Design of a migration assay for human gingival fibroblasts on biodegradable magnesium surfaces.

A novel regenerative approach to Guided Bone Regeneration (GBR) in dental surgery is based on the development of biodegradable and volume stable barrier membranes made of metallic magnesium. Currently used volume stable barrier membranes are made of titanium-reinforced PTFE or titanium-reinforced collagen membranes, both, however, are accompanied by a high incidence of wound dehiscence resulting in membrane exposure, which leads to an increased infection risk. An exposed membrane could also occur directly after insertion due to insufficient soft tissue coverage of the membrane. In both cases, fast wound margin regeneration is required. As a first step of soft-tissue regeneration, gingival fibroblasts need to migrate over the barrier membrane and close the dehiscent wound. Based on this aim, this study investigated the migration behaviour of human gingival fibroblasts on a magnesium surface. Major experimental challenges such as formation of hydrogen bubbles due to initial magnesium corrosion and non-transparent material surfaces have been addressed to allow cell adhesion and to follow cell migration. The designed scratch-based cell migration assay involved vital fluorescent cell staining on a pre-corroded magnesium membrane to simulate invivo wound dehiscence. The assay has been used to compare cell migration on pre-corroded magnesium to titanium surfaces and tissue culture plastic as control substrates. First results of this assay showed that human gingival fibroblasts migrate slower on pre-corroded magnesium compared to plastic and titanium. However, the scratch was finally closed on all materials. Compared to titanium surfaces and tissue culture plastic, the surface roughness and the surface free energy (SFE) could not explain slower cell migration on magnesium surfaces. Immunohistological investigations of cellular structure revealed, that magnesium ions increased focal adhesion at concentration of additionally 75 mM MgCl2 in cell culture medium. The use of our designed cell migration assay has shown that ionic medium alterations due to magnesium corrosion has a higher impact on the cell migration rate than surface alterations. STATEMENT OF SIGNIFICANCE: The design of a migration assay on non-transparent magnesium surfaces will add the option to study cell response to surface modifications, coatings and the corrosion process itself under life view conditions.

Three-dimensional fracture pattern analysis of the Obwegeser and Dal Pont bilateral sagittal split osteotomy.

The Obwegeser and Dal Pont modification of the bilateral sagittal split osteotomy (BSSO) is a well-established procedure in orthognathic surgery. The purpose of this retrospective study was to analyze the actual fracture patterns achieved with BSSO by Obwegeser and Dal Pont modification using postoperative cone beam computed tomography (CBCT) datasets from 100 patients. A total of 200 split osteotomies were assessed, which could be categorized into nine different split patterns. Only one of the observed split fractures (0.5%) followed exactly the fracture line described by Obwegeser and Dal Pont, whereas 40% followed the fracture line according to the Hunsuck and Epker modification and 13.5% were seen as unfavourable splits mainly running over the buccal plate. A significant correlation was found between unfavourable buccal splits and both horizontal osteotomies reaching the buccal surface at the dorsal ramus (P=0.001) and a vertical caudal bone cut end at the corpus with a buccal position (P<0.001). These results show that a complete antero-posterior horizontal osteotomy at the mandibular ramus does not lead to the intended fracture pattern, which rebuts the argument of a greater amount of bony overlap using the Obwegeser and Dal Pont modification.

Accuracy of peri-implant bone evaluation using cone beam CT, digital intra-oral radiographs and histology.

OBJECTIVES: The present study assesses the accuracy of three-dimensional (3D) cone beam CT (CBCT) and intra-oral radiography (CR) in visualizing peri-implant bone compared with histology. METHODS: 26 titanium dental implants were placed in dog jaws with chronic type vestibular defects. After a healing period of 2 and 8 weeks (n = 12 dogs) the animals were sacrificed. CBCT scans and CR of the specimen were recorded. Dissected blocks were prepared, and histomorphometric analysis was performed. Both modalities were measured twice by two observers and compared with histomorphometry regarding bone levels and thickness around implants as well as length and diameter of implants. RESULTS: Measurements of CBCT correlated well with histomorphometry of the vestibular bone level, oral bone thickness and implant length (all p-values <0.05). Compared with histomorphometry, the mean differences between CBCT and histomorphometry were between 0.06 and 2.61 mm. Mesial bone level (MBL) and distal bone level (DBL) were underestimated by both CR and CBCT. CR and histology measurements were only significantly correlated for implant length measurements. All intraclass correlations were highly significant. CONCLUSIONS: 3D CBCT provides usable information about bone in all dimensions around implants with varying accuracy. CR and CBCT perform similar in assessing MBL and DBL, but, within its limits, the CBCT can assess oral and buccal bone. Metallic artefacts limit the visualization quality of bone around implants and further research could elucidate the value of post-processing algorithms. When information about osseous perforation of implants is needed, CBCT may still provide clinically valuable information.

