Full text for dissertations and theses included in this collection dates back to 2011. For older dissertations, check the library’s catalog CatalogUSMAI or Dissertations and Theses database.

Recent Submissions

  • The Role of Nociceptors in Orthodontic Tooth Movement, Pain, and Alveolar Bone Remodeling

    Elnabawi, Omar; Pae, Eung-Kwon
    Objective: To determine the effects of selectively ablating transient receptor potential vanilloid 1 (TRPV1)-expressing nociceptors on orthodontic tooth movement, pain, and alveolar bone remodeling. Methods: Resiniferatoxin (RTX) or vehicle was stereotaxically injected into left trigeminal ganglia in adult C57BL/6 mice. After 1 week, orthodontic spring was placed between left maxillary first molar and upper incisors. Pain level was evaluated by measuring mouse grimace scale (MGS) and bite force before and after 1, 3, and 7 days following the procedures. After 12 days, micro-CT was used to quantify tooth movement and analyzing alveolar bone changes. Results: Experimental tooth movement increased MGS scores and decreased bite force. RTX ablation of TRPV1+ nociceptors attenuated MGS scores and relieved the reduction in bite force. The extent of tooth movement was decreased in RTX-treated group, but interradicular alveolar bone volume was not affected. Conclusion: Selective ablation of TRPV1+ nociceptors significantly decreases tooth movement and pain.
  • Elucidating the Role of Fatty Acid Synthase in Oral Carcinogenesis and Potential Therapeutics

    Wisniewski, David John; Schneider, Abraham; 0000-0002-7514-7918
    The 5-year overall survival rate in oral squamous cell carcinoma (OSCC) has remained relatively unchanged over decades, due to late stage diagnosis and high recurrence rates. This work investigates two potential contributing risk factors associated with OSCC development: nicotine, present in traditional combustible tobacco cigarettes and electronic nicotine delivery systems, and high glucose as associated with Type II diabetes and hyperglycemia. A novel therapeutic, TVB-3166, for OSCC treatment was also studied through in vitro experiments, which may help improve clinical treatments for fully developed, often late-stage OSCC. Through cell viability and growth assays, scratch assays to mimic in vitro migration, and western blotting, we determined that both nicotine and high glucose caused oral dysplastic keratinocytes to exhibit an increase in malignant-like behavior. High expression levels of fatty acid synthase (FASN), a key de novo lipogenic enzyme, have been implicated in OSCC, and this work presents the first evidence that both nicotine and high glucose markedly increase oral dysplastic keratinocyte FASN expression, which drives epidermal growth factor receptor (EGFR) signaling, a key pro-oncogenic signaling pathway commonly associated with oral carcinogenesis. We also demonstrate that TVB-3166, a novel selective FASN inhibitor, induces apoptosis and reduces in vitro OSCC cell migration. Moreover, TVB-3166 inhibits basal EGFR activity and several other oncogenic signaling proteins. This further establishes a potential role for FASN and EGFR not only in the progression of oral epithelial dysplastic pre-malignant lesions, but in fully-developed OSCC tumors. Overall, this work suggests that both nicotine and high glucose play a role in OSCC progression, specifically as it relates to FASN-dependent EGFR activation. Further, the novel drug TVB-3166 should be investigated in future pre-clinical animal models as a potential adjunct to OSCC therapeutics. Through an improved understanding of risk factors for OSCC development, as well as determination of novel therapeutic strategies, this work aims to improve overall patient survival through prevention of OSCC development, as well as discovery of new adjunctive treatments for fully established tumors.
  • Comparative Microbial Adherence to Various Implant Dental Restorative Materials

