[Effect of fiber position and orientation on flexural strength of fiber-reinforced composite]

One of the most important factors for increasing flexural strength of fiber-reinforced composite [FRC] restorations is the orientation, volume and geometry of reinforcement fibers. The aim of this study was to determine the effect of fiber position and orientation on the flexural strength of FRC specimens. In this experimental-laboratory study, five groups [N=8] of test specimens made of one indirect composite were reinforced with pre-impregnated fibers in different positions, orientations or geometry into the rectangle cube specimens [3x3x25mm[3]]. The control group did not contain fiber reinforcement. The test specimens were stored in distilled water for 1 week at 37°C before testing in a three-point loading test with 1mm/min cross head speed. Data were statistically analyzed at 0.05 significance level with Kruskal-Wallis and Mann-Whitney tests. The mean flexural strength of six experimental groups had significant differences [p[1]=0.005 and p[2] < 0.001]. The control group showed the lowest initial and final values. The maximum initial flexural strength was seen in the tension group [76.2 Mpa] and the maximum final flexural strength was seen in the middle horizontal group [173.9 Mpa]. Within the limitations of this study, it may be concluded that the position and orientation of the fibers influenced the flexural strength of the fiber-reinforced composites and the most effective position of the fibers was tension side reinforcement

[ effect of fiber reinforcement and composition of the overlying composite on the flexural strength of three laboratory-processed fiber-reinforced Composite resins]

Reinforcement with fiber is one of effective methods for improvement in flexural properties of indirect composite resin restorations. The composition of the overlying veneering composite plays a critical role in the flexural properties of the final fiber reinforced restoration. The aim of this in-vitro study was to evaluate the effect of fiber reinforcement on the flexural strength of three laboratory-processed fiber-reinforced composite resins. In this experimental-laboratory study, 72 bar type specimens [3225 mm] were constructed by using three types of fiber-reinforced composite resins [Gradia, Signom, Bellglass] and one Plexiglas mold. In each type of composite resin, two groups [one with fiber and one without fiber] were constructed. These specimens were tested by the three-point bending method to measure flexural strength. Data were statistically analyzed with two way ANOVA, Tukey and T-test at 0.05 significance level. The mean flexural strength of Gradia with fiber was higher than the other groups [150.14 MPa] and the mean flexural strength of Signom without fiber was the least [60.53 MPa]. There was a significant difference between the mean primary fracture force in the three groups [P<0.001]. Within the limitations of this study, it may be concluded that reinforcement with fiber considerably increases the fracture resistance of composite specimens and the overlying veneering composite may play an important role in the transverse strength of fiber reinforced composite specimens

[Evaluation of bond strength of four types of multilithic teeth to acrylic denture base material]

The wear resistance of composite denture teeth has been well investigated, but there have been few studies about the bonding of these teeth to acrylic denture base resins. The aim of this study was to evaluate the bond strengths of four brands of multilithic denture teeth to acrylic denture base material. In this experimental laboratory study four denture teeth groups [Glamour, Yaghout, Ivoclar and Apple] were used. Of each type of denture teeth 20 specimens were dogged into four wax prisms so that the lingual surface was faced upwards and the long axis of each of them made an angle of 90 degrees with the edge of the prism. After the placement of acryl and their curing stages, each sample was tested under shear-compressive force of 5 mm/min speed until fractured occurred. The data were analyzed by ANOVA and TUKEY test at 0.05 significance level. Apple teeth had the highest mean bond strength [1337 +/- 414/99] followed by Yaghoot [1097/36 +/- 142/86], Ivoclar [945 +/- 366/43] and Glamour [880 +/- 285/80]. Statistical analysis showed significant difference between the mean bond strength in some of denture teeth. Ivoclar specimens had the highest percentage of cohesive fracture followed by Apple, Glamour and Yaghoot. Nevertheless, statistical analysis showed no significant difference between the percentages of cohesive fracture in different groups of denture teeth. The results of this study showed that the bond strength of Apple denture teeth is more than Ivoclar and other denture teeth that were used in this study

[Comparison of linear dimensional changes of two heat-cure acrylic resins]

