Objective: The 2 goals that need to be served while placing dental implants are: 1) safe
placement without injury to adjacent structures and 2) implant positioning is well coordinated
to the anticipated prosthesis. These 2 goals may be achieved by planning the positioning of
the implants directly on the dental CT scan of the patient. Yet, this digital plan needs to be
transferred to the patient.
Solution: Currently, 2 major solutions are offered: 1) stereolithographic drill guides which are
made in a computerized manufacturing process based on the digital implant plan, 2)
computerized navigation surgery that use real-time motion tracking technology to navigate the
implant drilling and placement.
Conclusion: The accuracy range reported for stereolithographic drill guides is undoubtedly
unacceptable and raises a major concern on their reliability in routine usage. On the other
hand, computerized navigation surgery offers improved accuracy and real-time feedback
which allows better flexibility and is superiorly more reliable
FROM SIMPLE GUIDES TO STEREO LITHOGRAPHIC GUIDES AND TO REAL-TIME NAVIGATION
Implant surgery is challenging: The surgical placement of dental implants requires
complex coordination by the surgeon. The surgeon’s main concern is to ensure the safe
insertion of the implant without perforating the limited dentoalveolar bone compartment and
without conflicting with adjacent vital structures (roots, mandibular nerve, maxillary sinus, etc).
Still, the absolute objective of a dental implant is to effectively and aesthetically support a
crown replacement. Thus, the surgeon must simultaneously coordinate the position of the
implant to the future crown replacement.
Stereolithographic guides are an important step forward: In many cases there is an
unavoidable tension between placing the implant safely and coordinating the implant with the
future crown. Stereolithographic guides have developed as a solution for transferring the
implant plan from the dental CT scan to the surgical settings. In that sense, stereolithographic
guides have been the first step in implementing image guided surgery to facilitate more
judicious placement of dental implants. Indeed, there is scientific evidence that shows that
these guides provide superior accuracy in placing implants when compared with drill guides
that are fabricated without reference to CT imaging.1
Accuracy range of stereolithographic guides is too wide: Yet, stereolithographic
guides have significant limitations and are far from being an ideal solution for supporting
implant placement. The mean linear accuracy of implants placed with stereolithographic
guides is reported to range between 1.1mm to 1.45mm at the implant neck and between
1.41mm 2.99mm at the implant apical tip.2-5 The mean angular deviation is reported to range
between 2 degrees to 7.25 degrees. This mean accuracy might not be considered acceptable
in some clinical cases where the clinical settings require higher level of accuracy.
Furthermore, the range of linear and angular error is reported to be higher than 3mm and 9
degrees which is evidently unacceptable and could lead to surgical complications or improper
positioning of the implant.
Difficult to intercept errors in the drill guide: In using stereolithographic guides the
surgeon is compelled to follow the drilling sleeves BLINDLY without being able to verify the
accuracy of the guide. Furthermore the guide itself is bulky and obscures the sight of the
implant site which prevents the surgeon from intercepting errors in the drilling path of the
guide. Thus, inaccuracies in placing the implants may only be identified post placement and
are difficult to avoid. When the inherent accuracy of the guide is at the upper range as
reported above, this could lead to potential complications. In other cases, where the surgeon
is able to identify an error in the drilling path of the guide, the guide can not be corrected on
site. The guide becomes inadequate and can not be used. The surgeon is left with the option
of drilling the implant free handedly or to postponing the surgery until a corrected guide could
be delivered.
Real-time image guided surgery is interactive and offers higher accuracy: These
limitations of stereolithographic guides are overcome in using real-time image guided surgery.
While stereolithographic guides allow only 1-way flow of information from the pre-acquired
imaging to surgical field, real-time navigation systems are INTERACTIVE and allow backflow
of information. The accuracy of the navigation provided by the IGI was found to average
0.35mm.6 Furthermore, this accuracy can be verified in real-time thereby avoiding surgical
errors. The drilling is accomplished free handedly by following onscreen indicators while the
implant site in not obscured by a bulky drilling sleeve. Based on the clinical limitation of each
case the surgeon is at liberty to judge the level of accuracy required to accomplish safe and
effective implant positioning. In cases where the bone compartment is highly limited the
surgeon can achieve highly precise accuracy by following the very detailed and high
resolution indicators. Yet, in cases where accuracy is less critical the surgeon can accept
more leeway in the drilling path. This approach leaves the control over the surgery in the
hands of the surgeon. The technology enhances the surgeon’s orientation and does not
require the surgeon to blindly follow a pre-made drill sleeve.
IGI accuracy has been validated with real patient: This concept has been illustrated
in a recent study by Elian et at who studied the accuracy level in placing implants by the IGI.7
The mean linear accuracy was less than 1mm at both the implant neck and apical tip and the
reported mean angular deviation was less than 4 degrees. Despite the fact that all implants
were drilled free handedly and not through sleeves, Elian et al found an accurate match
between the planned implant and final implant. A major part of the error could be attributed to
human error in following the onscreen drilling path. In that context the important advantage of
real-time navigation is that even when the actual free handed drilling is deviating from the
planned drilling path the surgeon can still monitor the actual drilling onscreen. This accurate
and immediate feedback allows the surgeon to judge whether the actual drilling path is
clinically acceptable or should be corrected.
IGI is flexible allowing intraoperative changes to the drilling path: The interactive
nature of full navigation also allows intraoperative modification of the implant plan. Such
modifications are often necessary since the presurgical plan was based on the CT imaging
without direct view of the surgical site. This matter poses a problem for even experienced
surgeons and thus gives significant advantage to real-time navigation which allows fine-tuning
of the virtual drilling path. As mentioned above, this is not possible with stereolithographic
guides where the physical drilling sleeve can not be modified.
