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Date: 19 October 2018
computerized tomography (CT) that enables dentists to take 3D images of patients  

Topic Name: computerized tomography (CT) that enables dentists to take 3D images of patients
Category: Design technologies
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Research persons: Shayne Kondor,Shannon Fatehi-Sedeh,Barbara Boyan.

Location: Georgia Institute of Technology :: Atlanta, Georgia 30332, United States


computerized tomography (CT) that enables dentists to take 3D images of patients

Researchers at the Georgia Institute of Technology are applying engineering expertise to the dental industry – a field that is often as much art as it is science.

For example, the Georgia Tech Research Institute (GTRI) is working on the next generation of cone-beam imaging, a type of computerized tomography (CT) that enables dentists to take 3D images of patients. These machines take two-dimensional X-rays in one-degree increments around the head to construct a final 3D image. Cone-beam imaging exposes patients to much less radiation than traditional CT machines – and provides far more information than conventional dental X-rays.

“One area that needs to be improved is contrast resolution,” says Jeff Sitterle, GTRI’s chief scientist and director of its biomedicine initiative.

“When it comes to medical images, contrast resolution is more important than spatial resolution because it shows the difference between tissue densities. For example, current cone-beam systems have a difficult time depicting the TMJ (temporomandibular joint) because it’s essentially a bone socket with cartilage meniscus between it.”

To bolster contrast resolution, GTRI is investigating advanced signal processing algorithms that its Sensors and Electromagnetic Applications Laboratory has developed for military radar applications.

Another goal is to take advantage of the rich information that cone-beam imaging offers. “Right now, dentists and oral surgeons use the images to make a diagnosis,” Sitterle notes. “We want to move beyond diagnosis to treatment planning and fabrication of restorations.”

For example, GTRI hopes to develop software to create drilling and surgical guides that show surgeons precisely where to attach a prosthetic joint, position the mandible or drill holes for implants. By incorporating virtual communication tools with imaging systems, oral surgeons, restorative dentists and orthodontists could work together and know what’s happening with a patient at various stages.

What’s more, digital data could be sent electronically to dental labs, eliminating the need for plastic molds and yielding more accurate restorations.

“Right now 80 percent of the problems associated with crowns and other restorations are linked to inaccurate impressions,” Sitterle says. “If you have voids that are larger than 5 microns, bacteria can get underneath and form decay, which is one reason many crowns fail and need to be replaced.”

Making a better impression

Another technology that could revolutionize restorations is rapid prototyping.

“Rapid prototyping is a type of manufacturing process that builds parts layer by layer in an additive manner,” explains David Rosen, a professor in Georgia Tech’s School of Mechanical Engineering and director of its Rapid Prototyping and Manufacturing Institute. “One big advantage is that you can make just about any shape that you want – which makes it ideal for dentistry.”

Rapid prototyping would also save time and money over current dental-lab fabrication, which requires many steps and a lot of manual work, he adds.

Although existing rapid-prototyping machines can’t make parts small enough for dental restorations, researchers in Rosen’s lab have developed a micro stereolithography (SLA) system for producing parts at the 10-micron range.

Originally developed for microelectromechanical systems (MEMS) technology and microfluidic devices, this micro SLA system could be adapted to dentistry. Rosen says: “In conventional SLA, the smallest feature size you could get would be about 100 microns. We’re working at an order of magnitude smaller than that, which is necessary to get the right features, size accuracy and surface finish required for dental restorations.”

Rosen is also working on a new inkjet printing technology for high-viscosity materials. He believes this technology could be used to apply aesthetic coatings to restorations – work that is currently done by hand.

Although such rapid-prototyping equipment initially would be used in dental labs, the ultimate goal is to have a machine in the dentist’s office. “The idea is to make restorations on the fly – in an hour or so – so patients don’t have to deal with temporary crowns – or repeat visits to the dentist,” Rosen adds.

Combating cavities

In addition to innovative manufacturing techniques, Georgia Tech is transferring aerospace technology to dentistry. Shayne Kondor, a senior research engineer in GTRI’s Aerospace, Transportation and Advanced Systems Laboratory, is developing a new measurement methodology that could lead to more durable dental fillings.

“One area that needs to be improved is contrast resolution,” says Jeff Sitterle, GTRI’s chief scientist and director of its biomedicine initiative.

Polymer filling materials tend to shrink when cured, which can lead to several problems, such as causing the tooth to crack or bacteria to penetrate the tooth, causing the repair to fail.

Researchers usually study shrinkage by measuring changes in the volume of a drop of material, cured outside of a cavity. Yet this approach doesn’t provide a comprehensive picture of what happens in a tooth cavity, says Kondor, who is collaborating with Dan Chan, a doctor of dental surgery and professor at the Medical College of Georgia.

“The form of the cavity preparation has a lot to do with how the filling material adheres to its floor and walls,” he explains. “The curing light also has an effect on shrinkage. If you don’t replicate that, then you’re not going to see exactly how the filling material flows.”

In response, Kondor has developed an optical measurement system to study shrinkage. He first simulates a cavity by drilling a 5-millimeter hole in a plate of aluminum and then pours filling material into the hole. Next, the filling surface is speckled with minute carbon particles, which provide the necessary contrast for optical measurement under a microscope, and a blue light is used for both curing and illumination. By measuring particle activity throughout the curing process, he can determine deformation fields on the surface. The result provides a “3-D movie” of the filling material’s behavior.

“Most practitioners are aware of the shrinkage problem, but don’t understand its magnitude,” Chan observes. “Our method will help them better visualize shrinkage – we can show it in real-time media and also calibrate the force and direction of shrinkage, which is unique.”

