February 12, 2015
Computer-Assisted Guided Surgery enables clinicians to better visualise the anatomy of the bone in relation to the planned design and positions of replacement teeth, and then to use a specially fabricated stent to guide the installation of the implants in the pre-planned positions.
It has become very popular in recent times because, in theory, it appears to make it possible even for novice clinicians to undertake implant surgery. It certainly has been marketed in that way by companies that sell this technology, whereas quite the opposite is actually true.
I always stipulate in my lectures and training programs:
‘When going ‘blind’, you need to have developed your other senses’
What I mean by this is that this technology enables clinicians to blindly undertake implant surgery using a stent, but if they don’t have adequate experience in standard implant surgery, they usually lack the understanding of important parameters that are pertinent to the attainment of success with dental implants. They simply don’t know what they don’t know. They lack insight.
Whilst CAD-CAM technology is great for visualisation and planning, when it comes to the actual surgery there are numerous variables that cannot be pre-determined and often require modification to the surgical approach. As such, the use of stents for Guided Surgery should be done with extreme caution, taking the following into account:
1. The positioning of the stent in the mouth is subject to operator error. A very small error in the fit of the stent results in a much exaggerated error at the implant site;
2. The stent does not allow proper cooling of the bone during the implant-site preparation. This may lead to overheating of the bone at a biological cost;
3. The stent has metallic sleeves to guide the drilling process and implant positioning, and these sleeves cause traction and lead to false understanding by the operator of the actual quality of the bone, or the torque and stability of the implants. The high degree of false positives leads to loading the fixtures (connecting the teeth to the implants) in situations where the fixtures are not capable of being immediately loaded, leading to bone loss and/or failure.
The other problem with typical fully Guided Surgery is that the ability to improve the restorative space though alveoplasty (bone reduction), or to improve the biotype with soft tissue surgery, is quite limited. This detrimentally affects the overall aesthetics, durability, comfort and ease of hygiene.
The minimum amount of restorative space that is required for an adequate anatomical and durable prosthesis is 18mm for acrylic and 15mm for Zirconia. This is the height of the prosthesis from the abutment interface to the incised edge (or buccal cusp), regardless of how many implants are used. In some cases, such as gummy smiles, it is desirable to have taller prosthesis in order to hide the gingival-prosthetic transition line. The amount of bone reduction must always be determined by the clinical presentation and the aims, and must not be altered because of the limitations of a planned “Guided” approach.
Nevertheless, it is indeed possible to perform alveoplasty along with Guided Surgery through a modified approach where the stents are used only for the osteotomy, and are then removed for the alveoplasty and implant placement. I divide the possibilities with this technology into five categories, as shown below along with selection criteria and some tips: