Treatment of edentulousness in PPAC

Introduction :

Removable partial dentures are known as “the denture that ruins teeth.” Some studies reveal that nearly 50% of removable partial dentures made are not worn by patients because they do not “get used to” them. This results from a lack of adequate biomechanical study, a lack of oral preparations intended to receive the denture, and the poor technical quality of removable partial dentures in general.

The therapy of distal classes with mixed support of the restoration and its removable nature requires a detailed treatment plan with an adequate outline of the metal frame and a specific impression technique .

1. Definition of distal edentulism: (Also called: posterior, extension or terminal edentulism)

According to the Kennedy-Applegate classification:

• CL I KA: bilateral distal edentulism in extension (not delimited posteriorly by the remaining teeth)
• CL II KA: unilateral distal edentulism in extension (not delimited posteriorly by the remaining teeth).

A! These two classes can present modifications which correspond to edentulous segments added to the distal edentulism on the rest of the arch, we cite two which should be remembered:

• CL I mod 1: bilateral distal edentulism complicated by an embedded edentulism at the level of the residual arch
• CLII mod 1: unilateral distal edentulism complicated by an embedded edentulism at the level of the residual arch.

2. Characteristics of distal edentulism

• Class I KA : The loss of cuspid teeth results in an absence of distal occlusal blocking; this situation leads to significant disorders in the medium and long term, namely:

✠ Transfer of masticatory forces anteriorly, which results in a reduction in the height of the lower level of the face.

✠ Spreading of the sublingual glands and increase in the volume of the tongue.

✠ ATM disorders.

• Class II KA : This type of unilateral edentulism causes TMJ disorders due to unilateral chewing and the absence of posterior wedging.
• For both classes :

✠ Resorption of ridges due to afunction.

✠ Abrasion of teeth due to the presence of premature contacts or functional overload of a few teeth left alone in antagonism (anterior teeth in class I and posterior teeth in class II)

✠ Stagnation of bacterial plaque on the proximal surfaces opposite the hiatus

✠ Dental movements and extrusion of teeth deprived of their antagonists.

3. Objectives of partial restorations

• Compensation at all points for losses of alveolar and bone substances.
• Reposition the muscular and paraprosthetic organs in their most harmonious physiological position.
• Ensure the restoration of symmetrical mandibular positions and movements.
• Preserve the remaining teeth and their periodontium as well as the structures of the masticatory system.
• Restore essential functions: aesthetic and functional.

4. Treatment plan: The success of prosthetic treatment depends on compliance with the different operating times; no decision can be made without three elements: Clinical examination: (see clinical examination course)
   • Clinical observation
   • Radiological examination
   • Analysis of study models on articulator and parallelizer

Diagnosis and therapeutic decision:

Distal edentulism can be treated

• Fixed supra-implant prosthesis
• removable partial implant-supported prosthesis
• partial denture with metal frame (which is our subject of study)

5. The ideal layout of the KA Class I and II chassis:

Before tracing the removable prosthesis, the practitioner must choose the teeth that will support the clasps and the most suitable type of clasps as well as the most suitable plate. The design of the metal framework is the work of the clinician, because only he knows the problems inherent in the treatment of distal edentulousness and the Solutions that go hand in hand with these problems.

a- Problems related to the treatment of distal edentulousness: ^1st problem : Behavior of the supporting tissues:

In distal edentulousness (class I and II), PPAM requires two types of elements:

• the remaining teeth anchor supports
• alveolar ridges covered with adherent fibromucosa.

Knowing that the biomechanical behavior of these different tissues is dissimilar:

This is the notion of tissue duality or difference in compressibility between the fibromucosa of the edentulous ridges and the periodontal ligament of the hook-supporting teeth.

In fact, under the same pressure, the teeth depress by 0.1 mm and recover quickly and completely. While the fibromucosa depresses by 0.4 mm to 2 mm. This fibromucosa does not return to its initial shape as soon as the application of this pressure ceases, but very slowly ; this is viscoelasticity.

NB: due to this characteristic, any existing prosthesis must be removed several hours before taking an impression intended for making a new PPA frame.

Solution :

It is imperative to obtain a differentiation of movement between the fixed frame whose support is dental and the prosthetic saddles whose support is mucosal, and this By:

1. The creation of a secondary anatomical-functional impression: it allows to obtain the best possible relationships between the metal frame whose support is dental and the saddles whose support is muco-osseous, it allows to dissociate the support.
   • Definition: This is a partial impression that only concerns the ridges in extension. It uses the previously developed metal frame as support. This is a so-called partial correction impression, reconstructed model technique or McCraken technique.
   • Description

• Firstly, the frame is tried in the mouth to check that it fits properly. Afterwards, it is repositioned on the model and resin impression saddles are made over the grids (spaced by a thickness of a sheet of wax) and perforated to allow the impression material to escape and thus reduce the movement of the tissues on the support surface.
• In a second step, the shape of the edentulous ridges is recorded with a plastic wax at oral temperature (Korecta Wax® type). Currently we recommend elastomers or zinc oxide-eugenol paste and Kerr® paste. A remargination of the edges allows the functional play of the paraprosthetic organs to be recorded.

and ensure maximum coverage of the support surface, thus reducing the loads supported by the tissues.

• Finally, the impression of the support surfaces is taken while ensuring that the frame is held by the occlusal supports. After removal and inspection, the impression is sent to the laboratory.

