Thermal Stability of Chromium-Iron Oxidation Mixture Cermet-Based Solar Selective Absorbing Coatings.

The solar selective absorber coating (SSAC) are at the core of the efficient solar-thermal system. In this paper, for the first time, the Chromium-iron oxidation mixture cermet was successfully prepared on the surface of ultra-pure ferritic stainless steel by chemical coloring as SSAC. The coating surface has an optical trap structure, and the chromium-iron oxidation mixture cermet is used as an absorption layer to realize solar-thermal conversion. The solar absorptance (AM1.5) of the coating reached 93.66, and the thermal emittance was less than 13. After thermal shock tests at 25/300 °C done 32 times (accumulated 812.8 h), the Performance Criterion (PC) of the coating was 0.01375 < 0.05, showing outstanding thermal stability.

A functional Ag-TiO2 nanocomposite solar selective absorber with antimicrobial activity by photochemical reduction process.

A functional nanocomposite coating developed by wet chemical route in a photochemical reduction process will be a good candidate for low temperature solar thermal application. The low-temperature curable cermet comprises of two different type of nanoparticles, generated by photocatalytic reduction of silver ions under the sunlight with the aid of crystalline TiO2 (~8 nm) nanoparticles. The optimized base absorber layer of Ag-TiO2 nanocomposite exhibited absorptance (α) of 0.90 and emittance (ε) of 0.18 at 200 °C. Further to improve the optical properties a second layer of MgF2 has been added to get high selective (α/ε = 0.93/0.19 at 200 °C) nature. In addition, the coating was demonstrated to possess an antimicrobial activity against both Gram-negative and Gram-positive bacteria. The presented work will provide a new insight into the spectrally selective absorbers and its antimicrobial nature, which may useful for water disinfection, hot water, industrial heating and swimming pool applications.

Strength and fracture mechanism of iron reinforced tricalcium phosphate cermet fabricated by spark plasma sintering.

The present work studies the microstructure and mechanical performance of tricalcium phosphate (TCP) based cermet toughened by iron particles. A novelty arises by the employment of spark plasma sintering for fabrication of the cermet. Results showed partial transformation of initial alpha TCP matrix to beta phase and the absence of oxidation of iron particles, as well as a lack of chemical reaction between TCP and iron components during sintering. The values of compressive and tensile strength of TCP/Fe cermet were 3.2 and 2.5 times, respectively, greater than those of monolithic TCP. Fracture analysis revealed the simultaneous action of crack-bridging and crack-deflection microstructural toughening mechanisms under compression. In contrast, under tension the reinforcing mechanism was only crack-bridging, being the reason for smaller increment of strength. Elastic properties of the cermet better matched values reported for human cortical bone. Thereby the new TCP/Fe cermet has potential for eventual use as a material for bone fractures fixation under load-bearing conditions.

Microleakage in different primary tooth restorations.

BACKGROUND: Microleakage may cause tooth sensitivity, secondary caries, discoloration and even failure of the restoration. In order to overcome these potential problems, materials that are able to bind to the tooth structure have been developed, such as composite resin and glass ionomer cement. The purpose of the study was to compare microleakage arising from amalgam (Am), composite resin (CR), glass ionomer (GI), Ketac-Silver (KS), and GI filling with banding (GI+B) when these materials are used for class II restoration of a primary molar. METHODS: Fifty primary molars were collected and class II cavities were prepared on each tooth. The teeth were randomly divided into five groups (Am, CR, GI, KS, and GI+B), each of which received a different material as part of the restoration. The restored teeth then underwent 100 cycles of thermocycling that consisted of 55°C for 30 seconds, 19°C for 20 seconds, and 5°C for 30 seconds. The teeth were then immersed in 0.5% basic fuchsin solution for 24 hours. Afterwards, the teeth were embedded and sectioned mesiodistally through the center of each restoration. Dye penetration associated with the occlusal and cervical margins of each restoration was then assessed. RESULTS: Cervical leakage was greater than occlusal leakage in the CR, GI and KS groups (p < 0.05). When leakage on occlusal margin was examined, however, the Am group showed greater leakage than the CR, GI, and GI+B groups (p < 0.05). When leakage on the cervical margin was examined, the Am group showed greater leakage than the GI and GI+B groups, while the KS group showed greater leakage than the GI+B group (p < 0.05). CONCLUSION: Restorations using GI and GI+B indicated that these materials performed better than the other materials in this study overall. However, none of the materials were entirely devoid of leakage.

