Despite the successful clinical results, conventional therapeutic procedures present significant variability depending on the intrinsic healing potential of the patient, which are typically observed as long junctional epithelium and limited regeneration of the periodontal attachment apparatus due to minimal cementogenesis and limited bone formation (Listgarten and Rosenberg 1979; Steiner et al. 1981; Waerhaug 1978). Ideally, the healing process should reestablish the original tissue architecture and function of the support tissues previously destroyed, including the regeneration of alveolar bone, radicular cementum, and periodontal ligament (Caton and Greenstein 1993; Listgarten and Rosenberg 1979; Mellonig 1999). Therefore, several procedures have been employed to optimize the regenerative potential of periodontal lesions, including bone grafts and substitutes, barrier membranes for guided tissue regeneration, bioactive substances such as growth factors and enamel matrix derivatives and combination of these techniques and materials (Pretzl et al. 2009; Sanz et al. 2004, Siciliano et al. 2011; Thakare and Deo 2012; Yukna et al. 2002).

In conjunction with, and irrespective of, the selection of an adequate regenerative approach, the use of a sound treatment protocol and surgical technique is mandatory to optimize the clinical results including the flap design, treatment of the root surface, treatment of the bone defect, maintenance and control and timing of reevaluation.

Flap Design

Adequate flap design is an important element in periodontal regenerative therapy in order to provide adequate access for root instrumentation, bone defect debridement, placement of regenerative materials in the periodontal defect, and attaining primary coverage of the surgical site. Several types of flaps have been used, including the modified Widman flap (Cortellini et al. 1995; de Miranda et al 2013; Santana et al 1999), the papilla preservation flap (Takei et al. 1989), modified papilla preservation flap (Cortellini et al. 1995; Santana and de Santana 2015), simplified papilla preservation flap (Cortellini et al 1999), interproximal tissue maintenance (Murphy 1996), and single flap approaches (Trombelli et al. 2012). Traditionally, conventional flap designs such as the modified Widman flap were employed for the treatment of intrabony (Cortellini et al. 1999) and furcation defects (de Miranda et al. 2013; Santana and Van Dyke 1999); however, conventional surgical approaches performed with vertical releasing incisions and without interdental papilla preservation may result in deficient flap closure, limited blood clot stability and, possibly, negatively impacting periodontal wound healing. Thus, the necessity to obtain and maintain adequate levels of soft tissue coverage post-surgery led to the increased test and development of alternative approaches.

The coronally positioned flap was proposed as a method to obtain coverage of regenerative materials and primary closure of the surgical site; however, limited additional benefit in probing depth reduction and attachment level gain was provided after the use of this flap design in the treatment of human furcation defects, in comparison with the modified Widman flap, except for significantly reduced postsurgical gingival recession (Santana and Van Dyke 1999). However, positive outcomes were reported for this procedure when used in conjunction with guided tissue regeneration and bone substitutes (Santana and Van Dyke 1999, Santana et al. 2009).

In order to optimize the healing potential of human intrabony defects, several technical modifications were proposed in order to favor the maintenance of the interproximal soft tissue coverage flap closure (Cortellini et al. 1995; 1999; Murphy 1996; Takei et al. 1989; Trombelli et al. 2012). The preservation of the interproximal soft tissues may result in higher blood clot stability within the periodontal defect and faster vascular stability in the papillary area (Retzepi et al. 2007), promoting primary wound healing, improved wound instability and, ultimately, enhanced clinical results in the treatment of human intrabony defects (Cortellini and Tonetti 2007a, 2007b; Cortellini et al. 2008; Retzepi et al. 2007). Increased reduction in probing depth and attachment levels with minimal gingival recession and less postoperative discomfort has been reported (Graziani et al. 2012).

Bone Grafts and Bone Substitutes

Bone grafts and bone substitutes are biocompatible particulate biomaterials that are placed directly into periodontal bone defects to serve as scaffolds for cell attachment, migration, and differentiation.