Possibilities and limitations of implant placement by virtual planning data and surgical guide templates.

The use of computer-aided surgical systems for dental implant bed preparation and implant placement results in an average precision within 1 mm of implant position and within 5 degrees of deviation for implant inclination. The accuracy of axis and implant position is significantly more precise with the three-dimensional surgical guide than with the free-hand method. The three-dimensional assessment of the restorative goal (radiopaque simulation of prosthesis with scanning template) allows virtual planning of implants, which enables optimized positioning of implants with surgical guide templates in oral surgery. If there is a clear indication for three-dimensional diagnostics, it should always be checked whether the data can be used as planning data for a surgical guide template, otherwise the chance for guided surgery remains unused. Since uncertainties still exist despite the use of a drilling template, it is recommended that the minimum safety distance from adjacent structures be maintained. The successful use of surgical guide templates requires comprehensive knowledge of and experience in using three-dimensional information for the virtual planning of implant position.

Podoplanin expression in oral leukoplakia: prognostic value and clinicopathological implications.

OBJECTIVES: Current clinicopathological parameters cannot predict the risk of malignant transformation in oral leukoplakia sufficiently. Recent studies have shown that podoplanin is expressed in oral cancer and precancerous lesions. The aim of our study was to assess whether podoplanin expression in pretreatment biopsies could serve as a biomarker to predict the risk of malignant transformation in patients with oral leukoplakia. MATERIALS AND METHODS: In this retrospective study, podoplanin expression was analysed in 60 patients with previously untreated oral leukoplakia by immunohistochemistry. We investigated the associations between podoplanin expression and various clinicopathological variables including oral cancer-free survival (OCFS) and the SIN-classification. RESULTS: The chi-square-test revealed that high expression of podoplanin in pretreatment biopsies was associated with malignant transformation (P = 0.003) and increasing SIN-classification (P = 0.009). In univariate analysis, podoplanin expression in oral leukoplakia had a significant impact on OCFS (P = 0.009). The 5-year OCFS rate decreased from 100% for patients with no podoplanin expression to 41.7% for patients with the highest level of podoplanin expression. CONCLUSION: Although podoplanin expression and the SIN-classification served as factors to predict malignant transformation in patients with oral leukoplakia in univariate analysis, no significant impact was found for both factors in multivariate analysis.

Registration accuracy of three-dimensional surface and cone beam computed tomography data for virtual implant planning.

OBJECTIVE: Virtual wax-ups based on three-dimensional (3D) surface models can be matched (i.e. registered) to cone beam computed tomography (CBCT) data of the same patient for dental implant planning. Thereby, implant planning software can visualize anatomical and prosthetic information simultaneously. The aim of this study is to assess the accuracy of a newly developed registration process. MATERIAL AND METHODS: Data pairs of CBCT and 3D surface data of 16 patients for dental implant planning were registered and the discrepancy between the visualized 3D surface data and the corresponding CBCT data were measured on 64 teeth at seven points by two investigators in two iterations with a total of 1792 measurements. RESULTS: All data pairs were matched successfully and mean distances between CBCT and 3D surface data were between 0.03(±0.33) and 0.14(±0.18) mm. At two of seven measuring points, statistically significant correlations were determined between the measured error and the presence and type of restorations. Registration errors in maxilla and mandible were not statistically significantly different. CONCLUSION: According to the results of this study, registration of 3D surface data and CBCT data works reliably and is sufficiently accurate for dental implant planning. Thereby, barium-sulfate scanning templates can be avoided and dental implant planning can be accomplished fully virtual.

Surface- and nonsurface-dependent in vitro effects of bone substitutes on cell viability.

The aim of the present in vitro study was to evaluate the influence of different bone substitute materials (BSM) on the viability of human primary osteoblasts (PO), bone marrow mesenchymal cells (BMMC), and nonadherent myelomonocytic cells (U937). Six different bone substitute materials were tested: Bio-Oss Spongiosa (BOS), Tutodent Chips (TC), PepGen P-15 (P-15), Ostim (OM), BioBase (BB), and Cerasorb (CER). Cells were cultivated on comparable volumes of BSM in 96-well plates. Cell culture-treated polystyrol (Nunclon Delta surface; C) served as positive control. After 2 h and 3, 6, 10, and 14 days, viability of cells was evaluated using a standardized ATP viability assay (CellTiter Glo). Nonsurface-dependent effects of the materials were separately tested using nonadherent U937 suspension cells. For statistical analysis, the Mann-Whitney test was used. Results were considered statistically significant at P < 0.05. Cell viability of PO increased significantly on TC, C, and CER followed by BB. No changes were found for P-15 and decreasing viability for BOS and OM. BMMC showed similar results on C, TC, CER, and P-15. Lower viability for BB and no viability could be detected for BOS and OM (Mann-Whitney test, respectively). Nonadherent cells displayed increasing viability in presence of CER, BB, and BOS. No changes were observed for TC and P-15, whereas for OM, no viability was detected after a maximum cultivation period of 3 days. It was concluded that granular hydroxyapatite (HA; TC, BOS, P-15) and alpha- and beta-tricalciumphosphate (CER, BB) support, whereas nanosized HA (OM) limit or even inhibit surface- and nonsurface-related cell viability in the in vitro model used.

