Norbert R. Kübler

Osseointegration of zirconia implants compared with titanium: an in vivo study

BackgroundTitanium and titanium alloys are widely used for fabrication of dental implants. Since the material composition and the surface topography of a biomaterial play a fundamental role in osseointegration, various chemical and physical surface modifications have been developed to improve osseous healing. Zirconia-based implants were introduced into dental implantology as an altenative to titanium implants. Zirconia seems to be a suitable implant material because of its tooth-like colour, its mechanical properties and its biocompatibility. As the osseointegration of zirconia implants has not been extensively investigated, the aim of this study was to compare the osseous healing of zirconia implants with titanium implants which have a roughened surface but otherwise similar implant geometries.MethodsForty-eight zirconia and titanium implants were introduced into the tibia of 12 minipigs. After 1, 4 or 12 weeks, animals were sacrificed and specimens containing the implants were examined in terms of histological and ultrastructural techniques.ResultsHistological results showed direct bone contact on the zirconia and titanium surfaces. Bone implant contact as measured by histomorphometry was slightly better on titanium than on zirconia surfaces. However, a statistically significant difference between the two groups was not observed.ConclusionThe results demonstrated that zirconia implants with modified surfaces result in an osseointegration which is comparable with that of titanium implants.

Behavior of osteoblastic cells cultured on titanium and structured zirconia surfaces

BackgroundOsseointegration is crucial for the long-term success of dental implants and depends on the tissue reaction at the tissue-implant interface. Mechanical properties and biocompatibility make zirconia a suitable material for dental implants, although surface processings are still problematic. The aim of the present study was to compare osteoblast behavior on structured zirconia and titanium surfaces under standardized conditions.MethodsThe surface characteristics were determined by scanning electron microscopy (SEM). In primary bovine osteoblasts attachment kinetics, proliferation rate and synthesis of bone-associated proteins were tested on different surfaces.ResultsThe results demonstrated that the proliferation rate of cells was significantly higher on zirconia surfaces than on titanium surfaces (p < 0.05; Students t-test). In contrast, attachment and adhesion strength of the primary cells was significant higher on titanium surfaces (p < 0.05; U test). No significant differences were found in the synthesis of bone-specific proteins. Ultrastructural analysis revealed phenotypic features of osteoblast-like cells on both zirconia and titanium surfaces.ConclusionThe study demonstrates distinct effects of the surface composition on osteoblasts in culture. Zirconia improves cell proliferation significantly during the first days of culture, but it does not improve attachment and adhesion strength. Both materials do not differ with respect to protein synthesis or ultrastructural appearance of osteoblasts. Zirconium oxide may therefore be a suitable material for dental implants.

Osseointegration of zirconia implants: an SEM observation of the bone-implant interface.

BackgroundThe successful use of zirconia ceramics in orthopedic surgery led to a demand for dental zirconium-based implant systems. Because of its excellent biomechanical characteristics, biocompatibility, and bright tooth-like color, zirconia (zirconium dioxide, ZrO2) has the potential to become a substitute for titanium as dental implant material. The present study aimed at investigating the osseointegration of zirconia implants with modified ablative surface at an ultrastructural level.MethodsA total of 24 zirconia implants with modified ablative surfaces and 24 titanium implants all of similar shape and surface structure were inserted into the tibia of 12 Göttinger minipigs. Block biopsies were harvested 1 week, 4 weeks or 12 weeks (four animals each) after surgery. Scanning electron microscopy (SEM) analysis was performed at the bone implant interface.ResultsRemarkable bone attachment was already seen after 1 week which increased further to intimate bone contact after 4 weeks, observed on both zirconia and titanium implant surfaces. After 12 weeks, osseointegration without interposition of an interfacial layer was detected. At the ultrastructural level, there was no obvious difference between the osseointegration of zirconia implants with modified ablative surfaces and titanium implants with a similar surface topography.ConclusionThe results of this study indicate similar osseointegration of zirconia and titanium implants at the ultrastructural level.

