Joint and periodontal prosthesis

Joint and periodontal prosthesis

Introduction The success of all fixed prosthetic restorations is essentially represented by the maintenance of periodontal health. Indeed, these restorations are subject to mechanical imperatives which must not go against biological imperatives.

I – Periodontal evaluation of supporting teeth:

The assessment of the periodontal state is essential for the diagnosis and the implementation of the prosthetic treatment plan. This assessment must lead the practitioner to determine not only whether the periodontium is healthy or diseased, but also whether it is able to withstand the aggression represented by the creation and placement of a joint prosthesis.

1. Hygiene assessment and plaque control:

Oral hygiene should be assessed during the clinical examination; any fixed prosthesis will be contraindicated if the degree of hygiene is found to be insufficient. The longevity of any prosthetic restoration and the long-term prognosis of any prosthetic treatment are closely linked to the quality of oral hygiene.

2. Evaluation of periodontal health : This is done during the clinical examination and the radiographic examination.

B-1) Evaluation of the superficial periodontium:

• Color and surface appearance of the gum : the gum has a slightly granite-like surface appearance, coral pink, sometimes pale red.
• The height of the attached gingiva : According to Maynard and Wilson, a sufficient height of keratinized tissue is 5mm (safety zone), including 2mm of free gingiva, and 3mm of attached gingiva, therefore seems to limit in the long term the incidence of signs of inflammation and gingival recession.
• Keratinized Gingival Thickness: Regarding gingival thickness, the assessment test consists of placing a colored periodontal probe in the sulcus and assessing its visibility through the tissues. If the probe appears transparent, the gingiva is considered thin. Conversely, if the probe is not visible, the gingiva is considered thick.
• d) Examination of the gingivo-dental sulcus: assessment of the depth of the sulcus is essential to determine the future situation of the dento-prosthetic limit, it is done using a periodontal probe, the sulcus must not exceed 3mm, the maximum limit likely to be maintained by a well-performed plaque control
• Assessment of biological space:

The biological space was first described by Garguilo and Wintez in 1961, it is constituted by the zone of attachment of the gingival tissues to the root surface (epithelio-connective attachment), this zone plays the role of hermetic crimping allowing the isolation of the underlying aseptic periodontium from the septic oral environment, its average height is 2 mm.

Any damage to this space initiates an inflammatory response that results in bone resorption, which can lead to the formation of a periodontal pocket or gingival recession. Thus, crown lengthening is the preliminary intervention that can resolve this problem.

The evaluation of the biological space is done using probing and X-rays: the probe measures the gingivo-dental sulcus and the X-ray allows the bone crest to be located.

B-2) Evaluation of the deep periodontium:

The examination of the alveolar bone is carried out using an X-ray assessment which confirms an anomaly detected in the mouth; a certain number of elements must be observed:

• The height of the alveolar tissue should be located 1 or 1.5 mm apically to the enamel-cementum junction.
• The cortex or lamina dura must be continuous.
• The width of the ligament space should be between 0.2 and 0.5 mm.
• The integrity of the root.
• Cementum continuity and periapex health.
• For molars and first maxillary premolars, determine the height of the root trunk : the higher the root trunk, the less risk there is of exposing the inter-radicular space.

B-3) The periodontal assessment: Following the periodontal examination, three situations can be defined:

♣ Initially positive periodontal situation : characterized by:

• A shallow sulcus (0.5 to 1 mm)
• A junctional epithelium resistant to probing
• A thick attached gingiva with sufficient height (greater than 3)

It corresponds to a thick and slightly scalloped periodontium where any prosthetic restoration does not seem to compromise periodontal stability

♣ Initially negative situation: the periodontium appears thin and scalloped and the clinical examination reveals:

• A deep sulcus (at least 2 mm)
• Very thin adherent gum
• Attached gums of very low height or absent;

For this type of periodontium, any prosthetic restoration will require pre-prosthetic periodontal preparation as well as the adoption of certain precautions during the different prosthetic stages.

♣ Intermediate situation : which corresponds to:

• A sulcus of moderate depth (1 to 1.5 mm)
• A junctional epithelium resistant to probing
• Attached gum of limited height (less than 3 mm) and thin.

