meysam mahabadi

Adhesion to the surface of denture is a unique feature of oral candidiasis. Nanoparticles have antifungal and antibacterial properties that can be used in the structure of the dentures along with acrylic. The purpose of this study was to examine the inhibitory effect of zirconium oxide nanoparticles on the growth and adhesion of Candida albicans in the injection mold acryls. Materials &

In this experimental laboratory study, 90 acrylic blocks were prepared using the injection molding technique. The acrylic blocks were divided into three groups of 0, 2.5, and 7.5 weight percentages of zirconium oxide nanoparticles. All the plates with acrylic block were immersed and incubated in artificial saliva containing Candida. Then samples were taken from the control solution and the one containing block. After analyzing the number of colonies, blocks were removed from the culture medium and their adhesion was analyzed in Sabouraud dextrose agar culture medium. One-way Analysis of Variance and post-hoc Tukey test were used to evaluate the inhibitory effect of zirconium oxide nanoparticles on Candida.

The growth of Candida albicans significantly decreased compared to that in the control group (p value < 0.001). The number of Candida albicans colonies adhered to the block in the control group was significantly higher than that in the two groups with 2.5 and 7.5 weight percentages of zirconia However, there was no significant difference between the two groups with 2.5 and 7.5 5 weight percentages of zirconia. Nanoparticles of zirconium oxide with 2.5 and 7.5 weight percentages can significantly reduce the growth and adhesion of Candida, and due to the toxicity effect, it is better to use the lowest weight percentage of nanoparticles.

Zirconium oxide nanoparticles of 2.5 and 7.5 weight percentages can cause a significant decrease in the growth and adhesion of Candida.

 Zirconium oxide nanoparticles have high strength and transparency to light and have been used in dentistry in dental restorations, production of high glass fillers, and improving the material's resistance to mechanical impact. The aim of this study was to investigate the effect of zirconium oxide nanoparticles on the fracture strength of heat-cured acrylic resin.

 This laboratory experimental study was conducted in the laboratory of the Faculty of Dentistry of Khorasan Azad University and Dr. Mousavi Research Center of Isfahan University during the spring and summer of 2018, 90 samples (22 × 10 × 2.5) were made using wooden blocks to make acrylic samples. After flasking, the samples were divided into 3 equal groups. In the first group no powder of zirconium oxide was added. In the second group, 2.5% by weight of zirconium oxide and in the third group 7.5% by weight of zirconium oxide were added to the mixture. Then, the fracture strength of the samples was evaluating using a universal testing machine and 3-point bending test. The data were analyzed using ANOVA one-way and Tukey's test (α = 0.05)

 There was a significant difference (p value < 0.001) between the mean fracture strength of heat cured acrylic resin samples in the three studied groups (p value < 0.001). The lowest mean fracture strength was observed in the group with 7.5 % weight of zirconia.

 The average strength to failure of heat-cured acrylic is reduced by adding zirconia oxide.

Teledentistry is a valuable tool, which can be used in various dental specialties for the benefit of both patients and doctors. This study was conducted in Isfahan to determine the level of knowledge and attitude of general dentists regarding teledentistry .

A total of 96 general dentists from Isfahan City participated in this cross-sectional study. Each dentist was given a questionnaire to assess their level of knowledge and attitude regarding teledentistry. The questionnaire consisted of three sections which included general professional information, questions related to knowledge, and questions related to attitude. The collected data were analyzed using Pearson and Mann-Whitney statistical tests (α=0.05).

The results of the study showed that 56 women (58.3 percent) and 40 men (41.7 percent) with an average age of 28.20±2.38 years and an average working experience in dentistry of 3.30±2.10 years, participated in the study. In regards to knowledge about teledentistry, 62 people (64.6%) did not know, and 34 people (35.4%) had some knowledge. The level of knowledge of general dentists regarding teledentistry was moderate and unrelated to age, gender, and work experience (p>0.05). Also, the level of attitude of general dentists regarding teledentistry was moderate and was not related to participants 'age, gender, and work experience (p>0.05).

