Design of the metal frame layout

Design of the metal frame layout

The design of the chassis layout is the work of the clinician, many factors come into play in isolation or jointly that the sole observation of the model cannot highlight.

Interests of the route

* Clinical interest: its presence in the patient file allows us to perceive the importance of the planned prosthetic treatment as well as its impact on the support teeth.

*Role of vector of prosthetic directives intended for the laboratory prosthetist.

Principles of layout design

1.1. Biological principles:

• Rigid chassis, to ensure a balanced distribution of the forces developed during chewing
• Neckline and discharge: the outline must avoid all anatomically fragile areas. It must be at a distance from the marginal gingiva and respect the 5 mm rule of neckline. It must discharge all incompressible protruding areas and areas that are too depressible (such as the median raphe, retroincisive papilla, the internal oblique line, etc.) by interposing a spacer sheet.

The line begins at the proximopalatine angle on the side of the edentulousness and ends at the proximopalatine angle on the side opposite the edentulousness. The widest distance of the neckline is 5 mm from the middle of the palatine surface

• Occlusal stops: they prevent the prosthesis from sinking into the fibromucosa and the destruction of the deep periodontium.
• Anatomical functional impression: it will record the entire prosthetic support surface up to the functional limits and this to increase prosthetic stability.

Design of the metal frame layout

1.2. Biomechanical principles

• Class 3 case: The prosthesis fits inside the support polygon determined by the axes joining the occlusal supports àmechanically stable frame

• The prosthesis does not fit entirely within the polygon; rotational movement is possible around the axis joining the occlusal supports bordering the edentulous area.

1.3 Clinical principles: it takes into account:

* type of tooth loss:

• Extent : the importance of the edentulism requires us to extend the mucosal support when the dental support is insufficient
• Situation : a bilateral edentulism such as class I is more balanced than a unilateral edentulism such as class II, an additional edentulism located in the anterior region of the arch should prompt us to treat it with a joint prosthesis if possible because of the balance problems posed by these types of edentulism.

* the bio-morphological value of the remaining teeth and the osteo-mucosal base:

That is to say, the dento-osteo-mucosal factor (DOM): It specifies whether the support must be dental or mixed depending on the intrinsic and extrinsic value of the teeth and the biological state of the supporting fibromucosa, the DOM factor is said to be:

• Favorable when all of its components are morphologically normal
• Unfavorable when all of its components present anomalies or pathology.
• Moderately favorable when part of its elements presents an anomaly or pathology.

– occlusal relationships: Balancing occlusal relationships must be established in order to combat destabilizing movements of the prosthesis; the occlusal supports must in no case present any interference or occlusal prematurity.

1.4 Specific principles

Embedded teeth :  The prosthesis is tooth-supported:

• Support: occlusal stops on either side of the edentulous area.
• Stabilization: proximal, lingual or palatal guide surfaces.
• Retention: rigid connection,

                Short bracket hooks (Ackers or Ney ring type) · Attachments (slides or connecting bars)

The behavior of the non-deformable prosthetic element is in harmony with that of the dental support elements thanks to a rigid connection, therefore no scoliodontic effect. The support offered is dental, therefore ligamentous, in this case the prosthesis behaves like a joint prosthesis (bridge) the connection mode is rigid, it is obtained by short and non-deformable brackets connecting the hook to the saddle.

 Terminal edentulousness : The prosthesis is dento-mucco-supported,

• Support: mesial occlusal stop + dimensioned mucosal support.
• Stabilization: indirect supports, cingulo-coronary bars, guide surfaces and polished stabilizing surfaces.
• Retention: Semi-rigid connection hooks, Nally and Martinet type,                    

Flexible connection hooks, RPI type and Roach system, · Articulated connection attachments.

In this type of edentulism the problem posed is that of the duality of the support, it is a question of harmonizing the behavior of the prosthetic element with that of the elements of the support surface (teeth + fibromucosa) in order to avoid a scoliodontic effect and to distribute in an equitable manner the forces exerted on the entire support surface we realize what is called a semi-rigid connection which allows a separation of the saddle(s) in extension from the rest of the frame in this case the prosthesis can be broken down into two compartments one takes support on the teeth by means of the hook and the occlusal support the other part of the prosthesis rests on the crests by means of the saddles and whose movements are diverse.

CONCLUSION :

 The frame of a removable prosthesis with metal infrastructure is a high-precision prosthetic part. It must be constructed according to the tracings indicated on the model and the laboratory sheet, according to the practitioner’s instructions.

Design of the metal frame layout