Early reaction kinetics of contemporary glass-ionomer restorative materials.

PURPOSE: To investigate polyalkenoate reaction rates in conventional glass-ionomer cement (GIC) and resin-modified glass ionomer (RMGI) restorative materials using infrared spectroscopy. MATERIALS AND METHODS: Nine conventional GIC and six RMGI restorative materials were prepared according to manufacturer's directions and placed on a FTIR (Fourier transform infrared spectroscopy) diamond ATR (attenuated total reflectance) surface. FTIR spectra (700 to 1800 cm-1) were obtained each minute for 3 h. VLC specimens were light polymerized after 1 min; at 5 min, all samples were covered with gauze saturated with deionized water. Polyalkenoate reaction was determined by measuring area growth (Å/cm-1) between 1375 and 1500 cm-1. Mean peak areas were determined at 5, 15, 30, 90, and 180 min and compared using ANOVA (p = 0.05) RESULTS: For all RMGI materials, VLC polymerization inhibited the polyalkenoate reaction rate. Compared to conventional GIC, RMGI materials demonstrated less polyalkenoate reaction. Compared to dark curing, RMGI light polymerization significantly inhibited the polyalkenoate reaction rate. CONCLUSIONS: The addition of resin components to glass-ionomer products significantly retards and impedes the polyalkenoate reaction. The polyalkenoate reaction rate of RMGI products was significantly lower than that of self-curing GIC restorative materials. Furthermore, light activation of RMGI products further retards the polyalkenoate rate. When clinicians require the therapeutic benefit of a polyalkenoate product, perhaps a conventional GIC restorative product should be the first material of choice.

Improved bonding strength of bioactive cermet Cold Gas Spray coatings.

The fabrication of cermet biocompatible coatings by means Cold Gas Spray (CGS) provides prosthesis with outstanding mechanical properties and the required composition for enhancing the bioactivity of prosthetic materials. In this study, hydroxyapatite/Titanium coatings were deposited by means of CGS technology onto titanium alloy substrates with the aim of building-up well-bonded homogeneous coatings. Powders were blended in different percentages and sprayed; as long as the amount of hydroxyapatite in the feedstock increased, the quality of the coating was reduced. Besides, the relation between the particle size distribution of ceramic and metallic particles is of significant consideration. Plastic deformation of titanium particles at the impact eased the anchoring of hard hydroxyapatite particles present at the top surface of the coating, which assures the looked-for interaction with the cells. Coatings were immersed in Hank's solution for 1, 4 and 7 days; bonding strength value was above 60 MPa even after 7 days, which enhances common results of HAp coatings obtained by conventional thermal spray technologies.

Comparison of antibacterial activity of glass-ionomer cement and amalgam in class two restorations by Streptococcus mutans count analysis at fixed intervals: an in vivo study.

AIM: The purpose of the present study was to determine the influence of glass ionomer cement and amalgam restoration on the level of Streptococcus mutans in the interproximal plaque at periodic intervals and also to compare these values. MATERIALS AND METHODS: Seventeen adult patients having two proximal carious lesions on any quadrant of the jaw (either opposing or contralateral) were selected for this study. Carious lesions were diagnosed clinically and from bitewing radiographs. Of the two carious lesions, one was restored with glass ionomer cermet cement and another with amalgam. Plaque samples were collected from interproximal areas before and at 1 month and 3 months post-treatment in a test tube containing 5 ml of modified Stuart's liquid transport fluid. Identification of organisms in the colony was done after Gram staining. RESULTS: Comparison of values before restoration and after restoration at 1 month interval showed a statistically significant decrease (p<0.001). Similarly, comparison of values before and after restorations at 3 months also showed statistically significant decrease (p<0.02). But comparison of restorations of 1 and 3 months intervals showed no statistical significant difference (p>0.05). CONCLUSION: Glass ionomer restorations have definite advantage over the amalgam, as the tunnel preparation is more conservative and fluoride release from the glass ionomer inhibits the growth of S. mutans in the plaque. CLINICAL SIGNIFICANCE: Glass ionomer cement should be preferred over amalgam in conservatively prepared restorations as it reduces the microbial activities due to fluoride release.

