ABSTRACT
Statement of the Problem: Considering the limitations of conventional sintering of zirconium oxide [ZrO[2]] copings, shortening the sintering time can be proposed as an alternative method for making the copings
Purpose: This study aimed to assess the effects of sintering time on compressive strength of Yttria Tetragonal Zirconia Polycrystal [Y-TZP] copings
Materials and Method: Thirty copings of pre-sintered 3Y-TZP blanks were milled and sintered in a special furnace for three different durations [n=10 per group]. The sintering time was 1 h 15 min for IPS e.max ZirCAD, 4 h 20 min for Speed ZrO[2], and 7 h 20 min for the conventional ZrO2 group. The specimens were cemented on the brass dies by using conventional glass ionomer cement. The copings were verti-cally loaded until fracture by using a universal testing machine. The data were ana-lyzed through one-way analysis of variance [ANOVA] and post hoc test to compare the mean differences of compressive strength yielded in three study groups [Alpha=0.05]
Results: The mean +/- SD of compressive strength value was [3617 +/- 543.54] N for IPS-e.maxZirCAD group, [2663 +/- 508.11] N for Speed ZrO2 group, and [1662 +/- 466.71 N] for conventional ZrO2 group. There were statistically significant differ-ences among compressive strength values of the tested groups [p< 0.05]. The highest compressive strength values were obtained from the IPS e.max ZirCAD group
Conclusion: Within the limitations of this in vitro study, it can be concluded that compressive strength of the zirconia copings is affected by the sintering time. High compressive strength of zirconia copings can be obtained by shortening the sintering time
ABSTRACT
Statement of the Problem: Structural integrity and dimensional stability are the key factors that determine the clinical success and durability of luting cements in the oral cavity. Sorption and solubility of self-adhesive resin luting cements in food-simulating solutions has not been studied sufficiently
Purpose: This study aimed to compare the sorption and solubility of 2 conventional and 2 self-adhesive resin-based luting cements immersed in four different storage media
Materials and Method: A total of 32 disc-shaped specimens were prepared from each of four resin luting cements; seT [SDI], Panavia F [Kuraray], Clearfil SA Cement [Kuraray], and Choice 2 [Bisco]. Eight specimens of each material were immersed in all tested solutions including n-heptane 97%, distilled water, apple juice, or Listerine mouth wash. Sorption and solubility were measured by weighing the specimens before and after immersion and desiccation. Data were analyzed by SPSS version 18, using two-way ANOVA and Tukey's HSD test with p
Results: There was a statistically significant interaction between the materials and solutions. The effect of media on the sorption and solubility was material-dependent. While seT showed the highest values of the sorption in almost all solutions, Choice 2 showed the least values of sorption and solubility. Immersion in apple juice caused more sorption than other solutions [p
Conclusion: The sorption and solubility behavior of the studied cements were significantly affected by their composition and the storage media. The more hydrophobic materials with higher filler content like Choice 2 resin cement showed the least sorption and solubility. Due to their lower sorption and solubility, these types of resin-based luting cements are recommended to be used clinically
ABSTRACT
Statement of the Problem: Marginal fitness is the most important criteria for evaluation of the clinical acceptability of a cast restoration. Marginal gap which is due to cement solubility and plaque retention is potentially detrimental to both tooth and periodontal tissues
Purpose: This in vitro study aimed to evaluate the marginal and internal fit of cobaltchromium [Co-Cr] copings fabricated by two different CAD/CAM systems: [CAD/milling and CAD/ Ceramill Sintron]
Materials and Method: We prepared one machined standard stainless steel master model with following dimensions: 7 mm height, 5mm diameter, 90[degree] shoulder marginal finish line with 1 mm width, 10[degree] convergence angle and anti-rotational surface on the buccal aspect of the die. There were 10 copings produced from hard presintered Co-Cr blocks according to CAD/ Milling technique and ten copings from soft non- presintered Co-Cr blocks according to CAD/ Ceramill Sintron technique. Marginal and internal accuracies of copings were documented by the replica technique. Replicas were examined at ten reference points under a digital microscope [230X]. The Student's ttest was used for statistical analysis. p< 0.001 was considered significant
Results: Statistically significant differences existed between the groups [p< 0.001]. The CAD/milling group [hard copings] had a mean marginal discrepancy [MD] of 104 micro m, axial discrepancy [AD] of 23 micro m and occlusal discrepancy of 130 micro m. For CAD/Ceramill Sintron group, these values were 195 micro m [MD], 46 micro m [AD], and 232 micro m [OD]. Internal total discrepancy [ITD] for the CAD/milling group was 77 micro m, whereas for the CAD/Ceramill Sintron group was 143 micro m
Conclusion: Hard presintered Co-Cr copings had significantly higher marginal and internal accuracies compared to the soft non-presintered copings
ABSTRACT
Statement of the Problem: Although all-ceramic restorations are broadly used, there is a lack of information concerning how their fit is affected by fabrication procedure and marginal configuration