    Alshehri, Malek Rofidi A.; Masri, Radi, 1975-
    The oral cavity contains the most complex microbial community of the body, which has more than 700 bacterial species. These microbial species colonize different habitats in the oral cavity. The biological interaction between dental restorative materials and the encompassing oral microbes is one of the most important factors for their clinical prognosis. Many studies have shown that there are distinctive interactions between the rate of microbial formation and the restoration material itself. Currently, there are several Implant Dental Restorative Materials on the market like poly-methyl methacrylate, feldspathic porcelain, dental zirconia, and dental composite resin. The purpose of this study was to comparatively evaluate initial adherence for C. albicans and S. aureus on five different implant dental restorative materials. Ten samples/group were constructed as 5mm x 5mm x 2.5 mm rectangles and were fabricated as per the manufacturer's instructions for each groups. Five groups were made from different types of materials: Polymethyl methacrylate denture material processed with the compression molding technique (PMMA), computer-aided design and computer-aided manufactured dental acrylic (CAD/CAM PMMA), feldspathic porcelain, dental zirconia, and pink dental composite resin. There was a significant difference between the five groups for C. Albicans (F=891.16, p=.0005). CFUs/ml for the pink dental composite resin were significantly higher than the other four groups. However, The dental zirconia group showed the lowest CFUs/ml for initial adherence between all the groups. For S. aureus, CFUs/ml for the pink dental composite resin was significantly higher than the other four groups. Heat polymerized PMMA and the CAD/CAM PMMA group showed significantly higher CFUs/ml than Feldspathic porcelain and dental zirconia groups. In conclusion, there was a significant difference between the five groups for initial adherence of C. albicans and S. aureus. The dental zirconia group showed the lowest initial adherence and the pink dental composite resin group showed the highest initial adherence for both microbes. Within limitation for this study, understanding what is the best for final dental restorative material from aspect of how much it could harbor microbes is an important factor in the final success of treatment and this study investigated this aspect under control conditions.
  • Accelerated Orthodontic Tooth Movement in Adult Patients by Subsequent Micro-osteoperforations of Maxillary Cortical Bone

    Laraway, Robert Dane; Schneider, Monica, D.D.S., M.S.; 0000-0001-6539-7123 (2018)
    Objective: Determine if orthodontic tooth movement during space closure is accelerated after subsequent micro-osteoperforations (MOPs). Methods: Five adults requiring maxillary 1st premolar extractions participated. MOPs were performed unilaterally in the extraction site at the beginning of the study and four weeks later. Canines were retracted bilaterally and space closure was measured after two months. Results: Overall, the canine retraction rate was 0.34mm greater on the MOP side compared to the control side but showed statistically insignificant differences. When compared to our initial study, which only had one MOP application, canine retraction was 0.24mm greater but, again, was statistically insignificant. Conclusion: The results of this study show that the experimental side had greater retraction of than the control side. However, the difference was not statistically significant. More studies are needed to study the extent and duration of effects of MOPs on tooth movement in humans.
  • Development and Implementation of an Audiovisual Informed Consent Delivery System for Non-surgical Root Canal Therapy

    Aguilar, Lauren; Macek, Mark D. (2018)
    The aims of this mixed-methods study were (1) to explore patients' preferences towards informed consent for endodontic procedures, (2) to use focus group feedback to develop short audiovisual presentations, and (3) to determine whether the audiovisual format lead to a different level of understanding than traditional consent. First was a focus group to assess patient expectations and attitudes towards consent for non-surgical root canal therapy (NSRCT). Second was developing two short audiovisual presentations. Finally a clinical trial tested the videos with 50 patients at the University of Maryland School of Dentistry. A questionnaire was used to assess patient preferences, comprehension, and recall of the consent and analyzed. There were no significant differences between groups in terms of recall, comprehension, understanding, or attitudes. Nonetheless, the data collected may be useful to restructure informed consent procedures for NSRCT and set a precedent for innovative consenting procedures.
  • Development of a New Generation of Dental Rechargeable Nanocomposites with Anti-caries Properties

