Implant prostheses
The use of implantology in daily practice leads to a modification of the techniques and means implemented but also to synthetic management strategies. Indeed, the implant prosthesis is characterized by:
- a very good long-term prognosis,
- a high susceptibility to the biological environment,
- a high susceptibility to functional constraints;
Depending on the type of edentulism, different possibilities of synthetic reconstruction using implantology can be considered for total and partial edentulism.
1. Treatment of single tooth loss:
The treatment of single tooth loss is demanding and delicate. Its success depends on the choice, indications, and compliance with surgical and synthetic requirements.
- The sealed prosthesis:
It is defined as a restoration sealed on intermediate elements (false abutments) screwed onto the implants.
The major element of the sealed prosthesis is the false abutment C C is the intermediate piece between the implant and the sealed cosmetic superstructure.
Implant
Abutment
Screw
Cotton
Sealing Cement
Crown
- The screwed prosthesis:
C C is defined as a restoration screwed onto intermediate elements (abutments) themselves screwed onto the implants or “direct-implant” screwed, i.e. screwed directly into the internal screw thread of the implant.
Implant
Abutment
Crown
Screw
Cotton + Composite
- Indications and contraindications for sealed prosthesis:
- Indication:
- single cases or in small restorations,
- cases where the screw access hole of screw-retained restorations may compromise aesthetics and occlusal stability,
- restoration of poorly aligned implants, in the event of significant divergence of the implant axis,
- cases of small diameter teeth, thus avoiding screw access holes which would occupy a large portion of the occlusal table.
- Contraindications:
- cases of limited interocclusal space,
- long-range reconstructions or even of a complete edentulous arch where complications are more frequent, hence the need for re-intervention which only screw-retained restorations allow,
- situations where the cervical limit is more than 3 mm deep subgingivally.
- Advantages and disadvantages:
| Benefits | Disadvantages |
|---|---|
| – Preserved occlusal morphology; | – Risk of peri-implantitis due to excess cement, |
| – same protocol as on natural teeth; | – More difficult to demonstrate, |
| – easily correct, with great latitude, the implant axes if they are divergent from those of the crowns, | – unsealing, |
| – Aesthetic | – Great care must be taken when removing sealing cement. |
| – preserve the strength of the cosmetic material by limiting the risk of fracture, |
- Lower cost than using transscrewing,
- Easier accessibility in the posterior area in patients with reduced mouth opening,
- Possible compensation for an imperfect fit with cement.
❖ Indications and contraindications for screwed prosthesis:
- Indication:
- In restorations where the inter-arch height or inter-occlusal space (space between the implant tray and the opposing occlusal surface) is limited <7mm,
- In cases where the implant axis is favorable for this type of reconstruction.
- Contraindications:
- Prostheses representing a significant divergence from the implant axis,
- Prostheses where the screw access hole is located on a visible face which could compromise aesthetics,
- Cases of small diameter prostheses where the screw occupies a large part of the surface and could compromise occlusal stability.
- Advantages and disadvantages:
| Benefits | Disadvantages |
|---|---|
| – Easy disassembly, | – Altered morphology, |
| – the absence of cement. | – unscrewing, |
| – specific equipment, | |
| – Higher cost, | |
| – Need for a screw access well, ideally in the center of the occlusal surface or in the cingulate, |
- Need for perfect adaptation of the bridge on the:
implants or intermediate abutments (passivity), - Accessibility is sometimes difficult in the posterior sector due
to the significant height of the reconstructions which
require longer screwdrivers. - Screwing or sealing in implant prosthesis:
- Concordance of the implant axis and the prosthetic axis:
Thanks to modifiable abutments, the sealed prosthesis makes it possible to correct the divergence between
the implant axis and the ideal prosthetic axis.
- Screw access:
For cross-retained restorations, the emergence of the abutment screw must be located on the
lingual, palatal or occlusal side.
- Available prosthetic space:
This is the interocclusal space available between the implant tray and the occlusal faces of the
opposing teeth in ICM; reduced available height indicates the use of
screw retention.
- Maintenance and reintervention:
Thanks to the screw access hole, the screw-retained prosthesis is the most comfortable and
suitable solution for possible reoperations and maintenance.
- Cervical Limit Location:
The false stump-prosthesis boundary must not be too buried for the sealed prosthesis.
2. Treatment of partial edentulism:
In the presence of partial, embedded or distal edentulism, several therapeutic options
may be available and this depends on several criteria.
