Marginal fit of indirect composite inlays using a new system for manual fabrication.

AIM: This in vitro study compares a new system for manual chair side fabrication of indirect composite restorations, which uses silicone models after alginate impressions, to CAD/CAM-technology and laboratory manual production techniques. MATRIALS AND METHODS: and study design Each 10 composite inlays were fabricated using different types of production techniques: CAD/CAM- technology (A), the new inlay system (B), plaster model after alginate impression (C) or silicone impression (D). The inlays were adapted into a metal tooth and silicone replicas of the cement gaps were made and measured. Statistical analysis was performed using ANOVA and Tukey's test. Results and Statistics In group A the biggest marginal gaps (174.9µm ± 106.2µm) were found. In group B the gaps were significantly smaller (119.5 µm ± 90.6 µm) than in group A (p=0.035). Between groups C (64.6 µm ± 68.0µm) and D (58.2 µm ± 61.7 µm) no significant differences could be found (p=0.998), but the gaps were significantly smaller compared with group B. Conclusion Chairside manufacturing of composite inlays resulted in better marginal precision than CAD/CAM technology. In comparison to build restorations in a laboratory, the new system is a timesaving and inexpensive alternative. Nevertheless, production of indirect composite restorations in the dental laboratory showed the highest precision.

Miniaturized force/torque sensor for in vivo measurements of tissue characteristics.

This paper presents the development of a surgical instrument to measure interaction forces/torques with organic tissue during operation. The focus is on the design progress of the sensor element, consisting of a spoke wheel deformation element with a diameter of 12 mm and eight inhomogeneous doped piezoresistive silicon strain gauges on an integrated full-bridge assembly with an edge length of 500 µm. The silicon chips are contacted to flex-circuits via flip chip and bonded on the substrate with a single component adhesive. A signal processing board with an 18 bit serial A/D converter is integrated into the sensor. The design concept of the handheld surgical sensor device consists of an instrument coupling, the six-axis sensor, a wireless communication interface and battery. The nominal force of the sensing element is 10 N and the nominal torque is 1 N-m in all spatial directions. A first characterization of the force sensor results in a maximal systematic error of 4.92 % and random error of 1.13 %.

[Tribological assessment of articular cartilage. A system for the analysis of the friction coefficient of cartilage, regenerates and tissue engineering constructs; initial results]. / Tribologische Messungen am Gelenkknorpel. Ein Prüfstand zur Messung der Reibungszahlen von Knorpel gegen Knorpel, Regeneraten und TE-Konstrukten und erste Ergebnisse.

Values for the friction coefficient of articular cartilage are given in ranges of percentage and lower and are calculated as a quotient of the friction force and the perpendicular loading force acting on it. Thus, a sophisticated system has to be provided for analysing the friction coefficient under different conditions in particular when cartilage should be coupled as friction partner. It is possible to deep-freeze articular cartilage before measuring the friction coefficient as the procedure has no influence on the results. The presented tribological system was able to distinguish between altered and native cartilage. Furthermore, tissue engineered constructs for cartilage repair were differentiated from native cartilage probes by their friction coefficient. In conclusion a tribological equipment is presented to analyze the friction coefficient of articular cartilage, in vivo generated cartilage regenerates and in vitro tissue engineered constructs regarding their biomechanical properties for quality assessment.

[Osteointegration of an alumina matrix composite ceramic with a porous surface: mechanical and histological results of an animal experiment]. / Osteointegration einer Alumina-Matrix-Composite-Keramik mit poröser Oberfläche: Eine mechanische und histologische Untersuchung im Tierversuch.

INTRODUCTION: The aim of this study was to analyse mechanically and histologically the osteointegration of porous-surfaced ceramic implants made of an alumina matrix composite (AMC) by assessing maximum shear strength and histomorphometric bone ongrowth. METHODS: The surfaces of the cylindrically shaped AMC test implants were characterised by a porosity of 40% and a pore size of 150 to 300 microm. A total of 24 test cylinders was implanted bilaterally into the femurs of 6 female adult Goettinger minipigs. 12 weeks after surgery the animals were sacrificed. 12 test implants were used for a push-out test and 12 test implants were evaluated histologically. RESULTS: The mean maximum shear strength of the bone-implant interface was 7.6 +/- 2.0 MPa. Direct bone attachment was found in 7.4 +/- 3.4% of the histologically analysed surfaces. CONCLUSION: In summary, porous-surfaced AMC test implants demonstrated good mechanical stability in spite of a low percentage of bone ongrowth. This discrepancy could potentially be explained by bone ingrowth into the pores and subsequent interlocking mechanisms.

