Periodontics – dental prosthesis interrelations

Periodontics – dental prosthesis interrelations

Plan :

1. Introduction
2. Reminder

2-1- The periodontium

2-2- The dental prosthesis

3. Periodontal objectives of the prosthesis

3-1- Respect for the tissue environment

3-2- restraint

3-3- aesthetics 

4. Impact of the prosthesis on the periodontium

4-1- Position of prosthetic limits

4-2- materials and periodontium

4-3- gingival deflection

5. Impact of periodontics on prosthesis

5-1- restoration of biological space

5-2- management of edentulous ridges

6. Conclusion
7. Bibliographic references
8. Introduction :

The relationships between prosthesis and periodontium are often conflicting and complex. In order to avoid these conflicts between prosthetic and periodontal imperatives, the practitioner must carefully analyze the factors involved before undertaking his therapeutic act. The prosthetic project with its biomechanical, functional and aesthetic data must take into account the periodontal conditions.

2. Reminder :

2-1- The periodontium:

The four elements of the periodontium to consider when fitting a dental prosthesis are:

• The epithelial attachment  : it establishes contact between the gum and the tooth and constitutes the bottom of the gingivo-dental groove.
• The gingivo-dental sulcus (SGD)  : or sulcus, it faces the tooth, without being in contact with it, it is of the order of 1 to 2 mm vestivularly and lingually and 2 to 3 mm on the proximal faces.
• Biological space  : space between the bottom of the gingivo-dental sulcus and the top of the bony crest. Described by Gargiulo in 1961 as a space of approximately 2 mm occupied by the tooth attachment system, it is composed of an epithelial attachment (the junctional epithelium, measuring on average 0.97 mm) and a connective attachment (gingivo-cemental or supracrestal fibers, measuring on average 1.07 mm).

Periodontics – dental prosthesis interrelations

• The periodontal biotype  : the classification of Maynard and Wilson 1980:

This classification is based on the height and thickness of the gingiva, and on the thickness of the vestibular bone table. It differentiates 4 types. 

 • Type I: This is the ideal situation where the thick gingiva measures between 3 and 5 mm in height. The vestibular external cortex has a satisfactory thickness (the roots are not visible by transparency or palpable). This type is found in 40% of patients.

 • Type II: Palpation reveals an underlying bone of satisfactory thickness despite a reduced vestibular gingival height, often less than 2 mm. This situation is uncommon since it is only found in 10% of cases.

 • Type III: The gingival dimensions are correct. However, the vestibular alveolar thickness is reduced and is manifested on clinical examination by dental roots that are clearly visible by transparency or palpable. Its frequency is 20%.

 • Type IV: The alveolar bone and vestibular gingiva are of reduced dimensions. This type affects 30% of patients.

2-2- The dental prosthesis:

A dental prosthesis is a dental device that replaces one or more  missing teeth  and, if necessary, the associated anatomical structures. It can be attached or joined, total or partial, definitive or temporary.

3. Periodontal objectives of the prosthesis:
4. Respect for the tissue environment:

• Plaque control  : the prosthesis must allow direct access to the junction between the marginal gingiva and the dental root, to the prosthetic limits, and to the prosthetic surfaces if they are intrasculcular. Access to plaque controls using a toothbrush and/or interdental brushes will be checked with the patient around each element of the restoration. This check is carried out when the prostheses are fitted.

Periodontics – dental prosthesis interrelations

• The reduced periodontium:

The reduction of attachment levels is a more or less marked constant in patients who have suffered from periodontitis and constitutes one of the most critical difficulties in prosthetic management. Indeed, the functional and aesthetic requirements in the case of reduced periodontium should in no case limit access to plaque control. It is thus possible to identify three prosthetic regions that present distinct characteristics in terms of reconstruction:

• A periodontal-prosthesis interface region which is the area closest to the periodontal tissues and should allow access for oral hygiene;
• An aesthetic and functional region that reproduces intangible anatomical elements and must imitate nature
• A transition region that links the two previous regions and takes on its full importance in cases of extreme loss of attachment.

2. The restraint:

It is in the context of a very reduced attachment level (> 30-50%), frequently associated with a limited number of teeth (<8 teeth per arch) and often increased mobility, that the fixed prosthesis best fulfills its biomechanical function and can contribute to maintaining the teeth on the arch. The rigidity provided by the prosthetic framework makes it possible to distribute the stresses exerted on the prosthesis to all the residual roots and to participate in the reduction of micromovements of the dental roots to the most reduced periodontium. This dissipation of stresses has the effect, on the most mobile teeth, of improving patient comfort by reducing/eliminating mobility perceived as excessive.

Interrelationships between periodontics and dental prosthesisInterrelationships between periodontics and dental prosthesis

3. The aesthetics:

Widely open interdental spaces associated with unsightly black triangles, long teeth and secondary tooth migrations are the most frequent esthetic complications of treated periodontitis. These complications are directly related to the reduction of the attachment level due to the disease and the periodontal recessions that frequently accompany the healing of the attachment system.

The aesthetic analysis must take these diagnostic elements into account to enable prosthetic correction to be anticipated.

The aesthetic indication is mainly based on the well-being and demand of the patients, because it is not, in itself, therapeutic. It must therefore not be contrary to the major functional principles of maintaining teeth on the arch. Even if, strategically, periodontally conserveable teeth are extracted for prosthetic reasons, care will be taken as much as possible to preserve the teeth.

4. Impact of the prosthesis on the periodontium:
   1. Position of prosthetic limits:

The location of the prosthetic limit can be at three levels: supragingival, juxtagingival and intrasulcular (we prefer this term to subgingival because it implies a burial that is not compatible with periodontal health).

