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

  • Novel Bioactive Low-shrinkage-stress Nanocomposite with Antibacterial and Remineralization Properties and Thermal-cycling and Aging Resistance.

    FILEMBAN, HANAN; Xu, Huakun H.; Weir, Michael D. (2022)
    Dental composites continue to be the material of choice in daily dental practice for several reasons, including their good mechanical properties, conservative cavity design, and superior esthetics. However, the longevity of current resin composite restorations ranges only 5-10 years. Recurrent caries and tooth fracture are the most common types of failure during the first 6 years of clinical service. These failures are often caused by the polymerization shrinkage stress of the dental composite materials. Thus, there is an increased need to develop a new generation of bioactive dental composite with the ability to reduce polymerization shrinkage stress, long-term antibacterial, remineralization abilities, and excellent mechanical properties. Therefore, this dissertation aims to develop a new bioactive low-shrinkage-stress dental composite containing dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP) which could be a promising approach to increase the chances of success of composite restorations and strengthen tooth structures. First, we found that the new bioactive low-shrinkage-stress resin composite significantly reduced the polymerization shrinkage stress, without compromising their mechanical properties. Increasing the DMAHDM mass fraction increased the antibacterial effect in a dose-dependent manner. Next, we investigated the low-shrinkage-stress composite mechanical stability and antibacterial durability in thermal cycling for 20,000 cycles, equivalent to two years of clinical life. We found that the bioactive low-shrinkage-stress composite possessed good mechanical properties that matched commercial composite both before and after thermal cycling. The new composite had potent antibacterial activity, which was maintained and did not decrease after thermal cycling. Lastly, we further examined the mechanical and antibacterial durability of a bioactive low-shrinkage-stress after 50,000 and 100,000 thermal cycles which corresponds to 5 and 10 years respectively of in vivo function. We found that the bioactive low-shrinkage-stress composite maintained its antibacterial potency after thermal cycling, indicating long-term antibacterial durability. In addition, it possessed good mechanical properties that were comparable to commercial composite both before and after thermal cycling. The triple benefits of antibacterial, remineralization, and lower shrinkage stress have a great potential to inhibit recurrent caries and increase restoration longevity.
  • Soluble Immune Biomarkers as a Diagnostic Tool of Head and Neck Squamous Cell Carcinoma Histological Inflammatory Subtypes

    Ghita, Ioana; Younis, Rania H. (2022)
    Head and neck squamous cell carcinoma (HNSCC) is a devastating malignancy that occurs in close proximity to vital structures. Despite all advances in diagnostic and therapeutic measures, the overall 5-year survival rate stays at ~65% and can be dismal for recurrent and advanced stages. There is accumulating evidence indicating the immune suppressive potential of HNSCC by which it can escape and/ or suppress the immune system. The recent advent of immunotherapy showed unprecedented improvement in overall response of advanced stage HNSCC. Yet, the overall response rate of HNSCC to immunotherapy remains at ~ 15%. Hence, further understanding of HNSCC tumor inflammation is warranted. The hypothesis of the current work is that the histological inflammatory subtype (HIS) of HNSCC can provide the basis for patient stratification that can be distinguished from the cytokine profile in peripheral blood, therefore better treatment strategies and patient outcomes. Paired tumor tissue and plasma of 104 HNSCC cases were collected according to UMB IRB protocol. Scoring of the HIS subtype was carried out using immunohistochemistry (IHC) of the emerging immune biomarker Semaphorin 4D (Sema4D). Our cohort showed 52% HIS inflamed (HIS-INF), 40% immune excluded (HIS-IE) and 8% deserted (HIS-ID). Differential gene expression (DGE) analysis of 10 HNSCC tumor tissues using NanoString immune-oncologic (human IO-360) 700 genes set showed that tumors with HIS-IE clustered as IFN-γ negative/ low immune signature compared to HIS-INF and were higher in hypoxia gene expression and the myeloid cellular compartment, while the HIS-INF demonstrated higher lymphoid component. DGE revealed a novel association between the high soluble Sema4D in plasma (HsS4D) and higher transcriptional level of Osteopontin (OPN) in the tumor tissue, that we also demonstrated in vitro. Furthermore, using ELISA-Luminex™ system, HIS-IE tumor tissue was significantly distinguished from the HIS-INF, in almost 40 traditional cytokines detected in the paired plasma samples. In conclusion, our work demonstrated a stratification model of HNSCC based on the underlying HIS profile that can be detected via the soluble cytokine panel in blood. These findings can open new avenues for patient stratification and enhance personalized clinical care in the field of HNSCC.
  • The Trueness of additive and Subtractive Zirconia Crowns

