Tensile bond strength of soft and hard relining materials to conventional and additively manufactured denture-base materials.

PURPOSE: Studies comparing tensile bond strength of various soft and hard denture liner materials to conventionally and additively manufactured denture base resins are lacking. The purpose of this study was to investigate the tensile bond strength between chair- and laboratory-side soft and hard relining materials and denture-base materials produced by additive manufacturing and conventional methods. MATERIALS AND METHODS: A total of 120 dimethacrylate-based additively manufactured and polymethylmethacrylate (PMMA)-based conventionally fabricated dumbbell-shaped denture-base resins were produced. Heat-cured laboratory-side soft reline material, self-cured chair-side soft reline material, and self-cured chair-side hard reline material were attached to the denture bases. The tensile force was applied to the specimens with a universal testing machine at a crosshead speed of 5 mm/min. The obtained data were analyzed with two-way ANOVA and post hoc Tukey tests. The significance level was set at α = 0.05. RESULTS: The highest tensile bond strength values were obtained in the specimens from the conventionally manufactured base and self-cured chair-side hard reline material group, and the lowest was seen in the additively fabricated base and self-cured chair-side soft reline material group (p < 0.001). Conventionally manufactured base material's tensile bond strength was higher than that of additively fabricated resin, and self-cured chair-side hard reline material's strength was higher than that of laboratory-side and chair-side soft reline materials (p < 0.001). However, no significant difference emerged between laboratory-side and chair-side soft reline materials (p = 0.405). CONCLUSIONS: All the specimens used in the present study had tensile bonding stress values for clinical use. Both denture base resins provided an increased bond to the chair-side hard relining material, although an improved bond did not emerge for the chair-side and laboratory-side soft denture reline materials.

Investigation of the Presence of SARS-CoV-2 in Aerosol After Dental Treatment.

AIMS: The objective of the present study was to investigate the presence of SARS-CoV-2 in aerosol and COVID-19 contamination distance asssociated with ultrasonic scaling and tooth preparation. METHODS: Twenty-four patients with COVID-19 were included in this study. Removal of supragingival plaque with ultrasonic instruments for 10 minutes and high-speed air-turbine using for the simulation of cutting the maxillary right canine tooth with a round diamond bur for 5 minutes were performed. Patients were randomly assigned to 2 groups: In group A, medium-volume suction was used during treatment. In group B, high-volume suction with an aerosol cannula was added to medium-volume suction. Prior to treatment, 5 glass petri dishes containing viral transport medium were placed in the operating room. After treatment, petri dishes were immediately delivered to a microbiology laboratory for real-time polymerase chain reaction (RT-PCR) analysis. RESULTS: RT-PCR test results were negative for all specimens in group B. However, 5 positive test results for COVID-19 were detected in group A specimens. CONCLUSIONS: Suction with an aerosol cannula is very important to prevent COVID-19 viral contamination via aerosol. In addition, a high-volume suction capacity (air volume) of 150 mm Hg or 325 L/min is sufficient for elimination of viral contamination. Thus, high-volume suction should be used during dental treatments in COVID-19 patients.

Effects of boron on the mechanical properties of polymethylmethacrylate denture base material.

PURPOSE: The objective of this study was to determine whether the addition of different types of boron (Borax, Boric Acid and Colemanite) to polymethyl methacrylate denture base resin would improve flexural and impact strengths, and surface hardness of polymethyl methacrylate. MATERIALS AND METHODS: Borax, Boric acid, Colemanite were added to heat polymerized polymethyl methacrylate specimens were prepared for flexural strength (65x10x2.5 mm), impact strength (50x6x4 mm), and hardness (20x6x4 mm) tests according to the manufacturers' instructions (n=10). To determine flexural strength of the specimens, they were loaded until failure on a universal testing machine using a three point bending test. Specimens were subjected to the Charpy impact test machine. Hardness of the specimens was measured with an analog shoremeter Shore D. The data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α=0.05). RESULTS: The highest mean flexural strength value was seen in 3% Borax group and followed by 1% Colemanite group. In addition, the highest mean impact strength value was recorded in 1% Colemanite group, and differences between 1% Colemanite group and control group were found to be statistically significant (p=0,001). Furthermore, there was significant difference in hardness between control group and all other groups (p<0.001). CONCLUSION: The addition of 1% Colemanite to polymethyl methacrylate improved the mechanical properties of PMMA.

