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Beaming Toward Fully Digital Dental Laboratories

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BEAMING TOWARD

Fully Digital Dental Laboratories

How Cone Beam Computerized Tomography is revolutionizing dentistry.

Story and photos by Mark C. Jackson, RDT

Much the way CAD/CAM technology has stolen the hearts and captured the imagination of dental technicians, cone beam computerized tomography (CBCT) has revolutionized the way dental professionals view the patient's head and neck structure.

CBCT uses an image capturing technology that differs from conventional CT scanners. Instead of lying down, with a CBCT the patient is usually standing or seated. The data is captured in what is called a voxel or volume element. Patients are exposed to considerably less radiation than during a traditional CT. Also, the equipment is usually less cumbersome and less expensive than those found in a hospital or radiological laboratory.

All of this has made using CBCT technology more practical for dental professionals. Today, the machines can be placed in dental practices and dental radiological suites. But make no mistake, Cone Beam Computerized Tomography is not a simplified version of well-known medical technology. CBCT units are uniquely qualified for dental applications, while still providing data useful to other specialists and medical personnel. In fact, depending upon the available field of view, CBCT images are sometimes used by plastic surgeons and ear, nose and throat specialists.

Acquiring, manipulating, compiling and extrapolating massive amounts of data, CBCT scanners require sophisticated and powerful computers. However, once the data has been reconstructed into sensible volumes, a number of diagnostic functions can be performed. Many of these functions are important to dental technicians and can even be integrated into other newly established laboratory processes and CAD/CAM devices.

In some countries, dentists are not permitted to own CBCT scanners. Even where it is legal for dentists to own the CBCT scanners, the cost of purchasing the equipment and the special requirements for installing and operating the equipment may make private ownership prohibitively expensive.

In the U.S., state dental boards differ on their laws regarding dentist and dental laboratory ownership of CBCT scanners. Some states allow nondentists (such as x-ray laboratories) to own and operate dental CBCT systems. Others have laws that make it difficult for fully licensed dentists or radiologists to acquire a CBCT system. For example, Michigan requires a Certificate of Need (CON) to be in place before a dentist practicing in the state can purchase a CBCT system. CONs, which are common in the medical community but less so in dentistry, are designed to restrict unnecessary increases in healthcare costs and limit unnecessary health services and facilities based on geographic, demographic and economic considerations.

At Precision Ceramics Dental Laboratory CT Scanning and Implant Planning Center, we have the 3M Illuma, high resolution, broad field of view CBCT scanner. In order to own and operate this machine, we had to meet certain criteria:

1. Training, qualification and state licensing for personnel.
2. Our equipment is registered with the state of California.
3. Our facility had to be specially designed and inspected to meet shielding and safety requirements.
4. Staff has been issued monitoring devices (dosimeters).
5. We had to get a special professional (malpractice) liability insurance as well as a modified contract for product liability insurance.
6. Our legal team drew up liability waivers for patients and referring doctors.
7. We were required to review and update our HIPPA compliance.
8. Every scan we perform is reviewed by a board certified OMF radiologist.

This is new territory and an area of evolving precedent. Anyone considering anything that has to do with CBCT scanning or manipulation of the data should keep their eye on the laws as they pertain to this and review legal documents and insurance at least annually if not more frequently.

That said, CBCT technology is rapidly becoming the standard of care for certain procedures. In time, its use will become more widespread and it will influence the way dental laboratory technicians work. For this reason, it is important we understand the technology and how it will affect us. This article is an introduction to the fundamentals of CBCT technology. Further study will be needed if you choose to become professionally conversant on the subject.

Traditional Computerized Tomography acquires data by rotating the X-ray tube and image receptor around the patient. For each rotation, one cross sectional slice of data is acquired, which is comprised of about 1,000 images. The data slices are reconstructed into two-dimensional images, which are then stacked into volumes, creating the final 3D volume set.

