Investigation of the Fracture Surface of E Glass Fiber Reinforced PMMA Denture Base Resins

The interface between fibers and the acrylic resin matrix is considered to be an important factor in the reinforcement, and the microscopic surface structure may play a key role in the effectiveness of this reinforcement. Adequate adhesion of the fibers to the polymer matrix is one of the most important factors for strength. The optic microscope, although of limited resolution, is still a popular choice. The scanning electron microscope (SEM) provides measurements in 2 dimensions. The aim of the study was to examine the interfacial region of PMMA reinforced with chopped glass fibers coated with two different silans using the scanning electron microscope. E Glass fibers coupled with Silan 1 (silan + epoxy resin) and Silan 2 (silan + polyester resin) were used to reinforce denture base polymethyl metacrylate resin. Specimens were produced by two different methods in the first group, and the fibers were soaked with a mixture of polymer powder and monomer liquid. In the second group the fibers were soaked in the polymer liquid for 15 minutes and then blended with PMA polymers. All the samples were heat cured. Transverse strength of specimens was evaluated by a 3 point bending test. Fracture surfaces of the test specimens were examined with SEM to evaluate the degree of impregnation of fibers with the polymer matrix. SEM examination revealed well impregnated glass fibers with the polymer matrix. No difference was found between the test groups

The Effects of Investment Expansions on Soldering

The investments used in the soldering procedure should provide a good soldering connection without causing any dimensional changes. In this research, the influence of investments with different expansions on the investment soldering procedures was investigated. For this purpose, following the preparation of the experimental models which represented the abutment teeth, standard bridge restorations were fabricated. After placing bridge restorations onto the abutment teeth, 10 kilograms of standard force was applied for setting the restorations and marginal openings were measured from six fixed points. The bridge restorations, which were subjected to standard separations, were divided into three groups and embedded in the investment block by using investments with different thermal expansions. The samples were then soldered by preheating + torch technique and marginal openings of each bridge prosthesis at the six predetermined measuring points were evaluated and recorded. The marginal opening values before and after the soldering and the differences between them were statistically analyzed. In pre-ceramic soldering of base metal alloys, the usage of special soldering investments with low thermal expansion cannot compensate for the expansion of metal during the soldering process and therefore causes the soldering space to shorten and leads to dimensional changes in the prosthesis

The Effect of Two Different E Glass Fiber Reinforcements on Mechanical Properties of Polymethyl Metacrylate Denture Base Resins

Denture base polymers were reinforced with various types of fibers, such as glass, carbon/graphite and ultrahigh-modulus polyethylene fibers. These procedures were performed to take advantage of the good esthetic qualities of glass fibers and good bonding of glass fibers to polymers via silane coupling agents. The most common type of glass used in fiber production is the so-called E glass (electrical glass). This study investigated the effect of chopped fibers with two different silane coupling agents on the strength of denture base polymethyl metacrylate resins. E Glass fibers coupled either with Silan 1 (silan + epoxy resin) or Silan 2 (silan + polyester resin) were used to reinforce denture base polymethyl metacrylate resin. Specimens were produced by two different methods. In the first group, the fibers were wetted with a mixture of polymer powder and monomer liquid and in the second group the fibers were soaked in the polymer liquid for 15 minutes and then blended with PMA polymers. All samples were heat cured. Control group specimens were not fiber reinforced. Half of the prepared specimens were stored in distilled water at 37°C for 48 hours. The others were tested immediately. Transverse strength of all specimens was evaluated by a 3 point bending test. No significant difference was found between the wetted and immediately tested specimens (p=0.755). When all specimens were compared for transfer stength there was statistically significant difference between the wetted and unwetted specimens (p=0). When silanated and control specimens were compared the ones processed with Silan 2 (silan + polyester resin) showed the lowest transfer strenght values

Adherence of Candida Albicans to Different Finished Surfaces of PMMA Resins Reinforced with Glass E Fibers

Candida albicans has been widely associated with the etiology of denture-related stomatitis. When fiber reinforcement is used in the denture base as a total fiber reinforcement, the fibers may be exposed during the finishing of the denture. This may lead to oral disease if the fibers come into contact with the oral mucosa. In this study the adherence of candida albicans to the surface of PMMA and to the surface of E glass fibers of composite material used in dentures was compared. E glass fibers coated with Silan 1(silan + epoxy resin) and Silan 2 (silan + polyester resin) were used to reinforce denture base polymethyl metacrylate resin. Specimens were produced by two different methods. In the first group the fibers were wetted with a mixture of polymer powder and monomer liquid. In the second group the fibers were wetted in polymer liquid for 15 minutes and than blended with PMA polymers. All of the samples were heat cured. Half the prepared specimens were polished and the other half left unpolished. Replicates and yeast cells (Candida albicans ATCC, 90028, 1.0 x 107 cells/ml)were placed in wells and incubated for 1 h at 37°C on an orbital shaker at 80 rpm. The replicates were air dried and mounted on glass slides and stained with a solution of 0.5% crystal violet and 1.0% iodine. The number of adherant yeast cells were counted under a light microscope (400x). RESULTS: 1. Less Candida albicans adhered to the Polished surface (P< 0.01). 2. The highest Candida albicans accumulation was observed on the Silan 2(silan + poly ester resin) coupling samples.(P<0.001). The type of material used for silanization is an important factor, effecting the amount of Candida albicans accumulation

