Dr Pantelis Petrakakis, freelance journalist and dentist, Düsseldorf MDT
Dr Nina Rätscho, BEGO Implant Systems, Bremen
The long-term success of implant treatment depends on many biological, mechanical and patient-related factors. One aspect of the mechanical factors is the fit of the individual components in the implant system. A well-coordinated implant system strives for the highest possible accuracy of fit of the system components so as not to jeopardize the longevity of the implantprosthodontic reconstruction.
Prosthodontic components from third-party vendors or external suppliers, known as copycats, are being advertised more and more often. The question this raises is whether these cheaper and supposedly identical third-party components are comparable to the original components of the implant system, in terms of quality and safety.
The interface between the implant and the prosthodontic abutment is a sensitive area that could be affected by components that are supposedly identical but not fitting perfectly. For this reason the validity and supposedly comparable usability of the third-party components must be critically scrutinized.
Where signalling molecules orchestrate the body’s cells and the interplay of cells results in function and aesthetics, an implant system must be in harmony with the physiological, anatomical and mechanical events.
The focus of an implant system is the implant body (Fig. 1).
The special features of anatomical structures and indication-dependent characteristics are taken into account in the geometry and design, surface and joint of the implant body. The implantation bed is prepared with surgical tools that are tailored to the implant body. The protection of the bone and the controlled preparation of the implant bed are important steps for a successful osseointegration of the implant.
The implant-prosthetic junction is a sensitive area that deserves special attention. The type and construction of the internal connection and the design of the prosthodontic components are precisely coordinated with all manufacturers of dental implants and tested in combination as a functional unit with the prosthesis screw in conformance with DIN ISO 14801.
The exact dimensions, tolerances and geometries of the prosthodontic interface are the basis for a functional and long-lasting implant-prosthodontic restoration of the patients.
So far, few studies have been published on the use of original components compared to components from third-party suppliers, particularly the prosthodontic components. In the 1990s there were efforts to copy components of different implant systems and to offer them cheaper (ZANARDI et al., 2012). The components of the third-party manufacturers were already criticized at the time, as inaccuracies were observed in the fit, which led to biomechanical disadvantages for the implant-prosthodontic reconstruction as a result of higher micro-movements and micro-gap formation (BINON 1995, DELLOW et al., 1997). Publications warn of technical and biological problems that may arise from an inadequate fit, especially between the abutment and the implant (HURSON, 2016, IVANOVSKI, 2015). Fitting inaccuracies lead to an increase in stress in the area of the implant-prosthodontic connection and also cause an unfavourable stress transmission in the periimplant bone (ASSUNCAO et al., 2011).
Using abutments from various third-party manufacturers on an implant system allows the clinician the option to offer implant therapy more cost-effectively. The increasing number of suppliers of non-implant-system products in the market highlights the importance of extensive experimental in-vitro and clinical human trials, especially in terms of commitment of dentists and patient safety.
The use of non-implant components in an implantprosthodontic restoration can result in mating inaccuracies and technical problems (Fig. 2). Micromovements between implant and prosthodontics can cause major problems, both in materials and in the biological field. Thus, the use of third-party components causes larger micro-movements than when using original components. The results of a recent in vitro study show that an oblique load with an acting force of 200 N, causes an average gap formation at the implant-prosthodontic interface which is up to three times higher if third-party components are used instead of the original components (BERBERI et al., 2016).
Another special feature are custom-made abutments. In a systematic review, mean vertical gaps between 50 and 160 μm could be identified (LALITHAMMA et al., 2014, PEREIRA et al., 2017). Cervical discrepancies of 70 μm (BAE et al., 2017) and up to 100 μm (PEREIRA et al., 2017) are considered clinically acceptable. Other authors point out that there is a lack of a clear, agreed definition of tolerances in the fit between the implant and the superstructure (ABDUO & JUDGE, 2014, KANO et al., 2007, MORAIS ALVES DA CUNHA et al., 2012).
