Chemical Analysis of Dental Adhesives and Their Application with Self-Sealing Composites

Background and aims: Conventional resin composite materials typically require preconditioning of the tooth substrate, prior to their application, for reliable adhesion to the dental tissue. To simplify the adhesive process and reduce the potential for error arising from the additional steps, self-adhesive materials were introduced. These still, however, require improvements to overcome limited bonding and cavity sealing ability. The aim of this study was to develop novel methods to evaluate the chemical composition, polymerization and evaporation kinetics of different commercial adhesives. Furthermore, to compare their bonding to that of self-adhesive resin composite formulations. Methods: An FTIR model was used to evaluate the chemical component ratios of 8 commercial adhesive resins. The change in the chemical composition of three of those adhesives was further investigated during the processes of solvent drying and polymerization. Self-adhesive materials were developed by mixing a base monomer (UDMA), a diluent monomer (PPGDMA) and a functional monomer (4-META) with a hybrid filler at a 3:1 powder-to-liquid ratio. The filler included a remineralizing material, monocalcium phosphate monohydrate (MCPM), and an antibacterial material, poly-lysine (PLS) at varying levels. Bond strength and interfacial adaption observed via micro-computed tomography (Micro-CT), scanning electron and confocal microscopy were evaluated. VI Results: The FTIR analysis provided evidence that diverse bonding systems contained various concentrations and compositions of hydrophilic/hydrophobic monomers, functional acidic monomers, solvents, and fillers. In addition, the variable chemical composition of the adhesive systems affected the rate and level of solvent evaporation and degree of conversion. Micro-CT demonstrated that the experimental resin composite with the lowest MCPM and PLS concentration displayed the smallest gap at the interface compared to 3 commercial filling materials. In addition, it was also able to inhibit matrix metalloproteinase activity at the interface as observed under confocal microscopy. Conclusion: The type and concentrations of the monomers and solvents in the adhesives have a significant effect on polymerization and evaporation kinetics. Additionally, adding PLS and MCPM is beneficial in terms of gap reduction at the interface, dentine bonding strength and inhibition of matrix metalloproteinase’s activity

ANTIMICROBIAL EFFECT OF NEW RESTORATIVE DENTAL MATERIAL INCORPORATING SILVER NANOPARTICLES

Secondary or recurrent caries are dental lesions originated at the margins of an existing restoration, and are considered the most common reason for restoration failure. Usually, these lesions are histologically similar to the primary caries and can be difficult to detect unless somewhat advanced, resulting in a considerable loss of tooth structure. Over the past decades, resin-based dental materials have been used in restorative dentistry for their excellent esthetics and improved mechanical performance. However, they represent potential sources of carbon and energy for microorganisms including oral bacteria and fungi residual in the dental cavity. In addition, cariogenic bacteria can infiltrate the restoration-tooth margins compromise the restoration’s longevity. Because caries at the restoration margins is a main reason for restoration failures, it would be highly desirable for the composite and bonding agent to possess antibacterial capabilities. Novel antibacterial dental materials were developed by introducing quaternary ammonium monomers, including 12-methacryloyloxydodecylpyridinium bromide (MDPB), dimethylaminohexadecyl methacrylate (DMAHDM), and dimethylaminododecyl methacrylate (DMADDM). These monomers can form covalent bonds with the polymer matrix and be immobilized in the resin-based materials, representing a non-released, contact-killing agent. Several other antimicrobial formulations were also developed, including a methacryloxylethylcetyl dimethyl ammonium chloride (DMAE-CB) containing adhesive, quaternary ammonium polyethylenimine (PEI) nanoparticles for antimicrobial dental composites, antibacterial glass ionomer cements, and antibacterial nanocomposites and bonding agents incorporating a quaternary ammonium dimethacrylate (QADM). Quaternary ammonium acrylate (QAM) resins possess positively-charged quaternary amine N+ which can interact with the negatively-charged membrane of bacteria, leading to membrane disruption and cytoplasm leakage. It is postulated that long-chained quaternary ammonium compounds can be especially effective by inserting into the bacterial membrane, resulting in physical disruption and bacteria death. Aside from the antibacterial monomers added to the resin matrix, an alternative approach is to add silver nanoparticles. Indeed, silver (Ag) is known for its antimicrobial activity against a diverse group of bacteria and has been used for many years as an antimicrobial substance in the medical field. Composite containing Ag particles with long-lasting antibacterial activity have been manufactured and observed to inhibit S. mutans growth . In addition, resins containing Ag nanoparticles were able to inhibit biofilm viability. Although the restorative materials had significant evolvement in the past few decades, the high rates of treatment failure suggest that the current restorative approaches are not yet optimized and have a potential for improvement. The aim of this work is to synthesize and evaluate new bioactive and antibacterial composite materials based on photo-activated Bis-GMA/TEGDMA matrix, containing an hydrotalcite-like compound intercalated with Ag nanoparticles as filler. We have obtained a dental resin with improved physical and biological properties and, in addition, able to release low amount of silver in a controlled and tunable way for a long period of time. In contrast to the conventional and resin-modified glass-ionomers, our CR-Agx were able to release silver ions when intraoral pH values drop below the critical pH of 5.5, counteracting the demineralization process of the tooth surface. The caries protective effect of these materials may be related to the material’s ability to release adequate amounts of silver ions for sustained periods of time and during acidic attack

