The different elements of a metal frame
1. Introduction
- The frame is the metal skeleton of a PPMA. It has several elements to describe, each having a well-defined role in the prosthesis.
2. Definition of a chassis
- The frame, the mass of the prosthesis, defined by “Raout” as being: “a skeleton which rests on the gingivo-bony crests, on the one hand supports the replacement teeth, on the other hand attaches and rests on a certain number of persistent teeth while avoiding subjecting them to actions which could harm their integrity”.
2. Alloys intended for chassis
2.1 The qualities required for Alloys
- Biocompatibility: Absence of toxicity-allergy
- Sufficient elongation.
- Resistant to wear and corrosion in oral fluids.
- High elasticity and high rigidity
- Easy handling with laboratory techniques
2.2 Alloys used
- Chromium-cobalt alloys
- Precious alloys (type IV gold)
- Commercially pure titanium.
3. the different elements of the metal frame:
- The metal frame is made up of several elements:
- The main connection
- Secondary connections
- The stools
- Hooks or attachments
- Each of these elements has a specific function and indication in the balance of PPMA.
3.1 Main connection or reinforcement
3.1.1 Definition
- According to Borel, it is the basic element of the PPMA, it connects the saddle(s) to the synthetic elements with dental support and is part, with the resin saddles, of the base plate.
- The basic element of the prosthesis to which the other elements are connected and allows them to work in synergy. There are several forms, differing depending on the type of arch and the extent of the tooth loss.
DEMAS OVEN 7 years
3.1.2 Important
- Its characteristics and roles differ between the maxilla and the mandible, but meet three common requirements.
- Rigidity and mechanical resistance
- Respect for osteomucosal tissues
- Ensure patient comfort
3.1.3 Main connection to the maxilla
- The frame plays an important role in support and a lesser role in stabilization. Different shapes are available.
3.1.3.1 The full coverage plate
Indication : significant edentulism with very reduced number of abutment teeth, especially in cases of CL I, II, IV, subtotal.
Disadvantages:
- Absence of detachment at the level of the gingival ring of the residual teeth.
- Risk of inflammation of the marginal gum, hence the need for good polishing of the metal.
- Requires strict hygiene.
- Patient discomfort due to the total covering of the palate.
Design :
- The anterior edge: extended to the cinguli of the remaining anterior teeth, to compensate for the absence of undercutting of the gingival ring, a discharge made from the intrados (0.8 mm on the median raphe).
- The Posterior edge: is located 1 to 3mm in front of the post-dam, in certain cases it may be desirable to establish contact on the line of reflection of the veil (2mm behind the palatal dimples) as for a complete prosthesis, it is then recommended to provide in the plate of 4 or 5mm, a grid is intended to retain a strip of acrylic resin (for precise post joint and modifiable without difficulty: palatal bicycle joint).
3.1.3.2 The wide or full palatal plate
- These are cast metal elements that rest heavily on the palatine vault, providing satisfactory rigidity and stability. Their thickness is 0.4 to 0.6mm. (5mm turning).
Indicated: in case of edentulism with dento-osteo-mucosal support (CL I, II, IV(KA): Medium or large extent.)
Benefits :
- Relieves supporting teeth: even distribution of forces.
- Contributes to the balance of the prosthesis.
- Comfortable: because the thickness is reduced and the front part is clear.
Design: It is limited:
- Antecedently : by a line connecting the occlusal supports avoiding negative indices (palatal and bunoid papillae)
- Posteriorly : a few millimeters before the velopalate junction; sometimes in the medial post region it can be notched depending on the anatomical conditions or respect the horseshoe shape when the palate is ogival with a fissured shape in certain cases when there is the presence of a palatine torus and also the presence of a significant gag reflex provided that the support on the lingual side of the ridges is not reduced and that the tuberosities are covered.
- Laterally : by the junction with the saddles.
3.1.3.3 Narrow plate
Indication
It is indicated for classes III, VI (KA) of small extent which only require dental support.
Benefits
provides rigidity without being bulky (slightly thick in its center).
Design
The turning meets the same criteria as those of the wide plate.
- The anterior edge : is limited to the distal faces of the teeth bordering the gap mesially.
- The posterior edge : ends at the level of the massial surfaces of the teeth bordering the edentulous area distally.
3.1.3.4 Single spacer plate or palatal bar
Indication
in cases of small intercalated edentulism (class III, VI).
Disadvantages
Disadvantages
- May cause speech disturbances.
- Uncomfortable for the patient if it is thick to provide rigidity.
