Megapascals Research Articles

Microshear Bond Strength of a Self-adhesive Composite to Erbium Laser-Treated Primary Enamel.

Introduction: Advances have been made in the composition of flowable composites in recent years and self-adhering composites, which do not require a bonding agent, have recently been introduced to the market. This study aimed to assess the microshear bond strength (µSBS) of a self-adhering flowable composite (Vertise) to primary enamel treated with a graphite disc with silicon carbide particles (SIC) and laser irradiation, the result of which was compared to that of a conventional flowable composite (Premise). Methods: In this in vitro, experimental study, 72 samples of sound primary enamel were evaluated. A smooth enamel surface was obtained using a graphite disc. Next, the erbium chromium yttrium scandium gallium garnet (Er,Cr:YSGG) laser was used for enamel surface treatment in half of the samples (n=36). All the samples were then randomly divided into 4 groups of (i) Premise flowable composite (PF) without laser (n=18), (ii) Vertise flowable composite (VF) without laser (n=18), (iii) PF with laser (n=18), and (iv) VF with laser (n=18). The teeth were then incubated at 37°C for 24 hours and were then subjected to thermocycling. The µSBS of samples was measured using a universal testing machine and reported in megapascal (MPa). Data were analyzed using SPSS via the two-way ANOVA and independent-samples t test at P<0.05. Results: The mean µSBS of VF was significantly higher to the laser-treated samples (13.60±5.47) compared with the non-treated samples (5.89±2.42) (P<0.001). However, no significant difference was noted in the µSBS of PF to the laser-treated (13.18±3.45) and non-treated samples (16.06±3.52) (P=0.058). Conclusion: The µSBS of the conventional flowable composite is higher than that of the self-adhering flowable composite to the enamel of primary teeth. Enamel surface treatment with laser irradiation increases the µSBS of self-adhering flowable composites.

Natural Mordenite from Spain as Pozzolana.

This work deals with anomalous concentrations of natural mordenite in the southeast of Spain. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies evidenced that the samples contain mainly monomineral zeolitic phase of mordenite (70% to 74%), usually accompanied by smectite (montmorillonite), the principal component of bentonite. A study of the applicability of these zeolites is presented to establish the potential use as pozzolanic cements. For comparative purposes, synthetic commercial mordenite is also characterized and tested. The initial mixtures were prepared using cement and mordenite at a 75:25 ratio. Chemical analysis and a pozzolanicity test showed the high pozzolanic character. These mixtures were further added to sand and water, yielding the cement specimens to be used as concrete. Mechanical test results showed that the mechanical compression at 7 and 28 days fall into the range of 19.23 to 43.05 MegaPascals (MPa) for the cement specimens built with natural mordenites. The obtained results fall in the same range of cement specimens prepared with natural clinoptilolite, using mixtures within the European requirement for commercial concretes. Thus, these results and the low cost of natural mordenite of San José de los Escullos deposit supports the potential use of natural mordenite as pozzolanic cement.

Improving shear bond strength of metallic brackets after whitening.

ABSTRACTObjective: To evaluate a protocol for bonding metallic brackets after bleaching with hydrogen peroxide (HP). Methods: 60 extracted maxillary premolar were randomly divided into an unbleached control group and two groups bleached with a solution of 35% hydrogen peroxide prior to bonding. The teeth in one of the treated groups were bonded immediately after bleaching; while the other group was treated with 10% sodium ascorbate immediately after bleaching and before bonding. The teeth in all groups were stored in an artificial saliva solution for 7 days after bonding. The shear bond strength data was measured in megapascals (MPa) and the fail attempts were verified. The significance level was established at p< 0.05. Results: The unbleached group, in which brackets were bonded to untreated enamel, had the highest bond strength values (11.0 ± 5.7MPa) in comparison to the bleached group (7.14 ± 40MPa), in which brackets were bonded to recently bleached enamel. Slightly improved bond strength was observed in the antioxidant group (8.13 ± 5.4MPa), in which the teeth were bleached and then the antioxidant was applied to the teeth before bonding. Unbleached and bleached groups showed statistically significant difference for shear bond strength (p=0.03) and load strength (p=0.03); no significant differences were noted between unbleached and antioxidant groups (p=0.52).Conclusion: The antioxidant treatment applied immediately after bleaching was effective in reversing the reduction in shear bond strength of brackets after tooth bleaching.

