allow the stabilization of the removable prosthesis and improve the patient’s comfort thanks to various means of retention (bars, snap buttons, etc.).
Support, Stabilization and Retention in Complete Removable Prosthesis
Cracked teeth can be healed with modern techniques.
Gum disease can be prevented with proper brushing.
Dental implants integrate with the bone for a long-lasting solution.
Yellowed teeth can be brightened with professional whitening.
Dental X-rays reveal problems that are invisible to the naked eye.
Sensitive teeth benefit from specific toothpastes.
A diet low in sugar protects against cavities.