Fracture Resistance Test Research Articles

Microhardness and Fracture Resistance of Radicular Dentin Treated with Different Concentrations of Calcium Hydroxide in Endodontic Regeneration Procedures

Purpose: to reveal the effect of different concentrations of prepared calcium hydroxide pastes (70%, 50%, and 30%) used in regenerative endodontic on microhardness and fracture resistance of radicular dentin. Material and methods: Different concentrations of calcium hydroxide (Ca(OH)2) were prepared with measured pH, then forty eight single rooted teeth were prepared and randomized into three groups according to Ca(OH)2 paste concentrations (12 samples each) and 12 samples were availed as control group. Group I: root canal contained 30% Ca(OH)2 paste. Group II: root canal contained 50% Ca(OH)2 paste. Group III: root canal contained 70% Ca(OH)2 paste. Samples were stored at 37 0C with 100% humidity for four weeks for subsequent microhardness and fracture resistance tests. Results: There was a statistically significant reduction of microhardness and fracture resistance between test groups and control group (P≤ 0.05), group III showed a significant reduction in both microhardness and fracture resistance compared to group I. However, there was no significant difference in pH between different concentration of Ca(OH)2. Conclusion: Increasing concentration of Ca(OH)2 paste can negatively affect microhardness and fracture resistance of radicular dentin in revascularization procedure.

Rehabilitation of severely-destructed endodontically treated premolar teeth with novel endocrown system: Biomechanical behavior assessment through 3D finite element and in vitro analyses

ObjectiveRehabilitation of endodontically treated premolars with extensive coronal destruction through endocrown approach remains a controversial topic in reconstructive dentistry. There is no clear consensus in the literature which endocrown design with which material is the most effective restoration option for severely-destructed endodontically treated premolars. The aim of this study was to assess the biomechanical behavior of endodontically treated maxillary first premolars restored with a novel endocrown system compared to the conventional one varying the applied load type through finite element and in vitro analyses. Materials and methodsFor finite element analysis, two models representing two endocrown systems used for restoration of severely-destructed endodontically treated maxillary first premolar tooth were generated: Model C for the conventional monolithic IPS e.max CAD endocrown and Model P for the novel bi-layered endocrown (PEKKTON ivory coping veneered with cemented IPS e.max CAD). Modified von Mises stress values on the remaining tooth structure, cement lines and restorative materials were evaluated separately under axial and oblique loading of 450 N. For in vitro analysis, forty sound human bifurcated maxillary first premolars were collected, endodontically-treated, and divided into 2 main groups (n = 20) according to the system used for endocrown fabrication; Group C: the conventional monolithic endocrowns and Group P: the novel bi-layered endocrowns. All specimens were subjected to an artificial thermomechanical aging protocol. Each main group was subdivided into two subgroups (n = 10) according to the loading type (axial and oblique) applied during the fracture resistance test. Qualitative analysis using Stereomicroscopy and Scanning Electron Microscopy was performed. Data were statistically analyzed at p-value ≤ 0.05. ResultsRegarding stress distribution pattern of remaining tooth structure (enamel and dentin), both endocrown systems and cement lines under both axial and oblique load application, Model P resulted in lower stresses than Model C. The oblique stress values of all analyzed structures were higher than corresponding values resulted axially. Considering failure load, a significantly higher load was recorded for Group P when axial or oblique loading was applied (p = 0.00). A significantly higher failure load was recorded with axial loading for both main groups. With regard to failure mode, a statistically significant difference was observed between main groups (p = 0.033), with more favorable failures detected for Group P axially. ConclusionsCompared to the conventional endocrown system, the studied novel system improved the biomechanical behavior within tooth/restoration complex of the restored severely-destructed endodontically treated maxillary first premolar teeth, whatever the applied load type. Clinical significanceThe novel endocrown system using a PEKK coping veneered with cemented IPS e.max CAD can be considered a favorable promising option for restoration of severely-destructed endodontically treated premolar teeth, with more protection for residual tooth structure. It can be considered as a conservative alternative option to the conventional treatment modalities not only for normal clinical conditions, but also for parafunctional cases.