Evaluating the Effect of Ambient and Scanning Lights on the Trueness of the Intraoral Scanner.

PURPOSE: To determine the influence of different scanning and ambient light conditions on the trueness values of an intraoral scanning (IOS) device. MATERIAL AND METHODS: The present study was conducted among 20 complete dentate volunteers. After making complete maxillary arch impressions with vinyl polysiloxane material, type IV dental stone was poured, and working casts were obtained. Then, the models were digitized using a dental laboratory scanner (LS) and standard tessellation language (STL) files were acquired. Full arch digital scans of the volunteers were also performed using an IOS device with 2 ambient light conditions (RL: room light, 1003 lux, and ZL: zero light, 0 lux) and 2 scanning light modes (blue [B] and white [W]). Twenty digital scans per group at each light condition were consecutively obtained. Discrepancy between the digital scans and digitized working casts was analyzed using a 3D inspection software. The obtained data were analyzed using one-way ANOVA and Tukey tests (α = 0.05). RESULTS: Significant differences were obtained among different light conditions for the IOS device (p ˂ 0.0001, F = 42.958 for positive deviations and F = 29.278, for negative deviations). The room light and blue mode (RLB) condition had the lowest deviation values compared with the other light conditions, followed by room light and white mode (RLW), zero light and blue mode (ZLB), and zero light and white mode (ZLW; p =  0.008, p Ë‚ 0.0001, and p Ë‚ 0.0001, respectively). CONCLUSION: Lighting conditions are effective in assessing the trueness of the digital impressions made with an IOS device. RLB conditions are recommended for taking a digital impression.

Newly Reported Studies on the Increase in Gastrointestinal Symptom Prevalence withCOVID-19 Infection: A Comprehensive Systematic Review and Meta-Analysis.

BACKGROUND AND AIM: Although constitutional and respiratory symptoms such as cough and fever are the most common symptoms in patients infected with COVID-19, gastrointestinal (GI) tract involvement has been observed by endoscopic biopsies. Multiple GI symptoms, including diarrhea, nausea or vomiting and abdominal pain, have also been reported. This review aims to present the currently available data regarding the GI symptoms of COVID-19 patients, and to compare the frequency of GI symptoms in early stage (Eastern) mostly Chinese data to the current stage (Western) non-Chinese data. METHODS: We performed a systematic literature search to identify both published studies by using PubMed, Google Scholar, and CNKI (Chinese medical search engine), and yet unpublished studies through medRxiv and bioRxiv. We also reviewed the cross references of the detected articles. We conducted a Medical Subject Headings (MeSH) search up until 20 September 2020. We pooled the prevalence of symptoms of diarrhea, anorexia, nausea, vomiting, and abdominal pain by using the Freeman-Tukey's transforming random effect model. RESULTS: A total of 118 studies were included in the systematic review and 44 of them were included in the meta-analysis. There was a significant heterogeneity between the studies; therefore, the random effects model was used. The pooled prevalence estimate of any GI symptoms reported was found to be 0.21 (95%CI, 0.16-0.27). Anorexia was the most commonly reported GI symptom at 18% (95%CI, 0.10-0.27) followed by diarrhea at 15% (95%CI, 0.12-0.19). Diarrhea, abdominal pain, nausea/vomiting, and respiratory symptoms were more common in non-Chinese studies. The prevalence of abdominal pain was lower in the "inpatient-only" studies when compared with studies that included outpatients only and those including both inpatients and outpatients. CONCLUSIONS: In this comprehensive systematic review and meta-analysis study, we observed higher rates of diarrhea, nausea/vomiting, and abdominal pain in COVID-19 infected patients among non-Chinese studies compared to Chinese studies. We also observed a higher prevalence of GI symptoms in Chinese studies than was reported previously. Non-respiratory symptoms, including GI tract symptoms, should be more thoroughly and carefully evaluated and reported in future studies.

Effect of repetitive firing on passive fit of metal substructure produced by the laser sintering in implant-supported fixed prosthesis.

