Mean Flexural Strength Values Research Articles

Comparative Evaluation of Fracture Toughness and Flexural Strength of Four Different Core Build-up Materials: An In Vitro Study.

To evaluate and compare the fracture toughness and flexural strength of four different core build-up materials. A total of 60 samples were divided into four groups (n = 15) group I: dual cure composite resin reinforced with zirconia particles (Luxacore Z), group II: light cure composite resin (Lumiglass DeepCure), group III: zirconia reinforced glass ionomer cement (GIC) (Zirconomer Improved), and group IV: chemically cure composite resin (Self Comp) respectively. All the core build-up materials were manipulated according to the manufacturer's instructions and poured into the mold. A universal testing machine applied a central load to the specimen in a 3-point bending mode. Fracture of the specimen was identified and the reading was recorded by the universal testing machine. The data were analyzed statistically using one-way analysis of variance (ANOVA) and then compared. Group I showed the highest flexural strength (48.65 MPa) among all the groups while group IV showed the lowest flexural strength (17.90 MPa). Group I showed the highest fracture toughness (99.12 MPa) among all the groups while group IV showed the lowest fracture toughness (36.41 MPa.cm-0.5). When mean flexural strength and fracture toughness values of all four groups were compared by using one-way ANOVA, the compared data was highly significant. Based on the findings of this study, dual cure composite resin was the material of choice in terms of flexural strength and fracture toughness for core build-up material followed by light cure composite resin. The core buildup material serves to strengthen the tooth structure, allowing it to withstand the forces of chewing and preventing the risk of tooth fractures. This material is essential in restoring damaged or decayed teeth, as it provides a stable foundation for further dental work. By reinforcing the tooth structure, the core buildup material ensures that the tooth can function properly and remain healthy for years to come. How to cite this article: Nakade P, Thaore S, Bangar B, et al. Comparative Evaluation of Fracture Toughness and Flexural Strength of Four Different Core Build-up Materials: An In Vitro Study. J Contemp Dent Pract 2024;25(2):191-195.

Comparative Evaluation of Flexural Strength and Microhardness of Two Different Ceramic Reinforced 3-D Printed Resins with Cad-cam Milled and Conventional Tooth Coloured Heat Cured Polymethylmethacrylate Resins as Long-term Provisional Restorative Materials” – An in Vitro Study

Background: Long-term provisional restorations play a crucial role in complex clinical scenarios, Implant-supported prostheses, full-mouth rehabilitation cases & Maxillofacial Prosthodontics. Understanding the mechan-ical properties such as flexural strength and microhardness of newer commercially available provision-al restorative materials is necessary to select an optimum material for long-term provisional fixed den-tal prosthesis. This Research study was conducted to evaluate and compare the Flexural Strength and Microhardness of Two Different Ceramic-reinforced 3-D Printed Resins with CAD-CAM Milled and Conventional Tooth Coloured Heat Cured Polymethylmethacrylate Resins as Long-Term Provisional Restorative Materials. Methods: Twenty-one specimens of dimensions 25 mm × 2 mm × 2 mm (ADA-ANSI specification #27) were fabricated each using: Group A (Control group)-Conventional tooth colored heat cured polymethyl-methacrylate resin (DPI Heat cure tooth moulding powder), Group B-CAD-CAM milled resin, Group C- Ceramic reinforced polymer 3-D printed resin (Temporary CB resin) and Group D- Ceramic rein-forced polymer 3-D printed resin (Permanent CB resin). Flexural strength and microhardness were measured and the values obtained were evaluated. Results: The measured mean flexural strength values (Mega Pascals) were 39.41 (Group A), 153 (Group B), 124.91 (Group C), and 136.50 (Group D). The measured mean microhardness values (Knoop hardness number) were 37.9 (Group A), 40.5 (Group B), 34.67 (Group C), and 43.88 (Group D). The difference in flexural strength and microhardness values of the three groups was statistically significant according to the analysis of variance (ANOVA) as well as the intergroup comparison done using Tukey’s honest significant difference (HSD) Post Hoc test (P < 0.05). Conclusions: Flexural strength with higher values in Group B were noted and the Microhardness test showed higher values in Group D.