Effect of Cervical Lesions on Fracture Resistance and Failure Mode of Maxillary Central Incisors Restored with Fiber Posts and Complete Crowns.

To investigate the effect of a cervical cavity extending 1 mm apical to the cemento-enamel junction (CEJ) on fracture resistance and failure mode of maxillary central incisors that have been treated endodontically, present with complete and incomplete ferrules, and are restored with and without a fiber post. 50 intact human maxillary central incisors were divided into five groups (n=10): CG (control group) 6-mm fer-rule height, no cervical cavity, and without post; (CO) 6-mm ferrule height without post, with a cervical cavity (access to root canal and cervical cavity restored with composite resin), cervical cavity; and post with ferrule heights of 1 mm (CP1), 2 mm (CP2), and 6 mm (CP6) restored with fiberglass post and composite resin core. After complete metal crowns were cemented on all specimens, they were subjected to thermal cycling (6000 cycles, 5°C/55°C), followed by immediate testing of fracture resistance. After failure, the specimens were sectioned buccolingually to evaluate and identify the mode of failure. The data were analyzed with an analysis of variance (ANOVA) and the Student-Newman-Keuls multiple comparison tests (α =0.05). A 1-mm ferrule height (CP1) fracture resistance was significantly lower (531±125 N) compared to the 6-mm ferrule height (CP6) (769±175 N) (p<0.05). With respect to the groups with similar residual dentin, with and without a cervical cavity, CG (667±119 N) and CO (668±119 N), the presence of a post (CP6) increased the resistance to fracture, although no statistically significant difference was demonstrated. Partial decementation was observed in all specimens of CG and CP6, in nine of CP1 and CP2, and in three in CO. Root fractures occurred in 23 specimens. The root surface was exposed 2 mm below the CEJ to simulate bone level. Propagation of subosseous cracks occurred in four specimens in CG and CP2, in seven specimens in CP6, in two specimens in CP1, and in six specimens in CO. All were considered catastrophic failures. Within the limitations of this study it is suggested that, when restoring an endodontically treated maxillary central incisor that has a cervical lesion and needs to be restored with a complete crown, a fiber post is cemented to improve fracture resistance.

Stabilization of Pt in SiO2–Al2O3 Microspheres at High Mechanical Resistance, Promoted with W Oxides for the Combustion of CO

This study shows the development of a combustion promoter for the oil-refining process called fluid catalytic cracking (FCC). The investigation of a catalyst prepared for the combustion of CO composed of 0.05 wt% Pt supported on SiO2–Al2O3–0.5 wt% W microspheres with high mechanical resistance, promoted with tungsten oxides (WOx) that can inhibit the sintering of Pt, is reported. The addition of WOx in SiO2–Al2O3 inhibited the decrease in the specific area when calcined from 550 °C to 950 °C. SiO2–Al2O3 support in the form of calcined microspheres with average diameters between 70–105 µm were produced by spray drying, using two atomization discs with vanes of different geometry: a straight rectangular blade disc (DAR) and a curved rectangular vanes disc (DAC). The DAR disk produced whole microspheres, while the DAC had hollow and broken microspheres. The microspheres were characterized by XRD, SEM, optical microscopy, N2 physisorption (BET area) and fracture resistance tests. The Pt catalysts were evaluated by TPR, H2 chemisorption and CO combustion. The catalyst of 0.05 wt% Pt/SiO2–Al2O3–0.5 wt% turned out to be the most stable. A thermal stabilization effect was observed at contents lower than 1 wt% W that allowed it to inhibit the sintering of the Pt catalyst.

Fabricated CAD/CAM Post-Core Using Glass Fiber-Reinforced Resin Shows Innovative Potential in Restoring Pulpless Teeth.

