Background and Aim: One of the challenges of restoring endodontically treated teeth with fiber reinforced composite (FRC) POSTs is their deboning from root canal dentin. Different factors such as cement type, affect the POST retention. According to the controversies in this regard, this study aimed to evaluate the effect of three luting cements on retention of FRC POSTs in the root canal.Materials and Methods: In this in-vitro study 30 selected root canal treated premolar teeth were randomly allocated to three experimental groups. After POST space preparation, RTD fiber POSTs, with 10mm length and ¼ mm diameter, were cemented in the canal with one of the following luting agents: zinc phosphate(Harvard), Glass-Ionomer(GC) and resin cement Maxcem(Kerr). They were then fixed and force was applied using Instron 5500 machine. The Data was subjected to ANOVA for statistical analysis.Results: The observed retention in studied groups was as follows: resin cement 127±18.5 (MPa), zinc phosphate 102±29.7 (MPa) and glass-ionomer 51±14.8 (MPa).Conclusion: In order to increase the retention of FRC POSTs, cementation with resin cements is recommended.

Statement of Problem: The increasing popularity and widespread use of fiber POSTs have changed the procedure of reconstructing endodontically treated teeth. A reinforced composite (FRC) POSTs presents the advantage of having an elasticity modulus similar to the dentin, which reduces the risk of root fracture. Some factors like cement thickness may affect the bond strength of the POSTs.Purpose: This study aimed to evaluate the influence of resin cement thickness on the bond strength of a FRC POST system.Materials and Method: In this experimental study, eighteen singles-rooted human teeth were decoronated. (Length: 16 mm). The canals were prepared, and the specimens were randomly allocated to two groups (n=9): Group 1, (low cement thickness) in which size 3 FRC POSTs and group 2 (high cement thickness) in which size 1 FRC POSTs were cemented. The specimens were sectioned, producing 2 samples (thickness: 4.5 mm). For evaluation of the cement thickness evaluation, an optical microscope was used. Each sample was evaluated using push-out test and the data were statistically analyzed using T-test.Result: Bond strengths of the 2 groups, low cement thickness and height cement thickness, did not show a significantly different (p=0.14).Conclusion: The increase in cement thickness surrounding the FRC POST did not impair the bond strength.

Statement of problem: Using the POST is one of the most important sequences in restoring endodontically treated teeth. It dates back more than 200 years as the most popular method of root canal treated teeth restoration; and still is an acceptable method of increasing retention and resistance in such teeth. When there is enough sound tooth structure, restoring the tooth with adhesive restoration is the best choice. New tooth-colored adhesive POSTs are compatible with conservative and esthetic technique. But the question still remained: how much of remaining tooth structure is enough to resist the forces, without using the POST? Purpose: The purpose of this comparative in vitro study was to determine compressive fracture resistance of crown in endodontically treated maxillary incisor teeth restored with or without adhesive tooth colored POST and also in intact teeth.Materials and Method: Thirty extracted maxillary central incisors were selected and allocated to three groups each of ten teeth. Group 1 teeth were kept intact as control. Group 2 were endodontically treated teeth with two approximal class III cavities in the middle one third of incisogingivally that were connected to access cavity, then restored with composite. Group 3 were endodontically treated and prepared teeth, similar to group 2 and received light POST DT (RTDTM) and restored with composite. Then, the samples were loaded until fracture was happened in pull test machine. Mean values of forces required for fracture and mode of fracture were recorded.Results: Mean fracture strength in group 1 was 68.67, in group 2, 41.44 and in group 3, 21.45 Kgf. Comparison of fracture resistance with one way ANOVA was statistically significant. Failure mode of group 3 was more repairable than group 2.Conclusion: Fracture strength in teeth resorted with POST was less than the other groups. While considering more time and cost in using POSTs, this study does not recommend it in similar situations.