Although acrylic resin materials have great features for making artificial dentures, but still dimensional change is a common problem in processing them. The aim of this study was to compare the linear dimensional changes of two heat-cure acrylic resins. In this descriptive study, twenty specimens in two groups were made by "Acropars" and "Meliodent" acrylic resins according to the manufacturer's recommendations in a metallic mold. Dimensional changes were measured at one, thirty and sixty weeks after processing with a digital caliper. The results were analyzed using T-test, T-paired test and repeated measure ANOVA. Considering the dimensional changes, there was a difference in the first day equal to 0.42 +/- 0.28 mm, in day thirty: -0.09 +/- 0.42 mm, and in day sixty: 0.07 +/- 0.22mm between the two acrylic resins, showing no statistically significant differences [p=0.21]. However, there were significant differences between different times of measurements [p=0.001]. "Meliodent" acrylic resin had more dimensional stability when compared to "Acropars" resin but there was not any significant difference between the two acrylic resins in the day sixty. There were significant differences between different times of measurements; the maximum difference between these two types of acrylic resins was in first day after polymerization

[Retentive strength comparison between a local made and an imported brand of zinc oxide-eugenol cement]

Provisional cements are used to temporarily retain provisional and permanent fixed restorations on the prepared teeth. The retentive strengths of two different local made and imported brand of zinc oxide-eugenol provisional cements were evaluated in this study. This experimental study was conducted by using 36 cylindrical amalgam cores with a width of 5.9 mm and height of 6 mm that were made by condensing amalgam in brass molds. Thirty-three cylindrical spaces with a width of 6 mm and height of 6 mm were prepared in the center of Rexillium III alloy cast rods. Cores were divided into two groups and retainers were cemented with both types of cements. The samples were stored in 100% humidity at 37°C. DARTEK testing machine was used to test samples at 0.02 cm/minute cross head speed for their retentive strength. The data were analyzed with Mann-Whitney statistical test. Mean separation force in the group of local made cement was 38.2 +/- 10.02, while it was 153.9 +/- 26.05 MPA in the imported group. The difference between the two groups was statistically significant [P<0.0005]. Based on the findings of this study the retentive strength of local made provisional cement was significantly lower than the imported one

[In vitro investigation of the wear quantity of targis opposing the enamel, porcelain and composite]

Fracture of acrylic resin denture base is a common problem in maxillary dentures. Because the stresses in mouth on the denture base are of flexural type, the aim of this study was to determe the effect of palatal shape combined with acrylic resin thickness on the flexural strength of the denture base. In this experimental study, 48 stone casts in 3 groups [shallow, medium and deep palatal vault] were prepared. Eight casts of each palatal form were covered with a single layer of base-plate wax and eight were covered with two layers. Patterns were invested and processed with Acropars acrylic resin in the same manner. Flexural strength, deflection and fracture load were measured with DARTEC testing machine. Statistical analysis was performed using multivariate ANOVA, Kruskal-Wallis and Mann Whitney tests. The results showed that the flexural strength of shallow bases were significantly different from medium and deep palatal shapes at both thicknesses [P<0.001]. There were no statistically significant differences in flexural strength between the medium and deep palatal shapes [P=0.583]. Increasing the base thickness significantly increases the flexural strength in each palatal shape [P<0.001]. This study revealed that palatal shape and base thickness have significant effects on flexural strength of denture bases. In shallow palates, increasing the thickness of denture base can enhance flexural strength of denture

[Relationship between satisfaction and expectation with self-esteem and self-concept in patients using complete denture]

Denture acceptance as a complex process is dependent not only on ridge morphology, theoretical and practical skills of dentist, but on many psychologic factors which need to be considered seriously. The aim of this study was to determine the relationship between complete denture satisfaction and expectation with patient's self-esteem and self-concept. This descriptive-analytical study was undertaken on 52 patients [28 male and 24 female] referred to the prosthodontic department of Khorasgan Azad University. The mean age was 53.4 with the range of 35-70 years. The personality variables were measured using two standard psychological tests [Rosenberg and California tests]. Before and after full denture delivery, patients completed the denture expectation questionnaires. After using new dentures for 3 months, the patients" satisfaction was evaluated by related questionnaires. T-student, T-paired and Pearson coefficient tests were used for data analysis. There was no significant relationship between expectation and self-concept likewise between self-esteem and satisfaction [p= 0.42, 0.18]. A moderate relationship was found between self-esteem and expectation [p=0.05], while a significant relationship was obtained between self-concept and satisfaction [p=0.01]. According to this study, it was revealed that complete denture treatment did not have any significant effect on patients' personality variables, but there was a significant relation between patients' self-esteem and complete denture satisfaction. Also patients with high self-esteem scores showed better expectations with their dentures

effect of storage time on the accuracy and dimensional stability of two irreversible hydrocolloid impression materials

