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How Gum Shortening Can Improve Your Aesthetic Restorative Results by Dr. James Kohner

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Part I
Have you ever been frustrated when your beautiful aesthetic work is compromised by an existing display of excessive or uneven gingival tissue in the aesthetic zone? Have you been tempted by advertisements to remove the excess tissue by gingivectomy using a laser, electro-surgery unit or blade?

You are not alone. But... stop! Do not proceed until you read further. Dentistry in the 21st century has changed quite dramatically from the 20th century. Today, both aesthetics as well as use of technology are higher priorities. Both have revolutionized what we do. From more successes with implants to highly aesthetic veneers and stronger bonding materials, we now have powerful tools that were not available 10 years ago. But while utilizing these exciting technologies, it is essential to remember the basics. Today every complication or restorative challenge does not automatically need to become a titanium implant or a laser opportunity!

One basic procedure that many clinicians overlook, is crown lengthening. This procedure has remained essentially unchanged for 30 years and remains as useful now as ever. It has applications in all parts of the mouth. For posterior teeth often there is not enough tooth structure for retention (Figs 1.1 and 1.2). This can occur as a result of excessive gingiva, caries or fractures. When teeth are prepared in a subgingival fashion, problems can occur from impingement on the soft tissue. Crown lengthening can help create an abutment tooth that not only has better retention, but allows for a crown margin that will not impinge on the soft tissues by creating enough mechanical tooth structure for retentiveness while staying outside of the soft tissue dimension with the restorative margin.

The stated goal of crown lengthening in a restorative application, for all parts of the mouth, is to expose enough sound tooth structure to allow the placement of a restorative margin onto that sound tooth structure, for adequate mechanical retention, and at the same time, avoid disrupting or impinging on any of the delicate gingival fiber attachment to the tooth. In the rush to use the latest new materials and techniques such as implants or lasers, the benefits and applications of crown lengthening are often ignored. But instead of being pushed aside and forgotten, this old standard should make its way into every contemporary clinician's armamentarium. In the anterior aesthetic zone, errors of margin placement can be even more noticeable when inflammation occurs (Fig. 1.3).


Placing crown margins too close to the bone, and impinging on the soft tissues of the biologic width has long been known to cause inflammatory complications.1 Crown lengthening can allow for restorations being placed in a way to avoid those known complications. This article is making a case for learning to manage the bone to restorative margin interface, which is the key to successful crown margin placements.

Of course each tooth with restorative or soft tissue problems is not automatically an indication for crown lengthening! Extraction leading to an implant, a fixed or removable appliance, always needs to be in the differential diagnosis. Orthodontic extrusion, as well, should be considered as it is sometimes a viable option, but that is a topic for another entire paper and has been covered by others.1a

In my experience as a specialist, patients usually come on referral from their general dentist. It is interesting how many of those patients come in for consultation even though they have no idea what a crown lengthening actually is! At the same time, 40 percent of dentists I've personally surveyed reported frustration in gaining acceptance of their referrals for crown lengthening procedures. Why are some so successful and others not?

The frustrated dentists might gain more acceptance of their referrals if the patients understood what benefit the procedure meant for them, and if they could actually picture those benefits. For starters, consider using the term mentioned in the title, namely gum shortening, instead of crown lengthening. Patients more easily understand this term. A useful tool is to describe crown lengthening as the shortening of gum tissue to expose more tooth structure, and refer to the tissue as a turtle neck in an effort to use non-dental terms.

While patients demand higher and higher levels of aesthetics, it remains our responsibility to provide a high level of evidence-based, scientifically sound care. While implants and bridges have that evidence, so does crown lengthening. There also are many resources covering the biologic characteristics of human gingival tissues.2-6 Despite the availability of this information, patients still have crowns placed that impinge on the gingival tissues in an apparent effort to obtain mechanical retention where there was structurally insufficient clinical crown. Crown lengthening is a way to avoid these complications by creating sound tooth structure for a restorative margin, and manage the key bone to restorative margin interface.