    Almutairi, Eman Sager; Masri, Radi, 1975- (2021)
    Purpose: To assess the trueness of ceramic crowns fabricated using additive technology compared to crowns fabricated using subtractive technology. Material and methods: single crown was designed using Dental Designer Software. 3D design was used to fabricate milled and printed crowns. All crowns were scanned. Geomagic software was used for analysis. Best Fit and Marginal Fit Alignment used to analyze the 3D accuracy of the crowns. One Way ANOVA used to analyze the data, and p<0.05 was considered significant. Result: Significant differences found between the additively and subtractive manufactured crowns [p=0.003,F=11.172]. Additively manufactured crowns exhibited better trueness than subtractive crowns. For the additively manufactured crowns, the Best fit Alignment showed 42.81±40.8μm deviation, and the Marginal Alignment showed a 43.11 ±38.05μm deviation. For Subtractive manufactured crowns, the deviation in Best Fit Alignment was 62.67 ±50.79μm and in Marginal Alignment was 55.35±48.69μm. Conclusion: Additive technology fulfills surface trueness criteria.
  • Novel Bio-interactive Fixed Dental Restoration Cement with Potent Antibacterial and Remineralization Properties

    AlSahafi, Rashed A.; Weir, Michael D.; Xu, Huakun H. (2022)
    Resin-based cement is increasingly used in clinical practice due to its excellent mechanical and physical properties. The cementation and accurate placement of fixed dental restorations with an ideal marginal adaptation to the tooth structure remains a challenging laboratory and clinical task. The marginal gap of fixed dental restoration increases the opportunity for microleakage, plaque accumulation, and tooth demineralization by increasing the potential for food buildup around the margin and exposing the tooth-cement interface to the oral cavity. Thus, there is an increased need to develop a new generation of bio-interactive dental cement with antibacterial, long-term remineralization abilities, and excellent mechanical properties. Therefore, this dissertation aims to invent new bio-interactive resin-based cement containing dimethylaminohexadecyl methacrylate (DMAHDM), nanoparticles of amorphous calcium phosphate (NACP), and nanoparticles of calcium fluoride (nCaF2), which could be a promising approach to increase the chances of success of fixed dental restoration and strengthen tooth structures. All new cement formulations were subjected to a series of mechanical, antibacterial, and ion release assessments. In the first manuscript, we found that the new NACP+DMAHDM cement has excellent potential for fixed restoration cementation, as it efficiently inhibited S. mutans biofilm commonly associated with secondary caries and maintained an excellent mechanical property with high levels of Ca and P ions released. In the second manuscript, we found that incorporating DMAHDM and NACP into resin-based cement provides strong antibacterial action against saliva microcosm biofilm and presents a high level of Ca and P ion recharge abilities. In the third manuscript, we found that the new cement with both NACP and nCaF2 demonstrated the advantages of both types of bio-interactive fillers as it could release a higher level of ions than the resin cement with only nCAF2 and exhibits a better rechargeability compared to the resin cement with only NACP. Lastly, in the fourth manuscript, we found that the novel antibacterial low-shrinkage-stress resin-based cement provided strong antibacterial action and maintained excellent mechanical properties with reduced polymerization shrinkage stress, which could improve the long-term success of the fixed dental restoration.
  • Caries Experience Based on A Simulated Epidemiological Screening and Routine Examination with Radiographs