In vitro fluoride release from a different kind of conventional and resin modified glass-ionomer cements.

Fluoride release is important characteristic of glass-ionomer cements. Quantity of fluoride ions released from the glass-ionomer cements has major importance in definition of their biological activity. The objectives of this study were to define the quantity of fluoride ions released from the experimental glass-ionomer cements and to define the effect of fluoride ions released from the experimental glass-ionomer cements on their cytotoxicity. Concentrations of the fluoride ions released in the evaluated glass-ionomer cements were measured indirectly, by the fluoride-selective WTW, F500 electrode potential, combined with reference R503/D electrode. Statistical analyses of F-ion concentrations released by all glass-ionomers evaluated at two time points, after 8 and after 24 hours, show statistically higher fluoride releases from RMGICs: Vitrebond, Fuji II LC and Fuji Plus, when compared to conventional glass-ionomer cements: Fuji Triage, Fuji IX GP Fast and Ketac Silver, both after 8 and after 24 hours. Correlation coefficient between concentrations of fluoride ion released by evaluated glass-ionomer cements and cytotoxic response of UMR-106 osteoblast cell-line are relatively high, but do not reach levels of biological significance. Correlation between concentrations of fluoride ion released and cytotoxic response of NIH3T3 mouse fibroblast cell line after 8 hours is high, positive and statistically significant for conventional GICs, Fuji Triage and Fuji IX GP Fast, and RMGIC, Fuji II LC. Statistically significant Correlation coefficient between concentrations of fluoride ion released and cytotoxic response of NIH3T3 cell line after 24 hours is defined for RMGIC Fuji II LC only.

Gradual surface degradation of restorative materials by acidic agents.

The aim of this study was to investigate the effect of acidic agents on surface roughness and characteristics of four restorative materials. Fifty-two discs were created from each restorative material: metal-reinforced glass ionomer cement (Ketac-S), resin-modified glass ionomer cement (Fuji II LC), resin composite (Filtek Z250), and amalgam (Valiant-PhD); each disc was 12 mm in diameter and 2.5 mm thick. The specimens were divided into four subgroups (n=13) and immersed for 168 hours in four storage media: deionized water (control); citrate buffer solution; green mango juice; and pineapple juice. Surface roughness measurements were performed with a profilometer, both before and after storage media immersion. Surface characteristics were examined using scanning electron microscopy (SEM). Statistical significance among each group was analyzed using two-way repeated ANOVA and Tukey's tests. Ketac-S demonstrated the highest roughness changes after immersion in acidic agents (p<0.05), followed by Fuji II LC. Valiant-PhD and Filtek Z250 illustrated some minor changes over 168 hours. The mango juice produced the greatest degradation effect of all materials tested (p<0.05). SEM photographs demonstrated gradual surface changes of all materials tested after immersions. Of the materials evaluated, amalgam and resin composite may be the most suitable for restorations for patients with tooth surface loss.

A review of chemical-approach and ultramorphological studies on the development of fluoride-releasing dental adhesives comprising new pre-reacted glass ionomer (PRG) fillers.

This paper reviews our recent studies on fluoride-releasing adhesives and the related studies in this field based on information from original research papers, reviews, and patent literatures. A revolutionary PRG (pre-reacted glass ionomer) filler technology--where fillers were prepared by the acid-base reaction of a fluoroaluminosilicate glass with polyalkenoic acid in water, was newly developed, and a new category as "Giomer" was introduced into the market. On fluoride release capability, SIMS examination revealed in vitro fluoride ion uptake by dentin substrate from the PRG fillers in dental adhesive. On bonding durability, it was found that the improved durability of resin-dentin bonds might be achieved not only via the strengthened dentin due to fluoride ion uptake from the PRG-Ca fillers, but also due to retention of relatively insoluble 4-AETCa formed around remnant apatite crystallites within the hybrid layer in 4-AET-containing self-etching adhesives. On ultramorphological study of the resin-dentin interface, TEM images of the PRG-Ca fillers revealed that the dehydrated hydrogel was barely distinguishable from normal glass fillers, if not for the concurrent presence of remnant, incompletely reacted glass cores. In conclusion, it was expected that uptake of fluoride ions with cariostatic effect from PRG-Ca fillers would endow dentin substrates with the benefit of secondary caries prevention, together with an effective and durable adhesion to dentin.

