Restorative aspects of periodontal disease: an update part 2

Surgical crown lengthening

Surgical crown lengthening is designed to increase the length of the clinical crown. Crown lengthening techniques have been traditionally used as an adjunct to restorative procedures, particularly in cases where subgingival caries or fractures require the exposure of sound tooth structure and re-establishment of the biologic width space. Also cases of chronic gingivitis that result from the placement of restorations violating the biologic width may also be treated with crown lengthening procedures.11

With patients becoming more concerned for aesthetic-oriented treatment, an understanding of an interdisciplinary treatment approach has now developed. As a result, crown lengthening procedures have become an integral component of aesthetic treatment and are utilized with increasing frequency to enhance the appearance of restorations placed within the aesthetic zone.

Surgical crown lengthening is a procedure used to expose a greater height of tooth structure in order to allow proper restoration of the tooth prosthetically. Periodontal crown lengthening is a procedure that recontours the gingival tissue surrounding one or more teeth so that an adequate amount of healthy tooth is exposed.12 Crown lengthening is often used as part of a treatment plan for a tooth that is to be restored with a crown. This procedure provides the necessary space between the supporting bone and margins of the crown, preventing the new crown from damaging the periodontal tissues. Crown lengthening is recommended to make a restorative procedure possible. For example, if a tooth is badly worn, decayed, or fractured, below the gingival line, crown lengthening adjusts the gingival and bone levels to gain access to more of the tooth so that it can be restored.13

External bevel gingivectomy technique

This technique is generally used to improve aesthetics and takes the form of a gingivectomy to excise the soft tissue.15 Gingivectomy is a successful procedure for reconstruction of biologic width; but can only be used in cases where gingival hyperplasia or pseudopockets are present (>3 mm of biologic width) and in the presence of an adequate amount of keratinized tissue14 (Figure 1).

Classification and treatment sequence 11

Following an assessment of the alveolar crest position, four distinct clinical scenarios may be identified (Table 1).

Table 1. Proposed classification system for aesthetic crown lengthening procedures.

Classification	Characteristics	Technique	Advantages	Disadvantages
Type I	Sufficient soft tissue allows gingival excision without exposure of the alveolar crest or violation of the biologic width.	Gingivectomy/gingivoplasty procedure (Figure 1).	May be performed by the restorative dentist. Provisional restorations of the desired length may be placed immediately.
Type II	Sufficient soft tissue allows gingival excision without exposure of the alveolar crest but in violation of the biologic width.	Surgical repositioning of the gingival margin without exposure of the alveolar crest, but nevertheless in violation of the biologic width. Soft tissues will attempt to re-establish this dimension upon impingement. In thin periodontal biotypes, this may result in crestal resorption and subsequent recession, while in thick periodontal biotypes it may manifest as chronic gingival inflammation. Osseous recontouring surgery may be staged separately.	Will tolerate a temporary violation of the biologic width. Allows staging of the gingivectomy and osseous contouring procedures. Provisional restorations of the desired length may be placed immediately.	Requires osseous contouring. May require a surgical referral.
Type III	Gingival excision to the desired clinical crown length will expose the alveolar crest.	Providing a surgical template derived from a relevant aesthetic blueprint. This template will serve as a guide during surgery so that, following flap reflection, a constant relationship between the anticipated clinical crown and the osseous crest levels can be established and maintained through the bone contouring process. The periodontist should also be instructed to reposition the flaps coronally, rather than apically, in order to maximize tissue preservation and allow the anticipated revisions to the gingival margin that will follow once healing from the osseous surgery has been completed (Figure 2).	Staging of the procedures and alternative treatment sequence may minimize display of exposed subgingival structures. Provisional restorations of desired length may be placed by second-stage gingivectomy.	Requires osseous contouring. May require a surgical referral; limited flexibility.
Type IV	Gingival excision will result in inadequate band of attached gingiva.	Apically positioned mucoperiosteal flap.		Limited surgical options, no flexibility, a staged approach is not advantageous, may require a surgical referral.

