Epoxy Resin Block Research Articles

Shaping Ability of Different Rotary and Reciprocating File Systems in Simulated S-Shaped Root Canals.

This study aimed to examine the shaping ability of six rotary and reciprocating file systems, as well as hybrid techniques in simulated S-shaped root canals. A hundred and twenty S-shaped radiopaque thermosetting epoxy resin blocks were grouped according to the system used for biomechanical preparation. Six groups of 15 canals each were prepared using TruNatomy, Procodile, VDW Rotate, Hyflex CM, OneCurve, and WaveOne Gold, respectively. Two additional hybrid (Procodile/Hyflex CM and Procodile/TruNatomy) groups (n=15 each) were added after evaluating the results of individual systems. All canals were enlarged to 0.25 mm apically. Canal transportation, centering ability, diameter increase, and iatrogenic errors were assessed by superimposed pre-operative and post-operative images. AutoCAD was used for data analysis. All groups were statistically compared with analysis of variance and Tukey honest significant difference test (p<0.05). Hyflex CM resulted in the most conservative diameter increase in all thirds (coronal, middle, and apical; p<0.001). Procodile showed the best (p<0.001) centering ability in the coronal and middle thirds, while TruNatomy resulted in the least canal transportation and most centering preparation in the apical third (p<0.001). Hybridisation of Procodile and Hyflex CM produced the least canal transportation and best centering ability in the middle third (p<0.001). No instrument breakage occurred, and no ledge, elbow, or apical zip formation was observed during canal preparation. Hybridisation of Procodile and Hyflex CM showed remarkable results in preserving the canal diameter in all thirds and resulted in the least canal transportation and best centering ability in the middle third of the canal. However, when treatment cost and duration limit the clinical applicability of the hybrid technique, clinicians can use a single file system (Hyflex CM or TruNatomy) since it shows satisfactory results in all parameters when compared with a hybrid system.

Cut/puncture resistance and mechanisms of protective composite textiles reinforced with inorganic powder

This study presents a soft-rigid unified structure (SRUS) textile composed of an inorganic powder (IP) reinforced epoxy resin block (EIPB) array and a soft textile substrate via a pattern-controllable integrated molding method. The influence of IP content and alumina particle size on the cut and puncture resistance of the resulting SRUS textile was systematically investigated. Furthermore, the anti-puncture and anti-cutting mechanisms of the SRUS textile were comprehensively evaluated based on the analysis of damage morphology and process. The experimental results demonstrated a significant enhancement in the puncture and cut resistance of the SRUS textile upon the incorporation of IP. Moreover, the cut/puncture resistance of the SRUS textile increased with an increase in IP content and the size of Al2O3, and the optimal cut/puncture resistance was observed at 60 mesh-50 wt.%. Additionally, the anti-puncture mechanism of the SRUS textile was attributed to the presence of hard passivation at the EIPB, as well as friction self-locking at the gaps. The anti-cutting mechanism was ascribed to the reverse cutting action exerted by the hard particles on the blade, preventing further penetration. Overall, these findings provide valuable insights into the underlying mechanisms that contribute to its enhanced protective performance.

Direct observation of epoxy resin blocks for renal biopsy by low-vacuum scanning electron microscopy

To improve the resolution of low-vacuum scanning electron microscopy (LVSEM), the epoxy resin block for the transmission electron microscopy (TEM) was observed directly with LVSEM. After observing ultrathin sections from renal biopsies of IgA nephropathy, membranous nephropathy, lupus nephritis, diabetic nephropathy (DM), thin basement membrane disease (TBMD), Alport’s syndrome, Fabry’s disease, and renal amyloidosis, the epoxy resin blocks of the same sites were observed by LVSEM and compared. The LVSEM image of the epoxy resin block corresponds to the negative of the TEM image, and when the gradation is reversed, the LVSEM image was comparable to the TEM image. At a low magnification of 100 ×, the entire specimen, including the glomerulus, was obtained. LVSEM at 5000 × magnification was sufficient to identify paramesangial deposits in IgA nephropathy and subepithelial electron-dense deposits (EDD) and spikes in membranous nephropathy. Glomerular basement membrane thickening in DM and thinning in TBMD could be sufficiently diagnosed with LVSEM at 6000 ×. Accumulation of ceramide in Fabry's disease was easily identified, but amyloid fibril could not be identified by LVSEM. LVSEM of renal biopsy epoxy resin blocks can replace TEM up to moderate magnification.

