Accuracy of templates for navigated implantation made by rapid prototyping with DICOM datasets of cone beam computer tomography (CBCT).

The aim of this study is to evaluate the accuracy of a surgical template-aided implant placement produced by rapid prototyping using a DICOM dataset from cone beam computer tomography (CBCT). On the basis of CBCT scans (Sirona® Galileos), a total of ten models were produced using a rapid-prototyping three-dimensional printer. On the same patients, impressions were performed to compare fitting accuracy of both methods. From the models made by impression, templates were produced and accuracy was compared and analyzed with the rapid-prototyping model. Whereas templates made by conventional procedure had an excellent accuracy, the fitting accuracy of those produced by DICOM datasets was not sufficient. Deviations ranged between 2.0 and 3.5 mm, after modification of models between 1.4 and 3.1 mm. The findings of this study suggest that the accuracy of the low-dose Sirona Galileos® DICOM dataset seems to show a high deviation, which is not useable for accurate surgical transfer for example in implant surgery.

Model for nerve visualization in preoperative image data based on intraoperatively gained EMG signals.

While removing bone tissue of the mastoid, the facial nerve is at risk of being injured. In this contribution a model for nerve visualization in preoperative image data based on intraoperatively gained EMG signals is proposed. A neuro monitor can assist the surgeon locating and preserving the nerve. With the proposed model gained EMG signals can be spatially related to the patient resp. the image data. During navigation the detected nerve course will be visualized and hence permanently available for assessing the situs.

[A new X-ray-free measurement method for postoperative 3D-position analysis of navigated inserted implants]. / Ein neues Verfahren zur bildfreien Kontrolle der postoperativen Genauigkeit navigiert gesetzter Implantate.

In this article a new X-ray-free measurement method for postoperative 3D-position analysis of dental implants is proposed. The advantage of this new method is the possibility of precise 3D comparison to preoperative planning data without the use of X-rays. Standard methods for postoperative implant analysis are performed manually on the basis of orthopantomography or computer tomography scans. The proposed method uses a navigation system and a specially designed measurement device. Analysis of the measurement data shows a mean position error of 0.2 mm +/-0.1 mm and a mean depth error of 0.4 mm +/- 0.3 mm. Thus, this method is suitable for postoperative analysis of the horizontal implant position and for comparison to preoperative planning

A new concept for navigated laser surgery.

In this article, a new concept for navigated laser surgery is presented. Mechanically rotating instruments such as drills or mills for bone treatment have the disadvantage of damaging the surrounding bone by the generated frictional heat. Cooling of the instrument cannot avoid this damage completely. Laser systems are an alternative solution for bone removal. Areas of application for bone treatment laser systems are the dental implantology and the osteotomy. The goal of the approach presented here was to combine the advantages of laser treatment with the precision and safety of navigated control. During the use of medical laser systems, the tissue is not only removed exactly in the focus of the laser. It is removed inside of a remove range around the focus. The amount of removed bone cannot be determined only by performance adjustment and the position of the laser because the size of the remove range is unknown. The new approach is to use a position- and orientation-dependent power-controlled laser. Therefore, a calibration of the laser parameters has to be accomplished. The position and orientation of the laser handpiece is measured by an optical measurement system. The laser parameters and the tissue properties are determined by a calibration procedure. On the basis of a preoperative planning, the laser remove range is adjusted by modulation of the laser power. Near to border areas or sensitive structure, the laser power is decreased. Therewith, a precise and safe bone removal according to a preoperative planning without damaging the bone by frictional heat is possible. The inaccuracies as result of simplifications by the calibration procedure have to be verified.

A new approach for creating defined geometries by navigated laser ablation based on volumetric 3-D data.

This paper describes a new approach for laser bone treatment according to a preoperative plan. The advantages of using laser systems are the free choice of the cutting geometry and the possibility of bone treatment without any severe thermal damage. On the other hand, the control of bone removal depth is difficult. Due to the lack of haptical feedback, it is only possible to control the bone removal visually. In addition, by selecting wrong laser parameters and incorrect handling,the tissue can sustain thermal damage. To solve this problem, an approach of navigated and model-based calculation of depth ablation has been investigated. The focus of this paper was to verify the feasibility of precise and safe laser bone removal by combining navigation information with mathematical and volumetric modeling. For the mathematical modeling, known approaches are used. On the basis of CT data, cavities in a bovine bone were planned with a navigation system. With an optical measurement system, the position of the laser handpiece was calculated relative to the bone. Using a mathematical model, the theoretical cavity depth was calculated for each laser pulse and displayed on the navigation screen. Thereby, the material removal was determined in a volume model. With this information, five cavities were created by the laser using constant energy settings. A final measurement of the cavities' depths showed an error of less than 1 mm.

A new method for optimized laser treatment by laser focus navigation and distance visualization.

This paper describes a new method for optimized laser treatment. One of the goals of laser bone treatment is to avoid thermal damage to the surrounding tissue. Er:YAG laser systems are suited for gentle bone treatment. The laser result depends on the laser parameters like pulse energy, pulse frequency and pulse length. Additionally, the laser result depends on the distance between the laser focus and the bone surface. This dependency is founded in the laser beam geometry. The laser beam diameter increases with increasing distance to the focus. Therewith, the energy density of the laser beam decreases with increasing distance. To point the correlation between the focus position and the laser result an experiment with pig compacta was performed and validated. The results show a dependency between the focus distance and the carbonization of the bone cavities. Furthermore, the depth of the produced cavities decreased with the focus distance. To avoid laser treatment beyond the laser focus a navigation concept is presented. Therewith, laser focus is visualized relative to image data of the treated bone tissue.