    Al Dulaijan, Yousif Ali; Xu, Huakun H. (2018)
    Dental composites are popular for tooth cavity restorations due to their aesthetics, conservative approach, and direct-filling abilities. However, composite restorations have limited lifetime due to several limitations, including secondary caries, fracture, minimal abrasion and wear resistance and higher marginal leakage. Indeed, secondary caries is the primary reason for composite restoration failure. Besides, several studies have shown that conventional dental composites accumulate more biofilms/plaque when compared to other restorative materials. Therefore, this dissertation aims to develop a new generation of dental composites with antibacterial effects, protein-repellent activities, and remineralization properties. Recently, a rechargeable composite was developed, but this composite has no antibacterial or protein-repellent activities. In this dissertation projects, the nanoparticles of amorphous calcium and phosphate (NACP) as remineralizing agent, dimethylaminohexadecyl methacrylate (DMAHDM) as an antibacterial monomer, and 2- metha-cryloyloxyethyl phosphorylcholine (MPC) as a protein-repellent agent were incorporated into the rechargeable composite for the first time. Mechanical properties of the new nanocomposites were evaluated. The characterization of protein adsorption was measured. A human saliva microcosm biofilm model was used to determine biofilm metabolic activity, lactic acid, and colony-forming units (CFU). Calcium (Ca) and Phosphate (P) initial ion release, recharge and re-release were investigated. All rechargeable nanocomposites have good mechanical properties that were compared to those of a commercial composite. The rechargeable nanocomposites containing MPC showed the ability to reduce protein adsorption, as well as the biofilm metabolic activity, lactic acid, and CFU. The rechargeable nanocomposites containing DMAHDM showed strong antibacterial properties through the great inhibition of biofilm metabolic activity and lactic acid, and CFU. The incorporation of bioactive agents did not compromise the Ca and P initial ion release and rechargeability. The release was maintained at the same level with increasing number of recharge cycles, indicating long-term ion release. Therefore, this new generation of rechargeable nanocomposites with long-term Ca and P ion release, antibacterial and protein-repellent activities will provide the needed therapeutic effects to remineralize and strengthen the tooth structures, prolong the restoration longevity, and inhibit secondary caries.
  • Implications of underperforming light energy delivery for posterior composite: insights into delivered radiant exposure, degradation characteristics, and biofilm formation.

    Maktabi, Haifa; Melo, Mary Anne (2018)
    Poor curing of composites due to incorrect position of a curing unit may trigger a negative pathway of events related to the bacterial growth-stimulating effect of released methacrylate monomers. An increased bacterial adhesion and biofilm formation as a result of incomplete polymerization may contribute to premature failure of posterior composite via secondary caries formation. The objectives of each chapter are: 1) to review the literature concerning the light curing process and implications for failures on posterior composites (chapter 1), 2) to investigate in vitro how the variations on light curing tip placement and irradiance exposure can impact the degree of conversion of conventional 2mm-increment composite and S. mutans biofilm formation (chapter 2). In summary, this set of studies support the importance of proper light curing for an acceptable clinical performance of posterior composites.
  • Bacterial Adhesion to Various Implant Surfaces

    Khatra, Navpreet Kaur; Masri, Radi, 1975- (2018)
    Dental implants provide a major course of treatment for patients who are partially or completely edentulous. These implants are biocompatible metal anchors that are surgically positioned in the jawbone to support the prostheses where natural teeth are missing. However, the use of dental implants has some disadvantages, which can result in complications. Once the clean implant surface is exposed in the oral cavity, it is immediately coated with salivary pellicle and subsequently colonized by oral microbial species. In fact, microbial adhesion and accumulation on implants are considered to play major roles in the pathogenesis of peri-implant mucositis and peri-implantitis. The physico- chemical characteristics of specific material surface are known to significantly influence the bacterial adhesion process. Therefore, the surface characteristics of dental implants have been refined and restructured over a period of time to improve the interaction of implants with host cells and tissues. Hence, investigating the microbiological aspects related to implant surfaces will provide important insights relevant to expectations of treatment outcome. To that end, in this study, we aimed to comparatively evaluate microbial adherence and accumulation on five different types of implants. Specimens were provided by Dental Implant Systems, Biodenta Group and implant surfaces included: .3- .5 μm anodized surface, 1 μm BST surface, .8- 1.0 μm anodized surface, 1.6μm SLA surface and .3- .4 μm machined surface. To assess microbial adherence, the cariogenic bacterial species Streptococcus mutans and the bacterial pathogen Staphylococcus aureus were studied. Results from these studies were analyzed using analysis of variance (ANOVA) and significant differences were further analyzed by Tukey’s Honestly Significant Difference (HSD) test. Pearson’s r was also used to evaluate the association between surface roughness and bacterial accumulation. The present study has demonstrated that not only surface roughness but other physicochemical properties such as surface charge, energy, wettability and biological factors such as host immune response and oral hygiene influence bacterial adhesion and accumulation around implant surfaces.
  • Can treating oral inflammation lead to the reduction in a systemic outcome? A systematic review looking into pregnancy and diabetes.