This type of periodontium requires gentle, low-traumatic maneuvers during prosthetic development because it can cause recessions. It is advisable to perform pre-prosthetic periodontal preparation to recreate a more favorable periodontal environment.

2. Ethiopathogenesis of Periodontopathies linked to joint prosthesis:

Periodontal disease is a condition that affects all of the supporting tissues of the teeth. The triggering factor is primarily bacterial plaque.

The presence of a fixed prosthetic element is an aggravating factor of periodontal disease, it can generate in the cervical area the irritating triad:

• The overhang : which retains bacterial plaque and is responsible for inflammatory processes, these overhangs can exist on the edges of prostheses made on a poorly defined or non-respected finishing line.
• Open joints : result from a faulty fit or imperfect installation during sealing or bonding. In these conditions, the fixing material

It is in direct contact with the oral environment in which it is more or less degraded or dissolved and acquires a surface state conducive to the accumulation of plaque.

• Rough surfaces : come from a prosthetic material with surface alterations linked to defective casting, a manufacturing defect or insufficient polishing.

3. Justification of periodontal treatment before the development of a fixed prosthesis:

If the clinical examination reveals periodontal disease, the prosthesis cannot be performed before periodontal treatment. This is for the following reasons:

• Prosthetic restorations become destructive when superimposed on pre-existing periodontal disease and reduce the longevity of teeth and prostheses.
• Tooth mobility hinders chewing and denture retention.
• Inflammation and degeneration of the periodontium can prevent abutment teeth from coping with the functional demands of prosthetics.
• Prostheses constructed on models taken from impressions of diseased gums will not fit properly after periodontal treatment, which will leave spaces under the pontics (accumulation of plaque and inflammation) following gingival contraction + poor adaptation of the prosthesis to the cervical contour of the preparations.

Even if the periodontium is healthy, there may be defects that prevent a satisfactory prosthetic result from being obtained and that must be restored before the fixed prosthesis is placed. These corrections can be summarized as:

• Coronary elongation.
• Frenulumectomy.
• Recession Recovery
• Augmentation of attached gum.
• Alignment of the gingival scallop.
• Treatment of edentulous ridges by addition or subtraction of tissue.

4. Impact of the production of fixed prostheses on the periodontium and precautions to take:

During the production of the joint prosthesis, all the prosthetic stages can be the source of more or less significant and more or less reversible attacks on the pulp and periodontal tissues, leading to a risk of non-biological integration of the prostheses, and thus therapeutic failure.

1. When performing dental preparation: The periodontal stability of the abutment tooth is directly related to the cervical limit of the preparation which can have different shapes and situations.
   1. Shapes of cervical boundaries

Different forms of cervical boundaries have been proposed, each with advantages and disadvantages. Whatever the chosen form, it must ensure the continuity of the boundary and its readability in the laboratory, which allows for optimal precision of the dento-prosthetic joint. Two forms allow for achieving these objectives:

• The fillet, indicated for metal and metal-ceramic restorations.
• The shoulder with rounded internal angle, reserved mainly for ceramic restorations.

2. – Location of the cervical limits The choice of the location of the cervical limit is delicate and will depend essentially on the goal set to obtain the best overall final result. This choice depends on:

• respect for tissue integrity and pulp vitality,
• of retention,
• respect for the periodontium,
• hygiene and maintaining the result over time,
• aesthetics and the appearance of the patient’s face,
• ease of implementation.

From a periodontal point of view, the best location for cervical limits is supragingival. This limit has the advantage of facilitating prosthetic construction and reducing periodontal aggression. It is indicated in posterior sectors where aesthetic requirements are less demanding in the presence of abutments of sufficient height, and in anterior sectors on uncolored teeth in the presence of restorations based on biocompatible and mimetic materials (adhesives and ceramics). Conversely, juxta-gingival or intra-sulcular limits are a necessity to meet prophylactic, mechanical and especially aesthetic requirements. These intra-sulcular limits must not encroach on the biological space. Thus, the apical part of the sulcus should be avoided to avoid the risk of damaging the epithelial attachment; only the coronal part of this sulcus can be used. For this reason, we should not place our cervical limits more than 0.5 to 0.7 mm into the sulcus, a limit that is always accessible during hygiene maneuvers. Maintaining the cervical limit in a correct position is difficult, even with expert hands, and for this, it is necessary to take some precautions.

