Composite Restoration Design Effect During Curing and Chewing.

PURPOSE: The purpose of this work is to observe the effect of the cavity design of the direct composite restoration on a real case of the patient's tooth structures after applying his mandibular kinematics with finite element analysis. MATERIALS AND METHODS: Four complex maxillomandibular models of teeth 17 and 47 were constructed from the patient's cone-beam acquisition and the patient's kinematic data recorded with Modjaw® were added. Different shapes and sizes of mesio-occluso-distal (M.O.D.) composite restorations were simulated, including the polymerization shrinkage of this material. Finite element analyses were used to observe the Von Mises stresses occurring during polymerization and mastication. RESULTS: The stresses were observed at the cavity margin and the amplitude of the stresses was higher when the enamel volume was lower. The reduction in occlusal enamel volume with the open-angle vestibular and palatal walls resulted in a greater increase in stresses observed on the structures. CONCLUSIONS: The occlusal enamel is the area that bears the maximum masticatory stress, the loss of this enamel volume generates a much greater concentration of stress on the underlying structures. It is important to preserve as much enamel tissue as possible when designing a cavity for a direct composite restoration.

Misinterpretation of ISO 4049 standard recommendations: Impact on Young's modulus and conversion degree of dental composites.

OBJECTIVES: The purpose of this study was to study the effects on Young's modulus and conversion degree of variations in polymerization conditions during the 3-point bending test of composite samples in accordance with the ISO 4049 standard. METHODS: Three nanocomposites were used in the 3-point bending test based on the conditions described in the ISO 4049 standard. Samples of 2 mm × 2 mm x 25 mm were fabricated and tested with a different number of irradiation points and irradiation time. Conversion degree of the samples were also measured by micro-Raman spectroscopy and correlated with the Young's modulus values obtained for each one. RESULTS: The variations in curing protocol during specimen's realization influenced the Young's modulus and degree of conversion of all composites. These two properties correlated well. The ISO 4049 standard defines the conditions for performing the properties tests of composites to allow reproducibility and comparison of different studies. Concerning the 3-point bending test, even a minimal change in the state causes differences in the results obtained. The standard should thus clarify the tools that can be used when producing samples in order to minimize discrepancies. SIGNIFICANCE: The influence of the parameters surrounding the design of the samples should be controlled and defined so as not to include bias in the studies carried out. This will allow literature studies to be compared with more accuracy.

Matrix metalloproteinases MMP-2, -9 and tissue inhibitors TIMP-1, -2 expression and secretion by primary human osteoblast cells in response to titanium, zirconia, and alumina ceramics.

Osteogenic properties of bone cells are a key parameter governing osseointegration of implant devices. In this context, osteoblasts have a central role via extracellular matrix synthesis and remodeling that they regulate through different protease activity. In this study, we have analyzed the expression of two matrix metalloproteinases (MMPs): MMP-2 (72 kDa) and MMP-9 (92 kDa) and their specific tissue inhibitors TIMP-1 and TIMP-2 in primary human osteoblastic cells. The effect of titanium, zirconia, and alumina ceramics on the synthesis of these proteases was assessed using reverse transcriptase-polymerase chain reaction, enzyme-linked immunosorbent assay, and zymographic analysis. Our results showed that osteoblasts express MMP-2 and -9 mRNA. Furthermore, MMP-2 mRNA expression was decreased by titanium and increased by alumina whereas zirconia did not have any significant effect. Conversely, MMP-9 mRNA expression was stimulated by titanium but decreased with zirconia, whereas alumina induced no significant changes. Zymographic analysis has evidenced pro-MMP-2 gelatinolytic activity in all cell populations with time-dependent increase profile; pro-MMP-9, however, was not detected. Enzyme-linked immunosorbent assay data confirmed the production of MMP-2 and very low levels of MMP-9. In addition, TIMP-1 was secreted in 24-h-cultured cells and increased to maximal level at 48-72 h whereas TIMP-2 levels were very low. The interactions between human osteoblasts and the studied biomaterials altered both MMP-2, -9 and TIMP-1expression indicating that biomaterials may influence osseointegration and bone remodeling.

Influence of physicochemical reactions of bioactive glass on the behavior and activity of human osteoblasts in vitro.