PURPOSE: The aim of the present study was to investigate the passive fit of metal substructure after repetitive firing processes in implant-supposed prosthesis. MATERIALS AND METHODS: Five implants (4 mm diameter and 10 mm length) were placed into the resin-based mandibular model and 1-piece of screw-retained metal substructure was produced with the direct metal laser sintering (DMSL) method using Co-Cr compound (n = 10). The distance between the marked points on the multiunit supports and the marginal end of the substructure was measured using a scanning electron microscope (SEM) at each stage (metal, opaque, dentin, and glaze). 15 measurements were taken from each prosthesis, and 150 measurements from 10 samples were obtained. In total, 600 measurements were carried out at 4 stages. One-way ANOVA test was used for statistical evaluation of the data. RESULTS: When the obtained marginal range values were examined, differences between groups were found to be statistically significant (P<.001). The lowest values were found in the metal stage (172.4 ± 76.5 µm) and the highest values (238.03 ± 118.92 µm) were determined after glaze application. When the interval values for groups are compared with pairs, the differences between metal with dentin, metal with glaze, opaque with dentin, opaque with glaze, and dentin with glaze were found to be significant (P<.05), whereas the difference between opaque with metal was found to be insignificant (P=.992). CONCLUSION: Passive fit of 1-piece designed implant-retained fixed prosthesis that is supported by multiple implants is negatively affected by repetitive firing processes.

How should we describe, diagnose and observe the Barrett's esophagus?

Barrett's esophagus (BE) is one of the major complications of gastroesophageal reflux disease (GERD) commonly encountered in gastroenterology clinics. A consensus has not been achieved yet with respect to the definition of BE in published guidelines. It is advised to use the Prague classification and not to use the definition of short and long segments for the endoscopic standardization of BE. Undertaking biopsies with white-light endoscopy from each of the 4 quadrants at 2-cm intervals is the standard method for the diagnosis of BE. Because of the ability to perform targeted biopsies, the available data indicate that advanced endoscopic techniques may reduce the number of biopsies needed for diagnoses. In the presence of severe esophagitis along with BE, the biopsies should be taken after 8 weeks of PPI therapy. The evidence values of the suggestions about the surveillance requirements and surveillance frequencies are low because the available data mostly rely on retrospective studies. We suggest that all the patients with BE should be referred to specialized centers for surveillance in Turkey. Considering the additional risk factors of the patient, endoscopy surveillance intervals of the patients with BE without dysplasia should be in a range of 3-5 years and annual surveillance should be made in BE with low-grade dysplasia. In the presence of BE with high-grade dysplasia (HGD), the patients should be referred to specialized centers for treatment within 3 months at the latest.

Does the treatment of proton pump inhibitors reduce dysplasia or adenocarcinoma development in Barrett's esophagus?

Besides reducing the reflux symptoms, the benefit of proton pump inhibitors (PPI) in the treatment of Barrett's esophagus (BE) is not exactly known. The data in the literature show that although the PPI treatment does not reduce the Barrett's segment length, it can reduce dysplasia or the development of early-stage adenocarcinoma (odds ratio (OR): 0.46). Therefore, treatments with PPI may be considered in patients with a diagnosis of BE and at a high risk of adenocarcinoma, even though they are not symptomatic.

Radiopacity of Esthetic Post Materials: Evaluation with Digital Analysis Technique.

PURPOSE: To evaluate the radiopacity of five post materials using a digital image analysis method. MATERIALS AND METHODS: Twelve specimens from each post type (two zirconia and three fiber based) of 2 mm in thickness were obtained using a diamond blade mounted on a cutting machine, and digital radiographs were taken along with aluminum step-wedge and dentin discs under standard exposure conditions. The mean gray-values of specimens were measured using a computer graphics program. Data were analyzed using one-way ANOVA followed by Holm-Sidak multicomparison test (p = 0.05). RESULTS: The highest radiopacity was observed in custom zirconia (5.842 millimeters of equivalent Al [mmAl]), and the lowest value was detected with FRC-Postec (Ivoclar Vivadent) (1.716 mmAl). Significant differences were revealed between the radiopacity values among all groups (p < 0.05), except the Zr post materials (p = 0.56). CONCLUSIONS: All tested post materials had higher radiopacity than dentin. Further studies will be required to clarify optimum radiopacity properties of the post materials to provide a precise clinical observation.

Incidence rate of anemia in inflammatory bowel diseases.