A Comparative Evaluation of Shear Bond Strength of Seventh- and Eighth-Generation Self-etch Dentin Bonding Agents in Primary Teeth: An In Vitro Study.

ABSTRACTAimTo compare the shear bond strength of seventh- and eight-generation self-etch dentin bonding agents in primary teeth using universal testing machine.Materials and methodsForty extracted sound human primary molars were collected and randomly divided into two groups of 20 sample each. Shear bond strength of seventh-generation bonding agent [ADPER Single Bond Universal, (group II)] and eighth-generation bonding agent [Futurabond DC, VOCO Germany, (group I)] were calculated by using Universal Testing Machine (PTC/O83/ME, INSTRON, USA) and expressed in megapascals (MPa). Recorded data were compiled and subjected to statistical analysis using Student's t test.ResultsThe mean shear bond strength of group I (eighth-generation dentin bonding agent) and group II (seventh-generation dentin bonding agent) ranged from 22.10 to 37.10 MPa and 19.80 to 30.30 MPa, respectively Student's t test showed significantly different and higher (8.7%) shear bond strength in group I when compared to group II (p value = 0.017).ConclusionShear bond strength of eighth-generation dentin bonding agent (Futurabond DC) was better than seventh-generation dentin bonding agent (Adper Single Bond Universal).Clinical significanceAn effective bond to tooth would reduce marginal microleakage, bacterial penetration, postoperative sensitivity, possibility of pulpal inflammation, and preserve tooth structure by allowing minimal cavity preparation.How to cite this articleMishra A, Koul M, Upadhyay VK, et al. A Comparative Evaluation of Shear Bond Strength of Seventh- and Eighth-generation Self-etch Dentin Bonding Agents in Primary Teeth: An In Vitro Study. Int J Clin Pediatr Dent 2020;13(3):225–229.

Effect of radiotherapy on bond strength of different endodontic sealers to root dentin

AimThe aim was to evaluate the effect of radiotherapy on push-out bond strength of different sealers (Endosequence, MetaSEAL Soft, Tubliseal) to root dentin.Materials and methodsA total of 60 extracted premolars with nearly straight single root canals were selected. All teeth were decoronated leaving root sample of nearly 15 ± 1 mm length. Root canals preparation were performed using ProTaper rotary system. Roots were randomly divided into six groups according to radiation exposure and type of sealer used. Group I: MetaSEAL Soft positive, Group II: Endosequence positive, Group III: Tubliseal positive, Group IV: MetaSEAL Soft negative, Group V: Endosequence negative and Group VI: Tubliseal negative. After obturation, positive groups were subjected to a cumulative radiation dose of 60 Gy in 30 fraction for 6 weeks. Three dentin slices were obtained from each root third and push-out test was measured using universal testing machine. The maximum failure load was recorded in Newton (N) and then converted into MegaPascal (MPa). Bond strength values were analyzed using two-way analysis of variance and multiple pairwise Tukey's test at P value less than or equal to 0.05.ResultsIrradiated groups recorded lower bond strength values than nonirradiated groups. Groups obturated with gutta-percha/Tubliseal recorded the lowest values when comparing between sealers regardless radiation exposure and sections. Coronal sections had superior bond strength values than middle and apical sections in all groups.ConclusionRadiotherapy had a negative effect on bond strength of sealers to root dentin. Endosequence BC sealer had better bond strength to radiculer dentin than MetaSEAL Soft and Tubliseal sealers.