In addition to helping dentists find ways to prevent and remedy shrinkage, the optical measurement system will help manufacturers design better materials, Chan added. In fact, the researchers recently signed an agreement with an industrial partner to evaluate a new filling material.

This measurement approach applies “particle image velocimetry,” an aerospace technology used to visualize air flow over aircraft wings and to study how air loads cause an aircraft’s wing structure to deform over time. “The technique adapts easily to dentistry because shrinkage is really a liquid-flow problem,” Kondor explains. “Like ice freezing, the filling material is first a liquid that turns into a solid.”

Although Kondor is first studying shrinkage at the surface level, he also plans to take measurements in a cross-section simulation. By determining how filling material flows inside of the cavity preparation as it cures, researchers can see which cavity preparation shapes cause less stress and ultimately extend the life of the filling.

Kondor is also applying aerospace technologies to improve dental air-abrasion jets that remove tooth decay without the need for anesthesia.

Dental air abrasion jets use aluminum oxide particles instead of a drill to remove tooth decay. But existing tools have drawbacks preventing their widespread use among dentists. “For example, there is no feedback control to adapt the particle stream for optimum removal of decay,” Kondor explains.

So he is experimenting with passive and active flow-control techniques to design an autopilot system for a more precise, effective air-abrasion tool.

This research has led to another project – a single dental tool that will handle all conventional procedures, including cavity removal, fillings and preventive treatment. Such a tool would eliminate the need for multiple drills, hand instruments and restoration materials. Besides saving time and money for general practitioners, the tool could help dentists in rural areas and the military perform procedures more easily.

Biomaterial development

Understanding how cells interact with materials, such as those used for dental implants, is a key focus of research in the laboratory of Georgia Tech Professor of Biomedical Engineering Barbara Boyan. Her 20-plus years of research in the field is helping Boyan and her research team develop biomaterials for use in regenerative medicine, specifically craniofacial and maxillofacial plastic surgery. Her work is funded by the National Institutes of Health (NIH) and medical device companies, including DENTSPLY and Institut Straumann AG, a dental implant company in Switzerland.

“Our research team is well known for increasing the understanding of the ways in which cells interact with materials used for dental implants and how those materials can affect the healing of bone around the implant,” notes Boyan, who is also deputy director of the Georgia Tech/Emory Center for the Engineering of Living Tissues.

“Because we’re interested in this process, we’re also involved in developing a new class of materials called biologics,” she adds. “These are materials used for bone grafts, for example, and also proteins that regulate the rate at which cells heal around an implant.”

In addition, Boyan and her colleagues have investigated the use of biologics for reconstructive surgery in other parts of the face, such as the cheekbone area, and the reconstruction of cartilage in the ears and nose.

Recently, she began collaborative work with the craniofacial plastic surgery department of Children’s Healthcare of Atlanta (CHOA). A medical resident from CHOA is working in Boyan’s lab, applying her research findings to the development of new materials for reconstructive plastic surgery in children. Researchers are also collaborating on research to find the causes of birth defects in the jaw.

Boyan also recently received a four-year NIH grant to study cell-surface interactions with materials and the mechanisms involved in healing. She is collaborating with Professor of Materials Science and Engineering Rina Tannenbaum.

Among the research milestones in her dental-oriented studies, Boyan cites:

  • The discovery in the past year that cells from males and females respond differently to biomaterials, which has implications for treatment and recovery.

  • The finding that cells can sense the shapes of things at the micro and nano levels. Their responses to these shapes can affect other cells nearby, which can, in turn, affect how fast and how well tissue will heal. Researchers want to understand why this phenomenon occurs and hope that information will improve the design of dental implants.

    Health and ergonomics

    In addition to improving dental equipment and techniques, GTRI is also investigating health issues.

    For example, nanoparticles are now being used in some dental composite and filling materials. Nanoparticles raise concerns for both patients and dentists.

    “When it comes to nanotech safety, few health studies have been done, and the ones that have been conducted aren’t interdisciplinary,” says Charlene Bayer, a principal research scientist at GTRI.

    In addition, existing research has looked at how humans respond to ultra-fine atmospheric particles, which are not the same as engineered nanoparticles, Bayer notes.

    “These particles may be similar in size, but there’s a huge difference,” she says, adding that ultra-fine particles are heterogeneous. “They have different surface characteristics, which makes them more difficult to dissolve in the body. In contrast, engineered nanoparticles are homogenous and designed to be highly reactive. That’s why they work. Yet the very characteristics that help nanoparticles perform could also make them dangerous to people and the environment.”

    Designing instrumentation to measure engineered nanoparticles is one area where GTRI can help. “Besides possessing expertise in nanotechnology and environmental sciences, we have experts in building and integrating systems,” Bayer says. “And when it comes to understanding nanoparticles, that holistic view is critical.”

    Ergonomics is becoming another hot button as more dentists and dental assistants complain of musculoskeletal problems and repetitive stress disorders like carpal tunnel syndrome.

    “A lot of these problems can be traced to the design of dental tools and dentists’ posture while using them,” says Brad Fain, a senior research scientist in GTRI’s Electronic Systems Laboratory. “This is an area where GTRI can really contribute. Because of our work in other industries, we understand the importance of designing tools that reduce grip forces, awkward wrist postures and joint vibrations.”

    GTRI also can improve computer interfaces so emerging technology is easier to use. “It’s not enough to create innovative technology,” Fain says. “You also must consider the cognitive aspect of human factors – how to organize information and present it to people in a format that helps them increase efficiency and reduce error rate.”

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