Failure behavior of glass ionomer cement under Hertzian indentation.

OBJECTIVE: To investigate the load-bearing capacity and failure mode of various types of glass ionomer cement (GIC) under Hertzian indentation, exploring the relationship between the failure behavior and formulation, and examining claims of filler-reinforcement of GIC. METHODS: Discs 2mm thick, 10mm diameter, 8-18 replicates, were fabricated for two filler-reinforced GICs, four unmodified and unreinforced GICs, and four resin-modified GICs, with a dental silver amalgam and a filled-resin restorative material for comparison. Testing was at 23 degrees C, wet, after 7d storage at 37 degrees C in artificial saliva at pH 6, using a 20mm diameter hard steel ball and filled-nylon substrate (E: 10GPa). First failure was detected acoustically; mode was determined visually. At least 1/3 of specimens in each case were examined under scanning electronic microscope for corroboration. RESULTS: Reinforced and unmodified-unreinforced GICs were indistinguishable by failure load (one-way analysis of variance, P=0.425, overall 260+/-70N) and mode. Failure loads for resin-modified GICs were 360-1150N, amalgam approximately 680N, and filled resin approximately 1200N. Resin-modified GICs tended to be tougher (incomplete fracture), all others gave complete fracture (radial cracking). The stronger materials (two resin-modified GICs and filled resin) showed some cone cracking. SIGNIFICANCE: While resin-modified GICs showed various extents of increase of failure load over that of the plain GICs, consistent with the hybrid chemistry, filler-reinforcement was not evident for the two claimed products, consistent with structural and theoretical expectations.

Experimental model: dye penetration of extensive interim restorations used during endodontic treatment while under load in a multiple axis chewing simulator.

The purpose of this study was to design an experimental model that allowed extensive endodontic interim restorations to be tested for dye penetration while under simulated masticatory load. Extracted premolar teeth had standardized mesio-occluso-distal cavities prepared, and the root canals were instrumented. A cotton wool pellet was placed in the pulp chamber, and the cavities were restored with Cavit, IRM, Ketac-Fil Plus, Ketac-Silver, or composite resin (Z100). They were subjected to the equivalent of 3 months of clinical load while exposed to methylene blue dye. Results of this study could not support IRM as a suitable interim endodontic restorative material to use in extensive cavities. The dye penetration in the Ketac-Fil Plus and Ketac-Silver specimens was not predictable, and the results suggested Cavit and Z100 composite resin require further investigations as potentially useful materials for this purpose.

In vitro evaluation of five core materials.

PURPOSE: This in vitro study determined the fracture strength of five core materials supported by two different endodontic dowels. Diametral tensile strength and microhardness of the three resin composite core materials used in this study were also tested. MATERIAL AND METHODS: The fracture strength study used one lanthanide-reinforced flowable resin composite (Ti-Core Auto E), one titanium- and lanthanide-reinforced composite (Ti-Core), one lanthanide-reinforced composite (Ti-Core Natural), and two metal-reinforced glass ionomer core materials (Ketac Silver and GC Miracle Mix). Two types of dowels were used: a multitiered, split-shank threaded dowel with a flange (#1 Flexi-Flange) and one without a flange design (#1 Flexi-Post). The specimens were divided into ten groups. Each tooth/dowel and core specimen was placed in a special jig at 45 degrees and subjected to a load by a universal testing machine. The diametral tensile strength and the microhardness of the three resin composite core materials were measured by a universal testing machine and Barcol hardness tester, respectively. All test groups contained ten specimens. RESULTS: The fracture strength value of the resin composite core materials was significantly larger ( p < 0.0001) than those for the metal-reinforced glass-ionomer core materials. Analysis of variance (ANOVA) also showed that the Flexi-Flange dowel interacted with Ti-Core and Ti-Core Auto E to significantly ( p < 0.0013) increase the fracture strength relative to the Flexi-Post. One-way ANOVA revealed that there were no significant differences between them in terms of diametral tensile strength. The Barcol hardness values of the composite core materials were statistically different ( p < 0.0001), with the Ti-Core the highest, followed by Ti-Core Natural, then Ti-Core Auto E. CONCLUSIONS: Resin composite core material performed better than glass ionomer material in this in vitro study. The flowable composite core material performed about the same in terms of fracture strength and diametral tensile strength compared with nonflowable composites. Combined with certain core materials, the flange design increased the fracture strength of the tooth/dowel and core combination.

