As a restorative dentist, have you ever had a patient present without ideal implant placement for restoring them optimally? Conversely, if you’re a specialist placing implants have you ever had one of your restoring doctors tell you that you put an implant in a less than optimal position for them?
If this has ever happened to you, incorporating the use of surgical guides in your office may be exactly what you need. While fabricating a surgical guide may sound complex, the reality is that in many cases it's an easy process.
However, as the complexity of the case increases, so does the fabrication of the surgical guide. One of the simplest methods you can use is to form a material such as 1.5mm Biocryl over a model representing your final restorative goal and drill a hole through this matrix for each implant that is to be placed. Once this is done, the initial guide drill can simply be passed through this hole to start the osteotomy and subsequently guide the following drill. This will in turn guide the placement of the implant.
While this type of guide is relatively easy and quick to make, it does have its limitations. First, since you’re left with a shell with a hole or holes though the top of it, there is quite a bit of room for the implants to be unintentionally angled. This of course can pose challenges when it comes to restoring the implants.
The other main limitation is that this type of guide is flexible and is best reserved for simple cases with just a few implants and teeth to the implant site or sites to ensure that the guide is stable. The next step up in regards to surgical guides is to fabricate a template as described and fill the areas where any teeth are missing with acrylic. Once this is completed, holes are drilled through the guide where the implants are to be placed. This process has three benefits:
- It creates a channel through which the surgical drills are passed and aids in assuring the implants are placed at the desired angle.
- It increases rigidity of the guide.
- If you use a radiopaque acrylic such as Biocryl X, you can visualize this on your radiographs.
While there are clearly benefits, it’s important to note that there is a significant drawback. The acrylic that fills the surgical sites can impair visualization and irrigation of the surgical site.
Guide for a fully edentulous arch
As I said, there are two options for very simple surgical guides. While the guides I mentioned above were best suited for cases with remaining teeth, now let's focus on how to fabricate a guide for a fully edentulous arch.
Surgical guides for the these types of cases are a bit more complex to fabricate so planning goes a long way to ensure you'll have an easy to use and predictable guide.
Generally speaking when it comes to fully edentulous cases, in order to plan your placement and fabricate a surgical guide, a CT scan – typically a CBCT – is needed. It's best to scan the patient with a radiopaque stent in place in order to approximate the desired final tooth position.
In cases where the patient has a reasonably well-fitting existing denture my favorite option is to duplicate their denture with radiopaque acrylic and use this as the base for the surgical guide (above photo). Instead of using radiopaque material for only duplicating the teeth, I prefer to use a less radiopaque material (such as Biocryl XR) to duplicate the tissue, and a more radiopaque material (such as Biocryl X) for the teeth. Doing this allows you to visualize the proposed tooth position, as well as, verify the guide was seated properly when the scan was taken.
Of course if your patient doesn't have or you don’t want to make them a well-fitting denture, you have to look for another option. One option is to do a diagnostic wax-up of the case then fabricate a Biocryl suck down of the wax-up and fill this suck down with Biocryl X and Biocryl XR as described. The difficult part here is to fabricate the stent with enough overlap onto fixed surfaces (such as the palate on the maxilla) so that the guide can be placed in exactly the same position each time it's inserted in the mouth.
Once your CT scan with one of the radiographic stents is taken, you have to determine the appropriate implant placement. The final step is to drill the appropriate holes in the stent to complete your guide.
While this can be completed by hand, it has the potential for significant error. It’s best for cases of this nature to use a computer-assisted guide.
Computer-assisted design of surgical guides
Now let's discuss computer-assisted design and the manufacturing of surgical guides. The great thing about using computer-assisted guides is that you can have a guide fabricated that will precisely control the depth and angle of each drill and even the implant.
While these guides have the potential to be much more accurate, they do require that a CBCT scan be taken followed by the use of software to then virtually place the implants in the CBCT scan.
Depending on the system you are using and the complexity of the case, there are several ways you can go about creating a computer-assisted surgical guide.
Given the number of systems and possibilities, I’ll limit the specifics of this article to the system I most commonly use: The SICAT system by Sirona. However, the process is relatively similar between systems.
The first step in the SICAT process is determining if you will use a template of the proposed restoration with radiopaque acrylic similar to one discussed above, or if you will design the proposed restoration virtually in the planning.
I've found the more complex the case the better it is to create a radiopaque template of it that the patient can wear during the scan. However, for smaller cases it's easier to do this step virtually. Once you've decided on how to replicate the proposed tooth position on the scan, the next step is to fix what is referred to as a Scan Plate in the patient's mouth during the CBCT scan. This plate is plastic and has radiographic markers on it which allow SICAT to marry the data from your planning software to a physical model representing the condition of the patient mouth at the time your CBCT scan was taken.
In simpler cases doing this can be as easy as lining the Scan Plate with bite registration material to stabilize it in the arch. The key when using bite registration to stabilize the Scan Plate is there must be teeth distal to your implant site and enough teeth in the arch to predictably stabilize the Scan Plate during the CBCT scan. In cases when you use a Biocryl template, you simply fix it to the Scan Plate with radiolucent acrylic.
Once you have taken your CBCT scan of the patient with the Scan Plate in place, the next step is to place the implant or implants where you want them by using the planning software.
The final step is to send the file you have created into SICAT and have them manufacture your surgical guide. It’s important to note that there are many systems and options out there for you to choose from with their own pros and cons. If computer-assisted surgical guides are something you would like to incorporate into your practice, I suggest you talk with clinicians you trust to determine which system is best for you.
John R. Carson, DDS, PC, Spear Visiting Faculty. www.johnrcarsondds.com