Butt-joint Design Research Articles

Effect of different preparation designs and material types on fracture resistance of minimally invasive posterior indirect adhesive restorations.

To evaluate the impact of various preparation designs and the material type on fracture resistance of minimally invasive posterior indirect adhesive restorations after aging using a digital standardization method. One-hundred sixty human maxillary premolars free from caries were assigned into 16groups (n=10): bevel design on enamel substrate with mesial box only (VEM), butt joint design on enamel substrate with mesial box only (BEM), bevel design on enamel substrate with mesial and distal box (VED), butt joint design on enamel substrate with mesial and distal box (BED), bevel design on dentin substrate with mesial box only (VDM), butt joint design on dentin substrate with mesial box only (BDM), bevel design on dentin substrate with mesial and distal box (VDD), and butt joint design on dentin substrate with mesial and distal box (BDD). Each group was restored with pressable lithium disilicate (LS2) or disperse-filled polymer composite (DPC) materials. Adhesive resin cement was used to bond the restorations. The specimens were aged for 10,000 thermal cycles (5°C and 55°C), then 240,000 chewing cycles. Each specimen was subjected to compressive axial load until failure. A two-way analysis of variance (ANOVA) test followed by a post hoc Tukey test was used to analyze the data (α=0.05). The two-way ANOVA test revealed a significant difference among designs (p<0.001) and materials (p<0.001) with no interaction effect (p=0.07) between the variables. The Post hoc Tukey test revealed that the VEM group exhibited the highest mean fracture resistance value, while the BDM group had the lowest. The LS2 groups showed the highest mean fracture resistance values. The DPC groups showed a restorable fracture pattern compared to the LS2 groups. Bevel and butt joint designs with mesial or distal boxes are recommended for conservative posterior indirect adhesive restorations in premolar areas. Enamel substrate improved load distribution and fracture resistance. DPCs have restorable failure patterns, while pressed LS2 may harm underlying structures.

Comparative Evaluation of Two Different Preparation Designs and Materials on the Fracture Resistance of Laminate Veneers: An In Vitro Study.

Introduction Laminate veneers are thin porcelain or composite resin shells bonded to the front of teeth for cosmetic enhancement. The design of the tooth preparation is crucial; it involves minimal enamel removal to ensure a proper fit and strong bond. This careful preparation increases the veneers' fracture resistance by preserving tooth structure and evenly distributing stress, ensuring durability and natural appearance. Aim Our aim was to determine the fracture resistance of two preparation designs with two different materials for the fabrication of laminate veneers. Materials and methods An in vitro study was conducted on 40 laminate veneers divided into two groups based on the material used: Group 1 (Cerec Tessera (Dentsply Sirona, Charlotte, NC, USA)) and Group 2 (Upcera, Shenzhen, China). Each group was further divided into two sub-groups based on tooth preparation designs: butt joint and feather edge. The fracture resistance of these veneers following thermocycling was determined, and the mode of fracture was evaluated using a stereomicroscope. Results Feather edge preparation with Cerec Tessera laminate veneer restoration demonstrated the highest fracture resistance at 111.5 N, followed by butt joint preparation with Cerec Tessera laminate veneer restoration, which showed a fracture resistance of 90.8 N. The study identified laminate fractures as the most common type of fracture observed in the veneer restorations, followed by cement interface fractures. Conclusion The study suggests that the feather edge preparation design contributed to higher fracture resistance compared to the butt joint design. This finding aligns with the idea that modifying the preparation design can have a significant impact on the overall strength and durability of veneer restorations. The use of Cerec Tessera, especially in combination with the feather edge design, yielded the maximum fracture resistance.