This study revealed that the knowledge and attitude of many general dentists toward teledentistry is moderate. Therefore, more training is necessary to create awareness among dentists regarding remote dentistry.

The use of cyberspace and social media has increased in recent years and has been applied to improve the health of people in society. A study was conducted to determine the attitude of people in Isfahan towards the use of these platforms in the field of dentistry.

This cross-sectional study involved 257 randomly selected participants from three groups based on age and education level in each of Isfahan's 15 districts. The questionnaire used in the study was divided into two parts: general information and attitude-related questions. To analyze the data, Student's t-test, Chi-square, Friedman, and Kruskal-Wallis tests were used (α=0.05).

The study in Isfahan showed high use of cyberspace in dentistry, especially by women, young adults (16-35 years), and those with higher education. Users mainly seek dental information and select a dentist, with a significant relation to age (p<0.001), gender (p=0.048) and level of education (p=0.001) Positive online comments and reviews were more important for young adults (16-35years old )(p<0.001)  and have no significant relationship with gender and education (p>0.05).

In conclusion the people of Isfahan had a positive attitude towards using cyberspace and social media in. Age, gender, and level of education can affect the use of cyberspace for health training, and selection of type and place of treatment.

Fracture is the most common reason for the failure of provisional restorations. This study aimed to assess the effects of the fabrication method (conventional, computer‑aided design/ computer‑aided manufacturing [CAD/CAM] milling, three‑dimensional [3D] printing) and material type on the fracture strength of provisional restorations.

In this in vitro study, 60 provisional restorations were made through the conventional (Tempron and Master Dent), CAD/CAM milling (Ceramill and breCAM.HIPC) and 3D Printing (3D Max Temp) methods based on a scanned master model. The provisional restorations were designed by the CAD unit and fabricated with milling or 3D printing. Then, an index was made based on the CAD/CAM milling specimen and used for fabricating manual provisional restorations. To assess the fracture resistance, a standard force was applied by a universal testing machine until the fracture occurred. One‑way ANOVA and Tukey’s test were used to compare the groups (α = 0.05).

The mean fracture strength was significantly different among the five groups (P < 0.001), being significantly higher in the breCAM.HIPC group (P < 0.001), followed by the Tempron group (P < 0.05). However, the three other groups were not significantly different (P < 0.05).

Despite the statistical superiority of some bis‑acrylics over methacrylate resins, the results are material specific rather than category specific. Besides, the material type and properties might be more determined than the manufacturing method.

Marginal fit is a key factor in success of prosthetic restorations. This study aimed to assess and compare the marginal fit of endocrowns fabricated by three‑dimensional (3D) printing and the conventional method.

This in vitro, experimental study evaluated 20 endocrowns, of which 10 were fabricated by 3D printing and 10 were fabricated by the conventional wax‑up technique. The marginal gap was measured at 8 points under a stereomicroscope. The results were analyzed using the Shapiro–Wilk test, paired t‑test, independent t‑test, and one‑way analysis of variance (α = 0.05).

The mean marginal gap was maximum at the distal point, and minimum at the buccal point for the conventionally fabricated endocrowns with an overall mean marginal gap of 99.67 ± 4.59 µm. The mean marginal gap was maximum at the mesiobuccal and minimum at the buccal point before pressing (overall mean of 103.92 ± 2.19 µm) before pressing, and maximum at the distobuccal and minimum at the mesiobuccal point after pressing (overall mean of 117.67 ± 2.87 µm). According to paired t‑test, the mean marginal gap of endocrowns fabricated by 3D printing significantly increased after pressing at all 8 points and also in general, compared with before pressing (P < 0.001). Furthermore, the mean marginal gap at all points was significantly greater in endocrowns fabricated by 3D printing compared with those fabricated by the conventional method (independent t‑test, P < 0.001).

