Patrick Heimel

Dental and periodontal phenotype in sclerostin knockout mice

Sclerostin is a Wnt signalling antagonist that controls bone metabolism. Sclerostin is expressed by osteocytes and cementocytes; however, its role in the formation of dental structures remains unclear. Here, we analysed the mandibles of sclerostin knockout mice to determine the influence of sclerostin on dental structures and dimensions using histomorphometry and micro-computed tomography (μCT) imaging. μCT and histomorphometric analyses were performed on the first lower molar and its surrounding structures in mice lacking a functional sclerostin gene and in wild-type controls. μCT on six animals in each group revealed that the dimension of the basal bone as well as the coronal and apical part of alveolar part increased in the sclerostin knockout mice. No significant differences were observed for the tooth and pulp chamber volume. Descriptive histomorphometric analyses of four wild-type and three sclerostin knockout mice demonstrated an increased width of the cementum and a concomitant moderate decrease in the periodontal space width. Taken together, these results suggest that the lack of sclerostin mainly alters the bone and cementum phenotypes rather than producing abnormalities in tooth structures such as dentin.

Volume analysis of heat-induced cracks in human molars: A preliminary study

Context: Only a few methods have been published dealing with the visualization of heat-induced cracks inside bones and teeth. Aims: As a novel approach this study used nondestructive X-ray microtomography (micro-CT) for volume analysis of heat-induced cracks to observe the reaction of human molars to various levels of thermal stress. Materials and Methods: Eighteen clinically extracted third molars were rehydrated and burned under controlled temperatures (400, 650, and 800°C) using an electric furnace adjusted with a 25°C increase/min. The subsequent high-resolution scans (voxel-size 17.7 μm) were made with a compact micro-CT scanner (SkyScan 1174). In total, 14 scans were automatically segmented with Definiens XD Developer 1.2 and three-dimensional (3D) models were computed with Visage Imaging Amira 5.2.2. The results of the automated segmentation were analyzed with an analysis of variance (ANOVA) and uncorrected post hoc least significant difference (LSD) tests using Statistical Package for Social Sciences (SPSS) 17. A probability level of P < 0.05 was used as an index of statistical significance. Results: A temperature-dependent increase of heat-induced cracks was observed between the three temperature groups (P < 0.05, ANOVA post hoc LSD). In addition, the distributions and shape of the heat-induced changes could be classified using the computed 3D models. Conclusion: The macroscopic heat-induced changes observed in this preliminary study correspond with previous observations of unrestored human teeth, yet the current observations also take into account the entire microscopic 3D expansions of heat-induced cracks within the dental hard tissues. Using the same experimental conditions proposed in the literature, this study confirms previous results, adds new observations, and offers new perspectives in the investigation of forensic evidence.

Tissue-engineered hypertrophic chondrocyte grafts enhanced long bone repair

Bone has innate ability to regenerate following injury. However, large and complex fractures exceed bones natural repair capacity and result in non-unions, requiring external intervention to facilitate regeneration. One potential treatment solution, tissue-engineered bone grafts, has been dominated by recapitulating intramembranous ossification (bone formation by osteoblasts), although most serious bone injuries heal by endochondral ossification (bone formation by remodeling of hypertrophic cartilaginous anlage). The field has demonstrated that using endochondral ossification-based strategies can lead to bone deposition. However, stem cell differentiated hypertrophic chondrocytes, the key cell type in endochondral ossification, have not been studied for long bone defect repair. With translation in mind, we created tissue-engineered grafts using human adipose stem cells (ASC), a clinically relevant stem cell source, differentiated into hypertrophic chondrocytes in decellularized bone scaffolds, and implanted these grafts into critical-size femoral defects in athymic rats. Over 12 weeks of implantation, these grafts were compared to acellular scaffolds and grafts engineered using ASC-derived osteoblasts. Grafts engineered using hypertrophic chnodrocytes recapitulated endochondral ossification, as evidenced by the expression of genes and proteins associated with bone formation. Markedly enhanced bone deposition was associated with extensive bone remodeling and the formation of bone marrow, and with the presence of pro-regenerative M2 macrophages within the hypertrophic grafts. As a result, hypertrophic chondrocyte grafts bridged 7/8 defects, as compared to only 1/8 for osteoblast grafts and 3/8 acellular scaffolds. These data suggest that ASC-derived hypertrophic chondrocytes in osteogenic scaffolds can improve long bone repair.

