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Aims: Resistance form of full metal-ceramic crown is an important feature that determines longevity of these restorations. This study evaluated the resistance form of full metal-ceramic prepared with four different design features. Materials and Methods: An acrylic tooth was prepared with 20° total occlusal convergence (TOC) angle, 2.5 mm of occlusocervical dimension and a shoulder finishing line. This design lacked resistance form. The crown preparation was subsequently modified by preparing Mesial Occlusal Distal isthmus, placing occlusal inclined plane, and reducing TOC. Four metal dies from these designs were constructed by lathe machine and then 10 metal copings were fabricated for each preparation. Metal coping were cemented on metal dies with temp-bond cement. Force was applied at 45° from lingual to buccal direction with universal testing machine. Statistical analysis used: The data were evaluated by Kruskal-Wallis and non-parametric Mann-Whitney test. Results: All features increased resistance form when compare to control group. However, reduce TOC group showed greatest value of resistance. Conclusion: Within the limitation of this study, reducing the tapering of occlusocervival dimension is the most effective way in increasing resistance form, although, other features were also effective.

Aim: This study aimed to evaluate the marginal and internal discrepancy of nickel-chrome (Ni-Cr) copings made on implant bridges with conventional and 3D printing techniques., Materials and Methods: 30 three-unit Ni-Cr FDPs (60 copings) were made by 3D-printing technique (PolyJet group), lost-wax method with die spacer technique (die spacer group), and lost-wax method with burn-out the cap (burn-out cap group). Then, the frames obtained from the three methods were checked to examine the marginal discrepancy by stereomicroscope after preparation and polishing. The silicon replica method was used to investigate the internal discrepancy at 6 points (buccal portion of occlusal surface, lingual portion of occlusal surface, middle area of the axial surface in the lingual, middle area of the axial surface in the buccal, cervico-buccal area, and cervico-lingual area). Kolmogorov-Smirnov test was performed first to estimate the normality of data distribution. A one-way ANOVA and post hoc Tukey test were done for comparing marginal and internal discrepancies between groups. The significant level was considered p < 0.05., Results: The mean ± standard deviation of marginal discrepancy in the PolyJet group, die spacer group, and burn-out cap group was 37.9 ± 15, 68.8 ± 31.8 and 42.7 ± 3.6 µm for buccal margins and 40.4 ± 12.3, 64 ± 21.7, and 42.4 ± 2.1 µm for lingual margins, respectively. The means of buccal and lingual marginal discrepancy in the burn-out cap group and PolyJet group were significantly lower than the die spacer group ( p < 0.001). Marginal discrepancy was not statistically different between the burn-out cap group and the PolyJet group. The mean ± standard deviation of overall internal discrepancy in the PolyJet group, die spacer group, and burn-out cap group was 64.6 ± 3.7, 72 ± 22.2, and 58.7 ± 2 µm, respectively. There was a significant difference between the mean of internal discrepancy between three groups ( p = 0.001). The mean of internal discrepancy of the burn-out cap group was significantly lower than the die spacer group ( p = 0.001) and PolyJet group ( p = 0.005). Internal discrepancy was not significantly different between the PolyJet group and the die spacer group ( p = 0.168)., Conclusion: The marginal and internal gap rates of the three groups were within clinically acceptable limits. The 3D printing technique and lost-wax method with burn-out the cap had the lowest buccal and lingual marginal discrepancies. The burn-out cap method had better fitness and less internal discrepancy than 3D printing and die spacer groups., Clinical Significance: Lower marginal discrepancy of copings fabricated by using 3D printed patterns may improve clinical success of implant restoration. How to cite this article: Ziaei M, Bajoghli F, Sabouhi M, et al . Evaluating the Marginal and Internal Discrepancy of Nickel-Chrome Copings Made on Fixed Partial Denture Implants with Conventional and 3D Printing Techniques. J Contemp Dent Pract 2023;24(11):826-833.

