Perihan Oyar

Effects of post core materials on stress distribution in the restoration of mandibular second premolars: a finite element analysis.

STATEMENT OF PROBLEM Previous studies have not resolved the question as to which post and core combination optimizes the stress distribution within the post restoration and tooth. PURPOSE The purpose of this study was to determine which post and core combination provides the most favorable stress distribution upon loading. MATERIAL AND METHODS Three-dimensional models of teeth were created with the Ansys program to simulate different materials used for post and cores (Ti, NiCr, AuPd, zirconia, zirconia post/composite resin core, glass fiber post/composite resin core, and carbon fiber post/composite resin core) and metal ceramic crowns (nickel chromium alloy [Group NiCr] and gold palladium alloy [Group AuPd]). A force of 400 N was applied to the occlusal surface, and von Mises equivalent stress values were calculated. RESULTS Carbon fiber post/composite resin core/metal ceramic crowns with NiCr alloy core had the highest stress values in the weakened root, tooth/post interface, and post. NiCr post/NiCr core/metal ceramic crowns with NiCr alloy core had the lowest stress values in the weakened root and post. The zirconia post and core had the lowest stress value in the tooth/post interface. CONCLUSIONS A post material with a high elastic modulus led to lower stress in the weakened root (approximately 6%) and tooth/post interface (approximately 12%) and to higher stress in the post (approximately 5 times). A composite resin core led to higher stress in the weakened root (approximately 11% to 17%) and lower deformation in the tooth/post interface (approximately 17.5%) and post materials (approximately 24%). Group AuPd resulted in lower stress in the root and high stress in the post (approximately 4.5% to 7%) and affected the amount of deformation in posts with a composite resin core.

The effects of post-core and crown material and luting agents on stress distribution in tooth restorations

STATEMENT OF PROBLEM Cement microfracture, post-and-core dislodgement, and tooth fracture are related to the mechanical properties and deformation of restorations. PURPOSE The purpose of this study was to determine which combinations of post-and-core cements provide the most favorable stress distribution upon loading. MATERIAL AND METHODS Three-dimensional models of teeth were created with the ANSYS program to simulate the different materials used for metal ceramic crowns (nickel-chromium, gold-palladium), posts and cores (Ti, Ni-Cr, Au-Pd), and cement (glass ionomer, composite resin, zinc phosphate, polycarboxylate, Panavia). Models were divided into 2 groups according to the alloys used in the crown restorations. A simulated masticatory force of 400 N was applied to the occlusal surface at a 45-degree inclination in the linguolabial direction to the long axis of the tooth, and von Mises equivalent stress values were calculated. RESULTS The Ni-Cr metal ceramic crown/Au-Pd post-and-core/glass ionomer cement had the highest residual root von Mises equivalent stress value, whereas the Ni-Cr metal ceramic crown/Ni-Cr post-and-core/glass ionomer cement had the highest post stress value and the Ni-Cr metal ceramic crown/Au-Pd post-and-core/zinc phosphate cement had the highest cement stress value. For each post-and-core alloy, the stress values in the post and core were higher with Au-Pd metal ceramic crowns than with Ni-Cr metal ceramic crowns. The post-and-core material affected the amount of deformation. CONCLUSIONS The use of a post-and-core material with a lower elastic modulus and a cement with a higher elastic modulus led to a reduction in deformation in the residual root, cement, and post and core, and a reduction in stress in the post and core. The Ni-Cr metal ceramic crown/Au-Pd post-and-core/zinc phosphate cement or Panavia may therefore be favorable for post-and-core restorations.

Effects of environment on the release of Ni, Cr, Fe, and Co from new and recast Ni-Cr alloy.

STATEMENT OF PROBLEM The addition of previously cast alloy to new alloy for economic reasons may increase the release of elements. PURPOSE The purpose of this study was to analyze the effects of the immersion period, immersion media, and addition of previously cast alloy to new alloy on the release of elements. MATERIAL AND METHOD Disk-shaped specimens were prepared from a Ni-Cr alloy (Ni: 61 wt%, Cr: 26 wt%, Mo: 11 wt%, Si: 1.5 wt%, Fe, Ce, Al, and Co <1 wt%) (Remanium CS; Dentaurum) with new alloy (group N) and 50% new/50% recast alloy (group R). After the immersion of the specimens in both NaCl (pH 4) and artificial saliva (pH 6.7) for 3, 7, 14, 30, and 60 days, the release of ions was determined by using atomic absorption spectrometry. Data were analyzed with a 3-way ANOVA (α=.001). RESULTS The release of Ni was significantly affected by the immersion period, of Ni and Cr by the alloy and media (P<.01), and of Fe by the alloy (P<.01). Ion release from the recast alloy in artificial saliva was 109.71 for Ni, 6.49 for Cr, 223.22 for Fe, and 29.90 μg/L for Co. The release of Co in NaCl was below the detection limit in both groups. CONCLUSION The release of Ni in NaCl and artificial saliva increased with the length of the immersion period in both groups. The release of Cr and Fe was higher in artificial saliva than in NaCl in group R, regardless of the immersion period. The release of Co in NaCl was below the detection limit in both groups.

