August 4, 2016
by Yvan Poitras, DMD; Alex Pena, DMD
The use of a surgical guide is nothing new or revolutionary as clinicians have always had a need to more precisely position implants during surgery. Nearly 25 years ago, we at the Institut Canadien d’Implantologie developed a surgical guide. We wanted a better solution for the problems of conventional guides, which were often left on the operating table, and left us with no other choice than free-hand our way through surgery. Among other problems, guides would often lack the necessary stability once flaps had been elevated. Since then, numerous designs have been proposed but it is with the use of CAD-CAM technologies that we truly saw a significant change in the use of surgical guides. Their becoming truly was revolutionary and truly beneficial. However, there are now so many options available, so much marketing involved and so little formation given in our universities on the matter, that one can easily become lost as to which is the right one. How can one assess the value of a certain guide and what criteria are pertinent in comparing the different options in CAD/CAM surgical guides. Our purpose is now to cover the whole process involved in the realisation of a CAD/CAM guided surgery. We will be covering the basis for its planning and conception and then explore the fundamental notions of this technology. We will then present a case we performed with guided surgery comparing it to our experience with the PST and also discuss the benefits and limitations of CAD/CAM surgical guides. Then we will take a peek in the future of this young technology, since we believe this is only the beginning of what is a true revolution in the way we do implantology.
The past fifty years have seen a huge transformation in the world of implantology. This change has been propelled by the development of cad-cam technologies and processes. We have known for several years the importance of carefully planning the angulation and placement of dental implants in accordance with the prosthetic design. The goals of computer-guided surgery remain the same that we were pursuing 25 years ago when we proposed the PST (Poitras Surgical Template) as a mean to plan and guide the placement of implants. However, the technological innovations have helped us push further the boundaries of what can be accomplished in our field. The technology has allowed us to more precisely guide our hand in the surgical and prosthetic phases of our treatments but let us not forget the principles and foundations, which must guide us in the use of this technology.
Computer Assisted Planning and Conception of a Surgical Guide
A surgical guide is essentially a transfer tool. Its purpose is to transfer the diagnostic and planning of both surgical and prosthetic facets of treatment from the planning stage to the patient during surgery. Being a very precise transfer tool, CAD/CAM surgical guides demand a very precise planning. The basis of its conception begins with a well-conceived prosthetic design taking into account patients needs, desired aesthetics and functional outcomes. Then, one must plan the optimal implant positions and distribution in accordance with prosthetic planning, biomechanical factors, bone density and availability. The surgical guide will then allow the clinician to execute his surgery with the upmost precision, transferring the design carefully conceived during the planning phase. This whole process hinges on the acquisition of a specific dataset, which provides the diagnostic information necessary for such planning. There are numerous techniques, software and procedures, which have been developed to accomplish this process. However there are certain key common elements of information needed to produce a CAD/CAM surgical guide no matter the specific software or method and they are divided in three categories. First there is the radiological data, which is obtained from a cone-beam computed tomography. Then, there is the intraoral surface dataset, which can be provided by means of impressions or intraoral scanning technologies. The planning by the clinician will generate a third dataset containing the implants’ positions. The combination of radiological, intraoral surface and implants’ positions datasets through software will provide the necessary information for the manufacturing of the surgical guide.
Manufacturing and Design of a Computer Assisted Surgical Guide
The manufacturing of CAD/CAM surgical guides is in constant evolution. There are countless dental laboratories and companies who can produce a CAD/CAM surgical guide, each having different designs and materials. Nonetheless, the very first step in this process is the transmission of the planning datasets to the manufacturing party so it can design and create the guide. Once again, many software options exist to receive the planning data, and design the actual surgical guide. We have no intention of covering all existing surgical guide designs, but we can differentiate three categories according to how the guide will be supported. The support of a surgical guide being paramount to its stability and precision, we often see the support medium being used to categorize their designs. Consequently, we can observe three main tissues used for support of surgical guides. First, there are teeth supported guides, which make use of the remaining teeth to anchor the surgical guide in place. Then, there are mucosa-supported guides, which will find support on the soft tissues. Finally, we have the bone-supported guides, which will necessarily be in direct contact with the bone. Also, mucosa and bone supported guides are often use in conjunction with fixation pins directly inserted in the bone to help stabilize the guide. Research has been made to measure which method of guide support is the most precise and findings conclude that mucosa and teeth supported guides offer the best support. However, further research will be needed in order to better assess the precision, especially with so many different designs from various manufacturers. Nevertheless, no matter the design, surgical guides will all be dependent on one of the following methods to actually be produced. First, there is stereolithography, which consists in the use of a laser to selectively harden layers of a liquid resin bath to produce the surgical guide. Also, a similar method, known as selective laser sintering, uses a powder bed instead of a resin bath to manufacture the guide. Another technique uses 3D printing to literally print out the guide. There is also the use of milling technologies to manufacture the final product from a block of material. All of those methods of manufacturing allow the transfer of the planned surgery data with great precision. Once again, as to which of these techniques is better, further research will be needed to better compare them.
