Accuracy of Dental Implant Placement with CT Guided Surgical Stents

Your problem lies with the CT scan, planning software, guide fabrication, seating or stabilization. What CBVT machine and what brand of software are you using? Are you fabricating your own stents? The guided implants should be spot on as planned, and even a tiny discrepancy would be cause for alarm.

are you using a guided surgical kit or the standard length drills?

Hi I have use Simplant software and surgical guides by Materialize. I am very surprise that you had this experience. In my cases, I was amazed by the precision of the guide. In the first cases, I was very cautious, and double check every steeps, but the results were simply perfect. Can you share tne name of the software and who did the guide ?

Are you scanning your models as well as getting a surgiguide from your software provider? This is typically why there are discrepancies between the surgical guide and the patient. Also, are the guides made as soft tissue or hard tissue guides? That can also cause a problem for you.

I have had more than one problem with surgical guides made by my software provider. Our group uses Anatomage software (San Francisco) & Planmeca CBCT. We use them primarily for the All-On-Four cases. In one case the thermoplastic guide did not seat on the existing dentition. In the opposite arch the stabilizing pins had to be removed to access the trephine sites and the sites were placed in poor quality bone. I believe part of the issue is the lack of any head stabilizing mechanism on this machine allowing for some head movement.

Let me try to help you with this. I am in the field of guided surgery since 1994. I assume that the effect you described happend in maxillary bone with small crest. I would like to go in detail with you. Which guided surgery kit are you utilizing? Which diameter was your starter drill? How often are the starter drills used? Please give more info, possibly at my email dds.michael.gross@gmail.com There are some issues which have to be taken care of within guided surgery. Michael

Thank you guys for such a good response. I use CBCT "Picasso Duo " from E-Voo for last 4 years. My scanning appliances are hard and fabricated by lab. I use standard drills with Zimmer inserts for master sleeves on CT surgical stent. I scan my patients, models, and patients with scanning appliances in my office. The Lab that I am working with is very reputable lab and makes a lot of those stents. They are looking into my issue as well. But I want to get some other opinions.

I have used mostly materialise. I have had some very good experiences and a few bad ones. Usually I just use the pilot and then enlarge the osteotomies without a guide. This works well in bone and also gives you a good feel for the density. I don't believe I lose any accuracy. If there is any error in the system it will be propgated to the mouth. So a gouide is just that, a guide. Always double checK it with your eye and flap if something seems wrong.

Osteotomoes/Implant placement can well be done at accurate site by an accomplished dentist. There is need of the art/science of knowing the currect site at an individual patient/ arch. Stent may work as a guide, but your clinical accumen is best guide. In addition to stent as guide one can also use other guides available for the purpose of knowing the correct axial alignment of the implant for abutment to accomodate in order.

I think that optical scan of the stone model implemented in virtual 3D planing should help as well critical stability try in of surgical guide before surgery. Do you agree with me?

My 2 cents - always try-in the template before starting the surgery. Never assume, one guide company have instructions to 'remove' the 'rings before placing. If you have it seated accurately and verified seat, then take a pano/PA with the patient wearing the guide fully seated, you can tell if there is a problem before you start. Never assume everything is perfect . . . just part of common approach in prosth I take. LCM

Dr. Lambert Stumpel has published recently a study comparing Simplant, Blue Sky Plan and Nobelguide and he found that superimposing an optical scan of a model on top of the CT scan results in the highest accuracy. Guides that were made from the CT data alone showed and inaccuracy of about 1mm and in combination with an optical scan the inaccuracy dropped to .25mm. What happens basically is that the lab makes the guide on the optical scan of the model rather than on an inaccurate CT scan and gets the full accuracy that an optical scan can provide. In order to plan within the anatomic limits, the optical scan is superimposed and aligned with the CT scan. This can be done in several ways one being within the planning software, exporting an STL file and then refined in a second software such as VRmesh. Best, Albert

You may want to consider making your own 3D surgical guide. Nobody will take as much care as you will with your own case. I fabricate a diagnostic guide take a cone beam x-ray, Galileous, and use Invivo5 software to analyze and evaluate the guide sleeves. I make any corrections and then make the final Surgical guides right in the office. I use the Guide Right components by Deplaque.com to make the corrections in two planes, mesio-distal and bucco-lingual. The angle corrections are made by bending the guide posts in one plane and rotating it 90 degrees and making the correction in the second plane if needed. Their open guide sleeve allows the surgeon to visualize the depth markings on the drills to prepare the osteotomy according to the length of the implant selected in the invivo5 software. The invivo 5 software has a great selection of virtual implants to choose from. it only takes 15 minutes to correct and fabricate the corrected surgical guide in office and accuracy is similar to other outsourced guides.

Dr C-M Lee: Thank you for the common sence pointers. Much appreciated.

One comment I ran into the same thing with tooth supported guides and the problem was the impression I sent. Don't underestimate the impression of the arch you want the guide seated on. I got a guide back that didn't seat in the mouth at all. Started using PVS impressions for both arches and they all fit now. Can't use alginates. You need more accuracy

I have had incredibly accurate guides made using the Galileos Cbct and software and Sicat. Using a virtual model proposed using the cerec superimposed over the cbct confirms the scan accuracy, and the guide is tooth born and te fit verified on a stone model. Finally the 3rd party Sicat review provides an extra set of eyes to evaluate for possible planning errors concerning anatomy and or sleeve position. I am placing 3i nanotapered implants with the navigator surgical kit I find them reliable and incredibly stable.

The guides that are done on mechanical devices like Gonyx are very risky. That is due to the big distance between the cast and the adjusting mechanism. An error in the calibration of the device can generate more than 2mm shift. Check out this video http://www.youtube.com/watch?v=nPy5S2lA9kE

In this method because the entrance of the osteotomy is not a variable the chance to big offset is very small. In the aligning process as long as the stick as small is the error.

Recent study published in the journal of periodontology March or April edition of this year showed that there is deviation using software for surgical stent and they are not always accurate.

Hi Mark Can you give us the study? It is very interesting.

I suggest looking at the guide kits themselves. There can be some slop sleeve and the drill or spoon in the sleeve. The guides are accurate (yes, there can be failures of guides but the vast majority of guides made from reputable manufacturers are accurate). Place your drill into a sleeve and move it around. You will see the potential for misplaced implants. Most kits that I have observed have some play between the drill and sleeve and between the spoon and the master sleeve. Add those discrepancies up and there can be error (most times not enough to cause problems but in thin bone using a pilot bur and freehanding after the initial osteotomy might be considered.