Effect of margin designs and loading conditions on the stress distribution of endocrowns: a finite element analysis.

BACKGROUND: Margin designs and loading conditions can impact the mechanical characteristics and survival of endocrowns. Analyzing the stress distribution of endocrowns with various margin designs and loading conditions can provide evidence for their clinical application. METHODS: Three finite element analysis models were established based on the margin designs: endocrown with a butt-joint type margin (E0), endocrown with a 90° shoulder (E90), and endocrown with a 135° shoulder (E135). The E0 group involved lowering the occlusal surface and preparing the pulp chamber. The E90 group created a 90° shoulder on the margin of model E0, measuring 1.5 mm high and 1 mm wide. The E135 group featured a 135° shoulder. The solids of the models were in fixed contact with each other, and the materials of tooth tissue and restoration were uniform, continuous, isotropic linear elasticity. Nine static loads were applied, with a total load of 225 N, and the maximum von Mises stresses and stress distribution were calculated for teeth and endocrowns with different margin designs. RESULTS: Compared the stresses of different models under the same loading condition. In endocrowns, when the loading points were concentrated on the buccal side, the maximum von Mises stresses were E0 = E90 = E135, and when there was a lingual loading, they were E0 < E90 = E135. In enamel, the maximum von Mises stresses under all loading conditions were E0 > E90 > E135. In dentin, the maximum von Mises stresses of the three models were basically similar except for load2, load5 and load9. Compare the stresses of the same model under different loading conditions. In endocrowns, stresses were higher when lingual loading was present. In enamel and dentin, stresses were higher when loaded obliquely or unevenly. The stresses in the endocrowns were concentrated in the loading area. In enamel, stress concentration occurred at the cementoenamel junction. In particular, E90 and E135 also experienced stress concentration at the shoulder. In dentin, the stresses were mainly concentrated in the upper section of the tooth root. CONCLUSION: Stress distribution is similar among the three margin designs of endocrowns, but the shoulder-type designs, especially the 135° shoulder, exhibit reduced stress concentration.

Photothermal modulation of gingival fibroblasts via polydopamine-coated zirconia: A novel approach for promoting peri-implant soft tissue integration.

Achieving robust soft tissue integration around dental implants is crucial for long-term clinical success, as it forms a protective biological seal against bacterial invasion. However, the soft tissue attachment to implants is relatively deficient compared to natural teeth, particularly in the connective tissue region lacking sufficient gingival fibroblasts and collagen fiber alignment. This study proposed an innovative strategy to enhance peri­implant soft tissue integration by modulating gingival fibroblast behavior via photothermal conversion. Zirconia surfaces were coated with polydopamine (PDA), a melanin-like polymer exhibiting near-infrared (NIR) absorption for photothermal conversion. Under NIR irradiation, the PDA coating enabled mild hyperthermia (42-43 °C) on the zirconia surface. Remarkably, this mild photothermal stimulation significantly promoted human gingival fibroblast proliferation, adhesion, and collagen production compared to unmodified zirconia in vitro. By utilizing the photothermal properties of PDA coatings to modulate cellular behaviors beneficial for connective tissue formation, this approach provides a promising avenue to achieve improved soft tissue integration and long-term stability of dental implants. The findings highlight the innovative potential of combining biomaterial surface engineering with photothermal therapy for applications in implant dentistry.

[Recombinant human tumor necrosis factor-alpha promotes human adipose-derived stromal cells transforming into osteoblast in vitro].