    Kuchari, Abrar; Dhar, Vineet (2022)
    Purpose: To assess and compare caries experience based on an epidemiological “screening” examination and a routine examination with radiographs. Methods: 128 patients ages 5 to 10 years were included. An initial examination was done by a pediatric dentist in conditions simulating an epidemiological screening assessment. A second evaluation was done by eight postgraduate pediatric dental resident who conducted a routine clinical exam of the patient in the dental chair including radiographs. Results: By the epidemiological screening, the prevalence of untreated dental caries (Y/N) in primary and/or permanent teeth was 50% and the caries experience was 77%. After the routine examination with radiographs, the prevalence of untreated dental caries was 74.22% and caries experience was 90%. The severity of untreated dental caries was 2.0 and 3.9, and the severity of caries experience was 3.2 and 5.6 by the simulated epidemiological screening and routine examination with radiographs, respectively.
  • Generational Perspectives of Orthodontists in the U.S. and Canada– A Survey Study

    Hussain, Syed Rassal; Bosio, Jose A. (2022)
    Objective: To identify differences between generations of orthodontists in the U.S. and Canada and to evaluate the perspective of each generation on widely debated topics in orthodontics. Materials and Methods: A 22-item IRB approved survey was distributed to orthodontists in the U.S. and Canada. Participants were asked questions about the use of technology, future of clear aligner therapy (CAT), orthodontic education, student debt, marketing, and corporate orthodontics among other topics. Results: Significant increase in female orthodontists over generations and a decrease in orthodontic educators was found (P<0.001). Among generations, differences were found in regard to their amount of student debt, use of specific diagnostic tools, marketing preferences, and their opinion on the future of CAT. Conclusions: Clear distinctions exist between different generations of orthodontists. Issues such as increasing student debt load and a decrease in orthodontic educators over generations should be addressed to preserve the future of the orthodontic profession.
  • The role of Angiopoietin-like 4 in head and neck squamous cell carcinoma progression and dissemination

    Hefni, Eman; Montaner, Silvia (2022)
    Dysregulation of cellular signaling is instrumental in the promotion of tumor cell metabolism, proliferation, tissue invasion and metastasis. Molecular-based therapies for neoplastic diseases are designed to modulate or interact with cell surface receptors, intracellular cascades, or microenvironment components related to the extracellular matrix, tumor vasculature and immune response. To design these therapies, an improved understanding of the molecular underpinnings leading to tumor growth is essential. The overall aim of our investigation is identification of the molecular mechanisms associated with the induction of tumor cell migration and proliferation induced by Angiopoietin-like 4 (ANGPTL4), a pro-tumorigenic and pro-angiogenic factor, in head and neck cancer squamous cell carcinoma (HNSCC). HNSCC accounts for around 54,000 new cases and 11,000 deaths per year in the United States. Unfortunately, the clinical management of this tumor remains challenging. Our studies, divided into two research aims, use in vitro cell-based models together with signal transduction and cell and molecular biology methods. Our results demonstrate that: 1) ANGPTL4 is upregulated in human-derived dysplastic oral keratinocytes (DOKs) and HNSCC cell lines, but not in normal oral keratinocytes (NOKs), suggesting an early and sustained role for ANGPTL4 in disease progression. ANGPTL4 is a molecular marker in biopsies from patients with mild-moderate or moderate oral epithelial dysplasia, primary HNSCC and metastatic HNSCC. ANGPTL4 is necessary and sufficient to promote cell migration in DOKs and HNSCCs lines. Binding of ANGPTL4 to neuropilin-1 (NRP1) leads to paxillin (PXN) phosphorylation and cell migration in an ABL1-dependent manner, exposing the ANGPTL4/NRP1/ABL1/PXN cascade as a vulnerable target for HNSCC treatment. 2) Epidermal Growth Factor (EGF)- and Hypoxia-inducible Factor-1 (HIF-1)-mediated pathways cooperate in the upregulation of ANGPTL4 in normal and dysplastic oral keratinocytes and HNSCC cells. Besides EGF, the EGF ligand amphiregulin leads to an increase in ANGPTL4 and is upregulated in HNSCC lesions. ANGPTL4 activates the HNSCC molecular markers p38 MAPK, AKT and mTOR in NOKs; these kinases may act as potential intracellular regulators of the autocrine signals and paracrine secretions that ANGPTL4 activates to promote HNSCC tumorigenesis. Collectively, our findings suggest that ANGPTL4 and its associated signaling molecules are potential therapeutic targets in HNSCC clinical management.
  • Global Temporary Anchorage Device (TAD) Usage: A Survey of Orthodontists