Debonding Shear Strength of Orthodontic Tubes Bonded to Skeletal Anchorage Miniplates with Different Agents

Introduction: Most miniplates used for skeletal anchorage lack built-in orthodontic devices. To address this issue, orthodontists must use creative solutions, such as bonding buttons, brackets, or tubes directly to the miniplates, thus making them more versatile devices that provide a wider range of tooth movement possibilities. The purpose of the present study was to ascertain the debonding strength in Megapascals (MPa) of orthodontic accessories bonded to skeletal anchorage miniplates with different bonding agents. Methods: Forty specimens were divided into two equal groups by bonding agent: Group 1, resin (Transbond XT®, 3M ESPE); Group 2, cyanoacrylate (Scotchbond®, 3M ESPE). Shear strength testing was performed in an EMIC DL-2000 universal testing machine. Results: The results obtained were 2.28 ± 0.44 MPa for Group 1 and 4.90 ± 0.76 MPa for Group 2. The Kolmogorov-Smirnov test was used to assess the normality of data distribution. Student's t-test was used to compare means in the response variable. Conclusion: A statistically significant difference was observed between groups. However, both bonding agents provided strength in excess of that needed for secure orthodontic tooth movement.

Influence of Strontium on the Physical, Mechanical and In-Vitro Bioactivity of Glass Ionomer Cements

In this work, we investigated the effects of strontium incorporation in the glass phase of glass ionomer cements (GIC). Three different glass compositions were synthesized with 0, 5, and 10 mol% of SrO addition. GICs were prepared by the addition of 50 wt% polyacrylic acid (PAA) at powder to liquid ratio of 1:1.5. Initial characterization on the cement series was to study their rheological behavior. Cements represented working times between 50-64 seconds and setting times of 356-452 seconds. Rheological results indicated that the addition of strontium decreases the working and setting times of the cements. To analyze the mechanical properties, compressive and flexural strength studies were performed after 1, 10, and 30 days incubation in simulated body fluid (SBF). The compressive strength of the cements increased as a function of incubation time, with the strontium containing compositions showing the highest strength at 34 megapascal (MPa) and after 30 days of incubation. Biaxial flexural strength of the cements was not significantly affected by the composition and maturation time and ranged between 13.4 to 16.3 MPa. In-vitro bioactivity of the cements was analyzed using SBF trials and after 1, 10, and 30 days incubation periods. Strontium containing cements, showed higher solubility with higher amounts of calcium phosphate surface depositions only after 10 days incubation. The elemental identifications of the surface depositions indicated high amounts of Ca, P and Zn are present on the surface of SBF incubated samples.

A comparison between fly ash- and basic oxygen furnace slag-modified gold mine tailings geopolymers

Fly ash (FA) and Basic oxygen furnace (BOF) slag were used to as additives in the geopolymerisation of gold mine tailings (GMT).The aim of the research was to determine the effects of the two additives on the strength formation and mechanism of metal immobilisation by modified GMT geopolymers. GMT, FA and BOF were mixed, respectively, and made into a paste with the addition of potassium hydroxide (KOH) before curing at various conditions. 50% replacement of GMT in the starting materials gave the highest unconfined compressive strength (UCS). The UCS for BOF-based geopolymer was 21.44 Mega Pascals (MPa), whilst the one for FA-based geopolymer was 12.98 MPa. The BOF-based geopolymer cured at lower temperature (70 °C) as compared to the FA-based geopolymer (90 °C). The optimum KOH concentration was 10 and 15 M for BOF- and FA-based geopolymers, respectively. BOF-based geopolymers resulted in the formation of calcium silicate hydrate (CSH) phases which contributed to higher strength; whereas in FA-based geopolymers, no new structures were formed. BOF-based geopolymers resulted in over 94% iron (Fe) immobilisation, whereas FA-based geopolymers had 76% Fe immobilisation. Fe immobilisation was via incorporation into the CSH or geopolymer structure, whilst other metal immobilisations were thought to be via encapsulation. 12-month static leaching tests showed that the synthesised geopolymers posed insignificant environmental pollution threat for long-term use.

