Quality assessment of 150 dental implants with scanning electron microscopy and elemental analysis - Do we need a new standard of purity?
Dental implants are an integral part of the therapeutic armamentarium of contemporary dental practices. With their excellent success rates, they have become the globally established treatment alternative to purely prosthetic solutions for tooth loss. And with the variety of implant systems offered, it has become ever more difficult for the dentist to choose just the right system for his or her practice and patients. Specific surface topographies, material properties that promote osseointegration or surface treatments are often emphasized in advertising as significant advantages to distinguish a given system from its many competitors.
According to the Association of German Dental Manufacturers (VDDI), more than 1,300 different implant systems are currently available worldwide. Northern Italy alone probably has a hundred micro-enterprises that manufacture implants, primarily for regional dentists.
Background and objectives
There is commonly a significant discrepancy between the responsibility treatment providers must assume for the materials they use vis-a-vis their patients and their knowledge regarding the quality of these materials as confirmed by neutral and scientific sources. As stated in the interim report in the previous issue, CE marks do not protect the market, or rather the patient, from substandard quality in medical devices [4]. An international group headed by the University of Geneva School of Dental Medicine has embarked on the highly commendable quest to characterize, classify and code dental implants starting in 2010 – the so-called Implant Surface Identification Standard (ISIS) that might facilitate the future introduction of a possible ISO standard for dental implants [5,6]. The surface quality of implants depends on a number of different factors. Once the titanium implant blank has been CNC-machined, it is further processed using different techniques that ultimately result in the product’s specific surface structure. The various processes used for titanium implants were discussed in the first part of the report. Various production processes ultimately contribute to product quality: the production itself, the cleaning steps, post-production handling (i.e., quality control), packaging and sterilization processes and the packaging itself.
A striking feature of this study has been the many different types of sterile packaging that sometimes go to considerable lengths to prevent any kind of contact of the implant with the packaging. In fact, several implants in the study that did not feature contact-free packaging but were delivered in soft sealed polyethylene bags exhibited various amounts of organic contaminants or plastic residue, depending on their surface roughness. As described in the interim report, even a wellstructured implant surface proven in clinical practice for many years may accumulate not insignificant amounts of organic contaminants or plastic particles through abrasion, unless the implant was delivered in non-contact packaging. There have been reports in the literature that these organic contaminants are associated with early implant loss or with peri-implantitis [7].
The documented amounts of carbon in the regions that are already obvious on the material contrast images are considerably higher than the minor amounts of carbon adsorbed from ambient carbon dioxide as present on any titanium implant. The more or less sophisticated technical implementation of the sterile packaging has no direct relation to the price of the implants. But how far can we let manufacturers go in their drive to save cost if the result is sharp-edged cover screws that damage, and thereby breach, the simple sterile packaging even before they are used. Discussion
The clinical relevance of minuscule particles and contaminants on dental implants is a matter of debate. Even the manufacturers of implants on whose implants more or less large amounts of organic or inorganic contaminants were found in tests have reported statistical success rates that are not different from those of other implants, proving their point with specially conducted studies. Up to a point, biocompatible aluminium oxide residues are unlikely to affect the bone-implant contact (BIC) [18,19]. But how does the human body handle polyethylene or chromium-nickel-steel particles? Even if these particles are relatively firmly attached to the implant surface, they are likely to become detached by the resulting frictional forces in the bone bed as the implants are inserted at torques in the double digits to achieve the desired level of primary stability. Particles with a diameter of less than 10 μm are susceptible to uptake by macrophages through phagocytosis [20], so that questions related to the clinical relevance of such impurities cannot simply be brushed aside. From orthopaedics it is known that particle-induced macrophage activation is associated with an increased osteoclastogenesis and may therefore cause increased bone resorption [21].
One point of criticism that has been repeatedly expressed by some manufacturers in the context of the present study has already been responded to in the published report on the 2011/12 implant trial. The criticism goes roughly like this: The implant specimen used in this study patterns are only random samples. A scientific study requires at least five to seven implants of each implant type to make statistically valid statements about a quality standard. But the reply can only be that those implants are medical devices where – unlike with general technical goods – defects cannot be remedied or “repaired” once inserted. Each of the implants examined was sterile-packed and intended for use in patients. One might therefore counter by asking why the manufacturers’ quality management is obviously subject to daily fluctuations and why implants are released which yield suboptimal results in individual testing. Each day we are tasked with winning the trust of our patients, and each time we perform an implantological treatment we are trying to prove worthy of this trust. For individual manufacturers to reject studies like the present one or to allege image manipulation is not particularly helpful in this endeavour. But the vast majority of the studied implants presents an encouraging picture. By far most manufacturers are aware of their responsibility and provide implantologists in Europe with solidly made systems.