The prevention of root fractures of pulpless teeth is an important clinical issue to maintain healthy teeth through lifetime. The aim of this study was to examine a clinically effective treatment method for strengthening vulnerable pulpless teeth using CAD/CAM (computer-aided design/computer-aided manufacturing) fiber-reinforced post-core by conducting a fracture resistance test. A post-core made with a fiber-reinforced resin disk TRINIA (TR, SHOFU, Kyoto, Japan) was fabricated using a CAD/CAM system. The fiber-layer orientation of the CAD/CAM post-core was parallel to the axis of the restored tooth. A post-core using a conventional composite and a fiber post (CF) was also prepared. A fracture resistance test of teeth restored with the post-cores and zirconia crowns was conducted using a universal testing machine, and fracture patterns were identified by micro-CT observation. The fracture load of the roots restored with TR was 1555.9 ± 231.8 N, whereas that of CF was 1082.1 ± 226.7 N. The fracture load of TR was 43.8% that was significantly higher than that of CF (Student’s t-test, p < 0.05). The restored teeth with CAD/CAM resin post-core were found to be repairable even after fracture. These results suggest that the CAD/CAM indirect fiber post-core has the potential to strengthen the vulnerable pulpless teeth.

Impact of Two Different Designs and Materials on Fracture Resistance of Occlusal Veneers (In Vitro Study)

Abstract Statement of the problem: Occlusal veneer restorations represent a minimal invasive alternative to traditional crowns in treatment of severely worn dentition. However, the data regarding the mechanical performance of occlusal veneers designs and materials are still controversial. Aim of study: Evaluation of the effect of using two different designs and materials on fracture resistance of occlusal veneer restorations. Materials and Methods: Thirty-two freshly extracted premolars were randomly divided into two main groups (n=16) according to preparation design: Group B: butt joint preparation design and Group M: Modified occlusal veneer design. Each main group was further subdivided into two subgroups (n=8) according to type of restorative material used for occlusal veneer fabrication: Lithium disilicate and polymer-infiltrated ceramic network. Occlusal veneer restorations were fabricated by CAD/CAM technology and then cemented to their corresponding teeth using dual cured adhesive resin cement. Fracture resistance test was done using universal testing machine. The load needed for fracture of each specimen was registered automatically in Newtons (N) by a special software. Data were collected, tabulated and statistically analyzed. Results: Student's t-test results revealed that there was no statistically significant difference regarding the two variables (preparation design and material type). Also, Two-way ANOVA test results showed that there was no statistically significant difference regarding the interaction between the two variables in this study (P=0.309). Conclusion: There was no effect of preparation designs and material types on fracture resistance of occlusal veneers. The fracture resistance for all study groups exceeded the reported range of human masticatory forces.

Biomechanical behavior of different implant abutment materials

Purpose: to study the mechanical properties and Finite Element Stress Analysis of three implant abutment materials. Materials and Methods : Fifteen bars (25mm length, 4mm. thick and 5mm.width)of three abutment materials ;High Performance Polymer Hybrid abutments , Nano-Fiber Reinforced Composite and Fiber Reinforced Composite divided into three groups were exposed to Flexure Strength and Deflection tests. Fifteen implant abutments (two parts abutment) covered by all ceramic crowns divided into three groups were exposed to Static Fracture Resistance test and Finite Element Stress Analysis .Results: Flexure Strength tests mean and standard deviation of bar specimens showed significant difference, where Gp I, II, III were 519.29±0.46), 200.74±0.33and 315.43±0.59) .Also, Deflection test mean and standard deviation were 3.052±0.040, 0.984±0.106, 2.028±0.027 receptively revealed significant difference. The comparison between fracture resistance mean and standard deviation of the tested abutment three groupswere 642.00±.5.637,306.00±30.496 and 514.40±12.915 respectivelyand revealed significant difference. Finite Element Stress Analysis of applied vertical load on the three abutment materials did not have clear difference but the least stresses created on bone with Nano-FRC abutment(16.2) followed with FRC (17.32) then BioHPP abutment (18.55).Conclusion: Fracture strength of BioHPP abutments with ceramic crowns had the potential to withstand maximum occlusal forces, also showed better fracture patterns than the FRC and NFRC abutments. and showed a better stress distribution on the set, suggesting a good mechanical behavior.

Evaluation of the Effect of Long-term Use of Three Intracanal Medicaments on the Radicular Dentin Microhardness and Fracture Resistance: An in vitro study.