Biomechanical behavior and Weibull survival of CAD-CAM endocrowns with different marginal designs: A 3D finite element analysis

ObjectivesTo evaluate and compare the effect of tooth preparation designs and different CADCAM. materials on stress distribution and Weibull survival probability of endocrowns. applied to root canal-treated lower first permanent molar using the 3D finite element. analysis method. MethodsA root canal-treated lower first permanent molar was prepared for endocrowns with a. butt joint or with a ferrule design by placing, circumferentially, a 1-mm wide shoulder. finish line. The prepared molar was scanned for the two designs and modeled on a 3D. Finite element model. Monolithic zirconia (IPS e.max ZirCAD MT, FCZ), lithium. disilicate (IPS e.max CAD, EX), and nano-ceramic resin composite (Lava Ultimate, LU). CAD-CAM materials were used for each preparation to design the virtual endocrown. A. total of six models were built according to the different tooth preparation designs and. endocrown materials. An occlusal load of 600 N and a transverse load of 20 N in. magnitude that simulates the average occlusal load was directed toward the occlusal. surfaces. von Mises and maximum principle values were evaluated Weibull risk-ofrupture. analysis was used to analyze the survival probability of the restorations and. tooth in the different models. ResultsThe highest von Mises were found in the butt joint design for FCZ, EX, and LU (45.3. MPa, 35.2 MPa, and 24.2 MPa, respectively) compared to the ferrule design for the. same materials (42.6 MPa, 31.2 MPa, and 23.6 MPa, respectively). For von Mises. stress distribution in the remaining part of tooth structure (dentin), the highest stresses. were found in LUFerrule which was closely similar to LUButt joint (135.4 MPa and. 134.7 MPa, respectively), followed by EXFerrule and FCZFerrule (132.2 MPa and. 131.7 MPa, respectively), while the lowest stresses were found in EXButt joint and. FCZButt joint (129.0 MPa and 128.4 MPa, respectively). Shear stresses within the. resin cement were the highest in FCZ and EX compared to LU. EX was found to be the. most reliable material with the highest survival probability, while FCZ showed the. lowest survival probability according to the Weibull risk-of-fracture results. SignificanceMaterials with high elastic modulus transfer more stresses to the endocrown and less. to the remaining tooth structure. Endocrown tooth preparation with ferrule design has. better stress distribution and magnitude compared to the butt joint design.

Biomechanical Behavior of Lithium-Disilicate-Modified Endocrown Restorations: A Three-Dimensional Finite Element Analysis

This study aimed to assess the biomechanical behavior of endocrown-restored mandibular molars according to “margin design” and “coverage extent” using finite element analysis (FEA). Six 3D solid models were fabricated, namely, those with complete occlusal coverage: A (butt joint), B (anatomic margin); partial coverage (two mesial cusps): C (butt joint), D (anatomic margin); and partial coverage with mesial class II cavity: E (butt joint), F (anatomic margin). All models received lithium disilicate endocrowns (2.0 mm thickness and 4.0 mm central retainer cavity depth). A 300 N vertical load was applied to the occlusal surface, while a 250 N oblique load was applied at 45° to the lingual inclined planes of the buccal cusps. The maximum von Mises stress (VMS) distribution patterns were calculated for the endocrown, tooth structure, and cement layer. The VMS on the prepared teeth and cement layer showed subtle differences between the tested models under vertical loads. The anatomic margin (partial and complete coverage) exhibited a more homogeneous stress distribution and offered a more adhesive area of the tooth structure. Under oblique loading, the anatomic margin (complete and partial), except Model D, exhibited the lowest VMS in the cement layer. An anatomically based endocrown could be a promising alternative to the butt joint design, providing better-devised endocrown restorations, which could potentially yield a more benign stress dissipation.

Effect of incisal preparation design on the fracture strength of monolithic zirconia-reinforced lithium silicate laminate veneers.