Effect of chlorhexidine and isopropyl alcohol on immediate and delayed bond strength of glass fiber posts

Aim: To investigate the effects of dentinal treatment with chlorhexidine and isopropyl alcohol, alone or associated, on the bond strength and bond stability of glass fiber posts cemented with a self-adhesive resin cement. Materials and Methods: Forty bovine teeth were endodontically treated and randomly distributed into four groups, according to the dentinal treatment after post space preparation: distilled water (Control); 2% chlorhexidine (CHX); isopropyl alcohol (ISO); 2% chlorhexidine + isopropyl alcohol (CHX+ISO). Glass fiber posts were cemented with a self-adhesive resin cement and after 24 h specimens were cut into six 1.5 mm-thick slices. One slice of each root third (i.e. apical, middle and coronal) was subjected to immediate push-out test and the other was stored in distilled water at 37 °C for six months for delayed push-out test. Bond strength was registered in megapascal (MPa). Failure mode was evaluated by a stereomicroscope, with 40x magnification. Data analysis was performed using Kruskal-Wallis and Friedman tests, with 5% significance level. Results: No significant differences were detected between experimental groups or between root thirds in the same group in the immediate evaluation. After six months of aging, all groups showed a significant decrease in bond strength values, but ISO group presented higher bond strength than Control and CHX groups (p=0.0001). The most common type of failure for all groups was adhesive between resin cement and root dentine. Conclusions: Dentinal treatment with CHX and ISO, isolated or combined, did not affect the immediate bond strength of glass fiber posts, but the ISO group presented better bond stability after six-month aging.

Bond strength to radicular dentin of two experimental luting cements

Aim The aim of this study was to test two different of experimental cements based on two types of polymerization techniques comparing them with one already well known in the market. Materials and methods Thirty intact central incisors, extracted for periodontal reasons, were selected and endodontically treated, then were randomly divided into 3 groups of 10 samples: Group 1, light cured composite experimental material with self-etch adhesive and dual polymerization activator; Group 2, dual experimental core build-up with self-etch adhesive and dual-polymer activator; Group 3 (control group), dual cement with self-etch adhesive and dual polymerization activator. One fiber post was luted into the root canal strictly following manufacturer’s instructions. Each sample was cut in slices in order to perform the push-out bond strength test with a testing machine. To express the bond strength in MegaPascals (MPa), the breaking load recorded in Newton (N) was divided by the area of the bonded interface (A) in mm2. The area of the bond interface was calculated as the area of the surface of a truncated cone using the formula: A = I€ (R + r) [h2 + (Rr) 2] 1/2, where R represents the major radius of the coronal post, r represents the minor radius of the apical post and h is the thickness of the slice in millimeters. The diameters and thickness of the slice were measured individually using a digital caliper with 0.01 mm precision. After the test, each slide was observed to detect the type of failure and classified as adhesive between cement and dentin (AD); adhesive between the cement and the post (AP); fracture of the sample, cohesive inside the post and dentin (FR); cohesive in cement (CC); mixed (M). Results Group 2 recorded the highest values of adhesion strength, group 1 the lowest. There were no statistically significant differences among groups 1 and 2 and controls. The most common failure mode was the mixed one and the less frequent was the adhesive type between the post and the cement. Conclusions Within the limitations of this study, it can be concluded that the bond strength of experimental resin cements is comparable to that of a cement marketed by the same manufacturer, used here as a control and well known in the market.

Comparison of ISO and ASTM standards in determining the flexural strength of denture base resin.

The aim of this study was to compare the differences between the ASTM D790 and ISO 20795.1.2013 standards in evaluating the flexural strength of heat cure poly methyl methacrylate (PMMA) denture base resin. 30 heat cure denture base samples were fabricated in accordance to ISO 20795.1.2013 and ASTM D790 Standards. The specimens were finished and stored following the standardized protocol. The flexural strength was determined using universal testing machine at cross head speed of 1.50 mm/min and a span length of 40.00 mm. The mean flexural strength values were calculated in megapascals (MPa), and statistically analyzed. The mean flexural strength of heat cure PMMA found with ISO and ASTM ranged between 60.492 MPa and 61.470 MPa. There was no significant difference between the two methods. The quantitative differences existed in the flexural strength of denture base resin between ISO 20795.1.2013 and ASTM 790 protocols but those differences had no statistical and clinical significance.