Background: The temporary cement remaining inside the dental prosthesis can act as a source of microbial colonization and contamination and decrease the final cement retention. Consequently, complete removal of temporary cement before permanent cementation is suggested. This study aimed to assess the effect of different cleaning methods for removing temporary cement on the tensile bond force (TBF) of permanently cemented implant-supported zirconia copings., Materials and Methods: In this in vitro study fifty titanium abutments were screwed onto 50 analogs with 30 Ncm torque into in acrylic resin blocks. Each abutment was scanned separately, and 50 zirconia copings were designed and milled. Permanent resin cement was used to cement copings of control group ( N = 10). Copings were divided into two temporary cementation types that in each group, two cleansing methods were used: Temp-S (temporary cement with eugenol and sandblasted after debonding), Samples of the control group were placed in the universal testing machine, and the TBF values were recorded. Samples of the test groups after debonding and cleaning the abutments were subjected to cement with permanent resin cement, aging, and removing. Levene test, two-way analysis of variance (ANOVA), and Tamhane post hoc tests were applied. α = 0.05., Results: The highest and lowest TBF values were found for the TempNE-SU (554.7 ± 31.5 N) and Temp-S (492.2 ± 48 N) groups, respectively. The two groups of isopropyl alcohol baths in ultrasonics in combination with sandblasting showed statistically higher TBF values than the other two groups that used only sandblasting ( P < 0.001) and had similar values compared to the control group., Conclusion: Sandblasting combined with immersion in an ultrasonic bath containing isopropyl alcohol resulted in statistically similar values to the values of cementation with resin cement from the beginning. However, cleaning the inside of the copings only by sandblasting method reduced the values of the final retention force in comparison to cement with permanent resin cement from the beginning., Competing Interests: The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article., (Copyright: © 2023 Dental Research Journal.)

Aim: Abutment screw loosening of implant-supported prosthesis causes a mismatch between the abutment and the implant. This screw loosening is influenced by the implant-abutment connection type, however, with contradictory results reported in different studies. The present study evaluates the stability of abutment-implant connections in three different systems before and after the fatigue test., Settings and Design: Thirty implants (4.3 mm in diameter and 12 mm in length) were divided into three groups of 10: Implantium, Zimmer, and straight internal hexagonal connection (SIC) implants., Materials and Methods: Two torques of 35 Ncm with an interval of 10 min were applied, followed by measuring removal torque value (RTV). The samples were re-torqued and then underwent a simulation of 1-year chewing clinical performance of dental implant under axial force of 400 N, with a frequency of 8 Hz (one million cycles). After fatigue test, the RTV was calculated and recorded., Statistical Analysis: The mean RTVs obtained before and after cyclic load were analyzed by SPSS version 22 software using multivariate analysis., Results: Significant differences in RTV and role of cyclic loading were found between SIC and Implantium groups (P = 0.006 and 0.021, respectively), as well as between Zimmer and SIC groups (P = 0.032 and 0.006, respectively), but not between Zimmer and Implantium groups (P = 0.771 and 0.248, respectively)., Conclusion: The type of connection could affect the screw loosening, the preload loss, and the implant component stability. SIC group revealed the highest RTVs before and after cyclic loading., Competing Interests: None

Objectives:  Polymethyl methacrylate as the most common material used in denture bases has some problems. The aim of this study was to introduce a new nanocomposite of PMMA to improve flexural strength and antifungal properties., Materials and Methods:  In this experimental study, AgSiO 2 nanoparticles were prepared, and their characteristics were confirmed by scanning electron microscope and energy dispersive spectroscopy techniques. Then the nanoparticles in the weight ratio of 0.1, 0.3, 0.5, and 0.7% were incorporated to heat-cured PMMA and the control group included no nanoparticles.To measure the flexural strength before and after thermocycling three-point bending test was used. Eight samples per group with dimensions of 65 × 10 × 2.5 mm were used. Antifungal activity against Candida albicans (PTCC 5027) was investigated through colony count method. Statistical analysis was done by SPSS at significance level of p -value ≤0.05., Results:  The mean flexural strength in groups 0.1, 0.3, and 0.7% was significantly higher than the control. After thermocycling flexural strength of the control group was significantly lower than 0.3 and 0.5% groups. As the concentration of nanoparticles increased the antifungal activity improved ( p < 0.05)., Conclusion:  Addition of nanoparticles AgSiO 2 improved flexural strength and antifungal characteristics of PMMA., Competing Interests: None declared.M.S. was the supervisor of the project. H.D. made the nanoparticle and did the laboratory tests. F.B. was the advisor of project and edited the article. M.A.-P. made the sample and wrote the main text. R.M. was the advisor of project and did the microbial tests., (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/).)