- Non-rigid if it has a reduced section to ensure patient comfort, therefore it will be harmful to the supporting teeth, so avoid its use.
Design
It is a half-round section bar, located in the medial or post region of the palate (opposite the first or second molars), 6 to 8 mm wide and 2-3 mm thick in the center.
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1.3.5 Double palatal bar or double palatal spacer
Indication:
This is a point of work and dento-periodontal support and extended means.
CE III and CE VI, it can be used at the following table:
- Disadvantages:
- Lack of comfort for the patient due to the thickness of the anterior part which can require a more unpleasant tactile perception to the tongue than a plate developing more on the surface, but on a table thickness because in this type of double spacer plate the bars must create a rigid frame to ensure the distribution of forces over all the abutment teeth.
Design :
- The external contour conforms to the criteria described for the wide plate, namely the neckline, anterior and posterior extension.
- The double spacer provides a central palatal recess symmetrical with respect to the median axis:
- The anterior part : must free the retro-incisal area, frenulum so as not to hinder speech. 6 mm wide
- The posterior part : is located opposite the second molars. Symmetrical and parallel to the anterior bar and resting at the junction of the hard palate and soft palate, this posterior bar, slightly more rigid (9 mm wide) and thicker than the anterior bar, must be located in an area inaccessible to the tongue.
- The bar section has a half-played profile (convex shape), with a 2mm thickness in the center to ensure its rigidity. A 5 to 6mm undercut is provided at the level of the natural teeth.
- These bars are connected by two lateral segments, the latter must be symmetrical and 6mm apart from the remaining teeth.
3.1.3.6 The “U” or horseshoe plate
Indication:
CI I, II (KA) edentulousness with a large inoperable torus palate or a very deep palate with a fissured apex, nausea reflux.
Advantages:
patient comfort.
Inconvenience :
- Marginal periodontal trauma
- Lack of relative rigidity of the plate.
Design:
Two factors influencing the U-shaped plate layout are the number of remaining teeth and their value.
- Anti : the part affects 2 different tracings or it is limited by a line joining the mesial face of the abutment teeth limiting the edentulous segments joining the occlusal supports. Rests on the chapter of the anterior teeth (inverted U).
- Post: its post limit is delimited by 2 symmetrical lines which encompass the tuberosities following an orientation roughly parallel to the ridge line of the crests to meet towards the front, determining a more or less marked notch (their line corresponds to a horseshoe shape).
3.1.4 Main connection to the mandible
- The main connection cannot provide support or stabilization due to the small usable surface area at the anterior internal table. Its shape is guided by the anatomy of the internal table and the study of its axis to the parallelizer; its role is to connect the other elements of the chassis.
3.1.4.1 The lingual bar
- It represents the privileged connection to the mandible and only allows the saddles to be connected to each other and does not participate in support or stabilization because it is never in contact with the dento-mucosal support structures but is more or less erased depending on the classes of edentulism and the profile of the internal alveolar table.
Indication:
- Internal table with sufficient height.
- Low-insertion lingual frenulum.
- Oral floor in a low position.
- No gum recession.
Benefits :
- Allows good oral hygiene.
- Its height and thickness meet the criteria of mechanical resistance and regicide.
- Patient comfort: not perceptible by the tongue.
Design :
- Its section is shaped like a half-pear, the flat part facing the mucous membrane and the voluminous part facing the floor.
Dimensions: its thickness 1.7 to 2mm and its height of 3 – 3.5mm to meet the criteria of mechanical resistance and rigidity.
Situation :
- In the vertical direction; it must provide a clearance of at least 3.5 mm from the remaining teeth to protect the gingival rings and be 1 mm from the lingual frenulum.
- In the ant-post direction it depends on the orientation of the retro-incisal slope of the internal alveolar table.
- When the slope is vertical : the lingual bar is placed at a distance of 0.2 mm from the fibromucosa.
- When the slope is undercut , a gap of 0.4 to 0.5 mm must be left between the bar and the fibro-mucosa.
- When the slope is oblique from top to bottom and from front to back, the lingual bar will be 0.4mm away.
3.1.4.2 The lingual strip
Indications: contraindications for the lingual bar arise, in particular the space between the neck of the teeth and the floor of the mouth is insufficient to place the lingual bar (gingival recession, high insertion of the frenulum and floor of the mouth).
Contraindications: Contraindication of the lingual bar, poor oral hygiene.
Disadvantages: Using this type of main conjunction requires special precautions because it involves pardonable risks.
- Lack of comfort
- Discomfort during phonation
- Should only lose support on the cingulum of the teeth (food retention).