Background and Aim: Endodontically treated teeth, because of extensive structural defect, have the increased risk of fracture. For desirable reconstruction of coronal tooth structure, the POST provides retention, nowadays non - metal POST systems were introduced to dentistry. This study compared the fracture strength of maxillary central incisors restored with metallic, fiber composite and ceramic POSTs.Materials & Methods: Thirty human maxillary incisors were used in this invitro experimental study. The crown of each incisor was cut off 1 mm coronal to CEj and perpendicular to the long axis of the tooth by metal disk. The root canals of the teeth were prepared for POST after root canal therapy, then three groups of 10 specimen were formed. Teeth restored with Glass fiber, ceramic and prefabricated metallic POSTs and numbered as group 1, 2 and 3 respectively. Then, all teeth restored with composite core (Z100, 3M) and metal crowns were fabricated and cemented with glass ionomer vitremer luting cement. Specimens were embedded in autopolimerize acrylic resin 4 mm below CEj, and then secured in a universal testing machine. A compressive load was applied at 135 degrees angle to long axis with crosshead speed of 0.5 mm/min, till fracture occurred and fracture pattern was recorded. The data were collected and analyzed using ANOV A and LSD tests.Results: Fracture resistance by Newton was respectively: 765±113.26, 790±95.34, and 614±105.32 for glass fiber POSTs, ceramic and metallic groups. Resistance to fracture for glass fiber and ceramic POSTs was significantly more than Titanium POST (P<0.05), but there was no significant difference between glass fiber and ceramic POSTs. Conclusion: Considering the results, usage of prefabricated glass fiber and ceramic POSTs are more preferable than prefabricated titanium POSTs. Because of more undesirable fracture in ceramic POSTs group than glass fiber, glass fiber POSTs are recommended.

'POST-truth' has become a buzzword for numerous current crises: the fragmentation of the media landscape, the ongoing debate about 'fake news', the loss of trust in science, etc. Although these crises take place in society, it is claimed that the roots of POST-truth can be traced back to the history of philosophy. Occasionally, it is asserted that Karl Popper's critical rationalism gave rise to POST-truth: His rejection of verificationism has limited truth claims in the realm of science. Given the absence of infallible evidence and certainty, critical rationalism calls for challenging scientific authority. I argue that POST-truth is compatible with critical rationalism from an epistemological point of view, considering that both positions are critical of certainty. However, in critical rationalism, fallibilism, responsibility, and the idea of criticism are combined, and in this respect, it offers a possible way to overcome the problems that are associated with POST-truth. This treatment of the problems of POST-truth results from the recognition of moral responsibility to take action on the basis of a hypothesis that remains open to revision.

Introduction: The purpose of this in vitro study was to investigate coronal microleakage in anterior weakend teeth after root canal therapy, reinforced with different tooth-coloured material and FRC POST.Methods and Materials: A total 48 extracted intact central incisors were randomly divided into four experimental groups (n=12). All specimens were endodontically treated using lateral condensation and crowns were totally removed from 2mm of CEJ and were over flared to simulate weakened teeth . Control group (group I) was restored only with gutta percha .In other groups root canal walls were prepared (etching, washing and gentle drying, bonding) and the surface of the POSTs were cleaned with alcohol and after that covered with bonding agent and then light  polymerized for 40 seconds. Finally POST cementation was done during reinforcing of weakened root canal walls with packable composite in group II, self-cure composite in group III and dual cure composite in group IV. All specimens were thermocycled for 500 cycles between 5oc and 55oc0 with a dowel time of 20 seconds before immersion in dye. Then all specimens were sealed with sticky wax and coated with two layer of nail polish & then they were placed in 0.5% fuschine for 24 hours at room temperature and were sectioned longitudinally from the center of POST with tooth cutter. Dye penetration in both sections of each tooth were evaluated using a stereomicroscope equipped with digital camera at original magnification of 32× and microleakage recorded in mm. One-way analysis of variances (ANOVA) and least square difference were used for statistical analysis.Result: The control group showed the maximum microleakage and the minimum was related to the third group .There was a significant difference among the average microleakage of all groups.Conclusion: Combination of FRC POST and tooth-coloured materials did reinforce structurally compromised root and decreased microleakage and also the microleakage of root/bonding material is more than POST/tooth-colored material. Microleakge in selfcure Group because of its polymerization was the least.