Evaluation of flexural strength, impact strength, and surface microhardness of self-cured acrylic resin reinforced with silver-doped carbon nanotubes

BackgroundPoly-methyl methacrylate (PMMA) is a type of polymer mostly used to make denture bases. Self-cured acrylic resin (PMMA) can be used to repair a fractured acrylic denture base; however, even after repair, this area remains vulnerable. Carbon nanotubes (CNTs) could be used as a filler for polymer reinforcement. Furthermore, silver nanoparticles are efficient agents for the prevention of dental biofilm and improving their mechanical properties. The doping of CNTs with silver nanoparticles may lead to a synergistic interaction that is predicted to enhance the mechanical characteristics of the fillers.ObjectivesThe aim of the study was to assess the influnce of manual incorporation of 0.5% weight percent (%wt.) of silver doped carbon nanotubes (Ag-doped CNTs) into commercial self-cured PMMA on its flexural strength, impact strength, and surface microhardness.MethodsIn this investigation, a total of 60 specimens comprised of acrylic resin were employed. They are divided into two main groups: (a) the control group, which was made by using liquid monomer and commercial self-cured PMMA powder; and (b) the modified group, prepared by hand mixing the purchased silver-doped CNTs powder (0.5% wt.) to self-cured PMMA powder (99.5%wt.), and then the blended powder was incorporated into the liquid monomer. Flexural strength, flexural modulus, impact strength, and surface microhardness were evaluated. Independent sample t-tests were used to statistically analyze the data and compare the mean values of flexural strength, flexural modulus, impact strength, and surface microhardness (p-value ≤ 0.05).ResultsThe flexural strength of the modified groups with Ag-doped CNTs (132.4 MPa) was significantly greater than that of the unmodified (control) groups (63.2 MPa). Moreover, the flexural modulus of the modified groups with Ag-doped CNTs (3.067 GPa) was significantly greater than that of the control groups (1.47 GPa). Furthermore, the impact strength of the modified groups with Ag-doped CNTs (11.2 kJ/mm2) was significantly greater than that of the control groups (2.3 kJ/mm2). Furthermore, the microhardness of the modified groups with Ag-doped CNTs (29.7 VHN) was significantly greater than that of the control groups (16.4 VHN), (p-value = 0.0001).ConclusionThe incorporation of 0.5% wt. silver doped CNTs fillers to the self-cured acrylic resin enhanced its flexural strength, flexural modulus, impact strength, and surface microhardness.

Flexural strength of a polymethylmethacrylate resin produced by computer‐aided design and computer‐aided manufacturing system after repeated usage of tungsten carbide burs and thermocycling

AbstractThe purpose of this study was to examine how new and used burs affected the flexural strength of a polymethylmethacrylate resin produced by computer‐aided design and computer‐aided manufacturing system following thermocycling. A total of 40 rectangular‐shaped specimens (14 mm×4 mm×1.2 mm) for flexural strength test were fabricated from one brand of a polymethylmethacrylate resin produced by computer‐aided design and computer‐aided manufacturing system. Half of the specimens (Group N) were milled using the new tungsten carbide bur set, while the other half (Group U) was milled using the used (250 machining time) tungsten carbide bur set. The specimens were subjected to flexural strength test before and after thermocycling. The One way Analysis of Variance and Duncan tests were used for statistical analysis. Group N had the highest mean flexural strength values, while Group NT (specimens milled with the new bur/before thermal cycling) had the lowest mean flexural strength values. New and used burs have an effect on the flexural strength of a polymethylmethacrylate resin specimens produced by computer‐aided design and computer‐aided manufacturing system. Thermocycling process have an effect on the flexural strength values of specimens milled with the new tungsten carbide bur.