OBJECTIVE: To investigate the effect of recombinant human tumor necrosis factor alpha (rhTNF-α) on the osteogenesis potential of the osteo-induced human adipose-derived stromal cells (hASCs) in vitro. METHODS: hASCs at passage 4 were divided into four groups according to culturing conditions: basal medium [BM, DMEM + 10% FBS + antibiotics], BM with 10 µg/L rhTNF-α, osteogenic medium (OM, BM + dexamethasone + L-ascorbate + ß-glycerophosphate) and OM with 10 µg/L rhTNF-α. On days 3, 7, 14 and 21, alkaline phosphatase (ALP) activities were examined. On days 14 and 21, the staining and quantitation of calcium deposition were performed. For the cells under osteogenic induction, osteoblast-related genes, such as core-binding factor α1 (Cbfa1), Osterix (Osx) and osteocalcin (OC) were analyzed with reverse transcription PCR on days 3, 7, 14, and 21, and real time PCR was performed to confirm the effect of rhTNF-α on genes expression on day 3 . RESULTS: rhTNF-α promoted ALP activities of induced hASCs on day 14 (3.527 ± 0.415 vs. 2.345 ± 0.354,P<0.01) and on day 21 (3.106 ± 0.105 vs. 2.442 ± 0.163,P<0.01) and promoted calcium deposition of induced hASCs on day 14 (2.896 ± 0.173 vs. 0.679 ± 0.173,P<0.01) and on day 21 (2.231 ± 0.233 vs. 1.729 ± 0.229, P<0.01). RT-PCR and Real-time PCR assays showed that rhTNF-α augmented the expression of Cbfa1, Osx and OC of these cells. CONCLUSION: The findings indicate that 10 µg/L rhTNF-α can promote the osteogenic potential of osteogenetically induced hASCs in vitro.

[Application of human adipose-derived stromal cells in bone tissue engineering].

Human adipose-derived stromal cells (hASCs) can be obtained from adipose tissues that offer an abundant and easily accessible pool of stem cells. Thus, hASCs have become a highly attractive source of seed cells in bone tissue engineering and have promising prospects in bone regeneration. Since 2002, our research group has performed a series of experiments on hASCs and its application in bone tissue engineering, including: to substitute dexamethasone by 1,25 (OH)2 vitamin D3 to induce osteogenic differentiation of hASCs; to explore the effect of epigenetic regulation and to inflammation on the osteogenic differentiation of hASCs; to construct a novel and simple tissue engineered bone system by hASCs and human platelet-rich plasma (hPRP) and to investigate the bone formation capability of this tissue engineered bone and the stimulatory effect of simvastatin. Our results suggested that 1,25 (OH)2 vitamin D3 could replace dexamethasone to induce the osteogenic differentiation of hASCs; retinoblastoma binding protein 2 (RBP2), as one of histone demethylases, could regulate the osteogenic differentiation of hASCs epigenetically while tumor necrosis factor α (TNFα), as a inflammatory factor, could also influence the osteogenic differentiation of hASCs. Moreover, we found that in vivo bone formation could be detected by our novel tissue engineered bone composed with hASCs and hPRP; simvastatin could enhance the bone formation capability of this tissue-engineered structure.

[Comparison of biological characteristics of human, rabbit and rat adipose tissue-derived stromal cells in vitro].