Correction of interproximal embrasure form

A positive contact relation of one tooth with another, mesially and distally in each dental arch, must be present. Contact areas prevent the food from being trapped between the teeth and help to stabilize the dental arches by the combined anchorage of all teeth in either arch in positive contact with each other. In order to maintain the healthy gingiva in the interdental areas, the contact points should be located incisally or occlusally and buccally.17 Proper contact points and alignment of adjoining teeth allows proper spacing between them for the normal bulk of gingival tissue attached to the bone and teeth. On the facial aspect of the tooth, the tip of the papilla behaves differently as compared to the free gingival margin, with the free gingival margin being, on average, 3 mm above the underlying facial bone, and the tip of the papilla being, on average, 4.5–5 mm above the interproximal bone. This means that, if the papilla is farther above the bone than the facial tissue but has the same biologic width, the interproximal area will have 1.0–1.5 mm deeper sulcus than is found on the facial area.18

The open gingival embrasures could be found in two cases, when either the papilla is inadequate in height due to bone loss or the interproximal contact is located too high coronally. Restorative dentistry can correct this problem by moving the contact point to the tip of the papilla. To accomplish this, the margins of the restoration must be carried subgingivally 1–1.5 mm and the emergence profile of the restoration is designed to move the contact point toward the papilla, while blending the contour into the tooth below the tissue.18

The challenge for the restorative dentist who has to restore these teeth is always present, so as to leave open embrasures and establish the appearance of a natural-looking tooth, or close the embrasures but create square-looking restorations with long contacts. As long as the tooth contacts are equal in length and the papillary heights relatively level, the square tooth form with closed embrasures is aesthetically preferable to the open embrasures, while restoring the teeth.19

The height of the papilla is determined by three factors:

Tarnow et al evaluated the heights of the contact above the interproximal bone and level of papilla fill and stated that, when the contact was 5 mm from the bone, the papilla always filled the space; when the contact was 6 mm from the bone, the papilla filled the embrasure 56% of the time and, when the embrasure was 7 mm long, only 27% of the time did the papilla fill it. In general, then, a contact above the bone of 4.5 mm to 5 mm should always be filled by the papillae.20

Crown preparation

The following underlying factors should be considered before selection of the restorative material and the relative tooth preparation design:21

Crown preparation designs for full-coverage restorations are classified into four categories:

Shoulder (horizontal preparation)

The shoulder is probably the most popular design because it is easily read by the technician, and it allows sufficient bulk for porcelain to produce aesthetically pleasing restorations (Figure 3). It can be used for all-ceramic or metal-ceramic crowns with either a metal collar or a porcelain butt margin.^21,24

Whenever possible, crown margins should be placed supragingivally for ease of impression taking, margin finishing and overall periodontal health. Subgingival margin placement may be required when the root resected area needs to be covered. The crown margin should be apical to the pulpal chamber floor or root canal that was exposed by resection, especially if these structures have not been sealed with amalgam, but to prevent violation of the biologic width; the subgingival crown margins should not be closer than 3 mm to the alveolar crest. This may require additional lengthening of the crown. To preserve remaining tooth structure and encourage a better-fitting restoration, a knife-edge finish line or a chamfer design is recommended, which eliminates residual ledges, roots, furcation lips or horizontal components. In maxillary molars it eliminates the remaining internal furcation invasions (IFI).^25,26

Pontic design

Pontics should aesthetically and functionally replace missing teeth and, at the same time, be non-irritating to the mucosa and allow effective plaque control.27

While evaluating pontic design, four designs should be considered:

The restorative material for all four designs can be either glazed porcelain, polished gold or polished resin and, as long as the smooth surface finish is present, there is no difference in biologic response of the tissue on contact with the restoration.28 The sanitary and ovate pontics have convex undersurfaces that facilitate cleaning and allow for effective plaque control. The ridge lap and modified ridge lap designs have concave surfaces that are more difficult to access and clean with dental floss. A modified ridge lap design can be given where there is inadequate ridge to place an ovate pontic. In this type, the facial aspect of the undersurface has a concave shape; adequate access for oral hygiene is allowed by the more open lingual form.^18,25

Along with the biologic considerations during crown placement, restorative margin location and implications for soft tissue stability, as explained in the first article and initial part of this article, there are various restorative dentistry procedures and restorations which, if neglected, may aggravate periodontal disease.

Restorative dentistry procedures

The GDP may be guilty of perpetuating periodontal disease as a result of injudicious dental therapy, which may further aggravate periodontal disease. This damage to the periodontal structures is called iatrogenic damage and the factors causing it are called iatrogenic factors.29 Restorations, endodontic therapy, fixed and removable prosthesis and orthodontic therapy all have the potential to become iatrogenic to periodontal structures if not carried out properly (Figures 4 and 5).