The effect of different concentration of emodin nanoparticles, as an antibacterial agent, on the flexural resistance of acrylic resin used in orthodontics: An in vitro study

The aim of this study was to investigate the impact of emodin nanoparticles (n-Emo) on the flexural strength of acrylic resin used in orthodontics. A total of 24 acrylic resin discs were prepared according to ISO:20795-1 and divided into four groups (n=6): 0% n-Emo, 0.5% n-Emo, 1% n-Emo, and 2% n-Emo. The flexural strength of each group was measured using the Universal Testing Machine. One-way analysis of variance (ANOVA) and Tukey tests were used to analyse the data. The highest flexural strength values were observed in the groups containing 0% and 0.5% concentrations of n-Emo, while the lowest mean flexural strength was recorded in the group containing 2% concentration of n-Emo. There were significant difference in flexural strength values between the groups containing 0% with those containing 1% and 2% concentrations (P=0.045, P=0.011, respectively), as well as between those containing 0.5% and 2% concentrations of n-Emo (P=0.041). The results of the study showed that the incorporation of n-Emo had a negative impact on the flexural strength of the acrylic resin utilized in orthodontics. Nonetheless, the mean flexural strength values of all groups fell within the normal range, implying that the addition of n-Emo did not jeopardize the mechanical properties of the acrylic resin. It is therefore conceivable that the use of n-Emo as an antimicrobial agent in acrylic resin could be a promising approach to reducing enamel demineralisation and dental caries, while preserving its mechanical properties. This study was approved by the ethics committee of the Tehran University of Medical Sciences (1401-2-398-54892).

Fabrication of high-performance Magnéli phase Ti4O7 ceramics by in-situ hot-pressed sintering in a single step

Magnéli phase ceramics have gained extensive attention in a variety of fields, including batteries, electrocatalysis, and wastewater treatment, due to their distinctive properties. In this study, high-performance Magnéli phase Ti4O7 ceramics were synthesized by in-situ hot-pressed sintering of titanium (Ti) and titanium dioxide (TiO2) in a single step. The effects of the sintering temperature and Ti content on the phase transformation and morphology of ceramics were investigated. Moreover, the mechanical properties and electrical conductivity of the samples were systematically characterized. Results show that the sample with the Ti/TiO2 weight ratio of 0.09 sintered at 1000 °C has impressive comprehensive properties, including a high bulk density of 4.281 g·cm−1, a mean value of flexural strength of 125.58 MPa, and an excellent conductivity of 1129 S·cm−1. Furthermore, an evolution mechanism of the in-situ sintering for Ti/TiO2 was discussed based on the experimental data, and the pattern of variation observed by samples can be reasonably explained.

Experimental study on physical-mechanical characteristics of steel fiber reinforced concrete with worn rope fibers

This study examined the physical-mechanical properties of steel fiber reinforced concrete with different fiber orientations and vibration times. The concrete mixtures contained crushed stone, sand, Portland cement, Rheobuild 181A plasticizer, and 5 cm steel fibers with 2% reinforcement. Using steel fibers from worn ropes from Innotech LLP (Almaty, Kazakhstan) increased the average strength of concrete and improved its ductility, allowing for plastic failure instead of brittle failure. Joint mixing of steel fiber-reinforced concrete with randomly oriented fibers made from used cables increased the mean value of flexural strength. The concrete mixtures with a vibration time of 9 seconds showed the highest flexural strength, which was 2.1 times higher than that of concrete samples without fiber. These findings demonstrate the potential of steel fiber reinforcement to improve the mechanical properties of concrete, especially in applications requiring flexural strength.

Evaluation of the Effect of Nanoparticle Graphene Oxide on Flexural Strength of Glass Ionomer Cements.

Glass ionomer (GIC) is a widely used restorative material in dentistry, but it has relatively weak mechanical properties. In this research, the effect of graphene oxide (GO) on the flexural strength of GIC was investigated. In this experimental study, 60 GIC samples in 6 groups of 10 were prepared, including Group 1: control conventional glass ionomer (CGIC), Group 2: CGIC + 1% wt of GO, Group 3: CGIC + 2% wt of GO, Group 4: control resin-modified glass ionomer (RMGI), Group 5: RMGI + 1% wt of GO, and Group 6: RMGI + 2% wt of GO. The samples were kept for 24 hours. The flexural strength of the samples was measured by using a universal testing machine. Data were analyzed by two-way ANOVA and posthoc Tukey test. (P < 0.05). In the RMGI groups, the mean flexural strength value of the RMGI + 2% GO group was significantly higher than that of the RMGI control group (P=0.027). In the comparison of RMGI groups with their corresponding CGIC groups, the mean flexural strength values of all RMGI groups were significantly more than CGIC groups (P < 0.001). RMGI + 1% GO was not significantly different from control RMGI and RMGI + 2% GO (P=0.802, P=0.395, respectively). There was no significant difference between CGIC groups. Adding 2% by weight of GO to RMGI increases the flexural strength of RMGI, which could be of great importance in clinical practice in order to reinforce the mechanical properties of this dental material. The flexural strength of RMGI is higher than that of CGIC.