Test bed for assessment of the kinematical determination of navigation systems for total knee arthroplasty. Does a limited range of motion of the hip joint influence the accuracy of the determination?

OBJECTIVE: To locate the rotational center of the hip joint, CT-less navigation systems for artificial knee-joint replacement use movements of the femur with a rigid body attached. It cannot be assumed that the hip joint provides free mobility at all times. The purpose of the present study was: 1) To build a mechanical model to assess the system's accuracy in locating the rotational center of the hip by simulating a step-wise reduction of the range of motion (ROM) of the hip joint. 2) To determine the system's resolution by assessing a critical distance between two positions of the same femoral rigid body during the process of locating the rotational center of the hip. 3) To determine the sensitivity of the navigation system to the rotation of a femoral rigid body relative to the femoral bone while locating the rotational center of the hip joint. MATERIAL AND METHODS: To assess the impact that a limited ROM of the hip joint has on the accuracy of determination of the hip joint's rotational center, a test bed was built. This enables validation of the algorithm used by a CT-less navigation system. RESULTS: In the first part of the study, it was shown that a reduction of the ROM of the hip joint to 30% of its initial value had no evident influence on the accuracy of locating the rotational center of the joint. In the second part of the study, it was determined that the limit of resolution between two spatial points of the pivoting process is between 4.4 and 8.7 cm. The third part of the study showed that the examined system rejected the determination of the hip center even when the rigid body was only rotated through 22.5 degrees . CONCLUSIONS: The results show that osteoarthritis of the hip with a limited ROM, for example, cannot be taken as a contraindication for the use of the evaluated CT-less navigation system. However, the surgeon should ensure that the pivoting of the femur is performed without hindrance within the free range of motion of the hip joint. In accordance with the vendor's recommendation, a minimum distance of 10 cm should be maintained between two spatial points. To ensure safe and unconstrained operation, the rigid body must be firmly attached to the bone and must not be dislocated.

[A gearing mechanism with 4 degrees of freedom for robotic applications in medicine]. / Getriebe mit 4 Freiheitsgraden für robotische Anwendungen in der Medizin.

Applications in robot-aided surgery are currently based on modifications of manipulators used in industrial manufacturing processes. In this paper we describe novel rotatory kinematics for a manipulator, specially developed for deployment in robot-aided surgery. The construction of the gearing mechanism used for the positioning and orientation of a linkage point is described. Forward and inverse kinematics were calculated, and a constructive solution proposed. The gearing mechanism is based on two disk systems, each of which consists of two opposing rotatable discs. The construction was designed in such a way that the linkage point can be positioned freely anywhere within the mechanism's range of motion. The kinematics thus permits an x-y-positioning via rotating movements only. The spatial arrangement of two of such disc systems permits movements in four degrees of freedom (DOF). The construction is compact, but can be further miniaturized, is flexible and manufacturing costs are low. On the basis of this mechanical concept a new, small automated manipulator for surgical application will be developed.

[Robots, navigation, telesurgery: state of the art and market overview]. / Robotik, Navigation, Telechirurgie: Stand der Technik und Marktübersicht.

UNLABELLED: Currently surgical robots and navigation system are established in the OR. They assist the surgeon as active or passive navigators for orientation on the patient and for insertion of implants. In future, telesurgery will shaft medical experience over great distances. AIM: The goal of this paper is to describe applicable technologies, to analyse today's state of the art and to list the available products in tables. METHOD: An extensive search in literature databases and company's documents and personally conducted interviews were done for evaluation. RESULTS: The systems can be categorized in "active" or "semi-active" (robots), "navigation systems" and "telesurgical workstations". 14 robots, 22 navigation systems and four telesurgical workstations are described. Registration of anatomical structures can be performed with either pins, pair-point, surface, ultrasonic or fluoroscopic matching. At present optical, magnetic or mechanical localizer systems are used. CONCLUSION: The increased use of computer and image-guided methods (CAS and IGS) will optimize surgical treatment. The future has to show whether the necessary additional costs and time will bring better clinical results.