ObjectivesThe aim of this research was to evaluate the effect of long-term use of three intracanal medicaments on the radicular dentin microhardness and fracture resistance.Material and methodsA chemomechanical preparation was done using the Protaper rotary instruments up to F3. The teeth were stored in an incubator at 37°C at 100% humidity and were categorized in three groups by random allocation, namely: Triple Antibiotic Paste (TAP), Calcium hydroxide paste (Apexcal) and Ledermix. Following medicament application, the access openings of all teeth were sealed with 4 mm thickness of cavit. The samples were stored for periods of 1 week, 1 month and 3months. Two dentin cylinders measuring 5mm and 3mm were obtained from each sample. The cervical third was used for fracture resistance and the middle third was used for micro hardness evaluation. The microhardness testing was done using a Knoop microhardness tester, and the fracture resistance testing was done using the universal testing machine.ResultsCalcium hydroxide showed maximally negative effect on the physical properties of radicular dentin compared to TAP (p= 0.0100 at one month and Ledermix (p=0.0001 at one month). With an increase in the application time, there was an increased deterioration in the physical properties of radicular dentin.ConclusionLong-term placement of calcium hydroxide, Triple Antibiotic Paste, and Ledermix (p= 0.0001at 3 months) significantly affects the microhardness and fracture resistance of radicular dentin.

External Marginal Gap Variation and Residual Fracture Resistance of Composite and Lithium-Silicate CAD/CAM Overlays after Cyclic Fatigue over Endodontically-Treated Molars.

The purpose of this in vitro study was to evaluate the external marginal gap variation with a 3D quantitative method and the residual fracture resistance after cyclic fatigue in endodontically treated molars restored with overlays of different materials, with and without fiber posts-supported buildups. Forty-eight human maxillary molars were selected, endodontically treated, prepared with standardized MOD cavities and randomly allocated into 6 study groups considering the “core strategy” (build-up with composite resin; build-up with composite resin supported by a fiber post); and the “restorative material” of the indirect adhesive overlay (GrandioBlocks, Voco; Cerasmart, GC; CeltraDuo, Dentsply). All procedures were executed according with manufacturers guidelines. Micro-CT analysis prior and after cyclic fatigue were executed, followed by scanning electron microscope analysis and fracture resistance test. The Two-Way ANOVA analysis showed that interfacial gap progression was significantly influenced by the “core strategy” (p < 0.01) but not of “restorative material” (p = 0.59). Concerning fracture resistance, “restorative material” was statistically significant (p < 0.01), while “core strategy” (p = 0.63) and the interaction (p = 0.84) were not. In conclusion, the fiber post presence within the build-up promoted a lower interfacial gap opening after fatigue, evaluated through micro-CT scans. In terms of fracture resistance, teeth restored with Cerasmart and Celtra Duo were statistically similar, but superior to GrandioBlocks.

Comparison of Fracture Resistance and Failure Mode in Digitally Milled Restorations with Rapid Layering by Indirect Composite Resin: An In Vitro Study.

To evaluate the fracture resistance and failure mode of implant crowns made by polyether ether ketone (PEEK), zirconia, and chromium-cobalt frames, veneered by milled composite resin. Thirty-six implant analogs were mounted in acrylic blocks, and solid abutments were secured (n = 12). Single-unit frameworks were milled from PEEK, zirconia, or chromium-cobalt, and cemented to indirect composite veneers fabricated by the rapid layering technique. After thermal cycling, the fracture resistance test was performed at a speed of 0.5 mm/min, and the results were statistically analyzed by one-way analysis of variance (ANOVA) and Tukey post hoc test (P < .05). The failure mode was evaluated by a stereomicroscope ('L10). Veneer failure without damage to other components was considered desirable (repairable). The mean fracture resistances of PEEK, zirconia, and chromium-cobalt specimens were 2,037.24, 2,567.05, and 2,032.10 N, respectively. The Tukey post hoc test showed no significant difference between the PEEK and chromium-cobalt groups (P = .99); however, the difference was significant between zirconia and PEEK or chromium-cobalt specimens (P = .001). Failure mode was desirable in all chromium-cobalt (12 specimens), 9 zirconia, and 7 PEEK-based specimens. Zirconia-composite implant crowns had significantly higher fracture resistance. Given the range of maximum occlusal forces, all the specimens had clinically acceptable results. The failure mode was more desirable in chromium-cobalt, followed by zirconia-based crowns.