BACKGROUND/AIMS: To determine the incidence rate and distribution of anemia types over time from an Inflammatory Bowel Disease (IBD) patient cohort spanning 18 years. MATERIALS AND METHODS: Between January 1995 and November 2013, the University Hospital digital databases as well as hard copies of patients' files were reviewed retrospectively. IBD patients with at least one complete blood count (CBC) report were included in this study. RESULTS: We obtained 941 IBD patients' records; 375 (39.9%) patients were diagnosed with Crohn's disease (CD), and 566 (60.1%) patients had ulcerative colitis (UC). Anemia was detected in 548 (58.2%) patients. Female patients were more frequently anemic than male patients (68.4% vs. 49.7%, p=0.001). The frequency of anemia was slightly higher in patients with CD (62.1%) than in patients with UC (55.7%) (p=0.04). The incidence rate of anemia for the entire IBD patient cohort was calculated as 103.45 per 1,000 patient-years. The correlation between the age of the IBD disease and the presence of anemia exhibited a high correlation coefficient of Pearson's r=0.702. CONCLUSION: This is the first study to report the incidence rate of anemia (103.45 per 1,000 patient-years) in a long-term cohort of IBD patients.

Comparison of Doppler ultrasound and transient elastography in the diagnosis of significant fibrosis in patients with nonalcoholic steatohepatitis.

BACKGROUND: Liver fibrosis is an important prognostic determinant in patients with nonalcoholic steatohepatitis (NASH). Hepatic artery resistivity index (HARI) is a doppler ultrasonography (US) parameter that is used to follow up microcirculatory resistance in fatty liver. We aimed to asses whether it is possible to demonstrate significant fibrosis by means of doppler US in comparison with transient elastography (TE) and liver biopsy in NASH patients. PATIENTS AND METHODS: A total of 63 (mean age 47.1 ± 8.4 years, 39 male, 24 female) biopsy-proven NASH patients were enrolled in this prospective study. The study population was classified into two groups: significant and no-significant fibrosis patients. Doppler US and TE were performed in two groups. RESULTS: HARI and TE values were significantly higher in significant fibrosis group (0.81 ± 0.05 vs. 0.63 ± 0.14, p < 0.0005; 15.9 ± 4.8 vs. 6.2 ± 2.6 kilopascals, p < 0.0005; respectively). Based on the ROC curve, the optimal cut-off value of HARI for a significant fibrosis was >0.75, which yielded a sensitivity of 78% and a specificity of 75%, with the area under the curve at 0.90. The optimal cut-off value of TE for a significant fibrosis was >9.8 kilopascals, which yielded a sensitivity of 90% and a specificity of 91%, with the area under the curve at 0.95. HARI values were moderately correlated with TE values (r = 0.53, p < 0.001). CONCLUSION: Doppler US has moderate % sensitivity and % specificity, which is lower compared with TE for the diagnosis significant fibrosis. However, it may be used as an alternative method for the assessment of fibrosis in patients with NASH who are not good candidates for TE evaluation.

Tensile Bond Strength between Soft Liners and Two Chemically Different Denture Base Materials: Effect of Thermocycling.

PURPOSE: The bond strength of soft denture liner to a recently introduced denture base resin after thermocycling has not been compared to traditional denture base materials. The objective of this study was to investigate the effects of thermocycling on the tensile bond strength of soft denture liners to two chemically different denture base resins, polymethyl methacrylate (PMMA) and urethane dimethacrylate (UDMA). MATERIALS AND METHODS: A total of 48 PMMA and UDMA tensile test specimens were fabricated by attaching two different soft denture liners (Molloplast-B, Permaflex) according to the manufacturers' instructions and assigned to two groups. Half of the specimens for each group were stored in water for 1 week, and the other half were thermocycled (5000 cycles) between baths of 5°C and 55°C. Specimens were mounted on a universal testing machine with a 5 mm/min crosshead speed. The data were analyzed with three-way ANOVA and post hoc Tukey-Kramer multiple comparisons tests (α = 0.05). RESULTS: The highest bond strength was measured in the specimens from the UDMA/Molloplast groups, and the lowest was seen in the PMMA/Permaflex group. No significant difference in bond strength was detected in PMMA/Permaflex groups after thermocycling (p = 0.082), whereas other groups exhibited significant differences after thermocycling (p < 0.05). CONCLUSIONS: Thermocycling decreased the bond strength values in both the PMMA and UDMA groups. Regardless of types of soft liners, PMMA specimens presented lower bond strength values than UDMA specimens, both before and after thermocycling.

