Guided Implant Surgery: is it something for me?

Online Masterclass
Computer Assisted Implant Surgery is increasingly popular, with almost every implant system racing to deliver the most reliable technology and protocols. Either as static or dynamic, CAIS promises unprecedented accuracy in implant placement and evidence now shows that it delivers. 
But is this enough? Does increased accuracy really translate to benefits for your patients and your practice? 

Does precision really matter?  

 Before we discuss about accuracy of CAIS however, we will need to note that the actual guided surgery is only one final step of a long sequence in a digital workflow. This workflow includes a lot of steps, each of them with potential for errors.
- First, we rely on a CBCT. Unlike what you might think, the 3D image of the CBCT software we work with in our computer screens is not a radiographic image. It is an algorithmic reconstruction of many radiographic images. Every algorithm will use certain calculated “approximations” and might not always be absolutely loyal to the true anatomy. Importing the DICOM file to the treatment planning software invites one more algorithm in the party.
- Then transposing the STL file from the optical scan and the essential rendering has the potential to further influence dimensions. Finally, 3D printing of a surgical guide is a workflow step with potential to introduce some more distortion. Conclusively, by the time we are about to use our CAIS system to place the implant, there is already some accumulated error from the workflow, that even if the CAIS was to be perfect, we would still observe some deviation from the planned position.

Back to the main point now: how accurate is implant placement when we use CAIS?To answer this we can see the results accumulated through a major CAIS research project in the OMFS clinic at Chulalongkorn University in the past 3 years. This project has by now involved more than 200 patients and included research protocols in many different clinical scenaria. The strength of this project is that by standardizing the studies and using the same technology and software, the same operators , clinic set up, as well as the same patient pool , we can at least ensure that the workflow error is similar in all cases thus the observed differences can be attributed to the clinical conditions we investigate. Compiled from a series of same-workflow RCTs, this  table from Chulalongkorn University now shows a clear trend with the accuracy of CAIS being closer to this of conventional freehand placement at single gaps, while the deviation drastically increases as we move to partially and fully edentulous patients. The deviation also trends to be slightly higher in dynamic than static guided when we are dealing with partially and fully edentulous cases, but at the same time both static and dynamic CAIS perform increasingly (and significantly) better than freehand placement, as complexity increases. Of course, accuracy is just the tip of the iceberg and decision making involves several other clinical outcomes, cost effectiveness, many aspects of efficiency, surgical anatomy and site characteristics, learning curve, patient reported outcomes and more... 

Is system precision different to accuracy and why should we care?  

Talking about accuracy and precision can be quite a challenge, as we often use these terms interchangeably in daily life. I recall once a long lockdown-induced discussion whether cops in Hollywood movies shoot “accurately” or “precisely” and an endless academic argument another time on Google translation and if it lacks "accuracy" or "precision" (turns out it depends on the language )!
Luckily in Computer Assisted Implant Surgery, these terms are quite...precisely defined:
- "Accuracy" will assess how close your placement will be to our planned optimal position.
-"Precision" on the other hand will assess how reproducible is the process, that means if we repeat the same placement many times, how close will each placement be to the previous ones.In practice, they are both important for a CAIS system but for different purpose: A system of high accuracy is a system that fits the purpose and will ensure the implant is placed in the planned position. A system of high precision on the other hand will be a system which is streamlined and not vulnerable to any “systemic” or random influences. These influences could be anything, from calibration of the software to preferences of the operator (right or left handed), or accessibility for instruments.

A good system will need to be checked for both. A more common condition, low precision but high accuracy will reveal some systemic error, for example some error in the software, imprecise calibration or some mistake of the operator. To test accuracy, we would typically rely on clinical studies, which are the most relevant. Many studies are available on accuracy and we presented some in a previous discussion. However, in clinical studies we can only place each implant once, so to assess precision we would need simulation studies, where the implant is placed in multiple identical models under the same conditions and by the same operator. Try this for your own system to see how precise it gets.

In a simulation study with multiple placements, the deviations of each placement ideally should be scattered equally around the optimal centre, like a symmetric firework. In reality however deviations tend to cluster more towards some sides, pointing to some systemic influence mostly attributed to the operator such as right- or left-handed, ergonomics, optical field as well as specific anatomic locations of the implant site and more.

How much clustering of the deviation is acceptable and when should we seek and correct the systemic influence? Well, this is a wider discussion and it should be always be seen in conjunction with the accuracy readings. Maybe we can discuss this in more detail in the future.The image below is from one of our simulation studies with static CAIS and it shows the clustering of the deviations (precision) for the standard level of accuracy. As you can see, although not too bad, looks like the “firework” is a bit blown by the wind in some instances. To understand more why this happens however, you will have to read the paper
Thank you!