Efficacy of Different Dentin Posts for the Treatment of Primary Anterior Teeth (An In vitro study)

ABSTRACTIntroduction: Early childhood Caries is a distressing situation for patients andparents and pediatric dentists. Aim: current research was carried out to evaluatefracture resistance and bond strength for different types of dentin posts compared tofiber posts. Materials and Methods: This Current in-vitro study was conducted on48 extracted primary incisors. Samples were split randomly into 4 groups of 12 foreach group. Group-I (fiber posts 6mm length, 1.4mm diameter), Group-II (dentin posts6mm length, 1.4 diameter), Group-III (dentin posts 8mm length, 1.4mm diameter),Group-IV (dentin posts 8mm length, 1.6mm diameter). Each group was furthersubdivided into two subgroups (6 for the Push-Out bond strength test and 6 for thefracture resistance test using Universal Testing Machine). Results: It was observedin the fracture resistance test that, Group III showed the highest fracture resistancemeans (140.678±11.98) followed by Group IV (131.38±7.03), Group-II (94.23±9.84),and finally Group-I that showed the lowest fracture resistance means (80.465±2.82).Push-Out bond strength test revealed that the highest mean value with Group-IV(8.653±1.49), followed by Group-II (6.08±2.25) and Group III (5.67±2.44) have nostatistically significant difference between them, while the lowest mean value was forGroup-I. Conclusions: Dentin posts showed increased fracture resistance and bondstrength more than fiber posts. The use of dentin post as intra-canal retention in primaryanterior teeth possesses the most important advantages over the fiber post. Therefore,biological dentin post is a successful alternative for fiber post.

Assessing Fracture Resistance of Restored Premolars with Novel Composite Materials: An In Vitro Study.

During restorative treatment, premolars restored with resin filling materials using the conventional incremental-fill technique take longer restoration time and undermine the integrity of the tooth. The aim of this study was to assess fracture resistance of premolars restored by various types of novel bulk-fill composite resin materials. Forty-eight (n = 48) freshly extracted sound maxillary first premolars were used in this in vitro study. The teeth were divided into six groups, each having 8 specimens. Group A (positive control) was allocated for the intact teeth. For specimens in Groups B to F, a large cavity (Class-II MOD) was prepared with a standardized dimension of cavity (3 mm depth on the pulpal floor, 4 mm at the gingival seat, and 3 mm cavity width). Group B represented prepared teeth without any restoration. Group C, Group D, Group E, and Group F were restored with Tetric EvoCeram® incremental-fill (conventional), Beautifil bulk-fill, Filtek posterior bulk-fill, and SonicFill 2 bulk-fill restorative materials, respectively. All samples were finished and polished with an enhanced finishing kit and stored in distilled water for a month before the fracture resistance testing. All the samples were exposed to the axial loading (the speed of crosshead was 1 mm/min) in a computer-controlled universal testing machine (LARYEE, China) via a steel bar (6 mm in diameter) and the maximum applied force in Newton was recorded as the fracture resistance. One-way analysis of variance (SPSS 21) was used to compare the fracture resistance within the groups, and Tukey's post hoc test was used to determine the difference between the groups. The lowest value of fracture resistance was recorded for Group B, and the highest value was recorded for Group A followed by the values of Group D, Group C, Group F, and Group E. One-way ANOVA revealed a statistically significant difference between the groups (P < 0.05). Nonsignificant difference was found between the premolars restored by bulk-fill and conventional composites. Among the bulk-fill restored specimens, Beautifil restorative demonstrated significantly higher fracture resistance in comparison with the other two bulk-fill restored specimen groups (SonicFill 2 and Filtek). Bulk-fill composite such as Beautifil could be an alternative option to conventional incremental-fill composite for premolar restoration.

