Implants, restaurations and bone replacement material

Researchers at Fraunhofer IKTS develop novel material concepts and shaping technologies for oxide ceramic materials and silicon nitride for dental and orthopedic applications. All developments can be utilized through prototypes or targeted scaling up to industrial scale.

The basis of the developments is the in-depth understanding of microstructure-property relationships in the material systems Al₂O₃, ZrO₂, ATZ, ZTA and Si₃N₄. From this, options for microstructure design (preparation parameters, doping, specific heat treatment, etc.) are derived with the aim of optimizing mechanical, physical, chemical and biological properties. In addition to the consideration of mechanical properties, the targeted design of the surface using additive or near-net-shape methods plays a central role in improving ingrowth behavior and cell adhesion. Cost-intensive post-processing is thus minimized.

In particular, the shaping processes of uniaxial pressing, (pressure) slip casting, ceramic injection molding and additive processes are the focus of technology development. This allows complete coverage of the spectrum from individual implants to mass production of standardized components. For example, individual and AI-generated finger joint implants were produced using slip casting and additive methods, and standardized abutments were produced using injection molding.

One focus for dental and orthopedic implants made of oxide ceramics is on new concepts and technologies for structuring the ceramic surface in the shaping process, so that post-processing of the sintered ceramic is no longer necessary. A special TZ3Y ceramic is available for anatomical dental restorations, which exhibits increased translucency and wear resistance and no hydrothermal aging. In order to meet the esthetic requirements for crowns and bridge frameworks, the dental restorations are coated with a lithium silicate spray, which forms a very strong bond with the TZ3Y framework. The production of fine-grained dispersion ceramics (ATZ, ZTA) is also part of the range of services.  

Human bone consists of numerous macro-, meso- and micropores with a diameter of 100 to 700 μm. This porosity is particularly important for the stability and ingrowth of cells into the bone. The researchers at Fraunhofer IKTS use various replica and spacer techniques as well as direct foaming processes to produce bone replacement materials with defined porosities.

The replica process is used to produce open-cell ceramic and metallic foams that have a spongiosa-like structure, which is almost identical to the natural bone structure of humans. They are particularly suitable as a replacement material for bone defects because the body's own bone cells and blood vessels can grow through them and integrate them completely. Due to this high level of osteointegration, patients can heal quickly.

The choice of material and the structure of the cellular ceramics and metals can also prevent stress shielding. The implant stiffness is adjusted – particularly in the transition area between the full implant and the bone – in such a way that stress shielding of the bone by the implant is avoided. This improves the bone ingrowth behavior and avoids a cause of later implant loosening. The risk of revision operations, which represent a major burden for the patient, is reduced.

Furthermore, Fraunhofer IKTS and IFAM Dresden are jointly developing bone replacement materials made of metal foams with high biocompatibility. The materials currently used are titanium and its alloys, 316L stainless steel and tantalum. The results of the titanium foam developments in particular suggest that the implants are highly biocompatible with high rigidity and strength. Preclinical tests have shown that the titanium foams can be completely ingrown by the bone within six months and that the bone attaches itself directly to the surface of the titanium foam bars. This results in very good bonding properties and load-bearing capacity.

In addition, ceramic bone replacement materials made of hydroxyapatite and resorbable tricalcium phosphate are also being developed. A unique type of direct foaming is known as freeze foaming. It is used to produce potential bone replacement material from body-related materials such as hydroxyapatite or tricalcium powder [Ca₅(PO₄)₃(OH), Ca₂(PO₄)₃] and thus also allow the artificial material to be broken down and the body's own material to be rebuilt. Bioinert materials, such as Al₂O₃ or ZrO₂, are also conceivable for use in long-term stable implants. Fraunhofer IKTS evaluates and uses new process approaches such as additive manufacturing to create patient-specific biomimetic bone or tooth structures.