TREATMENT OF DISTAL EDENTULA
INTRODUCTION :
The success of prosthetic treatment depends on compliance with the different operating times and no decision can be taken in the absence of 3 elements:
-Clinical observation
-The radiological examination
-Analysis of study models on articulator and parallelizer
1- PROBLEMS POSED BY DISTAL EDENTULA AND THEIR SOLUTIONS
The ideal layout of the chassis of classes I and II K. A of class 1 modification 1 of class II modification 1:
Before moving on to the different elements making up the KA class I and II chassis, let’s see what the different problems are in the treatment of distal edentulousness and the proposed solutions:
The first problem is related to that of tissue duality
The second is related to the different movements that affect the prostheses in extension
1-1-The first problem: tissue duality:
Classes I and II KA can only be treated with an attached partial prosthesis since it is a posterior edentulism, the prosthesis will rest on a mixed dental and osteo-mucosal support, on the other hand, in the case of embedded edentulism of one of classes III, VI, V, VI, it is necessary to choose first between a fixed prosthesis and a removable prosthesis and in the case where we choose to treat with the removable the support will be essentially dental, therefore in the treatment of distal edentulism the prosthesis produced rests on both dental supports and on a muco-osseous support, under penalty of unbalancing or overloading one or the other of the support elements, how in these conditions can the construction be harmonized while respecting different if not opposing physiological and biomechanical requirements?
It was long believed that fibromucosa was elastic and that after applying pressure it could return to its original shape. Currently, if we accept that fibromucosa can be depressed by 0.4 to 2 mm under the effect of pressure, we know that the return to the previous volume does not occur as soon as the application of the force exerted ceases/
This behavior, which is none other than viscoelasticity, was brought to light by works to which are attached the names of Turk, Daly and Kydd, Pilloud, Nally and Cimasoni, Piton and Wills.
Through its desmodont, the tooth undergoes a physiological axial depression limited to 0.1 mm, whereas it is 0.4 to 2 mm at the level of the fibro mucosa.
It cannot therefore be denied that the ground on which the saddles of a class I or class II KA prosthesis rest is unstable: it is not elastic, but it transforms
Solutions:
- The secondary anatomical-functional impression: to the extent that it allows the best possible relationships to be obtained between the metal frame whose support is dental and the saddles whose support is muco-osseous, it allows the support to be dissociated.
- Regular monitoring and rebasing of stools: helps to remedy changes in muco-osseous support over time.
- The interest of using hooks with occlusal support: eight hooks which differ from each other by the position of the secondary connection, and the occlusal support, were subjected to experimental series, the best results were obtained with the Nally Martinet hook, then the posterior action hooks, both with mesial secondary connection.
A/The Nally – Martinet hook: it is a hook with a mesial secondary connection, used in order to distribute the loads between the bone tissues and the teeth in a balanced way. It promotes the decomposition of occlusal forces into:
- A component directed along the long axis of the tooth, well tolerated, using the numerous oblique fibers of the desmodont
- A horizontal component with a disto-mesial direction that maintains close contact with the neighboring tooth and therefore allows the teeth present on the arch to participate in the retention of the abutment.
TREATMENT OF DISTAL EDENTULA
*It allows more regular solicitation of the fibro mucosa by the stools by favorably modifying the axis of the movement described by it when they are loaded
*It allows relative independence of the saddle from the abutment teeth, therefore it allows the viscoelasticity of the fibro mucosa to be expressed.
*It avoids the distal version of the abutment tooth.
*This is the least traumatic hook for the tooth, its elasticity relieves the supporting tooth.
B- The posterior action hook : Differs from the Nally-Martinet hook only by the cleat which is located in the fossa opposite the connection due to the morphology of the abutment tooth, or a difficult occlusion.
The main indication for this hook is for isolated posterior teeth.
1-2-Second problem: the movement of the saddles in extension:
The analysis shows that these movements are directly linked to anatomical-physiological factors which are:
- Anatomy of edentulous ridges.
- Biomechanical behavior differs from support structures.
- Number and distribution of support teeth
For Tabet, the movement of a saddle in extension considered in isolation can result from the combination of 6 fundamental movements in the 3 planes of space
- 3 translation movements: Vertical translation/Horizontal translation/Mesio-distal (or disto-mesial) translation.
- 3 rotation movements: Vertical distal rotation./Rotation in the horizontal plane. Rotation around the crest axis.