Fracture strength, pull-out bond strength, and volume of luting agent of tooth-colored CAD-CAM post-and-cores

Statement of problemLittle is known about the fracture strength, retention, and adaptation of post-and-cores fabricated with novel tooth-colored materials by computer-aided design and computer-aided manufacturing (CAD-CAM). PurposeThe purpose of this in vitro study was to investigate the fracture strength, pull-out bond strength (POBS), and volume of luting agent of endodontically treated premolars restored with post-and-cores milled from different CAD-CAM materials. Material and methodsPost spaces were prepared in 80 human premolars in which post-and-cores fabricated with polyetheretherketone (PK; Ceramill PEEK), nanohybrid composite resin (BB; Brava Block), polymer-infiltrated ceramic (EN; VITA Enamic), and fiber-reinforced epoxy resin (GF; Fiber Cad Post & Core) CAD-CAM materials were luted (n=20). All specimens were subjected to thermal aging (3000 cycles at 5 °C and 55 °C with a 20-second dwell time). Half of the specimens were subjected to mechanical fatigue (250 000 cycles at 5 Hz) before fracture strength testing, while the other half was submitted to POBS testing and volume of luting agent measurement. Fracture strength data were analyzed by 1-way ANOVA, while POBS and volume of luting agent data were submitted to Kruskal-Wallis followed by the Bonferroni-Dunn multiple comparison tests. The correlation between POBS and the volume of luting agent was determined by the Spearman test (α=.05). ResultsPOBS of GF was significantly higher than that for PK (P<.001); however, failure load (P=.160) and volume of luting agent (P=.390) values did not differ. EN showed the highest percentage of catastrophic failures (20%), while PK exhibited only core deformations. POBS and cement film volume were not significantly correlated (P>.05). ConclusionsDifferent CAD-CAM materials did not influence the fracture strength and volume of luting agent of post-and-cores. Post-and-cores made with PEEK blocks showed lower bond strength to intracanal dentin than those made with fiber-reinforced epoxy resin blocks. No significant correlation was found between bond strength and the volume of luting agent.

Remineralization potential of P11-4 and fluoride on secondary carious primary enamel: A quantitative evaluation using microcomputed tomography.

The aim of this study was to assess the ability of self-assembling peptide (P11-4) diffusion, assembly, and remineralization to effect artificial secondary caries-like lesions in human primary teeth in vitro. Enamel-dentin blocks obtained from extracted human primary molars were embedded into epoxy resin blocks. Cavities (approximately 1 × 1 × 2 mm) were prepared on the surface using a high-speed diamond bur under constant water cooling and filled with composite restorative material (Filtek Z250; 3M ESPE). The samples were immersed in demineralizing solution (20 ml) for 96 h to produce secondary caries lesions and divided into two groups according to the testing materials: fluoride varnish (Duraphat; Colgate, UK) and P11-4 (Curodont Repair; Credentis, Switzerland). Except for the control areas, all samples were remineralized for 3-5min using the remineralizing agents, and then all the sections were placed in a pH-cycling system for 5 days at 35°C. The pH cycling procedure was followed by micro-CT analysis for the qualitative evaluation of surface changes. The Mann-Whitney U test was used to compare two independent groups. In the comparison of more than two dependent groups, Bonferroni smoothed pairwise analyses were used to determine the source of the Kruskal-Wallis H test difference. The results of the study revealed that the remineralization depths of the peptide group were higher than those of the fluoride group (p < .01). There was a statistically significant difference in remineralization effects between the fluoride and peptide groups. P11-4 can be considered as an effective remineralizing agent for secondary caries lesions.

Evaluation of customized cobalt-chromium abutments fabricated with different manufacturing process versus titanium stock abutments on the marginal misfit -An in vitro study.

Accurate fit of the abutment to the implant is required for the uniform load distribution throughout the assembly. The study aims to compare the marginal misfit of titanium stock abutments with the cobalt-chromium (CoCr) customized abutments fabricated with the different manufacturing processes in internal hex implant-abutment connection using an appropriate scanning technique. In vitro comparative study. A total of 40 abutments were included in the study. Ten titanium stock abutments were used as control (Group CN) and 30 CoCr abutments were fabricated and taken as the test group. Stock abutments were scanned and from obtained images test group abutments were fabricated as follows: Ten cast abutments (Group CA), 10 sintered abutments (Group SA), and 10 milled abutments (Group MA). Endosseous implanst having internal hex connections were matched with 10 stock abutments and 30 customized CoCr abutments. Implants were mounted in a clear epoxy resin block and the abutments were then fitted onto the implants with a torque of 30Ncm. The marginal discrepancy at implant-abutment connections was measured with confocal laser scanning microscope. One-way ANOVA and Tukey's post hoc test was done for statistical analysis. One-way ANOVA revealed a significant difference in marginal misfit of abutments. The mean marginal misfit was lowest for stock abutments (0.35 ± 0.009 μm). Among the customized abutments, the mean marginal misfit was highest for cast abutments (2.44 ± 0.445 μm) followed by sintered abutments (1.67 ± 0.232 μm) and least for milled abutments (0.65 ± 0.041 μm). A significant difference was found in marginal misfit with cast abutments and sintered abutments when compared to stock abutments (P < 0.001). The difference in marginal misfit was insignificant between stock abutments and milled abutments (P = 0.052). Difference in marginal misfit exists between the titanium stock abutments and customized CoCr abutments. Among the customized abutments, milled CoCr abutments have the least marginal discrepancy and cast CoCr abutments have a maximum marginal discrepancy. Milled CoCr abutments can be used as an alternative to titanium stock abutments.