Cone Beam Computerized Tomography imaging is genuine, 3D reconstruction technology. With CBCT, the X-ray tube generates a cone shaped field of radiation that is received and extrapolated using Flat Plane Detectors (FPD). This offers significant advantages over single slice, traditional CT scanning. CBCT images are acquired at a much higher rate because there is no re-adjustment of the tube and receptor system as the assembly is realigned for each new slice of data. Additionally, a thin beam of radiation applied over and over to acquire each slice of data during a traditional CT is inefficient and exposes the patient to a higher level of radiation than a single rotation with a cone shaped beam of energy. The exposure level from one CBCT scan is less than the annual environmental radiation a normal person experiences by a factor of 50 to 100.

Before we continue, a quick note about safety. There are three types of radiation exposure that can cause health problems for dental professionals. Primary radiation is the focused energy used to create the images captured on film or by a digital imaging receptor. Secondary radiation is any radiation that is scattered or deflected upon impact. It travels to all parts of the operatory or scanning suite. The third safety risk is not a type of radiation, but rather the cumulative effects of radiation exposure. When handled properly, radiation in a dental operatory or scanning suite is not harmful and the diagnostic benefits outweigh the risks for most patients. Because of the risk of exposure to secondary radiation and the cumulative effects of repeated exposure, it is important the operator is protected. At the very least, the equipment operator should stay six to eight feet from the X-ray tube, preferably behind a barrier such as an operatory or, if possible, a wall shielded with lead barriers or leaded glass. Editor's Note: Get more safety information on JDT Unbound at www.jdtunbound.com

CBCT scanners and other medical imaging devices generate large volumes of data that is grouped into data sets. These data sets were standardized in 1993 and given the acronym DICOM, which stands for Digital Imaging Communication in Medicine. DICOM files use the file extension .dcm.

Special software is needed to open and read DICOM files. There are some simple, free DICOM readers that allow the user to open and view non-compressed, raw DICOM files. However these free readers usually only read a small subset of the DICOM images. Other readers may open and allow viewing of single slices in a .BMP format. Most scanners come with a proprietary viewer allowing the clinician an easy way to quickly view images, adjust the contrast and magnify images.

More sophisticated DICOM software exists for specific applications, such as implant planning and the fabrication of surgical guides. These usually have features such as measurement tools, and implant library Hounsfield (bone density) analyzers and may even provide a list of surgical tools and implants needed to complete the finished case. Some of these software packages are sold and distributed by specific implant manufacturers. Other support multiple implant systems and surgical hardware.

Specific software exists for oral surgery applications that require diagnostic evaluation, documentation adn 3D visualization of planned surgical outcomes, including grafting and bone reduction guidelines. These specialized software packages bring a high level of accuracy to reconstructive surgery. Orthognathic surgery and tissue modeling capabilities are a powerful tool in predicting the outcomes of treatment that change the skeletal geometry. Impaced third molars with nerve involvement are frequent beneficiaries of this kind of imaging software.

There are a number of popular imaging software programs used to create cephalometric tracings, assessment of growth, treatment planning and outcome prediction using superimpositioning software. They are helpful in analyzing dentofacial deformitites as well as orthognathic and TMJ treatments.

DICOM images have other therapeutic applications such as airway assessment in treating obstructive sleep apnea, dual volume superimpositions such as models and impressions, or photgraphs. Some even export animated movie scripts using advanced graphical effects. Special software exists for exporting to rapid prototyping equipment. Radiologists use a number of template programs to generate radiology and pathology reports. Some software packages allow the user to stitch together multiple images from small field of view scanners into larger field of view images and perform virtual endoscopies.

Stereolithography and CBCT can be strong partners. Stereolithography allows the fabrication of physical replicas of 3D computer generated models using 3D printers. After the generation of a 3D rendition, software segments then file from top to bottom and then each slice of data is sent to a machine that fabricated the part slice by slice. The technology is mainly used for the quick fabrication of copings, partial denture frameworks and crown and bridge models in dental laboratories. It can be used to fabricate prototype bars before full scale fabrication from titanium or zirconia. The slice by slice fabrication technique found a strong marriage with the CBCT data for fabrication of anatomic structures, such as anatomical models and even custom made, biological grafting materials.

For surgical guides, stereolithography fabricates parts from a vat of photo-curing ploymer using a computer guided UV laser, as opposed to layer by layer resin jet printing. The most commonly used resins in medical applications is the stereocol resin, which is a medical grade resin which is FDA class VI approved for sterilization and use in the operating room. The finished surgical guides are assembled with stainless steel or titanium guide tubes before being sent to the surgeon.

