The mechanical properties of a material play a decisive role in its selection for fabrication of implants. Some of the important properties include hardness, tensile strength, modulus of elasticity and elongation. The response of the material to repeated occlusal loads is dependent on the fatigue strength of the material and determines the long term success of implant under recurring occlusal stresses. The modulus of elasticity of bone varies in magnitude from 4 to 30 Gpa depending on the type of bone and the direction of measurement [9, 10].

The material used for implants should have modulus of elasticity equivalent to that of the bone. Inadequate strength or any mismatch in mechanical properties between implant material and the bone is bound to lead to fracture of implant making it biomechanically incompatible. At the same time, an implant material that has a strength much higher than the bone will prevent transfer of the stress to the adjacent bone leading to bone resorption around the implant and implant failure. The biomechanical incompatibility that leads to death of the bone cells is known as ‘Stress Shielding Effect [11]. Therefore, the material of choice for dental implants has to have a combination of high strength and low modulus of elasticity closer to the bone.

The materials used for implants are expected to be well accepted and tolerated by the human tissues without causing any adverse effect or reactions in the body. This quality of a material is known as biocompatibility [12]. Interaction and some reaction start between implant surface and adjacent tissues immediately upon placement of implant in the human body. The reaction involves blood coagulation and adhesion of blood platelets to biomaterial surface and encapsulation of the biomaterial by fibrous tissues.

The biological compatibility of implant materials is directly dependent upon their chemical composition, design of the implant, topographic mechanics and wettability of the implant material. Use of nanotechnology may lead to the development of dental implants with controlled topography and chemistry leading to the development of implant surfaces with predictable and favourable tissue response during osseointegration [13, 14].

The implants should be developed using materials with high wear and corrosion resistance in order to ensure longevity of the dental implant under biological conditions. The longevity of the implant is usually determined by its resistance to abrasion and wear in the mouth. The implant materials having low wear and corrosion resistance release non-compatible metal ions in the body fluids. The released ions cause allergic and toxic reactions in the body [15].

A low resistance to wear leads to formation and deposition of wear debris at the implant-tissue interface causing several chemical and biological reactions in the tissues with ultimate failure of the implant due to its loosening [16].

Osseointegration is a term founded by Professor Per-Ingvar Brånemark after his important breakthrough in the 1950s when he discovered that bone can integrate with titanium components. Osseointegration has been described as a direct structural and functional bone to implant contact under load [17]. Professor Brånemark named his discovery after Latin word ‘os’ that means bone, and ‘integrate’ that means make whole. When conjoined together it points out to interactive coexistence. It was observed that when a screw-shaped implant fixture made of titanium was carefully placed in the bone, the genetic code that usually makes bone reject a foreign material was not activated. The bone cells were able to attach to the titanium surface resulting in a firm and permanent anchorage for a prosthetic reconstruction. It actually promotes bone regeneration that fills the micro gaps between the implant surface and the adjacent bone. The term has been used to explain the success or failure of the implants in medical and dental science ever since. In the absence of osseointegration, fibrous tissue is formed between the bone and the implant surface. The implant therefore, is not well integrated into the bone resulting in implant loosening and subsequent implant failure [18]. Surface topography, surface roughness, surface material and surface chemistry, all play a significant role for a successful osseointegration.

The observation that a micron-scale rough surface prepared by grit blasting and subsequent acid etching was capable of rapid and increased bone accumulation further strengthened an earlier report that a TiO₂ grit blasted surface also supported more rapid and increased bone accrual at cp titanium implants [27].

The study also pointed to a significant fact that the cp titanium surface could be modified to enhance bone accumulation and suggested that cp titanium was not only “bioinert” or “biocompatible”, but was also capable to influence cellular activity or tissue responses leading to better and greater osteogenesis and thereby promoting better osseointegration. Nano-topography seems to influence cell interactions at surface of the material being used. It also leads to changed cell behavior when compared to conventional sized topography. The cellular protein adsorption is altered by nanoscale modification of bulk material. Depending on the nano-architecture, cell spreading may be increased or decreased. The present undefined mechanisms indicate that cell proliferation appears to be enhanced by nanoscale topography. Several investigators have shown that nanoscale topography enhances osteoblast differentiation [28–30].

Alteration in initial protein surface interaction is believed to control osteoblast adhesion, a critical aspect of the osseointegration process [31]. When implant comes in contact with a biological environment, the initiation of protein adsorption (e.g. plasma fibronectin) promotes subsequent cell attachment and proliferation. Change in surface energy or wettability of a biomaterial corresponds to a typical way of altering cell interactions with the surface. Nano-scale topography is now an established way of altering protein interactions within a surface. An increased vitronectin adsorption has been observed on nano-structured surfaces when compared to conventional surfaces [32, 33]. The study also suggested an increased osteoblast adhesion when compared to other cell types, such as fibroblasts, on the nanosurfaces [33].

Irrespective of the surface-adsorbed proteins, cells are remarkable in their ability to sense nanostructure. Nano-features of a surface affect both cell adhesion and cell motility. Both of these cell traits are attributed in part, to the function of integrins [33, 34]. Underlying substratum topography influences cell behaviors by both direct and indirect interactions. In 20–40 nm features produced by H₂O₂/H₂SO₄ treatment there were definitive interactive points for lamellipodia of spreading cells (Fig. 3) [33]. Cell behavior is affected by both, the dimension and the density of the nano structures.

Nanosurface modifications promote adherent cell proliferation. Zhao et al., utilizing three distinct methods—electrochemical machining, anodization and chemical etching to produce reproducible submicron-scale structures on titanium surfaces reported an opposing relationship between cell proliferation and cell differentiation with increase in micro scale of surface features.

It has further been supported by studies that observed an increase in the osteoblast proliferation on nano scale materials like alumina, titanium and hydroxyapatite [35, 36]. However, the mechanism involved is still not clear as to how nano-structured surfaces modulate the adherent osteoblast response.

Selectivity of cell adhesion is an interesting feature attributed to nanoscale topographic surfaces. Several studies have revealed a relative lowering of fibroblast adhesion compared to osteoblast adhesion on evaluation of nano and micron-structured surfaces [37, 38]. The affinity ratio between osteoblasts and fibroblasts was 3 to 1 on nanosized materials as compared to the conventional materials depicting a ratio of 1 to 1 [33]. Studies on other cell types such as smooth muscle cells and chondrocytes have also reported similar results [39].

All these observations may lead to some major implications in specification of tissue response at bone and mucosal surface of the dental implant/abutment assembly.

A rapid differentiation of adherent mesenchymal cells along the osteoblast lineage is as significant for the process of osseointegration as supporting osteoblast-specific adhesion and adherent cellular proliferation. Studies have revealed that alkaline phosphatase synthesis and calcium mineral content increased in cell layers formed on nano sized materials after 21 and 28 days [40, 41] (Table 3).