Dr. Garry Fleming

Summary

Recent research suggests that single surface amalgam restorations produce a survival probability of 58% after ten years compared with 43 and 38%, respectively for resin-based composites (RBCs) (placed in Class III, IV and V cavities) and glass-ionomers (GIs) (placed in Class III and V cavities). Dental amalgam relies on mechanical interlocking for adhesion and the destruction of sound tooth structure is necessary with re-intervention in one in three cases being extraction or crowning. In addition, patient demand for the aesthetic treatment combined with the fear of mercury toxicity limit the appeal of amalgam. RBCs are aesthetic but time consuming, technique sensitive and require a series of preconditioning treatments of the tooth structure to ensure adhesion. The development of simplified bonding systems have not been as successful as expected despite the enormous research interest, with RBC performance reduced year on year since 1996. This proposed project aims to deliver a cost effective and predictable novel aesthetic posterior filling material to be placed in minimal intervention cavities with no associated loss of sound tooth structure. It is suggested that in principle re-intervention of like with like (GI with GI) could allow a tooth to survive indefinitely and eliminate the expense of crowing providing a major cost saving for the patient or the relevant health service provider namely the Health Services Executive. In short, the immediate beneficiaries are likely to be general dental practitioners (GDPs) and their patients who could take advantage of an enhanced GI restorative, thereby promoting minimal intervention techniques which would result in the preservation of sound tooth structure. The preservation of sound tooth structure would significantly impact on the quality of life of the general population as the extensive loss of natural dentition would result in extended patient visits to GDPs an in cases of extreme tooth loss would result in the patient requiring unsightly dentures which would significantly impact upon their quality of life. From a commercial viewpoint the ideal posterior filling material should be aesthetic and adhesive, qualities that only GIs possess and therefore an enhanced GI restorative would be an attractive commercial alternative to dental amalgam and RBCs. The development of advanced synthetic approaches and modern characterization methods for clinically applicable novel dental restorative glass-ionomer materials will result in a unique expertise of skilled researchers and is extremely valuable for the success in future research or academic careers. Conventional technical preparation methods often suffer not just from high costs but also from a reduced ability to produce multifunctional organic/inorganic composite structures and materials with hierarchical order; features that attribute unique mechanical and physiochemical properties to biomaterials including dental restorative materials. This project offers the opportunity for the Research Team at the Materials Science Unit to cement its place as one of the leading developers of dental materials worldwide. In short this collaboration between a Lecturer in Inorganic and Synthetic Materials Chemistry with a Senior Lecturer in Dental Materials Science offers the first step in a collaborative process that would see closer integration between two distinct scientific disciplines not noted for collaborations.

Funding Agency

Science Foundation Ireland

Programme

Investigator Programme 2013

Project Type

Developmental Materials Science

Person Months

48

Summary

While patient demand for aesthetic restorative treatment of posterior teeth combined with the enhanced public awareness of mercury toxicity from silver/grey dental amalgam restorations have resulted in the increased use of tooth-coloured resin-based composite (RBC) materials over the past two decades. Recent support for legislation from the European Commission to restrict the manufacture, use and disposal of mercury-containing materials has uncovered new challenges for dental practitioners and patients alike. Despite developments in light curing technology and RBC materials, the clinical performances of RBCs has not improved over a decade. Poor polymerisation protocols manifest as RBC restorations with inadequate mechanical and biological properties have resulted in significantly increased restoration failure rates and systemic health concerns, respectively even when compared with mercury-containing dental amalgams. Recommendations for the determination of a dental materials' biocompatibility status using ISO 7405 is wanting at best and perilous to patient health at worst. Our patient-focused multi-disciplinary research proposal offers an exceptional opportunity to strategically target and correct concerns with RBC eluents, ubiquitous throughout modern restorative dentistry. We have produced a primary human cell-based oral-mucosal-model, defined by distinct epithelial and connective tissue layers, metabolically viable and histologically resembling native human oral-mucosa. Our published data has highlighted significant cytotoxicity of nickel-containing base-metal alloys routinely used in dentistry and we believe that critically the activation of the innate immune response by RBC eluents can be demonstrated by initiation of proinflammatory responses in methacrylate and non-methacrylate-sensitised patients. It is anticipated that the multi-disciplinary patient-orientated research will provide a meaningful evidence-based questionnaire and clinical protocol for the Dublin Dental University Hospital (DDUH) which could be introduced across Dental Schools, Health Service Executive Institutions and Primary Care Dental Practices within Ireland and beyond. This would result in a research-driven modification to routine restorative dental treatment provision in methacrylate and non-methacrylate-sensitised patients. The patient-orientated approach involves an appropriate risk appraisal of the onset of inflammatory tissue responses by combining expertise in Materials Science and Cellular and Molecular Biology will be undertaken in a clinical environment. The main objective is to optimise clinical treatment protocols which will significantly reduce clinical re-intervention with an obvious cost saving to the patient and ultimately improve the patients' dental experience.