Besides this impingement scenario, there are instances where dentists overlooked basic biology when they performed gingivectomy to remove excessive or uneven tissues then place restorations in the space formerly occupied by the soft tissues. For example (Fig.1.4) shows an example of excess tissue. Whether the tissue is removed with a laser, blade or electro-surgery unit, this can be risky.5 It is not the choice of an instrument that causes the problems, but a technique that fails to respect the dimension of the gingival soft tissue to bone relationship, or biologic width. Without removing the same amount of bone, a violation of the biologic width will be created and a predictable chain of events will follow when restorative margins are placed where soft tissues were, and then the soft tissue regrows. Published reports show that the gingiva will grow back to its original dimension. While this process sometimes takes up to 12 months, the tissues will regrow.7 This resulting violation of the biologic width leads to red, sore or edematous tissues, which occurs as the tissue heals, re-establishing the original dimensions of the gingiva. While a different case (Fig. 1.3) illustrates that resultant redness when the restorative margins are too close to bone after gingivectomy and the soft tissues re-establish the normal dimensions of the gingival complex. While some would refer to that phenomenon of regrowth as rebound, many reports explain the phenomenon as normal redevelopment of biologic width.7,7a,7b

Thick ledges of bone, resulting in excess gingival height and small clinical crowns, leave potentially limited retention as often seen around second molars, as illustrated earlier (Figs. 1.1 and 1.2). This thick bone is common in both maxillary and mandibular molars, but is common also in the anterior, and knowing where the bone is located becomes the key to avoiding embarrassing red gingiva seen (Fig. 1.3). When this thick soft tissue is observed, the question becomes what makes it so thick? Typically bone is thick under the tissue, requiring removal of bone and not just soft tissue. Figures 1.5 and 1.6 illustrate that thick tissue biotype associated with thick bone. Predictable healing results only when the bone is properly managed.4,7,7a,7b When the healing and maturation of the soft tissues is complete, predictable results will be achieved only by removing enough bone and locating it correctly at 2.5-3mm from the expected restorative margin, and not just from apically positioning the soft tissue, or by doing a soft tissue gingivectomy.7a,7b Bone then becomes the key parameter. While some concern for crown to root ratio must be acknowledged, it is unlikely that with a periodontally sound tooth, that bone removal as described here would result in mobility issues as so little supporting bone is removed.

    In summary, indications for crown lengthening include:
  • Excessive gingival display in anterior—often associated with thick bone
  • Short posterior teeth with excess gingiva and thick bone
  • Uneven gingival levels
  • Fracture under gum margin
  • Subgingival caries
  • Previous crowns and finish lines too close to soft tissue attachment

Remember, it is generally sound advice to avoid removal of soft tissue without planning to remove a commensurate amount of matching bone as well. If you follow this advice, you will be one step closer to achieving predictable and aesthetically pleasing results. (Figs. 1.7 and 1.8). Part II will continue with the science behind these decisions and how they can be applied to clinical dentistry.


Part II
In Part I, you learned to resist the temptation of removing soft tissue in the aesthetic zone without also planning for an appropriate amount of bone removal. Managing the bone is essential in obtaining predictable soft tissue results, and the distance between bone and crown margin (or CEJ in an anterior aesthetic case) becomes the key component. Research has shown that the typical space from the gingival margin to bone on the labial or lingual is 3mm.8-11 This basic rule applies to 85 percent of mouths, 8,10,13 thus most of the time the biologic width will be similar but must be verified by bone sounding.

It is an exception when the gingival soft tissue dimension varies from that normal 3mm biologic width.8 In those situations, where the dimension of soft tissue to bone crest exceeds 3mm, this represents the single indication for soft tissue crown lengthening. The tissue exceeding the 3mm dimension, but not more, can be removed.8,13 To take more tissue would leave less than the 3mm soft tissue dimension, and could result in margins being too close to the bone as described in Part I. Thus, it is evident that other than when the biologic width exceeds 3mm, both aesthetic and functional crown lengthening will require bone management.

Conversely, there are some instances where the distance of gingival margin to bone crest is smaller than the normal 3mm. In these cases, as described by Dr. John Kois,8 the smaller biologic width must be identified ahead of tooth preparation time, and is a warning to avoid even the smallest amount of subgingival tooth preparation, or a biologic width violation might result.

