The Gingival-Restorative Interface: A Restorative Clinician's View

Dentists and ceramists are constantly striving to improve the quality and beauty of their final restorations. There are numerous parameters by which to judge the quality and esthetics of dental restorations. The most perfect restoration ever created is only as attractive as the gingival architecture into which it is placed. Patients have more sophisticated expectations than ever before. They will no longer tolerate dark lines, black triangles, and red gum tissue. Dentists must exhibit expertise at a very high level to deliver undetectable restorations (Figure 1). This article explores ways to understand and manipulate gingival tissues during evaluation, preparation, provisionalization, and delivery.

Ensuring a Predictable Outcome

A basic understanding of soft tissue is necessary to ensure a predictable outcome. This article assumes that surrounding gingival and bony tissues are in a state of good health. "In the presence of disease, no treatment is predictable."¹ It is wise to have a periodontist evaluate any patient considering major dental reconstruction. There are times when old restorations have to be removed to gain gingival health. This is logical and desirable; however, final restorations cannot be fabricated until excellent health is achieved with so-called "treatment provisional restorations."² Gingival tissues must be allowed time to heal and reorganize. It is not uncommon to fabricate more than one set of provisionals. Do not commence treatment without an adequate band of keratinized tissue (attached gingivae).^3,4

Vitamin C supplements and chlorhexidine rinses⁵ have been advocated as pretreatment adjunctive therapy. Some practitioners use tetracycline powder mixed with temporary cement to improve gingival response during provisional phase of treatment.^6,7 These protocols are recommended from anecdotal experience based loosely on periodontal treatment research.

Managing Soft Tissue

The first and most important aspect of soft tissue management is simple: Always respect fragile gingival tissues. Every violation of this concept can and most likely will cause unpredictable results. The majority of researchers have found that supra-gingival restoration margins are most desirable for gingival health.^8,9 The most accurately fitted margins are still open from 20 µm to 160 µm.^10,11 This "microgap" can host a sizable colony of bacteria. It stands to reason that keeping margins and dental materials away from the gingiva avoids local irritation. Susceptible patients will exhibit untoward responses to this gap.

Supragingival margins are a challenge to conceal. Many modern all-ceramic restorations are able to use the "contact lens" effect to effectively make their margins undetectable.¹² The porcelain veneer is the best example of this effect (Figure 2). Ceramic crown margins that can be bonded are often undetectable. Metal ceramic crowns with reduced metal frameworks and porcelain butt-joint margins can be done with acceptable esthetics.¹³ These porcelain butt-joint margins can be bonded, which helps integrate the crown visually into the cervical tooth surface.

Clinicians are involved with placing margins within the sulcus in the real world of restorative dentistry. Many factors preclude the possibility of using supragingival margins:

• discriminating patients who do not want to see a visual demarcation between restoration and tooth;
• old restorative margins within the sulcus;
• caries extension into the sulcus;
• retention/resistance form requirements;
• a need to change the emergence profile;
• dark cervical tooth structure; and
• a need to conceal metal-ceramic crown margins.

Respecting the gingival tissues becomes more difficult when working within the sulcus. Retraction cord helps the situation. Retraction cord defines the sulcular limit of preparations. Never prepare into the sulcus without first placing tissue retraction cord. Specific instruments are available to help protect lateral gingival walls.

Biologic Width

The concept of biologic width (see Diagram A) has been identified for several decades. Gargiulo described the dento-gingival junction in 1961.^14,15 It may be defined as the distribution of soft tissues interposed between crestal bone and the free gingival margin. Connective tissue attachment, epithelial attachment, and a healthy gingival sulcus are the three major components of the biologic width. As long as teeth are present, the body will maintain these three anatomical entities. When dental restorations encroach into this fragile system, problems can develop. It is imperative that dentists do not extend restorations beyond the healthy sulcus. Invasion of the epithelial attach-
ment, or even worse, the connective tissue attachment, will inevitably result in unpredictable results.¹⁶ The only predictable result of violation of biologic width is red, unhealthy gums and future periodontal breakdown.