Within the limitations of this in vitro study, the results showed that endocrowns fabricated by the conventional method had significantly superior marginal fit than those fabricated by 3D printing.

Given the surge in the restoration of infrastructures with zirconia and sintron and the use of different porcelain on them and the lack studies on marginal adaptation in different situations, this study aimed to evaluate the marginal gap before and after porcelain firing.

This cross sectional experimental laboratory research was performed in 2019 in the Transgenesis research center, Isfahan (Khorasgan) Branch, Islamic Azad University, where 40 abutments were divided into two groups of 20 with two types of substructures (zirconia and soft presintered chrome-cobalt alloy (Syntron) AmannGirrbach, Koblach, Austria)) then ,each group was subdivided into two porcelain subgroup of ten (noritake and creation).Marginal gap was evaluated by stereomicroscope before and after porcelain firing .Data was gathered and analyzed by means of one way and two-way ANOVA (α = 0.05).

The difference observed between marginal gap in studied groups was statistically significant (p value < 0.05). But marginal gap in respect to the type of porcelain did not show a significant difference between the groups (p value = 0.214). The lowest amount of change after firing with porcelain was related to the Syntron substructure group with Noritake porcelain, which was significantly different from the two zirconia frame groups (p value = 0.045), (p value = 0.006).

In this research after porcelain firing, sintron showed better results compared to zirconia regardless of porcelain type.

Metals are widely used in direct and indirect restorative materials, both in prosthetics and orthodontics. The biocompatibility of these metals depends on their chemical nature, the number of ions released, and the period of contact of these metals. This study aims to compare two different electropolish temperatures on the release of cobalt ion from chromium-cobalt alloy.

In this experimental study, 24 wax patterns were cut in the form of a circle with a diameter of 15 mm and a thickness of 1 mm. Then, the samples were sprued and invested. Burn out and casting were used to cast the alloy. The samples were sandblasted and polished with aluminum oxide. They were randomly divided into two 12-number groups and electropolished at 45° and 55° C. Samples were placed in artificial saliva and sent to atomic absorption spectrophotometer for 15 and 30 days to read the cobalt. Data were then analyzed by Independent t-test and Paired t-test (p value = 0.05).

The average release of cobalt from chromium cobalt alloy on the 30th day was higher than the 15th day at both 45° C and 55° C. This difference was significant at 45° C (p value = 0.036) while not significant at 55 ° C (p value = 0.0754). Regarding the comparison of the ion release at 45 ° and 55° C, the difference was not significant on the 15th day (p value = 0.067) and 30th day (p value = 0.0754).

The amount of cobalt ions released from the cobalt-chromium alloy at 45° C is fewer than at 55° C over time.

In recent years, using metal alloys has been expanding in dentistry, especially in dentures. Further research is needed on ion release in these alloys considering the potential harm to human health.
A total of 20 disk-shaped samples and two acidic environments with pH of 4.2 and 6.5 were used in the present study. Half of the samples without simulation of porcelain firing and the other half after the simulation were incubated for 7 days at 37 ° C in a closed sterile centrifuge tube containing 7.5 ml of acidic solution with pH of 4.2 and 6.5. Finally, the solution was analyzed by spectroscopic method to evaluate the amount of ions released from the Cintron alloy. The results were analyzed using ANOVA by SPSS software.
In the samples placed in solutions with pH of 4.2 and 6.5, the amount of released ions after firing was significantly higher than that without the firing process. Furthermore, the amount of released ions in a solution with a pH of 6.5 is significantly less than that in pH of 4.2 in samples without firing simulation. However, the amount of released ions in a solution with a pH of 6.5 is significantly higher than that in pH of 4.2 in the samples after firing.
The results demonstrate that porcelain firing changes the nature of alloys leading to the release of more chromium, cobalt, and molybdenum ions. Also, increasing the acidity of the environment before firing causes more ions to be released, while after firing, the ions are released less in a more acidic environment.