With those thoughts in mind, this second installment will address all those issues, and will look at the scientific rationale, treatment planning goals and clinical benefits of crown lengthening, or gum shortening. You will see a clear example that demonstrates how the removal of bone is used to create the predictability of the aesthetic results you and your patients want.

The research that offers guidance is the 1961 study by Drs, Anthony Gargiulo, Frank Wentz and Balint Orban.9 They measured and documented the dimensions of human gingiva and found the following average dimensions based on examining 30 human cadaver jaws:
  1. Sulcus depth: .69mm
  2. Epithelial attachment width: .97mm
  3. Connective tissue attachment width: 1.07mm
These numbers were their findings of an averaged soft tissue dimension across all specimens and all levels of gingival recession. Interestingly enough, these measurements were consistent even as passive eruption, or recession and associated bone loss, was taking place—consistency to the point that the 1.07mm for connective tissue attachment was almost identical at any phase of passive eruption or recession associated with either aging or disease.

Conventional wisdom and many clinicians now consider these dimensions of human gingiva, or the biologic width, to be a combination of three 1mm measurements,12 resulting in a more easily understood total of 3mm from the labial or lingual bone crests to the gingival margin. There are slight variances interproximally.8,12 It is this soft tissue dimension that must be respected when locating a restorative margin.

To avoid a mechanical impingement of the soft tissues, which is the classic biologic width violation, margin placement must remain outside the soft tissue attachment to the tooth. Thus, in the anterior where aesthetics is important, attention to limiting subgingival margin placement to no more than .5mm under the tissue is vital. Also, in the anterior the high rise of the interproximal CEJ must be accommodated or interproximal violations will occur there with all the sequelae discussed. Since we cannot feel or probe the exact spot where the delicate epithelial attachment begins, measuring apically from the gingival margin serves as our only reference point, and staying within that .5mm dimension is the parameter that guides proper margin placement. While we respect the research finding of .69mm as the approximate sulcus dimension, there is no way to probe the exact dimension of that sulcus. How is the end of the sulcus identified? Is it when patients jump from the pain of a probe? I contend that we really cannot feel it, so that is why the safe margin placement is typically no more than that .5mm distance below the marginal tissue. Yes, that is a small playing field for margin location, yet by understanding the normal dimensions of human gingiva, it is clear that is all the space available.

Many anterior gum shortening procedures are done in conjunction with restorations. The prosthetic requirements must be determined during the initial stages of diagnostic workup so the restorations will be biologically sound, aesthetically pleasing, properly functional and non-traumatic to the tissue. The following is a summary of what should be determined as early as possible:
  1. The eventual incisal edge position. Will it be the same or different from the existing location?
  2. Have you considered the desired size of the clinical crown, and will the gingiva need to be relocated to accommodate this size? This can be decided by reviewing a diagnostic wax up with the patient, using trial temporaries, a trial overlay, or Chu's Esthetic Gauges to help approximate the golden proportion ratio of 75-80 percent width to height in the maxillary anterior.
  3. The patient's pre-operative biologic width. While most people have a 3mm distance from the gingival margin to the labial or lingual bone crest, there are exceptions and variations.8 These exceptions must be recognized before beginning the tooth preparation.8 The location of the osseous crest on the labial or lingual can be determined by bone sounding through the sulcus under local anesthetic.
  4. If it is determined that the biologic width is less than the normal of 3mm, then extra caution is needed, since going sub-gingivally even a small amount with margin preparation might be too much. In these cases of biologic width being less than the normal 3mm, something Kois calls a "high crest,"8 there is danger of having margin placement too close to the bone even if we think we are safe with the .5mm sub-gingival location.
  5. If biologic width is more than the normal 3mm, then some soft tissue removal can be considered. Only the dimension of soft tissue exceeding the normal 3mm of biologic width can be removed. It has been shown that following surgery these dimensions heal to the normal 3mm dimensions.8a