A Novel Round Insulated Tip Papillotome as an Alternative to the Classic Needle-Knife for Precut Sphincterotomy in Endoscopic Retrograde Cholangiopancreatography.

Objective. The purpose of this study was to investigate the efficacy and safety of a new round insulated tip papillotome (r-ITP) as compared to that of the classic needle-knife sphincterotome (NKS) in difficult-to-cannulate endoscopic retrograde cholangiopancreatography (ERCP) patients. Materials and Methods. Patients with no exclusion criteria and an intact papilla referred for ERCP were invited to participate in the study. "Difficult-to-cannulate" patients, defined as failure to achieve deep biliary cannulation within five minutes from the first touch of papilla, with no more than ten attempts permitted, were randomly assigned for precut sphincterotomy using either the classic NKS or r-ITP. Results. Seventy and 69 patients were randomly assigned to the NKS and r-ITP groups, respectively. The groups were comparable regarding age, sex, indications, and associated conditions. There was no statistically significant difference in terms of successful cannulation or post-ERCP complications between the two groups. Only five patients (3.6%) developed mild to moderate post-ERCP pancreatitis and two had mild bleeding. No perforations or deaths were encountered. Conclusions. Although the round insulated tip papillotome was not shown to be superior to the classic NKS concerning efficacy and safety when used by an experienced endoscopist, it remains a simple, safe, and efficacious alternative.

Bactericidal permeability increasing protein gene polymorphism is associated with inflammatory bowel diseases in the Turkish population.

BACKGROUND/AIMS: Inflammatory bowel disease, a chronic inflammatory disease with unknown etiology, affects the small and large bowel at different levels. It is increasingly considered that innate immune system may have a central position in the pathogenesis of the disease. As a part of the innate immune system, bactericidal permeability increasing protein has an important role in the recognition and neutralization of gram-negative bacteria. The aim of our study was to investigate the involvement of bactericidal permeability increasing protein gene polymorphism (bactericidal permeability increasing protein Lys216Glu) in inflammatory bowel disease in a large group of Turkish patients. PATIENTS AND METHODS: The present study included 528 inflammatory bowel disease patients, 224 with Crohn's disease and 304 with ulcerative colitis, and 339 healthy controls. RESULTS: Bactericidal permeability increasing protein Lys216Glu polymorphism was found to be associated with both Crohn's disease and ulcerative colitis (P = 0.0001). The frequency of the Glu/Glu genotype was significantly lower in patients using steroids and in those with steroid dependence (P = 0.012, OR, 0.80; 95% confidence interval [CI]: 0.68-0.94; P = 0.0286, OR, 0.75; 95% CI: 0.66-0.86, respectively). There was no other association between bactericidal permeability increasing protein gene polymorphism and phenotypes of inflammatory bowel disease. CONCLUSIONS: Bactericidal permeability increasing protein Lys216Glu polymorphism is associated with both Crohn's disease and ulcerative colitis. This is the first study reporting the association of bactericidal permeability increasing protein gene polymorphism with steroid use and dependence in Crohn's disease.

Nonalcoholic Steatohepatitis Score is an Independent Predictor of Right Ventricular Dysfunction in Patients with Nonalcoholic Fatty Liver Disease.

