Prosthodontic- periodontic-restorative interrelationship

Most of the patients require a multi-disciplinary approach for complete restoration of their functional and esthetic demands. To achieve a long-term success of the treatment, an appropriate periodontal treatment should be followed by restorative treatment which helps in the long term maintenance of periodontal health. Patients with missing teeth require fixed prosthodontic treatment following periodontal treatment. The clinician should be well versed with the relationship between periodontal tissues and their inter-relationship with restorative treatments to ensure adequate rehabilitation of the dentition. In the following discussion, we shall read in detail the interrelationship between restorative treatment and periodontal health.

Why periodontal health is a pre-requisite for restorative treatment?

It is a must to restore periodontal health before definitive restorative treatments such as a crown, bridges or subgingival restorations are planned. It is because of the following reasons,

  1. After gingival inflammation subsides, the gingival tissue shrinks resulting in the relocation of gingival margin 1. So, tooth preparation and finishing of restorative margin should be done only after the gingival tissue is healthy 2, 3.
  2. Inflammation around the……………………

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Concept of biological width

The term ‘biological width’ was originally coined by Walter D. Cohen in 1962. The concept of definite dimensions of soft tissue attachment on the tooth surface was first put forward by Gargiulo et al. in 1961 4 who in their investigation found that there was some uniformity in the dimensions of the components of the periodontium attaching to the tooth surface. In their study, measurements were made from dentogingival components of 287 individual teeth from 30 autopsy specimens. They found that there was a definite proportional relationship between the alveolar crest, the connective tissue attachment, the epithelial attachment, and the sulcus depth. Their results demonstrated that the mean sulcus depth in these specimens was 0.69 mm, mean epithelial attachment dimensions were 0.97 mm, and mean dimensions for connective tissue attachment was 1.07 mm. These dimensions of soft tissue attaching to tooth surface are referred to as “Biological width”. So, based on a study by Gargiulo et al, the biological width is 2.04 mm (0.97 + 1.07 = 2.04 mm), which represents the sum of the epithelial and connective tissue measurements (Figure 76.1). However, the concept of biological width was described in detail by Ingber et al. in 1977 5.

Figure 76.1 The dimensions of biological width as proposed by Gargiulo et al. 1961.

Biological width as proposed by Gargiulo et al.

Other studies have also been done to evaluate the dimensions of soft tissue attachment on the tooth surface. In 1994 Vacek et al. 6 evaluated 171 cadaver tooth surfaces.  They observed mean measurements of 1.34 mm for sulcus depth, 1.14 for epithelial attachment, and 0.77 mm for connective tissue attachment.

While performing restorative treatments, maintenance of biological width is essential to………………………

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It has been shown that a distance 3 mm (1 mm supracrestal connective tissue attachment, 1 mm junctional epithelium and 1 mm for gingival sulcus on an average) between the preparation margin and alveolar bone was suitable for maintenance of periodontal health for 4 to 6 months 8. In a study, Nevins and Skurow (1984) 9 concluded that while placing subgingival margins, the attachment of junctional epithelium or connective tissue apparatus on tooth surface should not be disrupted during tooth preparation and impressing taking. They suggested keeping subgingival margins 0.5-1.0 mm below the gingival margins.

Diagnosis of biological width violation

The diagnosis of biological width violation can be made by clinical examination, bone sounding or radiographic examination.

Clinical examination:

The most important clinical finding associated with violation of biological width is chronic inflammation in gingiva associated with the restoration. The signs associated with gingival inflammation such as bleeding on probing, localized gingival hyperplasia with minimal bone loss, gingival recession, pocket formation and clinical loss of attachments can also be seen depending upon degree of biological width violation. The clinician must ensure that inflammation is not due to accumulation of local factors and does not resolve with scaling and polishing.

Bone sounding:

In this method the biological width is identified by………………………..

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Radiographic examination:

In this technique, the distance from the margin of the restoration and alveolar crest can be measured on radiographs. However, there are some limitations of this technique, including its inability to measure biological width on the facial and lingual aspects because of superimposition of the surfaces and enlargement associated with the radiographic image.

