Immediate loading of root-form dental implants has shown promising results and offers treatment cost and convenience advantages to patients. Although blade implants have been immediately loaded for over 2 decades, the ability of this implant design to achieve osseointegration has been debated. The aim of the present study was to histologically evaluate the peri-implant tissues of an immediately loaded blade implant retrieved for abutment fracture after a 20-year loading period. Histologic samples were prepared and examined by light microscope. Compact, cortical, mature bone with well-formed osteons was present at the interface of the implant. Bone-to-implant contact was 51% ± 6%. The histologic data showed that osseointegration was obtained in an immediately loaded blade implant inserted into the mandible, and that mineralized tissues were maintained at the interface over a long period (20 years).
Dental implants have been traditionally manufactured in 3 basic designs: cylinders, screws, and blades. Of these, blade implants generally feature a transgingival design for 1-stage surgical procedures.1 One-stage implants immediately loaded after surgical insertion are often found to be surrounded by collagen-rich connective tissue without any bone contact2; however, bone has been shown to be present around stable root-form implants.1,3 The high success rate of osseointegration with root-form dental implants is generally attributed to the absence of premature stresses on the tissue-implant interface during the early healing period, when the implant is completely submerged and unloaded; it is also believed that a premature loading of an implant leads to interfacial formation of fibrous tissue instead of bone.4–7 Although the presence of mineralized tissues at the interface with blade implants has been reported,4,8–13 the view that blade implants cannot osseointegrate still persists. Histologic evidence of osseointegration in clinically successfully osseointegrated implants can be found only rarely in the literature.14–26
The aim of the present study was to histologically evaluate the peri-implant tissues of an immediately loaded blade implant that was removed for abutment fracture after a loading period of 20 years.
A 58-year-old male nonsmoking patient presented with a blade implant that sustained an abutment fracture 20 years after placement (Figures 1 through 3). This implant had been immediately loaded and had been in use with no clinical problems before the fracture. The implant was stable, showing no peri-implant radiolucencies or crestal bone resorption. The peri-implant soft tissues appeared to be healthy, and no pain was present upon percussion. The blade was retrieved with a bur. Upon removal, mineralized tissue appeared to be attached to the implant surface. Subsequently, 2 root-form implants were inserted and a new bridge was installed.
The processing of specimens was as follows. The implant and the surrounding tissues were stored immediately in 10% buffered formalin and processed to obtain thin ground sections with the Precise 1 Automated System (Assing, Rome, Italy).27 The specimen was dehydrated in an ascending series of alcohol rinses and embedded in a glycolmethacrylate resin (Technovit 7200 VLC, Kulzer, Wehrheim, Germany). After polymerization the specimen was sectioned longitudinally along the major axis of the implant with a high-precision diamond disc at about 150 μm and ground down to about 30 μm. Three slides were obtained. The slides were stained with basic fuchsin and toluidine blue. A double staining with von Kossa and acid fuchsin was performed to evaluate the degree of bone mineralization, and 1 slide, after polishing, was immersed in silver nitrate for 30 minutes and exposed to sunlight. The slides were then washed under tap water, dried, and immersed in basic fuchsin for 5 minutes. They were then washed and mounted.
The histomorphometry of bone-to-implant contact percentage was carried out with a light microscope (Laborlux S, Leitz, Wetzlar, Germany) connected to a high-resolution video camera (3CCD, JVC KY-F55B) and interfaced to a monitor and PC (Intel Pentium III 1200 MMX, Santa Clara, Calif). This optical system was associated with a digitizing pad (Matrix Vision GmbH, Oppenweiler, Germany) and a histometry software package with image-capturing capabilities (Image-Pro Plus 4.5, Media Cybernetics Inc, Silver Springs, Md; Immagini & Computer Snc, Milano, Italy).
