Osseointegrated implantology, thanks to many studies, is now considered a surgical discipline with proven effectiveness. Success in implant dentistry consists in getting a good rate of integration between implant and host bone, which defines a good osseointegration according to the principles initially introduced by Branemark and subsequently developed by numerous studies over the years (1–3
The implant design is a key factor to achieve good primary stability. It should be designed to guarantee the establishment of a direct connection between bone tissue and implant surface during the early stages of the healing process, without the interposition of fibrous tissue, as well as to achieve an even distribution of the loads which, through the masticatory system, are transmitted to the peri-implant bone tissue whilst chewing (4,5
There are two fundamental aspects of implant design: the macro-structure, characterized by the shape of the body, the characteristics of the neck and the apex, by the design, by the number and pitch of the thread, and the microstructure, characterized by the surface treatment. In addition, there is also the good accuracy of the prosthetic components (6–8
It is known that differences in implant shapes induce significant changes in force distribution on the surrounding bone (9
). The macroscopic geometric pattern of a dental implant can assume a cylindrical or conical form. For some years some companies have marketed the tapered form, with the aim of combining the advantages of both designs. A tapered implant creates the basis for an excellent primary stability by gradually allowing thin ridge expansion and determining the least stress possible at the interface with the surrounding bone (10,11
). The design of the implant neck, or crestal module, has undergone considerable evolution in recent years. The implant neck represents the transosseous area of the implant body where the highest concentration of mechanical stresses are evinced and where the transition between the hard tissue and soft tissue support occurs. Discriminating elements of the crestal module could be identified in the geometrical design and in the surface type. The possible geometric profiles of the implant neck are essentially three: straight walls, diverging walls and converging walls. Despite the diverging walls type seeming to be the best form, as it can provide a slightly higher primary stability after the implant insertion, from the clinical point of view the behavior of the bone before and after the load is not dissimilar between the three geometric figures. In fact, an aspect commonly observed at the level of the crestal module is the different bone level before and after the occlusal loading. Before loading, if the implant was positioned so that the prosthetic platform is at the level of the crestal bone, there will always be a clinical situation where the bone covers the entire implant neck. After application of the load there is invariably a vertical bone loss, the level of which is located in correspondence of the first thread. All this takes place independently from the geometrical shape and the level of the first thread.
The crestal module height was reduced over time by various manufacturers, until today, when the height of the smooth collar is reduced to less than 2 mm.
The morphology of the crestal module evolved in the same way - from a smooth surface to a treated surface with microthreads for increased stability of bone in the coronal zone, to favour aesthetics and peri-implant health (12
The use of the smooth neck arises from the necessity to limit the plaque retention at the border zone between the implant, bone and soft tissue. The presence of micro retentions at the level of the crestal module is designed to adequately dissipate forces that are expressed at the cervical area of the bone-implant interface in the presence of occlusal stress, in all implant types, thus allowing to maintain the height of the bone spikes in accordance with the law of Wolff (13
), a phenomenon that in the presence of a smooth neck does not happen.
As regards the design and the pitch of the threads, these must be designed to maximize the transmission of forces between the implant and surrounding bone tissue, and to correctly distributed stress arising between the bone interface and the implant (14
). Their main role is to increase primary stability and extend the available surface of the implant for bone contact.
Among the various thread designs, the V-shaped threads and the broader square threads have been shown to generate less stress and to better distribute the loading forces compared to the thin threads and tapered apex threads (15
). The phenomenon is best appreciated in the bone marrow, while no difference have been found in cortical bone.
Another important factor necessary to achieve success in implantology is represented by the surface properties of the material used (16
). The micro-topography of the implant surface is able to affect the percentage of BIC (Bone-to-Implant Contact) and the cellular response of the host tissue (17
). The treated surfaces stimulate osteoblast proliferation, as demonstrated by the increased expression of biological markers, which transposes into an increase of osteogenesis, thus assuming an important role regarding the long-term survival of the osseointegrated implants (18
The titanium surface can be prepared with different techniques in order to obtain an optimal degree of roughness of the surface, as it has been shown that the wider the functional surface is in contact with the bone, the better the support for the prosthesis (19,20
The rough implant surfaces determine a slightly better bone tissue response in quantitative terms of bone-implant contact percentage (21–23
). The purpose of the surface treatment is to increase the contact area between the bone and the implant, thus improving the osseointegration. Even with only the threads, the resistance degree to tensile forces and compression is greater than smooth implants not threaded, and the presence of microretentions on the surface of the fixture allows to increase the tensile and torsion strength of the implant. In addition, some authors have demonstrated how macrophages, epithelial cells and osteoblasts, have a high tropism against rough surfaces (24,25
In order to obtain a surface topography able to promote the process of osseointegration, various surface treatments have been tried out, such as sandblasting (26
), acid etching (27
), combined treatment of blasting and etching (28
), surface coating with micro-granules of hydroxyapatite (29
) or particles of titanium oxide (30
), or electrochemical deposition (31
). Recent researches highlighted how the micro-roughness obtained by blasting and acid etching is compatible with best clinical and histological results.
Several options also affect the types of connections between the endosseous fixture and implant prosthetic components.
External hexagonal connection was the first connection system used in implantology which was ideated by Branemark only as coupling mechanism to easily guide the stump insertion; its function was then expanded to become a real anti-rotation mechanism. The interface and the tightening screw are subject to very high masticatory loads, subjecting the screw to insidious lateral bending forces, tilting and elongation that may mobilize it (32
Of the internal connections, the most widely used are internal hexagonal, internal octagonal, conical screw and Morse connections. The internal connections have shown an increased stability, better mechanical stability and resistance to lateral forces than external ones.
The aim of this study is to describe the macroscopic and microscopic appearance of a new implant design, with particular emphasis on the type of prosthesis connection.