Optimising novel dental composites for paediatric patients

Since amalgam use to restore children`s teeth is no longer an option due to Minamata agreement and with the absence of a viable strong and easy to apply material, a need for a novel restoration has become essential. The aim of this research was therefore to develop a novel children’s composite that would enable a simpler and pain-free restorative method and be a feasible alternative for the difficult to place resin restorations and the weak glass ionomers. The initial eight formulations studied incorporated an adhesion promoting monomer, 4META (3wt%) within a base monomer, UDMA (72wt%) combined with low shrinkage diluent monomer PPGDMA (24wt%) and the photoinitiator camphorquinone (1wt%). This was mixed with a glass powder phase at two Powder/ Liquid ratios (PLR, 5:1 or 3:1). The glass filler contained different levels of two new novel additives to enable placement on caries affected dentine following minimal tooth excavation; antibacterial PolyLysine (PLS, 5 or 2wt%) and a remineralising agent Monocalcium Phosphate monohydrate, (MCP, 8 or 4wt%). Tests were performed to determine maximum levels of active agents that could be added whilst maintaining properties that would enable compliance with composite ISO and safety requirements. Studies included light curing kinetics, interaction of cured material with water (sorption and solubility, mass and volume changes, and release of agents) and mechanical properties (Flexural strength and modulus). These studies lead to a predicted optimal formulation with PLS of 4wt%, MCPM of 8wt% and PLR 3:1. The optimal formulation was large scale manufactured and the above studies repeated. Furthermore, testing of adhesion to tooth structure by means of microleakage, adaptation to cavity walls, shear bond strength and formation of resin tags within carious dentine was assessed. Finally, the ability to precipitate minerals and inhibit enzymatic activity at the adhesion interface was tested. Results showed that the proposed formulations were stable when aged at 60ºC for 6 months and had high monomer conversion (~>65%) when light-cured for 40s even with samples of 3mm thickness. Formulations of higher PLS and MCP content also exhibited higher water sorption and solubility values due to the hydrophilicity and release of these components. This was expected and observed to reduce the early mechanical properties, but the results showed that flexural strength and modulus levelled off after 3 months of soaking cured discs in water. The flowability of the paste and the PLS and MCP content were all positive factors in achieving better penetration and resin tags formation within the collagen mesh. This collagen mesh was a standardised caries-like model which was created during this study. The final optimised formulation results showed the material to be radio-opaque. It achieved >75% monomer conversion and was mechanically strong (120MPa biaxial flexural strength and 3.5GPa modulus). The water sorption and solubility values were just higher than the ISO recommended maximum values that were set for composites of non-releasing ability. The material also outperformed commercial comparators in terms of self-etching the enamel and adapting to the sound cavity walls. Furthermore, it also formed long and extensive tags (more than 200µm long) within collagen mesh (formic acid demineralised coronal tooth slices) and naturally carious dentine. Finally, the optimised material exhibited precipitation of minerals at the adhesion interface. Tags and mineral precipitation helped explain observation of matrix metalloproteinase (MMP) inhibition at the tooth / carious dentine interface. The results were used to support applications to MHRA for clinical trials and a notified body for CE mark. In conclusion, the research presented has achieved its aim to develop a marketable material that has the potential to address problems arising with amalgam ban