Comparative Evaluation of Flexural Strength of Heat Polymerised Polymethyl Methacrylate Provisional Fixed Restorative Resin Reinforced with Different Percentages of Silanised Zirconium Oxide Nanoparticles: An In-vitro Study

Introduction: The purpose of providing a provisional restoration includes immediate replacement of missing teeth, for protection of pulp and maintenance of periodontal health, to maintain occlusal stability, to preserve the position of the teeth and for masticatory efficiency. Provisional restorations fabricated from heat processed acrylic resin have been used successfully. Incorporation of inorganic nanoparticles into Polymethyl Methacrylates (PMMA) resin has been shown to improve its physical properties. Aim: To evaluate and compare the flexural strength of heat polymerised PMMA provisional restorative resin reinforced with different percentages of silanised zirconium oxide nanoparticles. Materials and Methods: This is an in-vitro study performed in the Department of Prosthodontics, VSPM’s Dental College and Research Centre, Nagpur, Maharashtra, India, from June 2018 to February 2020. A die was used to create sixty heatcured PMMA resin specimens, which were then divided into four groups: group A includes controls with conventional heat polymerised provisional restorative resin (PMMA) and groups B, C and D conventional heat polymerised provisional restorative resin reinforced with different percentages of silanised zirconium oxide nanoparticles (1 wt%, 2.5 wt%, 5 wt%, respectively), having fifteen specimens in each group. Three point bending tests were conducted on all samples using a universal testing machine. The flexural strength of each specimen was calculated. Mean value of flexural strength of each group was used for statistical analysis. One-way analysis of variance test was used to find out the mean value of flexural strength of each group. Results: The mean flexural strength for control group was 53.76±2.97 MPa. For group B (1% Zirconium oxide) it was 58.14±4.86 MPa, for group C (2.5% Zirconium oxide) was 63.29±4.22 and for group D (5% Zirconium oxide) it was 59.02±3.99 MPa. Statistical analysis showed that maximum strength was obtained by reinforcement with 2.5% silanised zirconium oxide nanoparticles. Conclusion: Polymethyl methacrylate reinforced with silanised 2.5% of zirconium oxide nanoparticles promises to be better material in terms of flexural strength.

Effect of the region of the CAD/CAM block on the flexural strength and structural reliability of restorative materials

The aim of the study was to evaluate whether the region (internal or external) of the CAD/CAM block influences the mechanical performance of restorative materials. Blocks of different CAD/CAM materials (Composites: KAV – Katana Avencia; LULT – LULT Ultimate; Ceramics: ENAM – Vita Enamic; NICE - N!CE; EMP – IPS Empress CAD; VMII – Vita Mark II; EMAX – IPS e.max CAD) were selected, and direct resin composite blocks (APX - Clearfil AP-X; FSUP - Filtek Supreme) were built using the incremental technique on a mold from one of the CAD/CAM blocks. All blocks were sectioned into bar-shaped specimens (1 × 1 × 14 mm), which were separated into two groups according to the region of the block (inside or outside). 3-point bending tests were performed following ISO 6872:2015 and flexural strength data were analyzed using one-way ANOVA and Bonferroni post-hoc tests (p < 0.05). Weibull module and characteristic strength were also calculated. In general, the mean flexural strength values were not statistically different (p > 0.05) between the inside and outside regions of each material, except for LULT (inside > outside) and EMAX (outside > inside). Comparing the materials, a similar strength (only discrete variations) was observed for inside, outside or merged (inside and outside data assembled together) regions: EMAX > KAV = LULT > NICE = APX > EMP = ENAM = VMII ≥ FSUP (merged condition). Characteristic strength at 63.2% failure probability and at 5% failure probability generally corroborates such observations. There were no statistical differences for Weibull module data (inside, outside, or merged), except for KAV and NICE (outside > inside). Thus, the region from where the restoration is milled within the CAD/CAM block generally does not influence the mechanical performance hereof (flexural strength, failure probability, risk of premature failures, and mechanical reliability) of the material, except for LULT and EMAX.

