October 2010, Volume 6, Issue 9
Published by AEGIS Communications
Using cone-beam computed tomography and virtual surgery to improve implant diagnostics, planning, and surgical placement.
Dental implants are routinely placed to stabilize and totally support a prosthesis for a missing tooth or teeth and are positioned into the remaining native bone for support, resulting in a functional and esthetic outcome.1-5 Lost or missing teeth in either jaw will result not only in loss of function and esthetics for patients, but also loss of gingival and supporting bony tissues.6 The lack of some or all teeth could be congenital or caused by a disease process. The results are usually the same-bone deficiency, which might not be limited to alveolar bone.
Normally the alveolar bone supports the teeth and also the gingival tissues. Bone loss or atrophy also can be associated with the underlying basal bone. The loss of alveolar and or basal bone with soft tissue changes can be associated with replacement complications for the missing tooth or teeth, especially when implant dentistry is considered.6 In the case of the mandible, if all teeth are lost, lack of bony support is associated with instability and decreased function of the complete denture.7 When less than adequate bone position or support remains, grafting is considered essential for a functional and esthetic implant/prosthetic result. The prosthetic replacement determination and implant placement planning involves the need for 3-dimensional (3-D) presurgical prosthetic evaluation with either medical-grade computed tomography (CT) or in-office dental cone-beam computed tomography (CBCT) with implant treatment-planning software.8-10
One of the greatest advantages of pretreatment planning software is the virtual surgery that precedes the actual clinical treatment and eliminates the need for last-minute decisions. The actual surgery time is usually decreased because all surgical steps, including the surgical guide and patient acceptance prosthesis, are preplanned and the results are routinely consistent with the treatment planning.10 Thus, virtual treatment planning and computer-generated drilling guides benefit the patient by allowing flapless surgery, reduced surgical time, reduced discomfort and swelling, and faster recovery time.3,11,12 It aids the dentist by reducing chair time, stress at the time of surgery, and potential surgical complications. It also facilitates an accurate means of placing dental implants according to a predetermined restoratively driven treatment plan.13-15Cases can be treated as a two-stage, single-stage with healing abutments, or final prosthesis.
The Basics of CBCT Imaging
Using DICOM files of specific anatomical sites of the oral and maxillofacial structures, CBCT images provide high-definition, 3-D views at reduced cost to the doctor with less radiation to the patient. They are used in implant planning and placement, orthognathic surgery treatment planning, and 3-D root canal verification. They are also key in stereolithography analogue (SLA) modeling, and are used for implant surgical guides as well as orthodontic and orthognathic treatment planning.
Traditional 2-dimensional (2-D) imaging systems are limited by distortion, magnification changes, restricted clarity, lack of measurement accuracy, and do not allow for 3-D SLA modeling.
CBCT scans are particularly beneficial in pretreatment implant planning and implant placement. Pretreatment planning involves bone location, volume, and density, as well as consideration of the implant position, trajectory, and final prosthesis. To make the diagnosis, carry out the treatment plan, and place the implants with predictable results, it is essential to have 3-D radiographic visualization of the implant site, with a surgical template or surgical guide available besides the traditional diagnostically mounted casts and radiographs. The bone donor site also can be evaluated if autogenous bone blocks or membrane grafting are needed for functional and esthetic implant treatment planning. Using advanced dental imaging such as CBCT and implant interactive software for implant planning and placement can improve treatment outcomes. Alternatively, using CBCT and surgical navigation software coupled with a surgical handpiece at the time of implant placement allows visualization of the surgical site, which has been preplanned with interactive software and can result in exact 3-D visualization of the implant site at the time of surgery.
Key Features and Benefits
When purchasing a CBCT scanning system, it is ideal to choose a device that can obtain true anatomic measurements, emits low levels of radiation, and can produce 3-D volumetric images with high resolution for all views. It should be able to render images in 14-bit grayscale to provide the practitioner with more accurate and detailed information about the patient's anatomy. It is best to get a system with a small footprint, similar to the size of a panoramic unit, so that it is easy to store in any practice. Devices with faster patient scan times-around 10 to 20 seconds-increase productivity for the practitioner and convenience for the patient.
The system also should be able to export images in the DICOM file format, and reconstruction time for the files should only take about 1 minute. And to make storing and e-mailing the images more manageable, it is best to keep the file sizes smaller than 25 MB.
A good implant-planning software program should have precise preoperative planning capabilities that provide an increased level of confidence and extra margin of safety. It should incorporate real 3-D planning that facilitates ideal positioning of implants while taking both clinical and esthetic considerations into account. They should use custom surgical implant drill guides that provide a link between the implant plan and the actual surgery by transferring the simulated plan accurately to the surgical site. These surgical guides should be compatible with any manufacturer's implants as well as capable of being supported by teeth, soft tissue, or bone if a flap needs to be raised.
The use of such advanced digital technology is becoming more widespread with the increasing demand for real-time treatment options such as instant crowns, veneers, overdentures, implants, and braces (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10). By providing more anatomical information about the patient before treatment, it produces more predictable surgical outcomes and increases productivity, generating more profit per unit of chair time. This level of detail also helps to increase case acceptance, which reduces the number of uncompleted treatment proposals-the largest non-value-added activity for dentists.
Free downloadable CBCT software programs enable multiple practitioners and technicians to share these images in DICOM file format for more efficient case discussion and planning. This keeps the continuum of care intact from diagnosis through treatment, which improves patient care and decreases errors.
Patients presenting for dental implant placement often have many reconstructive issues that need to be resolved for successful treatment. These include bone atrophy, tooth loss or positional problems, congenital deformities, growth abnormalities, pathology, previous surgeries, medical and or psychiatric issues. CBCT scanning for treatment planning and guided virtual implant surgery are especially beneficial for any patient that presents with challenging issues to be resolved for implant/prosthetic treatment.
It has been said that implant dentistry is a prosthetic discipline with a surgical component. But it would be more accurate to say that implant dentistry is a prosthetic discipline with radiographic and surgical components, for it is truly necessary to visualize all treatment 3-dimensionally before getting started.
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About the Author
Edward M. Amet, DDS, BS, MSD, FACP
Overland Park, Kansas