Effect of Different Bonding Substrates on Fracture Resistance of Thin and Ultra-thin Occlusal Veneers constructed using Different CAD/CAM Materials

Objectives: The aim of this study was to compare the fracture resistance of thin and ultra-thin occlusal veneers constructed from ceramics and hybrid ceramics bonded to different bonding substrates after thermomechanical aging. Materials and Methods: A total of 96 extracted maxillary first premolars were used. The teeth were divided into three groups according to the bonding substrate/protocol: EN, IDS Dentin, DDS Dentin. Each group was further subdivided into two subgroups according to the material of construction: E.max CAD, Vita Enamic. Each subgroup was further subdivided into two subdivisions according to the thickness of the occlusal veneer: Ultrathin, Thin. All the teeth were prepared to receive occlusal veneers. All the occlusal veneers were constructed using CAD/CAM technique. All occlusal veneers were cemented using adhesive resin cement. Thermomechanical aging was applied on all samples. Fracture resistance testing was performed. Results: There was statistically significant difference between bonding protocols where IDS Dentin showed the statistically significantly highest mean fracture resistance followed by Enamel then DDS Dentin. Vita Enamic showed statistically significantly higher mean fracture resistance than E.max CAD. Ultra-thin occlusal veneers showed statistically significantly lower mean fracture resistance than thin occlusal veneers. Conclusions: Ultrathin occlusal veneers must be cautiously used when glass ceramics is chosen. However, this minimal thickness could be a favorable option on using hybrid ceramics. Increasing the occlusal thickness to 0.5-0.8mm could be promising upon bonding with either enamel or dentin with both materials used. Ultra-thin occlusal veneers must be used carefully upon bonding to dentin (IDS must be applied).

Effect of Thermo-Mechanical Aging and Repressing on Fracture Resistance of Lithium Disilicate Crowns

Objective: The recycling of heat pressed lithium disilicate glass-ceramic leftover material has been reported to be done by dental laboratories. The effect of this procedure on the fracture resistance of single crowns is unknown, especially when it is functioning inside the oral cavity with subsequent exposure to temperature changes and cycles of mastication. Material and Methods: A total of 28 lithium disilicate glass-ceramic crowns (IPS emax Press) were constructed and randomly assigned into two groups (n = 14); Group (P): Included crowns fabricated from new e.max ingots. Group (R): Included crowns fabricated from repressed e.max buttons. Specimens of each group were divided into two equal subgroups (n = 7) according to whether the aging of specimens will be performed or not before fracture resistance testing. Subgroup (N), samples were subjected to fracture resistance without thermo-mechanical aging, while subgroup (A), samples were subjected to thermo-cycling and cyclic loading before being subjected to fracture strength testing. Different methods; SEM, XRD, EDAX were used to characterize the properties of lithium disilicate glass-ceramics before and after repressing. Results: The highest statistically significant fracture resistance value was recorded for the subgroup (RN) repressed/non-aged, followed by the subgroup repressed/aged (RA), while the lowest statistically significant mean value was recorded for the subgroup pressed/aged (PA). There was no significant difference between pressed/non-aged (PN) and repressed/aged (RA) subgroups. Conclusion: Repressing of leftover buttons may increase the fracture resistance of IPS emax Press crowns. Thermo-mechanical aging may negatively affect the fracture resistance of IPS emax Press crowns, yet Repressing may decrease this effect. Clinical implications: This is a novel approach that targets a point of research that has not been investigated before. It elaborates how repressing may decrease the effect of aging and increase the fracture resistance of lithium disilicate crowns. Thus, recycling of lithium disilicate glass ceramics might decrease its failure and prolong their serviceability. Keywords Fracture resistance; Heat pressed; Lithium disilicate; Recycling; Repressing; Thermo-mechanical aging.

FRACTURE RESISTANCE OF ENDODONTICALLY TREATED TEETH RESTORED WITH LITHIUM DISILICATE CROWNS RETAINED WITH FIBER POSTS COMPARED TO CERASMART AND CELTRA DUO ENDOCROWNS (IN VITRO STUDY)