OBJECTIVE: Nonalcoholic fatty liver disease (NAFLD) is associated with increased risk of cardiovascular disease and impaired left ventricular (LV) function, yet the impact of NAFLD on right ventricular (RV) function remains unclear. We investigate the RV functional properties in patients with NAFLD. METHODS: Ninety consecutive patients with the diagnosis of biopsy-proven NAFLD and 45 age- and sex-matched controls were included. All patients underwent an echocardiographic examination. RV function was evaluated by two-dimensional (2D) speckle-tracking echocardiography (STE). RESULTS: Mean fibrosis stage and nonalcoholic steatohepatitis (NASH) scores were 1.3 ± 1.1 and 5.2 ± 1.6, respectively. NAFLD patients displayed decreased RV function compared to controls. NAFLD patients with liver fibrosis (67 patients) had significantly lower RV function assessed by GLS (global longitudinal strain) compared to patients without liver fibrosis (18.9 ± 3.4% vs. 21.6 ± 2.3%, P < 0.001). NASH score ≥5 was associated with lower RV-GLS (18.9 ± 3.1% vs. 21.0 ± 3.4%, P = 0.006). NASH score inversely correlated with RV-GLS (r = -0.370, P < 0.001) such as patients with impaired RV-GLS (<19%) showed significantly higher NASH score compared to normal RV-GLS group (5.8 ± 1.4 vs. 4.8 ± 1.7, P = 0.009). Logistic regression analysis revealed that NASH score was an independent predictor of impaired RV function in patients with NAFLD. CONCLUSIONS: Patients with NAFLD have impaired RV function. NASH score inversely correlates with RV-GLS and independently predicts impaired RV function in patients with NAFLD.

Surface roughness and bond strength of zirconia posts to a resin cement after various surface pretreatments.

OBJECTIVE: The purpose of this study was to investigate the influence of post surface conditioning methods on the surface roughness and microtensile bond strength (µTBS) of zirconia posts to a resin cement. BACKGROUND DATA: Debonding at the post-adhesive interface is a major problem for zirconia posts. METHODS: A total of 25 zirconia posts (n=5) were prepared as follows: untreated (control, group C), airborne-particle abraded (group AA), silica coated (group SC), Nd:YAG laser irradiated (group N), and Er:YAG laser irradiated (group E). Prior to application of a dual-cured resin cement on the posts, roughness values of the post surfaces were detected with a profilometer. Specimens were then sectioned to obtain rectangular sticks for µTBS. After sticks were stored in distilled water at 37°C for 24 h, µTBS values were determined in a universal testing machine at a crosshead speed of 1 mm/min until failure. Furthermore, scanning electron microscopic (SEM) analysis was performed for one specimen of each group to evaluate the post surface morphology. One-way ANOVA and post-hoc comparison tests (α=0.05) were performed on all data. RESULTS: All surface treatment groups demonstrated significant higher µTBS values than the control group (p<0.001). The highest mean force value was observed in group SC. In addition, similar bond strength results were detected between group SC and group E (p=0.669). None of treatment groups resulted in significant improvement in roughness values of the post (p<0.05), except group N. CONCLUSIONS: All surface treatments were found to be effective methods to achieve a durable bond between zirconia posts to resin cement.

Effect of different temporary crown materials and surface roughening methods on the shear bond strengths of orthodontic brackets.

OBJECTIVE: The aim of this study was to evaluate the effect of different temporary crown materials (TCMs) and surface roughening methods on the shear bond strength (SBS) of orthodontic brackets. BACKGROUND DATA: TCMs are widely used during orthodontic treatment in teeth in need of prosthetic treatment, to prevent damage to the final restoration. However, there is no consensus considering the best method for roughening of the surface of TCMs. METHODS: Five different TCMs [Dentalon Plus-(D), Basworth Trim II-(B), Voco Structure Premium-(V), 3M ESPE Protempt 4-(P), and Revotek LC-(R)] were used in this study. Different surface roughening methods (37% phosphoric acid, sandblasting, and Er:YAG laser) were employed in three subgroups (n=20). The SBS test was used to assess the durability of all groups. Scanning electron microscopy (SEM) analysis was performed on a representative specimen in each group. RESULTS: The highest mean SBS value was observed in group V, followed by groups D and P, regardless of the surface treatment. The lowest SBS values were observed in group B. The laser-irradiated groups had higher SBS values than the sandblasted and acid-etched groups. Furthermore, a significant difference in SBS values was observed between the laser-irradiated group V and all other groups (p<0.005). CONCLUSIONS: The effects of the chemical nature of TCMs on the SBS values appeared to be clinically negligible, whereas the type of surface treatments had a significant influence on bond strengths. Er:YAG laser irradiation caused a significant increase in bond strength between the TCMs and orthodontic brackets.

Magnetic Flux Density of Different Types of New Generation Magnetic Attachment Systems.

