Zirconia Use in Dentistry - Manufacturing and Properties.

Several types of metal-free ceramics have been developed to meet the patients demand for natural looking appearance restorations. Owing to their biocompatibility and good mechanical properties zirconia has been successfully used in recent years as a dental biomaterial. Due to its high opacity zirconia cores are generally covered with ceramic veneers that provide a more natural appearance but have frequent incidence of chipping. As an alternative to veneered zirconia full-contour zirconia restorations become more widely used nowadays. The paper reviews the current knowledge and scientific data of the zirconia use in dentistry in order to compare the zirconia based dental restorations with the metal-ceramic ones and also the two types of dental restoration based on zirconia, veneered or monolithic zirconia.

Theoretical study on the mechanics of the conjunct gnatoprothetic devices in the context of occlusive function rehabilitation.

The partially intercalated edentation offers the practitioner the possibility of the functional rehabilitation of the dental arcades through conjunct gnato-prosthetic devices. The functions of the dento-maxilar device, disturbed by the presence of edentation, require a treatment approach so that, without pre-planning or estimating, the result can lead most of the times to failure in terms of functionality. Clinical evaluation associated with pre- and proprosthetic treatment can also impose, in some situations the evaluation of the dental units involved in prosthetic rehabilitation. The association and implementation of the prosthetic construction in the occlusive-articular ensemble, as well as the counterbalancing of the mastication forces per dental unit and whole interarch system, linked to the distribution of the forces at the level of the pillar teeth and prosthetic construction, represent the goal of this theoretical study.

Microscopic aspects of angiogenesis and lymphangiogenesis in oral squamous cell carcinoma.

Despite various great scientific and financial efforts, head and neck carcinomas represent a public health problem, being the eighth cause of cancer death worldwidely. The rate of tumor growth, its local expansion, as well as the metastasis of cancerous cells depend on the tumor vascularization, on the ability of blood vessels to provide a constant supply of nourishing substances and oxygen and to eliminate the residual products resulted from tumor growth. That is why angiogenesis and lymphogenesis are considered to be essential processes within the neoplastic process. The assessment of tumoral neoformed blood vessels in oral squamous carcinomas, using the CD34 antibody, showed a significant growth of the microvascular density, the average number being 504.66±177.65 vessels/mm². The diameter of angiogenesis vessels varied between 3.42 and 121.27 µm. The density of lymphogenesis vessels was 508.78±235.93 vessels/mm², while the diameter varied from 2.82 to 165.28 µm. Both angiogenesis and lymphogenesis vessels were more numerous in the areas where the inflammatory infiltrate was more abundant, which suggests that chronic inflammation plays the part of a promoter factor of neoplastic lesions.

Microscopic aspects of pulpal changes in patients with chronic marginal periodontitis.

Chronic periodontitis is one of the most frequent and severe diseases involving the tooth. Untreated, they can lead to tooth loss. Our study involved 67 patients with chronic marginal periodontitis who underwent tooth extraction, of which 29 had moderate periodontal lesions and 38 severe periodontal lesions. The microscopic study of the dental pulp revealed significant changes in all patients. In patients with moderate periodontitis the pulp tissue was found to be the site of an enhanced process of collagenous fibrosis associated with a moderate inflammatory infiltrate, dystrophic mineralization, reduced blood vascularization and arteriolosclerosis. The dental pulp of patients with severe periodontitis showed an abundant chronic inflammatory infiltrate associated with pulpal necrosis, vascular congestion, microhemorrhages, dentin demineralization and odontoblast impairment.

Considerations regarding the optical properties of the composite resin restorative materials.

The purpose of this study has been to investigate the effects of certain substances frequently used in alimentation on the color stability of the composite resin restorative materials. The research hypothesis was that color stability of the composite resin is affected by the type of composite material used and by the polishing procedure. 14 samples of 5X15X2mm have been prepared from seven universal light curing restorative composite resins. The materials have manipulated and cured using LA 500 Blue Light lamp. A first color determination was done before the introduction of the samples in the dyeing agent with the help of an Easy Shade device. The samples have been splited into two lots each with seven samples. The samples from the first lot have been sectioned into three equal segments. The samples from the second lot have also been sectioned into three equal segments, and in addition to the previous group, their exterior surfaces were processed with a diamond burr. For each type of composite we have introduced a sample in one of the three chosen dyes: red alimentary colorant, coffee and red wine. The color of the samples has been determined again using the Vita Easy Shade device. From clinical point of view the results of this study shows that there are three important factors that matter when we talk about durable aesthetic results: the type of composite resin used for the restoration, the finishing and polishing procedures and the pacients' alimentation habits. The composite resins with a good representation of the anorganic structure are easier to be polished, therefore they have only slight color modifications. Using plastic matrixes for shaping the exterior surface of the restoration is the best solution for obtaining a very smooth surface. The most significant color modifications have been done by the red wine. Coffee and to a smaller extent the red alimentary colorant have modified the color of the restoration material in a smaller degree.

