Implant surface properties are considered key when it comes to advanced osseointegration – in particular when healing times are reduced or implants are placed under demanding bone conditions.
In the most recent edition of this newsletter, the authors described how TiUnite interacts with blood cells and tissues during early wound healing, and how osteoconductive bone formation is supported. Building on that foundation, they discuss new findings, which further explain how additional surface parameters, such as texture and design, may positively influence fast bone formation and osseointegration.
Just prior to the turn of the century, implants with a moderately rough surface were introduced by Nobel Biocare to enhance osseointegration. Over the ensuing years, an enormous number of in vitro studies have been performed to report upon and evaluate such variable conditions as surface energy; surface texture modification (down to the nano level); increased wettability; and surface chemical modifications.
Despite the great cumulative volume of these in vitro reports, pivotal questions about the biological rationale behind the faster bone formation, higher bone-to-implant contact, and greater removal torque values of these implants—when compared to smooth surface implants— remain to be definitively resolved.
Latest research reveals that in vivo reality may be substantially different from the in vitro situation. During the installation of a TiUnite implant, the moderately rough surface texture acts like a micro-grained sandpaper: It scratches along the walls of the cortical and trabecular bone of the osteotomy and emerizes the bone surface.
Interesting smear layer
This results in a several-micronsthick smear layer composed of bone debris and blood, covering the implant surface.
This smear layer provides osteoinductive potential due to the presence of growth factors needed for bone formation (Tabassum et al, 2011).
Consequently—because the bone smear layer masks them—such properties of modified surfaces as increased wettability, high surface energy and chemical alteration may not decisively influence either the initial wound healing or subsequent bone formation.
Decisive differences exist
Moreover, not all so-called “rough” implant surfaces are the same regarding their potential for establishing such a bone smear layer. In particular, implant design, surface texture—as well as the preparation protocol for the osteotomy—will influence the presence and amount of bone smear.
Following implant insertion, only the outer tips of the threads are often in direct contact with the adjacent bone: and implants placed in extraction sockets may not generate a bone smear layer at all in coronal areas where the osteotomy is wider than the diameter of the implant.
In the absence of a bone smear layer, TiUnite shows its full-strength versatility by speeding up the osseous healing process. Due to the presence of free phosphate groups at the surface (Schüpbach et al, 2005), TiUnite has a negative surface charge, attracting and activating thrombocytes immediately.
Subsequently, thrombocytes release enzymes and growth factors, thereby attracting osteogenic cells. TiUnite is highly osteoconductive and new bone formation occurs rapidly and directly on and along the implant surface.
Therefore, it’s not surprising that several animal and human studies have demonstrated enhanced osseointegration— both in terms of speed and amount of bone-to-implant contact on par with that of hydroxyapatite surfaces—which many still consider the gold standard for osteoconductivity.
The role of bone fragments
In the pursuit of fast and reliable osseointegration, another factor must be considered. When drilling—and even more pronounced when using self-cutting implants—bone fragments will be generated and accumulate in the osteotomy, especially in the apical region. In this area, they serve as nuclei for bone formation by guiding osteogenic cells through the wound and towards the TiUnite surface.
This effect is similar to that of a graft material—but here on an osteoinductive level. In conjunction with the osteoconductive TiUnite surface, this auspicious phenomenon serves as a powerful tool for speeding up osseointegration.
In particular, implants with a pronounced self-cutting design, such as NobelActive, demonstrate this effect most clearly. The worm-gearlike action of NobelActive during installation shovels bone fragments to its apical region, favoring accelerated osseointegration.
TiUnite and osseointegration
Taken together, these new observations not only complement earlier scientific findings but also help to elucidate the biological rationale that makes osseointegration possible. In particular, they explain why osseointegration with TiUnite implants is so highly predictable.
TiUnite fully meets current criteria from the surface technology research point-of-view and—at the time this is being written—has also demonstrated an impressive 12-year clinical performance track record, which is unmatched in the entire field of implant dentistry.
From a clinical perspective, TiUnite has enabled the predictable application of very short implants and implants placed in very demanding bone conditions. Moreover, TiUnite has both reduced the healing time necessary before functional implant loading can take place and lifted immediate function solutions to a very high and very reliable level of success (Glauser 2011).
The clinical behavior of an implant design or implant surface as documented by in vivo observations is of much greater value than in vitro experiments and animal studies.
Immediate biological effects of any surface modification may be neutralized due to the presence of an osteogenic/inductive bone smear layer created during the installation of moderately rough implants. In situations such as these, the theoretical benefit of such modifications will be masked, thus providing a rich field for further research.
NobelActive implant insertion. During the insertion procedure, the bone-condensing, self-cutting implant body and the TiUnite surface interact with the local bone by generating macro- and microscopic bone fragments along the implant body. As a result, the implant surface (once located in its final position in the bone defect) is covered with a bone smear layer and bone fragments. TIME (t)
Finally: The generation of bone fragments during both the drilling and installation of implants has an important clinical implication. Consequently, rinsing the osteotomy following drilling may be counter-productive and should be avoided.
More to explore:
Glauser, R. (epub ahead 2011). “Implants with an Oxidized Surface Placed Predominately in Soft Bone Quality and Subjected to Immediate Occlusal Loading: Results from a 7-Year Clinical Follow-Up.” Clin Implant Dent Relat Res. (An 11-year follow-up poster is being presented at the EAO this fall.)
To learn more about the TiUnite implant surface, please click here.
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