Five-year evaluation of the influence of keratinized mucosa on peri-implant soft-tissue health and stability around implants supporting full-arch mandibular fixed prostheses.

The question of whether a sufficient amount of keratinized tissue around natural teeth or dental implants is necessary for long-term periodontal or peri-implant health, as well as the question of what has to be considered ‘sufficient,’ are still controversial (Lang & Loe 1972; Krekeler et al. 1985; Wennstrom 1987; Wennstrom et al. 1994; Heckmann et al. 2004). More than 35 years ago, Lang & Loe (1972) found better periodontal health in teeth, which yielded at least 2 mm of keratinized gingiva with at least 1 mm being attached, compared to teeth with < 2 mm of keratinized gingiva. Although the latter findings have been challenged by subsequent studies (Miyasato et al. 1977; Wennstrom & Lindhe 1983a; Kennedy et al. 1985; Wennstrom 1987), a width of 2 mm of keratinized gingiva has been considered clinically desirable to provide an appropriate soft-tissue seal around natural teeth since then. Taking into account the considerable differences between the soft-tissue interface of dental implants and that of natural teeth, the questions arise, if peri-implant keratinized mucosa is necessary or at least beneficial for peri-implant soft-tissue health, and if the same 2 mm threshold recommended for natural teeth also applies to dental implants. If the amount of keratinized mucosa has an impact on peri-implant health, special measures would be required in patients with insufficient amounts of keratinized mucosa during maintenance therapy including specific oral hygiene instructions and closer maintenance intervals. Moreover, surgical procedures aiming at widening the keratinized tissue and increasing the vestibular depth may be indicated. Although it has been demonstrated that dental implants are successful in the treatment of edentulous jaws with fixed or removable prostheses (Ferrigno et al. 2002), augmentation of keratinized mucosa or vestibular depth may especially be required in the edentulous mandible, in which moderate to severe ridge resorption may have lead to reduced vestibular depth and a lack of keratinized mucosa. Numerous techniques to do so have been described, including free gingival grafts from the palate with or without combination of a vestibuloplasty (Edlan 1973; Buser 1987; Simons & Baima 1994; Han et al. 1995). Depending on the technique applied, some of these procedures may pose a significant challenge for the patient, especially when elderly or medically compromised. Accordingly, it would be of great importance both for clinicians and patients to better understand the significance of peri-implant keratinized tissue for long-term soft-tissue health and stability, in order to better assess the need for additional surgical procedures or special considerations during maintenance therapy. However, as of today, the literature is inconclusive, contradictory and lacks long-term human data. Therefore, the purpose of this study was to investigate the necessity of peri-implant keratinized mucosa as a prerequisite for long-term soft-tissue health and stability over a period of 5 years.