General dental practitioners should also be careful during certain procedures, such as the placement of interdental wedges, matrix bands, rubber dam, rubber dam clamps and temporary restorations. The presence of caries, fractured/faulty restorations, restorative overhangs or undercontoured restorations and open or light contacts may lead to altered chewing patterns due to food impaction or an unstable occlusal relationship. Repair of the defect may be all that is required to re-establish occlusal harmony.30

It is also important for the GDP/specialist to understand that, in order to prevent periodontal tissue damage, the properties of the various restorative materials available must be considered, as well as the hypersensitivity reaction that some patients may encounter with restorative materials.

Restorative materials

A great variety of dental materials are now available for use in restorative dentistry that differ in their capacity to retain plaque, owing to differences in their surface texture, but all can be adequately maintained if they are polished and accessible to patient care,31 but can lead to plaque accumulation and gingival inflammation if left unpolished with rough surface and margins (Figure 6). Willershausen et al32 studied the influence of resin-based restorations, amalgams and gold alloys, as restorative materials in immediate contact with the gingival tissues, and observed a high prevalence of gingival irritation in association with resin-based materials. The authors stated the reasons for such irritation as: non-indicated applications, failure of technique, or simply the chemical properties of the materials. Ababnaeh et al33 evaluated Class II, III and V restorations with amalgam, tooth-coloured materials (resin composite and glass ionomer), non-precious alloys, porcelain and acrylic, in addition to crowns and bridge abutments. They concluded that crowns, bridge abutments (especially acrylic and non-precious metals) and Class II amalgam restorations were associated with highest risk of periodontal breakdown. Similarly, Paolantonio et al34 compared and evaluated amalgam, glass ionomer cement, and composite resin subgingival restorations and concluded that these restorations do not significantly affect the clinical parameters recorded.

A close association between gingival recession and cervical lesions has been noted.35 Conventional restorative techniques may not meet the aesthetic demands of the highly concerned patients. Additionally, these anatomical root surface presentations can impair the mechanical root planing that may be carried out prior to surgical procedure for root coverage procedures. In such cases, combined restorative and periodontal surgical procedures should be undertaken.36 Clinicians in the past have used resin-modified glass ionomer (RMGI) restorations or fluoride-releasing resin materials with pre-reacted glass (PRG) in subgingival locations with predictable success.37 It has been demonstrated histologically that both epithelium and connective tissue can adhere to the RMGIs in the subgingival environment.38 Lucchesi et al,39 evaluated RMGIs or microfilled resin composite (MRC) and coronally positioned flaps (CPF) in the treatment of non carious cervical lesions associated with gingival recession, at 6 months following surgery. Root coverage improvement without damage to periodontal tissues was observed, supporting the use of a coronally positioned flap for the treatment of root surfaces restored with RMGI or MRC as being effective over the 6-month period.

Comparing the biocompatibility of the materials used for the restoration, gold, acrylic and porcelain caused adverse tissue reactions, especially when the surfaces were rough and unpolished.40 Glass ceramic restorations showed markedly reduced bacterial colonization compared with natural contralateral teeth.41

Hypersensitivity to dental materials

Hypersensitivity with the use of some dental materials has been observed. Patients with a known nickel allergy develop a reaction to an intra-oral nickelchromium dental alloy. Acrylic may be irritant to tissues, although the material, when fully polymerized, is not irritating to tissues. Similarly, phosphate cements and silicates are slight irritants. Gingival tissues adjacent to composite resin restorations extended subgingivally may develop gingivitis, even in the presence of good oral hygiene. More importantly, tissues respond more to the differences in surface roughness of the material rather than its composition. The rougher the surface of the restoration subgingivally, the greater the plaque accumulation and gingival inflammation. The permeability of the gingival epithelium enhances the penetration of leachable components and thus the potential for toxic and allergic reactions.42 The pulp devitalizers used in endodontic therapy, like formocresol if used injudiciously, may cause gingival tissue damage (Figure 7).

Restoration overhangs

Overhanging dental restorations have long been viewed as a contributing factor to gingivitis and possible periodontal attachment loss. It is generally accepted that overhanging restorations contribute to gingival inflammation owing to their retentive capacity for bacterial plaque, an increase of the specific periodontal pathogens in the plaque, and inhibiting the patient's access to remove accumulated plaque.^43,44 Subgingival restorative margins are associated with the development of plaque-associated inflammatory periodontal disease, with a shift in the subgingival flora from health to one associated with disease.^43,45

Evidence exists that any restoration with a subgingival margin is associated with some degree of inflammation, both clinically and histologically,46 and with increased gingival fluid flow.47

An overhanging Class II restoration may prevent access to interdental cleaning, even for patients with good oral hygiene (Figure 8). In addition to their effect on the inflammatory process, overhangs may also cause damage by impinging on the interdental embrasure and the biologic width.48 Mokeem49 has shown that removal of an overhang results in improved plaque control and restoration of gingival health, and therefore should be a part of initial periodontal therapy. A significant reduction in pocket depth was also observed after removal of the overhanging restoration.

