Browsing by Author "Paez de Mendoza, Carmen Y."
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Item Evaluation of Mechanical Properties of Provisional Fixed Partial Denture PMMA Material Containing Alumina Nanofibers(2012) Hajjaj, Maher Saeed, 1980-; Chu, Tien-Min Gabriel; Brown, David T.; Platt, Jeffrey A., 1958-; Paez de Mendoza, Carmen Y.; Levon, John A.Provisional restorative treatment is an essential part of fixed prosthodontics. Incorporation of adequately constructed provisional restorations will enhance the success rate of definitive restorations. Repairing or replacing failed provisional restorations is a concern for both clinicians and patients. The objective of this investigation was to study the effects of alumina nanofibers reinforcement on the mechanical properties of commercially available provisional fixed partial denture PMMA material. The hypothesis was that the addition of alumina nanofibers to commercially available PMMA resin will significantly increase its flexural strength, fracture toughness, and microhardness. Alumina nanofibers at 0.0 wt %, 0.5 wt %, 1.0 wt %, and 2.5 wt % were added to commercially available provisional fixed partial material (Jet Tooth Shade). A quaternary ammonium acetate dispersant (CC-59, Goldschmidt, Janesville, WI) was added to the acrylic monomer at 0.0 wt %, 1.0 wt %, 2.0 wt % and 5.0 wt % of the nanofiber weight (12 test groups, 1 control). Samples from each group were evaluated for flexural strength, flexural modulus, fracture toughness, and microhardness. The samples were tested after storing in distilled water for 24 hours and 7 days at 37ºC. Two-way analysis of variance (ANOVA) was used to test the effects of storage time and combinations of alumina nanofiber level and quaternary ammonium acetate dispersant level on the flexural strength, fracture toughness, and microhardness of the provisional PMMA resin. Pair-wise comparisons between groups were performed using Tukey’s multiple comparisons procedure to control the overall significance level at 5 percent. Three fracture toughness samples/group were randomly selected for Energy Dispersive Spectrometry (EDS) to qualitatively evaluate the dispersion of the fibers. The data obtained from this study showed that control sample values were in the acceptance range compared with previous research. The experimental samples did not reinforce the provisional resin in the flexural strength, modulus, fracture toughness, or microhardness. There are several factors may attribute to these results, such as poor bonding at the filler/matrix interface. The more homogeneous the mixture of PMMA and fiber, the stronger the acrylic resin. In fact, the presence of poorly bonded fibers, to which little load is transferred, can be almost equivalent to voids. In addition, as seen with EDS images, alumina nanofibers had a tendency to agglomerate. The use of a magnetic stirrer was not effective in physically separating nanofibers agglomerates. Direct dispersion of alumina nanofibers in methyl methacrylate monomer and quaternary ammonium acetate dispersant was not effective in separating the nanofibers into nano-scaled single crystals. The presence of fiber agglomerates acts as a structural defect that detrimentally affects the mechanical properties. Further studies are needed to evaluate the effectiveness of fibers, dispersion techniques, and coupling agents to enhance the mechanical properties of the provisional PMMA resin.Item A laboratory evaluation of detail reproduction, contact angle, and tear strength of three elastomeric impression materials(2011) Sun, Ming; Platt, Jeffrey A., 1958-; Levon, John A.; Cho, Sopanis D.; Paez de Mendoza, Carmen Y.; Brown, David T.Fabrications of desirable fixed or removable dental prostheses depend upon accurate casts or dies. Recently, the most frequently used impression materials have been polyether (PE) and polyvinyl siloxane (PVS). However, both have their limitations: PVS is inherently hydrophobic, and PE is rigid. In order to take advantage of the desirable qualities of both PVS and PE impression materials, a new generation of impression material is being developed called vinyl polyether silicone (VPES, GC). The purpose of the present study was to compare the properties of hydrophilic PVS, PE, and VPES in regard to surface detail reproduction, contact angle, and tear strength. The hypotheses to be tested were: 1) VPES will show a significant superiority insurface detail reproduction compared with PVS and PE impression materials; 2) VPES will show a significant superiority in wettability compared with PVS and PE impression materials; 3) VPES will show a significant superiority in tear strength compared with PVS and PE impression materials. In order to test the surface detail reproduction, impressions were made of stainless steel dies with a parallel series of 15 different width lines on the surface and tested under dry and moist conditions. The wettability was assessed by contact angles of saturated CaSO4 aqueous solution drops on flat impression surfaces. A trouser tear test was employed to test the tear strength. The trouser-shaped specimens were prepared and tested in the Instron