TREATMENT OF DISTAL EDENTULA
Solutions:
- The secondary anatomical-functional impression: allows to reduce to a minimum the movements of the saddles, thus obtaining a better possible balance between the prosthetic parts with osteo-mucosal support and those with dental support.
- 2- The overall design of the chassis: which must counteract Tabet’s movements:
- The vertical translational movement is counteracted:
In the apical direction: mainly by the extent of the saddles, partly by direct 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 wedging arms 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 saddle lifting is prevented by indirect occlusal supports
e-The rotational movement around the crests: • 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.
II- IDEAL TRACE OF THE CHASSIS OF CL I AND II (KA):
Let us recall that the PPA is made up of:
• From a main connection
• From a secondary connection
• Retention hooks and grids.
II/1-Class I Inf. (KA):
A-Main connection : lingual bar, when clinical requirements allow, i.e. the space between the floor of the mouth and the necks of the teeth is ≥ 7 mm
Its section is half-pear shaped with the flat part towards the mucosa and the most voluminous part towards the floor of the mouth, its width is 1.7 mm to 2 mm depending on its length, its height is 3.5 mm. Placed approximately 0.2 mm from the gum when the internal table of the mandible is vertical, when it is oblique it is moved away from the fibro mucosa.
When the space between the floor of the mouth and the neck is < 7 mm and if the teeth have an unfavorable morphology, a lingual strip will be made. The latter comes into contact with all parts of the lingual faces of the teeth located above the cingulum (line of greatest contour), then encroaches on the fibro mucosa without touching it with a discharge of 0.3 mm, to end 1 min from the lingual frenulum. Its thickness must be as minimal as possible without affecting its rigidity.
This strip must not slide along the lingual faces of the teeth, hence the creation of indirect supports. Their role is to transmit to the abutment teeth the forces developed by chewing, and increase the mechanical resistance of the frame.
They must satisfy three requirements: rigidity and resistance ensured with a section of 1.5 to 2 mm, respect for soft tissues, patient comfort, they are preferably located at the level of the interdental spaces because of the perceptibility by the tongue, they have a triangular section to avoid any pressure from the interdental papilla or the fibromucosa, a discharge of 0.2 to 0.4 mm must be provided.
TREATMENT OF DISTAL EDENTULA
B- Hooks:
- Nally-Martinet hook: with its direct mesial support and its secondary connection is one of the least traumatic hooks, indicated on premolars and canines (unaesthetic on the canine, we prefer the equipoise, or bar hook the Nally-Martinet has a continuous arm on ¼ of the circumference of the tooth, the rigid part of this hook rests above the guide line, its lingual end is connected to the framework by a mesial secondary connection extending by an occlusal cleat. Retention is ensured by the vestibular end crossing the guide line in the mesio-vestibular part.
- Rear action hook: differs from the previous one only by the position of the cleat which is located in the dimple opposite the connection.
- Equipoise hook This hook is made on a sealed restoration, it includes a mesial support related to a semi-precision slide. The hook principle is as follows:
-engage the abutment tooth on the mesial face by a stabilizing element and on its distal face by a clamping element acting reciprocally with respect to the first
-between these two elements, the rigid lingual arm of the hook ensures the tooth-prosthesis wedging; prosthesis – tooth
– the tooth support hook support mode is done according to a tenon-mortise system, the female part is made at the expense of an element sealed on the mesial face the male part is carried on the secondary connection, the flexible end of the retention arm on the distal face. this very inconspicuous hook is delicate, it requires the preparation of an element sealed on the support tooth, therefore it requires meticulous aesthetics it is contraindicated when the clinical crown of the abutment tooth is very short it is also contraindicated when the preparation of the stump does not leave enough space in the interdental space at the level of the mesial face of the abutment tooth .
4- bar hooks: the basic principle of Roach.
The most common shapes are T-hook / Y-hook / I-hook / RPI system
C-Indirect occlusal rests: Indirect rests include
- Secondary occlusal supports.
- Cingulate bars which are continuous type secondary supports resting on the cingulum of the anterior teeth. They ideally rest on surfaces prepared for this purpose.
- Role of indirect occlusal supports:
- They fight against the forces tending to dislodge the prosthesis, following a rotation of the saddles in the occlusal direction, or a horizontal translation of the latter.
- They limit the stresses applied to the abutment teeth
- They contribute to a better distribution of occlusal loads, these supports are essential for the mandible given the small extent of the support surface, or will use two supports on the mandible (C1 1 Inf.)