The levels of Cd, Cr, Cu, Fe, Mn, Pb and Zn were determined in floor dusts from mechanical (MRWs) and battery repairing workshops (BRWs) in Yazd, Iran. The study aimed to evaluate the anthropogenic contribution to the presence of heavy metals (HMs), the possible sources and the related risks that could arise from occupational exposure in the studied workplace microenvironments. Among the analyzed heavy metals, Cu, Pb and Zn exhibited enhanced concentrations in the floor dusts. The EF calculations showed an extremely severe enrichment of HMs, especially for Cd, Cu and Pb, while floor dusts were characterized as "extremely polluted" with regards to those metals. In any case, both EF and I geo values were significantly higher in the BRWs. These results were also supported by NIPI and PLI values, while contour maps of PLI values in both MRWs and BRWs outlined workshops in N-NE part of Yazd as more impacted compared to other spatial locations. Principal component analysis (PCA) and Pearson's correlation outscored workshops activities as the principal sources of heavy metals. The health risk assessment suggested considerable non-carcinogenic risks regarding Pb in the BRWs which exhibited HQ ing (mean 2.91) and HI (mean 3.03) values higher than safe level. Regarding carcinogenic risks, CR values for both Cd and Cr were below the safe level (1.0 × 10 -6 ). The occupational exposure to Pb was evaluated through the predicted BLL values, where with averages of 3.33 μg/dl and 21.4 μg/dl for MRWs and BRWs workers, respectively, indicated a severe Pb exposure for BRWs workers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Introduction: The aim of this in vitro study was to evaluate the effect of the type and design of the impression copings on the accuracy of implant impressions in 2 different conditions., Materials and Methods: A reference model with 2 implants inserted in bilateral mandibular canines was fabricated. The posterior teeth were inserted as tilted to simulate intra-oral undercuts. The teeth were eliminated to create an edentulous condition. Three different impression techniques were performed (open high retentive [OH], open low retentive [OL], closed [C]) for each condition. Total of 48 casts were made. Two scan-bodies were secured on each cast, scanned by an optical scanner. Then, they were compared to the scan of the reference model, and the calculated mean errors were analyzed with a 2-way ANOVA and Tukey test., Results: There was no significant difference between the complete and partially edentulous groups (F = 3.252, P = 0.079). There was significant difference between the different designs of the impression copings (F = 31.789, P < 0.001) but the interaction between the dependent variables was not significant (F = 0.511, P = 0.603)., Conclusions: The design of the impression copings was more important than the undercuts. The accuracy of the closed tray coping was greater than the low retentive coping and equal to the high retentive coping.

Background: Dental instruments, like endodontic files, are hardly disinfected. The aim of this study was to evaluate the efficacy of mechanical, chemical, and ultrasonic (in combinations or separately) techniques for removing debris from files, prior to sterilization., Materials and Methods: Totally, 90 new endodontic files with size of 15, 25, and 40 (30 files of each one) were sterilized and one files of each one kept as negative control (NC) group. The rest of files (29 files of each size) were divided into five groups after endodontic therapies and prior to autoclaving: (Positive control [PC]: Without interventions, A: Cleaned with scouring sponge soaked in chlorhexidine 0.2%, B: Stored in Micro 10 enzyme, C: Subjected to Micro 10 enzyme in both conventional and ultrasonic way for 15 min, D: Decontaminated by Micro 10 enzyme with ultrasonic). Finally, the samples were observed under a metallographic microscope, and the data were analyzed by Tuckey, paired t-test, two-way ANOVA tests using SPSS software version 15 at a significant level of 0.05., Results: Significant differences were observed in heads of the files among groups C and PC (P = 0.02), and high amount of debris were seen in the shafts of groups A and D (P < 0.001). The amount of remaining debris were significant in the shafts of sizes 15 (P < 0.001) and 25 (P = 0.01)., Conclusion: Using Micro 10 in both ultrasonic and conventional methods were acceptable for removing debris from the files. Furthermore, higher amounts of debris were found in the shafts and heads of files with lower sizes (15 and 25).

Background: Marginal adaptation is very important in cast restorations. Maladaptation leads to plaque retention, reduction of mechanical and esthetic properties. The aim of this study was to evaluate the precision of three different impression materials (including: Additional silicone [AS] and condensational silicone [CS] and polyether [PE]) for duplicating master dies., Materials and Methods: Three master dies from an acrylic tooth model-with supragingival and shoulder finishing line was made by using PE: Impergum, CS: Speedex, and AS: Panasil separately. The Ni-Cr copings were prepared from master dies separately. They were placed on the acrylic model and the mean marginal difference was recorded by using a stereomicroscope. Then 30 duplicate test dies were made by using the same impression materials and the marginal gaps were recorded. The comparison was done by one-way ANOVA and SPSS software (Version 13) at a significant level of 0.05., Results: The mean marginal difference of four walls from Impergum (38.56 um) was the lowest than Speedex (38.92 um) and Panasil (38.24 um). The Impergum had the highest capability in making duplicate dies (P > 0.05)., Conclusion: The Impergum impression material manifested the highest capability in making a better marginal adaptation of duplicate dies but further studies are needed to make a precise decision.

