Eight different examples of implant thread designs. (a) Power square thread, (b) power Acme thread, (c) buttress thread, (d) reverse buttress, (e) fixture thread, (f) vertical slot thread, (g) rounded off power thread, (h) Spiralock technique
Microthreads on the marginal part of the implant were introduced by the end of the 1990s. This implant design has in several controlled clinical studies been found to maintain the marginal bone levels [1–3], possibly due to the microthreads reducing peak stresses in the bone . Recent research has demonstrated microthreads between larger threads positioned over the entire implant may have some bone stimulating effect too, in particularly in soft bone quality .
Summary Millimetre Implant Topography
Screw–shaped implant dominates the market, but the optimal design of individual treads still remains to be concluded.
Micrometre Surface Topography
The first implants used clinically were produced with a turning process; the cutting procedure leaves clear marks on the surface; thus, this surface will have a clear orientation. In addition, turned oral implants are smooth to minimally rough according to a suggested classification , i.e. surfaces have an Sa (average height deviation) value less than 1 μm. However, a substantial number of experimental studies performed during the 1990s clearly demonstrated potential advantages with moderately rough surfaces (an Sa value between 1 and 2 μm), whereas smoother as well as rougher implants were found to integrate less well. Today the majority of commercially available implants are produced within this range of surface topography. Common approaches to increase the roughness above the turned implants could be either by techniques that will remove materials from the surface, i.e. creating pits, or by adding material, i.e. creating bumps on the surface. The major techniques that remove material are etching, blasting, combination of blasting and etching and oxidation. Although it should be noted, etching alone removes cutting marks from the turning process and leaves a surface with high-frequency irregularities; thus, the technique produces an enlarged surface area but the Sa value will not be significantly increased. Therefore, acid etching is not sufficient to produce a moderately rough surface. Moderately rough surfaces are most commonly manufactured by blasting, a combination of blasting and etching or oxidation. The roughness achieved with blasting depends on the blasting media (e.g. TiO2, Al2O3 sand and corundum particles), the size and shape of the particles, pressure during blasting and distance from blasting equipment to target (the implant). The reason for a combination of blasting and etching is that this will provide a moderately rough surface with rather long wave components due to imprints from blasting media and small pits due to etching contributing high-frequency components.
In unselected patient materials the old turned implants have demonstrated very good long-term clinical results with survival rates above 90 % after 10–15 years. However, for more compromised patients with poor bone quality and quantity due to various reasons, moderately rough surfaces have significantly improved the clinical results compared to the old turned implants, for example, when inserted in posterior regions, in the maxillary bone, in smokers or in transplanted bone .
Summary Micrometre Topography
Moderately rough implants dominate the market today. The clinical results have been improved with these implants compared to smoother, turned implants in particular for some groups of patients.
Nanometre Surface Topography
The latest generation of implant surfaces includes nano-modifications. One of the most common hypotheses behind nanotopography for improvement of implant incorporation in bone is that the nano-irregularities will form attachment sites for proteins important during the healing process. Thus, the blood proteins first to attach to the implant surface during insertion in the bone which governs further biological events through signalling systems, selection of adhered cells and further bone-forming processes. Nanostructures have even been speculated to improve marginal soft tissue adherence to implant components, which may have potential for maintaining marginal bone levels and a healthy surrounding mucosa.
The definition of nanostructures has been suggested as the range of 1–100 nm . Nanostructures can be coated on the surface. Common coats are hydroxyapatite or titanium dioxide. In particular the former has been evaluated in many experimental and clinical studies.
Nanostructures may, in addition to coating procedures, be spontaneously formed during manufacturing. It seems like etching procedures in combination with storage in liquid will lead to reorganisation of the outermost titanium oxide layer into nanostructures [9