Crestal Relationships

There are three types of crestal relationships described by Kois, who notes, "Importantly, the location of a margin of a restoration relative to the crest of the alveolar bone is more critical for preserving gingival health than its distance below the free gingival margin."¹⁷ Restorative dentists are fortunate that the most commonly observed crestal relationship (85%) is the most predictable to work with restoratively. When a periodontal probe is inserted through the sulcus and connective tissue apparatus to the bony crest, a measurement of 3 mm will be read (1 mm for connective tissue, 1 mm for epithelial attachment, and 1 mm for the sulcus). Kois refers to this as "sounding to bone."¹⁷ This patient will respond favorably and predictably as long as restorations are limited to the gingival sulcus.

The second crestal relationship is often found on interproximal tissues adjacent to edentulous sites or on patients who have recently had periodontal surgery. These "high crest" patients have a minimal dento-gingival complex. A periodontal probe inserted to the bony crest will measure less than 3 mm. As soon as a restoration enters the gingival sulcus, it begins to encroach on the biologic width. If restorations are indicated for a high-crest patient, it is wise to remain supragingival. These patients make up less than 2% of the patient population. Exercise caution when doing interproximal preparations adjacent to pontic sites (Figure 3). Patients with gingival recession and minimal attached gingiva will often exhibit minimal sulcular depth.

The third crestal relationship is the most difficult to predictably treat. When the probe is inserted to the bony crest, the measurement exceeds 3 mm. This type of patient reveals a band of unprepared tooth above the gingival crest after retraction cord is placed (the tooth has been prepared to the gingival crest originally and upon retraction the tissue moves a considerable distance). When this tissue is disturbed it recedes, forming visible margins and black triangles. In a perfect world, we would identify these patients before preparation. It may be desirable to have preprosthetic gingival surgery performed to reestablish "normal" architecture, if esthetic clinical crown length allows. This type of tissue is typically discovered during preparation. It is advisable not to take a final impression of the prepared teeth at this time. Rather, fabricate a precise-fitting provisional restoration and monitor the tissue for several weeks. Postponement is more desirable than sending cases back and forth to the laboratory or, worse, having to re-prepare and take new impressions.

Interproximal crestal relationships are different than mid-facial relationships. The "normal" crest patient will have a measurement of 4.5 mm to 5 mm from bony crest to the tip of the papilla. The high-crest patient will be less, possibly as little as 2.5 mm. The low-crest patient will be greater than 5 mm. This patient is particularly vulnerable to developing black triangles (incomplete soft tissue papillary fill of the gingival embrasure). It is important to quote Tarnow et al at this point.¹⁸ In that study it was found that papilla will completely fill the gingival embrasure space whenever the distance from bony crest to contact point is 5 mm. As the distance increases there is an alarming decline in papillary fill (6 mm had 56% and at 7 mm there was only 27% fill).

Caution should be exercised when a patient exhibits preoperative interdental papillae that extend over two thirds the length of the adjacent clinical crown (Figure 4). This patient always has a low crest. The tissues must be handled very carefully. The papillae can recede dramatically. Use only minimal intracrevicular margin placement. Delicate retraction cord placement with a single-cord technique is preferred. Develop a perfected provisional with excellent margins and lateral papillary support. Leave room for the tip of the papillae to rebound (Figure 5, Figure 6 and Figure 7).

Keep in mind that these concepts are simplifications of a complex system. Variable width of each tissue type may exist. Connective tissue attachment may vary from the average 1 mm. This is also true of epithelial attachment and the sulcus. Gargiulo's study results are commonly quoted, but be aware that the results were averages. His study actually quotes 0.69 mm as the average sulcus depth. Each patient must be evaluated individually. It has been found that the connective tissue attachment and the epithelial attachment are the most consistent elements of biologic width (2.04 mm). The most variable element is sulcular depth. It is dependent on tooth shape, adjacent teeth, diastemas, previous periodontal disease, and possible altered passive eruption.¹⁹

Gingival Character

It is important to evaluate the "character" of the gingival tissues after crestal relationships are identified. These so-called tissue biotypes/bioforms can be critical in choosing margin placement, margin type, and restorative material. Patients with very thin, friable, highly scalloped tissues are more likely to have recession. They will also telegraph underlying restoration margins and possibly root color (especially difficult if a metal collar or triphasic margin is planned). It stands to reason that thick, heavily stippled, flat-scalloped tissue is the most predictable to deal with. It conceals underlying color irregularities and is less likely to move away from restorations (Figure 8 and Figure 9). This biotype is more likely to develop pocketing rather than recession when biologic width is violated. Tissue bioforms may be categorized as normal, highly scalloped, or flat. Biotypes may be categorized as normal, thin, or thick.