Evaluation of Remaining Dentin Thickness After Manual and Evaluation of Remaining Dentin Thickness After Manual and Rotary Instrumentation In Primary Molars Using Cone Beam Rotary Instrumentation In Primary Molars Using Cone Beam Computed Tomography. (An In-Vitro Study)

Aim: To compare the radicular dentin thickness before and after instrumentation by manual stainless-steel (K-files) versus rotary files (AF™ Baby File) at coronal, middle, and apical thirds using Cone Beam Computed Tomography (CBCT). Materials and Methods: Forty roots of extracted mandibular primary molars were collected, and randomly and equally divided into 2 groups. Manual Group was prepared by K-files, and Rotary Group was prepared by rotary AF™ Baby File system. Samples were decapitated and stabilized in epoxy resin blocks. Samples were subjected to CBCT scan before and after instrumentation for radicular dentin thickness evaluation at 3 measuring points; apical, middle, and coronal. Results: An average amount of dentin removed was found to be significantly higher in Manual Group compared to Rotary Group in the 3 measuring points (P &lt;0.005). Conclusion: Rotary files can be considered more preferable than manual files in terms of preservation of radicular dentin thickness after root canal instrumentation, therefore rotary files can be a suitable substitute for conventional SS manual files

Regularities of plaque stabilization in various scenarios of neointimal calcification and vascularization

Aim. To study the relationships between phenotypes of extracranial arteries' plaques (stable/unstable), their calcification and its causes, in particular, vascularization.Material and methods. The study included 88 patients: patients (n=44) with ischemic stroke and those (n=44) with chronic brain ischemia. In all subjects, the parameters of systemic mineral homeostasis were assessed (total and ionized calcium, phosphate, total protein, albumin, and calcification propensity). Atherosclerotic plaques have been obtained during carotid endarterectomy, fixed in formalin, postfixed in 1% osmium tetroxide, stained in 2% osmium tetroxide, dehydrated in ascending ethanol series and acetone, stained with 2% alcoholic uranyl acetate and embedded into epoxy resin with its further polymerization. Epoxy resin blocks were grinded, polished, counterstained with Reynolds' lead citrate and sputter coated with carbon. Sample visualization was performed employing backscattered scanning electron microscopy. Number and area of calcium deposits and neointimal vessels were quantified using ImageJ. Statistical analysis was carried out using Mann-Whitney U-test and Spearman's rank correlation coefficient.Results. It was found that area of neointimal calcification, but not number of calcium deposits, was associated with the stable plaque phenotype. The stabilizing effect of calcification was manifested in retarding stenosis associated with plaque rupture and stroke. Calcification extent directly correlated with total and local plaque vascularization, which have been associated with unstable and stable plaque phenotype, respectively. In addition, plaque calcification negatively correlated with total protein and albumin, thereby reflecting the impaired systemic mineral homeostasis.Conclusion. Atherosclerotic plaque calcification and active local vascularization reduce stenosis extent and stabilize plaque. In contrast, total plaque calcification contributes to the atherosclerosis progression and promotes major acute cardiovascular events.

Megacircones ediacáricos de la sienita nefelínica de San José del Guaviare y su potencial como material de referencia para datación U/Pb mediante LA-ICP-MS