OBJECTIVE: This study aims to investigate the difference of proliferation patterns and osteogenic and adipogenic differentiation capability of adipose-derived stromal cells (ADSCs) obtained from human lipoaspirates, rat and rabbit inguinal subcutaneous adipose tissues in vitro. METHODS: Adipose tissues of healthy adults were obtained by liposuction. Human ADSCs were isolated from these adipose tissues and cultured in DMEM containing 10% fetal bovine serum (FBS). Rat and rabbit ADSCs were obtained from inguinal subcutaneous adipose tissues and cultured with the same methods. These cells were observed under inverted microscope each day and cell growth was measured with MTT assay. Adipogenic differentiation was induced by culturing ADSCs for 1 or 2 weeks in adipogenic medium (AM) containing 1 micromol/L dexamethasone, 10 micromol/L insulin, 200 micromol/L indomethacin, 0.5 mmol/L isobutyl-methylxanthine (IBMX), and assessed by Oil Red O staining as an indicator of intracellular lipid accumulation. Osteogenic differentiation was induced by culturing ADSCs in osteogenic medium (OM) containing 0.1 micromol/L dexamethasone, 50 micromol/L ascorbate-2-phosphate, 10 mmol/L beta-glycerophosphate, and examined via alkaline phosphatase (AP) activity and extracellular matrix (ECM) calcification by alizarin red S staining and quantification of matrix calcification. RESULTS: Fibroblast-like cells were digested from both inguinal subcutaneous adipose tissues of rabbit or rat and human lipoaspirates obtained from subcutaneous adipose tissues. Lipid-filled droplets were accumulated in human, rat and rabbit ADSCs upon treatment with adipogenic medium and were stained by Oil Red O. No lipid droplets were observed in the control undifferentiated ADSCs. After exposure to osteogenic differentiation medium, human and rat ADSCs were found to possess greater osteogenic potentials than cells isolated from rabbit inguinal subcutaneous adipose tissues, which was evidenced by significantly different osteogenic markers including alkaline phosphatase and mineral deposition. CONCLUSION: Rabbit ADSCs obtained from inguinal subcutaneous adipose tissues poorly possess osteogenic potentials compared with ADSCs of human lipoaspirates obtained from subcutaneous adipose tissues or ADSCs of rat from inguinal subcutaneous adipose tissues, although they all possess comparable adipogenic capacity.

The role of simvastatin in the osteogenesis of injectable tissue-engineered bone based on human adipose-derived stromal cells and platelet-rich plasma.

An injectable tissue-engineered bone (ITB) composed of human adipose-derived stromal cells (hADSCs) and platelet-rich plasma (hPRP) was preliminarily constructed, but its osteogenic capability needs improving. This study aimed to evaluate if simvastatin can be applied as a bone anabolic agent for this ITB. We found 0.01 microm, 0.1 microm, and 1 microm simvastatin could induce hADSCs' osteoblastic differentiation in vitro that accompanied with non-inhibition on cell proliferation, high alkaline phosphatase activity, more mineralization deposition and more expression of osteoblast-related genes such as osteocalcin, core binding factor alpha1, bone morphogenetic protein-2, vascular endothelial growth factor, and basic fibroblast growth factor. Simvastatin at 1 mum seemed the most optimal concentration due to its high osteocalcin secretion in media (P < 0.01). Quantitative mineralization assay also showed 1 microm SIM had the most obvious synergistic effect on hPRP's induction for matrix mineralization of hADSCs (P < 0.01). When 1 microm Simvastatin was applied to this ITB to restore the critical-sized calvarial defects in mice, more bone formation was observed in defected regions, and the peripheries just outside the defect margins by X-ray analysis, and H&E staining. These findings indicate that simvastatin at optimal concentrations can be used to promote this ITB's osteogenesis. However, simvastatin's effects on this ITB await long-term investigation.

Mild-onset presentation of Canavan's disease associated with novel G212A point mutation in aspartoacylase gene.

We describe two sisters with a mild-onset variant of Canavan's disease who presented at age 50 and 19 months with developmental delay but without macrocephaly, hypotonia, spasticity, or seizures. Remarkably, both patients had age-appropriate head control, gross motor development, and muscle tone. There were very mild deficits in fine motor skills, coordination, and gait. Both sisters had a history of strabismus, but otherwise vision was normal. The older child showed evidence of mild cognitive and social impairment, whereas language and behavior were normal for age in the infant. Both patients were found to be compound heterozygotes for C914A (A305E) and G212A (R71H) mutations in ASPA. Like all other known ASPA mutations, this previously unknown G212A mutation appears to have low absolute enzyme activity. Nevertheless, it is associated in these patients with an extremely benign phenotype that is highly atypical of Canavan's disease. Biochemical and clinical data were evaluated using a generalized linear mixed model generated from 25 other subjects with Canavan's disease. There were statistically significant differences in brain chemistry and clinical evaluations, supporting a distinct variant of Canavan's disease. Future studies of ASPA enzyme structure and gene regulation in these subjects could lead to a better understanding of Canavan's pathophysiology and improvements in ASPA gene therapy.