Comparison of the effect of preheating on the flexural strength of giomer and nanohybrid composite resin.

Background. Considering the increased use of preheating and novel resin-based materials to restore teeth, the present study investigated the impact of preheating on the flexural strength of a giomer and compared it with a nanohybrid composite resin. Methods. Two restorative materials (Beautifil II giomer and Alpha III nanohybrid composite resin) were used. Thirty rod-shaped samples (adding up to 60 samples) were prepared from the materials above and divided into two subgroups: with and without preheating (n=15). Before sample preparation, the giomer and nanohybrid composite resin tubes were preheated at 68ºC for 15 minutes in the preheating subgroups. In the subgroups without preheating, the tubes were kept in a room at 25ºC. Then the flexural strength was compared between the two groups with two-way ANOVA at a significance level of P<0.05. Results. The results showed significantly higher flexural strength in the preheated subgroups than in the non-preheated subgroups (P<0.001). In addition, the mean flexural strength values were significantly higher in the giomer groups than in the nanohybrid composite resin groups (P<0.001). Conclusion. Preheating increased the studied materials' flexural strengths significantly. The flexural strength of the giomer restorative material was higher than that of the nanohybrid composite resin, irrespective of preheating.

Evaluation of flexural strength of glass ionomer cement after immersion in fruit juices.

Glass ionomer cement (GIC) is a material used for restoration in dentistry. The stress in a material right before it yields in a flexure test is referred to as flexural strength. The aim of this study was to evaluate the flexural strength of two different glass ionomers after immersion in fruit juices. Five samples of D-Tech and Shofu GIC were prepared from each for the in vitro study. The eight samples were subjected to a flexural strength process and two were left as control which was followed by the determination of maximum force and displacement, then the collected data were used to determine flexural strength and analyzed using SPSS software (IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp). The mean value of flexural strength of the D-Tech GIC immersed in fruit juices is 4.4375 and the mean value of Shofu GIC immersed in fruit juices was 8.4975. Paired t-test was done between the two groups and the P value was 0.00, which is considered highly statistically significant. From this study, it is evident that the GIC brand Shofu has higher flexural strength compared to D-Tech. Flexural strength was decreased for both the GIC groups when immersed in grape juice.

Effect of thermocycling on the mechanical properties, inorganic particle release and low temperature degradation of glazed high translucent monolithic 3Y-TZP dental restorations

The influence of thermocycling on the surface deterioration of glazed monolithic high translucent 3Y-TZP dental restorations is still unclear. The purpose of this study therefore was to evaluate low temperature degradation (LTD), elemental release and surface degradation pattern after five years of simulated clinical time. A total of 123 specimens were prepared from second-generation high translucent 3Y-TZP as per ISO 6872:2015 standards (3 mm × 4 mm × 30 mm). They were classified as per glazing and thermocycling protocol; group CPT, DGT and IGT. Glaze materials were applied on one surface of the specimen and subjected to a thermocycling in artificial saliva, four-point bending test, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD). Flexural strength, characteristic strength and Weibull modulus values were derived from four-point bending test. Descriptive fractographic analysis of surfaces was conducted to observe the surface degradation characteristics and point of failure. Control/no glaze with thermocycling (CPT = 621.5, 1σ = 117.0 MPa) presented higher flexural strength values compared to glaze I with thermocycling (442.4, 1σ = 45.4 MPa) and glaze II with thermocycling (534.3, 1σ = 46.3 MPa). Characteristic strength from Weibull analysis also observed higher values (669.2 MPa) for the control specimens. XRD analysis showed that monoclinic volume fraction (Vm = 11.0, 1σ = 0.7%) was highest in control specimens. Fractographic analysis suggested that there was no correlation between the point of failure initiation and mean flexural strength values. Glazing protected the high translucent 3Y-TZP surface against LTD during thermocycling but negatively impacted on the flexural strength.