• Preparation of the first preparations with supragingival limits.
• Placement of a fine retraction wire in the sulcus and subsequent finishing of the intrasulcular cervical limits.

Following these precautions will allow for deflection of the gum and preparation of our limits under visual control, which will minimize any aggression to the marginal tissues.

2. When taking the impression:

Impression techniques can be a direct aggression factor on the periodontium, defects related to these techniques can have harmful repercussions on the periodontal balance. Thus, the choice of these techniques cannot be dissociated from periodontal reflection.

While the supragingival cervical limit has no particular impact on the choice of impression technique, the intrasulcular and juxta-gingival limits, on the other hand, require prior opening of the sulcus using different gingival retraction techniques in order to record the finishing line.

Gingival eviction techniques are potentially dangerous for the periodontium, but surgical methods present the greatest risks of damage, often irreversible, compared to chemomechanical techniques which reduce the risks of irreversible damage and allow maximum respect for periodontal integrity.

The technique of choice consists of using deflection by two cords; the first unimpregnated wire is left at the bottom of the sulcus during the impression while the second impregnated one is removed just before.

The appearance of Expasyl®, a thick paste injected into the sulcus, which ensures lateral deflection of the marginal gingiva associated with a hemostatic effect, which facilitates impression taking with minimal risk to the epithelial attachment, particularly in the case of thin periodontium.

The most used impression techniques in fixed prosthesis are:

• The Wach technique is a compressive method that allows for the recording of highly subgingival margins. It is indicated in the presence of favorable periodontium.
• The double mixing technique is a less compressive technique. It is less traumatic for the periodontium and allows cervical limits to be recorded in a normal subgingival situation (0.3-0.4 mm).

3. When developing temporary fixed prostheses:

The temporary prosthesis must meet the same requirements as the permanent fixed prosthesis despite its temporary presence in the mouth. Its adaptation must be correct so as not to induce inflammation and be the cause of periodontal aggression.

The temporary prosthesis must provide a clean and precise cervical joint with sufficiently open embrasures, correct contact points and correct and well-polished contour shapes. With respect to the periodontium, the temporary prosthesis will fulfill several roles:

• maintain the marginal gingiva in a physiological position after preparation
• facilitate the healing of periodontal tissues around prepared teeth
• improve and facilitate the conditions of the imprint
• anticipate the shape and morphology of the final prosthesis

It is imperative to ensure a good adaptation of the temporary prosthesis to be able to preserve periodontal health, for this

• It is recommended to adapt the temporary prostheses while ensuring maximum protection of the attachment system by placing a retraction wire in the sulcus which will only be removed after the temporary sealing.
• The polymerization of the resin must be carried out on the preparation. However, the harmful effects of the exothermic setting reaction on the periodontium must be countered by insulating the preparation and cooling the resin while it sets.

4. When assembling the prosthetic element and preparing the teeth

The final sealing must ensure compliance with two requirements with regard to the periodontium:

• Obtain the thinnest, most watertight seal possible.
• Do not leave cement debris in the sulcus.

The choice of sealing cement must be carefully considered because the majority of sealing cements are not neutral from a periodontal point of view.

• Zinc phosphate cements provide a very thin film that does not promote the accumulation of bacterial plaque, but its mechanical qualities are vulnerable, which can have consequences on periodontal stability.
• Polycarboxylate cements are characterized by their biocompatibility, adhesive capacity, and low solubility. They are criticized for their poor mechanical properties, which precipitates their deterioration.
• Glass ionomer cements have better mechanical performance, better sealing, high adhesive power and biocompatibility, but their use is hampered by significant solubility in the presence of moisture.

Conclusion

In fixed prosthetic restoration, the most difficult objective to achieve is, without doubt, the maintenance of periodontal stability . Only the correct periodontal assessment and respect for periodontal integrity during the various prosthetic stages can ensure the sustainability of the prosthetic treatment.

Joint and periodontal prosthesis

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Joint and periodontal prosthesis