A special role is played by the prefabricated, clearly oversized blanks, so-called pre-milled blanks or preface abutments. If manufactured by the implant manufacturer, these components have the original connection point to the implant. After the scan and design process, these abutments are clamped by standardized workpiece holders in milling machines, which are usually provided by the laboratory, and customized according to the clinical situation, while the original connection to the implant remains unaffected.
In a laboratory study conducted by GIGANDET et al. (2014), implants from three different manufacturers were supplied with the original abutments. Wax-up abutments were fabricated on one of the implant systems and then scanned with the respective scanning system of the other two implant systems and milled individually milled with titanium grade V using CAD / CAM technique. The abutments made using CAD / CAM technique differed greatly in the design of the interface between implant and abutment and showed a higher mean rotational latitude. The authors concluded that the poorer fit leads to a higher risk of implant and abutment fractures and recommended the use of native abutments.
- Different key widths of the prosthodontic tools
- Incongruence of the geometries of screw head and bearing surface in the structure
- Deviations in design and geometry of a third-party abutment at the implant connection site
- Different cone angles for implant and third-party abutment
- Shortened hexagonal socket in the design of the third-party abutment
- Third-party prosthesis screws with a different design
- Lack of torque transmission
- Screw loosening
- Undesirable transfer of load to the implant
- Positive effects of the platform switch in the implant design are not used in prosthodontics
- Niches may develop resulting in an increased risk of bacterial colonization
- No fit between implant and abutment in subcrestally placed implants
- Stress peaks and incorrect loads can damage the implant
- Risk of bone loss increases due to crestal overloading
- In joints that are not firmly fit, there is a risk of pumping effects and bacterial ingestion
- Low transmission of force with thrust distribution forces
- Insufficient anti-rotation protection of the abutment
- Inadequate fit
- Predetermined breaking point
- Insufficient torque transmission
- Torsion in the screw body
An in vitro study confirms the results of this study. By combining individually milled abutments of a third-party supplier with different implants, significantly higher clefts could be observed in the implantprosthodontic interface than when using original abutments (de MORAIS ALVES DA CUNHA et al., 2012).
In another in vitro study, major differences in fit and inaccuracies of fit were observed between titanium abutments of different manufacturers, when fitted on the same implant (MATTHEOS et al., 2017).
SUI et al. (2014) reported that in the implant-andabutment system, the preferred site of a fatigue fracture depends on the material properties of the components. If the material properties of implant and abutment are the same, fatigue fractures are more likely to be observed in the area of the screw, while if the material properties differ, the respective susceptibility to fracture of the material is decisive. Thus, individual abutments made of zirconium oxide that do not match perfectly, if fitted on titanium implants, the micro-movements did not lead to fractures of the prosthesis screws, but rather to an increased susceptibility to fractures in the area of the abutments.
The information about the nature of the implantprosthodontic connection and the resulting micromovements due to inaccuracies of fit and their biological effects given in the scientific literature is partly contradictory.
The results of a recent systematic review show that heavy stresses are transmitted to the bones if the fits of the abutments are inadequate However, contrary to expectations, these unsuitable conditions of stress and the marginal gap formation do not have biological consequences such as crestal bone loss and / or a negative influence on the osseointegration of the implants. In fact, technical complications such as fractures of the prosthesis screw were observed (KATSOULIS et al., 2017).
In addition to an inadequate stress transfer to the crestal bone, another problem that arises as a result of fit inaccuracies at the implant-prosthodontic connection site is the bacterial colonization of the micro-gap and this can lead to biological complications.
The material properties of the components play a crucial role in the interaction of the components of an implant system (SUI et al., 2014).
To avoid complications such as fatigue fractures within the implant-prosthodontic restoration, manufacturers of implant systems perform extensive regulatory examinations and tests, in which the implant, abutment and screw are always tested until they break (ISO 14801). Even within an implant system, varying material properties of the components can lead to measurable deviations in the developmental phase, the occurrence of which is taken into account in the development and testing of the implant systems by means of design optimizations.