Drought survival strategies of juvenile bromeliads of Alcantarea imperialis (Carrière) Harms

The establishment of bromeliad populations in rupicolous environments depends on the efficient survival strategy of juvenile individuals under adverse conditions, such as drought. Juvenile plants of Alcantarea imperialis do not form water reservoir (phytotelm) as adult individuals and then they require metabolic mechanisms to cope with water deficit during the initial stages of plant growth. It has been reported that sugar accumulation and crassulacean acid metabolism (CAM) photosynthesis are related to plant responses to water deficit. This study investigated whether these physiological adjustments could be dual strategies to drought survive of juvenile A. imperialis plants. Plants were cultivated in vitro with polyethylene glycol 6000 (PEG 6000) to simulate different degrees of water deficit (moderate stress, − 1.9 mega Pascal (MPa) and severe stress, − 8.5 MPa) and a control treatment without PEG (− 0.5 MPa) for 7, 15 and 30 days. Plant growth, biochemical and anatomical parameters were analyzed. Under 15 days in moderate stress condition, the plants initially accumulated soluble sugars and at 30 days, their leaves presented a thicker aquiferous parenchyma, which might facilitate the accumulation of high concentrations of carbohydrates and polyalcohols (sorbitol and mannitol) and perform CAM pathway due to the increase of phosphoenolpyruvate carboxylase (PEPC) activity and accumulate organic acids during the night. Under severe stress CAM was intensified and their leaves were less thick. The results showed that juvenile A. imperialis plants are able to make metabolic adjustments in response to water shortage, and these responses are dependent on the intensity and/or duration of the drought conditions. Overall, this work provides a better understanding of how rupicolous plants survive under different drought conditions. Rupicolous juvenile bromeliads of Alcantarea imperialis subjected to drought are able to survive by increasing the production of sugars under conditions of moderate stress or performing CAM under severe stress.

Energy performance and calorimetric behaviour of cements bearing granite sludge

Blending supplementary cementitious materials with portland cement is one of the current strategies for producing more eco-efficient binders by lowering the energy consumption and CO2 emissions intrinsic to OPC manufacture. The effect of such additions on heat of hydration and energy performance is a subject of particular interest, for higher heat may reduce the service life of a concrete structure, whilst energy consumption per tonne of binder or megapascal may prove not to be energy-efficient. This paper explores the energy performance of granite sludge (GS) as an active addition to clinker and the effect of this by-product on heat of hydration and eco-efficiency. The findings show that maximum heating and total heat released are lower in the additioned than in the conventional material, with the difference widening at higher replacement ratios. At 35% GS, maximum heating was 36% lower than in OPC and total heat released 24% lower. Optimal energy performance is observed at ratios of 15% to 30% (both inclusive), with the experimental materials requiring less energy (−1.6 kW·h·t−1/MPa – 0.8 kW·h·t−1/MPa) than ordinary cement per megapascal (MPa) of strength. Cements with 15% to 30% granite sludge are consequently eco-efficient. With 15% GS they can be classified as ordinary (>270 J/g at 41 h), with 20% to 30% as low heat cements (<270 J/g at 41 h) and with 35% as very low heat cements (<220 J/g at 41 h).

Effect of Fabrication Technique and Thermal Cycling on the Bond Strength of CAD/CAM Milled Custom Fit Anatomical Post and Cores: An In Vitro Study.