Morphometric characteristics of cortical and trabecular bone in atrophic edentulous mandibles

OBJECTIVES Adaptations of the alveolar ridge after tooth loss have been well described. However, studies on the morphometric characteristics of cortical bone are rare; hence, this study of human atrophic edentulous mandibles was undertaken. MATERIAL AND METHODS Total cortical area, porosity, and thickness, and the percentage of cortical area in the complete mandibular area as well as in an area (height, 10 mm) starting at the most caudal point of the trabecular compartment and extending in the coronal direction were determined in 185 thin ground sections of edentulous mandibles (incisor region, 49; premolar region, 76; molar region, 60; 95 from females and 90 from males; mean age, 78.2 years, SD ± 7.8 years; Caucasian donors; cause of death: cardiovascular disease). Further, mandibular height and width and degree of residual ridge resorption (RRR) were recorded. RESULTS The percentage of cortical area in the complete mandibular area increased with increasing RRR. Yet, evaluation of the 10-mm caudal portion corresponding to the basal part of the mandibular body did not confirm these changes in cortical bone. Cortical porosity and thickness decreased from the mesial to the distal region. Cortical porosity was unaffected by RRR, while cortical thickness increased, mainly at lingual aspects. CONCLUSIONS In conclusion, cortical bone remained stable in different degrees of RRR except for some modulations in the lingual aspects. Changes in the relative composition between cortical and trabecular bone are due to loss of height and total area, mainly at expense of trabecular bone area, but not to adaptations of the cortical bone.

A Novel Silk Fiber–Based Scaffold for Regeneration of the Anterior Cruciate Ligament Histological Results From a Study in Sheep

Background: Because of ongoing problems with anterior cruciate ligament (ACL) reconstruction, new approaches in the treatment of ACL injuries, particularly strategies based on tissue engineering, have gained increasing research interest. To allow for ACL regeneration, a structured scaffold that provides a mechanical basis, has cells from different sources, and comprises mechanical as well as biological factors is needed. Biological materials, biodegradable polymers, and composite materials are being used and tested as scaffolds. The optimal scaffold for ACL regeneration should be biocompatible and biodegradable to allow tissue ingrowth but also needs to have the right mechanical properties to provide immediate mechanical stability. Hypotheses: The study hypotheses were that (1) a novel degradable silk fiber–based scaffold with mechanical properties similar to the native ACL will be able to initiate ligament regeneration after ACL resection and reconstruction under in vivo conditions and (2) additional cell seeding of the scaffold with autologous stromal vascular fraction–containing adipose-derived stem cells will increase regenerative activity. Study Design: Controlled laboratory study. Methods: A total of 33 mountain sheep underwent ACL resection and randomization to 2 experimental groups: (1) ACL reconstruction with a scaffold alone and (2) ACL reconstruction with a cell-seeded scaffold. Histological evaluation of the intra-articular portion of the reconstructed/regenerated ligament was performed after 6 and 12 months. Results: After 6 months, connective tissue surrounded the silk scaffold with ingrowth in some areas. The cell-seeded scaffolds had a significant lower silk content compared with the unseeded scaffolds and demonstrated a higher content of newly formed tissue. After 12 months, the density of the silk fibers decreased significantly, and the ingrowth of newly formed tissue increased in both groups. No differences between the 2 groups regarding silk fiber degradation and regenerated tissue were detected at 12 months. Conclusion: The novel silk fiber–based scaffold was able to stimulate ACL regeneration under in vivo conditions. Additional cell seeding led to increased tissue regeneration and decreased silk fiber content at 6 months, whereas these differences were not present at 12 months. Clinical Relevance: ACL regeneration using a silk fiber–based scaffold with and without additional cell seeding may provide a new treatment option after joint injuries.

Comparison of nanoparticular hydroxyapatite pastes of different particle content and size in a novel scapula defect model

Nanocrystalline hydroxyapatite (HA) has good biocompatibility and the potential to support bone formation. It represents a promising alternative to autologous bone grafting, which is considered the current gold standard for the treatment of low weight bearing bone defects. The purpose of this study was to compare three bone substitute pastes of different HA content and particle size with autologous bone and empty defects, at two time points (6 and 12 months) in an ovine scapula drillhole model using micro-CT, histology and histomorphometry evaluation. The nHA-LC (38% HA content) paste supported bone formation with a high defect bridging-rate. Compared to nHA-LC, Ostim® (35% HA content) showed less and smaller particle agglomerates but also a reduced defect bridging-rate due to its fast degradation The highly concentrated nHA-HC paste (48% HA content) formed oversized particle agglomerates which supported the defect bridging but left little space for bone formation in the defect site. Interestingly, the gold standard treatment of the defect site with autologous bone tissue did not improve bone formation or defect bridging compared to the empty control. We concluded that the material resorption and bone formation was highly impacted by the particle-specific agglomeration behaviour in this study.

Comparing the osteogenic potential of bone marrow and tendon-derived stromal cells to repair a critical-sized defect in the rat femur

Despite significant advancements in bone tissue‐engineering applications, the clinical impact of bone marrow stromal cells (BMSCs) for the treatment of large osseous defects remains limited. Therefore, other cell sources are under investigation for their osteogenic potential to repair bone. In this study, tendon‐derived stromal cells (TDSCs) were evaluated in comparison to BMSCs to support the functional repair of a 5 mm critical‐sized, segmental defect in the rat femur. Analysis of the trilineage differentiation capacity of TDSCs and BMSCs cultured on collagen sponges revealed impaired osteogenic differentiation and mineral deposition of TDSCs in vitro, whereas chondrogenic and adipogenic differentiation was evident for both cell types. Radiographic assessment demonstrated that neither cell type significantly improved the healing rate of a challenging 5 mm segmental femoral defect. Transplanted TDSCs and BMSCs both led to the formation of only small amounts of bone in the defect area, and histological evaluation revealed non‐mineralized, collagen‐rich scar tissue to be present within the defect area. Newly formed lamellar bone was restricted to the defect margins, resulting in closure of the medullary cavity. Interestingly, in comparison to BMSCs, significantly more TDSC‐derived cells were present at the osteotomy gap up to 8 weeks after transplantation and were also found to be located within newly formed lamellar bone, suggesting their capacity to directly contribute to de novo bone formation. To our knowledge, this is the first study investigating the in vivo capacity of TDSCs to regenerate a critical‐sized defect in the rat femur. Copyright

