Effect of Hydrogen Peroxide on the Surface and Attractiveness of Various Zirconia Implant Materials on Human Osteoblasts: An In Vitro Study.

The aim of this in vitro study was to investigate the effect of hydrogen peroxide (H2O2) on the surface properties of various zirconia-based dental implant materials and the response of human alveolar bone osteoblasts. For this purpose, discs of two zirconia-based materials with smooth and roughened surfaces were immersed in 20% H2O2 for two hours. Scanning electron and atomic force microscopy showed no topographic changes after H2O2-treatment. Contact angle measurements (1), X-ray photoelectron spectroscopy (2) and X-ray diffraction (3) indicated that H2O2-treated surfaces (1) increased in hydrophilicity (p < 0.05) and (2) on three surfaces the carbon content decreased (33-60%), while (3) the monoclinic phase increased on all surfaces. Immunofluorescence analysis of the cell area and DNA-quantification and alkaline phosphatase activity revealed no effect of H2O2-treatment on cell behavior. Proliferation activity was significantly higher on three of the four untreated surfaces, especially on the smooth surfaces (p < 0.05). Within the limitations of this study, it can be concluded that exposure of zirconia surfaces to 20% H2O2 for 2 h increases the wettability of the surfaces, but also seems to increase the monoclinic phase, especially on roughened surfaces, which can be considered detrimental to material stability. Moreover, the H2O2-treatment has no influence on osteoblast behavior.

Differential osteopontin expression in human osteoblasts derived from iliac crest and alveolar bone and its role in early stages of angiogenesis.

In our previous study, we revealed significant differences of osteopontin (OPN) gene expression in primary human osteoblasts (HOBs) derived from iliac crest bone (iHOBs) and alveolar bone (aHOBs). The present study aims at assigning this discriminative expression to a possible biologic function. OPN is known to be involved in several pathologic and physiologic processes, among others angiogenesis. Therefore, we studied the reaction of human umbilical vein endothelial cells (HUVECs) to HOB-derived OPN regarding angiogenesis. To this end, human primary explant cultures of both bone entities from ten donors were established. Subsequent transcription analysis detected higher gene expression of OPN in iHOBs compared to aHOBs, thereby confirming the results of our previous study. This difference was particularly apparent when cultures were derived from female donors. Hence, OPN protein expression as well as the angiogenic potential of OPN was analyzed, originating from HOBs of one female donor. In accordance to the gene expression level, secreted OPN was more abundant in the supernatant of iHOBs than in aHOBs. Moreover, secreted OPN was found to stimulate migration of HUVECs, but not proliferation or tube formation. These results indicate an involvement in very early stages of angiogenesis and a functional distinction of OPN from HOBs derived from different bone entities.

Biomechanical strain-induced modulation of proliferation coincides with an ERK1/2-independent nuclear YAP localization.

Biomechanical strain induces activation of the transcriptional co-activator yes-associated protein (YAP) by nuclear re-distribution. Recent findings indicate that the mechanically responsive mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase (ERK) 1/2 is involved in the amount of nuclear YAP, reflecting its activation. In this context, we conducted experiments to detect how biomechanical strain acts on the subcellular localization of YAP in periodontal cells. To this end, cells were subjected to 2.5% static equiaxial strain for different time periods. Western blot and fluorescence imaging-based analyses revealed a clear modulation of nuclear YAP localization. This modulation fairly coincided with the altered course of the KI-67 protein amount in conjunction with the percentage of KI-67-positive and thus proliferating cells. The inhibition of the ERK1/2 activity via U0126 yielded an unchanged strain-related modulation of nuclear YAP localization, while YAP amount in whole cell extracts of strained cells was decreased. Administration of the YAP-inhibiting drug Verteporfin evoked a clear reduction of KI-67-positive and thus proliferating cells by approximately 65%, irrespective of strain. Our data reveal YAP as a regulator of strain-modulated proliferation which occurs in a MAPK-independent fashion.

Pilot investigation of the molecular discrimination of human osteoblasts from different bone entities.