- They will be all the more effective the further they are from the direct occlusal supports, with the aim of extending the support polygon (the support polygon is formed by connecting the support lines which connect the occlusal supports of each hemi-arch).
II/2- Class I Sup. (KA):
- Main connection: For a better distribution of forces over as large a surface as possible, the production of a full platinum plate is essential. At the back, this plate can end 1 mm in front of the palate; it can be slightly indented depending on the anatomical conditions. In front of the palate, the plate must be widely cut behind the remaining teeth, leaving the region of the anterior palatine foramen and the median papilla completely uncovered. If there is a median torus, provide a relief of 0.2 to 0.3 mm to prevent the prosthesis from tilting at this level.
- Secondary connection: In the upper jaw, it is important to minimize the number of secondary connections that may be more bothersome to the tongue.
- Hooks: Same type of hooks as for C1 Inf. (KA).
- Indirect occlusal supports: The presence of a full plate that rests largely on the palatal vault reduces the importance of the occlusal supports in relation to the lower arch; if necessary, they can be placed on the secondary connection of the hook.
II/ 3- Class II Inf. (KA)
A/The toothless side: this is a portion of the Cl Inf. (KA) chassis.
B/The toothed side: to balance the unilateral saddle of this type of class, it is necessary to take an effective and resistant anchor. On the opposite side, the double Bonwill hook is particularly indicated; it is most often located on the second premolar and the first molar on the side opposite the saddle. On the Bonwill hook side, the indirect and useless support is therefore eliminated.
II/4-Class II sup (KA)
In the upper jaw: for aesthetic reasons in particular, the Bonwill hook is sometimes placed between the first and second molars. The palatal plate must be cut not only anteriorly but also in the area of approach of the remaining teeth on the dentate side. A distance of free fibro-mucosa of 6 mm must be left between the plate and the neck of the teeth in order to avoid any alteration of the gum.
The wedging of the plate and the rigidity of the double hook make it possible to eliminate indirect support.
TREATMENT OF DISTAL EDENTULA
II/5- Class I modification 1: KA
It is always advisable to treat this type of tooth loss in two stages, namely, by first carrying out
- A fixed bridge to fill the embedded edentulous segment
- Then a removable prosthesis, typical of class I (KA)
It is particularly important to respect this principle when the embedded edentulism immediately follows the last remaining tooth on the arch. In fact, an isolated abutment tooth with a saddle extending backwards is always in a precarious situation from a biomechanical point of view. If the construction of a bridge is impossible depending on the patient’s budget, it is necessary to combine as best as possible the principles of making a frame for an extension prosthesis , with those that are respected in the treatment of embedded edentulism.
TREATMENT OF DISTAL EDENTULA
II/6- Class II modification 1 lower (KA):
On the contrary, it is in our best interest to treat the entire tooth loss with a removable prosthesis on the saddle side or as an extension; we design the frame like that of class 1 (KA) or class II (KA).
At the saddle level embedded on the opposite side, two Ackers hooks can be used if there is some doubt about the long-term preservation of the last pillar, a Nally-Martinet hook can be used for example on the premolar, in order to plan a transformation of the class II mod 1 prosthesis into class I after the loss of the last molar
II/7- Class II mod I sup (KA) the same remark can be made for the upper jaw it is necessary to insist on the need to take into consideration the saddle in extension by the outline of the main connection which always includes a palatal plate the creation of two occlusal supports (hook ring) on an isolated abutment tooth bordering an embedded edentulous zone seems like a simple and effective solution.
III- PREPARATION IN THE MOUTH:
The preparations only concern the enamel. To create the surfaces according to the chosen insertion axis,
This retouching allows the creation of guide surfaces allowing the insertion and removal of the prosthesis along an appropriate axis.
The 2nd touch-up concerns the creation of the support boxes using a ball mill,
IV – THE WORK FOOTPRINT:
It is obvious that the success of the prosthetic treatment depends on the quality and precision of the impression. This implies a judicious choice of the impression material such as synthetic elastomers meet this requirement. The casting is done with extra-hard plaster and the working model thus obtained is analyzed on the parallelizer.
V- TEST OF THE BARE CHASSIS IN THE MOUTH
Once the metal frame is cast in the laboratory it must be tried in the mouth
1-Control of adaptation to dental and osteo-mucosal structures
2-Control of the intensity of the forces used during insertion
3-Control of occlusion reports
VI- THE ANATOMO-FUNCTIONAL IMPRINT:
Clinical experience shows very clearly that there can be a clear difference between the profile of an edentulous ridge recorded at rest or <under load>. This reflects the settling of the mucosa under the effect of functional stresses and explains why cl I and cl II or VL prostheses made without taking this into account very quickly lose the essential support that the edentulous alveolar edges must provide them. They become unstable, the occlusion is disturbed and the pillars are abnormally stressed.