Universal Testing Machine. The data were analyzed by one-way ANOVA and Pearson‘s Chi square, (p < 0.05). All the materials showed better detail reproduction under the dry conditions than the moist conditions. There were no differences between the three materials in detail reproduction when impressing under either moist conditions or dry conditions. All the materials showed good wettability in the contact angle test. PVS rendered a contact angle as low as 34.19º. The contact angle of VPES was 44.84º, which was lower than 54.76º for PE. In the tear strength test, PE showed nearly two time higher tear strength than the other two impression materials. VPES showed slightly lower tear strength than PVS. The tear strength of the three materials tested in increasing order was VPES, PVS, PE. VPES showed comparable detail reproduction to PVS and PE and better wettability than PE, but showed the lowest tear strength compared with PE and PVS.Item Mechanical properties evaluation of denture base PMMA enhanced with single- walled carbon nanotubes(2010) Scotti, Kevin; Chu, Tien-Min Gabriel; Paez de Mendoza, Carmen Y.; Andres, Carl J., 1942-; Levon, John A.; Hovijitra, Suteena, 1944-Recent theoretical and experimental studies, suggest that Carbon nanotubes are 10-100 times higher than the strongest steel at a fraction of the weight. There are two main types of CNTs that can have high structural perfection. Single-walled nanotubes (SWNTs) consist of a single graphite sheet seamlessly wrapped into a cylindrical tube. Multi-walled carbon nanotubes (MWNTs) comprise an array of such nanotubes concentrically nested like rings of a tree trunk. Denture base acrylics have been reinforced with different materials with limited success. No single reinforced material has showed a great statistical difference in mechanical improvement. The goal of this investigation was to study the effects of Single Walled Carbon Nanotubes reinforcement on the mechanical properties of commercially available denture base PMMA. Denture Base material was reinforced with Single-walled Carbon Nanotubes (SWNTs) at dispersion of 0.25 wt % (group 1), 0.50 wt % (group 2), 0.75 wt % (group 3) and 0.0 wt % (group 4, control). Samples from each group were evaluated for microhardness, flexural strength, flexural modulus, and fracture toughness. The samples were tested in two conditions, as manufactured (dry) and after storing at 37 C for 7 days (wet). Data from four experiments was analyzed by ANOVA. All control sample values were in the range of acceptance compared with previous studies. Higher values were obtained for the control groups for flexural strength and modulus compared with the experimental samples. (p < 0.05) There was no statistical difference regarding fracture toughness between control and experimental groups. A statistical difference was observed in Hardness. The experimental group showed higher values under compression.Item Mechanical Properties Of Provisional Restorative Materials(2010) Shimizu Oliva, Graciela, 1976-; Paez de Mendoza, Carmen Y.; Andres, Carl J., 1942-; Brown, David T.; Chu, Tien-Min Gabriel; Levon, John A.A provisional restoration must fulfill biologic, mechanical, and esthetic requirements. These prostheses should provide comfort, pulp protection, positional stability, occlusal function, hygiene access, esthetics, strength and retention. Methyl-methacrylate acrylic has assumed many appli¬cations in the field of restorative dentistry. However, the material still has deficiencies, such as polymerization shrinkage, pulpal damage associated with exothermic polymerization and susceptibility to fracture. Bis-GMA composites, Bis-acryl composites and visible light-cured urethane dimethacrylate resins have been developed to address these issues. The purpose of this study was to compare the mechanical properties of provisional restorations made from composite resins (Protemp Plus, Luxatemp Solar, Radica, Protemp Crown) to those made of the traditional methacrylate resins (Jet, Snap, High Impact). Six groups of samples, two groups from methacrylate and four groups from composite based materials, were fabricated. Samples from each group were evaluated for microhardness (n=10), flexural strength and flexural modulus (n=20) according to ISO 4049, and fracture toughness (n=20) according to ISO 13586. From each of the six groups, ten samples were tested for flexural strength, flexural modulus and fracture toughness and 5 samples were tested for microhardness. These tests were done after storing at 37°C in a distilled water solution for 7 days followed by thermal cycling (2500 cycles, 5-55°C, 45 s. dwell). Identical sets of samples from each group were used as controls; these were tested after storing for 24 hours in dry conditions. The results were analyzed by two-way ANOVA with material type and aging conditions as the two main variables. Significance level was set at p=0.05. For flexural strength and flexural modules, the higher values were obtained for Radica. Protemp plus (7 days) and Radica (24h) had the highest fracture toughness value. Protemp crown showed the highest surface hardness. The mechanical properties of composite resin were superior.