In oral and maxillofacial surgery, autologous grafts from the iliac crest remain the 'gold standard' for alveolar ridge reconstruction, whereas intraoral bone grafts are considered in smaller defects. To date, a comparison of the osteogenic potential of osteoblasts with regard to their tissue origin is missing. Primary osteoblasts have proven useful for the investigation of the tissue-specific osteogenic properties. The present study compares primary human alveolar (aHOBs) and iliac osteoblasts (iHOBs) derived from three female patients undergoing routine intraoral bone grafting. Proliferation potential of the osteoblasts was evaluated using real-time impedance monitoring. Relative gene expression of bone specific biomarkers was analyzed and quantified using quantitative polymerase chain reactions (qPCR). Immunohistochemistry and phase contrast microscopy were performed, as well as alkaline phosphatase assay and alizarin red staining to visualize morphology and mineralization capacity. A twofold faster proliferation rate of aHOBs compared with iHOBs (130 h vs. 80 h) was observed. Alkaline phosphatase activity and alizarin red staining in both HOBs indicated similar mineralization capacity. Gene expression of seven genes (BMP1, CSF-1, TGFBR1, ICAM1, VCAM1, SPP1 and DLX5) was significantly higher in iHOB than in aHOB samples. These data suggest a higher osteogenic potential of osteoblasts derived from the iliac crest compared with primary osteoblasts from the alveolar bone and may lead to a better understanding of the molecular impact of bone cells from different bone entities on bone regeneration in alveolar ridge reconstructions.

Influence of ultraviolet photofunctionalization on the surface characteristics of zirconia-based dental implant materials.

OBJECTIVES: To examine the effect of ultraviolet light (UV) treatment on the surface characteristics of two acid-etched zirconia-based dental implant materials. METHODS: Discs of two zirconia-based materials (Zr1 and Zr2) with smooth (m) and roughened (r) surfaces were treated by UV light for 15min. The surface topography was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface elemental composition of all samples was determined by X-ray photoelectron spectroscopy (XPS), the crystalline property by X-ray diffraction (XRD) and the hydrophilic status by contact angle (CA) measurements of a water droplet. RESULTS: SEM and AFM revealed quantitative and qualitative differences between the roughened and smooth surfaces. UV treatment did not induce any topographic changes of the tested surfaces (p>0.05). All UV-treated samples showed a significant surface elemental content change with a decrease of carbon by 43-81%, an increase of oxygen by 19-45%, and an increase of zirconia by 9-41%. Upon UV treatment, a 19-25% increase of the crystalline monoclinic phase was observed on surfaces of material Zr1, whereas a slight increase on the smooth Zr2 surface (+3%) and a decrease on the roughened Zr2 surface by 20% was observed. For all samples, the hydrophilic status changed significantly from hydrophobic to hydrophilic by UV treatment (p<0.0001). The average contact angles were between 56.4° and 69° before and 2.5° and 14.1° after UV-light treatment. SIGNIFICANCE: UV treatment altered the physicochemical properties of the two zirconia implant surfaces investigated. The mechanism by which such changes are induced requires further investigation.

Comparison of four different allogeneic bone grafts for alveolar ridge reconstruction: a preliminary histologic and biochemical analysis.

OBJECTIVES: Allograft material for alveolar ridge reconstruction is quite promising and appears to be as equally successful as bone autograft material. The aim of the present study was to compare four different allogeneic bone grafts in terms of their histologic structure and DNA content before grafting. STUDY DESIGN: Four allograft specimens from different suppliers were analyzed histologically, and the DNA content was analyzed before clinical use of the allografts. RESULTS: Organic tissue remnants were detected in all of the evaluated samples. In the present samples adipocytes, fibroblasts, osteocytes, and chondrocytes were identified and DNA isolation and purification was possible. CONCLUSION: Demineralized freeze-dried allogeneic bone transplants can stimulate new bone formation and are a viable alternative to bone autograft material. However, the well-tolerated use of allograft material in regard to our findings should be further investigated.