Soft tissue attachment to titanium implants coated with growth factors.

Abstract

The process of osseointegration described by Brånemark (Brånemark et al 1969, 1977) and Schroeder (Schroeder et al 1981) plays an integral role in dental rehabilitation. Since the first observation 40 years ago, osseointegrated titanium implants have been used predictably in the dental rehabilitation of fully edentulous patients. The application of dental implants has evolved, and from the 1980s dental implants have been used increasingly in the treatment of partially edentulous patients, with equal or better long-term success (Buser et al 1990, 1997, Lekholm et al 1994, Behneke et al 2000, Bornstein et al 2005). The surgical procedures for the placement of endosseous dental implants are based on the original work by Brånemark and colleagues approximately 40 years ago. The two-stage surgical procedure was originally advocated to obtain an optimal process of new bone formation and remodelling after implant placement (Brånemark et al 1977). Osseointegration and good long-term success was also found to be achievable with non-submerged implants (Buser et al 1990, 1992, 1997, Ericsson et al 1997) with the added advantage of avoiding a second surgical procedure (Buser et al 1999). Implant dentistry has evolved over the last 15 years and has benefited from significant progress made in associated treatment protocols and the development of bone augmentation procedures (guided bone regeneration (GBR) and sinus floor elevation) allowing for correction of alveolar bone deficiencies. Additionally, improved osteophilic microtextured implant surfaces have been developed to accelerate healing, significantly reducing treatment time. Research and clinical focus in dental implantology in the last two decades has primarily concentrated on the bone-to-implant interface of osseointegrated implants. The soft tissue profile and seal around implants have been investigated to a much lesser degree. This interest has been largely due to the fact that a successfully osseointegrated implant depends on anchorage in bone and requires a direct bone-to-implant interface to provide long-term support for a prosthesis. Both bone and soft tissue integration onto dental implants are wound healing processes whereby several stages of tissue formation and degradation are involved (Berglundh et al 2003, Abrahamsson et al 2004). Osseointegration is the result of the modelling and remodelling of bone tissue that occurs after implant placement whilst the wound healing that occurs following the closure of mucoperiosteal flaps during implant surgery results in the establishment of a mucosal attachment (transmucosal attachment) to the implant. The establishment of the mucosal barrier around the implant is characterised by the gradual shift from a coagulum to granulation tissue followed by the formation of a barrier epithelium and the maturation of the connective tissue (Berglundh et al 2007). Like natural teeth, osseointegrated implants are transmucosal “masticatory devices” that penetrate the oral mucosa with the periodontal and peri-implant tissues expected to perform a protective function (Weber & Cochran 1998). Background: Peri-implant tissues form a crucial but fragile seal between the oral environment, the bone and the implant surface. Enhancing the seal formed by the peri-implant soft tissues at the titanium/connective tissue interface may be an important factor in implant survival. Additionally, enhancing soft tissue adherence to the implant surface when implants are placed in dehiscence type defects may mean that simultaneous osseous grafting procedures will not always be required. Objective: The aim of this study was to investigate the effect of implant surface modification with either platelet-derived growth factor (PDGF) or enamel matrix derivative (EMD) on the connective tissue attachment to moderately roughened titanium implants. Material and Methods: 18 moderately roughened titanium implants were subcutaneously implanted into 14 rats. 6 implants each were coated with PDGF and EMD immediately prior to implantation and 6 implants were left uncoated. The implants were retrieved with a sample of surrounding tissue at 4 and 8 weeks. The specimens were resin-embedded and sections viewed under confocal microscopy for collagen autofluorescence and prepared for qualitative and histomorphometric analysis under light microscopy. ANOVA and t-tests were used to compare the thickness of fibroblast encapsulation on the implant surface and the depth of connective tissue penetration onto the implant grooves. Results: Qualitative analysis under confocal and light microscopy showed encapsulation of all implants by fibroblasts and good soft tissue integration at the end of 4 and 8 weeks. Coating of the implants with growth factors did not alter the orientation of fibroblasts and collagen fibres. Histomorphometric analysis demonstrated that the depth of connective tissue penetration into the implant grooves was significantly greater for the implants coated with PDGF at 4 weeks (ANOVA, P value 0.0014). The thickness of the fibroblast encapsulation on the implant surface was significantly less for the implants coated with PDGF at 8 weeks (ANOVA, P value 0.0012). Conclusion: Good soft tissue integration can be achieved on a moderately roughened titanium implant surface. Coating the implant surface with rhPDGF-BB could increase the speed of soft tissue healing around an implant surface but this increased rate of healing with rhPDGF-BB coating could also result in a less robust titanium/connective tissue interface.