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.

Bone treatment laser-navigated surgery.

A new concept was developed based on the experience gained in dental rehabilitation with implantation in the oral maxillofacial region. Despite the use of cooling systems, mechanically rotating instruments may damage the surrounding tissue due to the frictional heat generated. An alternative approach for bone removal is laser application. A preoperative plan was prepared. Laser ablation was performed in accordance with the data set on bovine bone using a navigation system. This new concept allows precise bone removal and adjustment of the laser power according to the preoperative plan. The power of the laser automatically decreases as it approaches the border of the planned cavity or important anatomical structures. The advantage of this approach is precise and safe bone removal without damaging the bone by frictional heat.

First clinical application of a navigation-controlled shaver in paranasal sinus surgery.

Conventional, pointer-based navigated Functional Endoscopic Sinus Surgery (FESS) has been shown to have certain limitations: necessity of instrument change for navigation, changes in the surgeon's line-of-sight axis, and limited length of use of the navigation information. These limitations result in negative consequences regarding the surgeon's attentiveness in any given situation, as well as in his cognitive work-load. The principle of Navigated Control offers advantages concerning these problems and limitations of the conventionally navigated FESS. This Chapter analyzes the first clinical deployment of a navigation-controlled shaver in FESS on the basis of the following questions: (1) Is clinical deployment of the navigation-controlled shaver possible with the pre-clinic evaluated set-up? (2) What information relevant to the surgery is relayed in an intraoperative setting by the navigation-controlled shaver? (3) How does deployment of the navigation-controlled shaver affect the ergonomics of the surgery? Ten patients with chronic sinusitis ethmoidalis were included in the study (average age: 48 [22-71], m:w=4:6). The preoperative and intraoperative workflow was documented according to the Innovation Center Computer Assisted Surgery (ICCAS) Workflow protocol. Data regarding the surgical validity of the information and ergonomic characteristics were recorded by means of questionnaires. The average time required for segmentation of the workspace was 14.2 minutes. The shaver switched off through Navigated Control an average 16.5 times during an FESS. From this amount, five shutdowns on average were initiative and six were determined to be provoked. The shutdowns were indicated by the operators to be correct in 199 of 220 (90.5%) events and in agreement with the actual position and planned resection borders. The quality of the relayed navigation information was indicated with an average Level of Quality (LOQ) of 56.4 [50-80]. The most favorable evaluation was attained for navigation in the area of the sphenoid sinus with 71 points on average [60-80]. During an FESS, the navigation information led to a change in the planned surgical strategy an average of 0.9 [0-3] times. Throughout all surgical procedures, the situation awareness was assessed an average of 2.7 points better than with the conventionally navigated FESS. This also was the case for the cognitive workload (Workload shift) with 2.8 [1-3.5] points. This Chapter proves the clinical applicability of a navigation-controlled instrument by means of a shaver in Ears, Nose, and Throat (ENT) surgery for the first time. Reproduction of the dental splint registration, manual segmentation of the working space, and attachment of the registration star still prove to be critical aspects. Data regarding quality of the information relayed by the navigation system and resulting change in surgical strategy lead to the conclusion that the authors are dealing with, in the overall evaluation, supplementary and surgically relevant information. This information is more efficiently transferred to the surgeon by means of Navigated Control that allows, according to the following results, both an improved understanding of the information and cognitive easing of stress for the surgeon.

Robot-assisted placement of craniofacial implants.

PURPOSE: The purpose of this study was to improve and accelerate the rehabilitation process for patients with severe ear microtia with an implant-anchored auricular prosthesis. A medically approved robot system was used to place the craniofacial implants and a new process was developed for preoperative fabrication of the prosthesis using a rapid prototyping technique. MATERIALS AND METHODS: Preoperatively, after computerized tomography, the implant positions were determined in a planning tool according to bone availability and esthetic considerations. Intraoperatively, the robot showed the surgeon the planned implant positions and guided the placement procedure. RESULTS: The accuracy measurements showed that with this robot system, absolute implant position accuracy of approximately -0.5 +/- 0.4 mm, a relative accuracy between the implants of approximately 0.2 +/- 0.5 mm, and a deviation from the parallel position of approximately 0.6 +/- 0.5 degrees were achieved. Thirty implants were placed in 13 patients with robot assistance with no intraoperative injuries. DISCUSSION: This technique made it possible to apply the preoperatively fabricated auricular prosthesis directly after surgery. CONCLUSION: From this experience it can be concluded that the robot system and the new manufacturing concept for anaplastology can be applied advantageously in other areas of the head as well.

Application of stereolithography for scaffold fabrication for tissue engineered heart valves.

A crucial factor in tissue engineering of heart valves is the functional and physiologic scaffold design. In our current experiment, we describe a new fabrication technique for heart valve scaffolds, derived from x-ray computed tomography data linked to the rapid prototyping technique of stereolithography. To recreate the complex anatomic structure of a human pulmonary and aortic homograft, we have used stereolithographic models derived from x-ray computed tomography and specific software (CP, Aachen, Germany). These stereolithographic models were used to generate biocompatible and biodegradable heart valve scaffolds by a thermal processing technique. The scaffold forming polymer was a thermoplastic elastomer, a poly-4-hydroxybutyrate (P4HB) and a polyhydroxyoctanoate (PHOH) (Tepha, Inc., Cambridge, MA). We fabricated one human aortic root scaffold and one pulmonary heart valve scaffold. Analysis of the heart valve included functional testing in a pulsatile bioreactor under subphysiological and supraphysiological flow and pressure conditions. Using stereolithography, we were able to fabricate plastic models with accurate anatomy of a human valvular homograft. Moreover, we fabricated heart valve scaffolds with a physiologic valve design, which included the sinus of Valsalva, and that resembled our reconstructed aortic root and pulmonary valve. One advantage of P4HB and PHOH was the ability to mold a complete trileaflet heart valve scaffold from a stereolithographic model without the need for suturing. The heart valves were tested in a pulsatile bioreactor, and it was noted that the leaflets opened and closed synchronously under subphysiological and supraphysiological flow conditions. Our preliminary results suggest that the reproduction of complex anatomic structures by rapid prototyping techniques may be useful to fabricate custom made polymeric scaffolds for the tissue engineering of heart valves.

Accuracy of navigated control concepts using an Er: Yag-laser for cavity preparation.

This paper describes a method for measuring the shape accuracy of a cylindrical hole which is created by means of an automatically power-controlled laser system using navigated control. In dental surgery, drills or mills are used for bone treatment. For most patients the use of these instruments is very inconvenient. Furthermore, the bone treatment with rotating instruments can lead to thermal necrosis. Using a laser system could be a good alternative for the patient. The utilization of a laser system could also facilitate bone treatment without any severe thermal damage. An optical navigation system can be used for a safer handling of a laser system. The position and the orientation of the laser handpiece relative to the patient can be calculated. Thereby, the laser can be automatically switched off, if the end of the laser beam does not hit the preoperative planned area. In order to measure the accuracy of such a laser system, we created several cavities in a phantom with a manually guided, automatically power-controlled laser. Afterwards, the deviation between the planned shape and the shape created by manually guided automatically power-controlled laser treatment has been measured. The application of this system showed, that the required accuracy of <1 mm for dental implantology applications, could not be reached.

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.