March 3, 2020
by Preety Desai, BSc, DDS, Dip. Periodontics, MSc Laser Dentistry
One of the most gratifying, yet often overlooked procedures, in dentistry today, is the treatment of excessive gingival display (EGD), or the “gummy smile”. A multi-disciplinary approach to treatment includes: the general dentist; the periodontist; and perhaps the treating orthodontist. This approach enables the patient to receive the most comprehensive treatment, with the best final aesthetic results. Furthermore, this treatment philosophy can still be straightforward, regardless of the number of responsible clinical providers. It creates a harmony that rapidly provides the patient with facial and psychological enhancement.
In 1999, Kokich1 described the minimal threshold of awareness of what constitutes an unaesthetic gingival display, which for orthodontists was 2 mm, general dentists 3 mm, and for the patient, almost a 4 mm gingival display had to be attained before there was an aesthetic concern. If EGD is a result of an increased maxillary arch vertical height, orthognathic surgery is the treatment of choice. However, non-orthognathic treatment options can still provide patients with adequate esthetic improvement in their eyes, even if it is not a full resolution from the dentist’s perspective. If EGD cannot always be 100% eliminated, porcelain veneers, and other restorative or orthodontic procedures can reduce the severity of EGD to below the 4mm patient’s aesthetic threshold, thereby improving the patient’s self-image.
EGD was first discussed by Gottlieb and Orban, in 1933,2 where the natural dentition’s eruptive phases were portioned into active or passive eruption phases. The non-dental factors include gingival enlargement, vertical maxillary excess, isolated anterior dento-alveolar extrusion and a short or hyperactive upper lip or a combination of these factors. For treatment purposes, deciphering the portion of tooth enamel covered by gingival tissue vs. osseous tissue will determine the treatment approach from a surgical point of view. Active eruption is cited to be the natural eruptive force of the tooth from the follicular space into opposing occlusion, while passive eruption is described as the gingival drape overlying the osseous support and indeed past the natural CEJ of the tooth. Orthodontic forces can also contribute to altered passive eruption, by changing the tooth position into the desired occlusion at the expense of intrusion of the CEJ beyond the alveolar crests. Both processes, active and passive eruption, can occur simultaneously and independently of each other.
A modified classification of 1) simple, 2) compound, or 3) complex crown lengthening, as introduced by P.D. Miller3, were devised in order to comprehend and simplify the contributory roles of altered active eruption (AAE) and altered passive eruption (APE), to enable a much-simplified treatment. Clinicians must evaluate the etiology of EGD, be it tooth position, alveolar bone structure, jaw structure or quantity and quality of gingivae for appropriate treatment.
Two key papers by Gargiulo4 and Tarnow5 describe the physiology in order to achieve esthetic smile development, specifically the ferrule space, biological width impingement, and interpapillary space. A more recent study on biological width measurement6 evaluated 171 cadaver tooth surfaces and observed mean measurements of 1.34 mm for sulcus depth, 1.14 for epithelial attachment, and 0.77 mm for connective tissue attachment, compared to the classical Gargiulo dimensions. Newcomb7 analyzed sub-gingival margins of varying depths vs. uncrowned contralateral control and showed that subgingival crown margins closer to the epithelial attachment were more likely to have severe gingival inflammation. Parma-Benfenati et al.9 observed approximately 5 mm of osseous resorption when restorative margins were placed at the alveolar crest. Minimal resorption was observed when restorations were placed 4 mm coronal to the alveolar crest.
Bone resorption was particularly severe in areas with thin cortical bone. Many papers conclude that the restorative margin creates a micro-gap where microbial accumulation occurs and, itself, is bringing a foreign (cement) object into a natural biological width environment, violating the space and resulting in the body’s natural reaction to “pull back” with recession or swelling, or both.
We, as dentists, must accept that recommendations regarding placement of restorative margins, with respect to ferrule, are supported by opinion articles ONLY, which were written based upon clinical experience and interpretations of clinical studies. Regardless, an absolute MINIMUM of 3.0 mm of space between restoration and the supporting alveolar bone, circumferentially, is a conservative measurement for treatment planning. Wagenberg et al.9 listed a number of surgical limitations: the length of the clinical crowns, furcation location and esthetics, which limit the surgical field, and suggested a 5 mm distance from bone to the restorative margin. It was noted that experienced clinicians evaluated osseous reduction more accurately,10 which resulted in better long-term stability, less recession, and relapse of the crown lengthening procedure one year later.11
Regardless of the contribution of APE (gingival position with respect to crown) or AAE (osseous position with respect to CEJ) or both,3,12 biological principles must be respected. The amount of gingival and osseous tissues to be adjusted in order to achieve long term hard and soft tissue stability, and maintenance of the esthetic restorative margins, is essential. 90% of all anterior teeth have only bundle bone as its supporting fourth facial wall.13 The architecture of bundle bone is thin and often <1 mm in thickness, and is best handled surgically in a flapless manner, hence the popularity and anecdotal success rate of flapless crown lengthening procedures. The majority of orthodontic patients, however, are left with APE, and have a thicker gingival biotype and a much thicker facial plate (>1 mm). When esthetic crown lengthening is required in these cases, the buccal alveolar plate is not a knife edge and cannot simply be troughed in a flapless manner, as it needs flapping in order to obtain an appropriate ferrule in three dimensions, rather than blindly guessing where the alveolar profile needs to be. These cases will most certainly rebound following flapless crown lengthening leading to patient dissatisfaction.
