Ulrich Joos

Influence of titanium surfaces on attachment of osteoblast-like cells in vitro

Implant surface topography influences osteoblastic proliferation, differentiation and extracellular matrix protein expressions. Studies on preliminary interactions of osteoblast-like cells on implant interface through in vitro systems, can give lucid insights to osseo-integrative efficacies of when in vivo implants. In the present investigation two titanium surfaces of dental implants, a sandblasted and acid-etched surface and an experimental grooved surface were compared through in vitro systems. The titanium implants were seeded with osteoblast-like primary cells and maintained for a period of 1-7 days. Expressions of fibronectin and osteonectin were assessed through immunogold labelling by scanning electron microscopy. The grooved surface, supported better osteoblastic cell adhesion and proliferation than the rough surfaces. Further, osteoblastic cells on the grooved surfaces also displayed a strong labelling for fibronectin at the cytoplasmic extensions coupled with intense osteonectin expression in comparison to the rough surfaced implants. In conclusion, grooved surfaces offered better cell attachment and proliferation than the other rough surfaces studied.

Preliminary studies on the phenomenological behaviour of osteoblasts cultured on hydroxyapatite ceramics

SEM was used to investigate the phenomenological behaviour of osteoblasts towards sintered hydroxyapatite. The osteoblasts were seeded on to porous and dense hydroxyapatite and cultured for 4 to 28 d. They attached and adhered on to the hydroxyapatite surfaces, proliferated and secreted extracellular matrix. No signs of toxicity embarrassment were apparent. It is argued that cell phenomenology seems to be a prerequisite to morphogenesis, and on this premise it is speculated that surface-reactive bone replacement materials owe their compatibility to the ability of their surfaces to interact favourably with the peptides involved in osteomorphogenesis and bone repair.

HIF1-alpha overexpression indicates a good prognosis in early stage squamous cell carcinomas of the oral floor

BackgroundHypoxia-inducible factor 1 (HIF-1) is a transcription factor, which plays a central role in biologic processes under hypoxic conditions, especially concerning tumour angiogenesis. HIF-1α is the relevant, oxygen-dependent subunit and its overexpression has been associated with a poor prognosis in a variety of malignant tumours. Therefore, HIF-1α expression in early stage oral carcinomas was evaluated in relation to established clinico-pathological features in order to determine its value as a prognostic marker.Methods85 patients with histologically proven surgically treated T1/2 squamous cell carcinoma (SCC) of the oral floor were eligible for the study. Tumor specimens were investigated by means of tissue micro arrays (TMAs) and immunohistochemistry for the expression of HIF-1. Correlations between clinical features and the expression of HIF-1 were evaluated by Kaplan-Meier curves, log-rank tests and multivariate Cox regression analysis.ResultsHIF-1α was frequently overexpressed in a probably non-hypoxia related fashion. The expression of HIF-1α was related with a significantly improved 5-year survival rate (p < 0.01) and a significantly increased disease free period (p = 0.01) independent from nodal status and tumour size. In primary node negative T1/T2 SCC of the oral floor, absence of HIF-1α expression specified a subgroup of high-risk patients (p < 0.05).ConclusionHIF-1α overexpression is an indicator of favourable prognosis in T1 and T2 SCC of the oral floor. Node negative patients lacking HIF-1α expression may therefore be considered for adjuvant radiotherapy.

Cytokeratin 8/18 expression indicates a poor prognosis in squamous cell carcinomas of the oral cavity

BackgroundIntermediary filaments are involved in cell motility and cancer progression. In a variety of organs, the expression of distinct intermediary filaments are associated with patient prognosis. In this study, we seeked to define the prognostic potential of cytokeratin and vimentin expression patterns in squamous cell carcinomas (SCCs) of the oral cavity.Methods308 patients with histologically proven and surgically treated squamous cell carcinomas of the oral cavity were investigated for the immunohistochemical expression of a variety of intermediary filaments including high- and low-molecular weight cytokeratins (Cks), such as Ck 5/6, Ck 8/18, Ck 1, CK 10, Ck 14, Ck 19 and vimentin, using the tissue microarray technique. Correlations between clinical features and the expression of Cytokeratins and vimentin were evaluated statistically by Kaplan-Meier curves and multivariate Cox regression analysis.ResultsThe expression of Ck 8/18 and Ck 19 were overall significantly correlated with a poor clinical prognosis (Ck 8/18 p = 0.04; Ck19 p < 0.01). These findings could also be reproduced for Ck 8/18 in primary nodal-negative SCCs and held true in multivariate-analysis. No significant correlation with patient prognosis could be found for the expression of the other cytokeratins and for vimentin.ConclusionThe expression of Ck 8/18 in SCCs of the oral cavity is an independent prognostic marker and indicates a decreased overall and progression free survival. These results provide an extended knowledge about the role of intermediary filament expression patterns in SCCs.

TCP is hardly resorbed and not osteoconductive in a non-loading calvarial model

Tricalciumphosphate (TCP) has been used as a ceramic bone substitute material in the orthopedic field as well as in craniofacial surgery. Some controversies exist concerning the osteoconductive potential of this material in different implantation sites. This study was designed to evaluate the biological response of calvarial bone towards TCP granules under non-loading conditions to assess the potential of TCP as a biodegredable and osteoconductive bone substitue material for the cranial vault. Full-thickness non-critical size defects were made bilaterally in the calvaria of 21 adult Wistar rats. One side was filled by TCP granules, the contralateral side was left empty and used as a control. Animals were sacrified in defined time intervals up to 6 months. Bone regeneration was analyzed with special respect toward the micromorphological and microanalytical features of the material-bone interaction by electron microscopy and electron diffraction analysis. Histologic examination revealed no TCP degradation even after 6 months of implantation. In contrast, a nearly complete bone regeneration of control defects was found after 6 months. At all times TCP was surrounded by a thin fibrous layer without presence of osteoblasts and features of regular mineralization. As far as degradation and substitution are concerned, TCP is a less favourable material tinder conditions of non-loading.

