The components of the chassis
Definition
The soul of the prosthesis represents a framework adapting to a partially edentulous arch, taking support from the remaining teeth and the gingivo-osseous crests.
Metal chassis:
- Main connection
- The saddles
3. Secondary connection
4. The hooks
1. The main connection
It is the basic element of the prosthesis, it brings together the different components and allows them to work in synergy, and covers the gingivo-osseous support surface.
It must comply with certain requirements:
- Must be rigid.
- Ensures patient comfort.
- Respect for osteo-mucosal tissues
Main connection to the upper jaw
- Wide plate: it rests largely on the palatine vault, its posterior edge is located at the hard palate-soft palate junction, in order to ensure an equal distribution of occlusal loads. It is indicated for Class: I and II of large extent.
- Double spacer plate: This is a plate hollowed out in its center, consisting of an anterior strip and a posterior strip. Half-junction section;
Indicated for intercalary edentulism.
- Narrow plate: It is inscribed between two lines, one anterior and the other posterior, connecting the proximal faces of the teeth bordering the edentulous area.
Indicated for embedded edentulism.
Main connection to the mandible
- The lingual bar: half-pear shaped, its flat part facing the mucosa. And its bulky part facing the floor. It is 1mm from the frenulum.
- The lingual strip: Indicated in case of contraindication of the lingual bar, in front of a very reduced height of the internal table. It comes into contact with all parts of the lingual faces of the teeth then covers the internal table and ends 1mm from the floor of the mouth.
2. Secondary connections
These are metal parts used to connect the hook or indirect supports to the main connection, and have a roughly triangular section.
They must meet the following requirements:
- Rigidity: their diameter must be sufficient 2mm.
- Respect for osteomucosal tissues
- Patient comfort they will be located at the level of the interdental spaces of the teeth bordering the edentulousness
Their ROLES are: to transmit the applied forces to the abutment teeth, and to increase the mechanical resistance of the chassis.
- Saddles: These are metal parts located on the edentulous ridges. They are spaced 1.5 to 2 mm from the supporting mucosa of the edentulous ridges. Posteriorly located before the tuberosities and the retromolar trigones.
- The hooks: It is a metal part elaborated and cast at the same time as the infrastructure, allowing to solidify the prosthesis to the remaining teeth. It covers more than half of the circumference of the tooth, and ensures the RECEPROCITY OF ACTION.
The known functions of the hook are: support, stability, retention.
The cast hook is made up of different parts:
- Retentive arm.
- Wedging arm.
- Occlusal rests: These are metal elements resting on the occlusal surface of the teeth: occlusal stops or cingulate rests.
There are 2 types of dental supports:
- Direct dental supports : they will be located on the teeth limiting the edentulous segments and forming part of a hook.
- Indirect dental supports : located at a distance from the edentulous segments, and not forming part of a hook, they will have the additional function of opposing rotational movements.
Conclusion
The production of the removable partial prosthesis frame has undergone numerous improvements; it will only fulfil its therapeutic role with:
1. a clinical examination.
2. a good knowledge of the indication and role of each element of the chassis .
3. the conservation of the elements of the residual arch.
4. patient education and motivation .
The components of the chassis
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