• 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 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.
    • Development of Novel Nanostructured Therapeutic Root Canal Dental Sealers with Strong Antibacterial and Remineralization Capabilities

      Baras, Bashayer Hussain; Xu, Huakun H. (2019)
      Root canal therapy aims to remove microorganism or at least reduce them to subcritical levels that permit the host’s immunity to eliminate infection and regenerate damaged tissues. However, due to the complex and variable root canal anatomy and the resistant nature of root canal biofilm, complete elimination of root canal microorganisms is rarely accomplished. In addition, it has been frequently reported that some of the most commonly used irrigating solutions, such as, sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) can adversely alter the chemical and mechanical properties of dentin, resulting in a brittle dentin structure that is more susceptible to root fracture. This dissertation aims to develop a therapeutic root canal sealing material with potent antibacterial properties and remineralizaition capabilities through the incorporation of dimethylaminohexadecyl methacrylate (DMAHDM) to provide bacterial contact killing in case of micro leakage, nanoparticles of silver ions (NAg) to eliminate bacteria in the more complex root canal anatomy through release of silver ions, and nanoparticles of amorphous calcium and phosphate (NACP) to reverse the action of NaOCl and EDTA on root dentin and strengthen the root structure through the release of Ca and P ions. In this dissertation projects, the effects of incorporating DMAHDM, NAg, and NACP on the physical and sealing properties were evaluated. The antibiofilm properties were assessed by polysaccharide production, live/dead, and colony-forming units (CFU) assays. The antibiofilm properties of the developed sealer were assessed on cured sealer disks and utilizing a human dentin model. In addition, the effects of NACP on the Ca and P ion release, pH-alkalizing properties, and influence on dentin hardness were all measured. The triple incorporation of DMAHDM, NAg, and NACP did not compromise the physical properties of the root canal sealer and demonstrated sealing properties that were similar to that of a commercial control material. The incorporation of DMAHDM and NAg alone into the root canal sealer demonstrated great reductions in bacterial viability and quantity. However, when both agents were combined the antibiofilm effects were maximized, resulting in CFU reductions of 6 orders of magnitude. The DMAHDM NAg containing root canal sealer was able to kill bacteria not only on the surface of resin disks but also bacteria impregnated inside human dentin. The incorporation of NACP into the respective sealer allowed for the release of high levels of Ca and P ions, neutralized the acid and increased the solution pH, and increased the dentin hardness to match that of sound dentin. This bioactive antibacterial and remineralizing root canal sealer is promising to prevent endodontic treatment failure and secondary endodontic infections while releasing high levels of Ca and P ions that could remineralize and strengthen the tooth structures and potentially prevent future root fractures and teeth extractions.
    • Development of Novel Therapeutic Dental Adhesives to Inhibit Secondary Caries

      al-Qarni, Faisal Dhaifallah; Xu, Huakun H.; 0000-0001-8540-5979 (2018)
      Despite efforts to reduce the effects of caries at the margins of restorations, the prevalence of secondary caries remains stubbornly high. Dimethylamino-hexadecyl methacrylate (DMAHDM) reduced biofilm viability and acid production when added to dental adhesives. 2-methacryloyloxyethyl phosphorylcholine (MPC) greatly reduced protein adsorption and bacterial attachment. Nanoparticles of amorphous calcium phosphate (NACP) suppressed caries and promoted remineralization. This dissertation incorporated DMAHDM, MPC and NACP to develop an adhesive with antibacterial, protein-repellent and remineralizing properties possessing long-term ion-recharge and re-releases for the first time. The effects of MPC and DMAHDM on calcium (Ca) and phosphate (P) ion release and recharge were established. The objectives of this dissertation were to develop an anti-caries adhesive containing bioactive agents NACP, DMAHDM and MPC, and investigate the effects of DMAHDM and MPC on Ca and P ion release and rechargeability. Incorporating the bioactive agents had no influence on mechanical behavior, as the adhesives had shear bond strength matching commercially available control. Using a human saliva microcosm biofilm model, DMAHDM-containing adhesives had substantial antibacterial functions with significant reductions in biofilm metabolic activity, lactic acid production and colony-forming units (CFU). MPC adhesives also had substantial reductions in protein adsorption, biofilm metabolic activity and CFU. The incorporation of NACP provided continuous Ca and P ion release over 70 days. After the ion release was depleted, specimens were recharged with Ca and P ions, then the ion re-release was measured. One recharge treatment enabled the resin to continuously release high levels of Ca and P ions for about three weeks, thus allowing the patient o potentially use a mouth-rinse for one day every three weeks. With increasing the number of recharge and re-release cycles, the Ca and P ion re-release reached similarly higher levels, indicating a long-term and durable recharge function. The combined incorporation of the bioactive agents produced novel therapeutic and anti-caries adhesives that could greatly reduce biofilm formation on restorative margins, repel proteins, remineralize lesions, and ultimately prevent secondary caries, thus increasing the success rate and the longevity of composite restorations.
    • 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.