With the aim of expanding the reference materials of the Geochronology Laboratory of the Colombian&nbsp;Geological Survey (LG-SGC, in Spanish), zircons were collected from the nepheline syenite of&nbsp;San José del Guaviare, Jordán locality (Colombia). The SNG-1 sample was composed of 24 zircons&nbsp;selected from the fraction between 2 and 5 millimeters long, which were mounted and polished in&nbsp;an epoxy resin block. The zircons were dated by analyzing the isotopic ratios of uranium and lead&nbsp;using the LA-ICPMS method. In the LG-SGC, 92 points on the zircons were selected for analysis,&nbsp;and at the University of Rennes in France (LG-URF), 24 points from crystals found nearby were&nbsp;selected for analysis from a previous cathodoluminescence study. Concordant ages for the zircons&nbsp;for both laboratories corresponded to a crystallization age of 608 ± 1.2 Ma and 602 ± 3 Ma,&nbsp;respectively, which differ by less than 1% despite the difference in instrumentation and analytical&nbsp;procedures. For systematic error correction and quality control, international reference material,&nbsp;such as Plešovice, GJ-1, FC-5 Duluth and Mount Dromedary zircon, was used. The uncertainties&nbsp;generated during the analyses are similar (1.2 and 3.2 Ma), and the mean square-weighted deviation (MSWD) of the concordia diagrams was &lt; 1 in both cases, indicating low dispersion of the&nbsp;results. Some discordant ages show that the U/Pb ratios are not uniform, as expected for a primary&nbsp;reference material. However, we believe that the zircons of the Jordán syenite have potential use as&nbsp;a secondary reference material for the LG-SGC provided they are carefully selected and prepared,&nbsp;their geochemical content (including rare earth elements, REE) is characterized, and quality monitoring&nbsp;of U/Pb dating is performed, as these zircons are large, reaching up to 4 cm, abundant, and&nbsp;possible to collect in the Colombian territory.

Assessment of a Proposed Composite Restorative Monoblock Approach for Intact Endodontically Treated Anterior Teeth to Optimize Their Esthetic and Functional Outcome with Bonded Ceramic Crowns. “In-Vitro Study”

Statement of the Problem: There is general acceptance among different authors about restoring the access cavity of intact endodontically treated anterior teeth with just a composite filling. However, in many instances, for esthetic reasons these teeth need to be crowned. Here, a question is raised about the restorative approach that gives optimum esthetic and functional performance. Objectives: The aim of the present investigation was to test a proposed monoblock adhesive composite restoration bonded to a prepared channel in the coronal third of the root canal; in comparison to two other conventional approaches: composite filling of the access cavity and glass fiber post in the root canal as far as fracture resistance and failure mode are concerned after the teeth being bonded with CAD/CAM ceramic crowns.Materials and Methods: Twenty-one intact maxillary central incisors were randomly divided into three groups of seven each. All the teeth were endodontically treated to be restored with three different treatment options: in the first group just composite restoration (CR) of the access cavity and the second group was assigned for the proposed monoblock adhesive composite restoration (MACR) and the third group for the glass fiber post bonded in the prepared root canal (GFP). All the teeth were prepared to standardized specifications for CAD/CAM all-ceramic crowns that were adhesively bonded to their preparations in the three groups. All the test specimens were subjected to thermocycling between 5°C and 55°C for 2000 cycles before being dynamically loaded in the Instron testing machine for 10,000 cycles. The specimens were then subjected to static loading until fracture, and the load at failure (N) of each specimen was recorded for the statistical analysis. The fractured specimens were examined to detect the mode of failure.Results: All the test samples survived the 10,000 dynamic loading cycles without any signs of cracks or flaws as detected by magnification. The statistical analysis of the data obtained after static loading of the samples revealed that the group with glass fiber posts (GFP) showed the highest significant fracture resistance mean value (579.6 ± 48.3 N) compared to the other two groups: the conventional (CR) and the proposed design (MACR) that revealed (415.1 ± 58.6) and (370.6 ± 64.2 N) respectively, that were not significantly different statistically from each other. The detected mode of failure was an oblique fracture extending from the lingual surface to the labial surface at or just below the insertion of the tooth in the epoxy resin block. The majority of samples (fifteen test sample) presented repairable fractures (71%) and six samples (29%) showed non-repairable fractures. The proposed monoblock design (MACR) presented the highest percentage of repairable fractures (86%) followed by the glass fiber post group (GFP) (71%) and the least was the conventional group (CR) (57%).Conclusions: 1- The three treatment modalities offered successful options for restoring intact endodontically treated maxillary incisors in terms of mechanical and esthetic standpoints. 2- The fracture resistance values of the three tested restorative designs exceeded the normal masticatory forces in this anterior region considerably. 3- The teeth restored with glass fiber posts (GFP) presented the highest statistically significant fracture resistance mean value as compared to the other two groups. 4- The proposed monoblock adhesive composite restoration (MACR) together with the composite restoration (CR) groups provided comparable fracture resistance mean values. 5- The majority of the tested samples (71%) showed repairable fractures, with the proposed monoblock technique presenting the highest percentage (86%) of repairable fractures. 6- The mode of failure was mainly adhesive-cohesive in nature.