Types of margins of restorations

There are three types of gingival margins for restorative treatments. These include,

Supragingival margin:

Here, the margins of the restoration are kept above the gingival margin. It is the least irritating to the periodontium and is easy to prepare. The final fit of the restoration can be easily assessed clinically and any irregularities can be removed efficiently. The main disadvantage of supragingival margin preparation is their unesthetic appearance, especially in areas with esthetic concern.

Equigingival margin:

Here, the gingival margin is placed at the level of the gingival margin. Although, these margins are more esthetic as compared to supragingival margins, they favor more plaque accumulation and therefore result in greater gingival inflammation.

Subgingival margins:

These margins are of prime periodontal concern because…………………………

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Rules followed during placement of restoration margins

It must be clear that placement of restoration margins below the gingival margins is always a compromised treatment 10-13. However, to fulfil esthetic demands, placement of subgingival margins is necessary.  Whenever subgingival restoration is placed, it must be made sure that the margins of the restoration are smooth and non-retentive. Rough or open margins act as plaque accumulation sites and favor periodontal disease progression. It has been demonstrated that in areas with subgingival restorations are at greater risk of gingival bleeding and gingival recession than areas with supragingival restorations 14. In another study it was observed that interdental areas with well adapted subgingival amalgam fillings had more plaque retention as compared to sound tooth structure 15.  However, if the rules of gingival margin placement are followed, the gingival health can be maintained effectively.

According to Carranza 16, when determining the location of restoration margin, patient’s existing sulcus depth should be used as a guideline in assessing the biologic width requirement for that patient. Three rules have been suggested for placement of subgingival restoration margin. To implement following rules it must be made sure that the gingival tissue is healthy.

Rule I:

If the sulcus probing depth is 1.5 mm or less than that, the gingival margin is placed 0.5 mm below the gingival tissue crest.

Rule II:

If sulcus probing depth is >1.5 mm, the margin of restoration is placed one half the depth of the sulcus below the tissue crest.

Rule III:

If the sulcus depth is >2 mm, the gingival tissue is evaluated for going gingivectomy and for crown lengthening. Once the gingival sulcus depth around 1.5 mm is achieved, the restoration margin is placed following rule I.

The above rules are followed purely depending upon gingival sulcus depth. Kois (1996) 2 suggested placement of restoration margins based on bone sounding measurements. The measurement includes the total dimension of attachment and the sulcus depth. The placement of restoration margin after determining bone sounding measurements allows the clinician to determine long-term stability and esthetics in relation to the restoration. Three categories following bone sounding were suggested: normal crest, high crest and low crest.

Normal crest:

A normal crest measurement is……………..

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High crest patient:

Here, the mid-facial is less than 3.0 mm and the proximal measurement is also less than 3.0 mm. Almost 2% of all cases are high crest cases. In such cases, it is not possible to place an intracrevicular restoration margin because the margin will be too close to the alveolar bone. If intracrevicular margins are placed, the biological width is violated and chronic inflammation will result. The high crest situation is usually results following tooth extraction resulting in an edentulous site with collapsed interproximal papilla.

Low-crest patient:

In these cases, mid-facial measurement is greater than 3.0 mm and the proximal measurement is greater than 4.5 mm. The low crest is found in approximately 13% of all cases. These are most susceptible to recession following placement of subgingival restorations. However, not all patients with low crest respond similarly to intracrevicular restoration margin placement. In some patients, quite stable attachment apparatus may form which maintains a long-term stability and health.

Maynard and Wilson (1979) 17 suggested a distance of 0.5 to 1.0 mm of restorative margin from the base of the sulcus is safe for subgingival margin placement. Furthermore, to ensure long term esthetics and gingival health, minimum of 5 mm of keratinized gingiva consisting of 2 mm of free gingiva and 3 mm of attached gingiva is required.

Clinical procedure for placing subgingival restoration margins

Ideally, for placement of subgingival restoration margins, tooth preparation should be completed to the free gingival margin facially and interproximally. The preparation margins, thus created act as reference for subgingival extension of the restoration. Once the tooth preparation has been done till free gingival margins, gingival retraction can is done to retract gingival tissue opposing the tooth to extend the preparation subgingivally.