The recommended six to 12 weeks of post surgical stability, prior to any restorative placement, is dependent on thick or thin gingival biotype and its relapse capability. Analysis of gingival biotype quality is not precise, but by using a simple and reproducible method for gingival thickness assessment, we can confirm three main types: a) thin gingiva found in about one-third of cases, mainly women with slender teeth and narrow zone of keratinized tissue with highly scalloped corresponding gingival margin, b) thick gingiva found in about two-thirds of cases, mainly males, but half of this second category, could not be classified. These subjects showed clearly, c) thick gingiva but with slender teeth, a narrow zone of keratinized tissue with high gingival scallop.14 Stein12 suggested that crown form (crown width CW) vs. crown length (CL) and keratinized tissue width are helpful indicators for the thickness of the gingiva over the CEJ, while CW/CL ratio represents a predictor of the thickness of the buccal alveolar crest. Logically, the time frame of healing and maturation, gingival marginal stability is clearly dependent on the biotype. “Those with thick gingival biotype generally had more tissue regrowth than with thin biotype”.15 However, Batista et al.16 concluded that there is no relationship between hard and soft tissues for predicting thick or thin gingival biotype and CBCT should be used to evaluate the buccal hard tissue thickness more accurately. Deas17 showed significant tissue rebounding if proper ferrule dimensions were violated due to inadequate osseous adjustment, which was directly related to surgical skill of the dentist.
Crown lengthening must promote proper osseous and gingival contour harmony and needs to be extended beyond the tooth, or teeth, in question. Adjacent teeth need to be evaluated for periodontal health and structural support in order to eliminate the risk for unaesthetic crown length, black triangles, and flattened papillae.
Arora et al.18 and Pontoriero and Carnevale11 observed the influence of periodontal biotype on soft-tissue marginal rebound and noted that patients with thick biotype have increased post-surgical tissue rebound, when compared with patients with thin biotype. They also reported more coronal displacement of free gingival margin (FGM) for patients with thick periodontal biotype compared to a thin one. The position of gingival margin is dependent not only on bone removal, but also on periodontal biotype, and surgical technique of flap margin position after suturing. When assessing the periodontal biotype, probing depth should be measured before crown lengthening surgery, since the determination of the periodontal biotype helps in bone removal decisions.10
As mentioned previously, the presence of APE with the associated flattened thicker gingival biotype, shorter clinical crown lengths with gingival margin located up to 2 mm incisal to the CEJ, and buccal buttressing bony profile on flap elevation, is higher in post orthodontic therapy patients.19 Therefore, in order to achieve an esthetic smile design in these patients, full thickness flap osseous surgery is needed in three dimensions vs a flapless surgical approach.
Lanning’s paper20 noticed stability of the free gingival margin between three and six months of waiting post-operatively. So, regardless of whether posterior or anterior, waiting 12 weeks prior to finalizing the restorations is recommended. In contrast, Abou-Arraj21 demonstrated that six months are needed post-surgically for apically positioned flaps before gingival regrowth is finalized, particularly in patients with thick tissue biotypes. This wait time seems excessive because it is based on reattachment onto dentinal surfaces in the presence of the smear layer created by mechanical instrumentation of the dental burr and surgical instruments. This smear layer created by just touching the dentinal surface of the tooth discourages connective tissue reattachment in a surgical approach.
The trend in dentistry today, whether it is crown lengthening or implant surgery, is towards a minimally invasive approach to surgery which bypasses or minimizes the inflammatory cascade leading to the reduction in post-surgical symptoms and higher patient acceptance.
If surgeons were willing implement the Er,Cr:YSGG or the Er:YAG all-tissue lasers for this purpose, it would truly embody the minimally invasive approach on many levels. First, YSGG lasers remove only 25 µm of organic tissue per pulse, and in non-contact mode of operation there is no possibility to create smear layer; in fact, smear layer is removed, encouraging connective tissue reattachment. Second, the inflammatory cascade initiated by any mechanical tissue removal does not exist, therefore, there is no pain, discomfort or swelling factors associated with surgical trauma. With all the advantages of MINIETM (minimally invasive erbium) laser approach to surgery, there is no longer any fear to raise a flap as needed, even in the most esthetic zone. The lack of papillary reattachment, poor gingival margin esthetics, and recession beyond the crown margins post-restoration, are no longer an issue, resulting in long-term patient satisfaction.
Crown lengthening surgery is often underutilized and, as a consequence, too much reliance is placed on post-cores and restorations with deep subgingival margins to obtain adequate retention.22 This eventually leads to root fractures in the cases with post-core restorations, violation of the biologic width in the case of deep subgingival margins in anterior and posterior teeth, and in the worst-case scenario, treatment planning for implant replacement of teeth which had simply needed crown lengthening surgery prior to restoration.
As a periodontist, the most difficult thing to predict is the exact location for future crown margins, which is essential to the success of crown lengthening surgery. A diagnostic wax-up, temporization and excellent communication between collaborating clinicians is the key to the best possible aesthetic results and for the patient’s health.
Oral Health welcomes this original article.
About the Author
Preety Desai is the first Canadian periodontist implementing the all tissue laser into her specialty practice. After her periodontics board certification she has practiced in and called Kamloops BC her home. She has recently completed her specialty MSc Degree in Laser Dentistry from Germany and has implemented the erbium all tissue laser into all aspects of her surgical practice and now finds it indispensible for treatment of periimplantitis. In addition to full time practice, she is clinical associate professor at University of British Columbia, leading multiple study clubs. In addition, she has ALD Advanced Proficiency Status and is also a published author.