The treatment of multiple edentulism will depend on several parameters:
- Distal or recessed tooth;
- the condition of the teeth adjacent to the tooth loss;
- the extent of toothlessness;
- the location of the tooth loss;
- the aesthetic demand for toothlessness;
- The patient’s age;
- The patient’s psychological profile.
2.1 Partial supra-implant removable prosthesis:
- PAPSI indications:
- Kennedy Class I or II with one or both canines missing.
- Patients who, for aesthetic reasons, do not want the presence of hooks on their removable prosthesis.
- Kennedy Class IV with a long extension.
- contraindications to the placement of a large number of implants.
- Contraindications of PAPSI:
- Heart disease at risk.
- Major psychological disorders.
- Alcohol or drug addiction.
- The patient’s age.
- Local bone conditions.
- Advantages of PAPSI:
- Functional contributions: Increased retention and stabilization of prostheses.
- Aesthetic contribution:
- Has no hook, so very aesthetic,
- Severe resorption can be resolved by adding a false gum.
- Clinical contribution:
- Bone preservation around implants
- Better distribution of forces on the remaining teeth and implants.
- Scalable nature: This compromise solution gives the patient time to financially consider treatment with an implant-supported bridge (on 4 or 6 implants) or a PACSI on 2 or 4 implants.
Economic aspect: Treatment much less expensive than replacing each tooth with implants.
- Disadvantages of PAPSI
- Management of the temporary prosthesis
- Cost
- Duration of treatment
- Its removable character.
- Choice of PAPSI attachment system:
- Precision supra-implant attachments exist in various forms, chosen according to their location, the space available or the axes of insertion of the prosthesis.
- There are two main types of fasteners:
- axial attachments: ball, cylinder, magnetic;
- bar type fasteners.
2.2 Implant-supported dental bridge:
A dento-implant-supported prosthesis connects one or more dental elements, on the one hand, and one or more implant elements, on the other hand, in order to replace one or more missing teeth.
- Directions:
- Lack of healthy natural pillars;
- the implant indication(s) are limited:
- either because the anatomical constraints, reducing the implant possibilities, lead to an unfavorable distribution of the latter as support elements;
- either because there has been implant failure.
- Potential benefits of dental-implant-supported bridges:
- Increase in the number of therapeutic possibilities,
- Contribution of proprioception thanks to dental elements,
- Reduced cost and processing time.
2.3 Implant-supported bridge:
An implant-supported prosthesis:
- with an implant for each tooth
- or with a span.
In the case of implant-supported prostheses, there are two types of prostheses:
➢ Sealed prosthesis: The restoration is sealed onto the intermediate elements (pillars,
framework) screwed onto the implant.
- on abutment screwed onto implant:
- on screw-retained framework on implant:
➢ Screwed prosthesis: The prosthesis is screwed onto intermediate elements (pillars) which are themselves
screwed onto the implant.
- the prosthesis screwed directly onto implants:
- Prosthesis screwed onto abutment or framework screwed onto implant:
3. Treatment of total edentulism:
The advent of oral implantology over the past 30 years has made it possible to develop numerous reliable and effective implant-prosthetic solutions to rehabilitate completely edentulous
patients .
3.1 Implant-supported complete bridge:
- This prosthetic solution is chosen when bone resorption is low,
- The implant-supported full bridge is based on a large number of implants (8 to 12
implants), - From a biomechanical point of view, it most closely resembles a conventional full bridge.
- The practitioner has two means of assembly to ensure the connection between the
implants and the prosthesis: the implant-supported bridge can be sealed or screw-retained. - The number of implants needed to make this type of bridge is 8 to 10 implants.
- Directions:
- With a favorable inter-arch ratio,
- From poorly resorbed bone crest.
- Contraindications:
- An old tooth loss, associated with advanced resorption,
- Surgical contraindications for implant placement.
- The advantages:
- aesthetic;
- excellent patient comfort;
- maintenance similar to that of natural teeth;
- excellent psychological acceptance of the prosthesis.
- The disadvantages:
- inability to manage a significant inter-arch shift,
- Inability to manage lip and skin tissue support
- High number of implants to make this type of prosthesis.
3.2 Implant-supported fixed prosthesis with false gum (Prosthesis on stilts):
It is an intermediate solution between the implant-supported complete fixed prosthesis and the
supra-implant removable prosthesis. It attempts to combine the comfort advantages of a
fixed prosthesis with the aesthetic advantages of a removable prosthesis.
