This paper reviews the relationship of periodontics to restorative dentistry. The effect of various restorative procedures - operative techniques, endodontics, interim restorations, materials, design and contour of restorations - upon the periodontium are considered. Specific emphasis has been placed on the relationship of the restorative margin to the periodontium and the frequent need to alter the placement of the gingival margin so that the restoration will be constructed on sound tooth structure and have supragingival finishing line. All the available information conclude that a compliant patient and a strong periodontal maintenance programme are integral to success, which with a coordinated effort by the periodontist and the restorative dentist, best assures a successful long term dental treatment.
 

The tooth and its surrounding structures are continually challenged by microbial flora, and restorative dentistry may exacerbate this cha- llenge (Figs. 1A, IB). The dentogingival unit has been described by Schroeder and Listgarten¹ as a heterogenous and interconnected "sandwich," with its most vulnerable component being the gingival crevice. Frequently entered, but rarely understood, the crevice remains an enigma to many restorative dentists (Fig. 2).

Periodontal attachment loss begins when the epithelial integrity of the dentogingival unit is breached. Injury may be produced by microbial flora, by trauma, or by both. The progression of this injury appears to be related to host resistance, the competence of the surrounding tissue, and the bacterial pathogens. In turn, each of these elements may be influenced by the three aspects of a dental restoration: morphology, margin quality, and margin location (Figs. 3A-4D).

Glickman² has said that every restoration has a periodontal dimension. A mouth with a healthy periodontium may be affected by restorations of poor quality, and restorations of the highest quality may fail in a mouth with periodontal disease. It is important that the restorative phase of dental treatment is  commenced after periodontal health is established, and  after the patient has learned to maintain that health.³

Bacterial Plaque and the Periodontium

There is ample evidence that periodontal disease is caused by microbial infection, i.e., the retention of plaque at the gingival margin, either the sulcus or a pocket.⁴ It is a complex multi- factorial infection, in which the micro-organisms as well as the inflammatory reactions of the host contribute to the destruction of the periodontium. The individual lesions undergo continuous change, both in their nature and the outcome of the local host-parasite confrontations, i.e., host resistance and systemic factors. Inflammation is an indication of periodontal disease,⁵ and the inflammatory reaction which is visible micros- copically and clinically (bleeding on probing, attachment loss, pocket depth, and bone loss) in the affected area, represents the host response to   plaque    microbiota,   and   their  products.⁶

The inflammatory reaction in the periodontal tissues is not always beneficial because it may damage the surrounding cells and the connective tissue including the alveolar bone.⁷ Inflammation in the periodontal tissues is similar to that in other parts of the body in some respects, but is different partly because of the anatomy of the periodontium (Fig. 2) and the fact that bacteria which cause peridontal disease vary from one form of the disease to another. It is a mixed bacterial infection, and there is probably synergism between the species.⁸ Human perio- dontitis constitutes a range of infectious diseases involving specific pathogens. Orga- nisms implicated in periodontitis include Porphy- romonas gingivalis, Actinobacillus actinomy- cetemcomitans, Prevotella intermedia, Bacte- roides forsythus, Campylobacters rectus, Peptos- treptococcus micros, Eikenella corrodens, Sele- nomonas noxia and some Eubacterium, Fuso- bacterium, Treponema and Lactobacillus species.⁹

The disease process may be episodic, rather than continuous and slowly progressing, and recent data suggests that tissue destruction in some areas occurs during relatively short bursts of disease activity, followed by longer periods of quiescence.¹⁰"¹²

The severity of periodontal tissue often varies from tooth to tooth, and from one tooth surface to another. Findings of epidemiological studies have consistently revealed that the frequency and severity of periodontal disease increases with age, and with inadequate oral hygiene. Histologic studies of the tooth surface show that there is a close relationship between the accumulation of plaque deposits on the tooth surface, and extension of the inflammatory process into the adjacent soft tissues (Figs. 5A, 5B).¹³ Subjects maintaining a high standard of oral hygiene are not likely to develop gingival or periodontal disease, even with restorative defects.¹⁴ Long term clinical trials indicate that further periodontal disease can be arrested by judicious measures to remove bacterial plaque from subgingival areas. These include scaling, root planing, pocket elimination, removal of causes of plaque accumulation, such as "plaque traps," (overhangs on fillings) and the adoption of an effective oral hygiene programme for the individual concerned.¹⁴ In experiments with animals,¹³¹⁵ it was demonstrated that where there was accumulation of bacterial plaque, the deposits could remain for years, and then suddenly shift to a destructive periodontal disease, resulting in loss of connective tissue attachment, and alveolar bone disease.