To illustrate our subject, we intend to summarily present a case where we used a tooth supported surgical guide for a patient treated at the Institut Canadien d’Implantologie. This case will allow us to discuss our planning and design process as well as the surgical and prosthetic result. Our patient is a 74 years old male, he has been treated at our institute many times before. For different reasons, he had bilateral sinus lifts 23 years ago after which the implants were not placed. Recently, he came back to us wanting to proceed with the implant therapy. As expected, bone loss occurred on the sinus lift sites, therefore we performed a sinus lift on the left side. However, the right side had enough residual bone to proceed with implant placement directly.
Guided surgery was then selected in order to optimize the length and position of our implants, specifically on the right side, where we wanted to use as much of the residual bone in order to have optimal stability without a new sinus lift.
Moreover, the presence of sufficient bone and keratinized gingiva in combination with guided surgery had the added advantage of performing a flapless procedure reducing time and discomfort for the patient. The presence of remaining anterior teeth, among which an existing implant was to be used in the future prosthetic design, indicated the use of a teeth support guide during surgery.
The bone density being low on the posterior maxilla we choose to wait before loading the implants and waited before removing the remaining teeth as keeping them was a simple aesthetic temporary solution.
During the second intervention we removed the anterior teeth, the existing implant crown and placed a second anterior implant.
Finally the case was restored with a removable prosthesis according to the patient’s desires. The use of guided surgery allowed us to have a perfect disposition of our new implants while taking into account the position of the existing implant, using the residual bone in an optimal and efficient manner avoiding a sinus lift on the right side and obtaining a successful prosthetic result.
CBCT scan taken on consultation, bone loss can be seen on both sinus life sites.
CBCT scan taken after sinus lift on the left side. (Please note that the unseated healing abutment was replaced after the scan.)
Panoramic view of the guided surgery planning.
Volume render of prosthetic planning and implant position from occlusal view, red coloured tooth is an existing implant.
Close-up sectional view of the left side with sinus lifted site allowing longer implants selection for maximum initial stability in low-density recently grafted bone.
Close-up sectional view of the let side with sinus lifted site allowing longer implants selection for maximum initial stability in low-density recently grafted bone.
Pre-surgical photograph, abundant keratinized gingiva can be seen, allowing a flapless approach.
Per-operatory photograph, showing the surgical guide with right side implants in place.
Post-op CBCT scan.
Post-op scan of second intervention.
Screenshot of CAD CAM implant supported bar at the design stage.
Post-op scan after implant-supported bar placement.
The final implant-supported bar.
The patient’s smile shown with the final prosthesis in place.
Guide pins fixed on diagnostic wax-up ready for template fabrication.
Guide pins entering drilled holes in stone model to provide bone contact during surgery.
The guide pins contacting bone during surgery
Use of the bins to guide the osteotomy.
Panoramic radiograph with the template being used as a radiological guide. Template being used as a radiological guide.