Thin, friable tissue biotypes are best treated with medium-term (3 weeks to 6 weeks) provisionalization. Because these tissues have a tendency to recede, the provisional phase will allow the tissues to reorganize. Provisional restorations must be highly polished and contoured correctly with precise margins.

Tissue Illumination

Tissue illumination/transillumination is critical to esthetic integration of restorations into the gingival complex. This var-iable is related to tissue biotype, tooth vitality, lip morphology, and the material from which restorations are fabricated. Light enters teeth through the crown and also through the soft tissue. Shadows can develop from light entering through soft tissues into the root and reflecting off the interior of a metal-ceramic crown. Thin-tissue biotypes will allow more light to enter; therefore, they are more likely to reveal dark reflections (Figure 10). The preoperative soft tissue evaluation is critical for the selection of restorative materials. Patients with a high lip line and thin-tissue biotype will certainly obtain a more desirable esthetic result if non-metallic restorations are selected. There will be fewer tissue illumination problems. The all-ceramic crown will have a more inconspicuous junction between tooth and crown even with minimal sulcular incursion with margins.

Magne describes the "umbrella effect" of overhanging lips creating a shadow from light entering the mouth.¹³ This shadow blocks direct light penetration into the soft tissues and therefore emphasizes any darkness that is present at the gingival. This phenomenon is most readily understood when considering a bridge pontic that looks totally normal with the patient's lips retracted under operatory light, but has a dark shadow over the pontic when the patient is sitting upright with normal room light (Figure 11 and Figure 12).

Margin location, restorative material selection, and marginal design of restorations are all dictated by soft tissue considerations.¹³ Intracrevicular margins must be reduced adequately to allow for a healthy emergence profile. Restorative materials occupy a prescribed thickness. Inadequate facial reduction will result in facial overcontouring with the potential for subsequent gingival recession. Thin, highly scalloped tissue biotypes require the most technically sensitive approach. They are also most revealing of the limitations of dental materials.

Marginal Adaptation

Richter and Ueno state that marginal adaptation may be more important to gingival health than margin location.²⁰ Marginal adaptation begins with tissue management and ends with final seating and cementation. Tissue retraction must be tailored to the particular needs of the patient.

It has been the author's experience that a double-cord technique gives the most consistent success for normal-crest patients.²¹ Low-crest and high-crest patients are more safely treated with a single-cord technique. Gross crown preparation is carried to the level of the soft tissue crest, carefully following the gingival scallop. It is critical that final preparation follows the scalloped shape. A flat interproximal preparation will violate biologic width. A very small retraction cord is placed into the sulcular base. The preparation is then carried 0.5 mm to 1 mm into the intrasulcular area. This cord establishes the apical limit for preparation. Caution must be exercised not to place the cord beyond the sulcus into the epithelial connection. This connection is fragile and easily violated.¹⁷ After preparation is complete, take a white stone cylinder shaped like the preparation diamond and polish the entire preparation. This is best accomplished with a handpiece that has very concentric rotation, such as an electric handpiece or a midspeed air-driven handpiece. These polished margins will allow more precise final crown margin adaptation (Figure 13). Place a second cord. It is imperative that retraction is confirmed by looking for gum-cord-tooth (Figure 14). If there is any tissue superior to the second cord touching the prepared tooth at this point, a void will likely occur in the final impression. A 360° impression is the standard of care; without this, the laboratory will be unable to provide a restoration with precise fit. This is common sense, but laboratory owners report inadequate impressions are their number one problem.²² All other considerations are insignificant if this is overlooked.

Final impressions can be taken after adequate retraction is confirmed. It has been the author's experience that a small metal-tipped impression syringe will allow precise penetration into the retracted sulcus (Figure 15). After the sulcular area is injected, remove the metal tip and inject the remainder of the impression material with the larger remaining tip.

