Methods and physical chemistry of resin-based dental composites

Les propriétés des composites dentaires ont été nettement améliorées depuis leur invention, mais la compréhension de la physique qui guide leurs propriétés est toujours obscure. L’objectif de cette thèse est de découvrir les tendances et relations qui régissent l’effet des agents de remplissage sur les propriétés du composite qui en résulte. La photocalorimétrie (pDSC) a déjà été utilisée pour mesurer le degré de conversion des résines dentaires, mais les paramètres de mesure n’ont jamais été adéquatement définis. En utilisant des variations systématiques dans la séquence d’analyse, la température, la masse d’échantillon, l’intensité lumineuse ou la composition atmosphérique, un protocole optimisé a été établi pour obtenir des résultats fiables et reproductibles. Une série de composites dentaires a ensuite été formulée avec de la silice sphérique à basse dispersité de tailles gradées de 75 à 1000 nanomètres à différents taux de chargement. La viscosité de ces composites avant la polymérisation a été mesurée et utilisée pour améliorer le modèle classique Krieger-Dougherty de viscosité des suspensions de façon à ce qu’il inclue l’aire de surface des particules en plus du taux de chargement. Ce model étendu (EKD) a aussi été utilisé pour calculer la conversion du composite. C’est le premier modèle unifié qui permet de calculer la viscosité et la conversion des composites en utilisant seulement la taille des agents de remplissage et la composition de la résine. Le chargement maximal et les propriétés mécaniques de ces mêmes composites ont aussi été étudiées. Bien que le chargement maximal fonctionnel varie selon la taille des particules, la force flexurale ultime des composites dépend seulement du taux de chargement des particules et non de leur taille. D’autres tests avec ces composites ont démontré que la taille des particules est directement liée à la transparence des matériaux, ainsi l’opacité augmente avec la taille des particules. Cet œuvre avance les limites de la compréhension des matériaux dentaires. Le nouveau protocole de pDSC permet des mesures plus fiables de conversion et le model EKD nous permet de prédire plus précisément les propriétés des composites par leurs composantes seules. Les règles établies dans cette thèse peuvent donc être utilisées pour concevoir des composites avec les propriétés désirées de viscosité avant polymérisation, de conversion, de propriétés mécaniques et de transparence.The properties of dental resin composites have improved significantly since their inception, but the fundamental physics behind their properties remain to be explained or modeled comprehensively. The aim of this thesis is therefore to study the fundamental trends and relationships between the filler particles constituting these materials and the resulting properties. Photocalorimetry (pDSC) methods have been used previously to measure the degree of conversion in dental resins, but the measurement parameters have never been adequately assessed. Through systematic variations of the analysis sequence, sample mass, temperature, light intensity, and atmospheric composition, an optimized protocol was established to yield reliable and reproducible results. A series of dental composites was then formulated with spherical silica particles of graded sizes from 75 to 1000 nanometers at different loading levels. The viscosity of these composites before polymerization was measured and used to expand the classic KriegerDougherty suspension viscosity model to account for filler surface area in addition to filler loading. This extended model (EKD) was also used to model composite conversion, resulting in the first unified model of composite viscosity and conversion using only filler size and resin composition. The maximum loading and post-cure mechanical properties of these same composites were also examined. Although the maximum functional filler loading varied according to the filler size, the ultimate flexural strength of the materials depended only on the filler loading. Further tests with these composites showed that filler size was directly responsible for transparency of the materials, with opacity increasing as a function of filler size. This work pushes the boundaries of understanding in dental composites. The newly established protocol for pDSC measurements yields more reliable conversion data, and the EKD model allows for more accurate predictions of dental composite properties directly from their component parts. The guidelines established here can now be used to design new composites with the desired properties of viscosity, conversion, mechanical strength, and transparency. Keywords: photocalorimetry, pDSC technique, viscosity, loading, spherical silica, surface area, transparency, formulations, guidance, technical understanding

