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    Effect of heat polymerization conditions and microwave on the flexural strength of polymethyl methacrylate
    (Medknow Publications, 2018) Özkır, Serhat Emre; Yılmaz, Burak; Ünal, Server Mutluay; Çulhaoğlu, Ahmet; Kurkcuoğlu Işın
    Objective: The objective of this study is the effect of different heat polymerization conditions on the strength of polymethyl methacrylate (PMMA) resin base is unknown. Distinguishing one method that provides improved mechanical properties may be beneficial to the clinical success of complete and partial dentures and overdentures. The purpose of this study was to evaluate the effect of different polymerization methods on the flexural strength of a dental PMMA resin. Materials and Methods: Forty PMMA specimens (64 mm × 10 mm × 4 mm) were prepared with 4 different polymerization methods (n = 10); heat polymerization at 74°C for 9 h, at 100°C for 40 min, and with 620 kPa pressure at 100°C for 20 min. The remaining group of specimens was microwave polymerized at 180 W for 6 min. All specimens were thermocycled at 5°C and 55°C for 5000 times. Three-point flexure test was used to measure the flexural strength of specimens. One-way ANOVA and Tukey Honestly Significant Difference were applied to analyze the differences in flexural strengths (? = 0.05). Results: The flexural strength of heat-polymerized groups was similar. The flexural strength of microwave polymerized group was significantly different and lower than the other groups (P < 0.05). Conclusion: Polymerizing conventional heat-polymerizing PMMA resin with microwave energy resulted in a significant decrease in flexural strength. The results of this study suggest that clinicians may benefit from using heat polymerization when processing PMMA denture bases instead of microvawe polymerization when tested brand is used. © 2018 European Journal of Dentistry.
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    Effects Of Remover Techniques On Stress Distribution Of Implant Supported Fixed Partial Dentures And The Surroundıng Bone: A Finite Element Analysis
    (2017) Özkır, Serhat Emre; Ünal, Server Mutluay; Çulhaoğlu, Ahmet Kürşad; Şeker, Emre
    Background & Aims: Implant retained restorations may be retrieved due to many reasons. However, implant retained restorations have many components which may be damaged during removal. The aim of this study is to observe stress concentrations in the surrounding bone, the implant and its components, during retrieval of a three-unit implant-supported fixed partial denture using two different removal techniques. Materials and Methods: One three-dimensional digital model of an implant-supported three-unit restoration was constructed. The implants’ dimensions were 3.7 mm x 10mm. A pull out force of 40 N was applied on a single support and on the connectors with a loop device. The stress values were calculated within the dental implant, abutment, abutment screw and surrounding bone. Results: The highest stress concentration was observed at the collar of the abutment during load on a single support (16.246 MPa). The stress concentrations at the cortical bone were lower than the stress concentration at implants, while the maximum stress concentration in bone structure was 1.175 MPa. The loop device technique was enabled to share the load through both implants and reduce the stress concentration levels (9.941 MPa). Conclusion: The pull-out force, did not show a great effect in bone structure. However, implant components were under higher stress and abutment screw was the weakest part of the system. During a crown removal, more attention is needed in order not to damage implant components rather than the bone.