Researchers: Davide Crivelli (PI, Mechanical Design, Diamond Light Source – previously Cardiff University), Taslima Begum (Design, Cardiff Metropolitan University), Wayne Nishio Ayre, (Biomaterials, Cardiff University), Mark Eaton (Composite Materials, Cardiff University), Carly Harwood – Osteocare Ltd OC, David Thomas (Dentistry, Cardiff University)
Abstract:
Three million dental implants are placed every year in the U.S. and this number is increasing by 500,000 a year. Approximately 7% of these implants fail due to poor bone growth, which will subsequently require multiple surgeries to fix. This negatively impacts on patient quality of life, resulting in poorer dietary options, reduced self-esteem due to aesthetics, and additional costs.
During implant fixation, surgeons rely on experience and/or manufacturer guidelines to judge how tight the implant is. A small amount of cracking in the bone is needed to promote the growth of new and healthy bone around the implant. However, overtightening can cause unwanted damage to the bone tissue around the implant and impair bone healing; while under-tightening can cause the implant to move when chewing. Moreover, the different bone densities across patients, or even within a single jaw bone, can make it very difficult to judge the optimal tightening force required.
The aim of this work was to develop a new tool which listens to the implant as it is screwed into the bone. This will allow the surgeon to judge when sufficient cracking has occurred and, thus, whether the implant needs to be tightened any further. For this, we use a technique called Acoustic Emission which uses specialist sensors to listen to the inaudible cracking sounds made during the implantation process.
Figure 2: “pulling teeth”: the implant is being pulled out of the synthetic bone at Cardiff School of Engineering on a tensile testing machine.
In parallel, we conducted a user-centred design exercise where we asked both practitioners and implant manufacturers targeted questions in order to establish which characteristics of an implant tool are most important, and how they imagine future tools to be. We also arranged a focus group where experts were able to discuss and share their ideas about the tool, and used brainstorming sessions, journey mapping and creative activities leading to a co-creation workshop. Together, these allowed us to design a product around the requirements of the users from the outset.
We developed a prototype which allows measurement of how much noise an implant makes during fixation and how tightly the implant is in place. We fixed implants using different levels of force and then extracted them to measure how securely they were fixed. We used different densities of a widely-used synthetic bone-like material for this work.
Through this work, we discovered that there is a good relationship between the stability of an implant and the level of sound an implant makes during fixation. We will use the user-centred design information gathered from the questionnaire and the focus groups to build a near-market prototype, which will be used on mandible models, in addition to more realistic settings, to allow us to take development to the next stage.