The new polyomavirus (MCPyV) does not affect the clinical course in MCCs

Since 2008, a new polyomavirus (MCPyV) in Merkel cell carcinomas (MCC) has been described, but little is known about its impact on the clinical course. The purpose of this study was to determine the presence of MCPyV in a large sample and to correlate the results with the clinical course of the disease. 59 samples from 44 patients were analysed for the presence of MCPyV using the primers LT3, VP1 and LT1. The clinical records of these patients were evaluated and correlated with the presence of MCPyV. 58% of specimens were positive for MCPyV. Of these, LT3 was positive in 53%, VP1 in 37% and LT1 in 10%. 57% of primary tumours and 53% of metastases were positive for LT3; the numbers for VP1 and LT1 were lower. There was no correlation between the detection of MCPyV in the primary tumour and the appearance of metastases. The survival time was statistically independent from the presence of MCPyV. There is a striking occurrence of MCPyV in MCC, but whether it affects the clinical course remains unclear.

Prospects of micromass culture technology in tissue engineering

Tissue engineering of bone and cartilage tissue for subsequent implantation is of growing interest in cranio- and maxillofacial surgery. Commonly it is performed by using cells coaxed with scaffolds. Recently, there is a controversy concerning the use of artificial scaffolds compared to the use of a natural matrix. Therefore, new approaches called micromass technology have been invented to overcome these problems by avoiding the need for scaffolds. Technically, cells are dissociated and the dispersed cells are then reaggregated into cellular spheres. The micromass technology approach enables investigators to follow tissue formation from single cell sources to organised spheres in a controlled environment. Thus, the inherent fundamentals of tissue engineering are better revealed. Additionally, as the newly formed tissue is devoid of an artificial material, it resembles more closely the in vivo situation. The purpose of this review is to provide an insight into the fundamentals and the technique of micromass cell culture used to study bone tissue engineering.

Comparison of various approaches for the treatment of fractures of the mandibular condylar process.

UNLABELLED Fractures of the mandibular condyle process are the most common fractures of the lower jaw. Unfortunately, the type of treatment is still a matter of debate. PURPOSE The aim of this investigation was to compare the outcome of different treatment approaches regarding function and surgical side-effects. PATIENTS AND METHODS 111 fractures of the mandibular condyle representing all types according to the classification of Spiessl and Schroll were included. Both closed reduction (CR) and open reduction with internal fixation (ORIF) including the retromandibular/transparotid, submandibular, preauricular and intraoral approach were performed. The clinical examination included functional and aesthetic aspects at least 1 year after the fracture. RESULTS The majority of fractures (45%) were classified into Type II and IV according to Spiessl and Schroll followed by fractures without any displacement or dislocation (29.7%). The submandibular approach showed the worst outcome regarding permanent palsy of the facial nerve and hypertrophic scarring. No significant differences between the various approaches were detected in the functional status in any diagnosis group. CONCLUSION Inferior condylar neck fractures benefit from ORIF by an intraoral approach whereas in high condylar neck fractures the retromandibular/transparotid approach shows the best results. Fractures of the condylar head were almost all treated by CR and our results cannot contribute to the debate of CR vs. ORIF in this type of fracture.

Evaluation of the quality of life of patients with maxillofacial defects after prosthodontic therapy with obturator prostheses.

The purpose of this study was to investigate how patients with maxillofacial defects evaluate their quality of life after maxillectomy and prosthodontic therapy with obturator prostheses. 43 patients were included in the study (25 female, 18 male). 31 (72%) patients completed a standardized questionnaire of 143 items and then answered additional questions in a standardized interview. Global quality of life after prosthodontic therapy with obturator prostheses was 64% (±22.9) on average. Functioning of the obturator prosthesis, impairment of ingestion, speech and appearance, the extent of therapy, and the existence of pain had significant impact on the quality of life (p<0.005). Orofacial rehabilitation of patients with maxillofacial defects using obturator prostheses is an appropriate treatment modality. To improve the situation of patients prior to and after maxillectomy sufficient information about the treatment, adequate psychological care and speech therapy should be provided.