Evaluation of retention of two implant supported ceramic crowns using two temporary cements

Aim: The purpose of this in vitro study was to evaluate the effect of two temporary cements (Resin based cement and Eugenol Free Zinc oxide cement) on the retention of two titanium implant supported crowns made of (Polymer infiltrated hybrid glass ceramic and Yttrium stabilized tetragonal zirconia).Materials and methods: 20 dummy implants were inserted in epoxy resin blocks. The twenty blocks were divided according to the crown material into two groups (n=10): Group I: VITA ENAMIC™ crowns, Group II: BurxZir™ zirconia crowns. Each group were further sub-divided into two sub-groups (n=5), according to the temporary cement material used (Sub-group A: crowns cemented with DentoTemp™ cement, Sub group B: crowns cemented with Tempbond NE™ cement). The crowns were fabricated with CAD-CAM technology. Each crown had two wings on the mesial and distal surfaces to aid in retention analysis. The crowns were cemented to the titanium abutments and then retention was measured using uni-axial tensile force test.Results: DentoTemp™ cement showed a higher retentive values with both crown materials. The retentive values of the DentoTemp™ temporary cement was significantly higher than those of the Tempbond NE™ cement when used with BruxZir™ Zirconia crowns.Conclusions: Resin based temporary cement showed significantly higher retention results than non-eugenol temporary cement while the difference in crown material showed no significant difference.

Visualizing melanosomes, lipofuscin, and melanolipofuscin in human retinal pigment epithelium using serial block face scanning electron microscopy

To assess serial section block-face scanning electron microscopy (SBFSEM) for retinal pigment epithelium (RPE) ultrastructure, we determined the number and distribution within RPE cell bodies of melanosomes (M), lipofuscin (L), and melanolipofuscin (ML).Eyes of 4 Caucasian donors (16M, 32F, 76F, 84M) with unremarkable maculas were sectioned and imaged using an SEM fitted with an in-chamber automated ultramicrotome. Aligned image stacks were generated by alternately imaging an epoxy resin block face using backscattered electrons, then removing a 125 nm-thick layer. Series of 249-499 sections containing 5–24 nuclei were examined per eye. Trained readers manually assigned boundaries of individual cells and x,y,z locations of M, L, and ML. A Density Recovery Profile was computed in three dimensions for M, L, and ML.The number of granules per RPE cell body in 16M, 32F, 76F, and 84M eyes, respectively, was 465 ± 127 (mean ± SD), 305 ± 92, 79 ± 40, and 333 ± 134 for L; 13 ± 9; 6 ± 7, 131 ± 55, and 184 ± 66 for ML; and 29 ± 19, 24 ± 12, 12 ± 7, and 7 ± 3 for M. Granule types were spatially organized, with M near apical processes. The effective radius, a sphere of decreased probability for granule occurrence, was 1 μm for L, ML, and M combined. In conclusion, SBFEM reveals that adult human RPE has hundreds of L, LF, and M and that granule spacing is regulated by granule size alone. When obtained for a larger sample, this information will enable hypothesis testing about organelle turnover and regulation in health, aging, and disease, and elucidate how RPE-specific signals are generated in clinical optical coherence tomography and autofluorescence imaging.

Comparative study of the expansion dynamics of laser-driven plasma and shock wave in in-air and underwater ablation regimes

We compared the expansion characteristics of the plasma plumes and shock waves generated in laser-induced shock process between the two ablation regimes: in air and under water. The observation was made from the initial moment when the laser pulse hit the target until 1.5μs. The shock processes were driven by focusing a single laser pulse (1064nm, FWHM=13ns) onto the surface of epoxy-resin blocks using a 40-mm focal length lens. The estimated laser intensity at the target plane is approximate to 9×109Wcm-2. We used the fast-imaging technique to observe the expansion of the plasma plume and a custom-designed time-resolved photoelasticity imaging technique to observe the propagation of shock waves with the time resolution of nanoseconds. We found that at the same intensity of the laser beam, the plasma expansion during the laser pulse follows different mechanisms: the plasma plume that grows in air follows a radiation-wave model while a detonation-wave model can explain the expansion of the plasma plume induced in water. The ideal blast wave theory can be used to predict the decay of the shock wave in air but is not appropriate to describe the decay of the shock wave induced under water.