How to make the impression of edentulous ridges subjected to a functional load?
Only techniques resulting in a corrected working model validly meet the needs for this purpose we will use the secondary anatomical functional impression this impression aims to obtain the best possible relationships between the metal frame whose dental support and the saddles whose support is muco-osseous
It is functional in the sense that it is made using a material that exerts slight pressure on the soft tissues and that during its realization the patient is made to practice the different movements of the tongue, lips and cheeks.
The most widely used impression technique remains the partial correction impression.
This is an anatomical functional impression of interest only to edentulous ridges and allows the correction of the working model resulting from a global impression in a single stage on which the metal frame was developed.
TREATMENT OF DISTAL EDENTULA
1-Partial correction imprint : this technique described by Mac-Cracken
The material: In the original method the impression is taken with a thermoplastic wax at oral temperature: Kerr korecta-wax no. 4.
Technique: After the frame has been tested in the mouth, the outline of the future saddles is drawn on the model, taking into account the position of the mucogingival line as well as the muscular and frenal insertions. Self-polymerizing resin saddles are constructed on the model after adjustment of a 4 to 5/10 mm thick spacer wax on the model.
Checking the situation of the edges of the saddles, impression holders, retouching of the over-extensions. Brushing the intrados with wax liquefied in a thermo bath at 60°.
The frame is placed in the mouth without seeking optimal insertion and the patient is asked to close his mouth without clenching his teeth for 3 to 4 minutes.
During this time, the wax will acquire in the mouth the plasticity favorable to taking the impression.
The chassis is fully secured by pressing on the occlusal supports. Under no circumstances should any pressure be exerted on the saddles themselves so as not to distort the chassis-toothed ridge relationships. The excess wax flows outwards.
The frame is removed, the print is rinsed immediately with cold water and dried.
Examination of this first print reveals:
The shiny areas reflect intimate contact of the wax with the ridges.
Dull folded areas indicating a lack of material.
A supply of liquefied wax is applied to these areas and the internal part of the edges of the impression saddles.
A few minutes after insertion, apply new pressure and the patient repeats the functional movements (traction of the tongue, cheeks and lips) for 4 to 5 minutes.
The imprint is removed, passed under cold water and dried; its examination should reveal a perfect imprint of the tissues over the entire extent of the stool.
Otherwise, add wax to the areas where the imprint is insufficient and repeat the operation.
We remove all excess wax that may cover the external surfaces of the impression tray and cut half the length of the walls of wax number 4 with a scalpel. When making the impression of the peripheral seal.
Avoid putting it on the posterior lingual edge of the impression tray at the level of the mylohyoid crest where the prosthesis must end up thin.
A new layer of wax No. 4 is placed on all edges of the impression on the internal and external sides.
The frame is replaced in the mouth fully and, after letting the wax soften, the previous functional movements are repeated for 8 to 10 minutes.
Before removing the impression, it is thoroughly rinsed with ice water while the frame is firmly held in the correct position on the teeth.
The print is removed with great care, avoid touching its edges or surface with your fingers. It will be checked one last time after rinsing it with cold water and drying it.
2-Technique of the reconstructed or corrected model : its preparation requires 4 times:
- Removal of the material fixed on the intrados of the chassis.
- Cutting of the model allowing the chassis to be replaced without interference.
- Bonding the chassis to the model using sticky wax.
- Formwork of the imprint and pouring of the plaster
XII- RECORDING OF OCCLUSION AND PLACEMENT IN ARTICULATOR:
XIII- FUNCTIONAL TEST:
Phonetic control:
Stability control
Occlusion control.
TREATMENT OF DISTAL EDENTULA
XV- POLYMERIZATION AND FINISHING OF THE PROSTHESIS:
XVI- APPETIZATION AND CONTROL:
When placing the prosthesis in the mouth, it is essential to check:
- Insertion of prosthesis. Correct placement.
- Occlusion in centric relation and maximum intercuspation.
- Lateral and propulsive movement.
- The patient must be instructed on: how to put on and take off the prosthesis the rules of personal hygiene to apply the regular checks that are necessary.
- A first check after 6-8 months is essential for rebasing the stools; for this, the use of an anatomical functional impression is recommended.
Extension stool movement