Funding Agency

Health Research Board

Programme

Patient Orientated Research

Project Type

Biocompatibility

Person Months

36

Summary

The dental literature is replete with fracture resistance studies of all-ceramic materials with the 'crunch-the-crown' load-to-failure test routinely used despite the failure mode which involves indenter contact surface damage failing to replicate clinically relevant sub-surface radial fracture. Additionally, load-to-failure data provides no information on stress patterns within complex crown geometries and comparisons between studies are impossible owing to variable testing protocols. Testing geometric planar specimens allows for the calculation of failure stresses using bending theory. By employing standardised planar geometries, sample preparation and loading protocols, comparisons between materials and investigators are possible. However, planar data provides a conservative measure of fracture behaviour and fails to account for geometric factors which may modify the stressing patterns, or defect populations within a complex body such as a loaded restoration. Finite element analysis (FEA) methodologies have been widely used in dentistry as virtual case studies employing the adaptive capabilities of parametric simulations to assess sensitivities to discrete changes in variables defining the model, including material, dimensional and/or geometric parameters. While virtual case studies are insightful, the usefulness of FEA simulations are governed by the limitations of specific features of the model investigated. By implication features unspecified in the simulation cannot be manifest as determinants of the factors investigated. The idealisations employed in an FEA simulation may be detrimental by inaccurately representing material behaviour. Measured dental-ceramic strength depends upon the statistical distribution and configuration of defects thereby requiring a probabilistic approach. Whilst FEA methods can incorporate statistical elements, empirical measurements are essential to determine how geometric variability influences a statistical defect population in the fabricated complex shape. May et al. (2012) compared an FEA model derived with the probabilistic determination of boundary conditions, which included predicted failure criteria from experimental data, to investigate representative 'crunch-the-crown' load-to-failure testing. The assumed failure criteria was established experimentally but was associated with an 'uncertainty' in the FEA results, thereby limiting the authors confidence in the approach. Simplified non-planar geometries (curved-discs), with a single radius-of-curvature, have been proposed to examine the impact of geometric factors on radial fracture. However, in the absence of analytical solutions to describe the stress distribution in curved-discs tested in biaxial flexure, we aimed to investigate the influence of non-planar geometries on the maximum-principal-stress. Radii-of-curvature analogous to elements of complex dental geometries were investigated and the FEA simulation was integrated with load-to-failure testing as a surrogate solution to calculate the maximum-principal-stress at failure.

Funding Agency

Trinity College Dublin

Programme

Ussher Fellowship

Project Type

Materials Science

Person Months

42

Summary

Glass Ionomer Cements (GICs) are restorative dental materials consisting of two separate components - a glass powder and a polymeric liquid element. GICs are routinely employed in dental applications as cavity linings and bases, luting cements and as anterior filling materials especially in paediatric dentistry due to their minimally invasive nature. More recently, there is an increased interest in the use of glass-ionomer restoratives as posterior filling materials due to aesthetic demands of patients and the potential fear of mercury toxicity from dental amalgams. Unfortunately, conventional GIC cement formulations are not advocated for large messio-occlusal-distal (MOD) cavities due to their reduced mechanical properties (compressive fracture strength, fracture tougness and wear resistance) when compared with dental amalgam. The purpose of the study will be to validate the hypothesis that the mechanical properties of conventional GI restoratives can be improved to produce increased performance compared with conventional GI restoratives when placed in the posterior region of the mouth. The experimental GI restoratives will also be trailed for clinical performance, namely compressive fracture strength, fracture toughness and wear resistance. Consequently by targeting and eliminating the key failure mechanisms of posterior GI restorative and filling materials it is proposed that an experimental, commercially viable reinforced experimental GI restorative may improve conventional GI restorative performance in the mouth.

Funding Agency

Science Foundation Ireland

Programme

Research Fronteers Programme

Project Type

Developmental Materials Science

Person Months

48