Fracture Resistance and Retention of Metal-Free Inlay Retained Fixed Partial Dentures

Statement of the problem: Conservative esthetic restorative dentistry has become an essential component in modern clinical practice. However, the inlay retained fixed partial dentures (IRFPDs) have a higher risk of fracture and dislodgement due to minimal preparations. Purpose: to compare fracture resistance and retention of Lithium disilicate (IPS e.max) and Polyetheretherketone (BioHPP) IRFPDs fabricated with heat-press technique and CAD/CAM system. Materials and Methods: Forty models, each including extracted mandibular 2nd premolar and 2nd molar embedded in an epoxyresin block with 10 mm intra-abutment distance representing missing mandibular 1st molar were constructed. The premolar and molar of each model received standardized class II inlay preparations. The constructed models were randomly divided into four groups; Group (1): IPS e.max Press IRFPDs, Group (2): IPS e.max CAD IRFPDs, Group (3): BioHPP Granulates IRFPDs, and Group (4): breCAM.BioHPP IRFPDs. All IRFPDs were cemented using RelyX Ultimate adhesive resin cement. Samples were stored for 24 hours in distilled water at 37°C, and then thermocycled for 5000cycles. Universal testing machine was used to measure fracture and dislodging loads. Samples were examined for determination of failure mode using a magnifying lens. Results: The statistically significant highest mean dislodging load value was obtained in IPS e.max Press IRFPDs, followed by IPS e.max CAD, with the least value recorded in breCAM.BioHPP. In contrast, breCAM.BioHPP IRFPDs revealed the statistically significant highest mean fracture load value, followed by BioHPP Granulates, while the least mean fracture value was recorded in IPS e.max Press. Most failure occurred in IPS e.max groups was connector fracture, while in BioHPP groups was plastic deformation. Conclusions: Retention and fracture resistance of metal-free inlayretained bridges are significantly affected by both; material type and construction method. BioHPP has significant advantages for dental applications because of higher fracture resistance and better stress distribution. The bond strength at IPS e.max/ resin cement interface is considered a reliable bond presenting better retention to IRFPDs. Being a brittle material, connector fracture is the predominant failure mode of IPS e.max IRFPDs; however, BioHPP has low elastic modulus showing plastic deformation as a predominant failure mode.

FRACTURE RESISTANCE, FINITE ELEMENT ANALYSIS AND WEIBULL RISK OF FAILURE FOR ENDODONTICALLY TREATED MOLARS RESTORED WITH LITHIUM DISILICATE AND HYBRID CERAMIC ENDOCROWNS WITH TWO PREPARATION DESIGNS

Objective: The present study aimed at evaluating the fracture resistance of endodontically treated molars restored using IPS e.max CAD (e.max CAD) and Enamic endocrowns using two preparations designs after thermomechanical fatigue.Materials and methods: 40 intact mandibular molars were selected and endodontically treated following a standardized procedure. Molars were decapitated 3.5mm coronal to the cervical line then embedded in epoxy resin blocks. Samples received standardized preparations for endocrowns including the preparation of the pulp chamber, then they were divided into two groups; group 1 where No-Ferrule was included in the preparation and group 2 with 2.5mm Ferrule extracoronally. Each group was further divided into two subgroups according to the material used for constructing endocrowns; e.max CAD endocrowns and Vita Enamic endocrowns. Endocrowns were constructed using Cerec CAD/CAM machine. Constructed endocrowns were adhesively bonded to their respective teeth then subjected to a thermomechanical fatigue procedure (49N, 1.6Hz, 120,000cycle, 5o-55o C) in a chewing simulator. The fracture resistance of each sample was determined by subjecting the samples to a static compressive load until failure. Failure loads were recorded as an indication of fracture resistance. Stresses at failure were analyzed using finite element analysis (FEA) and failure probability percentage was evaluated using Weibull risk of failure. Data were collected, tabulated and statistically analyzed.Results: For fracture resistance, the highest fracture load values were recorded with samples of Ferrule with e.max CAD endocrowns, followed by samples of No-Ferrule with e.max CAD endocrowns and then samples of Ferrule with Enamic endocrowns. The lowest fracture load values were recorded with samples of No-Ferrule with Enamic endocrowns. The magnitude of stresses generated in different parts of the samples as reveled by FEA generally followed a different order than in the fracture resistance. Weibull Risk of failure showed that samples of No-Ferrule with Enamic endocrowns had the highest failure probability especially under high loads. Conclusions: Ferrule design would improve the fracture resistance of endodontically treated teeth especially when restored with lithium disilicate based (e.max CAD) endocrowns. Under low magnitude of forces, both materials would work safely with either design.