It has been stated that hydrocolloid impression materials [Alginate] should be poured immediately to gain maximum dimensional stability. With modem formulations of these materials, it is possible store the impression at 100% humidity for varying periods. The purpose of this study was to evaluate the effect storage time on dimensional stability of casts poured from two types of alginate impression materials. A metal model [CK steel] composed of two metal plates, one holding the impression tray and the other holding two dies, was used to make the impressions. Five impressions were taken with the Iranian [Golchai] and foreign [Alginoplast] alginates for each tested time interval. The impressions were stored in l00% humidity for 0, 15, 30, 60 and 180 minutes and then poured with type III dental stone. The stone casts were measured with a digital caliper and the results were compared between the groups using two-way ANOVA and Tukey tests. A statistically significant difference was encountered between the dimensions of the casts poured from the two alginates at the tested time intervals [p=0.027]. No significant difference was observed between the experimental casts' dimensions and the master model at the different storage times [p=0.0230]. A 0.06 mm and 0.01 mm difference was found between the master model and the mean height of dye no.2 in the Iranian and foreign groups, respectively. The results of this study show that the studied hydrocolIoid materials can be stored in a humid environment for 3 hours, without undergoing significant changes

comparison on dimensional changes of two irreversible hydrocolloid impression materials disinfected by immersion in sodium hypochlorite solution

One of the most important problems in disinfecting alginate impressions is the dimensional changes caused by hydrocolloid nature of alginate. The aim of this study was to determine and compare the dimensional changes of two irreversible hydrocolloid impression materials [Iralgin -Alginoplast] disinfected by immersion in sodium hypochlorite solution. One metal model consisting of one platform and two partial conical dies was made and 80 impressions were then prepared using two kinds of alginate impressions materials. The impressions were divided into four groups. In groups 1 and 3, impressions were first rinsed for 15 seconds and immersed in 0.525% sodium hypochlorite solution and finally were poured by type 111 dental stone. In groups 2 and 4, impressions made by these two materials were only rinsed by tap water for 15 seconds and kept in 10% moisture for another 10 minutes and then were poured by type III dental stone. Different dimensions of samples in four groups were measured by digital caliper and compared using variance analysis and Duncan tests. Diameters, heights and outer distances of all samples showed significant differences with the metal model [P=0.049], however; inner distances did not have any significant difference [P=0.269]. Moreover, significant differences, in diameter and height, were found between case and control groups. In all four groups, diameters and outer distances increased and heights decreased compared to the metal model which are in agreement with the similar studies. All such changes were estimated less in Iralgin than Alginoplast

[ evaluation on the consistency and working time of an Iranian impression material [Duralite] and comparing it with a foreign product [luralite]]

Background and aim: Zinc oxide eugenol [ZOE] impression material, due to its favorable characteristics, has numerous uses in removable denture impression making and jaw relation recording. In Iran, this material is commercially produced as Duralite. The purpose of this study was to investigate consistency and working time of Iranian ZOE [Duralite] and compare it with foreign ZOE ]Luralite] based on British standard 4284: 1981

Materials and Methods: in this invitro experimental study, forty samples were studied. An apparatus for the determination of material consistency and a penetrometer for working time measurement were used. For consistency measurement, 0.5cc of each impression paste was put between two glass plates and under one 1500gr. load. After 15 seconds, the diameter of resulting disk was measured with a digital caliper. For working time measurement, each paste was put in a metal ring [diameter: 30mm, height: 3mm] and then in 30-second intervals the penetration of penetrometer needle was measured. Data were analyzed by t-student test

Results: mean consistency of Duralite impression material was measured 43.42+/-2rnm and that of luralite was 45.22+/-lmm. Mean working time for Duralite impression material was measured 2':50"+/-01:19" and for Luralite was 81:30"+/-0:25". The results of this study revealed that the consistency and working time of Duralite and Luralite impression materials are within the range of British standard

Conclusion: no statistically significant difference was found in mean consistency of Duralite and Luralite impression materials [P=0.08], but there is a significant difference between their mean working times [P <0.001]

[Comparing the effects of using standard die-spacer and shellac on the retention of fixed prosthesis]

The application of die- spacer to crown preparation dies prior to the fabrication of cast crowns is an acceptable procedure that improves the fit of the restorations. Previous studies have shown that the retention of the restoration will be improved, unchanged or reduced when an appropriate thickness of die- spacer is used. But in our country shellac is used instead of die- spacer. No study has compared the effect of using standard die-spacer and shellac on the retention of fixed prosthesis. This study compares the effect of using these two materials on the retention of fixed prosthesis. Ninety eight cast copings were fabricated on dies coated with die-spacer and shellac, cemented on the dies and removed using an Instron Universal Testing Machine. T-test showed that there is statistically significant difference between the mean force required to remove crowns relieved with die- spacer and relieved with shellac. With regard to some practical difficulties in application of shellac and the results of this study; it appears that application of die-spacer is better than shellac