Electrode Impact on the Electrical Breakdown of Dielectric Elastomer Thin Films.

Dielectric Elastomer Actuators (DEAs) enable the realization of energy-efficient and compact actuator systems. DEAs operate at the kilovolt range with typically microampere-level currents and hence minimize thermal losses in comparison to low voltage/high current actuators such as shape memory alloys or solenoids. The main limiting factor for reaching high energy density in high voltage applications is dielectric breakdown. In previous investigations on silicone-based thin films, we reported that not only do environmental conditions and film parameters such as pre-stretch play an important role but that electrode composition also has a significant impact on the breakdown behavior. In this paper, we present a comprehensive study of electrical breakdown on thin silicone films coated with electrodes manufactured by five different methods: screen printing, inkjet printing, pad printing, gold sputtering, and nickel sputtering. For each method, breakdown was studied under environmental conditions ranging from 1 °C to 80 °C and 10% to 90% relative humidity. The effect of different manufacturing methods was analyzed as was the influence of parameters such as solvents, silicone content, and the particle processing method. The breakdown field increases with increasing temperature and decreases with increasing humidity for all electrode types. The stiffer metal electrodes have a higher breakdown field than the carbon-based electrodes, for which particle size also plays a large role.

Nanoscale Nickel-Based Thin Films as Highly Conductive Electrodes for Dielectric Elastomer Applications with Extremely High Stretchability up to 200.

This paper presents on electromechanical characterization of thin film nickel-based wrinkled electrodes for dielectric elastomer (DE) applications. The investigation of a sandwich composed of a very soft and flexible elastomer carrying an ultrathin metallic electrode, together with its prestretch-dependent wrinkled structure of the electrode, facilitates the understanding of some of its interesting properties. Compared to conventional screen-printed carbon black electrodes, nickel-based thin film electrodes offer an ohmic resistance that is about 2 orders of magnitude lower. This remarkable feature makes it an advantageous electrode material alternative for the development of energy-efficient and high-frequency DE applications. Ultrathin (10-20 nm) layers are sputter deposited as electrodes onto either biaxially or, under pure-shear conditions, uniaxially prestretched silicone membranes. After the sputtering process, the membranes are allowed to relax whereby wrinkled out-of-plane buckled surfaces are obtained. With an initial resistance smaller than 400 Ω/square and a strong adhesion to the silicone, some electrode configurations are able to withstand strains up to 200% while remaining electrically conductive. A linear dependence of the capacitance on strain is revealed, as well as a long-term stability over 10 million cycles of mechanical stretching. All investigated thin film configurations of nickel and nickel-carbon films are suitable as compliant electrodes for DE actuators, as demonstrated by measuring the force characteristics with and without a high voltage. An increased level of prestretch shifts the resistance threshold of the electrode layers to even higher strain levels. In general, the best performance is achieved with pure metallic electrodes deposited on biaxially prestretched silicone membranes.

Fully Polymeric Domes as High-Stroke Biasing System for Soft Dielectric Elastomer Actuators.

The availability of compliant actuators is essential for the development of soft robotic systems. Dielectric elastomers (DEs) represent a class of smart actuators which has gained a significant popularity in soft robotics, due to their unique mix of large deformation (>100%), lightweight, fast response, and low cost. A DE consists of a thin elastomer membrane coated with flexible electrodes on both sides. When a high voltage is applied to the electrodes, the membrane undergoes a controllable mechanical deformation. In order to produce a significant actuation stroke, a DE membrane must be coupled with a mechanical biasing system. Commonly used spring-like bias elements, however, are generally made of rigid materials such as steel, and thus they do not meet the compliance requirements of soft robotic applications. To overcome this issue, in this paper we propose a novel type of compliant mechanism as biasing elements for DE actuators, namely a three-dimensional polymeric dome. When properly designed, such types of mechanisms exhibit a region of negative stiffness in their force-displacement behavior. This feature, in combination with the intrinsic softness of the polymeric material, ensures large actuation strokes as well as compliance compatibility with soft robots. After presenting the novel biasing concept, the overall soft actuator design, manufacturing, and assembly are discussed. Finally, experimental characterization is conducted, and the suitability for soft robotic applications is assessed.