Introduction : Post and core are needed to regain retentions and functions after endodontic therapies. Also, risk of cross contamination from dental prosthesis is so high. The aim of this study was to compare dimensional changes of acrylic resin patterns (ARP) in three different storing environments. Materials and methods : conventional root canal therapy was done on one first premolar tooth and the canal filled with Guttapercha. 2/3 of the filling was expelled and 30 direct APRs were prepared by Duralay. The samples were divided into 3 groups based on storing environments: water, NaOCl 5% and air. Finally dimensional changes in coronoapical length (CAL), coronal (CD) and apical diameter (AD) of APRs were measured in 7 consecutive times (immediately after polymerization, 1, 2, 4, 8, 24, 48 hours later). All the data were analyzed by Paired T-test and Duncon test using SPSS software ver.13 at significant level of 0.05. Results : After 24 hours, the ARPs, which were stored in air, contracted 0.07, 0.06 and 0.12 mm in AD, CD and CAL; the ARPs, which were stored in water, showed 0.03, 0.06 and 0.12 mm decrease in AD, CD and CAL; But the ARPs, which were stored in NaOCl 5%, showed significant expansion in AD, CD and CAL (0.03, 0.06 and 0.10 mm) (all P values < 0.01). Conclusion : It is better not to use NaOCl for disinfecting; also the best time for storing APRs is 8 hours for water and 2 hours for air environments after setting time.

Purpose: The success of an implant-supported prosthesis is dependent on the passive fit of its framework fabricated on a precise cast. The aim of this in vitro study was to digitally compare the three-dimensional accuracy of implant impression techniques in partially and completely edentulous conditions., Materials and Methods: The master model simulated two clinical conditions. The first condition was a partially edentulous mandibular arch with an anterior edentulous space (D condition). Two implant analogs were inserted in bilateral canine sites. After elimination of the teeth, the model was converted to a completely edentulous condition (E condition). Three different impression techniques were performed (open splinted [OS], open unsplinted [OU], closed [C]) for each condition. Six groups of casts (DOS, DOU, DC, EOS, EOU, EC) (n = 8), totaling 48 casts, were made. Two scan bodies were secured onto the master edentulous model and onto each test cast and digitized by an optical scanning system. The related scans were superimposed, and the mean discrepancy for each cast was determined., Results: The statistical analysis showed no significant difference in the accuracy of casts as a function of model status (P = .78, analysis of variance [ANOVA] test), impression technique (P = .57, ANOVA test), or as the combination of both (P = .29, ANOVA test). The distribution of data was normal (Kolmogorov-Smirnov test)., Conclusion: Model status (dentate or edentulous) and impression technique did not influence the precision of the casts. There is no difference among any of the impression techniques in either simulated clinical condition.

Introduction: The aim of this study was to evaluate the effects of eugenol-free temporary cement's remnants on the retentive strength of full metal crowns luted via zinc phosphate and resin cement (Maxcem) to the tooth structure., Materials and Methods: Forty complete standardized Ni-Cr crowns in four groups were cemented by two types of permanent cements: zinc phosphate cement and resin cement (Maxcem). In the two groups before permanent cementation of crowns, temporary acrylic crowns were cemented by eugenol-free temporary cement. Crowns' retention was evaluated by Universal testing machine. All data were analyzed by means of one-way ANOVA test in SPSS software version 11.5 (α=0.05)., Results: There was no significant difference in groups with prior using eugenol-free temporary cement and groups with just using two permanents cement (p-value≥0.05)., Discussion: The application of temporary cement before permanent cementation of full metal crowns does not have any adverse effect on retention of full metal crowns, when temporary cements are removed properly.

Amelogenesis imperfecta (AI) has been defined as a group of hereditary enamel defects. It can be characterized by enamel hypoplasia, hypomaturation, or hypocalcification of the teeth. AI may be associated with some other dental and skeletal developmental defects. Restoration for patients with this condition should be oriented toward the functional and esthetic rehabilitation. This clinical report describes the oral rehabilitation of a young patient diagnosed with the hypoplastic type of AI in posterior teeth and hypomatured type of AI in anterior teeth.

The management of tooth wear has been a subject of increasing interest from both preventive and restorative points of view. This paper describes the full mouth rehabilitation of a 63-year-old bruxer man with a severely worn dentition and other dental problems including unsuitable restorations and several missing teeth. The treatment entailed using cast posts and cores, metal-ceramic restorations, and a removable partial denture. As with the treatment procedure of such cases, equal-intensity centric occlusal contacts on all teeth and an anterior guidance in harmony with functional jaw movements were especially taken into account.