This study aimed to assess the fracture resistance of monolithic zirconia-reinforced lithium silicate laminate veneers (LVs) fabricated on various incisal preparation designs. Sixty maxillary central incisors with various preparation designs were 3D-printed, 15 each, including preparation for: (1) LV with feathered-edge design; (2) LV with butt-joint design; (3) LV with palatal chamfer; and (4) full-coverage crown. Restorations were then designed and manufactured from zirconia-reinforced lithium silicate (ZLS) following the contour of a pre-operation scan. Restorations were bonded to the assigned preparation using resin cement and following the manufacturer's instructions. Specimens were then subjected to 10,000 thermocycles at 5 to 55°C with a dwell time of 30s. The fracture strength of specimens was then assessed using a universal testing machine at a crosshead speed of 1.0mm/min. One-way ANOVA and Bonferroni correction multiple comparisons were used to assess the fracture strength differences between the test groups (α=0.001). Descriptive fractographic analysis of specimens was carried out with scanning electron microscopy images. Complete coverage crown and LV with palatal chamfer design had the highest fracture resistance values (781.4±151.4 and 618.2±112.6N, respectively). Single crown and LV with palatal chamfer had no significant difference in fracture strength (p>05). LV with feathered-edge and butt-joint designs provided significantly (p<05) lower fracture resistance than complete coverage crown and LV with palatal chamfer design. The fracture resistance of chairside milled ZLS veneers was significantly influenced by the incisal preparation designs tested. Within the limitation of this study, when excessive occlusal forces are expected, LV with palatal chamfer display is the most conservative method of fabricating an indirect restoration.

Effect of three different preparation designs on the marginal adaptation of indirect overlay restoration fabricated from lithium disilicate ceramic material: An in-vitro comparative study

ObjectivesMarginal adaptation is considered one of the key factors influencing the success of indirect restorations. This study aimed to estimate the marginal fit of lithium disilicate overlays with three distinct preparation designs before and after cementation. MethodsThirty maxillary first premolars were divided into the hollow chamfer design (HCD11HCD: Hollow Chamfer Design.) group,butt-joint design (BJD22BJD: Butt-Joint Design.) group, and conventional occlusal box design (COD33COD: Conventional Occlusal Design.) group (n = 10 each). The samples were scanned using an intra-oral scanner, and overlays were fabricated using computer-assisted design and milled on a computer-assisted machine. The finished restorations were luted using a self-adhesive resin RelyX Ultimate. The marginal gap was assessed using a digital microscope with 230X magnification power. Statistical analysis was conducted using analysis of varianceandposthoc(Bonferroni correction) tests, assuming a significance level of 5%. ResultsThe HCD and BJD groups recorded significantly lower marginal gap, (11.39 ± 0.72, 16.29 ± 0.75) and (11.59 ± 0.75, 16.93 ± 0.65) respectively, than the COD group (24.57 ± 1.18, 34.45 ± 1.09) both pre- and post-cementation. ConclusionThis study demonstrated that modification of tooth preparation plays a significant role in the marginal adaptation of the lithium disilicate overlays. The gap was smaller with the HCD and BJD than with the COD, with a statistically significant difference.

Efficacy of preparation design on fracture resistance of hybrid-ceramic endo-crown on premolars: An in vitro study

Aim: The present study aims to evaluate the effect of different preparation designs on fracture resistance and failure mode of hybrid nanoceramic endocrown on premolars.Methodology: Fourteen endodontically treated maxillary premolars were prepared to receive a hybrid nanoceramic endocrown restorations and divided into 2 groups according to the preparation designs (butt joint and 2 mm ferrule). The endocrown restorations were cemented to the prepared teeth using dual cure adhesive resin cement. All specimens were subjected to a compressive force 5KN until fracture occurs by using universal testing machine. The maximum compressive force was recorded for all specimens, then failure mode of all samples were examined visually and photographically. All repairable samples were examined for extension of the cracks using scanning electron microscope.Results: Endocrowns with ferrule preparation recorded a highly statistically significant difference with the higher mean value of fracture resistance (1911.57 ± 341.29 N), compared to the endocrowns with butt joint which recorded the lower mean value of fracture resistance (1192.70±196.04 N). Regarding the failure mode; endocrowns with ferrule design showed a high percent of catastrophic failure while butt joint showed more repairable failure.Conclusion: Endocrowns with ferrule design showed a higher fracture resistance value but with a high percent of catastrophic failure mode compared to butt joint design that showed lower fracture resistance value with mostly repairable mode of failure.

