Clinical Application of a New Dental Reference System for Computer Assisted Surgery at the Lateral Skull Base

Abstract

Objective: The safest method for a reliable registration on the lateral skull base is the placement of fiducial markers into the patient's bone by screws. An alternative method is the use of a resin splint that is fixated to the maxillary dentition, which carries the fiducial markers. Then the invasive fixation using bone screws becomes unnecessary. The aim of this study was to evaluate the accuracy of a new dental reference array (DRA). Methods: The DRA was initially tested in laboratory settings and was then applied to ten patients with surgery on the lateral skull base. An individual formed maxillary dental splint was created out of polymethylmethacrylate. The Vector Vision compact® (BrainLAB, Germany) navigation system measured the deviation on several target markers at the lateral skull base in one phantom trial, one cadaver skull and ten patients. Results: The DRA was perfectly adjusted to the phantom. The average deviation was only 0.5mm. The average deviation on four different target markers in the cadaver trial was 0.6 mm. In five patients the accuracy was acceptable (<1.2mm). But in the other five cases the deviation was more than 10mm due to different problems which were analysed carefully. Discussion: The DRA could resolve the problem of invasive marker fixation with little additional effort and cost. However, the successful use depends on the individually formed dental splint, which has to be perfectly adjusted to the maxilla, because the additional weight of the extraoral part acts as a lever and may dislocate. It is essential that the splint does not cant; the reference extension must not graze the skin of the patient; during surgery no coverage should pull on the DRA, otherwise the repositioning is not accurate. When avoiding all this, the accuracy of the dental reference array is sufficient for image-guided surgery of the lateral skull base.

Image guided navigation by intraoperative CT scan for cochlear implantation

“…With the intraoperative acquisition of CT images to serve as a basis for navigation, surgical precision can be improved, thereby allowing successful cochlear implant surgery in patients with complex malformations or those who have undergone multiple previous ear surgeries and consequently lack anatomical landmarks. Our study clearly shows that the high-resolution dataset of iCT with automatic volumetric registration is superior to other registration methods (i.e., surface matching [11,12], point-pair matching [5,13], and even pin registration [14]), not only in terms of accuracy and precision, but also in time and effort required. In volumetric registration the highest spatial accuracy is obtained in the center of the operation field, which is normally the region of interest, whereas in all other registration methods the best accuracy is obtained near the registered region (in surface matching on the surface; in pin registration between the pins; and in point-pair matching between the points), and progressively decreases as the surgeon moves away from that region.…”

“…The use of surgical navigation is well accepted in anterior skull base and sinus surgery [9], but not in surgery of the lateral skull base because of the reduced accuracy associated with prolonged surgical duration for referencing and registration [5]. Navigation data are usually based on preoperative CT or MR images [10].…”

“…In the registration phase, the image data is matched to the patient intraoperatively by locating the fiducial markers on the patient's body. The safest method for achieving a reliable registration is by fixation of fiducial markers in the patient's bone with screws, as this prevents the displacement which can occur with soft tissue-mounted fiducials [4] or dental reference arrays [5]. In fact, the use of titanium screws drilled into the skull is considered the gold-standard method [6].…”