Several bone grafts/substitutes have been used in the regenerative treatment of periodontal defects, including autografts, allografts, xenografts, and alloplastic materials (Sculean et al. 2015). For many years, bone autografts were considered the gold standard for bone regeneration due to its potential osteogenic, osteoconductive, and osteoinductive potentials. Clinical evidence, however, did not demonstrate significantly enhanced clinical results in comparison to periodontal open flap debridement procedures without the use of bone grafting (Froum et al. 1976; Renvert et al. 1985). Histological evidence in humans is controversial, with some studies demonstrating periodontal regeneration (Dragoo & Sullivan 1973a, 1973b; Hiatt et al. 1978; Stahl et al. 1983), while others demonstrated the formation of a long junctional epithelium (Listgarten and Rosenberg 1979), particularly for bone grafts harvested from intraoral sources. Moreover, complications such as ankylosis and root resorption were also reported, particularly following the use of bone allografts from extra-oral sites, such as medullary bone from the iliac crest (Dragoo and Sullivan 1973a, 1973b). Taken together, the current evidence may limit the indication of bone autografts for the treatment of periodontal bone defects.

Bone allografts may contain bone morphogenetic proteins, providing these materials with osteoinductive activities (Miron et al. 2016; Schwartz et al. 1996, 1998). However, the osteoinductive activity of bone allografts such as DFDBA varies significantly depending on the manufacturer or the gender of the donor (Schwartz et al. 1996, 1998). Thus, adequate donor selection and manufacturing processes that preserve the bioactivity of the material appear to be critical for the production and clinical use of these materials (Schwartz et al. 1996, 1998). In conjunction with adequate clinical (Barnett et al. 1989; Flemmig et al. 1998; Meadows et al. 1993; Rummelhart et al. 1989) and histologic results (Bowers et al. 1989a, 1989b), robust histologic evidence of periodontal regeneration in humans were reported (Bowers et al. 1989a, 1989b) following the use of these materials.

Several xenogeneic materials, derived from bovine, swine, or equine sources, have also been employed, and act as an inert bone scaffold of tridimensional structure like the mineralized bone matrix. It has been hypothesized that these materials could present the risk of antigenicity, being derived from other species (Oliveira et al. 2008) and, despite controversial, the risk for prion infection has also being considered (Kim et al. 2013, 2016). Adequate clinical (Figures 8.10 to 8.17) results were reported for these materials in the treatment of periodontal defects (Camargo et al. 2000; Cosyn et al. 2012; De Bruyckere et al. 2018; Pietruska 2001; Richardson et al 1999; Scheyer et al. 2002; Sculean et al. 2002b).

Systematic analysis of histologic preclinical essays, in which regenerative therapies were used for the treatment of periodontal defects (Ivanovic et al. 2014), demonstrated that most of the biomaterials, used alone or combined, promoted more extensive periodontal regeneration than conventional open flap procedures without the use of biomaterials (Ivanovic et al. 2014). Systematic reviews also concluded that the use of bone grafts/substitutes resulted in significant enhancement in attachment levels, probing depth reduction, increased bone fill, and reduced crestal resorption in comparison with open flap debridement (Reynolds 2003). However, attachment level gains varied significantly among the several individual biomaterials (Trombelli 2002). Similar clinical results were obtained for allografts and alloplastic materials (Barnett et al. 1989; Bowen et al. 1989; Oreamuno et al. 1990). The combined use of bone grafts and membranes can result in increased gains of attachment, bigger probing depth reduction and more defect filling than membranes used alone (Murphy and Gunsolley 2003; Needleman et al. 2006). It has been reported that the use of alloplastic materials may reduce postsurgical gingival recession (Leknes et al. 2009), possibly by avoiding the collapse of the soft tissues into the bone defects. Histologically, DFDBA, autografts, and some xenografts result in the formation of new attachment and periodontal regeneration (Sculean et al. 2003a; Sculean et al. 2003b; Sculean et al. 2005b; Sculean et al. 2015), while the results for alloplastic materials are more limited, specially, when employed in monotherapy (Sculean et al. 2015). However, some alloplastic materials can result in periodontal regeneration when employed in conjunction with enamel matrix derivatives (Sculean et al. 2008c).