    Guy, Veronica; Oates, Thomas W. (2018)
    The contribution of periodontal disease to the development of adverse systemic consequences remains controversial. It is hypothesized that inconsistencies between studies is due in part to limitations in study design. This review assessed systemic conditions including adverse pregnancy outcomes and glycemic control for patients with diabetes in a combined manner based on a shared inflammatory mechanism of consequence. It is thought that the systemic consequences of periodontal inflammation can directly influence these systemic conditions. Therefore, this systematic review aimed to evaluate the consideration of the patients' medical management during the study and also the number of study participants as two important factors influencing the study outcomes. An article search was performed using OVID Medline, Cochrane library and EMBASE and a manual search was performed through November 2017. Randomized controlled trials published between 2000 and 2017 looking into the effectiveness of periodontal therapy on the rate of pre-term birth in a pregnant population and on glycated hemoglobin A1c in a type 2 diabetics were included. Primary outcomes were changes in HbA1c and differences in frequency of occurrence of pre-term birth. Medical management of the systemic condition under study was categorized from 0-3, based on stringency of study design and consideration for medical management during study participation. Risk of bias regarding randomization, allocation of sequence concealment, blinding, incomplete outcome data, selective outcome reporting and other biases were averaged using a cumulative assessment of factors considered in prior systematic reviews with shared studies. After article selection, randomized controlled trials including 17 on diabetes and 13 on pregnancy were combined for evaluation. Both increased sample size (R2=0.09, R value = 0.3) and improved stringency of medical management (Figures 13 & 14) were associated with diminished effects of periodontal therapy on systemic outcomes. Interestingly, risk of bias as assessed in previous systematic reviews showed a modest correlation (R2=0.104, R value= 0.32) with primary outcomes. This systematic review demonstrates that the disparate results in studies of periodontal therapy affecting systemic outcomes may be explained in part by study design, specifically stringency in consideration of medical management and sample size. The potential for confounding factors influencing outcomes remains a concern.
  • Parental Perception toward Dental Sedation in Pediatric Patients at the University of Maryland

    Almarwan, Marwah; Dhar, Vineet; 0000-0001-9351-9722 (2018)
    Purpose: To evaluate pre-operative parental perceptions towards sedation, through their knowledge, beliefs and attitude. The parents were also surveyed for post-operative satisfaction and acceptance of the sedation procedure within 2 days of the dental treatment under sedation. Methods: One hundred and one parents of children underwent dental treatment under sedation at University of Maryland responded to two questionnaires: pre-operative and post-operative (24-48 hours). Results: Most of the parents were the only one accompanying person with the child undergoing dental sedation (57.43%). Fisher's exact test was significant (0.006) in parents who thought that dental sedation was of a low risk and had education of college or more. Conclusion: Less than half of parents brought an additional responsible person with them to the child's dental sedation appointment, suggestive of inconsistent compliance with the pre-operative instructions. Parents with higher education (postgraduate) viewed dental sedation for children as a safe approach.
  • Estimating accuracy of the CBVT InVesalius Imaging Software to measure the volume of simulated periapical defects in a human cadaver mandible