Gingival retraction for placement of sub-gingival margins:

Presently, various gingival retraction techniques practiced. According to Benson et al. (1986) 18, gingival retraction methods can be broadly classified into following categories,

  1. Simple mechanical methods
  2. Chemo-mechanical methods
  3. Rotary gingival curettage
  4. Electrosurgical methods

The chemo-mechanical method of gingival retraction is the most widely used methods for gingival retraction usually in combination with electrocautery or soft tissue laser. There are various chemical agents that are used for the treatment of chords used in tissue retraction. These include,

  • 1% and 8% recemic epinephrine
  • 100% aluminum solution (potassium aluminum sulfate)
  • Ferric subsulfate (Monsel’s solution)
  • 5% and 25% aluminum chloride solution
  • 3% ferric sulfate solution
  • 20% and 100% tannic acid solution
  • 45% negatol solution
  • 8% and 40% zinc chloride solution

These chemical compounds diffuse in blood circulation through crevicular epithelium and cause vasoconstriction aiding in hemostasis. Furthermore, they cause transient gingival shrinkage facilitating impression making. The gingival retraction cord/cords are placed according to the sulcus depth.

Rule I (sulcus depth is 1.5 mm or less than that):

The cord is placed in……………………

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Rule II (sulcus depth is >1.5 mm):

In this case the sulcus is deeper and larger diameter cord is required to displace the tissue apically. Two larger diameter cords are placed in the gingival sulcus to deflect the tissue. After the tissue is deflected, the margins are prepared. In this case the top of second cord is used to identify the final margin of the restoration. Once the margins are prepared, third cord is placed to displace the previous two cords apically thus exposing the tooth structure apical to the margins of the preparation for impression recoding. Electrosurgery or laser is often required to remove the excess of the tissue overhang to appropriately record the margins of the tooth preparation.

Provisional restoration of tooth:

There are multiple purposes served by the provisional restoration of the tooth. Its primary advantage is that it helps in preservation in maintaining the gingival form and position. However, to achieve these goals from a provisional restoration, the soft tissue must rest in its normal location against a provisional restoration. The provisional restoration should be appropriately polished and should have a smooth surface with well adapted finish line. When temporization is done for fixed partial dentures, the restored teeth should have all the features which facilitate adequate plaque removal and maintenance of oral hygiene. When the provisional restoration is cemented, the excess of cement should be removed from the margins and form the sulcus so that appropriate healing can take place. Patient education regarding maintenance of appropriate oral hygiene during the period of temporization is essential to achieve desired results.

Crown contour:

The crown contour should be such that it facilitates the maintenance of periodontal health. Both over-contoured and non-contoured crowns are deleterious to periodontal health. A flat, contoured crown has a tendency to develop a thick free gingival margin and an over-contoured crown has tendency to increase both supra- and subgingival plaque accumulation. As a general rule, more is the convexity of the crown; more is the difficulty in plaque removal 19.

Know more…………….

Historical perspective of crown contours:

Historically, various theories have been proposed regarding the contour of the restorations or crowns in relation to maintenance of periodontal health. These are,

Gingival protection theory:

This theory suggests that cast restorations should be designed in such a way that it protects the marginal gingiva during mastication from mechanical injury. This theory was one of the earliest theories and was propagated during days of G V Black. In spite of the fact that this theory lacked any sound scientific justification, nobody questioned it till 1950’s. It was clear that over-contouring protects nothing but the accumulation of plaque.

Muscle action theory:

This theory proposed that over-contouring of the crown prevents the normal cleansing action of the tongue and cheeks. At the time this theory was proposed, our knowledge regarding role of plaque in the development of gingivitis was well documented with scientific evidence. This theory was accepted at that time because it had more scientific justification than gingival protection theory.