INFLUENCE OF DENTIN AND CORE PORCELAIN THICKNESS ON THE COLOR OF FULLY SINTERED ZIRCONIA CERAMIC RESTORATIONS

Statement of problem. The influence of the thickness of dentin and core porcelain, and the glazing procedure on the color of computer-aided design and computer-aided manufacturing ceramic restorations has not been investigated. Purpose. This study evaluated the influence of the thickness of dentin and core porcelain and glazing on the color of fully sintered zirconia ceramic restorations. Material and methods. Fully sintered zirconia core material was cut into 90 specimens of 0.3 mm (n=30, group ZC1), 0.4 mm (n=30, group ZC2), and 0.5-mm thickness (n=30, group ZC3). On a dentin disk obtained from an extracted molar, the L*, a*, b* values of the specimens were measured at different steps in the laboratory procedures (Zirconia core, Effect Bonder, Effect Liner, dentin porcelain, glazing) with a spectrophotometer. One millimeter dentin porcelain was applied on half of the specimens of each group and 1.5-mm dentin porcelain on the rest. To assess the ability of porcelain substructures to mask the underlying dark colored tooth structure, color difference (SE) values between the steps were calculated. Results were statistically analyzed with ANOVA. Results. Glazing caused a decrease in the L* values and an increase in the a* and b* values (P<.05). Increasing the thickness of dentin porcelain decreased the L*, a*, and b* values (P<.05). Increasing the zirconia core thickness resulted in an increase in the L* values and a decrease in the a* and b* values (PG.05). Increasing the dentin porcelain thickness from 1 mm to 1.5 mm resulted in a color change below the perceptibility threshold (Delta E<2.6). In the ZC1 group, glazing resulted in a color change perceptible to 50% of observers, whereas, in the ZC2 and ZC3 groups with 1-mm dentin porcelain, the SE value was higher than 5.5. However, the color change was perceptible to 50% of the observers in all of the groups with 1.5-mm dentin porcelain. Conclusions. Although the thicknesses of the dentin and core porcelain did not influence the final shade of the restoration, glazing resulted in a perceptible color difference

EVALUATING THE ABILITY OF DENTAL TECHNICIAN STUDENTS AND GRADUATE DENTISTS TO MATCH TOOTH COLOR

Statement of problem. The ability of dental technician students to match tooth shade with the Vita 3D-Master shade guide and Toothguide Training Box has not been investigated. Purpose. The purpose of this study was to evaluate and compare the shade-matching ability of dental technician students and graduate dentists using the Vita 3D-Master shade guide. Material and methods. Twenty-nine dental technician students (DTS group) and 30 graduate dentists (GD group) participated in this study. The Toothguide Training Box (TTB) was used to train the participants and test their shade-matching abilities. Shade-matching ability was evaluated with 3 exercises and a final test, all of which are components of the TTB. The number of mistakes for each participant for value (L), chroma (c), and hue (h) were recorded during the exercises and the final test, and the mistake ratios were calculated. Color difference (Delta E) values for each shade were calculated from the L*, a*, and b* values of the Vita 3D-Master shade guide for each participant in both groups. The Mann-Whitney U test was used to determine statistically significant differences between the L, c, and h mistake ratios of the 2 groups, and the Student t test was used to determine statistically significant differences between the final test scores and the Delta E values of the groups (alpha=.05). Results. The mistake ratio for L in the GD group was significantly higher than that of the DTS group (P.05). With regard to the final test scores and the Delta E values, no significant differences were found between the groups (P<.001), and the DTS group received higher scores than the GD group (912 and 851). The mean Delta E values for the DTS and GD groups were 1.72 and 2.92. Conclusions. DTSs made more mistakes in the h parameter than GDs, and GDs made more mistakes in the L parameter than DTSs. With regard to the final test scores and the Delta E values, DTSs were more successful in shade matching than GDs

Microstructural characterization and bond strength of the interface area between dental core and body porcelains

To fabricate all-ceramic fixed partial dentures with appropriate fracture strength and aesthetics, new ceramic core materials were recently introduced into the dental market. In this study, the bond strengths of the core and body porcelains of 3 different brands were determined by 4-point bending tests. Two of these brands were hot-pressed ceramics and one was glass-infiltrated presintered alumina. There were significant statistical differences in the bond strength values of the specimens of the three groups, the highest values belong to the combination of the glass-infiltrated presintered alumina as core and feldsphatic porcelain as body porcelain. Scanning Electron Microscopy investigations were carried out to examine the fracture surfaces