Influence of postprocessing rinsing solutions and duration on flexural strength of aged and nonaged additively manufactured interim dental material

Statement of problemAdditive manufacturing procedures for fabricating interim restorations include rinsing postprocessing procedures. However, the impact of different rinsing solutions and times on flexural strength is unknown. PurposeThe purpose of this in vitro study was to assess the influence of the rinsing solutions and duration, as well as accelerated aging (thermocycling) procedures, on the flexural strength and Weibull characteristics of an additively manufactured interim dental material. Material and methodsA bar design (25×2×2 mm) file was used to fabricate all the specimens with 3D printing and an interim material (Nextdent C&B MFH). Five groups were created based on the rinsing solution used during the postprocessing procedures: 91% isopropyl alcohol (IPA) (control or IPA-91), 99% IPA (IPA-99 group), bio-ethyl alcohol 100% (BE group), tripropylene glycol monomethyl ether (TPM) 100% (TPM group), and water miscible formula (Resinaway) (RA group). Each group was divided into 4 subgroups depending on the total rinsing time: 5, 6, 7, and 8 minutes (5, 6, 7, and 8 subgroups). Additionally, each subgroup was distributed between nonaged and aged thermocycling procedures (n=10). Flexural strength measurements were made by using a universal testing machine. Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0), were calculated. Three-way ANOVA and pairwise multiple comparison Tukey tests were used to analyze the data (α=.05). ResultsThree-way ANOVA showed that the rinsing solution (P<.001), rinsing time (P=.004), and thermocycling procedures (P<.001) were significant predictors of the flexural strength values obtained. The IPA-91 and IPA-99 groups obtained the highest flexural strength, while the RA, TPM, and BE groups obtained the lowest flexural strength. The 7- and 8-minute subgroups obtained the highest flexural strength, while the 5-minute subgroup obtained the lowest flexural strength. The nonaged specimens obtained significantly higher mean flexural strength values than the aged specimens. ConclusionsThe vat-polymerized additively manufactured interim dental material tested with differing rinsing solutions and times demonstrated significant differences in the flexural strength values measured. Accelerated artificial aging procedures significantly decreased the flexural strength of the vat-polymerized interim dental material tested.

Effect of phytochemical-filled microcapsules with antifungal activity on material properties and dimensional accuracy of denture base resin for three-dimensional printing

BackgroundStudies on the material properties and dimensional accuracy of three-dimensionally (3D) printed denture base containing microcapsules with antifungal phytochemicals are lacking.MethodsTwo types of phytochemicals (phytoncide A and B) with antifungal activity were microencapsulated. The 3D-printed denture base specimens with minimum and maximum effective concentrations of microcapsules (6 and 8 wt% for phytoncide A; 15 and 25 wt% for phytoncide B) were prepared. The morphological changes of C. albicans on 3D-printed denture base with microcapsules was microscopically observed. The degree of conversion of 3D-printed denture base with microcapsules investigated. The microhardness and flexural strength values were also measured to evaluate the mechanical properties of 3D-printed denture bases. The dimensional accuracy (trueness) of the specimens with microcapsules was measured as root-mean-square values (RMS) for the whole, upper, and side surfaces of the specimens as well as their total height. For the degree of conversion, microhardness, and flexural strength values, the Kruskal–Wallis analysis and a post-hoc comparison using Mann–Whitney U test was performed. For the analysis of trueness (RMS), the one-way analysis of variance and a post-hoc comparison using Tukey’s method was conducted (α = 0.05).ResultsAt both maximum and minimum effective concentrations of microcapsules, cell surface disruption or membrane breakdown of fungal cells were observed in the specimens. The groups with microcapsules (both phytoncide A- and B-filled) showed significantly lower microhardness and elastic modulus values than the control group (all, P = 0.001). For the trueness, all the RMS values of the whole, upper, and side surfaces of the specimens with microcapsules were less than 100 µm, although significantly higher than those without (all, P = 0.001). The mean flexural strength values of the groups with phytoncide A-filled microcapsule were higher than 65 MPa, not statistically different from that of the control group (all, P > 0.05). However, the groups with phytoncide B-filled microcapsules showed significantly lower values than the control (all, P = 0.001).ConclusionsWithin the limitations of this in-vitro study, the 3D-printed denture base containing 6 wt% of phytoncide A-filled microcapsules was clinically acceptable in terms of antifungal activity, dimensional accuracy, and flexural strength.

