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De bedoeling van deze masterproef is om aan de hand van een gerichte vragenlijst na te gaan of het steeds toenemende gebruik van composietmaterialen en de blootstelling hieraan, respiratoire of cardiovasc tandheelkundig personeel. We stellen ons hierbij volgende vragen; Hoe belangrijk is dit composietstof? Maken we ons zorgen om niets? Lopen tandartsen een groter risico voor bepaalde werkgerelateerde respiratoire of cardiovasculaire problemen? Het doel is echter niet om aan de hand van bepaalde symptomen een ziektebeeld te diagnosticeren. De eventuele preventieve maatregelen om de inhalatie van dit stof te vermijden wordt ook bondig besproken. Met het lage aantal resultaten dat we verkregen hebben, is het moeilijk een algemene conclusie te formuleren met betrekking tot onze onderzoeksvraag. We kunnen wel concluderen dat verder onderzoek naar de schadelijkheid van composietstof noodzakelijk is en dat er toch best zo veel mogelijk preventieve maatregelen genomen worden.

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To restore carious or traumatized teeth, a dental practitioner can choose between two direct (plastic) restorative materials, namely amalgam (silver-colored) or composite (tooth-colored). It is obvious that the aesthetic properties of composites are important for patients, but composites also have the advantage of a minimally invasive preparation technique. Moreover, dental amalgams have been alleged of environmental pollution and even negative health effects due to release of mercury.As a result, composite restorations have gained important popularity, and in many countries they have already become the standard restorative material. However, composite restorations clinically seem more prone to secondary caries (new caries lesion at the margin of an existing restoration). Several clinical trials reported that secondary caries is the most common reason for premature failure of composites. The short lifetime of composites has become a topic of scientific debate, as premature renewal of restorations is a burden on health care expenditure. In addition, secondary caries is always resulting in further tooth structure loss and may weaken the remaining tooth. Especially in case of extensive secondary caries lesions and repetitive restorative interventions, this may eventually lead to premature loss of the tooth.Caries is in essence a bacteriological disease caused by acidogenic bacteria that produce acidic metabolites, which demineralize enamel and dentin, and enzymes that degrade the dentin matrix. Research indicates that resin-based materials indeed may exhibit properties that stimulate bacterial growth and adhesion. Composites are not inert in the oral environment, and may release components, initially due to incomplete polymerization, and later due to degradation. Monomers leached from composites have been shown to be a good substrate for cariogenic bacteria, thereby explaining the higher cariogenicity of composites compared to amalgam. In contrast, amalgam restorations seal the cavity margins by forming metal oxides that exhibit antibacterial properties. Moreover, bacterial colonization of composites and bacterial metabolites may alter the surface topography and properties of composites boosting even more biofilm adhesion. Nevertheless, more research is necessary, as there is only limited scientific knowledge available regarding the bacteriologic interactions with composites. Therefore, the general hypothesis of this PhD project is that the substances that are released by dental composites do not stimulate the formation of caries.In Subproject 1 of the PhD thesis, different cariogenic bacteria (Streptococcus mutans and sobrinus, Lactobacillus acidophilus, Actinomyces naeslundii) and non-cariogenic bacteria (Streptococcus sanguinis) will be exposed to different concentrations of monomers (BisGMA, TEGDMA, UDMA, HEMA, ...). The bacterial growth will be evaluated using microbial techniques such as absorbance measurements (spectrophotometry), CFU-counting and qPCR. In Subproject 2, the influence of different restorative materials, including conventional composite, dental amalgam, glass-ionomer cement (GIC) and the composite with surface pre-reacted glass-ionomer fillers (giomer), as well as of the tooth hydroxyapatite (HAp), on the local pH and the composition of dental biofilm regarding the percentage of cariogenic and non-cariogenic bacteria, will be assessed using pH meter, spectrophotometry and viability qPCR techniques. In Subproject 3, surface of different composites will be exposed to single- (S. mutans) and multi-species biofilms (S. mutans, S. sanguinis, A. naeslundii and Fusobacterium nucleatum), after which the surface changes will be characterized by atomic force microscopy (AFM) and contact angle analysis. In addition, the number of bacteria accumulated on composite surface will be assessed by qPCR. In Subproject 4, an epidemiologic study will be set up to determine the incidence and prevalence of secondary caries in patients visiting the university dental clinic, and to characterize these lesions in more detail. Patients visiting the university dental clinic for a yearly check-up will be examined by calibrated clinicians and registered for the study. In addition, presence of secondary caries and patient related factors such as oral hygiene, sugar eating habits and possible parafunctional activities, will be noted. In case of diagnosis of secondary caries, the following parameters will be described: type and class of restoration, number of tooth, precise location of lesion and the age of the restoration.This multidisciplinary research will help to better understand the factors involved in the formation and development of secondary caries around resin-based dental materials. This represents the first step in the process of making strategies to overcome the problem of relatively early failures of composite restorations.

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Tooth-restoration materials need to withstand chewing forces and diverse forms of chemical and thermal stresses in the challenging oral environment. Dental restorative materials that combine the needed physico-mechanical strength and degradation resistance with ‘therapeutic’ potential, remain however to be developed. Nevertheless, ‘bioactive’ materials that would enable diseased tooth tissue to be healed in situ rather than that the dentist needs to replace it with an artificial restorative material, are highly desirable.Techniques to re-mineralize tooth enamel have well been adopted in clinical practice. However, in contrast to enamel, the process of dentin re-mineralization is more complex. Residual hydroxyapatite (HAp) crystals that can act as existing ‘seed’ crystals and thus re-mineralization initiation sites, are absent in dentinal carious lesions. Thus, the formation of organized nanocrystals is crucial for successful dentin remineralization. In fact, the first paper describing re-mineralization of fully demineralized dentin only very recently appeared. Besides inorganic minerals (mainly HAp), dentin includes an organic matrix that consists of Type-I collagen and non-collagenous proteins (NCP’s), some of which may even inhibit the re-mineralization process.‘Biomimetic re-mineralization’ imitates the natural process of mineralization; it involves a technique to grow HAp in demineralized dentin in a manner, shape and with mechanical properties similar to that of the natural mineral fraction of the host dentin substrate. More specifically, biomimetic re-mineralization has been described achievable by phosphorylation of Type-I collagen using phosphate solutions, followed by exposure to calcium in a suitable medium. The collagen matrix of demineralized dentin hereby serves as scaffold. Recent laboratory studies have indeed shown that it is possible to re-mineralize demineralized dentin surfaces.Clinically, biomimetic re-mineralization is especially thought to be very useful to prevent further progress of active dentinal caries. Obviously, the bacterial infected tissue remains to be removed, but the underlying bacteria-free and demineralized caries-affected dentin could be transformed into a mineral barrier that protects the dental pulp underneath. If this non-infected deep caries can be ‘healed’ (=re-mineralized) in situ, it should not necessarily be removed anymore by bur, thereby reducing the possibility of pulp exposure. From a clinical standpoint, it would indeed be advantageous to preserve the softened demineralized dentin, if it can be re-mineralized to a sufficient degree and so also restore the mechanical strength of the tooth needed to function in the mouth. Another important indication of biomimetic re-mineralization agents is to repair accidental (iatrogenic) pulp capping or (tiny) exposures of the pulp in an attempt to maintain the pulp vitality and thus to avoid root-canal treatment. The objective is to stimulate exposed pulp tissue to produce new dentin and so to seal the pulp exposure by dentin-bridge formation. Therefore, the main objective of this exploratory research is to develop a clinically applicable technique to repair demineralized dentin lesions and exposed pulps.