Nanofeatured surfaces in dental implants: contemporary insights and impending challenges

Abstract

Dental implant therapy, established as standard-of-care nearly three decades ago with the advent of microrough titanium surfaces, revolutionized clinical outcomes through enhanced osseointegration. However, despite this pivotal advancement, challenges persist, including prolonged healing times, restricted clinical indications, plateauing success rates, and a notable incidence of peri-implantitis. This review explores the biological merits and constraints of microrough surfaces and evaluates the current landscape of nanofeatured dental implant surfaces, aiming to illuminate strategies for addressing existing impediments in implant therapy. Currently available nanofeatured dental implants incorporated nano-structures onto their predecessor microrough surfaces. While nanofeature integration into microrough surfaces demonstrates potential for enhancing early-stage osseointegration, it falls short of surpassing its predecessors in terms of osseointegration capacity. This discrepancy may be attributed, in part, to the inherent "dichotomy kinetics" of osteoblasts, wherein increased surface roughness by nanofeatures enhances osteoblast differentiation but concomitantly impedes cell attachment and proliferation. We also showcase a controllable, hybrid micro-nano titanium model surface and contrast it with commercially-available nanofeatured surfaces. Unlike the commercial nanofeatured surfaces, the controllable micro-nano hybrid surface exhibits superior potential for enhancing both cell differentiation and proliferation. Hence, present nanofeatured dental implants represent an evolutionary step from conventional microrough implants, yet they presently lack transformative capacity to surmount existing limitations. Further research and development endeavors are imperative to devise optimized surfaces rooted in fundamental science, thereby propelling technological progress in the field.

Keywords: Bone-titanium integration; Dental and orthopedic implants; Microrough surface; Osseointegration; Osteoblasts.

Fig. 1

Osteoblast behavior on implant surfaces. The frustration of implant surfaces arises from the inherent behavior of osteoblasts (see Fig. 3). There is a dichotomy in osteoblastic behavior: high levels of proliferation and differentiation cannot be achieved simultaneously. Osteoblasts exhibit robust differentiation on currently used microrough titanium surfaces, while their proliferation is significantly reduced. Additionally, the number of osteoblasts attaching to microrough surfaces is compromised compared to machined, smooth surfaces

Fig. 2

A fundamental strategy employed to develop nanofeatured surfaces in dental implants involves adding nano-scale structures, less than 100 nm in size, to existing microrough surfaces via chemical methods. This approach aims to introduce new functions, mitigate existing disadvantages, while preserving the advantages of microrough surfaces. Importantly, the added nanofeatures are not crafted with titanium oxide but rather with extrinsic molecules

Fig. 3

The dilemma of implant surfaces arises from the inherent dichotomy of osteoblast behavior, characterized by an inverse correlation between proliferation and differentiation. Current dental implant surfaces, typically featuring microrough textures, prioritize promoting differentiation while compromising proliferation. Essentially, this means that while bone formation occurs more rapidly on microrough surfaces, the overall bone volume tends to be reduced

Fig. 4

Formation of micro-nano hybrid titanium surface. TiO₂ nano-scale nodules are genereated within micropits. This process was uncovered as TiO₂ molecular self-assembly occurs during TiO₂ sputter/vapor deposition onto microrough titanium surfaces. By adjusting the deposition time, the size of nanonodules can be controlled. It is important to note that the resultant surface is crafted entirely from titanium oxide, unlike the methods described in Fig. 2

Fig. 5

Scanning electron microscopic (SEM) images comparing the controllable micro-nano hybrid titanium surface with a typical microrough titanium surface created by acid-etching. The hybrid titanium surface was formed by allowing TiO₂ to self-assemble on the microrough surface. The formation of 300 nm nodules at the flanks, valleys, and ridges of the micropits is visible. For detailed morphological descriptions, refer to Table 1