It can therefore be assumed that periodontal disease is due to plaque retention and invariably starts as gingival inflammation, but if left untrea- ted could spread in an apical direction, with bone destruction, and eventual tooth loss.

Restorative Dentistry and the Periodontium

Restorative dentistry has an effect on the perio- dontal health in many ways, which include the materials from which the restoration is made, the way in which it is placed, and the contour of the restoration (Figs. 4A-4D).¹⁶ The degree of reten- tion of plaque is a prime factor; for example, the subgingival margins on fillings and crowns, the fit of dentures and bridges, the contour and mate- rials of the restorative material.¹⁷ Also if subgingi- val restorations are placed, they should be smooth and if possible done with the materials that would not deteriorate under plaque and indeed retard plaque formation.¹⁷ Efforts should be made to gain access to subgingival lesions by use of miniflaps,¹⁸ to provide access, vision and proper adaptation and finish of the restoration.¹⁹"²⁴

One should also consider the effect of various procedures on the tissues: the placement of matrix bands, interdental wedges, rubber dam, rubber dam clamps and temporary restorations (Fig. 6). The clinician would also have to consider the length of time a restoration had been defective, and that a gingival inflammation could suddenly become a destructive periodontal lesion (Figs. 7A-7D).

In general, the location and degree of convexity of surfaces is important. Clinicians believe that overcontoured crowns enhance plaque retention and make its removal difficult, and also prevent beneficial contacts between the marginal gingiva, cheeks and the lips and tongue.²⁵ Undercon- toured restorations result in trauma to the marginal gingiva, and in food impaction, with plaque retention (Fig. 8). There are numerous studies documenting a correlation between defective restorations and deterioration.²¹²³ There are also studies showing that where defective restorations exist, but oral hygiene is excellent, then there is no periodontal destruc- tion.¹⁹ The risk is always that motivation could fail or the patient's health could deteriorate causing periodontal disease to occur.²⁶

The placement of margins can be subgingival; half-way between the gingival margin and the bot- tom of the sulcus, or supragingival. Investigation of margins located subgingivally has consistently been associated with persistent gingival inflam- mation²⁷ when plaque control is poor (Figs. 7A- 7D). If the axiom of ending the tooth preparation on sound tooth structure is accepted, prepro- sthetic surgical or orthodontic intervention becomes a necessity (Figs. 9,10). Clinical indi- cation includes subgingival caries, root resorption, old tooth preparation margins from pre-existing dentistry, endodontic perforations, and fractured teeth. Regardless of how perfectly a fixed resto- ration fits, the cement line will always tend to accumulate plaque, which will eventually irritate the tissues,³-²⁷ and the roughness of interpro- ximal restorations encourages plaque retention.²⁵

The presence of caries, broken/missing resto- rations and open or light contacts may lead to altered chewing patterns due to food impaction or an unstable occlusal relationship. In doing so, occlusal trauma may be precipitated by overbur- dening those teeth required to bear the load. Repair of the defect may be all that is required to re-establish occlusal harmony.

Open contact may depict recent tooth movements. Broken restorations may be a result of heavy or misdirected occlusal forces.²⁸ Overhanging dental restorations are a major dental health problem, and can promote plaque accumulation, which can change from a non- destructive subgingival flora to a destructive one.²¹²² Lang et al²² summarized a review of articles on overhangs, and despite the different methods of measurement of the overhangs, the prevalence in adult populations is very high, at least 25% of restored surfaces being affected.²² They found that when radiographs alone were used to detect overhangs, less were found than when combined with a tactile instrument, such as an explorer. The periodontal disease included bone loss, pocket formation, attachment loss, and inflammation. They showed significantly greater severity of disease associated with overhangs (Fig. 8), compared to homologous teeth without overhanging dental restorations. This was true for radiographic bone levels, attachment loss, gingival inflammation and gingival crevicular fluid. It is the retention of plaque that is important.