- The marginal gingival region should be unloaded (0.3mm) to avoid marginal gingival atrophy.
- Patient hygiene must be rigorous in order to avoid the appearance of slick card because the band comes into contact with the dental surface promoting their decalcification (corrosion), hence the need for daily application of fluoride gel to the internal face of the band as a prophylactic measure (careful polishing).
Design :
- It comes into contact with all parts of the lingual faces of the teeth located above the cingulum and then encroaches without touching it on the fibromucosa with a discharge of 0.3mm to end 1mm from the floor.
- Its thickness must be as minimal as possible without affecting its rigidity; it must be uniform except for the slightly swollen and rounded lower part.
- The band must be well wedged and well supported so that it can slide in the apical direction along the lingual surfaces of the teeth as on an inclined plane (traumatic action on the gum; irritation or chronic inflammation) for this it is necessary to associate indirect occlusal supports with the band.
3.1.4.3 The cingulate band (cingulate spacer or lingual plate)
- It is a thick metal plate (1.5 to 2 mm) resting on the enamel of the incisor-canine lingual surfaces, distant from the marginal gingiva and cementum (1.5 mm). The cervical embrasures are exposed to promote hygiene. As with the lingual band, hygiene must be impeccable.
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Indicated in the case where:
- The moving floor of the mouth is close to the marginal gingiva;
- The internal table is reduced to a minimum.
Contraindication: poor hygiene.
3.1.4.4 Double lingual and coronocingulate bars:
- Formed by a lingual bar and a cingulate bar (anterior), or a coronal bar (posterior) or both at the same time: coronocingulate bar.
3.2 Saddles and retention grids:
- Saddles: They cover and encompass the edentulous ridges up to the vestibular and lingual limits determined by the anatomo-functional impression.
- Retention grids: Rigid grid with more or less wide mesh covering the edentulous ridges and serving as an anchor for the resin of the saddles. A 0.5 mm discharge is provided at the level of the ridges in order to receive the resin of the saddles and will be 1 mm from the abutment teeth and 5 mm from the
3.3 Secondary Connections
These are metal parts that connect the main connection to the other elements of the chassis. They can be called secondary junctions and must meet 3 requirements:
- Rigidity and mechanical resistance : ensured by an ovoid or almost triangular section of 1.5-2 mm.
- Respect for soft tissues : A discharge of at least 0.2 mm is expected in contact with the gum.
- Comfort : They are well tolerated when located on the proximal surfaces of the teeth.
The different connection modes : the way in which the secondary connection connects the hooks to the saddle or to the main connection constitutes a connection mode, there are several connection modes:
- The rigid connection
- The breaking link
- The semi-rigid connection
4. Anchoring methods:
- Traditional attachment system : hooks
- Precision fastening system : prefabricated attachments.
4.1 Traditional retention methods: hooks
4.1.1 Definition
- The clasps are metal pieces cast around the supporting teeth, developed and cast at the same time as the other elements of the frame, allowing the prosthesis to be attached to the natural teeth.
4.1.2 Imperatives
- Preservation of the integrity of supporting tissues
- Girdling : the hook must encircle the tooth over more than half of its circumference.
- Retention by hooking and not by tightening : the elastic retentive end must be passive as soon as the prosthesis is in place, it only becomes active to oppose the movement of the prosthesis.
- Reciprocity of action : each retentive portion of the hook must correspond to a rigid portion, so the thrust of the end of the retentive arm when passing the bulge of the tooth must be absorbed by the elasticity of the metal and not that of the ligament fibers (scollodontic cifet).
- Cervical third position : the different parts of the hook must be located as close as possible to the middle of the cervical third to avoid versions.
- Reciprocity within the arch by symmetry of the retentive parts : the parts of the hook of each hemi-arch must be symmetrically arranged so that a vestibular retentive arm corresponds to a vestibular retentive arm of the hook of the opposite hemi-arch.
- Occlusal supports : In order to prevent any slippage of the rigid portion of the hook under the guide line, it will be essential to place the occlusal supports.
- Must be distanced from the gum
- Must remain in contact with the enamel and well adapted to it and must be perfectly polished so as not to create lesions of a mesh.
- Using an alloy of lower hardness than enamel in addition to careful polishing will prevent any wear of the enamel.
4.1.3 Description
- They systematically include three elements which contribute to the balance of the prosthesis (BOREL et Coll., 1994):
- A flexible arm
- A rigid arm
- An occlusal support .
