Inside Dental Technology
September 2011, Volume 2, Issue 8
Published by AEGIS Communications
Digital Implant Planning Software
Integration of cone-beam CT scans with implant-planning software offer laboratories greater precision in fabricating surgical guides and final restorative solutions.
By Mark Jackson, RDT
When the author became a dental technician, dental implants were still largely blades and subperiosteal, and were considered an aggressive if not unreliable treatment. Over the years, root-form implants have improved and surgical success was no longer the challenge. Today, implants have moved beyond esthetics into what many people are referring to as “engineered implant dentistry.” Ideally, implants are inserted into the non-atrophied jaw. However, tooth loss frequently results in a reduced volume of the alveolar bone, and, consequently, anatomical conditions require a precise spatial orientation for implant positioning to ensure that both adequate quantities and qualities of bone exist.
For traditional implant planning, bone availability can be sufficiently determined via 2D tomography or dental films. The panoramic x-ray facilitates the localization of the anatomical structures that need to be protected, such as the inferior alveolar nerve, the floor of the sinus and nose, as well as the mandibular border and any remaining teeth. Depending on the system, these tomographs enlarge the anatomical structures by up to 30%. Further complicating placement planning, enlargement within the image is not uniform. The enlargement factor is distorted depending on the type of the equipment being used and the positioning of the patient during x-ray exposure. Therefore, such images were normally calibrated using precise 5-mm metallic radiographic markers so that the actual size of the anatomical structures could be calculated. However, panoramic x-rays only permit a limited evaluation of the existing structures, especially if a 3D representation of the vertical and horizontal bone bed is required. This could potentially result in erroneous positioning of implants and damage to these important anatomical landmarks.
3D diagnostics using cone-beam CT scans and digital implant-planning software is becoming the standard of care in implant dentistry.
Treatment Planning Digital
To determine the precise treatment plan, it is important to evaluate existing bone availability both quantitatively and qualitatively. The evaluation will indicate whether bone augmentation is necessary, identify the prosthetic options based on what is realistic, and it will provide an objective view of remaining structures. Through the visualization of the available bone and the analysis of the extent of required prosthetic treatment, the treatment plan can be worked out with the patient. This is much easier when using 3D diagnostics and animation than using photographs, drawings, and wax-ups, all of which are difficult for patients to visualize. Implant-planning software allows the implant team to generate a 3D image of the patient’s situation, identifies what treatment is proposed, and presents it graphically and sequentially to the patient.
Evaluation of Available Bone
Cone-beam imaging and digital implant-planning software both provide measurement features that are very precise. Because the CT scan slices have already been calibrated using algorithms, it is not necessary to use a reference ball for calibration, as required in the panoramic x-ray. In fact, metal markers will create radiographic scatter and noise, and should never be used as in 3D imaging. Bone availability can be determined in the horizontal and vertical dimensions using the measurement functions of the implant-planning software. In addition to measuring available bone, it is also important that the position of the prosthetic device that will be used—or hoped to be used—is oriented once the structural analysis is complete. This was formerly done via a laboratory-fabricated drill template whereby drill sleeves were positioned by the dental technician who may or may not be using an x-ray for reference.
The latter results in a prosthetic proposal by the dental technician, which is reverse planning. The problem is, anatomical landmarks are often missed or ignored, or there may be insufficient bone density in that area to support an implant. It also does not allow for implant re-positioning, which could lead to difficulties with the prosthetic axis.
By using a proposed prosthetic plan and 3D imaging and implant-planning software, the best implant position can be selected without requiring further augmentative procedures. This saves both the patient and surgeon time and money while ensuring higher success rates both structurally and esthetically.
Qualitative Evaluation of Bone Availability
A surgeon who is aware of the bone quality can plan the procedure, particularly for drilling pilot holes. The problem is that cortical structure is very hard, and in the posterior mandibular area, it butts up against the soft spongioid bone. Depending on the cutting character of the drill, a large amount of force may be needed to prepare the cortical bone. After preparing the implant cavity in the cortical plate, it is very easy to over-penetrate and make the preparation too deep in the subsequent soft sections, resulting in damage to anatomical structures such as the nerve or sinus. Implant-planning software and precision surgical guides help the clinician to sequentially drill and enlarge each osteotomy, as well as control angle and depth.
Implant Planning after the Treatment Plan
In prosthetic planning for multiple missing teeth, it is prudent to prepare a wax-up to simulate the prosthetic that is planned. A wax-up provides a point of reference for best prosthetic positioning of the implants and is used as a pattern for making a radiological template. In this process, the teeth intaglios are produced in barium sulfate acrylic, such as ScanoCryl (Precison Ceramic Dental Laboratory, www.pcdl-usa.com) or SR Vivo Tac/Ortho Tac (Ivoclar Vivadent, www.ivoclarvivadent.com). The teeth must make flush mucosal contact so the dimension of the soft tissue can be determined accordingly, or a denture case material of a different gradient must be used.
In addition, the crowns must be separated so that simple and logical orientation of the tooth position is possible. Depending on the digital implant- planning system used, the system-specific references must be fixed to the radiological template, ensuring a precise transfer to the planning software.