• The master model on which the frame was prepared will be modified. Two perpendicular sections are made, the first distal to the most distal tooth, the second section is located inside the lingual vestibule. Thus, this lateral fraction of the model containing the edentulous sector is removed.
• The frame containing the impression saddles can, at this stage, be repositioned on the model thus prepared. Retentions are made using a cutter at the level of the sectioned areas, to improve the bond between the plaster of the model and that which will be poured at the level of the impression saddles. Careful formwork is made at this level and the impression is poured.
• The resulting model shows an accurate recording of the edentulous bearing surfaces with very good delineation on the edges of the play of the paraprosthetic organs.

2. Regular monitoring and rebasing of stools : helps to remedy changes in muco-osseous support over time.
3. The advantage of using hooks with a secondary mesial connection is that they allow the loads to be distributed in a balanced way between the bone tissue and the teeth; they promote the decomposition of occlusal forces.

The hooks that can be used are:

• The NALLY-MARTINET hook.
• The rear action hook.
• The Equipoise hook.
• The RPI system.
• ROACH hooks with mesial secondary connection.

2nd problem: the movement of the saddles in extension:

Due to its removable nature, displacements of the prosthesis are always possible in relation to the teeth and ridges, so they must be counteracted so that their amplitude is minimal.

The analysis shows that these movements are directly linked to anatomical and physiological factors which are:

• Anatomy of edentulous ridges.
• Different biomechanical behavior of support structures.
• Number and distribution of abutment teeth.

For TABET, the movements of a saddle in extension are in number of six fundamental movements:

Solution :

1. The secondary anatomical-functional impression: allows the movements of the stools to be reduced to a minimum, thus achieving the best possible balance between the prosthetic parts with osteomucosal support and those with dental support
2. The overall design of the chassis : which must counteract the movements of TABET:

• The vertical translation movement is counteracted:
  • In the apical direction: Mainly by the extent of the saddles. Partially by direct and indirect occlusal supports.
  • In the occlusal direction, by the action of the retentive arms of the hooks
• Horizontal translation movement : It is prevented by the hooks’ wedging arms.
• The mesio-distal translation movement : it is blocked by the secondary connections of the hooks and indirect supports.
• The vertical distal rotation movement :
  • towards the mucosa, it is slowed down by a large support of the stools.
  • Posterior lifting of the stool is prevented by indirect occlusal rests.
• The rotational movement around the axis of the ridge: Cancelled alternately by the action of the retentive arms and the wedging arms of the hooks.
• Rotational movement in the horizontal plane : Cancelled by all elements of the prosthesis.

2. The layout of the chassis itself
   • Ideal outline for mandibular class 1

• Means of support : AOD of the hooks, AOI in front of the dental arch and the cingulate bar
• Retention methods : Nally-Martinet hooks on each tooth bordering the gap
• Stabilization and guidance means : rigid parts of the hook arms (BC)
• Connection methods : Depending on anatomical conditions: Lingual bar if not lingual band and secondary connections spaced 3/10 mm from the mucosa between the hook support teeth.
• Ideal outline for maxillary class 1
  • Sustenance : AOD, AOI represented by the cingulate bar and the widely extended palatine plate
  • Retention : Nally-Martinet hooks on each tooth bordering the edentulous area and adhesion of the palatal plate to the fibromucosa
  • Stabilization : rigid parts of the hooks and cingulate bar
  • Connection means : solid palatal plate (6/10 mm thick) respecting the principle of undercutting anteriorly and 1 mm from the veil posteriorly or being more indented depending on clinical conditions, and rigid secondary connections spaced 3/10 mm from the mucosa.

• Ideal outline for mandibular class 2

• Support : occlusal supports, cingulate bar
• Retention : retentive arms of the Bonwill hook on the toothed side and Nally-Martinet hook on the edentulous side
• Stabilization : all the rigid parts of the hooks and cingulate or coronocingulate bar depending on the extent of the tooth loss.
• Connection methods : Depending on anatomical conditions: Lingual bar if not lingual band
• Ideal outline for maxillary class 2

Same principles as for class 1. Cochet Bonwill placed between 26 and 27 for aesthetics.

• Distal classes and modifications :
  • CL I mod. 1 KA:

If the modification is large, a frame is recommended according to biomechanical principles. On the other hand, if the intercalated tooth loss is small, the treatment will be done in two stages: treatment of the intercalated tooth loss by the fixed prosthesis, treatment of the distal tooth loss by the CL I frame.

• CL II mod.1KA:

The treatment of this type of edentulism will be done exclusively with a removable prosthesis for reasons of balance

• Distal edentulous side: tracing of CL II KA
• Intercalated edentulous side: 2 Ackers hooks
• Note 1:

On an isolated tooth bordering the embedded area, prefer a Ring type hook with 2 occlusal supports (mesial and distal)

Note 2:

When the tooth bordering the gap is a canine, the morphology of its lingual surface and its cingulum often leads to moving the lingual arm of the circumferential hook to a close distance from the marginal gingiva or to removing the lingual arm using an RPI type hook or the Roach system.

Roach RPI T Hook

Conclusion

Performing a PPAM is not a mechanical act, but a noble therapeutic act involving all biological, physiological and mechanical knowledge. The success of PPAM treatment is therefore conditioned by compliance with all the steps.

Bibliography

1. Jean and Estelle Schittly – Partial removable prosthesis: Clinic and laboratory – CDP Editions – 2006.
2. Pierre Santoni – Mastering the removable partial prosthesis – Editions CDP – 2004.
3. JC. Borel, J. Schittly, J. Exbrayat – Manual of removable partial prosthesis – Editions Masson – 1994.
4. JC. Davenport, RMBasker, JR Heath, JP Ralph – Atlas of Partial Removable Dentures Edition CDP-1990.
5. JN Nally – The removable partial prosthesis with cast frame: Principles and technique – 1979

Treatment of edentulousness in PPAC

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Treatment of edentulousness in PPAC