[In vitro investigation of the amount of targis wear comparded to enamel, porcelain and composite]

In an ideal situation, the wear resistance of a restorative material should be similar to dental enamel. This study was performed to observe the wear resistance of targis wear compared with porcelain, composite, and natural enamel. In this in vitro study, 120 samples [2 x 8 x 13mm] were prepared including 60 Targis samples [140 Dentin Targis veneered with S1 Incisal Targis], 20 porcelain samples [VITA VMK95-A2 Incisal], 20 composite samples [Tetric-ceram HB-A2] and 20 natural enamel samples [buccal surface of maxillary central tooth]. The samples were mounted in Acrylic block and placed in a wearing machine [periods=30000 times, frequence=198 cycles per second, pressure=300gr invironment=artifitial saliva solution] after finishing by silicone carbide paper [240-1000] for 20 minutes. The samples were studied in three groups: Targis-Porcelain, Targis-Composite and Targis- Enamel. Vertical reduction of each sample was measured by a digital caliper [Mitutoyo, Japan] with a precision of 0.01mm. The results were analyzed by a T-test and SPSS software. Porcelain was 3.5 times more resistant to wear than Targis and the difference was statistically significant [P<0.05]. The wear resistance of targis was not significantly different from Tetric ceram HB composite [P>0.05]. When compared to enamel, it was observed that Targis was less wear resistant but the difference was not significant [P>0.05]. According to the results, targis, having suitable mechanical properties, maybe a good alternative for porcelain composite

[Comparison of flexure resistance between two rod and paste solders in base metal alloy]

Soldering is used in fixed prosthodontics, for different purposes such as connecting separate parts of the bridge, recontouring proximal and occlusal contacts and repairing casting voids. The aim of this study was to compare the flexural resistance of two rod and paste solders used in base metal alloys. Thirty rectangular specimens [1x4x30 mm] were made using super cast base alloy. The samples were sectioned into two equal parts and were placed in a soldering investment as pairs with 0.3 mm gaps between them. They were divided into 2 groups and soldered with rod solder in one group and paste solder in the other. The samples were subjected to a flexure test on a Universal Testing Machine. Statistically analysis was performed using F- and t-tests. The minimum and maximum flexural resistance was 107.2N and 301.2N for the rod- and 62.8N and 109.3N for the paste solders, respectively. The mean flexural resistance was 196.5N in the rod solder group and 89.8N in the paste solder group. A significant difference in flexural resistance was observed between the two study groups [P=0.001]. The results of this study indicated that flexural resistance of the rod solders was significantly higher than the paste solders

[Effect of pontic width on stress distribution in abutment teeth and their supporting structures by finite element analysis]

Fixed partial dentures and single restorations reveal differences in the pattern and quantity of stress. The most important factors affecting stress distribution in abutments are occluso-gingival height and bucco-lingual width. In this in vitro study a finite element analysis was performed to evaluate changes in the pattern and quantity of stress in pontics with different widths. Three PFM models were created, one with a conventional width and the other two demonstrating 20% and 40% width-reduction. The models were fabricated to replace a mandibular first molar. A load of 700 N was applied vertically to the center of the pontic and the stress patterns were examined by finite element analysis. Maximum stress concentration was observed in the supporting bone of the abutment teeth mesial to the premolars, distal to the molars and in the apical portions of the premolars. The 20% and 40% width-reduction of the pontics caused a similar amount of stress reduction in the supporting tissues of the abutment teeth. Stress concentration sites were also observed at the furcation area and the cervical regions of the distal aspect of the premolars and mesial aspect of the molars. The reduction in stress values within tooth structure was proportional but less than the 20% and 40% width-reduction of the pontics. Reduction of pontic width caused a considerable amount of stress reduction in the supporting bone and a smaller amount in tooth structure

[Finite element stress analysis on the effects of the changes in length of pontic on the stresses carried from pontic to abutments]