Statement of the Problem: 

Success of metal-ceramic restorations depends on the bond strength between porcelain and alloy. These restorations can be fabricated through different casting and computer-aided design/compute-aided manufacturing (CAD-CAM) techniques.

This study aimed to compare the bond strength of porcelain to milled sintered (Sintron) and casting (Co-Cr and Ni-Cr) base metal alloys.

In this in-vitro experimental study, 63 rectangular bars (25×3×0.5 mm) were fabricated of three base metal alloys: casting Ni-Cr, casting Co-Cr, and milled sintered Co-Cr alloy. Feldspathic porcelain (3×8 mm) was applied at the center of each bar with 1.5 mm thickness. The specimens were thermally aged. Bond strength was evaluated through three-point flexural test. Failure mode was evaluated by optical and electron microscope. Data were analyzed with one-way ANOVA and Tukey's post hoc test (α=0.05).

The mean flexural bond strength of porcelain to milled sintered Co-Cr alloy (24.58±5.16 MPa) was significantly higher than that of casting Ni-Cr (21.13±6.34 MPa) (p = 0.03) and casting Co-Cr (20.98±4.84 MPa) alloys (p = 0.04). However, the two casting alloys were not significantly different in this regard (p = 0.93). Failure mode in all specimens was of cohesive type.

Bond strength of CAD-CAM milled sintered Co-Cr alloy was better than that of the conventional casting alloys and can serve as a suitable alternative to those alloys.

 Fracture of the denture base and its repair are one of the main concerns of patients with a complete denture. This is often due to patients’ carelessness in maintaining dentures, or a low strength and resistance of the acrylic resin. This study aimed to compare the fracture resistance of heat-cured, self-cured, and injectable acrylic resins using a three-point flexural test.

 In this experimental study, 30 blocks of acrylic resin (Ivoclar VivaDent-Liechtenstein), measuring 2.5×25×50were prepared with three methods of heat-cured¸ self-cured, and injection. The samples were incubated for 24 hours to simulate the oral conditions. The samples were then subjected to three-point flexural testing in a universal testing machine. The force required for the failure of the samples was measured, and the results were compared and analyzed using Kruskal-Wallis and Wilcoxon tests with SPSS 22 (α = 0.05).

 Among the three samples, the fracture resistance of the self-cured acrylic resin was the lowest, and the fracture resistance of the injected acrylic resin was the highest. The differences in fracture resistance between the acrylic resins were significant (p value < 0.001).

 Since the injected acrylic resin exhibited the highest fracture resistance, it is more appropriate for the fabrication of fracture-resistant dentures.

Soldering has several applications in prosthodontic treatments; however, the effect of soldering on porcelain to metal bond strength has not been adequately studied. This study was designed to assess the bond strength of porcelain to metal, and the mode of failure at the soldered and non-soldered areas of cubic specimens.

In this in vitro, experimental study, 40 porcelain-metal specimens were fabricated under similar conditions and divided into two groups (n=20). In the test group, a hole was created at the center of the frame and was then soldered and veneered with porcelain. The second group was considered as a control group. The bond strength was measured at the center of the specimen using the 3-point bending test in a universal testing machine with a crosshead speed of 0.5 mm/min. The mean force required for debonding was determined. Photographs of the specimens were digitalized by a scanner and magnified on a computer screen with x10.5 magnification. Next, each image was divided into 100 squares (1×1 mm). The mode of failure was determined for each specimen. The two groups were compared using independent t-test (p-value˂ 0.05).

The mean porcelain-metal bond strength was 36.6±7.3 N for the soldered and 37.4±4.6 N for the non-soldered group with no significant difference between them (P>0.05). The mode of failure was cohesive in all specimens in both groups with no significant difference between them (P>0.05).

Within the limitations of this study, the soldered and non-soldered specimens showed no significant difference regarding the porcelain-metal bond strength.

All dental alloys release some elements into the oral cavity which may have negative effects on body cells. The purpose of the present study was to evaluate the effects of base metal and noble alloys on the survival rate of human gingival fibroblasts.