Compact, mature bone with well-formed osteons was present at the implant interface (Figure 4). Each osteon was constituted by a Haversian system and 10 to 20 bone lamellae (Figures 5 and 6). Many of these osteons were in contact with the implant surface. Most Haversian systems ran perpendicular to the major axis of the blade (Figures 7 and 8). Near the implant, the bone lamellae tended to run parallel to the implant surface (Figure 9). In some fields, bone modeling units were present, and it was possible to observe osteoblasts, osteoclasts, osteoid matrix, and newly formed bone. These bone modeling units constituted about 3% to 4% of all the peri-implant bone area. The newly formed bone was easily differentiated from the preexisting bone because of its higher staining affinity. A cement line was present at the interface between preexisting and newly formed bone. Bone-to-implant contact was 51% ± 6%. Bone constituted about 55% ± 5% of all the evaluated peri-implant area; the rest was constituted by marrow spaces (about 40% ± 5%). Osteocyte lacunae were in close contact with the metal surface. No gaps or fibrous tissue were present at the interface. Some of the marrow spaces abutted on the implant surface. In a few fields, some capillaries were located very near the implant surface. No inflammatory infiltrate or epithelial downgrowth was present.
Immediately loaded dental implants have shown good clinical results28–32 and offer advantages such as cost of treatment, convenience to patients, and avoidance of functional and psychological problems. Histologic examination provides the best evidence of the type of tissue at the interface with dental implants. This study affirms other reports in the dental literature9,33 that blade implants can present a direct bone contact even if they are loaded immediately after insertion; however, they have been reported very often to be surrounded by collagen-rich connective tissue without any bone contact.34–39 The most important factor is primary stability of the implant during the healing phase. The precise fit of the implant in the bone socket, which is related to the implant design, is relevant. Implant failure can result from insufficient primary stability or by an inadequately stabilized early loading of the implant.2
Primary stability of root-form implants can be achieved biomechanically by creating an osteotomy that has a diameter less than the diameter of the implant.2 If the implant is mobile, healing will lead to an encapsulation by a soft tissue layer40,41 and the bone cell differentiation process will be disturbed.42 A high amount of phagocytic or macrophage activity can also be created, which will prevent normal bone remodeling and stimulate the formation of granulation tissue.41 Moreover, the formation of connective tissue around the implants can be caused by an early loading of an adequately stabilized implant in a way similar to a bone fracture where an incomplete immobilization of the fracture fragments produces a pseudoarthrosis.2
Another important factor for the long-term success rate of the dental implants is the way to decrease the impact of deleterious micromotion at the interface.43 The threshold of critical micromotion appears to be between 50 and 150 μm.43 An effective way to reduce micromovements could be splinting of the implant, in addition to using an implant with a retentive shape (ie, screw shaped). In a rigidly fixed implant system, no significant distortional strains will be produced at the interface, and in such a way no fibrous tissue formation will be stimulated.44 Immediately loaded implants that are adequately stabilized have a clinical long-term predictability equivalent to 2-stage implants.45 Immediate loading markedly shortens the total rehabilitation time, and patient satisfaction increases because there is no need to wear a conventional denture during the healing period.46–48
The present histologic results show that osseointegration can be obtained in an immediately loaded blade implant and that this osseointegration could be successfully maintained over a long period (20 years). In addition, the peri-implant bone formation did not appear to be disturbed by the stresses and strains at the interface, and mineralized tissues were maintained at the bone-implant interface. Proussaefs and Lozada49 reported that blade implants retrieved after 13 and 21 years of function exhibited mature bone in tight contact with the implant and that it was present around most of the implant surface. In the present case, implant splinting may have helped decrease the amount of micromotion during the healing phase and contribute to the long-term success. This was probably obtained by the intimacy of initial fit and the percentage of implant surface in direct contact with bone. These histologic results could be explained by the fact that functional loading appears to stimulate bone apposition.50–53 More reports on long-term results of immediately loaded implants will certainly help our understanding of the corresponding bone response.54,55
This work was partially supported by the National Research Council (Rome, Italy); by the Ministry of Education, University, and Research (Rome, Italy); and by the Research Association for Dentistry and Dermatology (Chieti, Italy).
Danilo Di Stefano, MD, DDS, is in private practice in Milano, Italy.
Giovanna Iezzi, DDS, PhD, is a research fellow, Antonio Scarano, DDS, MD, is a researcher, and Vittoria Perrotti, DDS, PhD, is a student in the Dental School, University of Chieti-Pescara, Chieti, Italy.
Adriano Piattelli, MD, DDS, is a professor of Oral Pathology and Medicine in the Dental School, University of Chieti-Pescara. Address correspondence to Prof Adriano Piattelli, Via F. Schiucchi 63, 66100 Chieti, Italy (firstname.lastname@example.org).