Introduction: Application of light transmitting POSTs to restore greatly damaged endodontically treated teeth has been increased. It is suspected that light intensity decreases as it passes throughout different materials. This can reduce the degree of conversion required for adequate bond strength throughout the length of these POSTs. The objective of this study was to evaluate the amount of light intensity reduction after passing through different depths of FRC POSTs.Methods: Four groups of five extracted human central incisors were prepared to cement four types of FRC POSTs with Panavia F 2 resin cement. The apical end of the POSTs were exposed by sectioning with a diamond disk and then polished. The light intensity measurement was performed using a micro-voltmeter in 8 points or depths with 2mm intervals beginning from the apical depth of 16mm up to a coronal depth of 6mm. Two different output light intensities [HIP (High Intensity Program) and LOP (Low Intensity Program)] were evaluated.Results: Statistical analysis showed significant differences in light intensity at various depths between 6 and 16mm in all groups. These reductions were linear in all specimens; however, the rate of reduction was dissimilar among different FRC POSTs. HIP and LOP light exposure modes had not the same rate of light reduction.Conclusion: Light intensity decreased dramatically after passing through different depths of FRC POSTs. None of the POSTs had sufficient enough light transmission for satisfactory polymerization at the apical and middle levels.

Introduction: In POST-core crown restorations, the use of prefabricated composite POSTs concentrate stress at the cervical region and the use of metal POSTs (prefabricated and customized POSTs) concentrates stress at the interfaces. Fiber reinforced composite POSTs (FRCs) with oval cross-section (oval POSTs) were proposed for POST-core crown restorations to reduce the stress levels at the cervical region. The aim of the present study was to investigate the impact of oval cross-section composite POSTs on stress distribution of premolar with oval-shaped canal by using three-dimensional (3D) finite element analysis.Materials and Methods: An extracted premolar tooth was mounted, sectioned, and photographed to create a 3D model. The surrounding tissues of the tooth, periodontal ligament, as well as cortical and trabecular bones were modeled. Seven taper POSTs with two different cross-section geometries (circular and oval shapes) were modeled, as well. Then, the effect of POST geometry, POST material (carbon fiber and fiberglass), and cement material were investigated by 3D finite element analysis and the stress distribution results were compared.Results: In all the models, the highest stress levels of the dentin were accumulated at the coronal third of the root, and the highest stress levels at the bonding layers were accumulated at the cervical margin. Narrow circular POSTs induced the highest stress levels, whereas the stress levels were reduced by using thick oval POSTs. Application of elastic cement reduces the stress at the bonding layers but increases stress at the dentin.Conclusion: Finite element analysis showed that prefabricated oval POSTs are superior to traditional circular ones. The use of cement with low elastic modulus reduces the risk of debonding but raises the risk of root fracture.

Modern political thought is a substratum of modern thought and affected by its results. What referred to as modern political thought is, in fact, in many respects a reconstructed form of modern insight in the field of politics. Thus we cannot speak of modern politics unless the philosophic aspects of modem affair is considered.In the present paper, one of the features of modern thought, that is, the tendency to a constant reconstruction of order and the concern for substituting the new order for the old one in order to prevent crisis has been studied. The absence of this doctrine among POSTmodern scholars is one of the important factors in this philosophic shift of POSTmodernism. In POSTmodern discourse, the perpetuity and inevitability of crisis are accepted as a principle, while the political administration for regulating and establishing the new order is overlooked.This distinguishes the POSTmodern approach to politics from that of the modern. This article examines the consequences of this attitude for the POSTmodern political thought and discusses political participation as an illustration of the issue beforehand.