Finite element analysis of stress distribution in ceramic crowns fabricated with different tooth preparation designs

STATEMENT OF PROBLEM Information about the effect of occlusal preparation designs on the stress distribution in different ceramic crowns and the prepared tooth is limited. PURPOSE The purpose of this study was to investigate the effects of anatomic and nonanatomic occlusal preparation designs on the stress distribution in ceramic crowns, teeth, and bone. MATERIAL AND METHODS Finite element analysis was performed on models of a mandibular second premolar. A load of 400 N was applied to the models to test ceramic materials (In-Ceram, Empress Esthetic) and occlusal preparation (anatomic, nonanatomic) designs. RESULTS The lowest stress value occurred in the core material in the Empress Esthetic model prepared with the nonanatomic occlusal preparation design. In all groups, higher stress values were found to be concentrated in the lingual half of the dentin. Lower stress values were located near the apex of the pulp tissue and bony tissue that surround the root apex. CONCLUSIONS Differences in preparation designs did not result in differences in the distribution or amount of stress in pulp, dentin, or bone. The use of different ceramic materials resulted in no differences in the amount or distribution of stress in pulp and bone. The use of a crown with a high elastic modulus led to increases in stress values in the restoration and the dentin margin, and decreases in stress values in the occlusal surface of the dentin. The nonanatomic design can be recommended as a favorable preparation design for Empress Esthetic ceramic.

Yetişkin bireylerde yaş ve cinsiyet ile ilişkili diş kaybı ve parsiyel dişsizlik

Amac: Koruyucu onlemler ve restoratif tekniklerdeki gelismelere ragmen, dis kaybi gunumuzde hala onemli bir sorun olarak karsimiza cikmaktadir. Bir toplumdaki dissizlik oraninin belirlenmesi hastalara ozgu tedavi alternatiflerinin ortaya konulmasinda yeni bir bakis acisi saglayabilir. Bu bakimdan, calismamizda cinsiyet ve yas faktorlerinin dis kaybi ve dissizlik uzerine etkisini degerlendirmek amaclanmistir. Gerec ve Yontemler: Ankara Universitesi, Dishekimligi Fakultesi, Protetik Dis Tedavisi Anabilim Dali’ na 2015-2016 yillari arasinda dissizlik tedavisi icin basvuran hastalardan (188 kadin, 173 erkek hasta; yas araligi 28-79) 722 adet maksiller ve mandibular teshis modeli elde edilmistir. Tum modeler tam disli, Kennedy Sinif I-IV ve tam dissiz olmak uzere 6 grup altinda incelenmistir. Her bir model hastanin yas ve cinsiyetine gore siniflandirilmistir. Ki-kare testi ve log-lineer model analizi ile istatistiksel degerlendirmeler yapilmistir (p˂0,05). Ayrica odds oranlari da hesaplanmistir. Bulgular: Yas, dis kaybi ve dissizlik uzerinde etkili bir faktor olarak bulunurken (p 0,05). Cinsiyet esas alindiginda, 34, 36 ve 37 numarali dislerin kaybi bayanlarda daha yaygin gorulurken (p<0,05), 24 numarali dis kayip orani erkeklerde daha yuksek tespit edilmistir (p<0,05). Sonuc: Yas ile birlikte dis kaybi ve dissizlik onemli oranda artmasi ancak cinsiyet ile dis kaybi ve dissizlik arasinda onemli bir iliski bulunmamasi, agiz sagligini koruyucu onlemlerin ileri yaslardaki bireylerde arttirilmasi geregini ortaya koymustur.

ZİRKONYA DENTAL İMPLANTLAR: KLİNİK PARAMETRELER, YAPISAL ÖZELLİKLER, GÜNCEL SİSTEMLER

OZET Butun dunyada implant sistemleri ve materyal uretim endustrisindeki gelismeler ile biyoteknoloji urunleri olan titanyum implantlara alternatif olabilecek zirkonya dental implantlar uretilmistir. Zirkonya seramik implantlar ozellikle ust cene anterior bolge estetik implant protezlerinin yapiminda tercih edilen yontemlerden biridir. Bu makalede protetik dis hekimliginde kullanimlari giderek artan tek parca veya iki parcali sistemleri bulunan zirkonya dental implantlarda klinik parametreler, zirkonya implantlarin avantaj ve dezavantajlari ile yapisal ozellikleri ve guncel zirkonya implant sistemleri anlatilmistir. Anahtar kelimeler: zirkonya dental implant, tek parca zirkonya implant, iki parcali zirkonya implant Zirconia dental implants: Clinical parameters, structural features, current systems ABSTRACT All over the world zirconia dental implants are made as an alternative to biotechnology products of titanium implants by the advances in implant systems and material production industry. Zirconia ceramic implant is one of the preferred methods for the construction of maxillary anterior region aesthetic implant prostheses. This article describes the clinical parameters of single or two-pieces zirconia dental implant systems which is increasingly used in prosthetic dentistry and the advantages and disadvantages of zirconia implants, structural properties of them and current zirconia implant systems. Key words: zirconia dental implant, one-piece zirconia implant, two-pieces zirconia implant