PST and CAD/CAM Surgical Guides Compared
Here, we intend to compare the Poitras Surgical Template (PST) with a CAD/CAM surgical guide as a demonstration of the principles upon which guided surgery was developed and have been a constant since the beginning of implantology. With any surgical guide, the desired establishment of a logical continuity between diagnosis, prosthetic planning, and surgical phases, mandates the need of a transfer device. The clinician fabricates the surgical guide after the presurgical prosthetic appointments, once the final prosthetic design, occlusal sheme, implant location, size, and angulation have been determined. The surgical template dictates the implants’ placement that offers the best disposition to support the occlusal forces, render adequate aesthetics, and allow for proper hygiene. The clinician, having a well-developed plan, can then precisely reproduce it, leaving little decision at the time of surgery. As discussed earlier, a surgical template should be stable and rigid when in the correct position. If the arch being treated has remaining teeth, the template should fit upon enough teeth to stabilize it. When no remaining teeth are present, the template should extend onto unreflected soft tissue regions to remain stable after soft tissues have been reflected. However, for a completely edentulous upper arch, it is often difficult to precisely position a regular template. This is why we developed the PST 25 years ago. This device engaging the occlusal aspect of the opposing teeth provides the desired stability during surgery. However, being supported by the opposing arch, its fabrication needs to rely upon a model mounted against the opposing dentition, at the proper final occlusal vertical dimension and relationship in order to precisely transfer our planning. To achieve that, a full wax-up of the missing teeth in the edentulous regions is performed. A hole is prepared through the middle of the central fossa of each future posterior abutment tooth and through the incisal edge position of the anterior teeth. Then, on the stone model, each chosen site is drilled to a depth corresponding to the approximate soft tissue thickness assessed on a panoramic radiograph (approximately 2 to 3 mm). A stiff round orthodontic wire is then passed through the teeth and into the holes.
This allows each pin of the template to contact bone once the tissue is reflected during the surgery without modifying the occlusal vertical dimension and consequently the emergence position of the implants.
A small loop is made at the other end of the wire to create retention for the resin material. The wire loops should be within 1 to 3 mm of the opposing arch. Next, on the antagonist model covered with separator, an acrylic resin template is built on the anatagonist embedding the retention loops of the indicator pins. Each pin must be fully embedded in the acrylic at the proper centric and vertical relationships. Once in surgery with the soft tissues reflected, the template is positioned over the teeth of the opposing arch. The patient will then bite down on the pins, and each one will indicate the ideal center position of the teeth and implant. A pilot drill can be used to mark each implant position.
The angulation of the osteotomy also can be determined with the PST. The surgical guide easily guides the implants’ positions, yet the surgeon can have the patient’s mouth open and drill into the bone with complete access and vision. This template may also be used with a panoramic radiograph or a CBCT scan to visualise available bone at each implant site.
While the PST and CAD-CAM surgical guides are very different in the way they are designed, manufactured and used, we can note similar purposes in their design, allowing the clinician to orient the positioning of implants in order to precisely execute the surgery in accordance to the planned prosthetic goals. Both guides also depend on precise positioning via support provided by the available tissues. With the PST the opposing arch is used, as some techniques use it nowadays with CAD/CAM surgical guides, to obtain a support in the positioning of the guide. Finally, CAD/CAM guides and PST alike, allow better precision than free-hand technique, computer assisted conception and manufacturing taking the accuracy to the next level.
Benefits and Applications of CAD/CAM Surgical Guides
The use of guided surgery is a definite progression in the field of implantology. With the use of those guides, we benefit of shorter operating times, less invasive surgeries, enhanced precision, and the possibility of CAD/CAM immediate provisionals and/or final restorations and abutments.
Efficiency During Surgery
The CAD\CAM surgical guides allow the complete surgical drilling protocol and implant placement to be carried out with the guide in place, which provides the opportunity to use a flapless surgical approach when the available bone and keratinized gingiva are sufficient. The flapless approach allows great precision with a minimally invasive surgery and no compromise on the results. Moreover, the surgery can be performed in reduced times, once again reducing the morbidity of the intervention.
Precision and Optimization
The great precision of this technique allows to very precisely position the implants giving the clinician the possibility to optimize the planning, as close as possible to anatomic structures, with maximum bone support in immediate extractions, in accordance with the prosthetic design, all of this in a controlled and efficient way. The better disposition of implants will result in a better biomechanical design, and will improve the perennity of the final outcome.
Finally, the surgical guides have allowed the design and manufacturing of immediate CAD/CAM abutments and restorations, which have opened the possibility of having customized prosthetic parts available immediately during implant placement. Those custom abutments, restorations and prosthetics give us unprecedented control over the aesthetic outcome, allowing the guidance of the healing tissues with great control, precision, perfectly planning and delivering highly customized and precise restorations to our patients.
Limitations, Precautions and Complications with CAD/CAM Surgical Guides
The benefits of CAD/CAM surgical guides are many but no technology is without limits and clinicians must exercise caution to successfully perform guided surgery in a safe and predictable manner. Once a thorough examination of our patient has been conducted and one has chosen to conduct a guided surgery, there is a three-pronged monitoring that must be carried through all the steps leading to surgery.