• The juxta – or supragingival limit:

All prosthetic limits located on the tooth at or above the marginal gingiva are defined as juxta- or supragingival. 

The supragingival limit is the biological limit of choice in restorative dentistry and can very often be used on a reduced periodontium. It is a periodontally ideal limit because it does not interfere at any time with the biological space.

• The intrasulcular limit:

It is possible to place a subgingival prosthetic limit without inflammatory consequences. The indications can be aesthetic, most often in the anterior zone. The clinical elements that may lead to the choice of a subgingival limit for aesthetic purposes are:

• A visible tooth-gum boundary when smiling
• Unsightly root discoloration
• The patient’s desire not to see prosthetic areas appear.

Periodontally, subgingival limits, extending beyond the base of the sulcus, can cause tissue trauma at each clinical stage.

2. Materials and periodontium:

Acrylic resins used during temporization phases show the highest plaque retention. All-ceramic crowns appear to have lower plaque retention. 

The surface condition is also an element to take into account. Indeed, a rough surface facilitates the adhesion of dental plaque components, which can cause inflammation of the superficial periodontium. 

The prosthetic seal (interface between the preparation and the prosthesis) must be as thin as possible. Studies seem to show that all types of materials make it possible to obtain a clinically acceptable seal. 

Finally, the biocompatibility of the material is a parameter that should not be neglected. Ceramics appear to be the most biocompatible materials. They are bioinert materials, causing only very low cytotoxicity. Concerning metal alloys, the literature appears to be sparse. It would be advisable to choose materials with a low corrosion potential.

3. Gingival deflection:

Obtaining the gingival deflection before impression taking is a prerequisite for any practitioner wishing to correctly record the preparation limits and thus provide the greatest accuracy to the prosthetic laboratory. The most commonly used technique is the double cord technique.

Ruel et al. in 1980 reported that a cord causes destruction of the junctional epithelium, requiring eight days to heal and can cause gingival recession of the order of 0.2-0.1 mm. Using a cord that is too thick results in whitening of the marginal gingiva, meaning a local reduction in blood flow. Leaving this cord in place for several minutes creates strangulation of the free gingiva that can lead to gingival recession. Choosing a cord size that is adapted to the sulcus is therefore essential.

Periodontics – dental prosthesis interrelations

5. Impact of periodontics on the prosthesis:
   1. Restoration of biological space:

The restoration of biological space uses surgical means, allowing coronal elongation to be achieved. 

The decision on the surgical technique of crown lengthening depends on a number of clinical and radiographic parameters, such as assessment of the quality and quantity of keratinized tissue, depth of periodontal probing around the tooth, assessment of the height and thickness of the residual tooth walls, clinical crown-to-root ratio, root shape and proximity, root trunk height, and quality of endodontic treatment.

In most cases, the surgical crown lengthening technique combines apicalization of the gingival tissues associated with osteoplasty (remodeling of the bone contours) and/or osteectomy (bone resection) in order to re-establish the biological space while restoring a physiological bone morphology. A distance of approximately 3 mm must be found between the bone crest and the future prosthetic limit. Surgical crown lengthening must always respect a favorable crown/root ratio (maximum 1/1 ratio).

Preprosthetic surgery also includes periodontal plastic surgery techniques to increase the height or thickness of keratinized tissue, to obtain root coverage or to correct an asymmetry of the neck line. 

Despite the controversy, the presence of keratinized tissue of at least 2 mm is a favorable prognostic factor with regard to periodontal health, especially in the presence of an intrasulcular prosthetic limit.

Periodontics – dental prosthesis interrelations

2. Management of edentulous ridges:

After tooth extraction, the alveolus undergoes bone and gingival remodeling which is accompanied by more or less significant resorption of the crest which was classified by Siebert in 1983 into 3 classes (fig 8)

Bone resorption can complicate the placement of future implants ( pre-implant bone grafts ) and implant-supported prosthetic reconstruction, but also affect the aesthetic and functional results of tooth-supported fixed prostheses. Thus, a heavily resorbed edentulous ridge, especially in the vestibulo-palatal or vestibulo-lingual direction, can leave an empty space between the gingival margin and the pontic, responsible for immediate or secondary aesthetic damage with consequences on phonetics or food retention.

Preprosthetic periodontal surgery is intended to compensate for the loss of substance of the edentulous ridges and to reconstruct the ideal profile of the ridge before the pontics are made.

Surgical techniques can be divided into two broad categories: soft tissue augmentation procedures and hard tissue augmentation procedures. 

Soft tissues can be augmented by epithelial-connective tissue grafts, pedicled connective tissue grafts from the palate, and buried connective tissue grafts. 

Regarding hard tissues, we find all the procedures of guided bone regeneration and apposition bone grafts.

1                 2      3 3                      4   

6. Conclusion :

The integration of a single or multiple prosthetic element is conditioned by a perfect knowledge of the periodontal imperatives in order to ensure the durability of the restoration. It is therefore essential, before the start of the prosthetic treatment, to analyze the periodontal environment and to modify it in order to guarantee functionality, longevity and aesthetics.

7. Bibliographic references:

[1] Bouchard Philippe, periodontology and implant dentistry: volume 1, Lavoisier edition, 2015.

[2] Klaus H. Rateitschak ,  Edith M. Rateitschak ,  Herbert F. Wolf , Atlas of periodontology, Flammarion edition, 1986.

[3] MC. CARRA, C. DARNAUD, M. FREMONT, C. MICHEAU, Periodontics and prosthetics, clinical reality, 2014.

[4] Newman, Takei, Klokkevold, Carranza, clinical periodontology, 10th edition, Elsevier, 2006.

Periodontics – dental prosthesis interrelations