    Ashton, Kelsea; Bosio, Jose A.; 0000-0002-8045-3370 (2022)
    Objective: We aim to determine how often TADs are used worldwide and establish guidelines for implementing TADs in everyday practice. Methods: A 19 question survey was sent to orthodontists around the world asking opinion based, case-specific, and placement technique questions regarding TADs. The country of practice and length of time practicing orthodontics were the independent variables. Results: Most orthodontists use TADs rarely/sporadically. There were significant findings for how TADs are being used, sizes, and placement techniques amongst different continents. There was a significant difference in how many TADs orthodontists placed in residency according to how long they have been practicing, but it did not greatly affect frequency of use, mechanics, or placement technique. Conclusion: The frequency of TAD use is similar worldwide and amongst different age groups. Although significant data was found in this study, there is such variability in regard to TADs that clear guidelines were not established.
  • Optimal Antero-Posterior Position of the Maxillary Central Incisors and its Relationship to the Forehead in Adult African American Males

    Endres, Elise Tigani; Sanchez, Dina (2022)
    Objective: To determine an optimal antero-posterior (AP) position of the maxillary central incisors (CI) and its relationship to the forehead in African American males. Methods: 95 smiling profile photographs were taken, evaluated by orthodontists and laypersons, and categorized in Group B, R or F. The CI position and forehead inclination (FI) were measured relative to glabella vertical (GV). Statistical analysis evaluated the relationship between CI position and FI, differences between groups, and differences between orthodontists and laypersons. Results: Optimal CI position was -2.1mm behind GV. There were no significant differences between orthodontists and laypersons. All group comparisons were significantly different, except Group B v Group R. The optimal CI position relative to GV and FI were not significantly correlated. Conclusions: The AP position of the CI relative to the forehead in African American males can be evaluated to determine the optimal AP position of the CI and optimal esthetics.
  • The Perspectives of Middle Atlantic Society Orthodontists on COVID-19

    Vumback, Matthew; Schneider, Monica, D.D.S, M.S. (2022)
    Purpose: This study aims to survey Middle Atlantic Society Orthodontists on how COVID-19 has impacted and altered their practices and outlook on the profession. Methods: This cross-sectional study was designed using Qualtrics XM and consisted of 20 questions focusing on the licensed orthodontists in the MASO regions. Results: Responders had split feelings regarding the length of time out of practice due to regulations. Nearly 48% felt that it was too long, while about 49% felt that it was appropriate. During this time, over 32% have offered more aligner therapy but roughly 51% have seen a reduction in patients. Regardless, over 61% do not believe retirement plans have been affected. Conclusion: A meaningful difference in perspectives exists amongst MASO orthodontists regarding COVID-19 regulations and infection control. Treatment philosophy appears to be shifting towards clear aligner therapy and tele-dentistry. Despite the disruption to the profession, most orthodontists feel hopeful for the future.
  • A Novel Magnetic Nanoparticle Containing Adhesive to Enhance Microtensile Bond Strength of Composite Resin to Dentin: An in vivo Study.

    Bulloch, Brandon; Masri, Radi, 1975- (2022)
    Purpose: An in vivo study to compare microtensile bond strength and resin tag density of a novel adhesive that relies on magnetic force. Materials and Methods: Twenty-five teeth were obtained from subjects. In the experimental group, teeth were restored with a novel nanoparticle adhesive and magnetic force (n=16). In the control group (n=9), no nanoparticle or magnetic force was used. Teeth were extracted and cut into beams. Microtensile bond strength and resin tag density were measured. A two tailed student t test was used to compare groups. P<0.05 was considered significant. Results: There was a significant increase of microtensile bond strength of the experimental group compared to controls (P= 0.025). The SEM images showed resin tag density was increased by a magnitude of two with the experimental group. Conclusion: Magnetic force improves the microtensile bond strength and resin tag density of resin adhesive when used in vivo.
  • The effect of silver diamine fluoride on the surface roughness of dental ceramics

