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30 Sep 2015 | Australasian Dental Practice

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The very definition of synergy

By Dr Stefan Holst

Research Implant Failures

Nobel Biocare doesn't develop individual products. The company develops entire solutions that provide fully functional, natural-looking, long-lasting results. In order to secure long-term clinical performance, safety and cost-efficiency for everyone involved in the treatment process, each and every Nobel Biocare component has been designed to fit and function perfectly with related components. Together they produce a finely tuned system.

When assessing any implant-supported restorative solution for a patient, one has to keep in mind that the entire system under consideration is only as strong as its weakest link.

The performance of each specific component depends not only on the quality and design of the component itself, but also on its interface with the rest of the restorative system.

Consequently, each component should not be evaluated on its own. Clinically relevant conclusions can only be reached when a component is tested within the system of which it is a part.

Nobel Biocare therefore conducts testing and research not only on individual components such as implants, abutments and screws - and how they work together - but also on the entire system, which they collectively define.

Nobel Biocare study systems from their initial design to long after delivery to the end-user, the patient. We develop and scrutinize engineering and manufacturing processes; and we carry out quality assurance, clinical research and post-market surveillance. Only with this approach can we be sure that the system will function safely and reliably for many years to come.

Parameters that influence long-term performance

Computerised simulation tools, such as finite element analysis (FEA) and biomechanical testing in the laboratory have served to identify parameters that can impact the performance of an implant system. These parameters include joint compression (the force that acts at the implant/abutment interface under loading conditions), preload (the tensile force keeping the components together) and the friction coefficient (which depends on the surface materials that are in contact with each other).

Other significant parameters include the force that the patient exerts on the system by chewing (masticatory force) as well as the length of the contact between the abutment and the implant and - when using a conical connection implant - the angle of the abutment. A small change in any of these parameters - even one not visible to the eye - can lead to extreme load and stress conditions that result in system failure.

Precise fit for joint stability

The interface between implant and abutment is critical for joint stability. Manual adjustment of a cast or the use of a substitute abutment can alter the contact angle and contact length. Such an undefined contact situation entails a degree of risk for the patient that is difficult to predict, much less manage.

Furthermore, in vitro force application to an implant-supported prosthesis may additionally exacerbate such misfit. Consequently, using an abutment designed and engineered by Nobel Biocare to match the implant is crucial for system performance. It not only affects the fit of the restoration on the implant itself, but may also have an impact on performance-relevant parameters.

Preload, the force that holds the components together

Preload is defined as the tensile force created in the clinical screw as the result of screw tightening. It is generated by the application of torque to the screw, although only a fraction of the torque force is stored as preload, while a much larger percentage is spent on overcoming friction.

To account for this major loss of torque and to ensure that the system is sufficiently held together, the screw has to be inserted at the recommended torque. Fully manual screw insertion is likely to result in lower torque and, consequently, suboptimal preload.

Insufficient preload leads to increased relative motion between the system components, which can contribute to screw loosening and/or component failure. Conversely, preload values that are too high can result in component fracture.

Optimized to the last detail

Nobel Biocare abutments are delivered with a dedicated clinical screw that has been optimized for the implant-abutment system of which it is a part. Depending on the abutment, connection type and platform size, screws come with or without a surface coating. The absence or presence of the coating and the coating type all impact the preload. For example, diamond-like carbon (DLC), a coating for screws marketed under the TorqTite brand, shows higher preload values compared with screws that have a standard titanium surface. Nobel Biocare provides an appropriate screw type for each and every implant-abutment connection, ensuring a tight and stable fit for long-term performance.

Avoid substitutes, minimise patient risk

When you use substitute components, the parameters governing system performance are no longer controlled. Take maximum joint compression - which defines the load that the implant collar can bear - as an example: A substitute may result in a force that is higher than the allowed maximum, causing the implant to fracture.

To prevent such catastrophic results, the peak forces have to be distributed in a controlled way. This can only be achieved by using high-quality, precision-manufactured components that have been designed and tested both individually and as part of the system for which they have been designed.

About the author

Dr Stefan Holst is Global Head Research, Science and Regulatory Affairs at Nobel Biocare in Switzerland.

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