RESUMO
Luting cements are necessarily used to increase retention and enhance the marginal seal of fixed partial dentures [FPDs]. In this study, the finite element method [FEM] was used to investigate the effect of different types of luting agents on stress distribution in the luting cement layer in a three-unit implant-supported FPD. A three-dimensional [3D] FE model of a FPD was designed from the maxillary second premolar to the second molar teeth using CATIA V5R18 software, and analyzed by ABAQUS/CAE version 6.6 software. Three load conditions were statically applied to eight points in each functional cusp in horizontal [57.0 N], vertical [200.0 N] and oblique [400.0 N, =120°] directions. Five luting agents including glass ionomer, zinc polycarboxylate, polymer-modified zinc oxide eugenol [ZOE], composite resin and zinc phosphate were evaluated. The stress distribution pattern in the luting cement layer was almost uniform in all luting cements. In addition, the maximum von Mises stress in the luting cement layer [39.96 MPa] was at the cervical one-third of the palatal side of the second premolar when oblique force was exerted on zinc phosphate cement. Moreover, the minimum von Mises stress in the luting cement layer [0.41 MPa] was at the lateral side of the coronal one-third when the horizontal force was applied to the Polymer-modified ZOE cement. Likewise, the luting cement layers in the premolar tooth showed greater von Mises stress than that in molar tooth. The type of luting cement has no significant effect on the stress distribution pattern in the luting cement layer; however, von Mises stress values were different in various types of luting agents. USE of zinc phosphate cement is associated with more limitations
RESUMO
Introduction: A lot of industrial products and consumer resources have important role in human exposure and receiving yearly radiation dose limit. Radioactive products have been used in denture teeth and Porcelain powders for flourescence properties for long time in dentistry. Because of the most of the people used Porcelain powder and denture, this became an emotion to survey the rate of relative reactivity of powders and inform the laboratory personals
Objective: Determine the relative radioactivity of artificial teeth used in dentures and in porcelain powders
Materials and Methods: In this laboratovary-experimental study six samples of porcelain powders [ceramco III opaque, ceramco III dentin, ceramco II opaque, ceramco II dentin, noritake dentin EX3 and noritake incisal]and two samples of anterior and posterior artificial teeth with polymer base[marjan and shanghy]were used and about 3gr of each sample was placed in front of the scintillator detector NaI[ti]s' window. The number of emission in one houre was measured during each stage. Back ground radiation was measured in several stages. Samples and background radiations ratio were measured by means of paired t test. Data were analyzed by SPSS soft ware
Results: Radioactive properties of different porcelain powders and mentioned denture teeth were significantly lower than back ground radiation. Ceramco III opaque porcelain powder showed the most radioactive properties and marjan denture teeth showed the least
Conclusion: This study confirmed previous studies about low rate of radioactivity properties of samples relative to back ground radiation and indicated if safety precautionse are observed no problem should rise for dental technicians