Mandibular Implant Planning
Implant insertion in edentulous mandibles is still the most frequent indication prescribed. Bone availability varies depending on the level of atrophy, which may be severe before a denture patient seeks help. If the alveolar process is still intact, the bone is often significantly reduced in the orovestibular direction.
In a so-called “knife-edge” alveolar ridge, implant insertion is impossible without osteoplasty or significant shortening and flattening. As the height of the ridge drops, the ridge becomes appreciably wider. However, surgeons must avoid placing the implants too far lingually when planning the implant. In addition to the estimation of bone quality, 3D cone-beam imaging also allows the evaluation of cortical bone on the opposite side of the ridge. Through 3D imaging, the recesses created by the lingual artery can be evaluated. A basal or lingual perforation of the artery must be avoided because arterial damage can result in life-threatening bleeding. This is another reason why the author strongly advises laboratory technicians to avoid making model-based surgical guides.
Implantation in the posterior mandibular area is generally done unilaterally to obviate the need for a removable tooth replacement, or it is done bilaterally after a longer period of edentulism and loss of multiple support teeth. For implantation in the direct vicinity of the inferior alveolar nerve, the bone supply between the nerve channel and the alveolar ridge must be exactly measured. Implant-planning software permits a precise representation of the nerve channel profile, especially in the region of the mental foramen. This significantly reduces the risk of nerve damage during implant insertion in a nerve channel that runs anteriorly from the mental foramen.
Maxillary Implant Planning
Implant restorations in the anterior maxilla generally receive the greatest amount of attention. Patient expectations are extremely high, particularly where a high smile line and small spans are present. Patients expect that the contours of the crowns and the soft tissue will be restored to their appearance before tooth loss. Implant-planning software can help patients and doctors have realistic expectations of what can actually be achieved and help plan and predict the best outcome. At the very least, it improves communication and ensures that implants can be placed at the level of the cementoenamel junction of the adjacent teeth and in the correct axial position.
For edentulous patents, the implant prognosis significantly depends on the bone structure and bone availability in the anterior maxilla. If there is too little bone available it is preferable to place implants by performing a sinus-floor elevation in the posterior tooth area before placing the implant. In particular, the contour of the bone, with respect to the nasal spine, frequently results in retractions that result in inadequate bone coverage of the implants and thus limit the prognosis. Implant-planning software allows for a better planned and executed treatment approach, as well as structurally sound bone.
Implantation in the maxillary posterior area requires consideration of the maxillary sinus findings during planning. In the beginnings of modern implantology, attempts were made for optimal use of existing bone via short implants. However, today it is routine to raise and build up the maxillary sinus floor (ie, sinus-floor elevation and augmentation). If there is a sufficient bone bed, a minimally invasive sinus lift can also be achieved via crestal access, using osteotomes—also called bone condensors. The correct estimation of bone quality is crucial in this context and can only be achieved with the use of cone-beam CT imaging and implant-planning software.
CAD/CAM Surgical Guides
Once 3D imaging data and virtual implant planning are completed, a CAD/CAM manufactured surgical guide allows the surgeon to perform the surgical procedure quickly and accurately. Since 1997, there have been several sophisticated software programs for computer-aided implant planning, characterized by their ability to implement computer-generated plans using navigational methods generated from cone-beam CT scans, or medical CT scans.
Stereolithographically created surgical guides are based on rapid-prototyping technology and require exact 3D data of the patient’s anatomy. These virtual models are then used for construction by a rapid-prototyping machine. Any distortion in the image will result in a guide that will not fit the patient.
Other systems position a plaster model or a corresponding template to a drill so that the planned drill axis can be transferred to a model-based template. This is done either manually using corresponding positioning devices or with an automatic CAD/CAM drilling unit. The advantage to these types of guides is that they have been trial-fitted in the patient’s mouth at least once prior to the surgery and implant placement.
A disadvantage of many such systems is that different individual components have to be used for imaging, and software, and hardware treatment planning. All components being used must be optimally coordinated with one another and each needs to be completely understood by the user. The workflow requirements and the potentially high investment costs for imaging and planning software have resulted in a rather hesitant use of this technology by some dentists and laboratories. As more technicians become comfortable with the programs, and understand cone-beam CT imaging, it presents a unique opportunity for qualified participants.
After implantation, 3D imaging and implant-planning software are also suitable for postoperative assessments. The position of the implants can be represented in 3D and any incorrectly positioned implants can be immediately identified. Clinically noticeable findings can be clearly evaluated in this way. Integration of the implant can be evaluated and any bone loss can be accurately determined, measured, and documented. In addition to the clinical examination, this permits any complication to be measured and evaluated precisely. Even rare complications, such as retrograde peri-implantitis, can be diagnosed using 3D imaging and viewed with this software. Some manufacturers offer corresponding metal-artifact–reduction algorithms to improve image quality around implants, which of course produce radiographic noise and scatter. One can also overlay the preoperative virtual plan with the actual postoperative result.
Implant-planning software can help dental laboratories be more profitable, have fewer remakes and post-delivery failures, and can also ensure a higher level of patient satisfaction. Dentists will find that their costs are actually lowered by properly planning and executing cases while the cost of parts and tools necessary to overcome awkward or improperly placed implants is eliminated. Implant-planning software and precision surgical guides will also help to lower the cost of implant treatments for patients, which satisfies everyone.