Prefabricated iliac crest transplant.

PURPOSE: Our aim was to augment the extremely atrophic mandibular alveolar crest with a pedicled transplant as the best option for a satisfactory preprosthetic outcome. MATERIALS AND METHODS: After computed tomography of the mandible, a model was milled for 6 patients. The iliac crest transplant with its vascular pedicle was harvested and, after preliminary preparation, fixed to the model. The transplant was then placed in the axilla. After 3 months, the graft was removed and fixed to the mandible. RESULTS: The prefabricated transplant fit exactly in all 6 patients. The length of the pedicle and coverage with the newly developed alveolar mucous membrane were satisfactory. The grafts allowed prosthetic reconstruction with good functional outcomes. No bone loss was observed during 7 years of follow-up. Additionally, indocyanine green angiography showed good perfusion in 4 patients after 6 months. CONCLUSIONS: The results suggest that carefully prefabricated pedicled transplants can augment an atrophied mandibular alveolar crest.

Cephalometric and occlusal outcome in adults with unilateral cleft lip, palate, and alveolus after two different surgical techniques.

OBJECTIVE: To assess differences in the aesthetic and functional long-term results of one-stage and two-stage surgical and orthodontic treatment in patients with cleft lip, palate, and alveolus. DESIGN: Sixty adult patients who were operated on as children for unilateral cleft lip, palate, and alveolus were examined. In every patient the lip was closed using Tennison's technique. Thirty patients had soft and hard palate closure in two stages and 30 patients in a single stage. Lateral cephalometric and model analyses were conducted at a mean age of 18.4 years. RESULTS: In the model analysis, transverse narrowing was seen in all patients after two-stage operations and in three patients after one-stage operations. The deficit was more severe in the molar region in the two-stage group and nearly similar in the premolar and molar region in the one-stage group. A sagittal deficiency in the anterior maxilla was found in 26 patients after two-stage operations and in 16 patients after one-stage operations. In the lateral cephalometric analysis, the mean sella-nasion-point A angle in the one- and two-stage group was 78.2 degrees and 76.8 degrees, respectively. The ANB angle was normal in both groups. In both groups the inclination of the midface was low. There was a low posterior facial height. Minor scarring was seen in the single-stage group. CONCLUSION: A more severe impairment of growth of the maxilla in the sagittal and frontal plane was observed after two-stage operations on the cleft palate.

Evaluation of distraction implants for prosthetic treatment after vertical alveolar ridge distraction: a clinical investigation.

PURPOSE: The purpose of this study was to clinically evaluate the mucosal condition and the esthetic and functional results of distraction implants loaded with fixed or removable implant-supported restorations. MATERIALS AND METHODS: A total of 35 patients were treated with 62 distraction implants for correction of alveolar ridge deficiency. The distraction implants were loaded with prosthetic superstructures 4 to 6 months after distraction. Nine patients were provided with single-crown restorations, 16 received metal-ceramic fixed partial dentures, and 10 received removable overdentures. Recall was scheduled before and 3, 6, and 9 months after implant loading. Periotest values, periimplant probing depths, and radiographic marginal bone levels were recorded, along with any biologic or mechanical complications. RESULTS: Patients were followed for 9 months after implant loading. Two distraction implants were lost before abutment connection. After fabrication and placement of individual abutments, all implants were loaded with prosthetic superstructures. The results showed a decrease of the Periotest values, and thus an increase of implant stability, during the following 9 months. Periimplant probing depths also decreased in the first months after implant loading. Soft tissue around the superstructures and adjacent teeth was healthy. CONCLUSION: The distraction implant system has a high potential for osseointegration. Because of the gentle distraction technique and the possibility of using individual abutments at almost any angulation, satisfying esthetic and functional results are possible. The rate of complications was low in this short-term study.

