MANDIBLE RECONSTRUCTION PROJECT

 

3D rendering of jaw implant model with nerve placeholder.

 

PROJECT PARTICIPANTS

• Prof. Russ Jamison, Materials Science and Engineering , UIUC
• Michael Goldwasser, MD, DDS, Carle Clinic, Urbana, IL
• Benjamin Grosser, Director, Imaging Technology Group, Beckman Institute
• Janet Sinn-Hanlon, Biomedical Imaging Specialist, Imaging Technology Group
• Dr. Joseph Cesarano, Sandia National Laboratories

Read the official press release

Watch an Award-Winning animation that illustrates the process

SUMMARY · BACKGROUND · THE PROCESS · THE IMPLANT · THE NEXT STEPS · CONTACT

 

SUMMARY

 

The Mandible Reconstruction Project is a unique, ongoing, multi-disciplinary effort involving the University of Illinois College of Engineering, the Beckman Institute for Advanced Science and Technology, Sandia National Laboratories, and Carle Foundation Hospital to develop an alternative approach to bone replacement--one that obviates the bone harvest surgery without diminishing the superior clinical outcomes associated with autografting. In completing the first phase of the project, the team of collaborators have developed an integrated workflow from surgeon to modeler that yields a perfectly-fitting custom device that demonstrates the feasibility of this approach in a real clinical setting.

 

BACKGROUND

 

The replacement of bone lost through disease or injury presents a continuing clinical challenge. The current "gold standard" is autograft bone, i.e. bone taken from another site in the body. The surgical procedures for the harvesting of such bone can result in complications that are "minor" (hematoma, temporary sensory loss, acute pain); or "major" (permanent sensory loss, chronic pain, infection). Complication rates exceeding 30% have been reported for autograft harvesting from the iliac crest of the pelvis, a common source for autograft bone. The alternative to autografting is implantation of cadaver bone. From a clinical perspective this is an even less attractive option which increases the complication rates associated with autografting and adds the risk of disease transmission to the procedure.

 

THE PROCESS

 

Using the case of a 73 year old female who has experienced severe bilateral bone loss in the mandible, materials scientists, engineers, medical 3D artists, computer-aided designers, and the patient's attending physician created a workflow by which a synthetic ceramic scaffold was designed, and fabricated specifically for this patient. This workflow involved true collaboration between all parties involved, as the surgeon sought to transfer his intuitive knowledge of the precise structure of the implant to the 3D modelers at Beckman, who then in turn transferred their work to the fabricators of the implant at Sandia.

 

2D CT Scan Image Data (left) and Isolated Mandible (right) in Volumetric 3D Reconstruction

 

This process required ITG to extract the necessary 3D information from the 2D image slices of the CT scan. The surgeon then worked with with ITG in defining the boundaries for the implant and making accommodations for an existing nerve. ITG worked with CT technicians at Carle to ensure the accuracy of the CT data measurements and to establish that the extracted model was true to the original data.

 

Sketches by Sinn-Hanlon and Goldwasser defining the path of the inferior alveolar nerve (left) and the boundaries of the implant (right).

 

ITG then created a computer-generated 3D model whose bottom surface precisely fit the eroded mandibular surface that it would rest on. A canal was built into the ventral surface of the implant that was large enough to accommodate the exposed nerve, but would leave an adequate amount of contiguous surface on either side for jaw strength and the insertion of screws to anchor the implant into the mandible. The top surface of the implant was modeled with the intent of restoring the natural shape of the jaw and providing a surface that would support dentures. The two surfaces were welded together to complete the model for the implant.

 

The final precise-fit undersurface of the implant with nerve accommodating canal (left)
and the final model blended onto the new top surface of the implant (right).

 

Once the implant was created, the model was 'printed' use ITG's rapid prototyping machine so that the researchers could evaluate the fit of the implant with a physical model. Evaluation of these models concluded that the fit was very precise and well within the tolerances required. The 3D computer model was then e-mailed to Sandia, while physical prints of the jaw and implant for shipped for reference.

 

The final implant model (left) and a physical 'print' of the jaw and implant model (right).