VERTICAL MARGINAL GAP DISTANCE AND RETENTION OF DIFFERENT CAD/CAM CERAMIC ENDOCROWNS WITH TWO PREPARATION DESIGNS

Statement of the problem: The rehabilitation of severely damaged coronal hard tissue and endodontically treated teeth has always been a challenge in reconstructive dentistry. These teeth have been shown to exhibit a significantly shorter service life and an increased failure rate when compared with vital teeth. Objective: This study evaluated the vertical marginal gap distance and retention of bonded CAD/CAM Ceramic Endocrowns as a conservative alternative in endodontically treated molar teeth following thermal cycling and fatigue loading compared to post and core supported Ceramic crowns. Methods: Ninty caries free human molar teeth were selected and mounted in epoxy resin blocks. For vertical marginal gap distance test, sixty teeth were assigned into six groups (n=10) according to type of restoration as follows; GroupI: Endodontically treated teeth incorporating 1mm ferrule restored with IPS Empress CAD endocrowns. Group II: Endodontically treated teeth incorporating 1mm ferrule restored with IPS e.max CAD endocrowns. Group III: Endodontically treated teeth without incorporating ferrule restored with IPS Empress CAD endocrowns. Group IV: Endodontically treated teeth without incorporating ferrule restored with IPS e.max CAD endocrowns. Group V: Endodontically treated teeth incorporating 1mm ferrule restored with glass-fiber posts, composite cores and IPS Empress CAD crowns serving as a control group. Group IV:Endodontically treated teeth incorporating 1mm ferrule restored with glass-fiber posts, composite cores and IPS e.max crowns serving as another control group. For retention test, thirty teeth were divided into six groups (n=5). Same designs and types of restorations for the previous test were used for the retention test. All teeth were sectioned perpendicular to the long axis 2mm coronal to the proximal CEJ and then subjected to a standard endodontic treatment. A special milling machine was used for teeth preparation. All-Ceramic endocrowns and crowns were constructed using the Cerec InLab system and cemented with Rely x ARC dual cure adhesive resin cement. The vertical marginal gap distance was measured after cementation using a stereomicroscope. Measurements were made at twenty points for each specimen. In order to mimic the intraoral conditions, all the specimens were subjected to thermal cycling and fatigue loading in a pneumatic fatigue device. Mechanical fatigue was performed for 1,200,000 cycles in a water bath subjected to temperature changes between 5oC and 60oC. The vertical marginal gap distance was re measured at the same points to determine the effect of thermal cycling and fatigue loading. Retention was measured by dislodging the crowns along the long axis of the tooth using a computer controlled universal testing machine. The recorded data were tabulated and statistically analyzed. Results: Regarding the vertical marginal gap distance; endocrowns with 1 mm ferrule showed the statistically significant highest mean gap distance. There was no statistically significant difference between endocrowns without ferrule and post & core supported crowns. For endocrowns with 1 mm ferrule; Empress CAD scored statistically significant higher mean marginal gap values than e.max CAD. There was a statistically significant increase in mean gap distance after thermal cycling and fatigue loading for all test groups. Regarding the retention; endocrowns with 1 mm ferrule showed the statistically significant highest mean retention value. Post & core supported crowns showed statistically significant lower mean value. While, endocrowns without ferrule recorded the lowest mean retention value. In both endocrowns with 1 mm ferrule and post and core supported crowns e.max CAD scored statistically significantly higher mean retention values than Empress CAD, while for the endocrowns without ferrule there was no statistically significant difference between e.max CAD and Empress CAD. Conclusions: Endocrowns represent a successful conservative alternative to post and core supported crowns for restoring mutilated endodontically treated posterior teeth. All tested endocrown designs with both materials proved to have a clinically acceptable marginal gap distances. Preparation geometry for endocrown designs is a crucial factor for the retention of this kind of restorations

Effect of cyclic loading on marginal fit of implant–abutment interface for three different connections with telescopic attachment: in-vitro study

Objective The objective of this article was to evaluate the effect of dynamic cyclic loading on marginal fit at implant–abutment interface with three different implant connections using scanning electron microscope. Materials and methods Thirty implant fixtures were divided equally into three groups (N = 10): group I external hex fixture, group II internal hex fixture, group III conical hybrid fixture. Each fixture was vertically placed in the center of epoxy resin block using modified dental surveyor. Matched prefabricated titanium abutments were screwed to the implant and metal coping was adapted onto abutment. The samples were subjected to eccentric cyclic loading (at a distance 2–3 mm) away from center of abutment at three different intervals 10 000, 100 000, 500 000 cycles. Marginal fit was evaluated before and after each cycles by measuring microgap size in (μm) using scanning electron microscope with a magnification ×700. The values of microgap size in um before and after each cyclic loading were collected, tabulated and statistically analyzed using analysis of variance and Tukey's post-hoc test at 0.05 level of significance. Results After cyclic loading the microgap size was measured in all groups and high value was recorded to group I external hex connection 60.64 ± 4.3μm, while minimum value recorded to group III internal conical connections 0.94 ± 0.11 μm and internal hex connection in between 17.98 ± 2.07 μm. Two way analysis of variance showed significant effect upon marginal fit for both connection and cyclic loading. Conclusion The geometric factors of implant–abutment connection and dynamic cyclic loading have effect on marginal fit at implant–abutment interface. Internal conical connections showed a better marginal fit than internal and external hex connection so use of conical implants can be promoted as it has better sealing abilities compared to other systems.