Differences in cephalometric and occlusal outcome of cleft palate patients regarding different surgical techniques.

INTRODUCTION: The purpose of this study was to assess differences of the long-term results following surgical treatment in patients with cleft palate treated by two different surgical concepts. PATIENTS: Fifty-nine adult patients operated on for cleft palate were examined. Thirty palates were closed by a two stage (Widmaier and Veau) and 29 by a single-stage procedure (Veau's pedicled flap). METHODS: Lateral cephalometric and model analysis was performed. In the cephalometric analysis, the vertical and horizontal parameters of the position of maxilla and midface and transverse and sagittal dimensions of the models were compared between the two groups. RESULTS: Model analysis: According to the Bolton analysis the maxillary dental arch was too large in 22 patients in each group. The other patients had mandibular arches that were too large. In 18 patients with two-stage closure and in 9 patients with one-stage closure, a space deficit in the lateral part of the maxilla was observed. Persisting transverse deficits were seen in all patients with two-stage repairs and in 11 patients with one-stage repairs. The deficit was more severe in the molar area in the first group and almost equally severe in the premolar and the molar regions of the second group. A sagittal deficiency was found more often in patients with two-stage repairs while Angle's class I occlusion was seen more often in patients with one-stage surgery. Lateral cephalometry: Similar SNA-angles were seen in both groups whereas the ANB-angle was greater following two-stage repair. In both patient groups a low inclination of the midface was seen. The vertical dimension of the midface in comparison with the lower face was normal in the one-stage group; in the other group a deficiency of the anterior midface height was registered. CONCLUSION: There was a more severe growth impairment of the midface in patients with this type of two-stage palatal repair. The horizontal deficiency was similar in both groups. The long-term occlusal result revealed smaller sagittal and transverse deficiencies in patients with this type of single-stage closure.

Assessment of perfusion of facial microvascular transplants and early detection of ischemia by perfusion-CT scan.

OBJECTIVE: Perfusion-computed tomography (CT) is a promising new technique to assess ischemic lesions caused by ischemic brain stroke. In this study, the use of perfusion-CT scans to predict ischemia in microvascular transplants of the face was examined. STUDY DESIGN: Thirty-eight patients with microvascular latissimus dorsi transplants after tumor surgery were assessed by perfusion-CT scan 34 to 72 hours after surgery. In these cases, clinical examination of the transplant and examination by means of O(2)-probes were either unsuccessful or impossible. An electron beam tomography of the region of interest was performed by using an intravenous nonionic iodine-containing contrast medium (Ultravist 300, Nycomed, Germany) that was applied with an injector at a flow rate of 5 mL/min. Twenty scans with a scanning time of 300 ms and an interscanning time of 3 seconds were carried out. Changes in the Houndsfield units within the transplant as well as the region of the contralateral erector spinae muscle were measured. RESULTS: Central malperfusion resulting in later complete transplant loss was detected in 2 cases. Peripheral malperfusion was found in 6 cases, resulting in localized resection and secondary wound closure. When no malperfusion was registered, the straightforward healing process took place. CONCLUSION: Perfusion-CT scans are of great aid in the assessment of microvascular transplant perfusion in the face, when adequate perfusion is not verifiable clinically or by O(2)-probe because of removal or malfunction.

The transgingival approach for placement of distraction implants.

PURPOSE: Since 1997, distraction implants have been clinically used for alveolar ridge distraction and, later, for prosthetic treatment. While 63 patients have been treated by the authors by alveolar ridge distraction with distraction implants with an open approach, the aim of this study was to demonstrate a minimally invasive technique of distractor placement via a transgingival approach. PATIENTS AND METHODS: Twelve patients were treated with a modified surgical incision using distraction implants. A tissue punch was used to remove transgingival mucosa, and a segmental osteotomy was performed using a vestibular incision. The distracted segment was pedicled at the lingual and crestal mucoperiosteum. Distraction was carried out for 0.5 mm per day, divided into 2 to 4 turns per day. A distraction of 5 to 7 mm was performed. At the end of distraction, the distraction insert was changed into a definitive stable implant insert. Prosthetic treatment was performed 4 months after the distraction period with fixed superstructures. The follow-up was performed with the aid of dental radiographs, evaluation of peri-implant probing depths, and Periotest values (Siemans, Bensheim, Germany). RESULTS: The outcome of this technique showed minimal scarring of the gingiva with good aesthetic results, the clinical and radiologic findings were satisfying, and the Periotest values were negative at every examination. The rate of complications was low. CONCLUSION: Minimal scarring and good aesthetic and functional outcome resulted in patients with alveolar ridge distraction performed with a transgingival approach.

