[Evaluation of some of the temporomandibular disorder etiologic factors in women referred to Mashhad Dental School]

Various evidences show a higher prevalence of temporomandibular disorder [TMD] in women. The purpose of this study was to evaluate T.M.D etiologic factors in women referring to Mashhad Dental School. Twenty-five patients with jaw clicking and 19 with M.P.D syndrome were randomly selected among female patients referring to Mashhad dental school. Seventeen women with no signs and symptoms of temporomandibular disorder were used as the control group. The women were between the ages of 18 to 40. All of them were examined for TMD and etiologic factors such as Parafunctional habits [Bruxism and Clenching] and premature contacts in eccentric movements. The level of blood estradiol and progesterone status were also recorded. The data were analyzed by Kruskal Wallis and Chi-square tests through SPSS software. Although there was a difference in level of blood estradiol and progesterone between TMD patients and control group, this difference was not significant. There was a significant difference between the two groups regarding parafunctional habits [P<0.001]. There was no significant difference between the two groups regarding eccentric premature contacts [P=0.098] In this study, the most important TMD etiologic factor was parafunctional habits [Bruxism and clenching] and the second effective factor was eccentric premature contacts. There was no relation between the level of blood estradiol and progesterone and the incidence of TMD in women

[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

[Effects of alloys on porcelain color in three types of base metals]

Color matching, visual combination and accurate shade selection with natural teeth are important issues in restorative dentistry. In ceramometal restorations, the type of substructure alloy affects the final color of bonded porcelain. Minalux alloy, is the most commonly used Iranian product which is a base metal alloy [Ni-Cr]. The aim of this study is to compare the effect of three base metal alloys [Wirron 99, Bellabond and Minalux] on their masking of porcelain color and to assess various color dimentions between them. In this in vitro study, ten disks, approximately 0.3 mm thick and 1 cm diameter, were prepared from each alloy. Then a 1 mm thickness layer of vita VMK68 porcelain shade A[2] was baked onto them, following the manufacture's instruction. Ten samples with 5 mm thickness were prepared from the same porcelain and designated the "control group". All samples, with similartining and in similar conditions of environmental light were assessed by a computer colorimetry instrument; and color values such as 1*, a* and b* under CLE-LAB system were measured. The data were analyzed by one-way-Anova and Tukey tests. Three alloys in this study as compared with the control group, had significant effect on the three variables 1*, a* and b* [respectively P=0.004, P=0.037, P<0.001]. In these alloys, Wirron 99 and Bellabond, had significant difference on the two variables l* [P-value=0.025] and a* [P-value=0.037]; but Minalux alloy did not have any significant difference with other groups. The comparison between the average of deltaE quantities alloys, indicated that the difference of Vita porcelain shade A[2] baked on Wirron 99 and Bellabond was significant. The effect of Iranian minalux alloy on color's parts and it's related deltaE quantity, is in a similar range of two foreign alloy products Wirron 99 and Bellabond

[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

[Effect of warm saline mouthwash on reduction of pain after packing cord insertion for gingival retraction]

Although local anesthesia may be applied in different steps of fixed prosthodontics, patient complain about annoying pain after cord packing is sometimes reported. The aim of this study was to asses the effect of warm saline mouthwash on reduction of pain after packing cord insertion. 22 patients needing crowns for two symmetrical root either in mandibular or maxillary molars were selected. All of the procedures for making crown on both teeth were carried out similarlly. Inter dental anesthesia was used for packing cord. After elimination of anesthesia the patients scored their pain according to VAS method [scale]. Control group [all 22 patients after impression of their first tooth] used warm water mouth wash as placebo and experimental group [the same patients after impression on their second tooth] used warm saline. After using mouth wash the patients scored their pain again. The data were analyzed using a paired test. The mean pain intensity score in control group was not significantly different before and after mouthwash. In test group this difference was significant [P<0.001] [table 1]. Using warm saline [12 +/- 2gr/250cc] mouth wash for 5 minutes reduces or eliminates the pain after packing cord insertion

[ study on the effect of die separator [microfilm] on the surface hardness of stone dies in different situations]

One of the important stages in fixed partial dentures is the preparation of stone die which is in fact the replica of the prepared tooth and should have the maximum adaptation in replicating it. Plaster die may be scratched by the instruments during the wax up and this leads to loss of precision. Microfilm is used as a lubricant to prevent wax from adhering to the stone and is applied to die. The objective of this study was to evaluate the effect of die separator [microfilm] in different situations on the hardness of stone die. In this experimental study forty dies were made after taking PVC impressions with the diameter of 2 and height of 1 centimeter with gypsum type 4 [extra hard stackable type IV dental stone], according to the manufacture instructions. Dies were divided into four groups of ten and after 24 hours of keeping in the room temperature for reaching the maximum tensile strength [final dry tensile strength] they were used as follow: 1- Control group on which, microfilm was not applied 2- Group A were immersed in microfilm for ten minutes and were immediately examined for hardness. 3- Group B were immersed in microfilm for 10 minutes and were stored in room temperature for 12 hours and then microfilm was applied again by a brush. 4- Group C were immersed in microfilm and were stored in room temperature for 24 hours and microfilm was applied again using a brush. All of the groups were examined for hardness under 25 gram force for 5 seconds and the data was processed for statistical analysis. The one way variant analysis and multiple Dunnet, Tukey test and kruscal vallis test were used and the results were examined with 95% confidence interval. The maximum surface hardness was found in the control group equal to 77.8+/-12.5 and decreased in groups A, B and C to 41.1+/-7.4, 30.7+/-5.9 and 22+/-2.5 respectively. ANOVA statistical analysis showed a significant difference between the four groups [P=0.001]. Dunnet analysis showed a significant difference between all the groups and the control group [P= 0.001]. Groups were compared in pairs using the Tukey test and only groups B and C didn't show a significant difference. According to this study the following results were acquired: 1. Applying microfilm to the stone dies resulted in significant decrease in surface hardness. 2. Applying microfilm resulted in a significant decrease in surface hardness after 12 hours. 3. There was no significant difference in surface hardness between 12 and 24 hours after microfilm application

[ 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

[ 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