Generation and differentiation of microtissues from multipotent precursor cells for use in tissue engineering

This protocol describes an effective method for the production of spherical microtissues (microspheres), which can be used for a variety of tissue-engineering purposes. The obtained microtissues are well suited for the study of osteogenesis in vitro when multipotent stem cells are used. The dimensions of the microspheres can easily be adjusted according to the cell numbers applied in an individual experiment. Thus, microspheres allow for the precise administration of defined cell numbers at well-defined sites. Here we describe a detailed workflow for the production of microspheres using unrestricted somatic stem cells from human umbilical cord blood and adapted protocols for the use of these microspheres in histological analysis. RNA extraction methods for mineralized microtissues are specifically modified for optimum yields. The duration of running the complete protocol without preparatory cell culture but including 2 weeks of microsphere incubation, histological staining and RNA isolation is about 3 weeks.

CT-scan is a valuable tool to detect mandibular involvement in oral cancer patients

In patients with oral squamous cell carcinomas (OSSC) it is desirable to avoid unnecessary bone resection without neglecting the overall surgical treatment goal of tumor-free margins. Whereas computed tomography (CT) is most commonly used to detect mandibular invasion, there are conflicting reports regarding the accuracy of CT. Therefore, the aim of this study was to reinvestigate the accuracy of CT in predicting mandibular involvement by OSSC. One hundred and seven patients with OSSC who received a mandibulectomy were included. Before treatment all patients underwent a contrast-enhanced multi-detector CT. Axial 3 or 1.25 mm thick images were reconstructed for evaluation in overlapping technique and displayed in a bone (1400/400 HU) and a soft tissue window (350/50 HU). CT scans were examined by three investigators and compared with the histological findings. The radiological examination showed a high interrater reliability (Cronbachs alpha 0.982). Comparing the radiological findings with the histological results the CT showed 8 false-positive results and 8 false-negative patients. The quality criteria for detecting bone involvement of OSSC by CT were calculated as follows: sensitivity 82.6%; specificity 86.9%; positive predictive value 82.6%; negative predictive value 86.9%. However, in all false-positive patients a sagittal bone defect of 15.1mm could be found presumably caused by pressure of the tumor, but no histologically detectable bone infiltration. Modern CT (1-2 mm sections) is a valuable tool for surgical treatment planning. If bone invasion is detected, a mandibulectomy seems always reasonable. In radiologically negative cases histological assessment is necessary to detect mandibular involvement.

Induction of osteogenic markers in differentially treated cultures of embryonic stem cells

BackgroundFacial trauma or tumor surgery in the head and face area often lead to massive destruction of the facial skeleton. Cell-based bone reconstruction therapies promise to offer new therapeutic opportunities for the repair of bone damaged by disease or injury. Currently, embryonic stem cells (ESCs) are discussed to be a potential cell source for bone tissue engineering. The purpose of this study was to investigate various supplements in culture media with respect to the induction of osteogenic differentiation.MethodsMurine ESCs were cultured in the presence of LIF (leukemia inhibitory factor), DAG (dexamethasone, ascorbic acid and β-glycerophosphate) or bone morphogenetic protein-2 (BMP-2). Microscopical analyses were performed using von Kossa staining, and expression of osteogenic marker genes was determined by real time PCR.ResultsESCs cultured with DAG showed by far the largest deposition of calcium phosphate-containing minerals. Starting at day 9 of culture, a strong increase in collagen I mRNA expression was detected in the DAG-treated cells. In BMP-2-treated ESCs the collagen I mRNA induction was less increased. Expression of osteocalcin, a highly specific marker for osteogentic differentiation, showed a double-peaked curve in DAG-treated cells. ESCs cultured in the presence of DAG showed a strong increase in osteocalcin mRNA at day 9 followed by a second peak starting at day 17.ConclusionSupplementation of ESC cell cultures with DAG is effective in inducing osteogenic differentiation and appears to be more potent than stimulation with BMP-2 alone. Thus, DAG treatment can be recommended for generating ESC populations with osteogenic differentiation that are intended for use in bone tissue engineering.