Roughness in the subgingival area is also considered to be a major contributing factor to plaque accumulation and retention, leading to gingival inflammation, which could be the result of one or more factors:

A gap of 20–40 microns, on average, is present between the margin of the restoration and unprepared tooth surface in the subgingival environment, leading to colonization by bacterial plaque.51

Restoration of special cases

Root resection/hemisection/bicuspidization

Patients with advanced periodontal disease may place clinicians in a challenging situation. One such condition is multi-rooted teeth with furcation involvement, as most of the cases end up with extraction as the only option in advanced condition. The alternative treatment may involve combining restorative dentistry, endodontics and periodontics in order to retain the tooth in whole or in part.53

The term ‘tooth resection’ denotes the excision and removal of any segment of the tooth or a root with or without its accompanying crown portion. Various resection procedures described are:

Root amputation which involves the removal of one or more roots of a multi-rooted tooth, at the same time permitting retention of the remaining tooth portion;

Hemisection which is defined as removal or separation of the root with its accompanying crown portion; and

Bisection or bicuspidization which is the separation of mesial and distal roots of mandibular molars along with their coronal portion, where both segments are then retained individually^54,55 (Figure 9).

According to Newell,56 the advantage of the amputation, hemisection or bisection is the retention of some or the entire tooth. Farshchian and Kaiser57 have reported the success of a molar bisection with subsequent bicuspidization. However, there are a few associated disadvantages as follows:

Root surfaces that are reshaped by grinding in the furcation or at the site of hemisection are more susceptible to caries;

Failure of endodontic therapy for any reason will cause failure of the procedure;

An improperly shaped occlusal contact area may convert acceptable forces into destructive forces and predispose the tooth to trauma from occlusion and ultimate failure of root separation and resection (Garrett et al).58

The clinician also faces challenges while restoring these teeth because of the amount of tooth structure lost in the resection process. Conservative tooth preparation preserves as much of the remaining tooth as possible, but the resultant supragingival or minimally prepared subgingival finish lines lead to metal display in the final restoration.18

Another factor to be taken into consideration when restoring these teeth is the development of appropriate contours for proper oral hygiene access. The gingival embrasure form created in the restoration must be easily accessible with an interdental brush.18

External resorption

External root resorption can be divided into three categories:

Progressive inflammatory resorption;

Cervical resorption; and

Replacement resorption.

Cervical root resorption is not a very common type of progressive external inflammatory resorption.59 This is usually painless, and goes unnoticed by the patient unless pulpal or periodontal infection is present.60 In some cases, a deep lesion/defect can result in sensitivity to thermal changes because of pulpal proximity and can also lead to damage to periodontal attachment apparatus (Figure 10).

The treatment of external resorption is directed towards the complete removal of the resorptive tissue to obtain a sound dentinal margin.61 It must be decided if endodontic treatment is necessary and the defect restored with an appropriate restorative material.

A surgical approach generally involves reflection of the flap, debridement, curettage, restoration of the defect with restorative materials like amalgam, composite resin, or glass-ionomer cement, and repositioning of the flap to its original position. Periodontal reattachment with amalgam62 or composite resin63 is usually not seen, and is unlikely with glass-ionomer resin. There is experimental evidence to suggest that re-attachment may occur when ProRoot® MTA is used in this situation.64

Summary

The preservation and maintenance of a healthy natural dentition is the ultimate goal of all phases of clinical dentistry. In an integrated multidisciplinary approach to dental care, periodontal treatment should logically precede the final restorative procedures, and both restoration and periodontium should be in harmony for the long term maintenance and survival of teeth. Tissue management is of utmost importance and the real basis on which to determine whether prosthesis has been properly fabricated and integrated in the mouth of a patient. This can be achieved only through attention to detail and the allowance of an appropriate amount of time to carry out every single procedure.

These articles have reviewed some of the more significant concepts and clinical considerations relating to restorative procedures in order to maintain periodontal health. The aim has been to focus the attention of clinicians on the perio-restorative interdisciplinary aspects, that should always be kept in mind when trying to replace missing tooth structure.