    Chandy, Tintu Sara; Masri, Radi, 1975- (2022)
    Purpose: This study compared the effect of silver diamine fluoride, acidulated phosphate fluoride and distilled water on the surface roughness of dental ceramics. Materials and Methods: Rectangles of zirconia, lithium disilicate and feldspathic porcelain were treated with 38% SDF, 1.23% APF and distilled water. The surface roughness of each rectangle was measured using a profilometer before and after treatment with the solutions. Multiple comparison of the means among the ceramics and testing solutions was done using 2-Way ANOVA followed by Tukey’s test. P<0.05 was considered significant. Results: APF created the greatest surface roughness compared to SDF and water. Zirconia was unaffected by all solutions. SDF increased the roughness of lithium disilicate and felspathic porcelain, however the results were not statistically significant compared to the control group. Conclusions: With many topical fluoride preparations available, dentists should be aware of their effect on different ceramic systems to prevent surface roughening of restorations.
  • Comparing the Accuracy of Occlusal Vertical Dimension Transfer in Cad-Cam Dentures

    Satin, Sara Reanne; Masri, Radi, 1975-; 0000-0001-8470-6948 (2022)
    This laboratory-based study investigated the accuracy of transferring the VDO of the maxillary/mandibular relationship when designing and fabricating digital dentures by evaluating two commonly used workflows: duplicate dentures (DD) and occlusion rims (OR). 15 STLs were obtained for each workflow. Three measurements in deviation (mm) were obtained, then 3D-deviation values were averaged for each workflow at each location. A two-way ANOVA was used for the statistical analysis to evaluate differences between the methods and location of measurement. The average deviation for OR was higher than DD at all locations of measurement. There was a statistically significant difference between the DD and OR workflows [F=46.00, p<0.0001]. There was no statistically significant difference in deviation between the points of measurement [F=0.15, p<0.86] or between the location and method [F=0.02, p<0.98]. The DD workflow exhibited less deviation in transfer of VDO than the OR workflow. The location of the measurements had no significance.
  • Nanotechnology-Based Dental Materials for Root Caries Management: Design Concepts and Advanced Strategies to Modulate Dysbiotic Patient-derived Oral Biofilms

    Balhaddad, Abdulrahman Abubaker; Melo, Mary Anne; Xu, Huakun H.; 0000-0001-6678-7940 (2021)
    The distinctive challenges associated with root caries demand innovative interventions to preserve the tooth structure and surrounding soft tissues. This dissertation is composed of a set of manuscripts aiming to advance the anti-biofilm approaches to prevent root caries from two perspectives: (i) invasive approach via novel bioactive resin composites, and (ii) non-invasive approach via magnetic field-guided antimicrobial photodynamic therapy (MF-aPDT). The first chapter provided a general introduction concerning the clinical burden of root caries, current treatment modalities, and their limitations. In the second chapter, I provided an overview of contact-killing monomers and bioactive fillers in restorative dentistry. Then, in chapter three, we developed bioactive resin composite formulations containing dimethylaminohexadecyl methacrylate (DMAHDM) antibacterial monomer and 20% nano-sized amorphous calcium phosphate (NACP) and subjected them to a series of mechanical/physical tests and antibacterial assays. We found that the DMAHDM-NACP resin composites were associated with a potent antibacterial action against cariogenic and periodontal biofilms, as 2 to 6-log reduction was observed. Other virulence factors, as lactic acid production, and polysaccharide production, were also reduced. The mechanical properties, physical characteristics, surface features, and polymerization behavior were comparable to the commercial control at baseline testing and after one year of aging. We concluded that the designed bioactive formulations might present a pathway to preven recurrent caries and the onset of periodontal diseases around dental restorations. In chapter four, we reviewed the most recent updates related to the implementation of nanotechnology to enhance antimicrobial photodynamic therapy (aPDT). Then, in chapter five, we investigated the impact of encapsulating superparamagnetic iron oxide nanoparticles (SPIONs) and toluidine blue ortho (TBO) inside a microemulsion, named MagTBO, to enhance the TBO’s penetration and antibacterial action against S. mutans and saliva-derived biofilms. Besides, the ability of magnetic field (MF) navigation to serve as a biofilm penetration strategy was also investigated. The MagTBO microemulsions were synthesized successfully and demonstrated excellent biocompatibility and thermodynamic stabilities. Furthermore, the MagTBO microemulsions demonstrated more remarkable and significant antibacterial action than conventional aPDT, especially when the MF is applied. Thus, this approach can be an adjunctive technique to control dental caries and other oral diseases.
  • Novel Dental Nanocomposites with Low-Shrinkage-Stress, Ion Recharge, Antibacterial and Remineralization Capabilities to Protect Tooth Structures