    Khan, Mir MA; Tordik, Patricia (2018)
    TITLE: Estimating accuracy of the CBVT InVesalius Imaging Software to measure the volume of simulated periapical defects in a human cadaver mandible. AIM: This in vitro study tested the accuracy of CBVT InVesalius software to determine volumetric data as compared to true volume. METHODOLOGY: Ten artificial periapical osseous defects of similar size were created bilaterally in the posterior region of a human cadaver mandible. Vinyl polysiloxane impression material was injected to create a replica of each defect. The true volume of each replica was obtained using Archimedes' method and compared to volumetric measurements as determined by InVesalius. Statistical analysis was performed with one-way ANOVA and the significance level was set to p ≤ .05. RESULTS: The mean difference in volume measurement for InVesalius (.0454 cc) and Archimedes' method (.0436 cc) was very small (p = .48). CONCLUSION: InVesalius software appeared to accurately measure the true volume of the periapical defects.
  • Knowledge, Perceptions and Behavior regarding E-cigarettes among Dental Practitioners

    Joshi, Shashank; Oates, Thomas W. (2018)
    Background: The increased use of e-cigarettes represents an emerging concern for dental practitioners with the potential to impact clinical care. The concerns for, and effects of, e-cigarettes remain poorly understood, especially with long-term use. Given current limits to our understanding of the effects of e-cigarette use, the goal of this study was to assess the level of concern among dental practitioners and the effects of these concerns on the care provided for patients using e-cigarettes. Methods: Dental practitioners (n=187) in Maryland completed a 28-item survey of e-cigarette knowledge, perception and their current clinical practices for patients using e-cigarettes. A knowledge score was computed, and associations between participant demographic characteristics and knowledge survey items, perception survey items and knowledge score levels, and behavior survey items and knowledge score levels were explored. Results: Most practitioners do not see or do not ask patients about E-cigarette use (33%), switching from conventional cigarette to E-cigarette use (38%) or dual use (55%). Majority of practitioners classified as medium to high knowledge 75% (141/187), felt they were well-informed and have up to date knowledge about E-cigarettes compared to 25% classified as low knowledge (46/187). Practice behaviors were not significantly different across knowledge score groupings. High knowledge groups modified their practice behavior positively in all the categories, except high knowledge group did not feel concerned with recommending dental implants in e-cigarette smokers (mode=5). Low knowledge group consistently had negative practice behavior except more positive response within the group for recommending stopping of E-cigarettes before invasive procedures was observed (mode = 5). Conclusions: The evidence and knowledge about e-cigarette risks on oral health is lacking and is not yet fully influencing practice behaviors. This study reinforces the value of disseminating and translating this evidence to dental practitioners through early inclusion of this topic in dental and hygiene training programs and through continuing education courses.
  • Improved oral health quality of life and satisfaction with implant-supported overdentures for patients with type 2 diabetes

    Herrero, Frances; Oates, Thomas W. (2018)
    Diabetes mellitus is considered a relative contraindication to implant therapy. Recent studies suggest risks may be less than previously thought. The potential benefits for diabetic patients remains to be determined. The goal of this study was to examine the benefits of implant-supported mandibular overdentures (IOD) for patients with type 2 diabetes. One hundred fifty-seven patients received two mandibular implants. Patients completed an Oral Health-Related Quality of Life (OHRQoL), a Patient Satisfaction questionnaire, and HbA1c was measured at baseline and six and twelve months after restoration. Sixty-three patients reported no diabetes, 65 patients were well controlled (6.1%< HbA1c <8.1%) and 29 were poorly controlled (8.1%< HbA1c <12.0%). IOD treatment resulted in significantly higher OHRQoL summary scores and general satisfaction (100mm VAS) compared to baseline across all patient groups. No statistically significant changes in HbA1c were observed after treatment. Patients with diabetes benefit from IOD independent of glycemic status.
  • A clinically relevant viscoelastic FEA model of the mandible simulating the effect of a Herbst appliance