Shade evaluation for clinical color change of discolored teeth treated by bleaching vs laminate veneers (Randomized Clinical Trial)

Aim: Clinical evaluation for color change of discolored teeth treated by bleaching vs laminate veneers. Methodology: Patient with discolored anterior teeth were divided into two groups. Group1: treated by laminate veneers restoration (monolithic IPS e.max), while Group 2: treated by bleaching (hydrogen peroxide) in the same patient. Anterior teeth of one arch were prepared with butt joint design to receive laminate veneer restorations which constructed from IPS e.max and cemented by self-adhesive resin cement, while anterior teeth of the other arch was treated by 40% hydrogen peroxide bleaching agent material. Using spectrophotometer (Easy Shade) and digital photography with Photoshop software ,the color change (ΔE) and color stability assessment were carried out and repeated four times (after one week, four weeks, two months and three months) respectively, The results were calculated and analyzed using Kolmogorov-Smirnov and Shapiro-Wilk tests. Results: Result obtained by spectrophotometer revealed that the first color change shown was after three months follow up , where, higher statistically significant difference in (ΔE) were displayed from data obtained from bleaching teeth . While first color change (ΔE) with higher statistically significant difference displayed from data obtained by digital photography was after 4 weeks follow up of bleaching teeth also.

The Effect of Heat Input on Welding Combination of GTAW and SMAW SA537 Material on Mechanical Properties and Microstructure

The combination of GTAW (Gas Tungsten Arc Welding) and SMAW (Shield Metal Arc Welding) processes on SA537 Class 2 carbon steel using variations of heat input is the main choice to get the best quality welded joints. This research aims to joint SA537 Class 2 material using the GTAW and SMAW process with heat input variations to get the best joint and determine the joint results mechanical properties and microstructure analysis. The experimental method uses a combination of GTAW and SMAW processes with a single V butt joint design, groove angle of 60o, root face 2 mm and root gap of 4 mm as many as 7 passes, and variations in heat input of 2.5 kJ/mm, 2.8 kJ/mm and 3.2 kJ/mm. According to ASME section IX, the mechanical testing results showed that the specimen with a heat input of 2.8 kJ/mm gave optimum results with the highest tensile strength of 480 MPa compared to the other two specimens, and there were no cracks when tested for bending The higher the heat input, the greater the decrease in the percentage of ferrite. Using a heat input of 2.8 kJ/mm in this study provides a weld result with better mechanical properties and microstructure than the use of heat input of 2.5 kJ/mm and 3.2 kJ/mm.

In Vitro Comparison of Microleakage, Marginal Fit, and Cement Thickness of Conventional and Prepless Lithium Disilicate Veneers

To assess the influence of two preparation techniques on the microleakage, marginal fit, and cement thickness of lithium disilicate veneers. A total of 24 human maxillary central incisors were divided randomly into two groups according to preparation technique (n = 12): minimally invasive preparation with butt-joint design (0.3-mm depth) and a chamfer finish line (group MP); and no preparation (NP). All teeth were restored with lithium disilicate veneers cemented with photopolymerizable resin cement. Specimens were aged thermally (6,000 cycles of 5°C to 55°C) and mechanically (100,000 cycles at 100 N, 4 Hz). Specimens were immersed in fuchsin for 24 hours employing a standard dye penetration technique, then sectioned and evaluated under a stereomicroscope (x20). Data were analyzed by ANOVA and Kruskal-Wallis tests (P < .05). There was significant microleakage (P = .0163) at the cervical area compared to the proximal area. The marginal fit was similar, with no statistical difference (P = .212) between groups MP (153 ± 81 μm) and NP (111 ± 74 μm). Group MP showed a significantly (P = .006) reduced cement thickness at the cervical area (87 ± 27 μm) compared to group NP (210 ± 89 μm). Although the preparation technique was shown to influence the cement thickness, it did not show any influence on microleakage or marginal fit.