Purpose: The purpose of this study was to evaluate the marginal fit of zirconia CAD/CAM ceramic crowns before and after porcelain firing. The influence of finish line configuration on the marginal fit was also evaluated
Materials and Method: Twenty standardized zirconia CAD/CAM copings were fabricated for chamfer and shoulder finish line designs [n=10]. The marginal fit of specimens was measured on 18 points, marked on the master metal die by using a digital microscope. After the crowns were finalized by porcelain veneering, the measurements of marginal fit were performed again. The means and standard deviations were calculated and data were analyzed using student's t-test and paired t-test [alpha=0.05]
Results: There were significant differences between marginal fit of chamfer and shoulder finish line groups before and after porcelain firing [p= 0.014 and p= 0.000, respectively]. The marginal gap of copings with shoulder finish line was significantly smaller than those with chamfer configuration [p= 0.000], but there were no significant differences between the two marginal designs, after porcelain firing [p= 0.341]
Conclusion: Porcelain veneering was found to have a statistically significant influence on the marginal fit of zirconia CAD/CAM crowns. Both margin configurations showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy
ABSTRACT
The purpose of this article was to review the biocompatibility, physical, and mechanical properties of the polyamide denture base materials. An electronic search of scientific papers from 1990-2014 was carried out using PubMed, Scopus and Wiley Inter Science engines using the search terms "nylon denture base" and "polyamide denture base". Searching the key words yielded a total of 82 articles. By application of inclusion criteria, the obtained results were further reduced to 24 citations recruited in this review. Several studies have evaluated various properties of polyamide [nylon] denture base materials. According to the results of the studies, currently, thermo-injectable, high impact, flexible or semi-flexible polyamide is thought to be an alternative to the conventional acrylic resins due to its esthetic and functional characteristics and physicochemical qualities. It would be justifiable to use this material for denture fabrication in some cases such as severe soft/ hard tissue undercuts, unexplained repeated fracture of denture, in aesthetic-concerned patients, those who have allergy to other denture base materials, and in patients with microstomia. Although polyamide has some attractive advantages, they require modifications to produce consistently better properties than the current polymethyl methacrylate [PMMA] materials. Moreover, since there is a very limited knowledge about their clinical performance, strict and careful follow-up evaluation of the patients rehabilitated with polyamide prosthesis is recommended
ABSTRACT
PURPOSE: This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques). MATERIALS AND METHODS: Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (alpha=.05). RESULTS: Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (63.06 microm) was higher than press-over (50.64 microm) and CAD-on (51.50 microm) veneered groups (P<.001). CONCLUSION: Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CAD-on techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.
Subject(s)
Ceramics , Crowns , Dental PorcelainABSTRACT
Despite the high success rate, implant-supported prostheses fail in some cases. Control of the applied forces is an important factor determining the success or failure of implants. Comprehensive understanding of the biomechanical principles in implant-supported prostheses is necessary for offering an appropriate custom-made treatment plan for each patient and reducing the risk of functional complications. Finite element analysis is a quantitative method for the assessment of force distribution in complex structures. This study sought to compare the effect of different framework materials on stress distribution in bone supporting implants using three-dimensional finite element analysis. In this in-vitro study, a three-dimensional model of bone was obtained using Cone Beam Computerized Tomography [CBCT]. Using CATIA V5R20 [Dassault Systemes, France] software, a Nobel Replace tapered implant [Nobelpharma Co., Gothenburg, Sweden] measuring 13 mm in height and 4.3 mm in diameter was virtually inserted in the anterior maxilla. A titanium abutment, ZOE cement and superstructure with different frameworks [Ag-Pd, Ni-Cr, and fiber-reinforced composite] were designed. Force was applied in an amount of 178 N at three angulations of zero, 30 and 45° relative to the implant axis and the maximum von-Mises stress and maximum strain were calculated for cortical and trabecular bone. Changing the framework material caused a small change in level of stress and strain and their distribution pattern. By increasing the angulation of the applied force, amount of stress and strain in the implant-supporting bone increased. Maximum stress and strain were applied at 45° angulation. At zero degree angulation, maximum stress in the cortical bone was 17.326 MPa with Ni-Cr framework, 17.383 MPa with Ag-Pd and 17.321 MPa with fiber-reinforced composite. In loading at 30° angulation, maximum stress in the cortical bone was 136.95 MPa with Ni-Cr framework, 136.03 MPa with Ag-Pd framework and 136.18 MPa with fiber-reinforced composite framework. In loading at 45° angulation, maximum stress in the cortical bone was 161.37 MPa with Ni-Cr, 161.21 MPA with Ag-Pd and 160.4 MPawith fiber-reinforced frameworks. Different framework materials had no significant effect on the amount or distribution of stress in bone around implant