Quinn Mitchell

Louisiana State University Health Sciences Center New Orleans, New Orleans, Louisiana, United States

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Publications (3)6.75 Total impact

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    ABSTRACT: Fractured endodontic files present a major problem. A novel method has been proposed to retrieve fractured nickel-titanium (NiTi) endodontic files by using electrochemical dissolution. However, the effect of file dissolution on adjacent soft tissues such as the periodontal ligament (PDL) has not been investigated. The aim of this study was to determine the effects of the dissolution products on PDL fibroblasts. Endodontic files were dissolved in sodium fluoride (NaF) by passing a 50-mA current through the NiTi files while immersed in the NaF solution. NaF/NiTi solutions were diluted with minimal essential medium-α media containing 10% serum. PDL cells were treated for up to 24 hours, and cell viability was quantified by using calcein AM to label live cells and ethidium homodimer to label dead cells. This was repeated by using artificial saliva (AS) as an alternative to NaF. NaF solution reduced PDL cell survival, and the NaF/NiTi solution further reduced PDL cell survival. AS alone did not reduce cell survival, whereas AS/NiTi solution reduced PDL cell survival. Particles that resulted from the electrochemical dissolution of NiTi files were highly cytotoxic. Electrochemically dissolving NiTi files in NaF results in solutions that are cytotoxic to PDL fibroblasts. AS may be a less toxic alternative for dissolving NiTi files.
    Full-text · Article · May 2013 · Journal of endodontics
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    ABSTRACT: Smearing of unset root canal sealers over the pulp chamber dentin may adversely affect bonding of self-etching adhesives and jeopardize their coronal sealing potential. This study examined the influence of different sealer removal protocols on the microtensile bond strengths of two self-etching adhesives to AH Plus-contaminated dentin. Coronal dentin surfaces were prepared from extracted human third molars. In the positive control groups, these surfaces were not contaminated with sealer and were bonded with Clearfil SE Bond or Clearfil Tri-S Bond. For the experimental groups, dentin surfaces were contaminated with AH Plus and wiped with either dry cotton pellets, cotton pellets saturated with ethanol, or cotton pellets saturated with Endosolv R followed by rinsing the dissolved sealer with water prior to bonding with the two adhesives. Bonded specimens were sectioned into resin-dentin beams for microtensile bond strength evaluation. Additional specimens were prepared for transmission electron microscopy to examine the ultrastructure and nanoleakage within the hybrid layers. For both adhesives, microtensile bond strengths significantly declined when the sealer was removed with dry cotton pellets or cotton pellets saturated with ethanol. Only the Endosolv R/water sealer removal protocol restored tensile bond strengths to those of the uncontaminated positive controls without adversely affecting hybrid layer formation in intact dentin or increasing nanoleakage within the resin-dentin interfaces. The Endosolv R sealer removal protocol appears to be effective in preventing the deterioration of bond strengths of the two self-etching adhesives to AH Plus-contaminated dentin and warrants further clinical investigation.
    No preview · Article · May 2009 · Journal of endodontics
  • Parks · Quinn Mitchell
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    ABSTRACT: Pseudomonas aeruginosa is a Gram-negative pathogen which causes severe eye disease. This study examined individual genes as well as systems of virulence gene regulation in the context of restoring pathogenicity to an avirulent strain. Isolated from a human eye, P. aeruginosa strain Paer1 caused minimal pathology. In contrast another human isolate, strain KEI 1025, destroyed the cornea. Strain Paer1 was compared to KEI 1025 on a genomic level through suppression subtractive hybridization. Differences between the two strain's genomes were identified, and examined for relevance to ocular virulence. An adenylate cyclase (CyaB), the Las quorum sensing system (LasR, RsaL, LasI), and a major protease of P. aeruginosa (LasB) were restored to Paer1. Other quorum sensing response modifiers (GacA and Vfr) were examined in Paer1 as well. Polyphosphate kinase (PPK1), a potential target for antimicrobial therapy, was examined for its role in corneal virulence and stress response. Protein secretion in strains of Paer1 and KEI 1025 grown in a simulated ocular environment was examined, as well as an analysis of mRNA induced in these strains during a corneal infection. GacA, Vfr, CyaB were intact however LasB was not and this in part related to decreased virulence in Paer1. Like LasB, PPK1 played a role in ocular virulence. Without PPK1, P. aeruginosa was notably susceptible to oxidative stress. When restored to Paer1, the LasR/LasI quorum sensing was induced in a rich environment, and repressed in a minimal environment. A novel Southern blot based approach to expression analysis was attempted, but it requires some refinement. In conclusion, Paer1 was compared to KEI 1025 on multiple levels to assess differences that relate to ocular virulence. Paer1 lost a major mechanism of gene regulation (LasR/LasI) as well as an effector of that system (LasB). When LasR/LasI is restored to Paer1 the severity of the disease is lessened due to repression through an unknown mechanism. When LasB is restored to Paer1 the organism produces significantly more corneal pathology. Advisor: Jeffery A. Hobden. Thesis (Ph. D.) -- Wayne State University, 2005.
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Publication Stats

15 Citations
6.75 Total Impact Points

Top Journals


  • 2013
    • Louisiana State University Health Sciences Center New Orleans
      • Department of Endodontics
      New Orleans, Louisiana, United States
  • 2009
    • Georgia Health Sciences University
      • Department of Oral Rehabilitation
      Augusta, Georgia, United States