Remember the first day or two of dental school, when you were instructed to wet a cotton roll before its removal? Anneroth and Nordenram found that removal of a dry retraction cord tears the epithelial lining, initiates bleeding, and may cause irreversible recession.²³ It is a common practice to dry preparations and tissues before removing retraction cords. This is obviously the reverse order.

The literature is clear that cords and medications should only be in the sulcus as long as is necessary to accomplish margination and impression taking.^24,25 Avoid prolonged exposure to retraction cord and styptic/astringent solutions. Use the less caustic solutions in the anterior esthetic zone.²⁶ Aluminum chloride is reported to be the safest and most effective solution to use with retraction cord.²⁷ Tissue is not mature and healthy if a more aggressive solution is necessary. This is a clear indication to postpone impression taking.

Restoration Evaluation

Restorations returned from the laboratory should be evaluated for marginal adaptation on their respective dies and then on the solid model. After fit is verified, each crown should be individually checked in the mouth for marginal adaptation. Identify any casting irregularities that may prohibit complete seating. Multiple adjacent crowns can be difficult to verify for complete seating and marginal adaptation when placed simultaneously. Proximal contacts will often inhibit complete seating.²⁸ Work out proximal contacts between the crown and the first natural tooth distal to the teeth being restored. After those contacts are verified, work out occlusal holding contacts and excursions. Seat these crowns with final cement and then try in the crowns included between the two terminal crowns. Most times the remaining crowns will not fully seat (Figure 16). This is not readily apparent when all crowns are tried in simultaneously, as they all shift slightly on their respective preparations. If seated as a group, the same thing will happen, and the final result will be poor marginal adaptation. This is contraindicated for caries resistance as well as gingival response.²⁹ The order of adjustment may be changed to first seating the central incisors as a pair, then working out the contacts posteriorly. Holding a thin piece of articulating paper between the crowns in question can identify tight contacts. Seat them as much as possible. Draw the articulating paper out and the offending contacts will be marked on the proximal surfaces (Figure 17 and Figure 18). Only adjust one contact at a time. Exercise caution not to disturb embrasure contours. This can be a slow and painstaking process. Remove small amounts and refit each time. Repeat this process until complete seating is verified.

Cosmetic Gingival Surgery

Patients often present with inadequate gingival architecture. Gingival levels may be less than ideal. In many circumstances this can be corrected with cosmetic gingival surgery.³⁰ Clinical crowns can be made longer and gingival zeniths can be established at ideal heights. It is critical to allow total healing after gingival surgery. Time is not an adequate diagnostic criterion (Figure 19). Sounding to bone and sulcular depth are the diagnostic parameters that dictate total healing.³ Photographic evaluation is critical. Many patients will not reveal the gingival crest during a full smile. Additional surgery for these patients is of little value other than perfection of results.

Previous periodontal disease, tooth loss, root proximity, and previous restorations can lead to black triangles and blunted papillae in the natural dentition. This gingival inadequacy can disturb esthetic harmony (Figure 20). Several authors have described surgical correction of these papillary inadequacies; however, the results of these surgeries can be somewhat unpredictable.³¹ These treatments are primarily focused on the postrestorative/surgical patient with black triangles. The goal is to avoid this problem.

Papilla management begins with preparation. Atraumatic preparation is imperative. Tooth preparation must be harmonious tooth to tooth. Preparation sulcular depth should be equal on each side of the papilla so that final restoration emergence profiles can equally support the papillae. Positive emergence profile can be used interproximally to support and shape the interdental papilla (Figure 21).

Blunted papillae can be coaxed into a pleasing triangular shape with appropriate interproximal contacts and corrected emergence profile.³² Be aware that the soft tissue scallop does not follow the osseous crest exactly. Soft tissue requires support from adjacent teeth that is equal to or greater than the osseous contour.¹⁹ Provisional restorations can be used to manipulate tissues. The interproximal emergence profile can be increased to push papillae into position.³³ Provisional restorations must be meticulously fabricated with precise marginal adaptation, highly polished surfaces, and the corrected emergence profile. Studies have shown that positive interproximal emergence profile, within reason, will promote increased papillary height while increased facial emergence profile promotes gingival recession.⁴ It is logical then that the emergence profile must be carefully managed. Long-term provisionalization gives tissues an opportunity to heal and to respond to restorative manipulation (Figure 22, Figure 23 and Figure 24).³¹ It is critical that all vestiges of temporary cement be removed after provisionals are seated. Any speck of temporary cement will initiate an inflammatory response from the soft tissue (Figure 25).³⁴

