Objective:To explore the effect of carboxylated polyamidoamine (PAMAM-COOH) in combination with magnesium ions on the remineralization ability of amorphous calcium phosphate (ACP) in inducing remineralization of dentin collagen fibers in a 50% ethanol solution.Methods:Forty-five intact third molars extracted for impaction reasons were obtained from the College & Hospital of Stomatology, Guangxi Medical University. Two types of demineralized dentin specimens were prepared: ①Fully demineralized dentin ( n=30), specimens were immersed in 17% ethylenediaminetetraacetic acid (EDTA) (pH=7.4) at room temperature for 14 days with daily solution refreshment; ②Partially demineralized dentin ( n=15), specimens were treated with 37% phosphoric acid gel (Ultra-Etch, Ultradent) for 15 seconds followed by thorough rinsing with deionized water. Three remineralization groups were established for demineralized dentin treatment: ①Control group, 50% ethanol solution; ②ACMP group, 50% ethanol solution containing amorphous magnesium calcium phosphate (ACMP); ③PAMAM-COOH/ACMP group, 50% ethanol solution incorporating carboxylated polyamidoamine dendrimer-modified ACMP (PAMAM-COOH/ACMP). The chemical composition of remineralization solutions was analyzed by Fourier-transform infrared spectrum (FTIR). The morphology and particle size distribution of nanoparticles were characterized using transmission electron microscope (TEM). The fully demineralized dentin specimens were treated with three different remineralization solutions (37 ℃ for 7 days) respectively. The mineralization of the dentin collagen fibers surface was observed using scanning electron microscope (SEM) and the distribution of minerals inside and outside the collagen fibers was examined by using TEM. The partially demineralized dentin specimens were treated with fluorescence-labeled remineralization solutions (37 ℃ for 7 days) respectively, followed by analysis using confocal laser scanning microscopy (CLSM) to quantitatively evaluate the penetration depth of the mineralization agents. Results:FTIR analysis confirmed the presence of characteristic absorption peaks corresponding to phosphate (PO 43-) groups, carbon-nitrogen bonds, and amide linkages in the PAMAM-COOH/ACMP nanocomposite. TEM observed that the PAMAM-COOH/ACMP nanoparticles exhibited an average particle size of (36.85±8.02) nm in an amorphous state. SEM observation indicates continuous mineral deposition on dentin collagen fibers in the PAMAM-COOH/ACMP group, while no mineral deposition in the control group and only minimal deposition in the ACMP group. TEM showed no mineral deposition inside or outside the collagen fibers in the control group, only external mineral deposition in the ACMP group, and high-density mineral deposition both inside and outside the fibers in the PAMAM-COOH/ACMP group. CLSM analysis revealed a statistically significant difference ( P<0.05) in the depth of mineralized substances entering dentin tubules between ACMP group and PAMAM-COOH/ACMP group. Conclusions:The remineralization system of 50% ethanol solution incorporating PAMAM-COOH/ACMP successfully achieved the internal and external mineralization of demineralized dentin collagen fibers.