Influence of Different Marginal Preparation Designs and Materials on the Marginal Integrity and Internal Adaptation of Endocrown Restorations

ABSTRACT Objective: This in vitro study was performed to assess the marginal accuracy and internal adaptation of CAD/CAM fabricated endocrowns restoring endodontically treated molars with two different designs and materials. Materials and methods: Forty extracted maxillary first molar teeth were divided into two main groups (n=20) according to the preparation designs: group B: (Butt joint) & group S (Shoulder finish line): and each group was subdivided into two subgroups (n=10) according to materials: group E: lithium disilicate glass-ceramic (IPS e.max CAD; Ivoclar Vivadent AG) & group C: hybrid nanoceramic (Cerasmart; GC Corp). A digital scan was made with a digital scanner (Identica Hybrid Scanner; Germany) and virtual endocrowns were milled with a 5-axis milling machine ((Imes-Icore; CORiTEC250i; Germany). The silicone replica technique and a stereomicroscope (25X) were used to measure the marginal and internal gaps of endocrowns at different points. All data were statistically analyzed using three-way ANOVA test with Post Hoc Tukey test to detect pair-wise comparison. Student's t-test also was used. Results: There was a statistically significant difference between the preparation designs on the marginal integrity and internal adaptation (p 0.05). Conclusions: All tested groups showed acceptable marginal and internal gaps mean values. Butt joint design showed a better effect than shoulder finish line design on the marginal integrity and internal adaptation. Cerasmart showed a better effect than IPS e.max CAD on the internal adaptation.

One-year clinical evaluation of IPS Empress CAD versus polished Celtra Duo ceramic Laminate veneers (randomized controlled clinical trial)

Objective: To evaluate fracture resistance and survival rate of IPS Empress CAD versus Polished Celtra Duo ceramic laminate veneers. Material and Methods: Thirty-six ceramic laminate veneers were fabricated for maxillary anterior teeth. The patients were divided into two groups according to the material Group 1(control group) fabricated from IPS Empress CAD laminate veneers and group 2(intervention group) fabricated from Polished Celtra Duo laminate veneers. Standardized the same preparation with butt joint design and chamfer finish line located supra gingival were performed for all the teeth. The fabrication of the veneers was performed using Cad\Cam (Ceramill motion) machine, with software (Exocad). The veneers surfaces were treated and silanated according to the manufacture instruction of each ceramic and enamel surfaces were etched where total etch adhesive protocol was obeyed using BISCO. Follow up sessions were done every two months up to one year for each patient using dental probe and operator vision to evaluate the fracture, survival rate, marginal adaptation, sensitivity and caries. according to USPHS criteria (United States Public Health Service). This was performed by an experienced, blinded investigator. Results: Fracture resistance, marginal adaptation, retention, caries and sensitivity were evaluated according to the criteria of USPHS and we found there is no significant difference as both groups scaled zero score. Conclusion: Both IPS Empress Cad and Polished Celtra Duo laminate veneers revealed successful clinical performance in terms of fracture resistance, marginal adaptation, retention, and sensitivity after one year follow up period. Keywords Ceramic laminate veneers; IPS Empress CAD; Celtra DUO; Clinical performance.

Specific Features of Electron-Beam Welding of ITER Blanket First Wall Components

Specific features of fabricating welded structures of the international thermonuclear experimental reactor (ITER) blanket components are considered. The results from elaborating the technology for electron-beam welding of cooling system’s channel caps in the first wall bearing structure (FWBS) of the ITER blanket shielding module are presented. The design of welded joint samples made of Grade 316L(N) steel and the welding equipment are described. The welding techniques and butt joint design features whose use makes it possible to obtain the required strengthening of weld bead and to avoid metal droplets from appearing in the FWBS inner cavities are considered. A simplified thermal–mechanical model of the cap-welding technological process is described, and the results from experimentally evaluating the structural and mechanical state of the obtained welded structures are presented. A comparison between the modeling and experimental results is given. It is pointed out that the stressed and strain state varies in an active manner at the initial loading stage. Initially, the metal in the heat-affected zone (HAZ) experiences plastic deformation followed by elastic relief at the subsequent stages. It is pointed out that the postweld deformations are on the whole characterized by a low level and remain within the permissible limits. The distribution of mechanical properties in weld joint local zones determined using the indentation method is given. The results from tensile tests and an indenter impressing test show that the weld metal has even better mechanical characteristics than the parent metal. Data are presented from metallographic investigations, which testify that there is no growth of grains in the HAZ, which is due to high rates of cooling in the used welding method. Based on the results of elaborating the electron-beam welding technology and using the developed techniques, an FWBS mockup has been fabricated that complies with the class VQC 1A tightness requirements.

