Orhun Ekren

Effect of layered manufacturing techniques, alloy powders, and layer thickness on metal-ceramic bond strength

Statement of problem. Direct metal laser sintering (DMLS) and direct metal laser melting (DMLM) have become popular for fabricating the metal frameworks of metal‐ceramic restorations. How the type of layered manufacturing device, layer thickness, and alloy powder may affect the bond strength of ceramic to metal substructure is unclear. Purpose. The purpose of this in vitro study was to evaluate the bond strength of dental porcelain to metal frameworks fabricated using different layered manufacturing techniques (DMLS and DMLM), Co‐Cr alloy powders, and layer thicknesses and to evaluate whether a correlation exists between the bond strength and the number of ceramic remnants on the metal surface. Material and methods. A total of 75 bar‐shaped metal specimens (n=15) were fabricated using either DMLS or DMLM. The powder alloys used were Keramit NP‐S and EOS‐Cobalt‐Chrome SP‐2 with layer thicknesses of 20 &mgr;m and 30 &mgr;m. After ceramic application, the metal‐ceramic bond strength was evaluated with a 3‐point‐bend test. Three‐way ANOVA followed by the Tukey honest significance difference test were used for statistical analysis (&agr;=.05). De‐bonding surface microstructure was observed with scanning electron microscopy. Energy dispersive spectroscopy analysis was conducted to evaluate the correlation between ceramic remnants on the metal surface and bond strength values. Results. The mean bond strength value of DMLS was significantly higher than that of DMLM. While no statistically significant difference was found between layer thicknesses, alloy powders closely affected bond strength. Statistical comparisons revealed that the highest bond strength could be achieved with DMLS‐Cobalt‐Chrome SP2‐20&mgr;m, and the lowest bond strength was observed in DMLS‐Keramit NP‐S‐20&mgr;m (P≤.05). No correlation was found between porcelain remnants on the metal surface and bond strength values. Conclusions. The layered manufacturing device and the alloy powders evaluated in the current study closely affected the bond strength of dental porcelain to a metal framework. However, layer thickness did not affect the bond strength.

Effect of layered manufacturing techniques, alloy powders, and layer thickness on mechanical properties of Co-Cr dental alloys

Statement of problem. The popularity of direct metal laser sintering (DMLS) and melting (DMLM) has increased in dental practice. The layered manufacturing device, the alloy powder, and the layer thickness may affect the mechanical properties of layer‐fabricated metals. Purpose. The purpose of this in vitro study was to evaluate the mechanical, fractographic, and compositional properties of metals fabricated by using different layered manufacturing techniques (DMLS and DMLM), cobalt‐chromium (Co‐Cr) alloy powders, and layer thicknesses. Material and methods. A total of 90 dumbbell‐shaped test specimens (n=15/group) were fabricated by using either DMLS or DMLM. Powder alloys used were EOS Co‐Cr SP‐2 and Keramit NP‐S, each with layer thicknesses of 20 and 30 &mgr;m; their mechanical properties were evaluated by using a test for tensile strength. Three‐way ANOVA, Student t test, and 1‐way analysis of variance, followed by the Tukey honest significant differences test were used for statistical analysis (&agr;=.05). The fracture surface was analyzed by using scanning electron microscopy, and energy dispersive spectroscopy was used for compositional evaluation. Results. Different layered manufacturing equipment affected the mechanical properties of the final objects, but the powder and layer thickness did not affect mechanical properties. Conclusions. The powder and layer thickness did not affect mechanical properties of the layered manufactured alloy, but different manufacturing methods did affect the mechanical properties of the final product.

Influence of ozone and paracetic acid disinfection on adhesion of resilient liners to acrylic resin

PURPOSE The aim of this study was to evaluate the effect of paracetic acid (PAA) and ozone disinfection on the tensile bond strength (TBS) of silicone-based resilient liners to acrylic resins. MATERIALS AND METHODS One hundred and twenty dumbbell shaped heat-polymerized acrylic resins were prepared. From the mid segment of the specimens, 3 mm of acrylic were grinded off and separated parts were reattached by resilient liners. The specimens were divided into 2 control (control1, control7) and 4 test groups of PAA and ozone disinfection (PAA1, PAA7, ozone1 and ozone7; n=10). While control groups were immersed in distilled water for 10 min (control1) and 7 days (control7), test groups were subjected to PAA (16 g/L) or ozone rich water (4 mg/L) for 1 cycle (10 min for PAA and 60 min for ozone) per day for 7 days prior to tensile tests. Measurements of the TBS were analyzed using 3-way ANOVA and Tukeys HSD test. RESULTS Adhesive strength of Mollosil decreased significantly by application of ozone disinfection. PAA disinfection had no negative effect on the TBS values of Mollosil and Molloplast B to acrylic resin. Single application of ozone disinfection did not have any negative effect on TBS values of Molloplast B, but prolonged exposure to ozone decreased its adhesive strength. CONCLUSION The adhesion of resilient liners to acrylic was not adversely affected by PAA disinfection. Immersion in ozonated water significantly decreased TBS of Mollosil. Prolonged exposure to ozone negatively affects adhesion of Molloplast B to denture base materials.

KİMYASAL TEMİZLEYİCİLERİN AKRİLİK DİŞLERİN YÜZEY SERTLİKLERİNE ETKİSİ

Aim: The aim of this study was to investigate the effect of three chemical denture cleansers on the Knoop hardness of the acrylic denture teeth. Material and Method: Premolar and molar acrylic denture teeth from two manufacturers were embedded in cold cured acrylic resin. The occlusal surfaces of teeth were flat grounded and polished. The specimens were randomly divided into 4 groups and immersed in three different chemical disinfection (Protefix, Corega Tabs and %1 NaOCl) and distilled water (Control group) for 8 hours/day during 7 days. The specimens were submitted to Knoop hardness measurements procedures. Data were analyzed with one way ANOVA and Tukey’s statistical test. Result: All Vitapan group exhibited higher Knoop hardness values than Major Dent groups both in control and experimental groups. The tested chemical denture cleaning methods did not show any significant effect on Knoop hardness of the artificial teeth. Conclusion: Within the limitations of this study it can be concluded that exposure of artificial teeth to chemical disinfectants did not affect the hardness of the acrylic teeth