Data and Planning Errors
First, one must consider the planning phase prior to the guide manufacturing. The actual gathering of data through CBCT scanning and impression or intra-oral scanning have to be carefully evaluated for errors since they are the base upon which all will be developed. Once the data is approved, the planning of the prosthetics and implant positioning must be carefully carried out as an erroneous planning will result in a really precise yet erroneous result.
Secondly, there is the manufacturing phase that needs to be overseen, as there are hardware limitations that need to be taken into account for the surgical guide. Therefore, implant length, distribution and orientation can be limited by the inter-arch space. Also, the guide’s vertical thickness and the minimal thickness of materials and sleeves on the guide can limit the minimal distances of inter implant and implant tooth positions.
Lastly, the actual use of the guide during surgery can be complicated by per-operatory limitations. As discussed earlier, the inter-arch space and mouth opening of our patients can limit the length and position of the implants used, due to physical access.
Surgical Guide Stability
The outstanding precision of CAD/CAM surgical guides is dependent on its stability once positioned in the mouth. The guide stability having great influence on the clinical outcome of guided surgery, a careful assessment of occlusal surface adaptation for tooth borne guides needs to be carried. Likewise, mucosa and bone supported guides stability must be verified and could benefit of opposing arch bite indexing and/or bone pins fixation. Nonetheless, mucosa swelling caused by local anaesthesia, CBCT distortions and artefacts can all be possible causes for errors in bone and mucosa supported guides positioning and consequently accuracy. Notwithstanding the limits and complications that can arise in the use of CAD/CAM surgical guides, a number of studies have assessed their accuracy and tend to confirm their high precision, although the advised clinician should always meticulously assess and approve every step of the guide’s conception and manufacturing.
The exponential evolution of computer assisted design and manufacturing makes for a very bright future for guided surgery. More and more options are becoming available, with increasing precision, faster turnaround times, and cheaper fabrication costs. The software options available allow for more complete integration of surgical and prosthetic planning than ever before. The level of customization of implant therapy is getting constantly improved with the contribution of CAD/CAM on the prosthetic department. However, the increasing number of manufacturers, labs and solutions available presents a risk as it becomes difficult to compare and evaluate the different options and calls for further research to better understand the CAD/CAM surgical guides. The future will certainly allow for better integration between CBCT imaging, intra-oral scanning and new possibilities in designing custom parts all the way from restorations, to maybe implant themselves, and all thanks to the CAD/CAM surgical guides who allow to very precisely plan and carry those custom-made designs.
The advent of CAD/CAM technologies in the dental world has brought a new realm of possibilities. The development of guided surgery in implantology is truly a revolution of the way we can treat patients. It brings incredible benefits for the patients and the practitioners alike. The pursuit of more efficient, precise and minimally invasive procedures with superior customisation and aesthetics is worth investing our efforts, time and money for the sake of delivering more predictable and successful treatment to our patients. Clearly, further research is needed to better understand this technology and be able to set clear standards of care regarding the use of guided surgery. Clinicians, laboratories and manufacturers will need to develop better communication tools to seamlessly integrate the different software and hardware components of CAD/CAM surgical guides. Finally, caution must be used regarding this advancing technology because thorough planning and sound clinical judgment are still paramount to the success of treatments in spite of the precision and efficiency provided by guided surgery.
Yvan Poitras and Alex Pena declare that they have no competing interests. This study was self-supported.
Dr. Yvan Poitras graduated from Laval University in 1984. In 1993, he founded the Institut Canadien d’Implantologie where he offers a complete surgical and prosthetic program in implantology. Dr Poitras is related to the biomedical research department of the Polytechnique de Montréal. He is co-director of the Franco-canadien university degree from the University d’Evry Val d’Essonne. He is expert for the Fonds d’assurance-responsabilité professionnelle de l’ODQ. He is a collaborator at the Implant Dentistry journal and an Ambassador for the ICOI. He maintains a private practice limited to implant dentistry in Montmagny, Quebec.
Dr. Alex Pena graduated from Laval University in 2010. He established a private practice in Quebec city in 2013. He is a graduate from the Institut Canadien d’Implantologie, where he is an associate in the private practice as well as being a faculty member in the education branch. He now shares his time between his private practice in Quebec city and Montmagny with a focus on cad/cam orthodontics and prosthodontics and implantology.
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