Effect of Cavity Design and Cusp Inclination on Fracture Resistance of Indirect Overlay Restorations In Maxillary First Pemolars: An In Vitro Study

Aim: to evaluate the effect of cavity design and cusp inclination on fracture resistance of indirect overlay restorations in maxillary 1st premolars. Subjects and Methods: Hundred extracted human maxillary 1st premolars were selected and divided into ten groups; Gr1: control group (CG), Gr2: shoulder design with normal cusp inclination, Gr3 & Gr4: shoulder design with 33° & 22° cusp inclinations (respectively, Gr5: butt joint design with normal cusp inclination, Gr6 & Gr7: butt joint design with 33° & 22° cusp inclinations respectively, Gr8: Anatomical design with normal cusp inclination, Gr9 & Gr10: Anatomical design with 33° & 22° cusp inclinations respectively. All restorations were fabricated indirectly and cemented by RelyX Ultimate adhesive resin cement. Samples were stored for 24 hrs in distilled water at 37°C and then thermocycled for 5000 cycles. Universal testing machine was used to measure fracture loads. Samples were examined for determination of failure mode using a magnifying lens.Results: ANOVA test revealed that the difference between groups was statistically significant (p=0.00). Tukey’s post hoc test revealed no significant difference between Sh/33°CI, Sh/22°CI, B/33°CI, B/22°CI, A/NCI and A/33°CI. Conclusions: The teeth restored with cusp shoulder designs exhibited the highest percentages of restorable fractures (70-90%). Anatomical design presents the highest fracture resistance. However, 70-100% catastrophic failure is suspected. Fracture resistance increases significantly by decreasing cusp inclination of overlay restorations.

The PC-GTAW of Ti–6Al–4V Thin Sheets and Its Effects on Mechanical and Microstructural Properties

In this study, annealed Ti–6Al–4V alloy sheets with a thickness of 1 mm and with a butt-joint design were welded using gas tungsten arc welding without using filler metal. The aim of this study was to compare the specimens of the welding process with different current ratios (Ib/Ip) to find sample with high tensile strength and toughness. The welded specimens with optimal pulsed current ratios (Ib/Ip = 50, 75%), which made a basket-shaped structure with appropriate distribution alongside Widmanstatten layer phases, resulted in a soft fracture in the base metal zone as well as high strength in the tensile test.

Finite-element analysis of mandibular first molar with two marginal designs of endocrown for the repair of different defects

This study aimed to evaluate the stress distribution of the mandibular first molar with different thicknesses and heights of the axial wall restored by the endocrown with two marginal designs and thus provide a theoretical basis for selecting clinical preparation through the finite-element method. Two marginal endocrowns of the mandibular first molar with different axial-wall thicknesses (t=1, 2, 3 mm) and heights (h=2, 3, 4 mm) were established. Group A was the butt-joint design, whereas group B was the shoulder-surrounded design. After applying vertical and oblique loads , the size and distribution of the maximum principal stress and equivalent stress of residual tooth tissue were recorded. The maximum principal stress and equivalent stress distribution of residual tooth tissue were similar among different models. Group A showed a lower maximum principal stress and equivalent stress than group B at the same thickness and height under vertical load. Meanwhile, under oblique load, the maximum principal stress values of groups A and B decreased with increased thickness at constant height. Group A showed lower equivalent stress than group B at the same thickness and height of 2 and 3 mm. However, when the height was 4 mm, the trend was reversed. In mastication, when bearing the vertical force, the retention of the butt-joint marginal endocrown preferred to the shoulder-surrounded one. Given the higher axial wall of the shoulder-surrounded marginal endocrown, it showed better ability to bear the oblique force than the butt-joint one.