This study is to investigate the effect of milling custom fit anatomical post and cores from fiber reinforced composite and high-density polymer blocks using CAD/CAM technology on the bond strength to root canal dentin compared with prefabricated fiber posts, and to evaluate the influence of thermal cycling on the push out bond strength of the tested materials. Eighty extracted single-rooted premolars, endodontically treated and prepared to receive the posts, were randomly divided into four groups (n = 20): BLC: Custom-milled fiber-reinforced composite posts and cores (Trilor, Bioloren), AMC: Custom-milled high-density polymer posts and cores (Ambarino, Creamed), BLP: Prefabricated fiber-reinforced composite posts and composite core buildups (Bioloren; Filtek Bulk Fill Posterior, 3M). The posts used have the same matrix and fiber composition as BLC, RXP: Prefabricated posts and composite core buildups (RelyX fiber post, 3M; Filtek Bulk Fill Posterior); used as a control group. All of the posts were cemented using a self-adhesive resin cement (RelyX U200, 3M). Half of the sample was randomly assigned to thermal cycling in distilled water for 6,000 cycles to simulate aging, while the other half was tested for bond strength without thermal cycling. A push-out test was conducted using a universal testing machine until failure. Bond strength values were calculated in megapascals (MPa). The mode of failure was observed using a stereo microscope. Results were analyzed by two-way ANOVA followed by a Bonferroni post hoc test for comparison. The level of significance was set at p < 0.05. Push-out bond strength was significantly higher (p<0.001) in the CAD/CAM post groups than in the groups with prefabricated posts regardless of the post material, while aging of the teeth did not significantly affect the push-out strength (p = 0.536). Failures were adhesive between cement and dentin for all groups except for AMC, where adhesive failure between the cement and the post was also observed. The CAD/CAM manufacturing technique was proved to ameliorate the retention of the post and cores in the root canal. Thermal cycling did not affect the bond strength of the tested groups.

Evaluation of initial displacement and stresses in the maxillary dentition following en masse retraction using fixed lingual appliance and micro-implants: A finite element analysis

To evaluate and compare the stress and displacement pattern between conventional and micro-implant supported retraction in lingual orthodontic system. A finite element model of the maxilla, teeth, periodontal ligament, lingual-orthodontic appliance and a micro-implant complex was constructed using ANSYS 12.1 software. Two sizes of micro-implants, 6mm and 8mm, were constructed producing a simulated model of 99,190 nodes and 32,4364 elements. A retraction force of 200g was applied from an anterior retraction hook to the molar tube in the conventional model and from the micro-implants in the implant supported model. The initial displacement and stress patterns in the X-Y-Z axes were obtained using Hyper-view software. The maximum von Mises stresses in the 6mm, 8mm and conventional model were 22.164 Megapascals (MPa), 28.603MPa and 16.491MPa respectively. The bucco-lingual displacement of the maxillary anteriors was greater in the 8mm implant model with 23×10-3mm lingual displacement observed. The least lingual displacement of 11×10-3mm was noted for the conventional model while a slightly higher moderate reading of 15×10-3mm was seen in the 6mm micro-implant supported model. The maximum displacement of the periodontal ligament was noted in the 8mm micro-implant model. Within the limitations of this research, the 8mm micro-implant model displayed high initial stresses and greater initial displacement of the anterior teeth in the X-Y-Z coordinates in comparison to conventional retraction method.

Evaluation of shear bond strength of orthodontic molar tubes bonded using hydrophilic primers: An in vitro study

To evaluate and compare the shear bond strength (SBS) of orthodontic molar tubes bonded using two hydrophilic primers along with a moisture tolerant adhesive system to dry and saliva-contaminated enamel surfaces; and to assess the mode of their bond failure. A total of 60 extracted human mandibular molars were randomly divided into three major groups according to the primer used, each consisting of 20 molars: XT group acts as a control and bonded with the conventional hydrophobic Transbond XT primer, OS group bonded with the hydrophilic Ortho Solo primer, AP group bonded with the hydrophilic Assure Plus all surface bonding resin. Each major group was further divided into two subgroups, of 10 molars each, according to presence or absence of saliva. All the specimens were thermocycled 500 cycles between 5̊ and 55°C. Shear forces were applied to the specimens with a universal testing machine at a crosshead speed of 1mm/min and SBS was measured in megapascals (MPa). The mode of failure was determined using the adhesive remnant index (ARI). Data were analysed using two-way analysis of variance (ANOVA) followed by univariate analysis and Bonferroni post hoc tests. The three tested primers did not show a significant difference in the mean SBS in dry conditions (P=0.137); the mean SBS of OS and AP primers were 15.60±5.879MPa and 12.51±2.583MPa respectively which were comparable to that of the hydrophobic XT primer (12.76±2.952MPa). In saliva-contaminated conditions, the mean SBS values were 10.41±4.457MPa and 9.22±3.422MPa for OS and AP primers respectively, which were significantly higher than that of XT primer (4.82±2.050MPa) (P=0.004). When comparing the mean SBS for each group according to the bonding condition, it was significantly higher in dry bonding compared to saliva-contaminated bonding for the three primers; XT (P<0.001), OS (P=0.003) and AP (P=0.011). In the dry field, most of the bond failures of the three primers were adhesive (score 3), whereas in the saliva-contaminated field, most of the failures were cohesive (score 1). Dry bonding yielded the highest SBS for the three primers. Saliva contamination significantly decreased the bond strength of both hydrophilic primers; however, the values were above the clinically acceptable limit. The hydrophilic primers tested in the present study can be successfully used for bonding orthodontic molar tubes under dry and saliva-contaminated enamel surface conditions.