    Heidari Zadi, Zahra; Pae, Eung-Kwon (2018)
    As a powerful numerical solution to partial differential equations with sophisticated boundary conditions, Finite element analysis (FEA) has been vastly used to solve engineering problems. This tool also found to be useful in predicting load-strain patterns and biological failures in mechanics of dental applications as well. In orthodontics field, several studies addressed the benefits in use of FEM models to predict stresses and strains in jaws. These studies mostly considered only the linear elastic phase which corresponds to the immediate response of the bone to the loading during functions. On the other hand, it is the prediction of long-term stress and strain distributions that are useful for clinical purposes. Therefore, it is suggested in this study that the viscoelastic properties of the bone need to be incorporated in the analysis to render long-term stress and displacement patterns. In this research, for the first time to our knowledge, effects of viscoelasticity of the mandibular bone are incorporated into finite element analyses of force distribution and displacement of anatomical structures in response to a Herbst appliance. Our models clearly demonstrate how displacements of the mandible occur in accordance with distributions of force vectors.
  • Non-invasive Motor Cortex Neuromodulation Reduces Secondary Hyperalgesia and Enhances Activation of the Descending Pain Inhibitory System

    Meeker, Timothy Joseph; Greenspan, Joel D. (2017)
    Studies have demonstrated analgesic effects of motor cortex (M1) stimulation for several chronic pain disorders such as neuropathic pain and syndromes involving central sensitization. Central sensitization is an important factor in neuropathic pain, clinically manifested as hyperalgesia and allodynia beyond any apparent injury. We predicted M1 transcranial direct current stimulation (tDCS) would mitigate secondary hyperalgesia, with little or no effect on primary hyperalgesia. We used a capsaicin-heat pain (C-HP) model to elicit heat allodynia and secondary mechanical hyperalgesia in pain-free subjects. In an assessor and subject blind randomized sham-controlled trial, we found anodal M tDCS decreased the intensity and area of pinprick hyperalgesia more than cathodal or sham tDCS with a small to moderate effect size. In contrast, we found no difference among treatments on pain ratings during heat allodynia. These findings confirmed our predictions and support the hypothesis that M1-targeted neuromodulation diminishes central sensitization. To elucidate the mechanism driving analgesia, we repeated application of the C-HP model during anodal, cathodal or sham tDCS in an assessor-blind randomized controlled trial while capturing neurophysiological correlates using functional magnetic resonance imaging (fMRI). We hypothesized M1 anodal tDCS would enhance engagement of a descending pain modulatory (DPM) network in response to mechanical pain compared to cathodal or sham tDCS. Anodal tDCS normalized effects of central sensitization on mechanical pain responses in the DPM network. Anodal tDCS disrupted the normal covariation of mechanical pain processing with subjective pain intensity and blunted the effect of sensitization in primary somatosensory cortex. There were treatment associated differences in functional connectivity (FC) within the DPM network. We found M1 to PAG FC was significantly greater during pain after anodal versus cathodal tDCS. Differences in FC between pain and control states for anodal tDCS included disrupted FC between PAG and sensory regions in the parietal lobe as well as the rostral ventral medulla. No disruptions in FC between control and pain state were found after cathodal or sham stimulation. These results support the hypothesis that analgesia via M1 neuromodulation occurs through modulation of activity in the DPM network even at the earliest stages of therapy.
  • The Effect of CAMBRA Agents on Fracture Strength of Lithium Disilicate Crowns

    Sinada, Naif Ghazi; Masri, Radi, 1975- (2017)
    The Caries Management By Risk Assessment (CAMBRA) protocol outlines an approach in which certain agents can be used to serve as protective factors toward the management of dental caries. In this study, the effects of particular CAMBRA agents on the fracture strength of lithium disilicate ceramics (commonly used in dentistry) are studied. While Chlorhexidine exhibited no effects on the fracture strength of these ceramics, Prevident showed a decrease in the fracture strength of all the ceramics studied. These results indicate that clinicians should proceed with caution when using these CAMBRA agents in patients restored with lithium disilicate ceramics. Further studies on the particular mechanisms whereby this reduction in fracture strength occurs are indicated.
  • The Association of Statin Intake and Healing of Apical Periodontitis After Root Canal Treatment