Access for oral hygiene:

 By late 1960’s the role of plaque in causing gingival inflammation became more established and it became clear that neither gingival protection nor muscle stimulation is needed for maintenance of periodontal health around the crowns. It was realized that a tooth contour which facilitates plaque removal with regular oral hygiene measures was most suitable for maintenance of periodontal health. The main guidelines for designing crowns suggested in this theory include,

  1. The natural tooth crown is approximately 1mm wider at the maximum buccal-lingual dimension than the buccal-lingual width at the CEJ. The crown designed to restore the tooth should mimic these features.
  2. Embrasure space should be kept open to facilitate plaque removal.
  3. The contacts of the teeth should be kept high and buccal to central fossa to facilitate plaque removal.
  4. Furcations should be “fluted”. In molars where furcation has been exposed due to periodontal destruction, the crown contour should be designed to mimic the fluted contour of the furcation to minimize plaque accumulation and facilitate plaque remove.


In case where hemisection of lower molar has been done and one root has been removed, the remaining part of tooth serves as abutment of for bridge. The contour of the crown should be smooth, extending till the most apical portion of tooth preparation. In upper molars of one root has been removed, the crown should be contoured in such a way that the patient has access for removing plaque and deposits.

Pontic design:

The primary requirements of pontic are: it should replace the missing tooth esthetically and functionally, it should be non-irritating to the underlying mucosa and it should allow effective plaque control and periodontal health maintenance 20-23. There are four classic pontic designs evaluated for their esthetic, functional and periodontal health maintenance. These include sanitary, ridge lap, modified ridge lap and ovate designs. Various restorative materials which have been investigated using these pontic designs include glazed porcelain, polished gold or polished resin etc. It has been shown that there is no difference between biological tissue response towards any of these materials provided they have a smooth surface finish 20. The sanitary and ovate pontics have convex undersurfaces which facilitates their easy cleaning. Ridge lap and modified ridge lap designs have a concave under surfaces which is more difficult to clean with the help of a dental floss. The ovate pontic design is commonly used but in case where there is an inadequate ridge to place an ovate pontic, modified ridge lap design may be used.

Interproximal papilla and embrasure design:

The interproximal embrasure created by………………………………………….

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Wide interdental embrasures are commonly associated with an un-esthetic appearance, defective phonetics and excessive lateral food impaction. There are various factors which determine the status of interdental papilla. These include 24,

  • Height of alveolar bone crest
  • Dimensions of interproximal space
  • Location and type of contact
  • Biological width

According to Tarnow et al. (1992) 7, interdental papilla fills the interdental space when the distance between the alveolar crest and the contact point is ≤ 5 mm. It was observed that when the contact point was 6-7 mm from alveolar bone crest, only 56% and 37% of papillae could fill the interdental space respectively. Patients with advanced periodontal destruction have alveolar bone crest levels at a distance from the contact point more than 5 mm and thus show interdental papilla incompletely filling the interdental area.

Management of violated biological width

The violated biological width may be corrected by surgical means or orthodontic extrusion. Both the procedures are aimed at moving the alveolar bone crest away from the restoration margin.

Surgical crown lengthening:

In this procedure the crown length of the tooth is increased by removing the alveolar bone at bone crest. The procedure results in reduction of the alveolar bone support of the tooth (Figure 76.2 a-c). The indications for this procedure include,

  • Relocation of margins of restorations those impinge on biological width.
  • Placement of subgingival restoration margins
  • Root fracture in the cervical third of the root
  • Root resorption in the cervical third of the root
  • For esthetic improvement in the smile by increasing clinical crown length
  • Teeth with excessive occlusal wear or incisal wear
  • In conjunction with tooth requiring hemisection or root resection

Contraindications of the clinical crown lengthening:

  • In case where excessive bone removal will significantly jeopardize periodontal support
  • Tooth with unfavorable crown root ratio
  • Cases where procedure may result in clinically un-esthetic results
  • Teeth where the procedure will cause increased risk of furcation involvement.
  • Non-restorable teeth

The clinical procedure for crown lengthening includes following procedures,

  1. Gingivectomy
  2. Apically positioned flap

Gingivectomy:

The procedure is indicated only in those cases where pseudo-pockets or gingival enlargement is present. The procedure involves only the soft tissue removal by placement of an external bevel incision. It must be kept in mind that an adequate zone of attached gingiva should remain following the procedure and esthetics should not be compromised. The procedure can be accomplished using the following techniques,

  • Conventional (Scalpel or Kirkland knife)
  • Laser
  • Electrocautery

Apically positioned flap:

The procedure is indicated where crown lengthening of multiple teeth in a quadrant or sextant is required. This procedure should not be done for surgical crown lengthening of a single tooth in the esthetic zone. Apically positioned flap can be done with or without osseous reduction.