Effect of photodynamic therapy and ErCrYSGG laser irradiation on the push-out bond strength between fiber post and root dentin.

To evaluate the push out bond strength and modes of failure of fiber post by using photodynamic therapy (PDT), Er,Cr:YSGG laser and conventional cleaning and shaping (CCS). Sixty maxillary anterior teeth were sectioned horizontaly 2 mm incisal to the cemento-enamel junction, and root canal were prepared for post space. Tapered fiber posts were placed inside the root canal after post space was made. The fiber posts were subjected to PDT, Er,Cr:YSGG laser and CSS with 20 specimens in each group. The specimens obtained were sectioned in cervical and apical sections. A universal testing machine was used to perform the push out test and the push out bond strength was formulated by σ = C/A, expressed in mega-pascals (MPa). The highest mean push out bond strength was achieved by PDT group (8.08 ± 2.73 MPa) and the lowest was shown by specimens in CCS group (7.45 ± 1.04 MPa). ANOVA showed no statistical difference among the experimental groups (p = 0.481). In the cervical segments, the mean push-out bond strength was found to be slightly higher for all three groups compared to apical segments (P < 0.05). The independent t-tests results showed that the mean push-out bond strength values of the cervical segments were slightly higher than the apical segments in PDT, Er,Cr:YSGG and CSS groups (P < 0.05). Significant differences were observed when mean push-out bond strengths were compared for both cervical (p = 0.037) and apical (p = 0.019) segments between all the groups. Twenty-one failures were found at the interface between the adhesive and the dentin surface, 6 failures were observed at the interface between the adhesive and post, whereas 5 failures were mixed. Push-out bond strength to root canal dentin were not affected by Er,Cr:YSGG compared with conventional cleaning and shaping. However, PDT produced the smallest number of failure modes and slightly higher push-out bond strength to root dentin.

Emplacement and inflation of the Al-Halaq al Kabir lava flow field, central part of the Al Haruj Volcanic Province, Central Libya

Numerous of lava rise plateaus and tumuli developed in the medial and distal portions of the Al-Halaq al Kabir lava flow field during the last (Holocene) eruption in the central part of the Al Haruj Volcanic Province (AHVP). These inflation structures provide important data on the lava-emplacement mechanism in this part of the Al Haruj region where the widespread occurrence of tumuli and lava rise plateaus are good indicators of the mode of emplacement. We report the results of detailed measurements of the maximum and minimum diameters in plan-view of 551 lava-rise plateaus and 289 tumuli from the distal part of the Al-Halaq al Kabir lava field using ArcGIS and field observations. Tumuli and lava rise plateaus may be divided into subpopulations according to abrupt changes in the scaling exponents on log-log plots of their frequency versus diameter. Using the estimated stiffness (Young's modulus) of the basaltic rocks in the study area of 10–34 GPa, numerical and analytical results show that theoretical maximum tensile stresses in the inflated upper (solidified) crustal layers of the developing tumuli and lava rises at tens of mega-pascals (MPa). This theoretical stress is orders of magnitude higher than typical in-situ tensile strengths of rocks (0.5–9 MPa) and thus high enough to rupture the crustal layers of the lava rises and tumuli. The high tensile stresses are generated during crustal doming driven by a magmatic overpressure of only about 1 MPa. Our results partly explain the abundance of tension fractures at the surface of the Al-Halaq al Kabir lava flow field. Tumuli observed in the area are remarkably similar in morphology and aspect (height/width) ratios to the flow-lobe tumuli in Holocene lava flow fields in Iceland, suggesting an analogous mechanics of formation. There appears to be a coincidence between the age of an initial volcanism in the AHVP (7.9–5.3 Ma) and a local fauna and flora disappearance in the As-Sahabi area, NE Sirt Basin, during Messinian-Zanclean time (7–5 to 5 Ma). We speculate that the volcanism may have had a local negative environmental impact and contributed to the reported decline in the fauna and flora in the area.