 

Once received at Sandia, they proceeded to investigate methods for fabrication of the object using their patented process called 'robocasting'--a technology similar to the rapid prototyping machine used by ITG, but unique in its ability to work with various speciality materials. In this project, the device is used to create scaffolds of a substance primarily made up of hydroxyapatite--a substance chemically identical to those found in human bone. These scaffold structures, developed by Dr. Jamison, are unique in their ability to withstand the extreme forces that a bone implant would undergo.

 

The robocasting device is used to create a block of scaffolding material that can later be milled to a precise shape. The block is temporarily embedded in wax to provide strength to the object during the milling process.

 

The milled implant from a wax-embedded scaffold of hydroxyapatite.

 

Once the device is milled, the wax is melted out, and the implant is finished. The porous structure of the scaffold allows bone to grow into it, providing the future basis for the growth of new bone in a patient.

 

The final implant scaffold after the wax has been removed.

 

The underside of the final implant scaffold, showing the modeled canal for the nerve path.

 

The final implant scaffold fit tested in the previously 'printed' jaw.
Exterior side (left), and interior side (right).

 

Finally, during the patients' previously scheduled autograft procedure, the implant was sterilized in an autoclave and inserted into place for fit testing. The surgeon proclaimed the implant to 'fit like a glove'.

 

The final implant scaffold fit tested in the patients jaw.

 

THE IMPLANT

 

In order for an implant designed and fabricated in this way to be available for general clinical use, a number of important questions must be answered. One of these questions relates to biocompatibility - will the body react adversely to the material and will the device serve its intended function? The choice of hydroxyapatite was made in part because of its successful use in a number of clinical applications. Its long-term compatibility with body tissue in these applications is now well-established. Its chemical similarity to the natural mineral of bone makes it an attractive candidate for our research.

The task of developing a device for bone replacement in the mandible carries with it the additional requirement of high strength. The pressure transmitted through the teeth to the mandible during chewing can exceed 400 pounds per square inch. Consequently we have designed the scaffold for this application to exceed the strength of the natural bone it replaces. Current research is directed toward understanding the change in strength that occurs as the scaffold is broken down over time in the body and is built up by ingrowth of new bone tissue. The purpose is to ensure that adequate strength is maintained throughout the period of bone remodeling.

For laboratory testing we use model scaffolds like that shown here in
order to precisely control the conditions. The diameter of each rod in
this image is approximately 300 microns.

 

The encouragement of ingrowth of bone and vascular tissue into the scaffold is in fact an essential function of the device at the microscopic level. It is known that bone cells attach to hydroxyapatite surfaces (a property known as “osteoconductivity”). Our research is directed to understanding the ways in which these cells migrate and attach to the scaffold. We do this by studying scaffolds of various designs immersed in “simulated body fluid” in the laboratory. An example is shown below.

 

Test scaffolds are seeded with bone cells in the laboratory
using simulated body fluid. The cells in this picture are too
small to be seen.

 

We modify the surfaces of the scaffolds during fabrication to influence these “cell-scaffold” interactions. The example shown below demonstrates that bone cells attach to the scaffold surfaces in distinctive ways according to surface characteristics of the scaffold. Of particular interest now is the influence of micron-scale porosity that we create during fabrication on cell attachment and function.

 

Bone cells attach to scaffolds by extending cell processes to the surface.
In this case the processes engage microscopic pores in the surface
after three days in simulated body fluid.

 

THE NEXT STEPS

 

A good deal of research remains to be done before these devices will be available for clinical use. While our initial findings have been encouraging, the rigorous process of establishing the safety and efficacy of this device will require a number of years of laboratory and clinical research and substantial investment. It is our objective to develop a design approach that provides to the surgeon customized synthetic bone scaffolds that rival the healing and remodeling results now achieved with autografting. And one that provides to the patient safe and rapid healing without the risk and discomfort of the additional surgery that autografting requires.

 

Contact

 

For further information regarding the project, please call Prof. Russ Jamison at 217-265-8048, or email the project team.

 

 

All images are copyrighted. Please contact the group at Mandible for permission

to use them, and/or for higher-resolution images for print.