41 - Effect of Polishing Technique on Flexural Strength of Glass-Ceramics

Aim of the study was to evaluate the influence of polishing on the flexural strength of dental glass-ceramic materials performed according to chairside techniques, laboratorial procedures or glazed. Specimens were produced of two dental ceramics (IPS e.max CAD/IPS e.max Press, both Ivoclar Vivadent, Schaan, Liechtenstein) as bars of 4 ×3 x 25 mm. Specimens were grinded wet with a rough diamond-copper wheel (D19) to standardize a rough surface (served as negative control, group 5). To simulate chairside conditions students of the 10th semester polished one side of the bars with either Diapro (two-step system, group 1) or Diapol (three-step system, group 2) (both from EVE Ernst Vetter GmbH, Keltern, Germany) dry with a KAVO handpiece. The positive control (group 3) was polished in laboratory with an automatic polishing machine (Buehler) with SiC papers up to 4000 grit under water-cooling. Group 4 was glazed (Crystal/Glaze Spray, Ivoclar) following manufacturers intructions. Afterwards all specimens were tested for flexural strength in a four-point-bending test. Stress at fracture was analyzed using Weibull statistics. The unpolished negative control group 5 showed the lowest mean flexural strength values for both materials. The chairside polishing groups (1/2) showed the highest mean flexural strength values. For e.max CAD those were significantly higher than in group 3 (lab polish), for e.max Press no significant difference between those groups could be found. Group 4 (glaze) reached similar mean flexural strength values to lab polishing (3) for e.max CAD; for e.max Press the values were significantly lower than in all polished groups (1-3). Polishing of dental ceramics increases flexural strength, independent if done dry chairside or in laboratory under water-cooling. Glazing can increase strength depending on material but is not more effective than polishing.

Evaluation of the effects of different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC

Considering the studies on the effects of bleaching materials on properties of dental materials, The aims of this in vitro study were to evaluate the effects of two different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC. In this experimental in vitro study, 30 rectangular-shaped specimens (2 mm width × 2 mm height × 12 mm length) for flexural strength and 30 specimens (5 mm width × 5 mm length × 2 mm height) for microhardness tests were prepared from VITA ENAMIC blocks 12 × 14 × 18 mm. The specimens were polished using silicon-carbide sandpapers 400, 600, 800, 1200, 2000 under flow of water for 60 s each. The prepared samples for flexural strength and microhardness were divided into 3 subgroups (n = 10): control group (C), samples bleached using Opalescence PF 15% (B15), and samples bleached with Opalescence Xtra Boost 40% (B40). Flexural strength measurement was done using a universal testing machine, and microhardness test was done using Vickers. Data were analyzed using analysis of variance and post hoc tests and P < 0.05 was considered significant. The mean microhardness values of C, B15, and B40 groups were 255.46 ± 3.02, 249.86 ± 4.18, and 235.53 ± 4.61 kgf/mm2. Opalescence PF 15% and Opalescence Xtra Boost 40% affected microhardness of ENAMIC significantly (P < 0.05). The mean flexural strength values of C, B15, and B40 groups were 155.26 ± 16.13, 142.14 ± 11.52, and 133.39 ± 16.13 MPa. A significant decrease in flexural strength was found between the C and B40 groups (P = 0.007). However, the difference between flexural strength of the C and B15 groups was not significant (P > 0.05). Our study showed that both concentrations of bleaching agents can affect microhardness of ENAMIC. Moreover, hydrogen peroxide 40% has a negative effect on the flexural strength of ENAMIC.