4.1.4 Functions
- It helps ensure essential balance functions:
- Support : provided by the occlusal stop.
- Stability : ensured by the hook support arm.
- Retention : ensured by the flexible terminal part located under the guide line of the retention arm.
4.1.6 Classification
- There are several classifications, the simplest being based on the location of their junction with the metal frame.
4.1.6.1 Proximal Junction Hook
Ackers Hook (Ney No. 1)
- The most used.
- Rigid hook.
- It has an occlusal support, a retentive vestibular arm and finally a reciprocal buccal arm.
- The stem directly connects the hook to the saddle (ensures a rigid connection).
- The cleat is on the side of the tooth and the retention is on the side opposite the tooth.
- Indication : Embedded toothlessness.
Ring Hook
- A single arm goes around the entire tooth.
- The shape of an open ring in the mesio-vestibular angle where they take their retention.
- They have two occlusal supports. Their main indication is an isolated molar in the mesioventral region.
- It is characterized by the presence of 2 occlusal supports including:
- One is mesial, it extends the rigid task to the saddle.
- The other is distal located between the rigid part and the flexible part of the hook.
Modified Ring Hook : two arms with disto-vestibular retention.
4.1.6.2 Buccal Junction Hook
Nally-Martinet hook
- A single arm which starts from the stem and surrounds 2/3 of the tooth to end with a retentive end in the mesio-vestibular angle.
- The stem is long (side opposite the edentulousness) connected directly to the main connection (ensures a semi-rigid connection) and an occlusal support in the mesial position.
- Indication : Indicated on canines and premolars in posterior edentulous areas in extension.
- The advantages of these hooks are :
- Minimum trauma to the tooth with its mesial occlusal support avoiding coronal disto-version.
- Allows free play of the saddles thanks to its mesial secondary connection.
Rear action hook
- It is a variant of the Nally-Martinet, it presents a distal occlusal support opposite the mesial secondary connection.
- Indications : same indication as for the Nally-Martinet, tight occlusion, isolated molar.
The Equipoise hook
- Tooth-mortise system.
- Without visible vestibular arm.
- The use of this hook requires the development of a fixed prosthesis.
- Indication : Limited to embedded edentulousness because it is a source of harmful forces for the teeth when rotating the saddle in the sagittal direction.
- Contraindication : short teeth.
- Advantage : Aesthetics.
- Disadvantages : Tissue mutilation and loss of vitality.
The double crochet (Cavailer or Bonwill)
- Description : Very rigid hook consists of two fused Ackers which are connected to the framework on the lingual side and occupies the occlusal embrasures of two contiguous teeth and ensures retention thanks to two diverging arms on the vestibular faces, this type of hook requires the preparation of the marginal ridges which allow the passage of an arm sufficiently resistant to better meet these requirements.
- Indication : unilateral elements (CL II, cl VI) and for small class IV elements.
4.1.6.3 Vestibular Junction Hook
Roach System
- The majority of these hooks originate from the system developed by Roach.
- The bar hooks in C, L, U, S, I, R, T, Y,…..
- These are hooks with a gingival starting point.
- For all these hooks, there is a stabilizing element placed on the lingual surface ensuring reciprocity.
This vestibular arm ends in a flexible arm. - Indication : class I and II (KA).
- Advantages : They are aesthetic, because they approach the retention area through a cervical route.
- Disadvantages :
- The belt is not secured.
- The vestibular position of the retention arm can irritate the lip.
RPI Hook (RPI System)
- R (rest) : A mesial restraint with a lingual connection.
- P (Proximal plate) : distal plate.
- L : hook in “!”.
- Indication : cl I, II.
- Advantage :
- Limitations of torsion effects (I-arm).
- Reciprocity by opposition (Cleat and plate).
- Aesthetic and low cariogenic (Low contact surface).
4.2 Precision retention means: attachments (course of attachments)
5. Conclusion
- The partial prosthesis must first and foremost be considered as a therapy . The design of a metallic PPA requires:
- A precise knowledge of anatomical and physical conditions .
- An understanding of mechanical laws and their application.
- Knowledge of various systems and their elements.
- You should know that:
- Each element of a chassis must meet a precise indication.
- Any element that does not have an essential role must be removed.
- The simplest frames are the best tolerated by the patient.
The different elements of a metal frame
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Bleeding gums when brushing may indicate gingivitis.
Short orthodontic treatments quickly correct minor misalignments.
Composite dental fillings are discreet and long-lasting.
Interdental brushes are essential for cleaning narrow spaces.
A vitamin-rich diet strengthens teeth and gums.