    Bhadila, Ghalia Yaseen; Xu, Huakun H.; Weir, Michael D.; 0000-0002-7361-9221 (2021)
    The objectives of this dissertation were to: (1) investigate a bioactive nanocomposite with strong antibacterial and ion-recharge capabilities containing dimethylaminododecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP), and evaluate long-term Ca and P ion recharge by testing for 12 cycles of recharge and release; (2) develop a low-shrinkage-stress (LSS) nanocomposite with antibacterial and remineralization capabilities through the incorporation of DMAHDM and NACP to reduce marginal enamel and dentin demineralization under recurrent caries biofilm-model; (3) investigate the effects of the new composite on biofilm inhibition, mechanical properties, shrinkage stress, degree of conversion, and Ca and P ion releases; and (4) investigate the cytotoxicity of the new LSS composite and its monomers in vitro. For the antibacterial and rechargeable nanocomposite, biofilm lactic acid and colony-forming units (CFU) were measured. Ion recharge was tested for 12 cycles. For the LSS antibacterial and remineralizing nanocomposite, mechanical properties, shrinkage stress, and degree of conversion were evaluated. The growth of Streptococcus mutans and multi-species salivary biofilms was assessed using biofilm CFU, lactic acid production, and confocal laser scanning microscopy. Ca and P ion releases, and human gingival fibroblasts cytotoxicity were measured. The bioactive rechargeable nanocomposite reduced biofilm acid production and viability. High levels of ion releases were maintained throughout 12 cycles of recharge, maintaining steady-state releases without reduction in 6 months, representing long-term remineralization potential. The LSS composite with DMAHDM and NACP had flexural strength matching that of a commercial control composite. The bioactive low-shrinkage-stress composite substantially reduced the biofilm CFU and lactic acid production compared to control composite. The bioactive LSS composite exhibited no significant difference in antibacterial performance before and after three months of aging, demonstrating long-term antibacterial activity. The shrinkage stress of the bioactive low-shrinkage-stress nanocomposite was 36% lower than that of traditional control composite, with similar degrees of conversion. The new bioactive nanocomposite had a satisfactorily low cytotoxic effect toward human gingival fibroblasts and the new monomers had fibroblast viability similar to that of commercial control. The two developed nanocomposites are promising to inhibit recurrent caries and protect the teeth with an intended application for reducing recurrent caries.
  • Design, Development and Assessment of Dental Sealants with Anti-caries Functionalities Using Bimodal Agents