Figure 76.2 The crown lengthening procedure demonstrating insufficient tooth margins pre-operatively (a). Flap was raised and bone margins were reduced to achieve adequate tooth margins (b). One week post-operative view (c).

Crown lengthening procedure

(a)

Crown lengthening procedure

(b)

Crown lengthening procedure

(c)

Apically positioned flap without osseous reduction:

The procedure is done in cases where there is insufficient width of attached gingiva and biological width of more than 3 mm is available on multiple teeth. A detailed description of the procedure has been given in “Periodontal flap surgeries: current concepts”.

Apically positioned flap with osseous reduction:

The procedure is indicated where…………………..

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Orthodontic tooth extrusion:

Orthodontic crown lengthening is indicated when traditional surgical crown lengthening would result in a negative architecture and may lead to removal of bone from the adjacent teeth, which can compromise the function of these teeth. Orthodontic extrusion may be done alone or in combination with a surgical bone reduction to achieve desirable clinical results. The primary advantage of orthodontic extrusion include reduced hazard to the adjacent teeth with very little change in crown/root ratio. The procedure provides better results in the esthetic zone because there is a better crown root ratio and improved esthetics than surgical procedure alone. The extrusion can be executed in two ways,

Slow orthodontic extrusion:

Extrusion is executed by applying low orthodontic forces. By doing this, the tooth is extruded slowly, bringing the alveolar bone and gingival tissue with it. The tooth is extruded until the bone level around the tooth is carried coronally to level that is required to be removed surgically to correct the attachment violation. After extrusion is completed, the tooth is stabilized in the extruded position.

If the bone levels are acceptable and biological width is not violated after restoration, no surgical intervention is required to reduce the bone levels around a tooth. However, on the other hand, if the bone levels around extruded tooth are above the bone levels around neighboring teeth or biological width is violated after restoration, surgical reduction in bone levels is required.

Rapid orthodontic extrusion:

As the name indicates, in this procedure tooth is extruded rapidly. A supercrestal fibrotomy is performed weekly in an effort to prevent the tissue and bone from following the tooth. After the desired extrusion has been achieved, the tooth is stabilized for at least 12 weeks to confirm the position of the tissue and bone. As the bone levels remain almost unaltered, usually there is no need for surgical bone level reduction. The soft tissue surrounding the tooth can be reshaped by simple excision 26.

Healing following crown lengthening

The restorative procedure should ideally be started after the complete healing of tissue has taken place. As a general rule, restorative procedure should be started after new gingival crevice has been established. Restorative procedures should be delayed until 3 to 6 months post surgery 27. The longer period reduces the risk for gingival margin shrinkage in areas requiring maintenance of subgingival restoration margin. The reshaping of provisional restorations may be done 3-4 weeks post surgically, making sure that the margins of the provisional restoration are subgingivally placed.

Conclusion

To achieve adequate harmony between periodontal tissue and restorations, it is important to determine the biological response of tissue that is anticipated after placement of the restoration. Principals of biological width and esthetic smile should be followed so that desirable esthetically acceptable results can be achieved. It is clear from the above discussion that placement of subgingival margins is a compromised treatment to fulfil esthetic demands. There is a strong evidence which suggests that that even minimal encroachment on the subgingival tissue can lead to deleterious effects on the periodontium. When subgingival restoration is placed, it should have a highly precise finish line so that minimal inflammatory reaction is there after the restoration is placed. If it is necessary to place the restoration margins near alveolar crest, surgical crown lengthening or orthodontic extrusion should be considered.

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References:

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