Titanium Nitride and Nitrogen Ion Implanted Coated Dental Materials

Titanium nitride and/or nitrogen ion implanted coated dental materials have been investigated since the mid-1980s and considered in various applications in dentistry such as implants, abutments, orthodontic wires, endodontic files, periodontal/oral hygiene instruments, and casting alloys for fixed restorations. Multiple methodologies have been employed to create the coatings, but detailed structural analysis of the coatings is generally lacking in the dental literature. Depending on application, the purpose of the coating is to provide increased surface hardness, abrasion/wear resistance, esthetics, and corrosion resistance, lower friction, as well as greater beneficial interaction with adjacent biological and material substrates. While many studies have reported on the achievement of these properties, a consensus is not always clear. Additionally, few studies have been conducted to assess the efficacy of the coatings in a clinical setting. Overall, titanium nitride and/or nitrogen ion implanted coated dental materials potentially offer advantages over uncoated counterparts, but more investigation is needed to document the structure of the coatings and their clinical effectiveness

Evaluation of the physicochemical and antibacterial properties of experimental adhesives doped with lithium niobate

The aim of the present study was to formulate dental adhesives with different concentrations of LiNbO3 and to evaluate their physicochemical and antibacterial properties. A dental adhesive was formulated using methacrylate monomers and photoinitiators and used as a control filler-free group. Subsequently, three experimental adhesives doped with LiNbO3 at different concentrations (1 wt.%, 2 wt.%, and 5 wt.%) were also formulated. All the experimental adhesives were assessed to evaluate the degree of conversion (DC), softening in solvent, immediate and long-term microtensile bond-strength (μ-TBS), radiopacity, ultimate tensile strength, and antibacterial activity. The incorporation of 1 wt.% of LiNbO3 had no negative effect on the DC of the adhesive resin compared to the control group (p > 0.05). We observed a decrease in the percentage of softening in solvent in the group LiNbO3 at 1 wt.% (p 0.05). After six months, the group with 5 wt.% still presented the highest μ-TBS (p 0.05). LiNbO3 was successfully incorporated in dental adhesives, increasing the radiopacity and their resistance to degradation. Although LiNbO3 offered no antibacterial properties, the reliability of LiNbO3 incorporation in the adhesive encourages new tests to better investigate the antimicrobial action of LiNbO3 through temperature variation

Principles of Periodontology

Periodontal diseases are among the most common diseases affecting humans. Dental biofilm is a contributor to the etiology of most periodontal diseases. It is also widely accepted that immunological and inflammatory responses to biofilm components are manifested by signs and symptoms of periodontal disease. The outcome of such interaction is modulated by risk factors (modifiers), either inherent (genetic) or acquired (environmental), significantly affecting the initiation and progression of different periodontal disease phenotypes. While definitive genetic determinants responsible for either susceptibility or resistance to periodontal disease have yet to be identified, many factors affecting the pathogenesis have been described, including smoking, diabetes, obesity, medications, and nutrition. Currently, periodontal diseases are classified based upon clinical disease traits using radiographs and clinical examination. Advances in genomics, molecular biology, and personalized medicine may result in new guidelines for unambiguous disease definition and diagnosis in the future. Recent studies have implied relationships between periodontal diseases and systemic conditions. Answering critical questions regarding host‐parasite interactions in periodontal diseases may provide new insight in the pathogenesis of other biomedical disorders. Therapeutic efforts have focused on the microbial nature of the infection, as active treatment centers on biofilm disruption by non‐surgical mechanical debridement with antimicrobial and sometimes anti‐inflammatory adjuncts. The surgical treatment aims at gaining access to periodontal lesions and correcting unfavorable gingival/osseous contours to achieve a periodontal architecture that will provide for more effective oral hygiene and periodontal maintenance. In addition, advances in tissue engineering have provided innovative means to regenerate/repair periodontal defects, based upon principles of guided tissue regeneration and utilization of growth factors/biologic mediators. To maintain periodontal stability, these treatments need to be supplemented with long‐term maintenance (supportive periodontal therapy) programs

Shrinkage Stresses Generated during Resin-Composite Applications: A Review

Many developments have been made in the field of resin composites for dental applications. However, the manifestation of shrinkage due to the polymerization process continues to be a major problem. The material's shrinkage, associated with dynamic development of elastic modulus, creates stresses within the material and its interface with the tooth structure. As a consequence, marginal failure and subsequent secondary caries, marginal staining, restoration displacement, tooth fracture, and/or post-operative sensitivity are clinical drawbacks of resin-composite applications. The aim of the current paper is to present an overview about the shrinkage stresses created during resin-composite applications, consequences, and advances. The paper is based on results of many researches that are available in the literature