Graded ephrin-A2 expression in the developing hamster superior colliculus

During development, ephrin gradients guide retinal ganglion cell axons to their appropriate topographic locations in the superior colliculus (SC). Expression of ephrin-A2, assessed immunohistochemically in the developing hamster SC, revealed a rostral^low to caudal^high gradient that is most prominent at postnatal days (P)4 and P7 when topography is established. Double-labelling immunohistochemistry for ephrin-A2 and cell specific markers revealed that ephrin-A2 is expressed exclusively by a subset of neurons. The expression pattern has implications for mechanisms underlying establishment of topography during development and following injury.     

Evaluation of the True Self-etching Potential of a Fourth Generation Self-adhesive Methacrylate Resin–based Sealer

IntroductionThe limited diffusion of self-adhesive resin cements into crown dentin raises doubts on whether self-adhesive root canal sealers are capable of creating micromechanical retention in instrumented canal walls in the absence of adjunctive use of calcium chelating irrigants. This study evaluated the true self-etching potential of MetaSEAL, a self-adhesive sealer.MethodsMixed MetaSEAL sealer was applied to (1) fractured radicular dentin that was devoid of smear layers, (2) instrumented canal wall radicular dentin that was irrigated with water as the final rinse to preserve the smear layer, and (3) instrumented canal wall radicular dentin that was irrigated with ethylenediaminetetraacetic acid (EDTA) as the final rinse to remove the smear layer. Cryofractured tooth halves without sealer application were examined by scanning electron microscopy to identify the characteristics of the bonding substrates. The other tooth-halves were filled with sealer and processed for transmission electron microscopy.ResultsMetaSEAL did not demineralize fractured radicular dentin that was devoid of smear layer and smear plugs. The self-adhesive sealer was incapable of etching beyond the 1- to 2-μm-thick smear layer retained on water-irrigated instrumented dentin to demineralize the underlying radicular dentin. Smear layer and smear plugs were absent in EDTA-irrigated radicular dentin. The EDTA also partially demineralized the intact dentin, creating a thin bed of collagen for infiltration of the self-adhesive sealer.ConclusionsThe limited self-etching potential of MetaSEAL is a clinically legitimate concern. Incomplete smear layer removal from instrumented canal wall regions that are not reached by calcium chelating agents might jeopardize its bonding and sealing performance.     

Determination of Matrix Metalloproteinases in Human Radicular Dentin

Matrix metalloproteinases (MMPs) are present in sound coronal dentin and may play a role in collagen network degradation in bonded restorations. We investigated whether these enzymes can also be detected in root dentin. Crown and root sections of human teeth were powderized, and dentin proteins were extracted by using guanidine-HCl and EDTA. Extracts were analyzed by zymography and Western blotting for matrix metalloproteinases detection. Zymography revealed gelatinolytic activities in both crown and root dentin samples, corresponding to MMP-2 and MMP-9. MMP-2 was more evident in demineralized root dentin matrix, whereas MMP-9 was mostly extracted from the mineralized compartment of dentin and presented overall lower levels. Western blot analysis detected MMP-8 equally distributed in crown and root dentin. Because MMPs are also present in radicular dentin, their contribution to the degradation of resin-dentin bonds should be addressed in the development of restorative strategies for the root substrate.     

Contemporary Methacrylate Resin–based Root Canal Sealers Exhibit Different Degrees of Ex Vivo Cytotoxicity When Cured in Their Self-cured Mode

The cytotoxicity of four methacrylate resin–based sealers was investigated by the 3-(4,5-dimethyl-thiazoyl)-2,5-diphenyl-tetrazolium bromide assay, which measures cell viability by assessing its succinate dehydrogenase activity. The sealers were polymerized in the self-cured mode to simulate the setting condition upon their extrusion into periradicular tissues. Disks were prepared from EndoREZ (Ultradent, South Jordan, UT), RealSeal (SybronEndo, Orange, CA), MetaSEAL (Parkell, Farmington, NY), and RealSeal SE (SybronEndo) together with positive and negative controls. After setting, they were placed in direct contact with rat osteosarcoma (ROS 17/2.8) cells and for 5 succeeding weeks after immersing in simulated body fluid (SBF). All sealers exhibited severe toxicity initially (week 0). EndoREZ and RealSeal remained severely toxic after five cycles of SBF immersion. Toxicity of the two self-etching resin-based sealers MetaSEAL and RealSeal SE decreased gradually over time. Transmission electron microscopy of cells exposed to RealSeal SE showed variable degrees of cell injury that reflect its toxicity status. Cells with intact mitochondria were identifiable after the sealer became noncytotoxic at week 5.     

Regulatory analysis on the medical use of ephedrine-related products in Taiwan

To prevent ephedrine-related products from being misused to produce amphetamine and/or its analogs, there's a need for more effective and achievable regulatory mechanisms for the health, police, investigational, prosecution and judiciary authorities in Taiwan. This review was conducted to evaluate the international and Taiwan's regulatory policies and management of medical ephedrine-related products through the corresponding information collected from international and Taiwan government agency authorities. The combat of illegal drugs should involve both supply and demand sides to be successful. Health authorities in Taiwan do not have the investigational power to manage the forbidden transformation, abusing and manufacture of the illegal drugs from ephedrine-related products. Take the judicial interventions in the United States and in Japan as the examples, the organizational cooperation in Taiwan can be one of the main key strategies to combat against illegal drugs from ephedrine-related products. It is necessary to integrate the judicial, police and health agencies to prevent the production of illegal drugs from the ephedrine-related products in Taiwan. The efforts and regulatory control measures should be integrated to speed up the collaboration between different government authorities. It might be achieved through reorganization involving Taiwan Food and Drug Administration.     

Retention of fiber posts cemented at different time intervals in canals obturated using an epoxy resin sealer

OBJECTIVES: To evaluate the effect of immediate versus delayed post space preparation and cementation on the retention of different types of fiber posts in canals obturated with an epoxy resin sealer. METHODS: Sixty-eight single-rooted human teeth were decoronated and the root canals were shaped with rotary instruments and obturated with gutta-percha and an epoxy resin sealer. The teeth were divided into four experimental groups according to the different times of post space preparation and cementation: immediate (group 1), 24h (group 2) and 1 week (group 3) after root canal filling. Control group (group 4) with no root canal obturation was included. Two teeth were randomly selected from each group for SEM examination. Each group was further divided into three subgroups of five teeth each (n=5), according to the type of post and the materials used for luting the posts. A push-out test was performed and differences among experimental groups were analyzed with two-way ANOVA and Tukey test (alpha=0.05). RESULTS: Interfacial strength values achieved in group 1, where an immediate cementation was performed, were significantly lower (p<0.05) than those in group 2 and group 3 in which post cementation was performed 24h or 1 week after the root canal filling. Post type affected post retention, FRC Postec and DT Light Post posts achieved higher interfacial strengths than ENA Post (p<0.05). SEM examination revealed a more conspicuous presence of sealer remnants on the walls of immediately prepared post spaces. CONCLUSIONS: Delayed cementation of fiber post resulted in higher retentive strengths irrespective of the post type.