Stress in fixed partial dentures is different in pattern and quantity compared with single restoration. Length of bridge has a direct effects on stress of abutments. This study evaluates the changes in pattern and quantity of stress with the pontic length variation. We can use the results to design the dimension of pontic and also in fixed partial denture treatment planning when the load applied to bridge is important. In this in vitro study, the finite element method was used to analyze mechanical behavior of prosthesis and its supporting structures when a fixed prosthesis with two designs replaces a mandibular first molar. In finite element stress analysis method, models were designed similar to the actual one with ANSYS computer software. Two PFM bridge models with normal pontic were designed which one of them was 3-unit F.P.D and the other was 4-unit F.P.D. Physical properties of Ni-Cr-Be alloy, dentine, PDL, spongy and compact bone were determined for the software program. A 700 N load was applied vertically to the center of pontic, and then stress in abutment, bone and prosthesis were analyzed by ANSYS software. Stress concentration was in the mesial of premolar, apex of premolar and distal of molar [13.4 MPa] in the supporting bone of 3-unit F.P.D. Stress pattern in the bone was the same in 3-unit F.P.D and 4-unit F.P.D. When the length of pontic was doubled, stress in the bone was doubled too [26.2 MPa]. Stress concentration in 3-unit F.P.D was in distal of premolar [cervical region], mesial of molar [cervical region] and Furca in tooth structure [45.8 MPa]. Maximum stress in 3-unit F.P.D prosthesis was respectively in joints [511 MPa], distal margin of premolar and mesial margin of molar. Maximum stress in 4-unit F.P.D was in the joint of two pontic [1903 MPa]. When the length of pontic was doubled, stress in the bone was doubled too. Maximum stress concentration in 3-unit F.P.D was in the distal joint. In 4-unit FP.D, maximum stress was in the joint between the pontics

[ in vitro study on the effect of the temperature of cylinders and liner on the dimensions of casting posts in base metals]

Casting posts are recommended for endodontically treated teeth, specially in cases with extensive damaged crowns. Because the length and diameter of the post are effective in generating stress on the roots, and can be influenced according to the casting conditions, the purpose of this research was to study the effect of using liners and the temperature of burn out on the dimensions of the casting posts in base metals. In this experimental study, 80 acrylic posts with the length of 12.095 mm and the diameter of 2.096mm were made. On top of each post a reference point was contrived and the posts were grouped into 4 groups of 20. In the first group, humidified liner and casting temperature of 900 degree C were used, the second group were without liner and the temperature was 900 degree C, the third group were with humidified liner and temperature of 600 degree C and the fourth group were without liner and were casted in 600 degree C temperature. The lengths of the posts were measured from top to the bottom in the center [diameter in the upper most part in the reference point] with a metallurgy microscope and the results were statistically compared using student-t, Mann-Whitney and Kruskal-wallis tests. Mean and standard deviation of the acrylic post lengths were obtained. The difference [0.127mm] was significant [P<0.001]. Also, mean and standard deviation of the diameter of the acrylic posts [2.87mm +/- 0.118] was significantly less than that of metal post [2.97mm +/- 0.166], [P<0.001]. Differences in length was significant among studied groups so that in the group with 600 degree C temperature and without liner, the least measures occurred compared to the other groups [P=0.001]. Difference in the diameter of the acrylic and metal posts in the four groups showed that the use of 600 degree C temperature without humidified liner produced the least differences compared with the other groups [P=0.001]. It can be concluded that the best condition for investing and casting the casting posts is 600 degree C temperature without using the liner

[Laboratory evaluation of targis color stability in comparison with porcelain and composite by colorimeter]

Color stability is crucial for the success of any restorative material. Despite composites, color stability of ceromers has not been studied widely. The purpose of this study was evaluation of color stability of one type of ceromers and comparing it with porcelain and composite. In this invitro experimental study, one type of ceromers [targis], a light cured direct composite [tetric ceram] and a porcelain [vita] were chosen. The samples were evaluated in CIELAB color order system by a colorimeter in 3 stages: before UV exposure, after 100 hours UV exposure and after 200 hours UV exposures. l*, a* and b* peculiarities and their changes in examination steps were calculated. The results were analyzed by ANOVA and LSD statistical tests. The results revealed the porcelain and targis had the highest and lowest color stability after 100 [P=0.05] and 200 [P=0.014] hours periods, respectively. In comparison among the different colors of ceromers, C3 and D3 had the highest and the lowest color stability respectively [P= 0.001 in 100 and P= 0.008 in 200 hours]. In all of studing groups, the final color change were clinically acceptable. All of the groups revealed acceptable color stability and among them porcelain had the best characteristics

[ effect of metal ring and liner on dimensional precision of base-metal casting]

Introduction: several procedures have been suggested for compensating the solidification shrinkage of the casting through investment expansion, among which using the metal ring or liner inside the ring may be mentioned. The purpose of this study was to evaluate the effect of metal ring and liner on the marginal integrity of base metal crown

Materials and Methods: 30 metal dies were made and divided into 3 groups of 10 .Metal copings were waxed up for all dies and invested using 3 methods. Group 1: with metal ring and liner; Group 2: with metal ring and without liner; Group 3: without metal ring and liner. Castings were cemented on their dies. Horizontal and vertical marginal discrepancy was measured microscopically. The results were analyzed using ANOVA test

Result: group1 [using metal ring and liner] showed the least horizontal and vertical marginal discrepancy [p=0.001] and group 3 showed the highest discrepancy

Conclusion: considering the results, it is suggested that a metal ring and liner should be used for casting base metal restorations