Bioactive glasses are characterized by a bond to bone with a hydroxyl carbonate apatite layer. They enhance bone tissue formation and for this purpose are used in orthopedic surgery and in dental implantology. In the current work, we studied the biological response of human osteoblasts with a bioactive glass. This bioactive glass is based on 50% Si0(2), 20% Na(2)O, 16% CaO, 6% P(2)O(5), 5% K(2)0, 2% Al(2)O(3) and 1% MgO and designated A9. Cracks and irregularities were observed on the material surface when it was immersed in the culture medium. In addition, energy dispersive X-ray analyses highlighted a selective release of the elements at the surface of the bioactive glass, such as Na(+) and K(+) ions, released from the first day, contrary to the Si, Al, Ca, P, and Mg elements, which were released more slowly. Cell proliferation kinetics, total protein synthesis, and DNA content of the osteoblasts in contact with bioactive glass were similar to control cells. The morphological studies by light and scanning electron microscopy revealed an increasing cellular density in culture with bioactive glass without contact inhibition. The immunohistochemical studies highlighted the expression of types I, III, and V collagens by osteoblasts cultured in the presence of bioactive glass. The pH measurement of the culture medium in the presence of bioactive glass demonstrated a slight alkalinization. We thus conclude that human osteoblasts preserve their properties in the presence of bioactive glass (A9).

In vitro reactions of human osteoblasts in culture with zirconia and alumina ceramics.

The biocompatibility of two implantable materials, zirconia and alumina ceramics, was investigated in vitro using human osteoblast cell cultures. The viability of osteoblast cells with the materials was evaluated by the methylthiazole sulfate test that revealed an absence of any cytostatic or cytotoxic effect. Cell proliferation kinetic and total protein synthesis in osteoblasts with zirconia or alumina were similar to that observed in control cells cultured on glass coverslips. Light and scanning electron microscopic examinations showed an intimate contact between osteoblasts and the substrates; well-spread cells were observed on the surfaces of both materials. Adhesion ability and morphological characteristics were preserved in osteoblast cultures with these substrates. Moreover, immunohistochemical staining in osteoblasts with zirconia and alumina showed the capacity of these cells to elaborate the extracellular matrix composed of types I and V collagen, osteocalcin, osteonectin, bone sialoprotein, and cellular fibronectin. Finally, DNA image cytometry and interphase silver-nucleolar organizer regions quantification were applied as complementary biocompatibility tests to detect any changes in DNA synthesis and cell proliferation, respectively. The results showed that neither material altered cell ploidy or cell growth rate in accordance with the absence of any inducing effect on DNA synthesis or proliferation.

DNA image cytometry and Ag-NORs-staining application in biocompatibility studies on human osteoblast cells in vitro.

We report here the study of the biocompatibility of a bone graft material, the Pyrost, using a previously established in vitro model of human osteoblasts. The effect of this material on cell proliferation was evaluated by the MTS assay. Results indicated the absolute absence of cytotoxic or cytostatic effect of Pyrost on cultured osteoblasts. Viability rate was more than 90% in cells cultured with the material compared to the control. Morphological analysis, undertaken by scanning electron microscopy showed a good adhesion and a spreading of osteoblasts in contact with the material that was colonized by cultured cells. In the second part of this work, we have introduced two methods as complementary biocompatibility tests: DNA image cytometry and interphase Ag-NORs quantification. DNA content was measured in cells cultured with or without Pyrost for 3, 9, 15 and 30 days. The determination of DNA indicated that the majority of osteoblasts population was diploid without aneuploidy. The DNA index and cell distribution profile in DNA histograms were similar in all cell populations. The Ag-NORs amount was used as a parameter for cell kinetic evaluation. We have measured the Ag-NORs index like DNA quantification. The proliferation rate, evaluated by Ag-NORs counts in osteoblasts cultured with or without the material, was identical. However, a decrease in Ag-NORs index was observed from day 3 to day 15 of incubation. These results showed a satisfactory biocompatibility of the Pyrost in human osteoblasts culture. The material did not alter cell viability and had no inducing effect either on proliferation rate or on cell ploidy as demonstrated by DNA image cytometry and Ag-NORs proteins staining.

[Biomaterials in an osteo-articular environment. Report of 129 anatomoclinical cases]. / Biomatériaux en milieu ostéo-articulaire. A propos de 129 observations anatomocliniques.

Actually, there is a range of biomaterials which are synthetic or metallic (or the both). They are employed as prosthesis (biostability property) or as bone graft (bioresorbability property). To understand the interactions between cells and such materials, we studied with human bone cellular cultures the cytologycal, immunohistochemical, cytogenetical and ultrastructural aspects of biomaterials in cell cultures. This paper concerns bioceramics like Pyrost, coral, biosorb, oxbone and polymers like polyethylene and silicones. The aim of this work is to evaluate the efficiency of some biomaterials. We found that porosity is primordial to promote biodegradation of bone substitutes. In fact, the biomaterials is integrated and lead to an osteoconduction, an osteoformation and finally an osteoinduction. Our observations show the implant resorption and ossification occurring in the matrix which penetrate it.