PENAMBAHAN NANOPARTIKEL TITANIUM DIOKSIDA TERHADAP KEKUATAN FLEKSURAL DAN KEKERASAN BASIS GIGI TIRUAN RESIN AKRILIK POLIMERISASI PANAS

Introduction: Heat polymerized acrylic resin is one of the polymers commonly used in dentistry included denture base materials because their manipulation, finishing, and polishing are easy and do not require expensive equipment. However, heat-polymerized acrylic resin denture bases also have several disadvantages including, low mechanical properties such as flexural strength and hardness. This study aims to determine the effect of adding titanium dioxide nanoparticles on the flexural strength and hardness of the heat polymerized acrylic resin denture base. Method: This type of research is an experimental laboratory with a sample size of 50mm x 10mm x 3mm for flexural strength test and 25mm x 10mm x 3mm for hardness test. The total sample of 48 samples consisted of the control group, the group with the addition of titanium dioxide nanoparticles with concentrations of 0,5%, 1%, and 1,5%. Results: The highest mean value of flexural strength was in the group of adding titanium dioxide nanoparticles with a concentration of 1% and the lowest was the control group. The highest mean value of hardness was in the group of adding titanium dioxide nanoparticles with the concentration of 1,5% and the lowest was the control group. Based on ANOVA test results, there was a significant effect of adding titanium dioxide nanoparticles with a concentration of 0,5%, 1%, and 1,5% on the flexural strength and hardness of the heat polymerized acrylic resin denture base. Conclusion: The addition of titanium dioxide nanoparticles can increase the flexural strength and hardness of the heat polymerized acrylic resin denture base. The addition of titanium dioxide nanoparticles to heat polymerized acrylic resin denture base recommended by the researchers was with a concentration of 1%.

Microstructural changes and fracture resistance of nano-crystalline monolithic zirconia restorations upon aging

To assess the effect of nano-modification of two CAD/CAM monolithic Zirconia systems (wet and dry-milled) on microstructural changes and fracture resistance upon aging. Twenty monolithic Zirconia discs (10mm x1.5mm) were divided into 2 groups (n=10) according to fabrication system;wet-milled (Incoris TZI) and dry-milled (CeramillZolid). Each group was subdivided into two subgroups (n=5), whether subjected to aging or not. Aging proceduresincluded accelerated hydrothermal aging and cyclic loading. Microstructural changes were assessed quantitatively and qualitatively using x-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Discs were subjected to fracture resistance test usinguniversal testing machine. Meansandstandard deviations were recorded for phase transformation (t-m)of Zirconia and repeated ANOVA was used to correlate phase transformation with fracture resistance results (p≤0.05). For aged subgroups, XRD analysis revealed significantly higher phase transformation of wet-milled than dry-milled (p≤0.05) and SEM analysis revealed wide zone phase transformation for wet-milled zirconia and minimal zone for dry-milled. For both systems, no significant difference between the mean flexural strength values ofnon-agedand aged zirconia (p≤0.05). Nanocrystalline microstructure of monolithic zirconia improved its resistance to aging. The fracture resistance of the two systems was not affected by aging.

Effects of laser debonding treatment on the optical and mechanical properties of all-ceramic restorations.

The objective of this study was to evaluate how erbium-doped yttrium aluminium garnet (Er:YAG) laser debonding treatment affects the optical and mechanical properties of dental ceramics. In total, 120 rectangular (22*5*1.2mm) IPS E.max Press specimens were fabricated and divided into 4 groups: the control group, 3W laser group, 4W laser group, and 5W laser group. For each group, 10 specimens were used for the colour test (colour difference (△E) and transparency parameter (TP)), 10 specimens were used for the flexural strength test, and 10 were used for the Vickers hardness test. One random sample from each colour test specimens was observed by scanning electron microscopy (SEM). The L*, a*, b*, △E, TP, flexural strength, and Vickers hardness values were measured and calculated. According to the Kruskal-Wallis test, the L*, a*, and b* values showed no significant variations (P > 0.05), except for the b* value in the 5W laser group (P < 0.05). The △E, TP, flexural strength, and Vickers hardness values were analysed by one-way analysis of variance (ANOVA). The 5W laser group exhibited a higher △E value, which exceeded the perceptible threshold and significantly lower TP values than the other groups (P < 0.05). The mean flexural strength and Vickers hardness values after Er:YAG laser debonding revealed no significant changes (P > 0.05). Microcracks were detected during the SEM analysis of the 5W laser group. Er:YAG laser debonding treatment did not affect the mechanical properties, but changed the optical properties of dental ceramics.