Dimensional ridge alterations following socket preservation using a nanocrystalline hydroxyapatite paste: a histomorphometrical study in dogs.

The aim of the study was to evaluate the histological response and dimensional ridge alterations following application of a nanocrystalline hydroxyapatite paste (NHA) into fresh extraction sockets in dogs. Immediately following vertical tooth separation and extraction, NHA was inserted in the extraction socket of the second molar in the lower jaws of 10 dogs. Untreated extraction sites on the opposite side served as controls. Wounds were closed using resorbable sutures after vertical flap elevation. After three and six months, 5 animals were killed. Lingual and buccal bone height, alveolar wall and total bone width 1, 3 and 5mm underneath the top of the crest were evaluated. Histological analysis revealed a high variability of NHA resorption and osteoconductive properties with different rates of material resorption. No statistically significant differences could be observed between the corresponding aspects of test and control sites. Both groups revealed higher alveolar wall resorption on the buccal than on the lingual side at both time periods. NHA does not seem to be useful for socket preservation procedures since it failed to prevent dimensional ridge alterations while revealing osseous integration but unpredictable material resorption. The role of non-resorbed hydroxyapatite remnants for implant placement is unclear and requires further investigation.

[In vitro testing of thrombocyte adhesion to different collagenous hemostyptic agents]. / In-vitro-Testung der Thrombozytenaggregation an zahnärztlich verwendeten kollagenen Hämostyptika.

AIM: The aim of the present study was to evaluate the adhesion of thrombocytes to different collagenous hemostyptics in a new blood flow chamber. MATERIAL AND METHODS: Three hemostyptics were tested: (1) Resorba (RE, native equine collagen, Resorba Wundversorgung GmbH, Nürnberg, Germany), (2) Hemocol (HE, native porcine collagen, Medical Biomaterial Products GmbH, Neustadt-Gleve, Germany), and (3) an experimental sponge (ES, chemically cross-linked porcine collagen, Geistlich Biomaterials, Wolhusen, Switzerland). Ten specimens of each sponge were exposed to a laminar 40 ml/h anticoagulated blood flow and adhering thrombocytes were examined using a confocal laser scanning microscope (CLSM). Pure collagen (Kollagen S, Roche) served as positive control and fetal calf serum (FKS, Roche) as negative control. Examination time was set at 0, 60, 120, and 180 s. Furthermore, pH measurements of defined sponge volumes were evaluated after incubation with NaCl and human blood serum after 3, 30, and 60 min. RESULTS: All specimens showed a comparable amount of fluorescence units on the surface over time which was statistically not significantly different from the positive control (p>0.05, ANOVA). Nevertheless, acidity of all specimens could be observed after incubation with NaCl and in cases of HE and ES after incubation with human blood serum. CONCLUSION: Within the limits of the present in-vitro study it was concluded that (1) all hemostyptics examined showed similar results in thrombocyte adhesion; (2) chemical cross-linking of collagen does not affect the thrombogenicity of the tested collagen; (3) however, the acidity might have a negative effect on thrombus formation in vivo.

Autogenous bone chips: influence of a new piezoelectric device (Piezosurgery) on chip morphology, cell viability and differentiation.

AIM: The aim of the present study was to investigate the influence of a new piezoelectric device, designed for harvesting autogenous bone chips from intra-oral sites, on chip morphology, cell viability and differentiation. METHODS: A total of 69 samples of cortical bone chips were randomly gained by either (1) a piezoelectric device (PS), or (2) conventional rotating drills (RD). Shape and size of the bone chips were compared by means of morphometrical analysis. Outgrowing osteoblasts were identified by means of alkaline phosphatase activity (AP), immunhistochemical staining for osteocalcin (OC) synthesis and reverse transcriptase-polymerase chain reaction phenotyping. RESULTS: In 88.9% of the RD and 87.9% of the PS specimens, an outgrowth of adherent cells nearby the bone chips was observed after 6-19 days. Confluence of cells was reached after 4 weeks. Positive staining for AP and OC identified the cells as osteoblasts. The morphometrical analysis revealed a statistically significant more voluminous size of the particles collected with PS than RD. CONCLUSION: Within the limits of the present study, it may be concluded that both the harvesting methods are not different from each other concerning their detrimental effect on viability and differentiation of cells growing out of autogenous bone chips derived from intra-oral cortical sites.