For the purposes of the study, fibroblasts were isolated from healthy human gingival tissue during crown lengthening surgery. In the third passage, fibroblasts were exposed to different concentrations of two base metal alloys (i.e., VeraBond 2, Commend) and two noble alloys (i.e., Degubond 4, Pal Kermit 2). To ensure the repeatability of the results, at least six samples of each material were prepared (n=18) and the survival rate of fibroblasts was evaluated using the MTT assay after 9 and 15 days. The collected data were statistically analyzed in SPSS software (version 20) using the ANOVA test.

According to the findings, the alloy type, alloy concentration, and the duration affected the remaining-cell ratio. The most and least remaining cells were observed in the presence of Degubond 4 and VeraBond 2 alloys, respectively. Moreover, the average percentage of the remaining cells at the concentration of 20 was significantly more than that at the concentration of 60 which was, in turn, more than that at the concentration of 100. Besides, the average percentage of the remaining cells in Degubond 4 and Commend on day 9 of the research was significantly more than that on day 15. Furthermore, no significant difference was observed in Pal Kermit 2 and VeraBond 2 on days 9 and 15 of the research.

VeraBond 2 base metal alloy decreases the survival rate of fibroblasts, based on the concentration, significantly more than the other alloys. Degubond 4 noble alloy has significantly the lowest negative effect on the survival rate of fibroblasts. Therefore, given the average percentage of the remaining cells, VeraBond 2 alloy has mild toxicity, and the other ones are biocompatible.

The study’s purpose was to study buccal pouch grafting (BPG) with xenograft, freeze‑dried bone allograft (FDBA), or FDBA + decalcified FDBA (DFDBA) on alveolar ridge width preservation and overlying soft tissue thickness at dog premolar extraction sites.

In this animal study, 4 dogs had their mandibular first premolar (P1) and distal roots of P2, P3, and P4 extracted (after endodontic treatment of the mesial roots) bilaterally. A small buccal pouch was created at each extraction socket and four treatments tested: nothing, xenograft, FDBA, or FDBA + DFDBA. Casts made pretreatment and at 1 and 3 months after treatment allowed measurements of buccolingual alveolar ridge width (BLRW), while overlying buccal soft tissue thicknesses were measured clinically. Data were assessed using analysis of variance to compare changes in soft tissue thickness and BLRW between times and treatments. Tukey–Kramer adjustment for multiple comparisons was applied for doing post hoc, pairwise comparisons. Results were considered significant if P < 0.05.

Control sites showed significant (P = 0.0067) decreases in soft tissue thickness over time while there was a trend for increased soft tissue thickness at all grafted sites. There were significant losses in BLRW over time for control (P = 0.0032) and FDBA groups (P = 0.015) with a trend for loss with FDBA + DFDBA. Pairwise comparison using Tukey–Kramer adjustment revealed significant increases in BLRW from T1 to T3 for the xenograft group relative to all the others.

BPG using xenograft is effective in maintaining hard and soft tissue stability following tooth extraction.

Short implants are used in the posterior mandible where the bone is insufficient. In these cases, the clinical crown is often made to match the level of the occlusal. As a result, the length of the lever arm and the stress of the implant complex, as well as the surrounding bone, are increased leading to the biomechanical problems. The purpose of this study was to evaluate dynamically the effect of increasing crown height space on the maximum stress induced in the abutment screw and the surrounding bone of the short dental implants in the posterior mandible using finite element analysis. Mandibular bone resorption in the posterior region, second premolar with three-crown lengths of 8.8, 11.2, and 13.6, two implants of 4 and 8 mm, two abutments, and two abutment screws were modeled using Solidworks software in this laboratory experimental study. In addition, Abacus software was used to the dynamic reconstruction of screw tightening and external load at an angle of 75.8 degrees with the occlusal plane. The stress values were calculated for the screw, abutment, fixture, and bone. In both 4- and 8-mm implants, the increased vertical height of the crown decreased the stress on the abutment screw and increased the stress on the abutment and fixture. For a 4-mm implant, the stress to the abutment screw at all three heights was less than 8 mm. At all heights, the stress values to the abutment and the fixture were more than 8mm for the 4-mm implant. The increased vertical height of the crown resulted in an increase in compressive and tensile stress in the surrounding bone for both 4-mm and 8-mm implants. The magnitude of these stresses in the 4-mm implant was more than 8 mm.   Increased vertical height of the crown and crown-to-implant ratio reduced the stress on abutment screws as the weakest member of the implant. However, it probably increased the failure due to fatigue in the abutment and fixture as well as bone resorption.