    Salem Ibrahim, Maria; Melo, Mary Anne; Xu, Huakun H. (2019)
    Dental caries presents a high prevalence worldwide despite the availability of various prophylactic means, including the daily use of fluoride toothpaste, water fluoridation, dental sealants, oral health educational programs, and various mouth-rinses. Dental sealants were introduced to prevent dental caries in the pits and fissures of the occlusal surfaces. Sealants act as a physical barrier to prevent food accumulation in the pits and fissures. The current evidence suggests that sealing the occlusal surfaces of permanent molars in children and adolescents reduces caries up to 24 months when compared to no sealant. However, epidemiologic findings have shown an increase in sealant failures with increasing caries risk status due to biofilm accumulation at the sealant-tooth interface with further caries development. Thus, there is a need to develop new approaches to improve oral health care and decrease dental caries through the suppression of cariogenic biofilm formation in the sealant-tooth interface and dental materials surfaces. We proposed the development of novel dental resin-based sealant formulations with anti-caries functionalities intended to prevent caries development or progression. The sealing formulations contain two biointeractive agents; nano amorphous calcium phosphate (NACP) dimethylaminohexadecyl methacrylate (DMAHDM), a promising antibacterial monomer. The role of NACP content as a source of localized calcium and phosphate ions release delivered from a dental material for sealant applications and its combined use with the antibacterial monomer, DMAHDM, to impair anti-biofilm function were investigated. We comprehensively assessed the newly-designed formulations using in vitro biofilm models and analytical testing to investigate the potential biological effects of these novel materials on human enamel repair. We found that the formulation containing 20% NACP and 5% DMAHDM greatly reduced and modulated the cariogenic biofilm with effects on the virulence factors of key microorganisms. The combinatory formulation also presented a robust release of calcium and phosphate ions that imparted changes in the mineral loss of enamel. The formulation of a dental sealant with antibacterial and remineralizing potentials is a promising approach to prevent dental caries on the occlusal surfaces of children’s and adolescents’ teeth.
  • Development of New Formulations of nCaF2 Dental Nanocomposites with Antibacterial and Remineralizing Properties

    Mitwalli, Heba; Weir, Michael D.; 0000-0003-3877-6632 (2021)
    It is desirable to use a minimally invasive approach in dentistry through conservative techniques in order to prevent destruction of the tooth structure. Since resin-based dental materials are increasingly used, the occurrence of re-infections is also increasing. Recurrent caries and secondary infections are major problems in the restorative dentistry field. The prevalence of recurrent caries associated with resin-based restorative materials was previously shown to reach 60%. It is the most common reason recognized for composite resin restorations replacement and failure. Many efforts have been made to incorporate antibacterial agents into restorative materials. However, the majority of these materials act by releasing these agents into the surrounding environment, leading to their depletion over time. There is a clinical need for durable bioactive composite restorations that resist the formation of secondary caries for an extended period of time. Dimethylaminohexadecyl methacrylate (DMAHDM) is an antibacterial agent that is immobilized in resin and not lost or released with time. Therefore, this dissertation aims to develop new composite resin formulations containing DMAHDM antibacterial, 2-methacryloyloxyethyl phosphorylcholine (MPC) protein repellent, and nanoparticles of calcium fluoride (nCaF2) remineralizing modalities which could be a promising approach for management of recurrent caries around or under restoration margins. This dissertation incorporated DMAHDM, MPC and nCaF2 into composite resin restorations to achieve potent, long-lasting antibacterial, protein repellent, and Ca and F ion release and recharge/re-release capabilities. Mechanical testing was performed for all composite formulations. To determine biofilm properties, a human salivary microcosm biofilm model was used. Biofilm colony-forming units (CFU), minimum inhibitory concentration, lactic acid production, and metabolic activity of biofilm were investigated. Fluoride (F) and calcium (Ca) initial ion releasing, recharging and re-releasing capabilities were tested. The majority of nCaF2 nanocomposites show matching mechanical properties to the commercial control composite. The nCaF2-DMAHDM nanocomposites have potent antibacterial effects that substantially reduce biofilm activities in all biofilm experiments. Similarly, all nCaF2 nanocomposites have higher values of F and Ca ion release- recharge, and re-release when compared to the commercial control composite. Therefore, these new composite resin formulations may potentially lead to a fundamental contribution in restorative techniques that can be used to fight this most common limitation of composite restorations - recurrent caries - and contribute to the longevity of composite restorations through long-lasting antibacterial and protein repellent properties and remineralization capabilities.
  • Incidental Findings in Cone Beam Computed Tomography Images During Prosthodontic Evaluation: Characteristics of Head and Neck Atheromas