Transient spray cooling: Similarity of dynamic heat flux for different cryogens, nozzles and substrates

Spray cooling is widely used in industries. Understanding of the complex surface heat transfer characteristics is essential to enhance cooling efficiency. In the present study, surface heat transfer of transient spray cooling with different cryogens, nozzles, and substrates were investigated. Minimum surface temperature reached −46.1°C, −55.9°C, and −57.9°C and maximum surface heat flux values were 294.9, 364.1, and 377.4kW/m2 for R134a, R407C, and R404A, respectively, on an epoxy resin block. Results proved that R404A has the best cooling capacity. Compared with that of the straight nozzle, qmax of the expansion-chamber nozzle increased from 266.9, 364.1, and 403.9kW/m2 to 339.3, 442.8, and 445.1kW/m2 or 16.6%, 18.6%, and 16.7% for R134a, R407C, and R404A, respectively. Transient cooling could be divided into two stages, namely, fast boiling cooling and film evaporation cooling. The similarity of dynamic heat flux with different cryogens, nozzles, and substrates was observed, and the dimensionless correlation was proposed by the spray Biot number, which is defined as the ratio between the internal thermal resistance of the substrate and the surface convective heat transfer resistance. The dimensionless Reynolds number Rel and Fourier number Fol were proposed to represent the maximum heat flux (qmax) and the corresponding time (tmax), respectively. By coupling the Jakob number with Rel and the droplet Weber number (We), dimensionless correlations of maximum heat flux and the corresponding time were proposed, through which it is indicated that We number was the key factor in spray cooling.

Functional graphene nanoplatelet reinforced epoxy resin and polystyrene-based block copolymer nanocomposite

GRAPHICAL ABSTRACT

EFFECT OF IMPLANT PLATFORM SWITCHING ON STRAIN DEVELOPED AROUND IMPLANTS WITH STRAIGHT AND ANGLED ABUTMENTS

Statement of the problem. Implant placement in an ideal position where stresses are transmitted vertically along the long axis of the implant rarely if ever coincides with the most esthetically pleasing position dictated by prosthetic planning. This situation could be dealt with by placing the implant at an angle in the most favourable position surgically and using angled abutments to compensate for the deviation from the previously planned prosthetic site of the final restoration. This may lead to excessive stresses on the inclined side of the implant which could cause bone resorption. Purpose. The aim of this study was to evaluate the effect of implant platform switching on strain developed around implants with straight and angled abutments. Materials and Methods. Twenty root-form titanium implants were inserted in epoxy resin blocks. According to the direction of implant insertion in the epoxy resin block, the twenty implants were divided into two main groups: Group I: (n=10) Straight implants with straight abutments. Group II :( n=10) Inclined implants with angled abutments (15 degrees). Each group was sub-divided into two sub-groups according to the abutment diameter in relation to the implant diameter: Sub-group A :( n=5) 4.5 mm diameter Implants received 4.5 mm diameter abutments. Sub-group B:(n=5) 4.5 mm diameter Implants received smaller 3.75 mm diameter abutments (platform switching). The 20 implant abutments received Ni-Cr full metal crowns. The blocks were trimmed to 1mm thickness around the implant then each sample received four strain gauges to represent the mesial, distal, buccal and lingual surfaces around the implant. A computerized universal testing machine was used for loading the implants by 300N, at a rate of 1 N/Sec. The load was applied progressively starting from zero to 300 N during which readings from the strain meter were recorded on the computer. Results. It was found that Group II (Angled abutments) with matching diameter Sub-group A showed statistically significantly (P ≤ 0.05) highest mean micro-strains (435.1± 215.7) followed by Group I (Straight abutment) with matching diameter Sub-group A (346.2 ± 175.3) followed by Group II (Angled abutments) with platform switching Sub-group B (307.1 ± 135.0). Group I (Straight abutment) with platform switching Sub-group B showed statistically significantly lowest mean micro-strains (239.0± 165.4) . Conclusions. Straight implants with straight platform-switched abutments were associated with the least micro-strain values.