    Algofaily, Maha; Tordik, Patricia (2017)
    The aim of this study was to analyze the association between statin intake and apical periodontitis healing after root canal treatment. Patients who self-reported statin use during the treatment and patients who reported never taking statins were included. All who received treatment on a tooth with a periapical radiolucency in the Postgraduate Endodontics Clinic, University of Maryland School of Dentistry (2011-2014) were invited for a two to five-year follow-up examination. Sixty teeth were examined, in 30 patients taking statins and 30 not taking statins (control). Healing was determined using the periapical index. Two calibrated endodontists assessed outcomes blinded to preoperative status. Fisher's Exact Test (FET) showed a significant difference in healing at the two-year or greater follow-up in patients taking statins compared to those who did not (93.0% vs. 70%, FET, p=.02). This study revealed a significant association between statin intake and healing of apical periodontitis after root canal treatment.
  • Clinical and Therapeutic Implications of Biofilm-associated Fungal-Bacterial Interactions: Candida albicans and Staphylococcus aureus

    Kong, Eric Fei; Jabra-Rizk, Mary Ann (2017)
    Biofilm-associated polymicrobial infections, particularly those involving fungi and bacteria, are responsible for significant morbidity and mortality and tend to be challenging to treat. Candida albicans and Staphylococcus aureus are considered leading microbial pathogens primarily due to their ability to form biofilms on indwelling medical devices. However, the impact of mixed species biofilm growth on therapy remains largely understudied. Here, we demonstrate that in mixed biofilms, C. albicans confers S. aureus significantly enhanced tolerance to antimicrobials mediated by impairment of drug diffusion through the biofilm matrix composed of C. albicans secreted fungal cell wall polysaccharides. Further, we demonstrated a key role for the C. albicans secreted quorum sensing molecule farnesol in modulating S. aureus response to therapy via modulation of drug efflux pumps. Importantly, farnesol was also found to inhibit the production of the carotenoid pigment staphyloxanthin, an important virulence factor in S. aureus involved in protection against oxidative stress. The significance of this inhibition was established through demonstration of the enhanced susceptibility of the depigmented S. aureus cells to oxidants and macrophage phagocytic killing. Theoretical computational binding models indicated that the mechanism for pigment inhibition may be due to farnesol competitively inhibiting the binding of farnesyl diphosphate to CrtM, an essential enzyme in the biosynthesis of staphyloxanthin. To begin to explore the implications of this fungal-bacterial interactions in a host, we utilized a clinically relevant subcutaneous catheter mouse model where central venous catheter segments infected in vitro with S. aureus and C. albicans individually or in combination, are implanted subcutaneously in mice. Vancomycin treatment of mice with infected catheters demonstrated that where therapy significantly reduced S. aureus recovery from catheters in mice infected with S. aureus, in co-infected animals, vancomycin had no impact on S. aureus recovery, underscoring the therapeutic implications of mixed biofilm-associated infections. The combined findings from this work provide lacking mechanistic insights into interspecies interactions in biofilm with great clinical relevance. The understanding of the interspecies dynamics of signaling central to the persistence and antimicrobial resistance of polymicrobial infections will greatly aid in overcoming limitations of current therapies and in designing novel therapeutic strategies to target these complex infections. Therefore, future research should focus on designing animal model systems to study the role of secreted quorum sensing molecules in mediating these interactions in vivo, and the impact of these interactions on pathogenesis.
  • Th17 Cells in Gingival Immunity and Their Key Role in Periodontitis Pathogenesis