A complete prosthesis reproducing teeth and gums is screwed onto implant abutments
. The prosthesis is not in contact with the gum, hence its name of fixed prosthesis
on stilts. It consists of a metal frame which is screwed onto the
implant abutments on which commercial teeth are mounted, secured using
pink resin.
3.2.1 Branemark Bridge:
This is a complete fixed prosthesis without a palate that reproduces teeth and gums.
These are mounted on a metal framework, the whole thing screwed onto
implant abutments.
The prosthesis does not come into contact with the fibromucosa, hence its name “fixed prosthesis on
stilts.”
- Directions:
- A fixed-implant-supported total prosthesis is indicated when an implant-supported bridge cannot
be made. Indeed, this type of rehabilitation allows for the compensation of a shift in the
bone bases by mounting prosthetic teeth.
- A fixed-implant-supported total prosthesis is indicated when an implant-supported bridge cannot
- Contraindications:
- Contraindications are mainly surgical. On the other hand, this type of prosthesis allows for the compensation of moderate inter-arch discrepancy and is not indicated in the most severe cases.
- Advantage:
- non-removability of the implant-supported prosthesis;
- clear palace;
- prosthesis removable by the practitioner because it is most often screwed;
- possible replacement of part of the lost gum tissue using false gum.
- Disadvantages:
- difficulty managing lip and skin tissue support;
- difficulties in predicting the phonetic result (in the maxilla);
- aesthetic problem in the presence of a gummy smile;
- sometimes delicate maintenance.
3.2.2 Bridge all on 4:
In the case of total edentulism, with moderate to severe resorption, the All on 4 concept described by Paolo Malò finds excellent indications.
It could be considered as an alternative to procedures that require more advanced surgery (e.g. sinus lift, graft, etc.)
Only four implants for total rehabilitation in the maxilla or mandible:
- Two anterior implants.
- Two posterior implants angled at 45°.
- Possibility of performing distal extensions.
3.2.3 Bridge all on 6:
By analogy with the All-on-4 proposed by Maló, the term “All-on-6” is used to designate
screw-retained rehabilitations on six implants with an inclination of the distal implants.
3.3 The complete removable supra-implant prosthesis (PACSI):
In the maxilla, the reference treatment in removable prosthesis remains the
conventional prosthesis, the PACSI can meet the demand of certain patients requesting an
improvement in the retention of their removable prosthesis,
In the mandible, the McGill and York consensus (2002) clearly states that the
reference treatment in removable prosthesis for the completely edentulous mandible is the
implant-retained prosthesis on two implants and that patient satisfaction and oral quality of life
are clearly improved with this type of treatment.
Biomechanically, it is a removable implant-retained prosthesis, meaning that
the entire support surface is provided by the osteofibromucosal support surface.
Implants
- Benefits :
- Mechanically, improve the retention and stability of a conventional complete removable prosthesis.
- From an aesthetic point of view, compensate for bone resorption through the prosthetic base.
- To correct significant shifts in the bone bases (skeletal class 2) with a mounting of anterior mandibular teeth outside the edentulous ridge.
- Easy cleaning of prostheses, the attachment system and around implants.
- Treatment cost significantly lower than that of a BFIP on stilts, except in the case of PACSI with bar/counter-bar.
- Disadvantages:
- Removable solution, which can have a negative psychological impact on the patient.
- Crowding of the prosthetic base of the removable prosthesis, which covers the palate or lingual edges.
- Need for periodic maintenance and regular changing of the attachment system (abutments, retentive attachments, riders, etc.).
- In fact, the number of sessions and the cost of maintenance and re-intervention are the criticisms most often expressed towards this type of prosthesis.
Number and location of implants:
- In the maxilla:
- It is recommended to use at least 4 implants to achieve a maxillary overdenture , the implants will be placed in front of the anterior wall of the sinus in the premaxilla on either side of the nasal-palatine foramen .
- At the mandible:
- The implants are placed in the mental symphysis, in front of the mental foramina .
- Due to the quality and quantity of bone allowing good primary stability of the implants, but also less mechanical constraints than in the posterior sectors or even easier accessibility to hygiene means.
- In the interforaminal region, 1 to 4 implants may be necessary to stabilize a complete removable prosthesis.
- A single implant:
- A single implant for retaining a complete mandibular denture was first introduced by Cordioli et al in the 1990s.
- PACSIs connected to a single symphyseal implant may be indicated in geriatrics, in certain cases of severe atrophy or for financial reasons.