Further, Lang et al²² reported that in a study of dental students where gold restorations were temporarily placed for a limited period, with overhangs, the flora changed from gingival health to one of chronic periodontitis. The group of organisms which increased the most, was black pigmented bacteriodes which has been strongly implicated in the aetiology of periodontal disease.²⁹"³¹ Lang et al concluded that mecha- nism by which overhangs contributed to perio- dontal disease is probably multifaceted i.e. overhangs increase plaque mass, and specific periodontal pathogens; and may also damage the embrasure by impinging on the interproximal space and the biologic width (Fig. 2).

Endodontics. Periodontics and Restorative Dentistry

The increasing use of endodontic treatment leaves the dentist with a difficult legacy. Endodontically treated teeth often have a minimal amount of tooth structure coronal to the alveolar bone, making them susceptible to fracture. These fractures may be supragingival, may extend into connective tissue, or may even split the tooth to the apex. Restorations for these teeth should strive for adequate retention; more importantly, they should be designed to protect the tooth from fracture. Therefore, amalgam, resin, or ionomer cores retained by pins, posts that extend into canals, or a combination should only be used if the circumferential clinical crown has 3mm or more of height. If the clinical crown is shorter, a cast post/core with a ferrule encompassing the circumference of the tooth is mandatory.²⁸

Extending posts deep into molar roots, especially those with significant mesial and distal concavities, should be avoided. These posts often create root fracture or perforations and consequent tooth loss. In mandibular molars, there is usually enough of the coronal portion remaining to support an amalgam core extending less than 2mm into each canal. These molar cores are usually successful and offer conservative solutions for the root perforation or root fracture problem.

Interim Restorations

The quality of an interim restoration influences the longevity of the permanent restoration.³²³³ The fact that a restoration is temporary does not preclude that it may cause permanent damage.

Gingival inflammation and also attachment loss can result from hastily shaped acrylic resin provisional crowns, aluminum shells with rough overextended margins, and temporary cement extruded into subcrevicular areas, even though these may be in place only a few weeks.

The fit of temporary crowns is important (Fig. 6). It should be done carefully in order to avoid damage to the periodontium.³⁴³⁵ If the margins are over extended, there may be permanent damage to the marginal gingiva. Under extension may lead to sensitivity, resulting in poor oral hygiene and periodontal damage.

An interim restoration should protect both the dentogingival unit and the tooth. It should prevent the tooth from drifting or extruding. It should allow flossing without being dislodged and should not interfere with occlusal function. In the anterior region, interim restorations should allow normal phonetics and should duplicate or improve upon prior aesthetics.³⁵ The tongue and lip act as guides in the shaping of anterior restorations (Figs. 3A, 3B, 4A - 4D & 6).

When interim restorations are removed, the surrounding tissue should be reasonably normal in appearance (Fig. 6). Improperly constructed interim restorations can obviate the benefits of recently performed periodontal therapy. If multiple teeth are restored with full coverage restorations, some or all of these interim restorations should be luted together to enhance retention. However, care must be taken to avoid violating embrasure tissue and to allow access for personal oral hygiene.³³

With full-coverage restorations, tooth prepa- ration is followed by the interim restoration. The patient is reappointed at least 14 days later for impression making. This allows the marginal tissue to heal. If slight recession does occur, the clinician has the option to re-dress a facial margin. If the interim restoration reveals inadequate tooth reduction by temporary cement "showing through," these sites may be re-prepared as well, prior to final impressions.

Contours may also be examined and adjusted at the impression visit. The lower lip should govern the facial-incisal prominence of interim and final restorations. Excessive labial   projections should also be adjusted if necessary. Once corrected, the lower lip will feel comfortable during function. The now properly shaped interim restoration may be photographed and impressed with irreversible hydrocolloid. Casts and photographs are sent to the laboratory technician as a guide. Otherwise, the dentist is totally dependent upon a technician to shape the patient's crowns, possibly resulting in final restorations that interfere with phonetics, aesthetics, occlusion or periodontal health.³⁴

Rubber dam protects against gingival abrasion, and damage from chemicals used, but care must be taken not to retract the gingival tissues, or strip the junctional epithelium or connective tissues.