Guided Tissue Regeneration

Guided tissue regeneration is a treatment concept based on the use of membranes or barriers interposed between the surgical flap and the periodontal defect to mechanically exclude non-regenerative cells from the gingival epithelium and connective tissue from the regenerative events at the defect area (Figures 8.1 to 8.9). The modern biological concepts of guided tissue regeneration (GTR) is based in the establishment of a protected environment for the blood clot and competent regenerative cells via the interposition of a physical barrier between the soft tissues of the gingival flap and the osseous defect/root surfaces in order to isolate a secluded space, thus, allowing cells from the periodontal ligament and bone to recolonize the defect area and regenerate the periodontal attachment apparatus (Caffesse et al. 1988; 1990; Gottlow et al. 1986; Magnusson et al. 1988; Nyman et al. 1982; Pitaru et al. 1987; Pfeifer et al. 1989). These concepts have been used clinically for the treatment of several periodontal and bone deformities such as periodontal intrabony (Cortellini and Tonetti 2000), furcation (Santana and Van Dyke 1999; Santana et al. 2009) (Figures 8.6 to 8.10), and recession defects (Trombelli and Calura G 1993); closure of oro-antral communications (Waldrop and Semba 1993); surgical treatment of periodontal defects associated with palato-gingival developmental grooves (Rankow and Kassner 1996); reconstruction of bone defects following surgical removal of oral cysts or tumors (Vitkus and Meltzer 1996); autogenous tooth transplantation (Hurzeler and Quinones 1993); surgical treatment of advanced apical or combined apical-marginal lesions associated with absence of buccal alveolar bone wall (Rankow and Kassner 1996, Santana and Santana 2013) (Figures 8.1 to 8.5); maintenance or enhancement of the osseous ridge, following root amputation of multi-rooted teeth (Conner 1996); and prevention or treatment of distal osseous defects following the removal of impacted third molars (Oxford et al. 1997).

Several materials have been tested as barrier membranes for GTR. These materials exhibit differences in chemical composition, physical properties, and macroscopic and microscopic structure. Criteria for the design of GTR membranes have been proposed (Scanttlebury 1993), and include tissue integration capacity, cell occlusivity properties, clinical manageability, space making ability, and biocompatibility. The biological response to implanted biomaterials is a critical element in reconstructive biology. Significant differences have been described for the response of living tissues to implanted barrier membranes, possibly related to the surface topography and porosity of the device (Buchmann et al. 2001; Lu et al. 2004; Lundgren et al. 1995; Scanttlebury et al 1993; Santana et al. 2010; Wikesjo et al. 2003).

Nonabsorbable Devices

Polytetrafluorethilene (PTFE) is an inert and biocompatible material. Due to a unique molecular composition and configuration PTFE presents with low chemical reactivity, great stability, and low superficial energy of the polymer. There is no solvent that can dissolve PTFE in temperatures lower than 3,000°C. PTFE can be utilized as barrier devices in porous, dense, and expanded forms (Crump et al. 1996; Scattlebury 1993). Other materials tested as nonabsorbable barriers include microfibrillar alkali-cellulose, aluminum, and titanium. Microfibrillar alkali-cellulose is a safe and biocompatible material, primarily used as a skin substitute for burned people (Novaes Jr. et al 1990a, 1990b, 1992). A core of commercially-pure aluminum (minimum 99.35% of Al), superficially coated with aluminum oxide (minimum of 99.48% of Al₂O₃), in a laminated form, Al₂O₃ is a ceramic material which has biocompatibility characteristics similar to titanium and tantalus oxides (TiO₂, Ta₂O₅) that has been used as constituents of endosseous dental implants, both in single-crystal and polycrystalline forms (Babbush et al. 1987; Kawahara and Hirabayashi 1980). Biocompatibility of this material appears to be derived from its high dielectric constant, biomolecule adsorption capacity, chemical inertness to corrosion, low dielectric potential difference, and catalyst activity (Kawahara and Hirabayashi 1980; Yamagami et al. 1988). Among the several alternatives for nonabsorbable devices, PTFE is the most studied and well characterized.

Synthetic Absorbable Devices

Several synthetic materials have been tested as resorbable GTR membranes. Calcium sulfate is one of the materials that have been tested as a barrier for GTR applications (Conner 1996; Sottosanti 1992, 1993, 1995). Although reintroduced in the 90s, similar materials have been used for more than 100 years in medicine and dentistry as adjuncts for bone regeneration (Peltier 1959; Shaffer and App 1971). At present, it is composed of absorbable medical grade calcium sulfate monohydrate (CaSO₄), plaster of Paris, mixed with a premeasured accelerator solution. It is used as a barrier over autogenous or allogenous bone grafts, in order to maintain the graft in place. Spagnuolo and Bissada (1995) proposed a new resorbable composite barrier for the treatment of adult periodontitis membrane composed of calcium sulfate monohydrate (CaSO₄) combined to DFDBA and doxycycline in a 4:1:1 ratio by volume.

