Implants are commonly used in dental surgery for restoring teeth. One of the challenges in implantology is to achieve and maintain the osseointegration as well as the epithelial junction of the gingival with implants. An intimate junction of the gingival tissue with the neck of dental implants may prevent bacteria colonisations leading to peri-implantitis while direct bone bonding may ensure a biomechanical anchoring of the artificial dental root ().
Tissue integration of dental implant. Note the intimate contact with gingival tissue in the upper part and the desired contact osteogenesis in the tapered lower part rather than distance osteogenesis.
The first step of the osseointegration of implants is called primary stability and is related to the mechanical anchorage, design of implants, and bone structure [1
]. This primary interlock decreases with time at the benefit of the secondary anchorage, which is characterized by a biological bonding at the interface between bone tissues and implant surface. Between the primary mechanical and secondary biological anchorage, a decrease of implant stability could be observed. Many studies have attempted to enhance the osseointegration of implants by various surface modifications. The aim is to provide metal implants with surface biological properties for the adsorption of proteins, the adhesion and differentiation of cells, and tissue integration. These biological properties are related to chemical composition, wettability, and roughness of metal implants surfaces. However, the control of these surface properties at the protein and cell levels, thus in the nanometre range, remains a challenge for researchers and dental implants manufacturers.
Nanotechnologies may produce surfaces with controlled topography and chemistry that would help understanding biological interactions and developing novel implant surfaces with predictable tissue-integrative properties [2
]. Various processing methods derived from the electronic industry such as lithography, ionic implantation, anodization, and radio frequency plasma treatments may be applied to the surfaces of dental implants to produce controlled features at the nanometer scale. These surfaces may then be screened by using high throughput biological assays in vitro
. For instance, specific protein adsorption, cell adhesion, and differentiation of stem cells should be studied in relation to the surface properties. This approach may define the ideal surface for a specific biological response. Following in vitro
screening, nanostructured surfaces may then be tested in animal models to validate hypothesis in a complex in vitro
New coating technologies have also been developed for applying hydroxyapatite and related calcium phosphates (CaP), the mineral of bone, onto the surface of implants (). Many studies have demonstrated that these CaP coatings provided titanium implants with an osteoconductive surface [4
]. Following implantation, the dissolution of CaP coatings in the peri-implant region increased ionic strength and saturation of blood leading to the precipitation of biological apatite nanocrystals onto the surface of implants. This biological apatite layer incorporates proteins and promotes the adhesion of osteoprogenitor cells that would produce the extracellular matrix of bone tissue. Furthermore, it has been also shown that osteoclasts, the bone resorbing cells, are able to degrade the CaP coatings through enzymatic ways and created resorption pits on the coated surface [5
]. Finally, the presence of CaP coatings on metals promotes an early osseointegration of implants with a direct bone bonding as compared to noncoated surfaces. The challenge is to produce CaP coatings that would dissolve at a similar rate than bone apposition in order to get a direct bone contact on implant surfaces.
Figure 2 Scanning electron micrographs and energy dispersive analysis for X-ray of (a) nanostructured titanium surface obtained by anodization and (b) nanosized thin calcium phosphate (CaP) coating on titanium produced by electrochemical deposition. Note the regular (more ...)
This paper reviews the different steps of the interactions between biological fluids, cells, tissues, and surfaces of implants. Recent nanoscale surface modifications and calcium phosphate coating technologies of dental implants are discussed. The sequence of biological events in relation to surface properties is related. Mechanisms of interaction with blood, platelets, hematopoietic, and mesenchymal stem cells on the surface of implants are described. These early events have shown to condition the adhesion, proliferation, and differentiation of cells as well as the osseointegration of implants. Future implant surfaces may improve the tissue-integrative properties and long-term clinical success for the benefits of patients.