- Other advantages include reduced operating time, post-operative complications and cost for patients.
- Two implants:
- The use of two implants to stabilize a complete mandibular prosthesis is the standard treatment. The distance between two symphyseal implants must be between 21 and 27 mm.
- Three to four implants:
- Using 3 to 4 implants would be of interest in clinical situations of high resorption to limit the support on areas that are painful to pressure when the opposing arch is toothed.
- When the number of implants is greater than 2, the distance between the centers of the implants must be between 12 and 16 mm, for the case of four implants it must be less than 12 mm.
The different means of retention:
- There are two main categories of attachment systems:
- Axial attachments of the ball, cylinder or magnetic type;
- Bar type attachments or solid attachments.
- Ball type attachments:
- Are the most frequently used. They include:
- A male part (the patrice) connected to the implant: it consists of a screw thread, screwed to the implant, a transgingival collar and a ball-shaped retentive part (receiving the female part).
- A female part (the matrix) embedded in the base of the prosthesis: it consists of a metal cap in which there is generally a retentive part made of activatable gold alloy, nylon or silicone.
- Their mode of action is based on mechanical retention.
- Are the most frequently used. They include:
- Cylindrical attachments:
- are made up of:
- From a cylindrical male part.
- A female part composed of a titanium matrix in which there is a nylon retentive part, called a “sheath”.
- There are different sheath colors depending on the desired friction force intensity.
- The mode of action of this type of attachment is based on:
- Either on a friction system alone, which does not require any deformation: the two parts of the attachment come into intimate contact over the largest possible surface area.
- Either on a mechanical retention and friction system (for example the Locator® system).
- are made up of:
- Electromagnetic attachments:
- They are rarely used. Their retention method is ensured by the production of magnetic fields. However, this type of attachment is the cause of many problems such as corrosion, wear, or demagnetization.
- Bar attachments (solidified):
- Consist of:
- From a male part: a metal bar (gold alloy or machined from titanium), with or without distal extensions, connected to implant abutments, themselves screwed into the implants.
- From a female part, the riders (in gold alloy or hard plastic), embedded in the intrados of the prosthesis.
- Their mode of action is based on friction or mechanical retention. These attachments require more vertical space and are more expensive, which limits their indications.
- Consist of:
- Clinical criteria influencing the choice of overdenture:
- PACSI location:
- In the maxilla: we have chosen to secure the implants in the maxilla, and therefore to use a connection bar.
- Shape of the alveolar ridge:
- A straight anterior arch between the two implants is the favorable situation which allows the use of a retention bar.
- Implant parallelism:
- Implants supporting axial attachments must be parallel.
- The alternative to this choice is to use a conjunction bar.
- Cost of treatment and implementation:
- The retention bar requires more sophisticated design and is more expensive than axial attachments.
- Implementing axial connections requires fewer laboratory steps than connecting bars.
- PACSI location:
2.4 The implant-supported telescopic complete removable prosthesis:
It is a prosthesis inspired by the first retention systems for supraradicular removable prostheses with telescope crowns.
The system consists of two parts: one part consisting of parallel abutments with a low taper screwed onto the implants, and one part with gold copings integrated into the complete removable prosthesis.
The friction developed by the interlocking of the elements ensures retention and stability.
Biomechanically, it is an implant-supported removable prosthesis, meaning that support, retention and stability are essentially provided by the implant abutments.
The mechanical principle is based on friction, so the higher the number of pillars and their symmetrical distribution, the more the biomechanical behavior of the prosthesis makes it comparable to that of a fixed bridge.
- Benefits:
- Easy to clean prostheses and implant abutments, they do not cause food retention or halitosis.
- Easy insertion/disinsertion thanks to the guidance of the telescopic pillars.
- Longer-lasting retentive effectiveness than the complete supra-implant removable prosthesis.
- Lower treatment cost than a full implant-supported bridge.
- Disadvantages:
- Removable solution which can have a negative psychological impact on the patient.
- Retention is sometimes too high, some patients may have difficulty removing the prosthesis.
- Need for a prosthetic space of at least 10 mm from the opposing arch to place the abutments.
Conclusion:
Implantology has radically changed the practice of dental surgery. Conventional prosthetic treatments must now be compared with implant-supported prosthetics in terms of benefit/risk for the patient.
It is therefore essential that general practitioners can master the design and production of implant-supported prostheses .
However, this implies for practitioners the acquisition of the necessary knowledge through appropriate quality training.
Implant prostheses
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