Strain Mapping in Teeth with Variable Remaining Tooth Structure

Problem: The effect of remaining tooth structure on strain in compromised teeth is not fully understood. Different remaining tooth quantities may affect stress and strain concentration within the remaining structure and potentially the longevity of the related restoration. Objectives: The aim of this project was to map and evaluate tooth strain levels at different stages and areas of structural tooth loss created by dental preparation (simulating caries created lesions) or soft drink demineralisation (simulating external acid erosion lesions), before and after restoration, and to evaluate and compare different strain measurement techniques: strain gauges (SG), the surface displacement field measured using digital image correlation (DIC), electronic speckle pattern interferometry (ESPI), and finite element analysis (FEA). In addition, testing teeth affected by erosion required testing and verifying different acid demineralisation protocols. Material and methods: Part I: Enamel samples (sound, polished) were subjected to extended 25 hours (hr) soft drink immersion protocols (accelerated, prolonged) with different salivary protection conditions (no saliva, artificial saliva, and natural saliva) to compare enamel surface loss. Moreover, enamel surface loss of extended erosion periods simulating different levels of clinical erosion lesions was calculated by different imaging methodologies. Microscopic analysis was performed to compare subsurface changes of early and extended erosion protocols. Part II: Strain under static loading was compared in teeth with different stages of unrestored occlusal and buccal accelerated soft drink demineralisation lesions and after restoration using different techniques (strain gauges, electronic speckle pattern interferometry, and finite element analysis). Part III: Strain under static loading was compared in prepared teeth with different remaining tooth dimensions and different restorations using strain gauges and digital image correlation techniques. Results: Part I: No statistical significance was detected in enamel thickness loss between sound and polished enamel samples in the accelerated erosion groups under all salivary conditions or between early and extended erosion groups tested. Part II: All testing methodologies measured an increased strain reading after 1 day in occlusal erosion group followed by gradual decrease, while, continuous increase in strain was observed with buccal erosion progression. For both groups, all restorative materials used were able to restore strain close to pre-treatment level. However, strain distribution pattern was more favourable in ceramic and gold occlusal onlays than composite onlays. Part III: for both strain gauges and digital image correlation, remaining tooth height ≥ 3 mm and width of 1 to 1.5 mm of the remaining tooth structure had a positive effect on strain. Tooth compositions of enamel and dentine resisted strain better than dentine counterparts at all dimensions. Both core restorations (with and without cuspal coverage) were found to support the remaining tooth structure and reduce strain. However, only cuspal coverage recorded significantly lower strain than their unrestored counterparts. Conclusion: Restorations bonded to advanced erosion induced lesions restored strain levels to pre-treatment condition and produced a more favourable strain distribution pattern highlighting the role of adhesion in reducing strain. Remaining tooth structure suffers less strain under loading when enamel is part of the structure and when the minimum dimension of 3 mm in height and 1.5 mm in width is preserved. Bonding of core restoration or cusp coverage aids in reducing strain under loading. All strain measuring methodologies were comparable, where similar strain behaviour was recorded. Remineralisation of enamel and dentine is effective in the management of initial erosion

Characterization of dental bonding systems and commercial versus novel self-adhesive restoratives