PURPOSE: The purpose of this study was to analyze the static magnetic flux density of different types of new generation laser-welded magnetic attachments in the single position and the attractive position and to determine the effect of different corrosive environments on magnetic flux density. MATERIAL AND METHODS: Magnetic flux densities of four magnetic attachment systems (Hyper slim, Hicorex slim, Dyna, and Steco) were measured with a gaussmeter. Then magnetic attachment systems were immersed in two different media, namely 1% lactic acid solution (pH 2.3), and 0.9% NaCl solution (pH 7.3). Magnetic flux densities of the attachment systems were measured with a gaussmeter after immersion to compare with measurements before immersion (α = 0.05). The data were statistically evaluated with one-way ANOVA, paired-samples t-test, and post hoc Tukey-Kramer multiple comparisons tests (α = 0.05). RESULTS: The highest magnetic flux density was found in Dyna magnets for both single and attractive positions. In addition, after the magnets were in the corrosive environments for 2 weeks, they had a significant decrease in magnetic flux density (p < 0.05). No significant differences were found between corrosive environments (p > 0.05). CONCLUSION: The leakage flux of all the magnetic attachments did not exceed the WHO's guideline of 40 mT. The magnets exhibited a significant decrease in magnetic flux density after aging in corrosive environments including lactic acid and NaCl.

Effect of different veneering techniques on the fracture strength of metal and zirconia frameworks.

PURPOSE: To determine whether the fracture strengths and failure types differed between metal and zirconia frameworks veneered with pressable or layering ceramics. MATERIALS AND METHODS: A phantom molar tooth was prepared and duplicated in 40 cobalt-chromium abutments. Twenty metal (IPS d.SIGN 15, Ivoclar, Vivadent, Schaan, Liechtenstein) and 20 zirconia (IPS e.max ZirCAD, Ivoclar) frameworks were fabricated on the abutments. Each framework group was randomly divided into 2 subgroups according to the veneering material: pressable and layering ceramics (n=10). Forty molar crowns were fabricated, cemented onto the corresponding abutments and then thermocycled (5-55℃, 10,000 cycles). A load was applied in a universal testing machine until a fracture occurred on the crowns. In addition, failure types were examined using a stereomicroscope. Fracture load data were analyzed using one-way ANOVA and Tukey HSD post-hoc tests at a significance level of 0.05. RESULTS: The highest strength value was seen in metal-pressable (MP) group, whereas zirconia-pressable (ZP) group exhibited the lowest one. Moreover, group MP showed significantly higher fracture loads than group ZP (P=.015) and zirconia-layering (ZL) (P=.038) group. No significant difference in fracture strength was detected between groups MP and ML, and groups ZP and ZL (P>.05). Predominant fracture types were cohesive for metal groups and adhesive for zirconia groups. CONCLUSION: Fracture strength of a restoration with a metal or a zirconia framework was independent of the veneering techniques. However, the pressing technique over metal frameworks resisted significantly higher fracture loads than zirconia frameworks.

In vitro comparison of the cytotoxicity and water sorption of two different denture base systems.

PURPOSE: Denture base resins have the potential to cause cytotoxicity in vivo, and the mechanical properties of resins are affected by water sorption. There is a correlation between residual monomer and water sorption. Thus, the purpose of this study was to evaluate water sorption and cytotoxicity of light-activated urethane dimethacrylate (UDMA) denture base resin compared to a conventional heat-activated polymethyl methacrylate (PMMA) resin. MATERIALS AND METHODS: Two denture base resins, heat-activated PMMA (Meliodent) and light-activated UDMA (Eclipse), were used in this study. Cytotoxicity (5 × 1 mm(2) ) and water sorption (1 × 1 mm(2) ) specimens were made following the manufacturers' instructions (n = 10). Cytotoxicity tests of denture base resins were performed according to ISO10993-5:1999, and water sorption was evaluated according to ISO 1567:1997. ANOVA tests were employed for evaluating data (α = 0.05). RESULTS: There was no cytotoxic effect in either the PMMA or UDMA group. In addition, contrary to short-term water storage, a significantly lower water sorption value was shown for UDMA resins compared to PMMA resins in both 3- and 6-month storage periods (p = 0.043 and p = 0.002, respectively). CONCLUSION: The tested denture base materials adhered to the ISO standards for both cytotoxicity and water sorption. The cytotoxicity of the light-activated UDMA resin tested was statistically similar to that of the heat-activated PMMA resin; however, the UDMA resin exhibited decreased water sorption in long-term water storage.