    Dutzan, Nicolas; Reynolds, Mark A., D.D.S., Ph.D.; Moutsopoulos, Niki; 0000-0001-8343-0214 (2017)
    Periodontitis is a very common human disease characterized by inflammatory bone destruction in the oral cavity. It affects more than 64 million adults in the United States and is often linked to systemic or distant co-morbidities. T helper (Th) cells and specifically Th17 have been identified as important constituents of the inflammatory lesion in periodontitis. However, the specific role of Th17 cells in periodontitis and whether they drive inflammatory pathology is not fully understood. We performed a detailed characterization of gingival tissues and found that Th17 are amplified in the lesions of human periodontitis. In fact, Th17 cells represent the major source of IL-17A in humans and in animal models of periodontitis and we show that their accumulation in gingival tissues is IL-6 dependent. Th17 differentiation and IL-17A expression are tightly regulated by signal transducer and activator of transcription-3 (STAT3). To analyze the role of Th17/STAT3 in humans with periodontitis we have evaluated a large cohort of patients with autosomal dominant mutations in STAT3. Autosomal Dominant Hyper IgE Syndrome (AD-HIES) patients have a defect in Th17 differentiation and lack Th17 cells in the circulation. We clinically characterized patients with AD-HIES and evaluated Th17 responses in their oral tissues. We find that AD-HIES patients have reduced susceptibility to periodontitis and present minimal oral inflammation, consistent with blunted Th17 tissue responses. To mechanistically dissect the role of Th17 cells and STAT3 in periodontitis, we performed periodontitis induction in mouse models specifically lacking Th17 cells. Cd4creStat3floxed mice lacked Th17 cells but other sources of IL-17 producing cells were unaffected in gingival tissues and importantly, were resistant to inflammatory bone loss. These results demonstrate the key role of Th17 in periodontitis and suggest inhibition of Th17 through Stat3 in the treatment/prevention of disease. Indeed, we performed preclinical studies of Stat3 inhibition (using C188-9 inhibitor, a small-molecule compound designed to prevent Stat3 activation) and demonstrated that pharmacologic inhibition of Stat3 prevented inflammatory bone loss in periodontitis models. Our work uncovers the pathogenic potential of Th17 cells in periodontal inflammatory bone loss and suggests pharmacologic inhibition through STAT3 in the prevention of this common inflammatory disease.
  • IL-17/Th17 responses and their influence on oral microbial communities

    Abusleme, Loreto; Moutsopoulos, Niki (2017)
    T helper 17 (Th17) cells are key regulators of immunity and inflammation at mucosal surfaces. This T cell subset has been reported to mediate protective responses, but also immunopathology at the oral cavity. However, the requirements for Th17 cells to arise at this site remained minimally explored. Our initial objective was to examine the role of oral microbial communities in local Th17 induction, as the development of these cells had been shown to be determined by commensal bacteria at other barriers. To this end, we established assays to analyze the murine oral microbiome and found that Th17 accumulation occurred independently from microbial colonization at the oral mucosa, underlining the unique properties of each tissue barrier. Th17 cells are relevant mediators in mucosal defense against extracellular bacteria and fungi. Yet, their role in shaping human microbial communities at the oral barrier was not well-understood. To appreciate how Th17 immunity affects the oral microbiome establishment, we performed studies in a patient cohort with Autosomal-Dominant Hyper IgE Syndrome (AD-HIES) that exhibits impaired Th17 differentiation due to loss-of-function mutations in the transcription factor STAT3. We confirmed that AD-HIES patients display a significant susceptibility to oral fungal infections. Our characterization of their mycobiome during active candidiasis revealed a dominance of Candida albicans, alongside a generalized depletion of health-associated bacteria with the exception of Streptococcus, which were overrepresented. These results demonstrate the critical role of Th17 immunity in the containment of C. albicans as a commensal and suggest a synergistic relationship of C. albicans with streptococci, that may influence oral disease susceptibility. Finally, to understand the effects of excessive Th-17/IL-17 inflammatory responses on oral microbial communities, we evaluated patients with Leukocyte Adhesion Deficiency type-I (LAD-I), that present with severe periodontitis driven by IL-17 mediated immunopathology. Our findings revealed that exaggerated IL-17 responses are linked to dysbiosis of subgingival communities. Additionally, IL-23/IL-17 blockade treatment of an LAD-I patient demonstrated reversal of microbial shifts with immune-modulation, suggesting a causative role for IL-17 responses in LAD-associated microbial dysbiosis. In sum, our studies reveal critical roles for the IL-17/Th17 responses in establishment of the oral bacteriome/mycobiome in health and disease.

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