Polyglactin 910 is a lactide-glicolide copolymer which has been long used as a resorbable suture material (Conn et al. 1974). Such material seemed to be inert, non-antigenic, and non-pyogenic, presenting only a mild tissue reaction during absorption (Conn et al. 1974). It has been manufactured as a mesh for use in neurosurgery (Maurer and McDonald 1985) and is composed of undyed fiber, identical in composition to that of the absorbable sutures. This mesh has also been tested for GTR procedures (Cristgau et al. 1998; Eikholtz and Hausman 1998; Fleisher et al 1988).

A synthetic, liquid polymer of lactic acid, poly(DL-lactide), dissolved in N-methyl-2-pyrrolidone(NMP), has been developed for GTR purposes (Polson et al. 1994, 1995).This material exists as a fluid which transforms to a solid on contact with water or other aqueous solutions. This property is used to form an adaptable partially set barrier extraorally, which is rigid enough to provide GTR function but flexible enough to be easily adapted to the surgical site. The barrier continues to solidify in situ and subsequently bioabsorbs via hydrolysis (Garrett et al 1997). It has a similar composition, rate of absorption, and safety performance as that of Polyglactin 910. It has been shown to be safe, nontoxic, resorbable, and efficacious for GTR attempts in animals and humans (Garrett et al. 1997; Polson et al. 1994, 1995).

Various other polylactic acid-based products have been evaluated for their potential use in GTR surgeries, such as (a) polylactic acid dissolved in chloroform (Magnusson et al. 1988), (b) polylactic acid blended to a citric acid ester (Gottlow 1993), and (c) a polylactic acid porous sheet (Vernino et al. 1995). Such materials are absorbed by hydrolysis and seem to break down with minimal inflammatory reaction (Vernino et al. 1995), which seems to be consistent with a material that was biologically acceptable in the wound healing environment (Vernino et al. 1995). A hydrophilic, biodegradable membrane fabricated from D,L-polylactic acid was introduced (Vernino et al. 1998, 1999). The thickness of this membrane measures from 175 to 250 μm, and the polymer of the membrane is organized in an architecture of randomly sized, randomly positioned, intercommunicating interstices ranging in size from 10 to 15 μm. One surface of the membrane, constituting approximately 10% of the total thickness, is considerably denser than the remainder of the device (Vernino et al. 1998). Another of these polylactic acid-based products is a bioabsorbable material consisting of polylactic acid comprising L-and D-lactic acid enantiomers, and acetyl-tributyl citrate, a citric acid ester. It has a multilayered matrix designed for ingrowth of gingival connective tissue. Periodontal ligament and alveolar bone can also migrate into the matrix and merge with the gingiva. Thus, the matrix barrier would allow for simultaneous regeneration and integration following a single surgical procedure (Gottlow 1993). Clinical results were reported for the treatment of human gingival recession, furcation, and intraosseous lesions with this material (Cristgau et al. 1998; Luepke et al. 1997; Pini Prato et al. 1995).

Organic Absorbable Devices

Among the products of organic or natural sources, collagen-based devices of different types and origins are probably the most commonly used as barrier membranes due to its weak immunogenic capacity and long-term experimental use in animals and humans (Pitaru et al. 1988). Several characteristics of collagen seem to support its use as barrier membranes for GTR purposes (Pitaru et al. 1988). Collagen is the major extracellular macromolecule of the periodontal connective tissues (Posthlethwaite et al 1978) that can act as a barrier for migrating gingival epithelial cells (Pitaru et al. 1987) by providing a thrombogenic surface (Blumenthal 1993) that inhibits the mitotic function of the basal epithelial cells during the initial phases of wound healing (Numabe et al. 1993), thus limiting the apical migration of epithelium. Simultaneously, the hemostatic properties of collagen (Pitaru et al. 1988) may enhance blood clot stability in the bony defect, while exhibiting a chemotactic activity for fibroblasts (Posthlewaite et al. 1978). Despite the past controversies regarding the safety of using collagenous membranes in human clinical trials, due to localized hypersensitivity reactions developed in sites where collagen was injected (Kammer and Chukurian 1984), collagenous membranes did not elicit any abnormal immunologic responses when implanted as a barrier membrane during GTR attempts in humans (Black et al. 1994; Blumenthal 1993; Mattson et al. 1995; Numabe et al. 1993).

