12.8 Regeneration of Keratinized Gingiva 12 12.8 Regeneration of Keratinized Gingiva Michael K. McGuire 12.8.1 Overview The augmentation of keratinized gingiva (KG) around teeth with mucogingival defects has been an achievable goal in dentistry for many years. Compared with the more elastic and unattached alveolar mucosa, “tougher” and attached KG is thought to improve the long-term prognosis for Fig 12.8-1 The mucogingival junction (MGJ) can clearly teeth, particularly in patients with questionable be seen in this patient. The probe extends to the MGJ, oral hygiene (Lang and Löe, 1972; Wennström et indicating that this patient has no attached gingiva. al., 1981). The distinct change between kerati- nized, attached gingiva and non-keratinized and tial healing, transplanted graft “shrinkage” loosely attached alveolar mucosa is delineated by occurred, but the resultant dimensions could be the mucogingival junction (MCJ) (Fig 12.8-1) and anticipated and maintained long-term. The sub- distinguished histologically by the distribution and epithelial connective tissue graft (CTG) was also nature of elastic (mucosal) and inelastic (gingival) investigated as an onlay graft (Edel, 1974; Calura collagen fibers and the short, wide (mucosal) and long, slender (gingival) papillae, with a defining layer of keratin on the surface of KG epithelium Gingival sulcus (Fig 12.8-2). Gingival margin In the 1960s, denudation and pushback pro- cedures were early attempts at increasing the Free gingiva amount of KG, but the outcomes were unpre- Nonelastic connective dictable and painful (Costich and Ramfjord, tissue 1968; Karring et al., 1975). The apically pos- itioned flap (APF) encouraged KG regeneration from the wound bed and margins and, when Keratinized gingiva indicated, was combined with a vestibuloplasty (APF + V) to expose more of the alveolus and Attached gingiva remove the mechanically disruptive influence of muscle pull (Friedman 1962; Robinson and Agnew, 1963). Soft tissue grafting investigations in the 1960s demonstrated that it was possible to Elastic increase KG through the free gingival graft connective tissue Mucogingival (Bjorn, 1963; Pennel, 1969). Studies also indi- junction cated that tissue specificity was retained. Gingi- Alveolar mucosa val grafts harvested from the keratinized gingiva or palate and transplanted into the mucosa, for example, retained their keratinized and inelastic Fig 12.8-2 Diagram of the periodontium adjacent to determination (Karring et al., 1971). During ini- the tooth. 277 Clinical Research Protocols for Indications in Dental Regeneration In the late 1970s and early 1980s, there were some favorable reports of freeze-dried skin as a substitute for the FGG, but the biomaterial was never widely adopted (Yukna et al., 1977). Cadaveric tissue resurfaced in the late 1990s, when acellular dermal matrix (ADM) was intro- duced as an FGG substitute. Because ADM does not perform well when placed over open wound beds for regenerating KG, the periodontal litera- ture regarding ADM focuses on root coverage procedures with ADM beneath a CAF (Harris, Fig 12.8-3 Postoperative photograph of the 2001; Wei et al., 2000). appearance of a free gingival graft facial to the cuspid Starting in 2003, researchers began reporting and bicuspids. cases in which the patients’ own fibroblasts were cultured and implanted for gingival augmenta- et al., 1991), with the advantage that the CTG tion. In a series of investigations from 2005 to could be harvested via a pouch procedure and 2011, expanded fibroblast and expanded, bilay- might be less uncomfortable postoperatively for ered fibroblast plus keratinocyte (BL) sheets were patients. The regeneration of keratinized and studied (McGuire et al., 2008). Though the attached gingiva appeared to be influenced by amount of KG generated with these tissue-engi- the tissue phenotype of the subepithelial, trans- neered biomaterials was significantly less than planted connective tissue, as well as the remain- the traditional APF + V + FGG standard, over ing periodontal ligament. Accordingly, CTG from 95% of patients in a BL multi center study attached palatal gingiva was placed beneath cor- (McGuire et al., 2007) obtained ≥ 2 mm bands onally advanced flaps (CAF) to accomplish both of KG, and in all of the studies, patients preferred root coverage and improved KG width. However, the esthetic outcome and overall therapy alter- when root coverage was not indicated and a sig- native provided by the tissue engineered solu- nificant amount of KG was desired, the gingival tions. autograft and particularly the free gingival graft (FGG) were adopted as the standard of treat- 12.8.2 Research Question ment (Bjorn, 1963; Nabers, 1966; Sullivan and Though there are abundant systematic reviews