Show Your Work: Guided Implant Surgery (Part 2) by Dr Alif Moosajee

Dr Alif Moosajee discusses how he uses digital planning to predictably place implants in their optimal position.

>> Read Part 1 Here <<

by Dr Alif Moosajee

I have to admit that I much prefer screw-retained prostheses, but I understand that the challenge is ensuring that the positioning of the implants is optimal so this design of restoration can be delivered.

I use a Cerec scanner and the Orthophos XG cone beam CT scanner from Sirona, and the information gleaned from these scans can be merged so I have all of the prosthetically driven planning that I need. It must be noted that implants should be placed in position to optimally support the crown.

To work out where the crown should be placed, one needs to assess the mouth and create a diagnostic wax-up, which can be done either in an analog fashion or digitally. With Cerec, a digital wax-up is incredibly easy to obtain.

This patient needed a lot of work to get to the stage where he was ready for implant placement: He had periodontal treatment carried out, and had a palatally impacted canine removed under general anaesthetic.

The prerequisite of any implant planning is to have a mouth that is free of disease and a patient for whom implant placement is a suitable option.

The first step is an appointment I call ‘scan and plan’. A CT scan is taken and also a Cerec scan. This is an appointment that I delegate to my therapist.

I use the Cerec scan to create my digital wax-up. I do this by selecting ‘Crowns’ in the administration phase for teeth that are missing and will be restored with implants. The upper and lower jaws and bite scans are then completed as normal.

The next step is to ‘marginate—but instead of marginating around prepared teeth, I ‘marginate’ a tooth-shaped ring on the gum where I want the crown to be. I suggest turning it to manual margination, which I find much easier than using auto, and then asking the Cerec to design the crowns as you normally do if providing any kind of restoration. It will then propose what it thinks is the optimal sizes, shapes and positions of the teeth, although this can of course be adjusted in the same way that any restoration designed with Cerec can be.

I like to then use ‘Control-G’ to switch on ‘Grid Mode,’ so I can assess symmetry and the length of the anterior teeth. I position the model so I can see the ‘smile’, then move the model around and assess it from different angles, including the occlusal surface.

The last step is to proceed to manufacture. Often this can seem artificial, as you can see from my illustration. In this case the restoration wouldn’t even fit into the block, but this is irrelevant because we are not going to mill this wax-up.

The ‘wax-up’ information is then exported as an SSI file, which I save on a USB stick and plug into the computer I have the CT software on (Galaxis).

The important part is that when you press ‘Export,’ you must be in the manufacture stage; otherwise, it doesn’t allow you to do this. It can be very frustrating if you forget!

The digital wax-up of the tooth is now sat upon the Cerec scan. The next step is to import that data into the CT scan. This allows the teeth to be used as common reference points so that the data can be merged and the outline of the digital wax-up is on the CT.

This means that you will have a scan that indicates where the bone is, and also how to position the implant so that it optimally supports the crown and even allows you to angle the implant so that you will get screw retention, if possible.

From the screenshots from the Galaxis implant planning software, you can see that the model has been superimposed upon the CT in the beige colour, and the digital wax-up of the bridge has been superimposed in blue.

You can always click off the model or the wax-up, so you can see more clearly where the implants are and assess their orientation. Another handy feature is that a planning report can be generated once you’ve virtually positioned the implants; this means that the printout can be ready on the day of surgery to remind you which implants you’re placing and where.

In this particular case, there were multiple implants to place. One of the limitations with the Cerec system is that although the guides can be milled in-house on the Cerec milling unit, you are limited to milling a guide to place a single implant; when there are multiple implants to place you need to mill multiple guides. 

An alternative to this is sending the information to Sirona’s online digital lab (Sicat) and asking them to mill a guide that allows you to place multiple implants.

The option you would use if you have a Cerec scan and your in-house CT would be ‘Optiguide,’ which is the second option shown in this picture.

A summary of the plan then comes up ,and you’re able to keep clicking ‘Next’ until you go to the page where you can upload the CT information to Sicat and it can confirm your order.

Planning a case like this takes some time, and you need to sit down and concentrate to do it properly. I find that this forces me to look at the case, really think it through well, and troubleshoot any problems long before the day of surgery.

I also find that whatever time I invest in the planning pays massive dividends on the day of surgery, because it speeds up my surgical placement. I found that I would spend a long time agonising over exactly where to start my osteotomy, and then worked very hard to ensure that I was angling the drill in the correct plane so that the implant was placed optimally. This is now the easiest part of the procedure, because that initial osteotomy position and orientation is controlled by the fabricated guide. 

This has genuinely made implant placement a far easier procedure for me and well worth the time and effort to do this kind of planning.

Please read Part 1 of this article if you have not already done so, because it outlines how straightforward the placement of these three implants was. You can see the postoperative X-ray taken after the implants were placed. Hopefully you agree that the positioning of the implants is virtually exactly where we planned they should go!

We have been talking as a profession about how digital dentistry is coming for a long time. I believe that digital dentistry is here now and I am massively impressed by the scope of applications on how we can use this wonderful technology to enhance the way that we practice and ultimately the care that we can deliver to our patients.