Candidiasis is the most common fungal infection in oral cavity, usually caused by Candida albicans. Since one of the most common complications of denture wearing is denture stomatitis, presence of opportunistic microorganisms such as C. albicans and colonization of denture base by these microorganisms, the aim of this study was to compare the effects of three different methods of acrylic resin processing on adherence and colonization of C. albicans. In this experimental study, 60 square acrylic resin samples, measuring 10×10×10 mm3 (Ivoclar Vivadent, Liechtenstein) were processed with three methods of preparation: cold-cured [CC], heat-cured [HC] and injection-molded [IM]. Yeast suspensions were incubated on the surface of resin blocks for 40 minutes and then washed with 1 mL of sterile saline solution; 20 µL of this solution were inoculated on Sabouraud dextrose agar and incubated at 37 C. The colony counts were determined after 24 and 48 hours. At 60- and 120-minute intervals the colony counts were determined again. Data were analyzed with SPSS 20, using two-way ANOVA and paired t-test (α = 0.05). The method of preparation of acrylic resin (p value = 0.001) and duration of proximity of acrylic resin with the yeasts (p value < 0.001) were significant. The lowest colony counts were observed in the cold-cured method. In all these three methods and durations of proximity of acrylic resin and C. albicans, the colony counts at 48 hours were significantly higher than those at 24 hours (p value < 0.001). The acrylic resin preparation method affected the adhesion and colonization of C. albicans. Considering the lower colonization in cold-cured acrylic resin, it is the most appropriate acrylic resin, especially for those with poor oral hygiene or those susceptible to fungal infections.

  One of the important factors in the success of implant-supported prostheses is the marginal fit of abutment-restorations. The aim of this study was to evaluate the effect of screw access channel filling method and cement type on the marginal adaptation of implant-supported fixed restorations. One of the important factors in the success of implant-supported prostheses is the marginal fit of abutment-restorations. The aim of this study was to evaluate the effect of screw access channel filling method and cement type on the marginal adaptation of implant-supported fixed restorations. In this experimental in vitro study, 40 implant analogs were mounted in autopolymerizing acrylic resin blocks using a dental surveyor. Forty two piece titanium abutments were placed in each implant analog and torque up to 35 N cm. The following acrylic blocks of implants were randomly divided into 2 groups, including 20 abutment samples fully filled by the silicone, and 20 abutments sample filled partially with silicon. The marginal discrepancy of samples was measured from 4 sides with a magnification of ×50 by stereomicroscope before final cementation. In each study group, 10 samples were cemented by zinc-oxide eugenol temporary cement and 10 other samples with zinc-oxide non-eugenol temporary cement. The marginal discrepancy was measured at the same points again. Data were analyzed with ANOVA and, t-test (α=0.05). In all surfaces there were no significant differences in the mean marginal discrepancy between the group in which screw access channels were partially filled and the group in which screw access channels were completely filled before (P˃0.05)and after (P=0.052) cementation. However after cementation significant differences were found between the means of marginal discrepancy in two cement types (P=0.02). Non-eugenol cement showed significantly higher marginal discrepancy than eugenol cement (P=0.03). The mean marginal discrepancy in both full and partial access cavity filling groups did not differ significantly, but a marginal discrepancy with the use of non-eugenol cement was greater than eugenol cement