Atkins, 1968; Pennell et al., 1969). concerning gingival augmentation procedures for Despite the predictability of the FGG, the tissue root coverage, there are limited reviews concern- texture and color mismatch of the healed trans- ing KG augmentation studies on teeth not requir- plant, sometimes referred to as a “tire patch,” was ing root coverage. A recent and thorough review less than ideal (Fig 12.8-3). Also, complications, (Thoma et al., 2009) underscores that the combi- such as postoperative bleeding and pain coupled nation of APF + V with autogenous graft yields with the finite supply of harvestable donor tissue, the most favorable KG and attached gingiva (AG) prompted researchers to look for substitute bio- results. More randomized controlled trials (RCTs) materials (Griffin et al., 2006). Though regenera- comparing alternative therapies are needed, but tion of a functional zone of KG continued to be with suitable standardization and calibration, the overriding goal, investigators turned to tech- more patient-reported outcomes (PROs), and niques and biomaterials that might minimize mor- adequate statistical analyses and analytical meth- bidity and create tissue indistinguishable from ods, especially with regards to thickness measures, what nature provides. biopsies and histological analyses. The primary 278 12.8 Regeneration of Keratinized Gingiva 12 outcome variable of these KG studies is usually Inclusion change in KG, but secondary outcomes including • Teeth indicated for KG regeneration. change in AG and periodontal health measures • At least two non-adjacent treatment sites of should also be followed. New metrics comparing 1 to 4 teeth span, with <2 mm KG. alternative therapies – for example, surgery time • 18 to 70 years of age. required and PROs measures for anxiety, pain and • (if female) A negative urine test for pregnancy preference – should be compared with the bench- and practicing birth control. mark APF + V + FGG therapy. Ideally, the regen- • Able to read and understand informed consent. erated KG should be indistinguishable from what • Able and willing to follow instructions. nature provides. • Demonstrate good plaque control. • If patients have parafunctional habits, fit with 12.8.3 Time Points bite guard. Six months has been a standard endpoint for most • For PROs – able and willing to participate in gingival augmentation studies, and meta-analyses phone interviews or employ other, “real time” have adopted this endpoint, perhaps by default, monitoring methodologies. as a comparator metric. Early autogenous graft transplant primate research indicated that the Exclusion amount of KG gained at 1 month following initial • Systemic healing conditions.* shrinkage is maintained long term (Karring et al., • Acute infections in the area intended for treat- 1971). In the author’s experience (McGuire et al., ment. 2005, 2008 and 2011), KG width measures • History of tobacco use within past 6 months. observed at 3 months with APF + V + FGG ther- • Intravenous or intramuscular bisphosphonates. apy are maintained to 6 months and beyond. The • Hypersensitivity to any biomaterials to be stud- tissue specifics, i.e., attachment and durability of ied. KG regenerated by new test biomaterials and tis- • Simultaneous participation in other clinical tri- sue-engineered alternatives, however, are still als. unknown. Though the attachment and durability • Previous grafting in the area intended for treat- of the regenerated KG may be initially assessed at ment. 6 months to match historical study metrics, it will • Class V restorations (instability measurement be important, when possible, to design studies landmark). that permit long-term follow-up for 3 to 5 years • Mobility greater than Miller Class II. (Table 12.8-1). • Subjects who, for any reason in the opinion of the investigator, will not be able to complete the 12.8.4 Inclusion and Exclusion Criteria study (e.g., it is not uncommon for patients to The following table provides inclusion and exclu- find out about the study and want to partici- sion guidelines for patients in a contralateral, pate, even though they may not live in the city within-patient, controlled clinical trial. In essence, where the study is being conducted. Also, the systemic health and/or compliance issues should be avoided, while normally encountered, prac- tice-based conditions (e.g., the inclusion of both * Patients with diabetes mellitus, cancer, HIV and/or bone metabolic diseases that could compromise wound healing maxillary and mandibular teeth) should be or preclude periodontal surgery; or who are currently embraced. These latter conditions can sometimes receiving or have received within 2 months prior to study be teased from the results during statistical analy- entry, systemic