Underwater submerged dissimilar friction-stir welding of AA5083 aluminum alloy and A441 AISI steel

This paper deals for the first time with the effects of additional cooling medium by submerging underwater on the feasibility of dissimilar bond formation between aluminum and steel in solid-state during friction-stir welding (FSW) process. Sheets of AA5083 Al-Mg aluminum alloy and A441 AISI steel are considered into the investigation with a butt-joint design and immersing under the cooling water mediums with three different temperatures of 0, 25, and 50 °C besides ambient processing in the air atmosphere without excessive cooling. Thermo-mechanical cycles during the FSW process are monitored as well as the soundness of produced dissimilar weldments in terms of materials inter-mixing, grain structural features, possible phase transformations, mechanical property, and subsequent fracture behavior. The results showed that by increasing the cooling capability of the environment and employing the low-temperature water as the submerged medium, the peak temperature during the FSW process is continuously reduced down to ~ 400 °C. The impact influence is on suppressing the dissimilar metals inter-mixing as well as the grain structural coarsening during dynamic recrystallization and the kinetics of intermetallic compound (IMC) formation. By decreasing the peak temperature and submerging under cooling medium, the thickness of the IMC layer at the interface is continuously decreased as affected the indentation hardness resistance and subsequent transverse tensile behavior. All samples are failed at the joint interface along the IMC layer, with an excellent combination of tensile strength (~ 310 MPa) and elongation (~ 13%) for the room temperature cooling medium, as the optimum condition based on the evolution of experimental trends. The dominant flow mechanism as plastic constraint induced some fractural aspects of ductile in dimpler form or catastrophic on the corresponding failed portion depending on the joint brittleness.

Sub-cable Butt Joint Design for CS Magnet of CFETR

The China Fusion Engineering Test Reactor (CFETR) is a new superconducting TOKAMAK fusion reactor. In Central Solenoid (CS) magnet of CFETR, the highest magnetic field in CS magnet will get 17.5 T,...

Fracture resistance and failure modes of polymer infiltrated ceramic endocrown restorations with variations in margin design and occlusal thickness

PurposeThe purpose of this in vitro study was to assess the effect of varying the margin designs and the occlusal thicknesses on the fracture resistance and mode of failures of endodontically treated teeth restored with polymer infiltrated ceramic endocrown restorations. MethodsRoot canal treated mandibular molars were divided into four groups (n=8) and were prepared to receive Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) fabricated polymer infiltrated ceramic endocrowns (ENAMIC blocks). Group B2 represents teeth prepared with a butt joint design receiving endocrowns with 2mm occlusal thickness and the same for group B3.5 but with 3.5mm occlusal thickness. Group S2 represents teeth prepared with 1mm shoulder finish line receiving endocrowns with 2mm occlusal thickness and the same for group S3.5 but with 3.5mm occlusal thickness. After cementation and thermal aging, fracture resistance test was performed and failure modes were observed. ResultsGroup S3.5 showed the highest mean fracture load value (1.27±0.31kN). Endocrowns with shoulder finish line had significantly higher mean fracture resistance values than endocrowns with butt margin (p<0.05). However, the results were not statistically significant regarding the restoration thickness. Evaluation of the fracture modes revealed no statistically significant difference between the modes of failure of tested groups. ConclusionsFor the restoration of endodontically treated teeth, adding a short axial wall and shoulder finish line can increase the fracture resistance. However, further investigations, especially the fatigue behavior, are needed to ensure this effect applies with small increases of restoration thickness.

Influence of core joints in sandwich composites under in-plane static and fatigue loads

Most designers are unaware of the influence of core junction in lightweight sandwich structures under axial load. Quantifying this effect and its criticality on the life of the structure is still a challenging task. In this study, a novel testing methodology was used to characterize this effect. Scarf and butt core joints in foam core sandwich composites were subjected to axial static and fatigue loads (R=0.1 and R=−1). Under cyclic axial load, differential movement (through-the-thickness) between the foam and core joint was more significant than anticipated. Non-destructive evaluation techniques were used to locate the damage and assess the failure mechanisms. The root-cause-failure analysis showed that cracks were initiated in the facesheets for the butt-joint, and in the core for the scarf-joint samples, respectively. Consequently, at 80% residual strength, the butt-joint reduced the predicted fatigue life by 42% and 32% at low and high cycle fatigue, respectively. Residual tensile tests revealed the sizeable damage induced by the traditional butt-joint design. This research confirmed that despite the facesheets' primary in-plane load carrying mechanisms, core junction will substantially influence the axial fatigue life of the structure.