Biological aging of implant surfaces and their restoration with ultraviolet light treatment: a novel understanding of osseointegration.

The topographic and physicochemical features of implant surfaces influence the process of osseointegration. The biologic properties of implant surfaces have been considered to remain stable over time, ie, the capability of osseointegration of implant surfaces presumably does not change over time after manufacturing. However, recent reports have demonstrated that titanium surfaces undergo a progressive change in their biologic characteristics over time, resulting in a significant decrease in osseointegration capability. In comparison to newly prepared titanium surfaces, 4-week-old titanium surfaces (ie, stored for 4 weeks after processing) required more than twice as much healing time to achieve a similar strength of osseointegration. The boneimplant contact percentage for the 4-week-old surfaces was less than 60%, as opposed to more than 90% for the new surfaces. In vitro, the 4-week-old surfaces showed only 20% to 50% of the levels of recruitment, attachment, settlement, and proliferation of osteogenic cells versus new surfaces. On the other hand, a series of recent papers reported the generation of highly cell-attractive and osteoconductive titanium surfaces by ultraviolet (UV) light treatment. The phenomenon, defined as photofunctionalization, caused a fourfold acceleration in the process of osseointegration and resulted in nearly 100% bone-implant contact. Remarkably enhanced behavior and response of osteogenic cells around UV-treated surfaces exceeded the levels observed for the newly prepared surfaces. These studies indicated that UV treatment reverses the time-dependent biologic degradation of titanium and even enhances the surface beyond its innate potential. The present paper summarizes the findings about the aging-like time-dependent biologic degradation of titanium surfaces as well as about the discovery of UV photofunctionalization as a solution for this phenomenon. It also provides a novel understanding of osseointegration and calls for immediate attention to a new avenue of exploration in the science and therapeutics of implant dentistry.