Aim: The purpose of this study wasto evaluate the fracture resistance of cerasmart and Celtra Duo endocrowns compared to endodontically treated teeth restored with glass fiber post and lithium disilicate crowns. Methodology: Eighteen sound maxillary premolars were endodontically treated, then divided into three groups: Group (GE) received fiber post, resin core and lithium disilicate (IPS E.max CAD, Ivoclar-Vivadent) crown. Group (GC) received endocrown with butt joint finish line design fabricated from hybrid ceramic (CERASMART, GC Dental USA). Group (GD) received endocrown with butt joint finish line design fabricated from zirconia reinforced lithium disilicate (CELTRA DUO, Dentsply Sirona). All restorations were fabricated using (CEREC MC XL SW 4.0) milling machineand cemented with self-adhesive dual cureresincement. Thermo-mechanical fatigue was applied on all samples and fracture test was then done. Scanning electron microscope was used for examining the fractured samples. Results: Fracture resistance test showed that there was statistically significant difference between the three groups (P-value = 0.001, Effect size = 0.603).GE showed statistically significant highest median fracture value (1866 +/- 399.9).Meanwhile, there was no statistical difference between mean fracture resistance values of GC of (1045.1 +/- 122.1) and GD (1377 +/-307) where both showed statistically significant lowest mean fracture resistance values. Conclusion: Conventional post, core andcrown treatment option remains the gold standard for treating endodontically treated maxillary premolar, nevertheless endocrown restoration on premolars needs further research to become a viable restoration in this condition.

Evaluation of Fracture Resistance of Endodontically Treated Maxillary Premolars Restored with Different Restorative Materials - An In Vitro Study

Aim: In this study was evaluated the fracture resistance of endodontically treated maxillary premolars restored with different restorative materials. Methods: Sixty maxillary premolars were submitted to the same mesio-occlusal-distal cavity preparation, endodontic treatment and divided into 5 groups (n = 10): Coltosol Group – GCO restored with calcium silicate material; Glass Ionomer Cement Group – GGIC, restored with Maxxion R; Modified Glass Ionomer Cement – GMGIC, restored with Gold Label 2; Composite Group - GC, restored with Z100, and the positive control group (GP) - left unrestored. One group remained intact (n=10) serving as negative control (GN). Samples were subjected to fracture resistance testing by the universal testing machine until fracture occurred and was registered in newtons (N). Fracture pattern was assessed and described as favorable or unfavorable. The results were statistically analyzed by 1-way analysis of variance and the post hoc Tukey test with significant statistical difference at P &lt; 0.05. Results: Higher fracture resistance results were found for GC (1,128.35 ± 249.17), GMGIC (1,250.77 ± 173.29), and GN (1,277.22 ± 433.44) (P &lt; .05). More favorable fractures were observed in the GCO (6), GC (7), and GN (7) (P &lt; .05). Conclusion: Teeth restored with composite and modified GIC presented the same resistance as intact teeth. Teeth restored with Coltosol and GGIC presented similar resistance to unrestored teeth.

Fracture resistance and 3D finite element analysis of machined ceramic crowns bonded to endodontically treated molars with two planes versus flat occlusal preparation designs: an in vitro study.

Background: The flat occlusal preparation design (FOD) of posterior teeth offers promising results of fracture resistance and stress distribution, but its application in vital teeth is limited as there may be a danger of pulp injury. Although this danger is omitted in endodontically treated teeth, there is no research work assessing the impact of FOD on the fracture resistance and distribution of stresses among these teeth. The aim of this study was to assess the impact of FOD of endodontically treated molars on the fracture resistance and distribution of stresses among a ceramic crown-molar structure when compared to the two planes occlusal preparation design (TOD). Methods: 20 human mandibular molars were endodontically treated and distributed equally to two groups: Group I (TOD) and Group II (FOD). Ceramic CAD/CAM milled lithium disilicate (IPS e.max CAD) crowns were produced for all preparations and adhered using self-adhesive resin cement. Using a universal testing machine, the fracture resistance test was performed. The fractured samples were examined using a stereomicroscope and scanning electron microscope to determine modes of failure. Stress distribution was evaluated by 3D finite element analysis, which was performed on digital models of endodontically treated mandibular molars (one model for each design). Results: Group II recorded statistically non-significant higher fracture resistance mean values (3107.2± 604.9 N) than Group I mean values (2962.6 ±524.27 N) as indicated by Student's t-test (t=0.55, p= 0.57). Also, Group II resulted in more favorable failure mode as compared to Group I. Both preparation designs yielded low von-Mises stresses within the factor of safety. However, the stress distribution among different layers of the model differed. Conclusions: FOD having comparable fracture strength to TOD and a more favorable fracture behavior can be used for the preparation of endodontically treated molars.