MicroCT-based evaluation of the trabecular bone quality of different implant anchorage sites for masticatory rehabilitation of the maxilla.

In the severely atrophied maxilla, implant anchorage in the zygomatic bone is considered a viable alternative to conventional dental implants with preceding bone augmentation procedures. The present microCT-based study compared the trabecular bone quality of the maxilla and zygomatic bone. MicroCT scanning was conducted in 12 halves of cadaver heads (5 male, 7 female) with edentulous, atrophied maxillae. Relevant trabecular bone quality parameters were determined in the anterior and posterior maxilla and in the zygomatic bone and compared by region and sex. Any difference in mean values between the anterior maxilla and the zygomatic bone was insignificant. Comparison of both with the posterior maxilla presented significantly higher values for bone volume fraction, surface density, and trabecular thickness and number, and significantly lower values for specific bone surface, structure model index, and trabecular separation. A significant sex-specific difference was not detected. The present microCT-based analysis is, to the best of our knowledge, the first intra-individual comparison of different implant anchorage sites for masticatory rehabilitation of the maxilla. The trabecular compartment of the zygomatic bone offered bone quality and, thus, an implant bed comparable with those of the anterior maxilla, and both were superior to the posterior maxilla.

Bone-related Circulating MicroRNAs miR-29b-3p, miR-550a-3p, and miR-324-3p and their Association to Bone Microstructure and Histomorphometry

The assessment of bone quality and the prediction of fracture risk in idiopathic osteoporosis (IOP) are complex prospects as bone mineral density (BMD) and bone turnover markers (BTM) do not indicate fracture-risk. MicroRNAs (miRNAs) are promising new biomarkers for bone diseases, but the current understanding of the biological information contained in the variability of miRNAs is limited. Here, we investigated the association between serum-levels of 19 miRNA biomarkers of idiopathic osteoporosis to bone microstructure and bone histomorphometry based upon bone biopsies and µCT (9.3 μm) scans from 36 patients. Four miRNAs were found to be correlated to bone microarchitecture and seven miRNAs to dynamic histomorphometry (p < 0.05). Three miRNAs, namely, miR-29b-3p, miR-324-3p, and miR-550a-3p showed significant correlations to histomorphometric parameters of bone formation as well as microstructure parameters. miR-29b-3p and miR-324-p were found to be reduced in patients undergoing anti-resorptive therapy. This is the first study to report that serum levels of bone-related miRNAs might be surrogates of dynamic histomorphometry and potentially reveal changes in bone microstructure. Although these findings enhance the potential value of circulating miRNAs as bone biomarkers, further experimental studies are required to qualify the clinical utility of miRNAs to reflect dynamic changes in bone formation and microstructure.

Micro-CT evaluation of marginal and internal fit of cemented polymer infiltrated ceramic network material crowns manufactured after conventional and digital impressions

PURPOSE Purpose of this study was to evaluate the accuracy of fit of cemented polymer infiltrated ceramic network (PICN) material crowns manufactured after digital and conventional impression techniques using micro computed tomography (CT). Furthermore to determine the cement space volume and porosities in the cement layer. METHODS A molar typodont tooth was prepared for PICN material crowns and replicated thirty times. The dies were randomly divided into three groups of 10 specimens each according to the impression technique: 3M True Definition Scanner (TDS), cara TRIOS (Trios) and Impregum Penta Soft (Impregum). PICN material crowns were milled for each specimen from Vita Enamic blocks and cemented on their respective dies. The absolute marginal discrepancy (AMD), internal fit (IG), total cement space volume (TVC) and marginal porosities (VP) were measured using Micro-CT. RESULTS Mean and standard deviations values in μm for the AMD were: TDS 140.1 (28.4); Trios 253.7 (56.8); Impregum 220.2 (101.1). IG values in μm: TDS 173.1 (27.7); Trios 222.2 (22.4); Impregum 211.6 (55.9). TVC in mm3: TDS 19.82 (2.9); Trios 23.67 (2.01); Impregum 23.77 (5.09). VP in mm3: TDS 0.38 (0.09); Trios 0.36 (0.10); Impregum 0.51 (0.31). CONCLUSIONS TDS group showed significantly better marginal and internal fit than the Trios group. No difference of the parameters was detected between the Impregum and both digital groups which implies that the digital impression technique is suitable in the manufacturing process of PICN material crowns.