Metal-ceramic restorations have been commonly used in dentistry. These restorations have both the esthetics of porcelain and the strength and durability of metal. Noble alloys and base-metal alloys are usually used for metal-ceramic restorations. Applications of base-metal alloys has been developed because of economic consider-ations, mechanical properties and low density. Remelting of used alloys is a common way in dental labs to reduce the costs of fixed prostheses. Few studies have been performed on the effect of recasting alloys on the metal-ceramic bond strength. The purpose of this study was to evaluate the effect of commond alloy recasting on metal- ceramic bond strength.
In this laboratory – experimental study, 23 waxed patterns in the size of 0.5 325 millimeter were cut with bisturi blade. Wax patterns were sprued, burned out and casted with commend alloy. The second group has the same method although they consisted of equal amount of fresh alloy and alloy remnants cast only once, the third and fourth group contained 50% fresh alloy and 50% used alloy of last group. After sandblasting, grinding and surface preparation, porcelain application was done with Noritake porcelain .samples fractured with 3-point bending test by Universal Testing machine at the speed of 0.5 mm per minute. Finally, the results were analyzed by ANOVA (p value = 0.007).
The results indicate that the highest mean values of fracture strength of porcelain to metal was in the first group (30.9 N) and then squencely in the group 3 (28.7 N), group 2 (26.8) and group 4 (24.3 N).There is a significant difference between group 1 and 2 (p value = 0.03), group 1 and 4 (p value = 0.001) and group 3 and 4 (p value = 0.02). There was no significant difference between group 1, 3 (p value = 0.26), group 2 and 3 (p value = 0.3) and group 2 and 4 (p value = 0.18).
Recasting of base metal alloys statistically decrease the bond strength of porcelain to metal.

There is limited data on the factors affecting the retention of cemented fixed prostheses to implant abutment. The aim of this study was to evaluate the effect of screw access channel filling method and cement type on retention of implant-supported fixed restorations.
In this experimental study, 40 implant analogs were mounted in autopolymerizing acrylic resin blocks, and two-piece titanium abutments were placed in each implant analog. Twenty abutment samples were completely filled with silicone, and 20 other samples were filled partially. In each of the study groups, Temp Bond® eugenol-containing temporary cement was used for 10 samples, while in another 10 samples non-eugenol temporary cements were utilized. Prior to the retention test, samples were placed in the rmocycling machine with 1000 cycles for 24 h. Each sample was stretched using a Universal Pull-out Test Machine with a force of 5000 N. The required load for removing the crown was recorded. The data was analyzed USING two-way ANOVA and least square difference (α=0.05).
Among the four groups, the highest retention rate was observed in the group of partial screw access channel filling with eugenol cement. Also, the rate of retention in the group of complete screw access channel filling with non-eugenol cement was significantly lower than in any other group. A significant difference was observed between all the groups except for the groups of complete screw access channel filling with eugenol cement and partial screw access channel filling with non-eugenol cement (P=0.27).
The mean rate of retention in partial access cavity filling group was greater than that of the complete access cavity filling group; moreover, this rate was higher in the eugenol cement group than the non-eugenol cement group.

Different methods and materials are available for post and core (P&C) fabrication. We aimed to compare the fracture resistance and failure modes of endodontically treated maxillary central incisors restored with six different P&C systems.
In this in-vitro study, after endodontic treatment and coronal preparation of 60 maxillary central incisors, six different P&C systems were used: 1) cast base metal P&C, 2) cast gold alloy P&C, 3) zirconia post and casting ceramic core, 4) zirconia post and composite core, 5) titanium post and composite core, and 6) fiber post and composite core. Thermocycling (5-55°C, 60 seconds, 1500 cycles) was performed after cementing the full metal crowns on each tooth. A 130° force was ap-plied at a crosshead speed of 1.5 mm/minute in a universal testing machine. The frac-ture force (N) and fracture patterns were recorded. Data were statistically analyzed by using Kruskal-Wallis, Mann-U-Whitney, and Fisher’s exact tests (α=0.05).
The highest mean fracture resistance was recorded in the first group (904±302.77 N) followed by the third group (725±202.11 N), second group (723±224.15 N), fourth group (675±358.64 N), fifth group (424±156.85 N), and sixth group (416.5±81.58 N). The groups with casting P&Cs and zirconia post and casting core showed significant differences with the other two groups with non-casting cores (P The highest fracture resistance was recorded for cast metal P&C, which may be due to a better stress distribution. Zirconia post and ceramic core may be a proper and aesthetically appealing substitute for cast metal P&C.