CAD-FEA modeling and fracture resistance of bilayer zirconia crowns manufactured by the rapid layer technology.

In the RLT (Rapid Layer Technology), veneering ceramic and framework are fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) and then cemented to obtain the restoration. This study aimed to evaluate the effect of the thickness of veneering ceramic manufactured by the RLT technique on the fracture resistance (FR) of bilayer crowns with zirconia frameworks. Twenty zirconia frameworks and twenty feldspathic posterior crowns with two different veneering ceramic occlusal thicknesses (1mm=TF1; 2mm=TF2) were manufactured using CAD/CAM system. The specimens were luted to an epoxy resin abutment with resin cement and mechanically cycled (200N and 4.5×105 Pa, 37°C, 2×106 cycles, 3Hz). The FR test was performed (10kN, 0.5mm/min), and the specimens were analyzed in a stereomicroscope. For the stress analysis (finite element analysis, FEA), a 10kN load was equal to the in vitro test, and the principal stress was evaluated. The FR data were analyzed by Student's t-test and Weibull's analysis. The thickness influenced the FR of bilayer crowns. The FR was higher in the TF2 than in the TF1 group. The TF2 group presented the highest characteristic strength compared to the group TF1. The predominant type of failure was delamination. The FEA showed higher stress concentrations below the loading application point at the veneering cement interface in the 1-mm-thick model. The bilayer crowns manufactured using the approach of 2mm of veneering ceramic promoted higher FR compared to the group with 1mm veneering ceramic. Also, the FEA showed that the veneer ceramic thickness has an effect on stress distribution in zirconia-based bilayer crowns.

Effect of Die Spacer Thickness on the Fracture Resistance of CAD/CAM Lithium Disilicate Veneers on Maxillary First Premolars.

ObjectiveThe purpose of this study was to compare the fracture resistance of ceramic veneers with digital die spacer settings at 20 µm, 40 µm, and 100 µm.Materials and MethodsEighteen sound maxillary first premolars were divided into three groups (n=6) according to their digital die spacer settings: group A=20 µm, group B=40 µm, group C=100 µm. Each tooth was prepared to a depth of 0.5 mm to receive lithium disilicate veneers (IPS e.max CAD, Ivoclar Vivadent). All groups were thermocycled (2500 cycles at 5–55°C) and subjected to fracture resistance test using a universal testing machine until failure. Failure modes were examined using a stereomicroscope.ResultsThe values (N) for group A=1181.34±301.33, group B=1014.29±291.12, and group C=841.89±244.59. One-way ANOVA showed no statistical difference among the three groups (p=0.145). However, chi-square test showed that a significant difference was present in the modes of failure (p=0.009). Tukey’s post hoc test indicated that the failure modes of group A were statistically different from those of group C, showing 83.3% adhesive failure for group A compared to 0% adhesive failures in group C. A p-value of ≤0.05 was considered as statistically significant.ConclusionDigital die spacer thickness did not influence the mean fracture resistance values of CAD/CAM lithium disilicate veneers. However, the way the failure occurred differed significantly at various die spacer thicknesses.

Effects of various thicknesses and levels of mineral trioxide aggregate coronal plugs on nanoleakage and fracture resistance in revascularization: An invitro study.

The aim of this study was to evaluate the effects of mineral trioxide aggregate (MTA) applied at varying levels and thickness in the cervical region of the root on the leakage and fracture resistance of the simulated immature teeth. 3 study groups (n = 16) (Group 1: 2 mm MTA, Group 2: 4 mm MTA, Group 3: 2 mm MTA+2 mm RMGIC below cementoenamel junction) and 2 control groups (Group 4: Complete canal obturation, Group 5: No coronal plug) were used for the study. Nanoleakage was measured using a micro-computed tomography system. For the fracture resistance test, a universal testing machine was used. The amount of silver nitrate penetration decreased while MTA thicknesses increased (P < 0.001). However, the placement of MTA as a thicker layer did not make any additional contribution on the fracture resistance (P > 0.05). The 4-mm coronal MTA plug can be suggested in RETs for its superior sealing and reinforcement abilities.