Papers by Author: Yang Xi Chen

Abstract: The purpose of the present study was to observe the response and changes of cranial suture to the distraction forces in growing goats and to examine the expression patterns of TGF-β and BMP during suture distraction.Twenty growing goats were divided into three groups: control (n=4), experimental (n=12), and sham (n=4). A pure titanium distractor was placed in the coronal suture in both the sham and experimental groups. After healing, the distractor was activated for distraction of the coronal suture at a rate of 0.5 mm/day for 8 days in the experimental group. Three animals were killed respectively, at 0，2，4 and 8 weeks after completion of suture distraction. No force was applied in the sham group. X- Ray examination was taken and the coronal suture samples were harvested and processed for histological analysis and scanning electron microscopic analysis and immunohistochemistry of TGF-β and BMP. The coronal sutures of experimental group were separated successfully. Signs of intramembranous bone formation and remodeling were found in the distracted suture，and the sutural structure almost return to its normal state at 8 weeks after end of distraction. At 0 and 2 weeks after completion of suture distraction, the collagen fiber bundles were strengthened and aligned in the direction of the distracted forces. Strong expression of BMP and TGF-β were detected in the fibroblast-like cells and the active osteoblasts. At 4 weeks after suture distraction, signs of intramembranous ossification were found in the edge areas of the distracted suture, and the positive staining of BMP and TGF-β was still noted in the osteoblasts around the newly formed bone trabeculae. This study suggests that cranial suture expansion can be achieved in growing animal by distraction osteogenesis. Mechanical strain resulted from distractor can induce the adaptive remodeling in the cranial suture of growing goats. It also suggests BMP and TGF-β may play very important roles in the process of bone formation and remodeling during suture distraction osteogenesis.

Abstract: Dental ceramic materials do not always show linear expansion behavior. In general, thermal contraction behavior of dental porcelain can be described with the polynomial function: L/L= C+α1 T+α2 T2. In addition, a new method for taking into consideration of nonlinear contraction behavior of dental ceramics is proposed for calculating thermal mismatch value (α) between substrate and veneering materials. Discs of eight substrate/veneer combinations (n=10) were fabricated for thermal shock testing. In this study, a stepwise multiple regression analysis was performed to determine the relationship between thermal shock test results and thermal mismatch value (α) on these combinations. A high degree of correlation was found between αs-b and T. The new method proves to be a reliable one to predict thermal compatibility of multi-layer dental ceramic composites.

Abstract: The objectives of this study are to investigate the influence of class III orthopedic forces generated by repelling rare earth magnets of class III magnetic orthopedic appliance (MOA-III) on the zygmaticomaxillary suture of Rhesus monkeys. Six male Rhesus monkeys in the stage of mixed dentition were used in this study. Fluorescent dyes were injected intravenously in each animal before and during the experimental period. Distinct changes from physiologic growth remodeling were observed in some sutures but not in the control groups. No inflammation was noted in both experimental and control monkeys. The results show that MOA-III is a small intraoral appliance to treat class III malocclusion, and the 300gm per side heavy orthopedic forces are safe and effective for Rhesus monkey.

Abstract: Cranial sutures produce new bone at the sutural edges of the bone fronts in response to external stimuli. Little is known regarding the mechanism of osteogenesis in cranial sutures. Ets1 and Cbfa1 are two important osteogenic transcription factors regulating the differentiation and maturation of osteoblasts. But their function in cranial sutures is not still elucidated. We have investigated the gene expression of Ets1 and Cbfa1 in rat’s calvarial sutural osteoblast-like cells under a single period of mechanical strain. The cells were isolated from the cranial suture of SD rats and cultured in vitro, and subjected to a single 40 minutes mechanical strain using a four-point bending apparatus. The gene expression patterns of Ets1 and Cbfa1 were examined by RT-PCR. Both mRNA levels of Ets1 and Cbfa1 have increased significantly within 6 and 12 hours respectively after mechanical strain were applied, and the increase returned to control level thereafter. However, Ets1 and Cbfa1 exhibited different temporal expression patterns: Ets1 expressed immediately after the mechanical loading and reached the maximum transcription at 0.5h; whereas Cbfa1 experienced a latency period first, then increased slowly within 2 hours, and reached the maximum transcription at 6 h. The maximum transcription of Cbfa1 was about 2.58 fold of that of Ets1. Ets1and Cbfa1 may play different roles in regulating bone matrix protein expressions in osteoblast-like cells during suture distraction and their function is time-dependent. High frequency distraction (>2times/24h) is favourable to the maximal expression of the two genes.