Just as in other industries and medicine, software advancements will push the envelope of 3D imaging and data acquisition systems. The FDA is evaluating surgical navigation systems that use anatomical landmarks and precise measurements (similar to global positioning system) to guide the mechanical placement of implants, custom grafts and delicate nerve surgeries.

The day is coming when we in the laboratory will receive the DICOM files, merge it with data from scanned models or intraoral scans and use superimposition technology to overlay the patient's 3D photograph over their own CBCT generated skeletal framework. When combined with 3D digital reconstruction of the patients' temporal mandibular joint and condylar profile, we will be creating an anatomically specific, human articulator. A virtual patient in living color.

With developments like the Cone Beam Computerized Tomography scanners, only our imaginations can predict what will come next.

However, one thing is for certain: The shift will help continue the push from conventional analog dentistry to the realm of the fully digital dental laboratory.JDT

Cone Beam Applications

• Implants - Planning and site development
• Extractions: Helps determine location of nerves, sinus and roots
• Orthodontia: Jaw symmetry, configuration of roots and impaced canines
• Maxillofacial: Orthognathic surgery, fractures and jaw pathology
• Periodontics: Sinus augmentation, advanced grafting procedures and periodontal defects
• Endodontics: Canal measurements, additional canals and configuration of root canals
• TMJ/TMD: Detection of bony defects, asymmetry, spurs and condylar changes
• ENT specialists: Sinus and airway studies

SAY WHAT?

To communicate better with your dental clients about Cone Beam Computerized Tomography, knowing its specialized language is crucial. Here are some of the terms you need to know.

Cone Beam Computed Tomography (CBCT) - Uses as cone-shaped beam and digital processing to create a 3D image using a single rotation.

Field of View (FOV) - The size of the area to be examined.

Large FOV - Ideal for the examination of complete dentition, both TM joints and upper cervical spine or maxillofacial area with airways.

Medium FOV - Works best for the examination of the entire dental complex, including mental and mandibular foramen.

Small FOV - Used for the examination of single implant sites, planning third molar extractions, endodontics or localized dental problems.

Voxel - The volume element (voxel) is the smallest element of a 3D image. The size of each voxel determines the resolution of the image.

Digital Imaging and Communications in Medicine (DICOM) - The file format for images produced by a CBCT scanner.

Hounsfield units (HU) - A quantitative measure of the radiolucency of different materials. The amount of Hounsfield units changes according to the relative densities of various biological structures.

Radiation Dosage - Effective radiation dosages for CBCT scans are approximately 68 micro-Severts, less than half the level of exposure from a full-mouth series of radiographs.

Multiplaner Reconstruction - CBCT data is sorted into this format, which has three interactive views: the coronal (x-y axes), the sagittal (z-y axes), and the axial (x-z axes). Plane locator lines can be moved within each section, allowing scanning through the entire volume of information in the three planes.

Orthogonal Studies - A specialized study can be constructed using a perpendicular line in either a straight or curvilinear from when using the axial views.

Maximum intensity projections (MIPs) - Images that show the compilation of the entire volume of data and projects in the visualization plane with maximum intensity. The MIP gives the illusion of a 3D image and is the basis for 3D software applicaitons. This software renders the folume fo data in a format which can be manipulated as a single object and then rotated 360 degrees.

Stereolithography - Also known as rapid prototyping. Dental CBCT scans can be digitally transformed for creating stereolithographic models.

Beaming Toward Fully Digital Dental Laboratories

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DENTISTS

Precision Ceramics takes pride in fabricating quality laboratory products and services, delivered consistently, ON TIME and to your specifications.

CBCT SCAN

On-site Cone Beam CT scanner, complete radiographic services, implant planning assistance and surgical guide fabrication.

LABORATORIES

Ceramic copings & frameworks, implant services, and removable prosthetics. All delivered FAST, with expert technical support and strict quality control.

VETERINARIANS

25 years experience providing a full range of veterinary dental laboratory services, including orthodontic appliances, crowns and custom fabricated implants.