Strain-related bone remodeling in distraction osteogenesis of the mandible.

Distraction osteogenesis has become a mainstay in craniofacial surgery. However, there are several unresolved problems concerning the biology of bone regeneration. We investigated the biomechanical effects of mandibular lengthening in 32 rabbits on a cellular and histologic level. The mandible was subjected to a corticotomy, held in a neutral position for 4 days, and then lengthened at various strain rates and frequencies for 10 days. Radiographic, histologic, and electron microscopic examinations showed a strain-related bone regeneration. Application of physiologic strain rates (2000 microstrains or 0.2 percent) led to a bridging of the artificial fracture exhibiting woven ossification, whereas at 20,000 microstrains trabecular bone formation was demonstrated. In contrast, hyperphysiologic strain magnitudes (200,000 microstrains and 300,000 microstrains) showed a fibrous tissue formation. Multiple strain applications (10 cycles/day versus 1 cycle/day) increased the width of the distraction gap without changing the stage of bone regeneration. The gradual distraction of bone in physiologic magnitudes at higher frequencies seems to be desirable for a bony differentiation and may help to improve clinical applications.

Electrical stimulation influences mineral formation of osteoblast-like cells in vitro

The aim of the present study was to assess the structure of newly formed mineral crystals after electrical stimulation of osteoblast-like cells in vitro. Pulsed electrical stimulation was coupled capacitively or semi-capacitively to primary osteoblast-like cells derived from bovine metacarpals. Computer calculations revealed that the chosen input signal (saw-tooth, 100 V, 63 ms width, 16 Hz repetition rate) generated a short pulsed voltage drop of 100 microV (capacitive coupled mode) and of 350 microV (semi-capacitive coupled mode) across the cell-matrix layer. Stimulated cultures showed an enhanced mineral formation compared to the non stimulated controls. In cultures exposed to capacitively coupled electric fields and in control cultures nodules and mineralized globules were found. Nodules with a diameter of less than 200 nm covered the cell surface, whereas mineral globules with a diameter of up to 700 nm formed characteristic mineral deposits in the vicinity of the cells similar to biomineral formations occurring in mineralizing tissues. In contrast, large rod-shaped crystals were found in cultures stimulated by semi-capacitive coupled electric fields, indicating a non-physiological precipitation process. In conclusion, osteoblasts in culture are sensitive to electrical stimulation resulting in an enhancement of the biomineralization process.

Clinical relevance of erbB-1 and -2 oncogenes in oral carcinomas

To gain a better understanding of molecular changes in oral squamous cell carcinomas, we tested fresh tumour specimens from 110 patients for erbB-1 and -2 oncogene aberrations using the competitive differential polymerase chain reaction. The significance of established tumour characteristics such as TNM stage, differentiation and oncogene aberrations for tumour progression were analyzed. ErbB-2 amplification with a gene copy number > 1.6 in tumour tissue and erbB-1 deletion with a gene copy number < 0.4 in tumour-surrounding mucosa are of clinical relevance and indicate an early tumour recurrence or metastasis (p < 0.05). In T1/T2 tumours an erbB-2 gene dosage study allows differentiation between tumours with high or low risk for early progression. In a multivariate statistical analysis T stage (p < 0.01) and erbB-2 amplification in tumour material (p < 0.05) were independent prognostic variables.

Rehabilitation with dental implants of oral cancer patients.

The aim of this study was to evaluate the risks and complications of rehabilitation with dental implants after tumour surgery and radiotherapy. After a disease-free survival of 18 months, 29 patients who had undergone oral cancer treatment were rehabilitated with dental implants. The complication rate of implants in irradiated, non-irradiated and grafted bone was analyzed at least 3 years after implant placement. In the healing period, 28.6% of the implants in irradiated bone and 8.4% in non-irradiated bone showed soft tissue complications. Of the implants, 26.7% in the irradiated and 14.7% in the non-irradiated mandibular bone were lost in the first 36 months after placement. Thirty-one point two percent of implants inserted in non-irradiated bone grafts were affected and did not osseointegrate. Of 109 inserted implants, 70 were suitable for prosthetic rehabilitation. There are high complication rates after implant placement in oral cancer patients. Irradiation adversely affects soft tissue healing. Osseointegration is frequently disturbed, especially when implants were placed in non-vascularized bone grafts.

Magnesium in newly formed dentin mineral of rat incisor.

Small amounts of magnesium are always detectable in addition to calcium and phosphorus in mineralized tissues such as dentin or bone. Magnesium has been considered to influence the mineralization process, especially crystal growth. The present study reports on the location and enrichment of magnesium in the newly mineralized dentin by using the high lateral resolution of energy dispersive X‐ray microanalysis combined with scanning transmission electron microscopy. To this end, we have used the continuously growing rat incisor as a model for a collagenous mineralizing system. Dental tissue was dissected free and cryofixed in liquid nitrogen–cooled propane. The distribution of elements was measured in freeze‐dried ultrathin cryosections. The magnesium distribution of the newly formed dentin area near the predentin area was found to be inhomogeneous. In certain small dentin areas, characteristical magnesium enrichments were observed. Further, high magnesium‐to‐phosphate molar ratios were found in these areas, and these were correlated with low calcium‐to‐phosphate molar ratios. Our results support the theory that magnesium is involved in the process of biological apatite crystal formation.