The involvement of metalloproteinases and their tissular inhibitors in the processes of periodontal orthodontic remodeling.

The orthodontic treatment uses forces that produce structural and biochemical changes in the periodontal space breaking the balance between the synthesis and the breakdown of the collagen in the periodontium. Matrix metalloproteinases (MMP) plays a central role in the normal tissular remodeling processes, those in the tissular morphogenesis and the tissular repair (including the remodeling of the periodontal space of the periodontal ligament, during the dental orthodontic translations). The inter-relation between the molecular mechanism of orthodontic remodeling and MMPs is still unclear.

Immunohistochemical aspects of the evaluation of the inflammatory answer of the dental pulp.

The inflammatory answer of the dental pulp in front of an antigen presents a series of particularities caused by its special anatomical conditions. The evaluation of the inflammatory answer in the evaluation tests of the biocompatibility of the dental materials is made by histological methods without defining precise quantitative criteria to measure the pulp reaction. In this study, we followed the reaction of the pulp tissue to five antibodies (CD20, CD45Ro, CD4, CD8, and CD68) in order to evaluate the inflammatory aspects of the dental pulp. We did not find positive answers for the CD20 protein, specific for B-lymphocytes, for the fragments of normal pulp tissue taken into study. Even if they are in small number among the pulp cells, the T-lymphocytes that express the protein CD45Ro may be also found in the normal dental pulp. Of the two subsets of T-lymphocytes, we found positive answers on the studied preparations only for the CD8 protein. For the CD68 protein, strongly expressed by the macrophages, we obtained positive results both for the inflammated pulp tissue, and for the normal dental pulp, yet in a very small amount. The use of immunohistochemical techniques, with well-defined markers of the pulp inflammation, can offer better results for a highly accurate evaluation of the inflammatory answer of the dental pulp.

Contributions on the study of the compressive strength of the light-cured composite resins.

The mechanical properties of the light-cured composite resins are related to the material composition, but also vary according to the light-source characteristics used for polymerization. In this study we followed the compressive strength variation for a light-cured composite resin according to the time of exposure to the curing light. With that end in view,18 test pieces were made from a light-cured hybrid composite material (Filtek Z250). The test pieces where then submitted to a compressive force by a mechanical properties universal testing machine. Our results didn't show an increase of the compressive strength according to the light-curing time increasing, than only in the light-curing time limit indicated by the manufacturer. A longer light-curing time may induce a shrinkage polymerization growth with the formation of internal tensions inside the material. The composite materials light-curing in short layers as long as there is indicated by the manufacturer seems to be a safer method to make the best from a resin qualities, then an exaggerated increase of the light-curing time. The light-curing is indicated to be done in the direction of the compressive forces. To confirm this supposition other mechanical tests are also necessary.

Considerations on the ultrastructural particularities of the dental pulp cells.

We realized an ultrastructural study of the cells of the dental pulp, having in view their particularities relative to other types of conjunctive tissue. For this purpose, we selected five cases represented by teeth without subjective or objective symptomatology. Within the paper there are exposed the morphological aspects observed by means of electron microscopy. The results are then discussed in relation with a series of observations made by other researchers regarding the particularities of the pulp cells structures.

Modifications of the dental pulp in marginal periodontitis. Electronomicroscopical contributions.

Histological studies on teeth with marginal periodontitis, but without cavity lesions have shown a frequent apparition of modifications in the pulp tissue structure. In this study, by using the electron microscopy method, we have shown a series of interesting aspects of the intimate modifications that appear on the level of all components of the pulp tissue. The observations show that the degree of affecting can be correlated to the type of marginal periodontitis, and at the same time they contribute to a right evaluation of the defensive abilities of the pulp of the teeth with marginal periodontitis.

Radiological and microscopic aspects of the denticles.

In this paper we have realized a study on 43 patients on which the retro-alveolar radiological exam has shown the existence of a calcareous structure within the pulp chamber having in view a better knowledge of this structure and its etiology, way of forming and pathological implications. For 16 of the patients the radiological exam was supplemented by a microscopic examination. Radiologically, the denticles were noticed more often in the pulp chamber of the molars. The examination of the histological samples has evidenced aspects such as the size, shape and structure of the denticles. The concentric disposition of the tissue elements shows that in the formation of a denticle there is a "center" around which a conjunctive substance avid of calcium salts is deposited. The microscopic aspects noticed on large denticles allowed us to sustain the hypothesis that in a large pulp chamber many denticles form simultaneously and grow up and merge generating a large-sized unique calcareous structure.

Electronic microscopic evaluation of the Beta insular cells in type 2 diabetes.

In this work it has been done an electronic microscopic evaluation of the intra-cytoplasmic organelle devices of the pancreatic beta insular cells in the type 2 diabetes mellitus (insulin independent). The motivation of this study is the lesions noticed within another study, photonic microscopic, reason why we have considered it important to show up as well the interest modifications of the constitutive organelles of the beta insular cells.