The removable partial denture (PPR) is designed to replace lost parts. Able to resist the forces produced during chewing, swallowing and phonation that can dislodge it. They return the masticatory function and the lost aesthetic appearance ( Removables, Frameworks )
The PPR have conventional retainers that for reasons of cost, time, clothing, are reversible and not very aggressive. These prostheses are not rigidly fixed. They are subject to movements that cause stress and displacements of the prosthetic base. The retainers are designed and used to control these possible movements.
The prosthetic base is defined as the resistance against vertical forces that prevent prosthetic intrusion into the tissues.
The main support function in the dental loading route is given by the beds that contain the support of the retentive complex.
In cases of mixed load pathway, soft tissues also participate, determining a dual support of different resiliences. Obtaining good support, we protect periodontal structures and better distribute occlusal forces.
Retention is the resistance to displacement of the prosthesis in vertical sense that tends to dislodge it. This function is in charge of the retentive arms.
The flexibility of the retentive arm will allow its location in less or deeper retentive areas, establishing a lower or greater retention, respectively. The flexibility of the retainer is determined through the manufacturing material, shape, volume and length thereof.
In parallel guide planes, contact with its smaller connector provides a retention function through friction resistance.
Stability is the resistance of the prosthesis against
horizontal or oblique forces. This function is fulfilled by the rigid elements of the retentive complex, that is, the proximal two thirds of the retentive arm, the reciprocal arm, the occlusal supports and the minor connectors
Reciprocity is the ability to neutralize force
produced by the retentive arm on the pillar with an equal and opposite force.
The containment function is determined by the reciprocal arm, the two proximal thirds of the retentive arm and other rigid elements.
The circumscription is the extension of the perimeter of the pillar that must be covered by the retentive complex, with three quarters of the total circumference being accepted as ideal. Thus, the movement of the pillar outside the retainer structure is avoided.
Passivity is obtained by being the retainer seated in its final position on the pillar, without exerting any active force
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