The osseointegration implants initially utilized by the Swedish and the Swiss groups were the turned (or the so-called machined) implants, which in reality has the longest clinical documentation. The term ‘machined’ should be avoided as much as possible in this book since it is well known that implants are manufactured by a turning process in a turning machine. The term ‘machined’ could be any surface finish, since as long as a ‘machine’ is involved in the manufacturing process, the surface could be called ‘machined’; thus, it is clear that the terminology is not suitable especially for a book focusing on implant surfaces. For example, implants that have a mechanically polished surface finish are often rightfully called ‘machined’ and compared with turned ‘machined’ surfaces. However, these polished implants possess a much smoother surface topography in the micro-level compared to the traditional Brånemark turned implant surfaces; thus, the comparison is not correct from a topographical point of view. Turned surface implants have indeed a long clinical history. Until the mid-1990s the turned implants dominated the market. One of the first long-term documentation concerning the survival of the turned osseointegrated implants stated that 81 % of the maxillary implants and 91 % of the mandibular fixtures remained stable after a 15-year period [15]. Attard and Zarb had replicated the studies performed in Sweden and reported in their prospective study that over a 20-year period (range 18–23 years), the implant success rate with fixed prosthesis in edentulous patients was 87 % [16]. These studies clearly highlight that the turned implants present good prognosis over a long period. According to Wennerberg and Albrektsson [4], these once commercially available turned Brånemark implants had a surface topographical value of Sa of 0.9 μm and an Sdr of 34 % [4]. Thus, it can be said that the effect of surface micro-topography may have contributed in the long-term clinical success of the turned commercially available implants. However naturally, their definitive role during functional loading over a long period is difficult to distinguish since implant success is a complex blend of multiple factors.

In general, the traditional Brånemark turned implants placed in the mandible, or the maxilla, followed a 2-stage protocol, which allowed the implants to heal (osseointegrate) [17]. Clinically, it has been suggested that the turned implants required a healing period of 3 months in the mandible and 6 months in the maxilla. This was probably one of the reasons why the so-called rough implant surfaces appeared on the market in order to provide higher grip between the implant surface and the bone. It can be said that back in the days when the development of these surfaces took place, there was little evidence on what is the optimal roughness. Although in general, from a mechanical viewpoint, the rougher surfaces have been known to provide higher stability, the clinical performance of these surfaces was without proper evidence. More on the optimal roughness, namely, the moderately roughened surface, will be introduced later in this chapter.

In this section, the two major surface-roughening procedures, i.e. evidence with regard to the titanium plasma spraying technique and hydroxyapatite coating technique, will be briefly introduced.

As of 2014, a majority of the implant surfaces have textured micro-topographies. In principle, the turned implants as a substrate are treated with different roughening procedures such as sand blasting [42–44], acid etching [45–47], anodic oxidation [48–50], and laser etching [51–53]. More importantly, a majority of the commercially available implants of today are strategically roughened in the micro-level to present the optimal bone responses. The moderately roughened micro-roughness, as mentioned in the introduction, is the major key to the success of the implant from a surface topography viewpoint.

This success stands on the knowledge that bone responds in a different manner to different surface topographies. Wennerberg et al. have shown that implant surfaces blasted with titania particles of 25 μm and alumina particles of 75 μm presented higher bone-to-implant contact than the turned implants. For the roughness parameters, especially the average height deviation, the Ra presented differences between the turned and the blasted surfaces, with the blasted surface presenting two to three times higher topographical values (Ra = 0.4 μm, and Ra = 0.9–1.3 μm, respectively) [54]. It was suggested in another study from Wennerberg et al. that the mode of roughening, in other words, the material used to roughen, did not play a significant role on the biological outcome and the alterations in surface topography were the influential factors with regard to osseointegration (direct bone-to-implant contact) [55, 56]. Although these experimental results suggested a linear relation between the surface roughness and osseointegration, another report from Wennerberg et al. has suggested that highly increased surface roughness presents lower bone-to-implant interactions. In brief, the implants blasted with 250 μm particles (average surface height deviation Sa = 1.88 μm) presented significantly lower bone-to-implant contact than the implants blasted with 25 μm particles (average surface height deviation Sa = 1.16 μm). Interestingly, the removal torque values and the bone area presented no significant differences, which combined with the bone-to-implant contact suggests a non-linear relation between surface roughness and osseointegration [57]. As shown in Fig. 3.2, which is a summary of the series of articles presented with regard to this topic by Wennerberg et al., there seems to be a range of surface roughness that presents the strongest bone responses, and as stated in the introduction, many of the commercially available implants of today possess a moderately roughened micro-topography.

Clinically, we know from experience that the moderately roughened implant surfaces osseointegrate faster and the time to functionally load has significantly reduced compared to the turned implant surfaces. Although it is difficult to prove that the implants are osseointegrating faster in the patients’ bone, the alterations in loading protocols (from delayed to early or immediate) and their success clearly suggest the effects and benefits of the moderately roughened implants [58].

With regard to the clinical outcomes of the implants possessing moderately roughened surface topography after a 5-year period, the prognosis has been reported to present good outcomes. Gotfredsen and Karlsson have reported that commercially available implants with a moderately roughened surface topography presented 100 % survival after 5 years with low levels of marginal bone loss with a fixed partial prostheses as superstructures [59]. Akogulu et al. reported that three implants from different manufactures all possessing moderately roughened surfaces presented no differences in survival rates after 5 years (100 %) with marginal bone loss less than 0.4 mm with an overdenture reconstruction in the mandible.

When compared to the turned implants, the long-term implant survival of the moderately roughened implants presented no significant differences, if the implants are placed in sites such as fully healed sites or sites with good bone quality [60–62]. Thus, it seems that the moderately roughened implant surfaces do not present significant differences compared to the turned surfaces in normal situations; however, in compromised situations such as in poor quality bone, or in irradiated bone, the moderately roughened implants present their benefits. Khang et al. conducted a multicentre study testing the success of turned and dual acid-etched surfaces and reported that the success rates were notably higher for the dual acid-etched surfaces compared to the turned surfaces in poor bone quality conditions [63]. Pinholt has reported that in grafted maxillary bone, the moderately roughened implant surfaces outperformed the turned implant surfaces in terms of implant survival [64]. Buddula et al. investigated the differences in implant survival after 5 years using turned or moderately roughened implant surfaces in sites where radiation of at least 50 Gy was irradiated [65]. The results presented significantly higher survival rates for the moderately roughened implants both in the mandible and maxilla. In addition, a recent paper summarized 10 different non-controlled studies of moderately rough implant and found those to present a combined failure and peri-implantitis frequency within 5 % if followed up for 10 years or longer [66].