A limited number of studies have evaluated factors influencing the retention of fixed prostheses cemented to implant abutments. The aim of this study was to compare the effect of varying degrees of screw access channel obturation on retention of implant-supported cast fixed restorations.
In this experimental study, 40 implant abutments with a diameter of 4.5 mm were connected to implant analogues and mounted in acrylic resin blocks. The samples were divided into four groups randomly. In groups 1, 2 and 3, the access channels were obturated with a 1-mm, 2-mm and 3-mm free space and in group 4 the access channels were obturated completely with silicone material and the copings were cemented with a temporary bonding agent containing eugenol. After thermocycling, the retention of the samples was evaluated in a universal testing machine under 5000 N at a strain rate of 5 mm/min. Data were analyzed with one-way ANOVA and post hoc LSD test (α = 0.05).
The mean retention for the group with abutment access channel completely obturated was less than that in others. One-way ANOVA showed statistically significant differences between the groups (p value = 0.032). The difference between the group with completely obturated access channels and the other groups was significant (p value 0.05).
The retention of castings cemented to implant abutments might be influenced by the obturation mode of screw access channel. Complete obturation of access channel with poly vinyl siloxane results in a decrease in retention.

Presence of keratinized tissue around implants for maintaining peri-implant health and their long term stability has been a controversial issue. The aim of this study is to assess the correlation between the width of keratinized tissue and periodontal indices around implant-supporting fixed partial dentures.
In this cross-sectional study, 90 pateints who had implant-supported fixed partial dentures were divided into three groups with 30 patients in each one. Based on type of their prostheses it would be single crown, bridge or splinted. Peri-implant examinations were accomplished by means of measuring the width of keratinized mucosa (KM), the width of attached mucosa (AM), probing depth (PD), bleeding on probing (BOP), gingival recession (GR), gingival index (GI), and plaque index (PI) and collar metal show. The data was analyzed by Pearson & Spearman correlation test by SPSS20 software.
There was significant relationship between KM and AM in all groups (P With limitations of this study, it can be concluded that increasing the width of keratinized and attached mucosa is not necessarily associated with objective peri-implant health.

One of the most common problems in metal ceramic restorations is the loss of porcelain‒metal bond. The aim of this study was to evaluate the bond strength of two porcelain types to base metal alloy after different surface treatments. In this experimental research, 64 wax sheets were selected and after casting with base metal alloy were randomly divided into 8 groups. Surface treatment in each group was randomly accomplished by one of the four different methods to improve metal‒porcelain bonding. After surface treatment, porcelain application was carried out with Ceramco porcelain in half of the samples and Noritake porcelain in the remaining half. All the samples underwent 3-point bending test and the force at failure of each sample was recorded. Kruskal-Wallis test was used to compare 4 surface preparation techniques in the two porcelain groups and Mann-Whitney test was used to compare Ceramco and Noritake porcelains (α=0.05). There were significant differences between the means of four methods of surface treatment in Ceramco porcelain (p value = 0.022); there were significant differences between the four methods of surface treatment in Noratike porcelain (p value = 0.012). There were no significant differences between the two porcelain group (p value = 0.412). In this study, degassing increased the metal‒ceramic bond strength and steam- cleaning before degassing decreased it. There were no significant differences in the bond strength of the two types of porcelain with different surface treatments of base metal alloy.