Laboratory technicians must have a thorough understanding of the relationship between restorations and soft tissue. It is the responsibility of the clinician to communicate soft tissue parameters as clearly as possible. Some clinicians will cut a small reference line in the preparation to communicate the unretracted papilla height. Typically, interdental papillae will recede approximately 0.5 mm because of restorative manipulation.¹⁷ Impressions are taken with retracted tissues that are distorted by retraction methods. The most accurate way to communicate soft tissue contours is by a try-in appointment. The laboratory returns the restorations in a bisque-bake finish and the restorations are tried in the mouth. Photographs are taken and the restorations are picked up in a new impression. Some practitioners try in copings (metal or ceramic). Be aware that supported tissues will begin to collapse almost immediately after provisional restorations are removed. Most anterior restorations are done without try-ins in real world, day-to-day dentistry. This is where laboratory technicians must have complete understanding of the soft tissues. Die models give no indication of soft tissue contours. Second-pour models (solid models) are used for interproximal contact development and for a reference to soft tissue levels. Master ceramists often develop a Geller Model (Figure 26 and Figure 27).³⁵ This model has removable dies and maintains the reference gingival contours in stone. It allows the technician to manipulate the tissues by shaping the interproximal gingival stone replica. This is far more desirable than a soft tissue moulage model that simulates the soft tissue in a resilient material.³⁶ The resilient material does not allow any manipulation, as does the adjustable Geller Model. The Geller Model can be developed from a bisque-bake pick-up impression or from a retracted impression. The key issue here is to allow the technician to have maximum information and flexibility when dealing with soft tissue adaptation and contours.³⁵ This specialized model will allow the ceramist to control the final interproximal emergence profile by shaping the papillae.

Conclusion

Inconspicuous dental restorations are dependent on their surrounding soft tissue frame. There are a number of steps a clinician can use:

• Start with healthy gingival tissues or plan on a provisional treatment phase to establish gingival health.
• Always respect gingival tissues. Avoid rotary gingival curettage, electrosurgery, or laser surgery in the critical esthetic zone.^4,37
• Carefully consider supragingival margin placement.
• Never prepare into the sulcus without placing retraction cord.
• Match margin type, margin placement, and restorative material to tissue biotype and bioform.
• Preparations should follow the gingival crest. Flat preparation profiles will violate interproximal biologic width and lead to red gingivae and black triangles.
• Do not "bury" the margins. It seems logical to put a margin deep enough to never be seen again. Unfortunately this creates a biologic width violation, making it nearly impossible to capture an accurate impression. It leads to poor-fitting restorations, difficulty in removing excess cement, and ultimately leads to red gingivae, recession, and dark triangles.
• The impression technique must be as noninvasive as possible while still capturing a complete 360˚ impression. Use gentle retraction techniques and minimal quantities of noncaustic styptic/astringent solutions.³⁸
• Provisional restorations are critical in proving the efficacy of tissue management.
• Provisional restorations must be contoured correctly and have highly polished surfaces. Marginal adaptation can be accomplished by using meticulous technique. Excess temporary cement can create irreversible changes in sensitive gingival tissues.
• Long-term provisional treatment adds predictability.
• Use a laboratory with a commitment to excellence. The very best clinical dentistry can be sabotaged with mediocre laboratory support.
• Restorations must be completely seated. Laboratories work diligently to get excellent marginal adaptation. Clinicians have the responsibility to confirm complete seating during delivery.
• If the laboratory adjusts the interproximal emergence profile, look for tissue blanching. If blanching resolves within 5 minutes, the new contour is acceptable. The emergence profile must be highly polished.

This article offers a review of contemporary thinking on the integration of dental restorations into their biological housing. Treatment results can be far more predictable when these concepts are considered during planning and subsequent treatment delivery. The case photographs will summarize some of the concepts discussed (Figure 28, Figure 29, Figure 30 and Figure 31).

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About the Author

Larry R. Holt, DDS
Adjunct Associate Professor
University of North Carolina School of Dentistry
Chapel Hill, North Carolina
Private Practice
Hickory, North Carolina