Assessment of accuracy of navigated implant placement in the maxilla.

PURPOSE: The use of computed tomography (CT) based intraoperative navigation has greatly improved surgery in many specialties. In this study, the precision of the SMN system (Zeiss, Oberkochen, Germany) for navigated drilling and following implant placement in the maxilla was evaluated. This study should demonstrate the suitability of navigation systems for computer-assisted implantation in the maxilla to avoid perforation of the maxillary sinus. MATERIALS AND METHODS: Sixty target drillings were carried out on 10 standardized polyurethane milling models after CT scanning. The models were produced with cranial open maxillary sinuses. The CT scans were performed with a slice distance of 1 mm. Then the CT data were transferred to the workstation of the SMN system and registration of the reference markers (fiducials) for superposition of the native and CT model was done. Referencing of the model was performed with the aid of a drilling tool. This drilling tool was used for later navigation-assisted drilling into the maxilla. The target of drilling was the maxillary sinus floor. The aim was to come as near as possible without perforation. The distance from the bottom of the drilling holes to the maxillary sinus floor was measured after sectioning of the model. In another 10 models, implants were placed after performing 60 navigated drilling holes. RESULTS: In the first part of the study, an average drilling depth of 6.97 mm and a mean distance to the sinus floor of 0.11 mm (standard deviation = 0.2) was found. In 13 specimens, the inferior border of the sinus was perforated. In the second part of the study, a perforation of the sinus floor by the implants was seen in 47 cases. The mean distance to the maxillary sinus was 0.25 mm (standard deviation = 0.2). DISCUSSION AND CONCLUSIONS: High precision of CT-based navigation for controlled preimplant drilling was seen, but a high incidence of penetrations into the maxillary sinus was caused by the subsequent implant placement.

Stability of dental implants in microvascular osseous transplants.

Microvascular iliac crest and scapula transplants have been used in reconstruction of the lower jaw following tumor surgery. It has only been with the insertion of dental implants that a satisfactory prosthetic rehabilitation of the patient has been achieved. For this study, a follow-up of 38 patients with lower jaw tumors was carried out. The patients had been treated with partial resection of the lower jaw and neck dissection with microvascular iliac crest transplants (n = 20) or microvascular scapula transplants (n = 18); this was followed with dental implants (n = 143) in the region of the transplants or the local lower jaw. One hundred thirty-nine of the 143 dental implants were loaded by prosthetic superstructures. In all patients, the implant situation was evaluated on average 2 years 5 months after implantation. Periotest values, periimplant probing depths, and contact bleeding were registered, and the extent of periimplant bone loss was defined radiographically. The clinical situation in the region of the implant was compared for both types of implants and also with the nonresected lower jaw. The average Periotest values were within the normal range for all groups. In one scapula implant, however, a better average of Periotesting, -3.3, was found compared with implants of the iliac crest with Periotest values of -0.7. A measurement of -2.1 was found for the local lower jaw, similar to that of scapula implants. Pathologic probing depths were found for all three compared groups. The radiographically determined vertical loss of bone was the same for all three groups, on average 1 mm at 27 months postoperatively. The highest incidence of sulcus bleeding was found in the scapula implant group. Thus, it can be stated that the scapula transplants provide a similar transplant site to local lower jaw bone, whereas implants in iliac crest transplants show lesser bony stability. Periimplant soft-tissue conditions are worse for both types of transplants compared with local tissue of the lower jaw.