In a recent in vitro study, an implant type was screwed to third-party abutments made of zirconium oxide, titanium and gold. In abutments and prosthesis screws discrepancies and inaccuracies of fit were found between the different material groups of the abutments as well as within the material groups (FOKAS et al., 2018). In another in-vitro study, major differences in fit and inaccuracies of fit were observed between titanium abutments of various third-party suppliers, when fitted on the same implant (MATTHEOS et al., 2017). The increased susceptibility to fracture of zirconium oxide abutments with poor fit has been described in another in vitro study (SUI et al., 2014).
Screw loosening between implant and abutment leads to a prosthodontic failure, particularly in the case of cemented intermediate implant structures. Therefore, for the implant-prosthodontic treatment to be a success, an appropriate pre-stress (Preload) is a mandatory requirement when fixing the prosthesis screw.
The material of the prosthesis screws is of great importance for the generation of the appropriate preload when fixing the abutment on the implant.
If the preload is too low, it causes a loosening of the prosthesis screw, while too high values often end up in screw fractures (DOOLABH et al., 2014).
When using third-party abutments and their prosthesis screws on an implant, the risk of technical complications in a prosthodontic restoration is very high. Due to various reasons, such as the patient's change of location or the so-called health tourism, the prosthesis screws that originally belong to the implant end up being used in prosthodontic third-party abutments, resulting in poor adhesion. In addition to the question as to whether the material properties allow a long-lasting function, the fit of the screw’s bearing surface in the abutment is another aspect. For these second generation combinations of original and third-party components there are risks for technical and biological complications that are unpredictable.
The option of using third-party components instead of native original components in implant-prosthodontic restorations initially provides a more cost-effective solution. Whether these options are comparable to the original components of the implant system with regard to quality and safety, will only become apparent with long-term observations (Fig. 3).
On careful consideration of the currently available evidence of technical complications, it should be noted that the use of third-party components in systems with existing system-inherent inaccuracies of fit is more likely to result in further deterioration of fit.
Regardless of previous considerations when using third-party prosthesis alien to the implant system, experimental studies have shown that, even between original abutments and implants of the same system, the fit may not have the required precision due to limitations during the manufacturing process (ALVES, et al., 2016, LALITHHAMMA, et al., 2014, ZANARDI, et al., 2012). Surface defects can occur during the fabrication of implants and abutments, adversely affecting the fitting and this can contribute to increasing the microgap (LOPES, et al., 2018). Positioning errors are possible due to manufacturingrelated rotational tolerances causing a faulty fixation of the abutment and ultimately a less precise fit of the prosthodontic superstructures (Nicoll et al., 2013 SEMPERVIRENS-Hogg et al., 2013).
From a legal perspective, the use of copy cats is perhaps questionable. A ruling of the Frankfurt district court in 2012 (Az 2-03 O 84/12) confirms that components from different suppliers cannot be combined without a special Certification of conformity. Accordingly, in the opinion of the court, due to the limited conformity assessment a curative treatment using third-party components or copycats with system parts from other manufacturers may not be carried out.
Based on the current studies, it can be seen that supposedly identical components from third-party providers are primarily associated with an increased risk of technical complications. An increased risk of biological complications is currently unclear, but cannot be ruled out.
If follow-up care is required, the legal liability considerations should be taken into account. If third-party components are used, no warranty can be given, which leads to an increased cost. Therefore, careful consideration should be given to the extent to which copycats are a substitute for matched, quality-tested and clinically proven original system components, and whether they are ultimately worthwhile. This decision should always be made with the patient's involvement and after his clarification in the form of an informed consent.
The critical importance of the fit and the interaction of original components can be clearly demonstrated at prominent points.
- The Original Semados® prosthodontics have a precisely fitting screw seat in the abutment.
- The implant has an integrated Platform Switch in the shoulder area, and the original prosthodontics are tuned to it, thus bringing about the complete. Platform Switch.
- The original Semados® prosthodontics with the hexagonal guide inside the implant have a precisely fitting and symmetrical seat for the best possible mechanical properties.
- Third-party prosthodontics have significantly different cone angles for the screw seat and the screw head of the prosthesis screw.
- The design geometry of the third-party components with the much larger diameter in the area of the integrated Platform Switch does not use this to its advantage.
- The third-party prosthodontics have unequal gaps on the right and left of the hexagon inside the implant.