Shear Bond Strength of Resin Cement to Saliva-Contaminated Metal Alloys after Various Surface Treatments

The bonding ability of resin cement to metal alloys of conventional dental restorations is critical for the retention and long-term survival rate. Contaminated saliva during try-in process which is resistant to simple water rinsing could reduce bond strength. Surface treatment before cementation might have an important role in optimizing resin-metal bond strength. The purpose of this study was to study the effect of surface pretreatment on the shear bond strength of dental base metal alloys after saliva contamination using a self-adhesive resin cement. Forty dental wax patterns (7-mm diameter) were made and cast with dental base metal alloy (Argeloy N.P. (V)). Cast metal specimens were embedded in PVC tube using self-curing acrylic resin and then flattened with 600-grit silicon carbide paper. PVC tube holders were specifically designed for the shear bond strength test device. Forty resin composite specimens were prepared in plastic mold (diameter of 3 mm and depth of 3 mm). The resin composite specimens were treated with sandblasting. Fifty-μm aluminum oxide particle was blasted for 10 seconds from the distance of approximately 5 mm perpendicular to the bonding surface. Metal alloy specimens were immersed in artificial saliva for 1 minute and rinsed with water-spray for 15 seconds. The specimens were also air-dried for 15 seconds. Specimens were divided into four groups, which received one of the following surface treatments: (1) No surface treatment (Control), (2) 37% phosphoric acid, (3) 37% phosphoric acid and then rinsed with 70% ethyl alcohol, and (4) 70% ethyl alcohol. After rinsing and drying, the resin composite specimens were cemented with Panavia SA Cement (Kuraray Noritake Dental Inc., Okayama, Japan) at the center of metal alloy specimens followed by the manufacturer’s instruction. Before testing, the specimens were stored in distilled water at 37oC for 24 hours. For testing, specimens were dried and mounted to universal testing machine (EZ-S, Shimadzu Co., Kyoto, Japan) at the crosshead speed of 1 mm/minute. Failure loads was recorded in Newton (N) and then analyzed to Mega Pascal (MPa). The highest shear bond strength was observed for group 2 and 3. The failure mode in all the materials was adhesive failure which occurred at the resin-metal interface. Within the limitations of this study, phosphoric acid was effective in removing saliva contamination and enhancing bond strength at the resin-dental base metal interface.

Stress distribution & deflection in an Aramany class II obturator fabricated with cobalt-chromium & titanium alloys – 3D FEA

Purpose/objectivesThe aim of the research was to develop a model that accurately represents an Aramany class II defect and its obturator prostheses fabricated with Cobalt Chromium alloy & Titanium alloy to compare the deflection and the stress distribution in the rehabilitated area. MethodsAramany class II defect and the obturator prostheses was generated geometrically utilizing ANSYS 14.5, both overlaid on each other to impressionist prostheses and the maxilla as one element. Meshing of models was carried out utilizing HYPERMESH software & materialistic properties were assigned. The 120 N load was constituted on the teeth in different directions. ResultsThe stress distribution & deflection executed by ANSYS provided results that enabled the tracing of Von Mises stress and deflection field in the form of color veiled bands with standards in Mega Pascal (MPa). ConclusionThe study shows that Von Mises stresses are higher for the frame work fabricated with cobalt chromium alloy compared to Titanium alloy. The framework made of titanium alloy showed more deflection than cobalt chromium alloy. Clinical implications3D FEA can be performed on a computer without putting any stress on the human body from technical materials, which is especially difficult for maxillectomy patients.