Autogenous “periosteum” grafts were proposed by Lekovic et al. (1991) as an alternative for GTR barriers. In this technique, a partial thickness connective tissue graft is obtained from the palate of the patient, then trimmed and adjusted as a barrier to cover the periodontal defect to be treated according to the principles of GTR. In controlled studies, this technique demonstrated significantly better results than the controls treated by a modified Widman flap procedure (Lekovic et al. 1991), and similar results to those obtained by ePTFE barriers (Bouchard et al. 1993) in the treatment of human mandibular furcation lesions. However, the necessity of a second surgical site to obtain the graft, the limited and great variability of the results obtained with this technique diminished its applicability in routine regenerative periodontal therapy.

Particulate decalcified freeze-dried bone allografts (DFDBA) have been used for many years as a periodontal grafting material (Gouldin et al. 1996; Mellado et al. 1995; Mellonig 1984; Pearson et al. 1981; Quintero et al. 1982; Wallace et al. 1994) due to the safety, biocompatibility, and very weak immunogenic properties of these materials (Friedlaeder et al 1984; Quattlebaum et al. 1988; Turner and Mellonig 1981). Moreover, possible osteoinductive capacity, due to the presence of bone morphogenetic proteins (BMPs), may be retained in the material following its processing (Urist 1965; Urist and Dowell 1968; Urist et al. 1967), promoting bone inductive abilities in vivo (Mellonig et al. 1981a, 1982, 1981b, 1983). Despite the demonstration of biological activity of DFDBA (Shigeyama et al. 1995), such activity could be variable, depending on the source of the product, donor characteristics, and the processing of the material (Schwartz et al. 1996). Thus, the effectiveness of particulate DFDBA on periodontal regeneration has been questioned (Becker et al. 1994, 1995). Laminar sheets of DFDBA are available and have been successfully employed as barriers for GTR (Rankow and Kassner 1996; Scott et al. 1997; Yamaoka et al. 1996). Positive results were reported in the treatment of human furcation defects (Scott et al. 1997; Yamaoka et al. 1996).

Bioabsorbable composite matrixes were also tested as a barrier for clinical use in GTR applications (Costa-Noble et al 1996). The basic components of this material are elastin and fibrin monomers that are combined under specific physicochemical conditions. The crude product obtained is then further processed with fibronectin, type I collagen, and other aggregating agents as sulfur derivatives and gamma-rays to obtain optimum cohesivity. The derived material is also associated with polyglactic networks to obtain good saturability and treated with aprotinin to control the degradation rate.

Histologic preclinical studies demonstrated that barrier membranes used alone or combined with bone grafts/substitutes result in bone (Santana et al. 2010) and periodontal regeneration (Sculean et al. 2008c). Enhanced results were observed for the combined therapies employing membranes and bone grafts/substitutes in comparison to the use of membranes alone in noncontained two-wall defects and supra-alveolar defects, while no additional benefit was observed for the combined therapy for three-wall defects (Sculean et al. 2008c). Results from histological studies in humans are partially divergent than these results obtained in animals.

The results of clinical studies and systematic reviews demonstrated that regenerative therapies with barrier membranes provide significant clinical benefits, in comparison with open flap procedures alone, as evaluated by reduced gingival recession, probing depth reduction, attachment level gain, and bone fill (Cortellini and Tonetti 2000; Murphy and Gunsolley 2003; Needleman et al. 2005). Clinical results may be maintained for several years in most patients enrolled in frequent periodontal supportive therapy, even with severe intrabony defects (Cortellini et al 2004). Positive outcomes have also been reported for the combined use of membranes and synthetic graft materials in the treatment of human furcation defects (Santana and Van Dyke 1999; Santana et al. 2009). No significant difference was reported for the several types of membranes evaluated; however, the use of different types of membranes may explain the significant variability of clinical results reported in different studies (Murphy and Gunsolley 2003; Needleman 2006).

Bioactive Substances

The use of bioactive substances offers a new paradigm in periodontal reconstructive therapy as a resource to amplify or accelerate the endogenous healing potential with new therapies that act at the cellular and molecular levels to enhance the periodontal wound healing and regeneration of the attachment apparatus.