Contemporary materials designed to replace lost tooth tissues due to caries include resin-based composites. These require bonding systems to bond to tooth substrates. As their use involves multiple steps, is technique sensitive and prone to degradation, they need improvement and simplification. Recently, self-adhesive materials were developed but are yet to overcome difficulties related to low surface interaction and bonding to dentine. The aim of this study was to test current commercial bonding systems and self-adhesive restorative materials in order to understand their properties. This allows optimisation and development of a competitive self-adhesive material with adequate physico-chemical properties. Four commercial bonding systems and three commercial self-adhesive materials were studied. An FTIR data model was built, to identify relative component ratios in the materials. Polymerisation kinetics, contact angles, pH, filler/solvent analysis and bond strength were assessed. Self-adhesive experimental materials were made by combining adhesion promoters (4-META or 10-MDP), a bulk monomer (UDMA) and a diluent monomer (PPGDMA) with a hybrid filler phase at a powder-liquid ratio of 3:1. The filler phase combined antibacterial poly-l-lysine and remineralising monocalcium phosphate monohydrate (MCPM) particles. Interfacial chemistry, penetration depth and in situ conversion were assessed through micro-Raman Spectroscopy, and other techniques such as FE-SEM/EDX and Confocal Microscopy were used for interfacial characterization. The novel formulation containing 10-MDP was assessed regarding stability, polymerisation, bond strength, flexural strength and modulus. Bonding systems were found to be variable in what concerns component ratios, polymerisation kinetics and mechanisms, pH and fillers. They still outperform self-adhesive composites in dentine interdiffusion due to their viscosity and chemical composition. The experimental composite is able to penetrate etched dentine and form long resin tags, with good conversion levels. The optimised formulation containing 10-MDP showed comparable conversion and good mechanical properties to formulations containing 4-META and may be a viable alternative to enhance material properties and bonding

Bacterial Interactions with Dental and Medical Materials

The interaction of bacteria with biomaterials’ surfaces has critical clinical implications on the development and progression of biofilm-related diseases. In this book "Bacterial Interactions with Dental and Medical Materials", encouraging findings on tissue-contacting biomaterials to control biofilms, enhanced understanding of key mechanisms, and clinical perspectives are discussed toward improving healthcare

Sviluppo e caratterizzazione di una sorgente Plasma Gun per applicazioni biomedicali

Cold Atmospheric pressure Plasma (CAP) devices are gaining great interest for their potentials in medical applications, ranging from the inactivation of microbial load to the induction of apoptosis in malignant cells. Therefore, the dissertation was focused on the development of a prototype CAP medical devices, based on Plasma Gun configuration, evaluating its performances in endodontic and oncology fields. Regarding dental applications, a biological investigation of the antibacterial efficacy of Plasma Gun source was carried out on realistic root canal models in collaborations with a group of dental practitioners. Furthermore, the CAP-derived enhancement of adhesion performances of tooth restoration was evaluated along the whole length of ex-vivo root canals. Concerning cancer applications, the CAP-induced apoptosis in Jurkat cells was tested and studied by means of cyto-toxicological analyses. This study represents the first step of a national research project aiming at evaluating the selectively induction of apoptosis in leukemia cell models. Finally, great effort was addressed to the study of optical spectroscopy techniques for the characterization and control of plasma processes: in particular, the poisoning effect of ozone, a molecule extremely relevant for biomedical applications, was investigated through the analysis of O3 and NOx kinetics

Management of bone defects with Bio-oss

Introduction: The defects in the alveolar bone might appear as a result of congenital malformations, traumatic injuries, periodontal disease, surgical traumas, chronic periapical changes and tumors from benign or malignant origin. The aim of this study was to provide solid and healthy area with application of Bio-Oss in the defect. Materials and methods: Based on the clinical diagnosisestablished by previously taken history, clinical examination and radiographic images oral-surgery interventions was made. To realize the aim of this work, augmentative material was implicated in the bone defects made in the patients after removal of follicular cyst, chronic periapical lesion, and parodontopathia. During the first and seventh day of the interventions, the patients have been followed through from aspect of possible development of local and general complications after the oral-surgery intervention. After period of one, three and six mount control x-ray was made. Results: Obtained results confirmed that: volume of the socket and defect of the bone was kept, fast revascularization was achieved, bone formation and slow resorption of the augmentative material was achieved, and period of normal healing without infection was also achieved. Conclusions: The augmentative materials used for treatment of bone defects besides their basic chemical and physical characteristics referring to their solubility in the body fluids, the transformation, modulation and resorption must be completely safe or secure, i.e. not to bring any risk of infection, immunological risk, physiological intolerance or inhibition of the process of restitutio ad integrum. In our study Bio-Oss was confirmed as augmentative material who had this characteristics. Keywords: bone defect, resorption of the bone, augmentative material, Bio-Os