Traumatic Occlusion - Periodontics and Resto- rative Dentistry

Excessive occlusal forces have been implicated in the development of infrabony pockets in plaque associated lesions, and enhance the rate of tissue destruction in periodontal disease. There was a difference of findings of Lindhe and Svanberg,³⁶  Ericsson and Lindhe³⁷ who stated that plaque and pressure tension zones that could not adapt would lead to destruction and bone loss, and of Poison et al,³⁸ who stated that trauma superimposed on periodontal lesions associated with angular bony defects caused increased loss of alveolar bone, but no additional loss of connective tissue attachment.

Mounted casts are important in planning complex interdisciplinary treatment. Recent, good quality right-angle periapical radiographs are also necessary. Somewhat less helpful, but occa- sionally useful are panographic radiographs. Root shape and size, caries, bone to tooth and tooth to tooth interfaces, unexpected pathoses and proximity of anatomical structures (maxillary sinus, mental foramen, mandibular canal, etc) should be carefully noted on radiographs before treatment is begun. An intellectual summary of conclusions drawn from these and other diagnostic tools must be integrated with the patient's health history, aesthetic preferences, and perceived commit- ment prior to treatment.

Crown Margin

Carnevale et al³² investigated 510 crowned and 510 uncrowned teeth and found that the gingival status of the crowned teeth was good irrespective of the position of the margin. The crowns had been fitted for a period of one to nine years, and the patients were on prophylaxis recalls from one to six months. The times for each individual obviously varied according to the patient's needs, and it was probably a good indication that it was the prevention of plaque formation, rather than the margin placement that maintained the health of the tissues.³⁹⁴⁰

Removable partial dentures can be detrimental, and the abutments often show increased mobility and gingival inflammation and pocket depth. But, if these are designed and fitted carefully, and checked regularly and the oral hygiene is perio- dically reinforced, there is no deterioration.²³"²⁴

Impression techniques can cause harm to the periodontium. The injudicious use of gingival retraction cord can injure the biologic width, and cause permanent alterations like recession.⁴¹ It is therefore, essential to have consideration for the tissues when taking impressions for crowns and bridges.²⁷'⁴¹

Matrices must be contoured properly, and carefully designed and burnished, in order to prevent damage to the periodontium and to avoid damage when a filling is placed with an overhang. Wedges should be placed to avoid injury to the tissues (Fig. 8).
 

The inter-relationship between restorative dentistry and periodontics is important and closely connected and cannot be over emphasized. Restorative dentistry affects the periodontium and the health of the periodontium affects restorative dentistry. The health of the periodontium and follow-up care of restorations both require the cooperation of the patient. The patient must attend for regular recalls, to monitor the state of the periodontal tissues and the restorations. All studies indicate the necessity of a clean oral cavity and the provision of a well-organized main- tenance programme as vital to successful treat- ment. It is obviously of paramount importance that the periodontist and restorative dentist work in tandem in a coordinated effort during every phase of treatment ranging from diagnosis to corrective treatment to maintenance.

The clinical application of restorative dental treatment must be compatible with periodontal health. Sometimes, well-intentioned efforts to obtain an accurate impression, to hide a crown margin, or to reach and remove decay could permanently harm periodontal tissues. The clinical evidence of this damage may become apparent quickly or not for some years. Therefore, guidelines should be established that allow quality restorative care and at the same time would also protect the periodontium (Figs. 1 A, 1B & 7A - 7D).

Before implementing final restorative dentistry, the total environment that is to surround the restoration must be evaluated. This evaluation should be ongoing, should be punctuated with appropriate reevaluation, and with complex restorative care, should seldom take place at the first visit. Much can be learned from both tissue and patient reaction as early treatment evolves.

Whereas a simple supragingival restoration may require only periodontal health and sustained plaque control as restorative pre-requisites, complex or multi-tooth restorations demand far more (Figs. 11 A, 11B). Tooth proximity, the amount of attached gingiva, the depth of existing restorations, any many other factors affect restorative success. The dentist must project how the anticipated restorations will influence, or will be influenced by the restorative environment.

The patient's motivation would also have to be taken into account, as well as the need to constantly monitor, encourage and point out areas missed. Where periodontal disease exists and thorough scaling is supported by good home care, it will often lead to resolution of gingivitis and reduction of pocket depth, to a depth which is controllable without surgery. But it is also important to realize that where pockets exist, only the dentist can control the subgingival disease and gingivitis and that regular subgingival scalings and motivation and dental education are essential.