Once these decisions have been made, and the amount of soft tissue removal to accomplish the objectives is determined, it can now be decided how much bone removal is needed to create the desired tooth size. Removing comparable bone will then allow space for biologic width, and restorative dimensions, without the complication of impingement or gingival regrowth. Just shortening gum and not the bone has been demonstrated to allow for regrowth of soft tissue.15,16 This regrowth, sometimes called rebound, is the normal re-development of the body's 3mm biologic width that occurs when gingiva is shortened or surgically positioned too close to bone level. If flaps are elevated, tissues shortened, and replaced at bone crest, the biologic width does redevelop, or rebound.11,15,16 If restorative margins are placed on the newly exposed tooth after the soft tissue alone is shortened, the restorative margins will be in the way when the tissue regrows. Impingement will often result. It is not a matter of if the gingiva will rebound, but a matter of when. The process may take a year, but the soft tissue will regrow.11,15,16

Observing this skull specimen in figure 2.1, the absence of the soft tissues gives solid evidence that the body knows the 3mm dimension of human gingiva. Clinical procedures must accommodate it as well in choosing the location of final crown margins.

As the above five diagnostic decisions are made, the need for bone removal becomes clearer. Note in figure 2.2 that the patient has 7.5mm of clinical crown showing. She requested longer teeth, and after workup with her general dentist (Fig. 2.3), they decided on 11mm long central incisors. She understood that gum shortening would expose cementum, and agreed that veneers would be an acceptable solution. After those parameters were reviewed, the surgical goals were defined. If she starts with 7.5 mm long teeth and 11mm is desired, it becomes clear that 3.5 mm of soft tissue, and the associated 3.5 mm of bone, need to be removed (on the central incisors).

Clinical situations like this develop when there is an altered pattern of bone development, such as thick bone biotypes, or tooth eruption resulting in relationships of bone crest to CEJ levels that depart this normal 3mm. In the high crest scenario, the CEJ and bone are, by definition, closer together than in the typical 3mm biologic width.8 In this situation, there is no room between bone crest and CEJ for the 2mm of soft tissue attachment, plus 1mm of sulcus, found in the average anatomy, yet the body knows that the soft tissue dimension should be 3mm, as illustrated by the skull example (Fig. 2.1), so the gingival margin ends up more coronally. This is what causes shorter clinical crowns with the gingiva on enamel.

Interdisciplinary teamwork can be very satisfying in solving these problems and giving patients the aesthetic result they want. When working as a restorative dentist/periodontist team, the two clinicians can develop ways to communicate clearly about diagnostic workups and patient goals in order for the periodontist to accurately relocate the bone to its correct position.14 Relocating bone to the correct biologic position will not only allow for achieving a predictable size of clinical crown, but will also avoid crown margin impingement on the soft tissues via rebound.15,16

Clinical crown length gained has been shown to last as little as just six months if inadequate bone is removed.16 Thus in the case illustrated here, (Figs. 2.4 and 2.5) shows the correct bone removal with the original bone to incisal edge distance at 10.5mm. That 10.5mm dimension (Fig. 2.4) is a combination of the 7.5mm of the clinical crown plus the 3mm dimension of the biologic width, which results in the expected 10.5mm dimension from incisal edge to bone crest. This is quite logical and follows what is expected of the gingival dimensions. To create a 11mm central incisor, the crestal level has to be relocated to 14mm from the chosen incisal edge position, namely 11mm plus the 3mm biologic width as discussed above. In this case, the final incisal edge position will replicate the original incisal edge.


In my experience, I have found that using a periodontal probe (Fig. 2.5) during this surgical bone removal is an essential reference point, as it is impossible to judge dimensions only by visual observation. Making an eyeball judgment will often result in too little bone removal, as without measurement references it looks like an extreme amount of bone removal is taking place, when in fact that is not the case (Fig. 2.5). While the result looks like extreme amounts of bone were removed, it is the reliance on the known dimensions of human gingiva that guides success.