Objective:To explore the effect of carboxylated polyamidoamine (PAMAM-COOH) in combination with magnesium ions on the remineralization ability of amorphous calcium phosphate (ACP) in inducing remineralization of dentin collagen fibers in a 50% ethanol solution.Methods:Forty-five intact third molars extracted for impaction reasons were obtained from the College & Hospital of Stomatology, Guangxi Medical University. Two types of demineralized dentin specimens were prepared: ①Fully demineralized dentin ( n=30), specimens were immersed in 17% ethylenediaminetetraacetic acid (EDTA) (pH=7.4) at room temperature for 14 days with daily solution refreshment; ②Partially demineralized dentin ( n=15), specimens were treated with 37% phosphoric acid gel (Ultra-Etch, Ultradent) for 15 seconds followed by thorough rinsing with deionized water. Three remineralization groups were established for demineralized dentin treatment: ①Control group, 50% ethanol solution; ②ACMP group, 50% ethanol solution containing amorphous magnesium calcium phosphate (ACMP); ③PAMAM-COOH/ACMP group, 50% ethanol solution incorporating carboxylated polyamidoamine dendrimer-modified ACMP (PAMAM-COOH/ACMP). The chemical composition of remineralization solutions was analyzed by Fourier-transform infrared spectrum (FTIR). The morphology and particle size distribution of nanoparticles were characterized using transmission electron microscope (TEM). The fully demineralized dentin specimens were treated with three different remineralization solutions (37 ℃ for 7 days) respectively. The mineralization of the dentin collagen fibers surface was observed using scanning electron microscope (SEM) and the distribution of minerals inside and outside the collagen fibers was examined by using TEM. The partially demineralized dentin specimens were treated with fluorescence-labeled remineralization solutions (37 ℃ for 7 days) respectively, followed by analysis using confocal laser scanning microscopy (CLSM) to quantitatively evaluate the penetration depth of the mineralization agents. Results:FTIR analysis confirmed the presence of characteristic absorption peaks corresponding to phosphate (PO 43-) groups, carbon-nitrogen bonds, and amide linkages in the PAMAM-COOH/ACMP nanocomposite. TEM observed that the PAMAM-COOH/ACMP nanoparticles exhibited an average particle size of (36.85±8.02) nm in an amorphous state. SEM observation indicates continuous mineral deposition on dentin collagen fibers in the PAMAM-COOH/ACMP group, while no mineral deposition in the control group and only minimal deposition in the ACMP group. TEM showed no mineral deposition inside or outside the collagen fibers in the control group, only external mineral deposition in the ACMP group, and high-density mineral deposition both inside and outside the fibers in the PAMAM-COOH/ACMP group. CLSM analysis revealed a statistically significant difference ( P<0.05) in the depth of mineralized substances entering dentin tubules between ACMP group and PAMAM-COOH/ACMP group. Conclusions:The remineralization system of 50% ethanol solution incorporating PAMAM-COOH/ACMP successfully achieved the internal and external mineralization of demineralized dentin collagen fibers.

BACKGROUND: Nowadays, stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) signal axis has been used extensively because of its biological effects and particularly a great progress has been achieved in the mechanism of SDF-1/CXCR4 signal axis as well as in its use for tissue regeneration. OBJECTIVE: To summarize the factors affecting the regulation of SDF-1 and CXCR4 and to review the research progress in the biological characteristics of SDF-1/CXCR4 signal axis. METHODS: The first author searched the PubMed, CNKI, WanFang and VIP databases for relevant articles published from January 1990 to August 2018. The keywords were "tissue engineering; cell homing; chemokine; regeneration; pulp regeneration; HIF-1; SDF-1; CXCL12; CXCR4; NOX-A12" in both Chinese and English. RESULTS AND CONCLUSION: Hypoxia-inducible factor-1 plays a key role in the regulation of SDF-1, and there are multiple factors which can affect the expression of CXCR4. SDF-1/CXCR4 signal axis formed by the combination of SDF-1 and CXCR4 plays an important biological role in various physiological and pathological processes. Blocking SDF-1 is used to inhibit the pathogenic effect of the SDF-1/CXCR4 signal axis for therapeutic purposes, while increasing SDF-1 can strengthen the SDF-1/CXCR4 signal axis and enhance the ability of chemotactic endogenous cell homing for tissue regeneration. To further illustrate the mechanism of the SDF-1/CXCR4 signal axis, we upregulate or downregulate the expression of SDF-1 or CXCR4 by exogenous means to influence the biological function of the signal axis, and thus provide theoretical basis for optimizing clinical treatment strategies, and developing the biological function of the signal axis for human health benefits.

Objective To develop a new-type animal dental stent for the experiment of canine pulp regeneration.Methods The stent was composed of an upper support frame,an oral limit bracket and a lower support frame,which were aligned from top to bottom.A sleeve joint was made for the connection structure of the bracket,and the height and the width both could be adjusted to adapt to different animals' mouths.The rubber dam could be spread into tension and concave form by rotating the upper and lower support frames' ends.Results By resizing the animal dental stent based on the structure of animal facies maxillaris,medical staffs could proceed the examination and treatment to animals effectively,including the throat examination,oral examination,oral care,dental treatment (such as root canal therapy and dental filling) and other medical behaviors.Conclusion The experimental result shows the feasibility of utilizing the stent in the process of animal experiment or diagnosis and treatment.Moreover,the stent proves the capacity in protecting the soft tissue,widening the vision of operation field,getting rid of the saliva contamination,which is worthy popularizing in animal experiments and animal medical care.