    Amarin, Rula Sabah Odeh; Masri, Radi, 1975- (2021)
    Objectives Atheromas can be incidentally detected in routine CBCT images. This study aims to assess prevalence, and risk factors associated with these vascular lesions. Materials and Methods Full-volume CBCT images of 458 patients were evaluated and divided into 4 groups: Subjects with no atheroma, subjects with intracranial atheroma (ICA), subjects with extracranial atheroma (ECA), and subjects exhibiting combined lesions. Age, sex, medical conditions, family history, and size were documented. Results Of the 458 subject scans, 29.9% presented with incidental atheromas. Atheroma’s incidence was significantly higher in older patients and in males compared to females. Patients with atheroma were significantly more likely to have a history of hyperlipidemia, hypertension, and myocardial infarction. Patients exhibiting combined lesions were more likely to have cardiovascular risk factors. Conclusion Incidentally detected atheromas are common and subjects with combined lesions are at higher risk for CVD, and this warrants early referral to medical specialists.
  • Determining the Neural Correlates of Burning Mouth Syndrome

    Payano Sosa, Janell; Seminowicz, David A.; 0000-0003-1337-3749 (2020)
    In the United States, nearly 1 million people suffer from burning mouth syndrome (BMS), a chronic orofacial pain condition that is largely unrecognized by the medical community and predominantly affects post- and peri-menopausal women. Relatively little in-depth research is available on the condition, and patients often give up seeking treatment. The pain in BMS arises spontaneously (i.e. in the absence of stimuli), but the mechanisms of this spontaneous pain is unclear, and there is limited research on structural and functional brain changes that may occur in a BMS sufferer. The goal of this dissertation was to investigate the central nervous system mechanisms of pain experienced in BMS. We collected: 8-day diaries, morning and afternoon quantitative sensory testing of both orofacial and forearm regions; afternoon structural and functional MRIs, and questionnaires from 27 BMS patients and 33 healthy post-menopausal women. Our hypotheses that, compared to healthy participants BMS patients have: higher pain sensitivity, especially in orofacial regions during the afternoon; lower grey matter volume and higher functional connectivity in nociceptive pathways associated with noxious heat during rest and evoked thermal pain, even after accounting for anxiety, were not supported. Instead, we found a time-of-day-dependent effect during warm detection and cold detection of face and forearm; lower grey matter volume of the dorsolateral prefrontal cortex (DLPFC), and higher grey matter volume of the inferior temporal gyrus and parabrachial nucleus (PBN); lower PBN connectivity with the DLPFC and primary somatosensory cortex (S1); higher connectivity of the right lateral hypothalamus (LH) with posterior insula during warm condition; connectivity of right medial hypothalamus and LH to left DLPFC and right PBN to bilateral S1 not associated with anxiety in BMS compared to healthy participants. Altogether, BMS showed abnormal responses to innocuous stimuli. This was supported by fMRI data, where connectivity differences were mostly present during innocuous stimulation. These altered sensory and brain responses could reflect heightened anticipation of thermal stimuli (both pain-specific and non-pain specific) associated with disruption of communication between regions associated with negative affect of pain (insula), attention modulation of pain (left DLPFC), somatosensation (S1), and thermoregulation (LH and PBN).
  • Surface Roughness of Zirconia Produced by Additive and Subtractive Manufacturing

    Triana, Frank James; Masri, Radi, 1975- (2021)
    Purpose – The purpose of this in vitro study was to compare surface roughness of full contour zirconia restorations produced by additive and subtractive manufacturing Materials and Methods – Full contour restorations were designed using 3Shape Dental System. The stl files were exported and utilized to guide production of all specimens. Zirconia samples were manufactured by two methods – additive manufacturing (n=10) and subtractive manufacturing (n=18). A two-step polishing protocol was used following sintering. All specimens were subject to profilometry to measure average Ra values. Ra values for both groups were compared. Statistical analysis was performed using t-test (p=0.05). Results – The average Ra value for zirconia restorations in the subtractive manufacturing group was 0.35 ±0.07µm while average Ra for additive manufacturing groups was 1.06 ±0.49 µm. Differences were statistically significant (p < 0.00001). Conclusions – Zirconia restorations produced by subtractive manufacturing were significantly smoother than those produced by additive manufacturing even after post-sintering polishing.

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