The scope of this article is not intended as a detailed technique dissertation. Rather it is meant to be a guide for a restorative/periodontal team, or as an incentive for further learning. Keeping these parameters in mind, carefully studying and learning the dimensions of human gingiva, developing a periodontal/restorative team, and applying these principles will help you to create predictable aesthetics, satisfied patients and pleasant results (Figs. 2.6 and 2.7)

References
  1. American Academy of Pediatric Dentistry Reference Manual, 2009 http://www.aapd.org/media/Policies_Guidelines/G_Pulp.pdf
    2. Newcomb, GM. Relationship between the location of subgingival crown margins and inflammation. J. Periodontology 1974; 45:151-154
    1a. Durham TM, Goddard T, Morrison S. Rapid forced eruption: a case report and review of forced eruption techniques. Gen Dent 2004 Mar-Apr;52(2):167-75
  2. Coslet J, Ingber J, Rose L. The "Biologic Width" A Concept in Periodontics and Restorative Dentistry. Alpha Omegan 1977;70:24-28
  3. Gargiulo A, Orban B, Wentz F. Dimensions and Relations of the Dentogingival Junction in Humans. J Periodontology 1961;32, 261.
  4. Kois, John. Altering Gingival Levels: The Restorative Connection, part 1: Biologic Variables. Journal of Aesthetic Dentistry1994; 6:3-9
  5. Nevins M, Mellonig J. Periodontal Therapy: Clinical Approaches and Evidence of Success. Quintessence Books, Hanover Park, IL. 1998
  6. Oh SL.: Biologic Width and Crown Lengthening: Case Reports and Review. Gen Dent. 2010 Sep-Oct;58(5):e200-5.
  7. Pontoriero R, Carnevale G. Surgical Crown Lengthening: A 12-month Clinical Wound Healing Study. J Periodontology 2001;72:841-848
    7a. Deas DE, Moritz AJ, McDonnell HT, Powell CA, Mealey BL. Osseous surgery for crown lengthening:A 6-month clinical study. J Periodontology 2004;75(9):1288-1294.
    7b. Arora R, Narula SC, Sharma RK, Tewari S. Evaluation of supracrestal gingival tissue after surgical crown lengthening: a 6-month clinical study. JPeriodontology. 2013; 84(7):934-40.
  8. Kois, John. Altering Gingival Levels: The Restorative Connection, Part 1: Biologic Variables J of Aesthetic Dentistry 1994; 6:3-9
    8a. Kois, John; Personal communication. 2014
  9. Gargiulo A, Wentz F, Orban B. Dimensions and Relations of the Dentogingival Junction in Humans J Periodontology 1961; 32, 261-267
  10. Coslet J, Ingber J, Rose L. The "Biologic Width" A Concept in Periodontics and Restorative Dentistry Alpha Omegan 1977;70:24-28
  11. Pontoriero R, Carnevale G. Surgical Crown Lengthening: A 12-month Clinical Wound Healing Study. J Periodontology 2001;72:841-848
  12. Nevins M, Mellonig J. Periodontal Therapy: Clinical Approaches and Evidence of Success. Quintessence Books, Hanover Park, IL. 1998
  13. Kois J. The Restorative: Periodontal Interface: Biologic Parameters, Periodontology2000, pub 1996; 11, 29-38
  14. Small, BW. Interdisciplinary Treatment for Esthetic Restorative Dentistry. Gen Dent. 2002 May-Jun;50(3):230-2, 234, 236.
  15. Deas DE, Moritz AJ, McDonnell HT, Powell CA, Mealey BL. Osseous surgery for crown lengthening:A 6-month clinical study. J Periodontology 2004;75(9):1288-1294.
  16. Arora R, Narula SC, Sharma RK, Tewari S. Evaluation of supracrestal gingival tissue after surgical crown lengthening: a 6-month clinical study. J Periodontology. 2013 Jul;84(7):934-40.
Dr. James Kohner is a periodontist living in Scottsdale, Arizona. He has over 35 years clinical experience and more than 20 years teaching and lecturing, with presentations all over the US and eight foreign countries. He currently teaches hands-on surgical training workshops on crown lengthening and soft tissue grafting for the Perio Institute (www.Perio.com), and many state association meetings, plus is a visiting professor at the Harvard School of Dental Medicine. He recently posted online CE programs about both crown lengthening and soft tissue grafting on Dentaltown.com. He can be reached at James@JamesKohner.com.

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