As defined by the American Academy of Periodontology (AAP), gingiva [1] is a term that designates “the fibrous investing tissue, covered by keratinized epithelium that immediately surrounds a tooth and is contiguous with its periodontal ligament and with the mucosal tissues of the mouth.” Microscopically, the oral epithelium of the gingiva presents four layers with the corneum stratum consisting of squamous keratinocytes that are believed to serve as a “mechanical barrier” against mechani- cal/environmental trauma to the gingival tissues (Fig. 10.1). For instance, in a recent systematic review, Chambrone and Tatakis [2] evaluated the long-term outcomes of untreated buccal gingival recessions through the assessment of potential factors influencing the development and progression of these defects. These authors found that (1) within individuals presenting good oral hygiene standards, approximately 80% of the untreated gingival recessions progressed/worsened (i.e., experienced recession depth increase) during long-term follow-up and (2) the keratinized tissue (KT) band appears as an important component in preventing such detrimental
changes in the gingival margin position overtime (i.e., sites lacking KT seemed to be more prone to additional clinical attachment loss) [2].
Regarding to the importance of KT, it has long been suggested that a minimum 2 mm band of KT (with at least 1 mm of attached tissue) appears to be required to preserve the health of periodontal tissues [3]. Furthermore, the dilemma as to the need to augment the band of KT was thoroughly reviewed by the AAP in 2015 dur- ing its most recent Regeneration Workshop. According to the authors of that sys- tematic review [4] and the base of evidence available to October 2013, there are unprecise definitions on the least extent of KT necessary to maintain periodontal stability (i.e., there are no specific dimensions fully acceptable in the literature). On the other hand, clinical data included in this AAP commissioned paper [4] provided conclusions/responses to the five most common clinical scenarios found in daily practice (these are reproduced as reported in the original publication):
1. What circumstances require an increased zone of KT, or is KT important? [4]
Conclusions/Response: “Authors have noted the limitation of recent clinical studies, randomized clinical trials (RCTs), and systemic reviews to answer this question. However, clinical observations would suggest that sites with minimal or no gingiva and associated with restorative margins are more prone to gingival recession and inflammation. Thus, gingival augmentation is indicated for sites with minimal or no gingiva that are receiving intracrevicular restorative margins based on clinical observations (SORT [Strength-of-Recommendation Taxonomy criteria] level B [inconsistent or limited-quality patient-oriented evidence])” [4].
2. What is the ideal thickness of an autogenous gingival graft? Is a thick autog- enous gingival graft more effective than a thin autogenous gingival graft? [4]
Conclusions/Response: “A palatal graft should be ≥1-mm thick. Thin grafts tend to result in more esthetic outcomes, whereas thick grafts provide more func- tional resistance. Thick grafts tend to follow significant primary contraction, whereas thin grafts are more prone to secondary contraction. The type of biotype may play an important role in maintaining optimal periodontal health, but
Fig. 10.1 Microscopically, the human buccal gingiva is formed by four epithelial layers (i.e., basale, spinosum, granulosum, and corneum) and a connective tissue layer. Note that the corneum stratum (red arrow) is no longer seen in an apical direction beyond the mucogingival junction (black arrow)
disagreements exist among clinicians when describing the types of biotypes (SORT level B [inconsistent or limited-quality patient-oriented evidence])” [4].
3. What are the alternatives to autogenous gingival grafting to increase the zone of attached gingiva? [4]
Conclusions/Response: “Modified apically positioned flap may be an effec- tive technique in increasing the apico-coronal dimension of the KT and attached gingiva without donor areas or use of commercial products”….“alternative methods and materials (i.e., acellular dermal matrix grafts, extracellular matrix, xenogenic porcine bilayer collagen matrix and living cellular construct) have been shown to provide enough attached KT to correct areas lacking or with mini- mal gingiva (<2 mm) around teeth in short-term and in small–sample size stud- ies. The advantages of these approaches are avoidance of donor areas and unlimited supply. However, long-term follow-up studies and RCTs should be conducted to strengthen this treatment approach (SORT level C [consensus, disease- oriented evidence, usual practice, expert opinion, or case series for stud- ies of diagnosis, treatment, prevention, or screening])” [4].
4. Does orthodontic intervention affect soft tissue health and dimensions? [4]
Conclusions/Response: “Historic clinical observations and recommenda- tions can be referenced to answer this question. The direction of the tooth move- ment and the bucco-lingual thickness of the gingiva play important roles in soft tissue alteration during orthodontic treatment. There is a higher probability of recession during tooth movement in areas with <2 mm of gingiva. Gingival aug- mentation can be indicated before the initiation of orthodontic treatment in areas with <2 mm (SORT level C [consensus, disease-oriented evidence, usual prac- tice, expert opinion, or case series for studies of diagnosis, treatment, prevention, or screening])” [4].
5. What is the patient-reported outcome for minimal KT compared with that for an enhanced zone of KT? [4]
Conclusions/Response: “Alternative methods and materials appear to result in less patient discomfort after gingival augmentation procedures when com- pared with FGG. They have also shown to result in better color and texture match to surrounding tissue when compared with FGG. However, study investigators need to standardize how they collect the patient-reported outcomes so the obtained results can be compared with other studies (SORT level C [consensus, disease- oriented evidence, usual practice, expert opinion, or case series for stud- ies of diagnosis, treatment, prevention, or screening])” [4].
Furthermore, recent clinical long-term data (18–35 years) by Agudio et al. [5, 6]
reported in several practice-based studies comprising of patients with high stan- dards of oral hygiene shed light on the importance of gingival/KT augmentation. In the first study, it was found that teeth with single recession defects and lacking a minimum KT band of 2 mm undergoing gingival augmentation (via free gingival graft-based procedures) may display a phenomenon called “creeping attachment”
(i.e., a coronal shift of the gingival margin), leading to noteworthy gingival reces- sion reduction 10–27 years after treatment [5]. In the second publication, the authors confirmed that gingival augmentation might influence the biologic remodeling of periodontal dimensions associated with the aging process, as well as that use of free
gingival grafts can produce more beneficial KT band proportions and reduce gingi- val recession depth [6]. The second study also reported that some degree of shrink- age will occur, thus “the corono-apical dimension of the graft should be calculated on the basis of the KT width of adjacent untreated teeth plus an additional 1.00–
1.50 mm considering an estimated tissue contraction during the early healing, and long follow-up period” [6]. As a result, the authors suggested that clinicians prepare grafts with an additional apical dimension of 1.00–1.50 mm of the mucogingival junction of adjacent untreated teeth [6].
Similar to the concepts established for natural teeth, current evidence (even though minimal) clearly indicates the positive gains of increasing the KT band at dental implant sites [7, 8]. Improvements in KT width and thickness at periodontal and peri- implant sites may be essential to create a “mechanical/physical and biological epithe- lial barrier” that will give protection to peri-implant structures in view of cytokine, chemokine, and antimicrobial peptide production (i.e., interleukin-1α, interleukin-1β, interleukin-6, interleukin-8, and tumor necrosis factor-α) in response to toothbrushing trauma and dental biofilm [8, 9]. In general terms, it has been shown that an increase in KT in areas of elastic peri-implant mucosa by gingival augmentation procedures (i.e., free gingival graft and apically positioned flap) may promote the formation of a firm KT band and thus reduce the probability for gingival recession [7, 8].
Consequently, the above reported studies and reviews support the key role of KT dimensions in the maintenance of the gingival margin stability around natural teeth and dental implants. In addition, these aspects rationally indicate that such grafting procedures will promote a “biotype modification” (i.e., KT width and thickness gain) and should be considered when deemed necessary.