The development of nano-modified Ti(C,N) cermets.

The unique combination of mechanical properties such as excellent wear resistance and good chemical stability at elevated temperature helps titanium carbonitride based (Ti (C, N)-based) cermets to play an important roles in metal cutting operations. Nowadays, cermets cutting tools are widely used for semi-finishing and finishing works on steel and cast iron. However, their brittleness is still an unavoidable limitation for their utilization. With the development of nano-technology, nano-modified cermets have received more attention due to the high toughening enhancements. In this review, the development of nano-modified Ti(C,N) cermets is discussed including the fabrication, microstructure, mechanical properties, cutting performance and the practical applications in different fields. Many patents having important effect on the development of cermets were noticed, too.

Evaluation of canal filling after using two warm vertical gutta-percha compaction techniques in vivo: a preliminary study.

AIM: To evaluate the quality of root canal filling when comparing two warm gutta-percha filling techniques in vivo. METHODOLOGY: Human teeth were randomly divided into two equal groups, with 30 canals each. The root canals were shaped by hand and ProFile 0.04 rotary instruments to size 20-40 at the end-point and then filled with gutta-percha cones and AH-Plus. In group A, a traditional warm vertical compaction technique was performed using the Touch'n Heat, and back-filling with the Obtura II. In group B, a modified warm vertical compaction technique was used: small amounts of gutta-percha were removed, and the remaining most apical 3 mm were compacted with a 1 mm movement; then thermomechanical back-filling was performed. The teeth were extracted, stored in dye, cleared, and the distance between the apex and apical limit of the filling, linear dye penetration, and voids were measured from the buccal, lingual, mesial and distal perspective. The homogeneity of variance and means was verified using Levene's test and t-test. ANOVA and Dunnett post hoc test were used to establish the significance and to analyse the effects through multiple comparisons. RESULTS: Compared with the specimens of group A, the specimens of group B exhibited less mean linear dye penetration (P < 0.05), smaller void length (P < or = 0.05) and maximal width (P < or = 0.05) when examined in all four views, and a more precise filling when viewed from the buccal aspect (P < 0.05). CONCLUSIONS: The modified warm vertical compaction technique with apical back-filling produced a more effective and precise three-dimensional filling.

Effect of an adhesive resin luting agent on the dowel-head retention of three different core materials.

STATEMENT OF PROBLEM: A dowel-and-core restoration may fail due to failure at either the dowel-tooth or dowel head-core material interface. Long-term clinical success of a dowel-and-core restoration depends on retention of both the dowel to the tooth and the dowel head to the core material. Thus, strengthening of the dowel head-core interface is important. PURPOSE: This study evaluated the retention between a prefabricated dowel and 3 different core materials with or without a dual-polymerized adhesive resin luting agent. MATERIAL AND METHODS: Sixty prefabricated dowels (Gold Plated Anchorage Post) were divided into 3 groups (n=20) consisting of 1 of 3 core materials, amalgam (Standalloy F), light-polymerized resin composite (Clearfil Ray), or glass ionomer (Chelon-Silver). Each core group was divided into 2 subgroups (n=10), and a dual-polymerized adhesive resin luting agent (Panavia F) was applied to the dowel heads of 1 of these subgroups before application of the core material. The manufacturing procedure was standardized by using a plastic index (4.5-mm internal diameter and 5-mm height) and a custom-made dowel holder, which held the dowel head. Prepared specimens were stored in water at room temperature for 3 months and then loaded to fracture in a universal testing machine with a crosshead speed of 0.05 mm/min until failure. Bond strengths were recorded (MPa). Data were analyzed with 2-way analysis of variance (ANOVA) in a 2 x 3 factorial randomized design (alpha=.05). Afterward, core material differences were computed with 1-way ANOVA for both of the bonded and nonbonded groups. Post hoc multiple comparisons were made with the Dunnett C multiple range test. RESULTS: Dowel-head retention values (MPa) of the tested core materials (mean +/- SD) from the highest to the lowest were as follows: bonded amalgam core, 296.1 +/- 108; bonded composite core, 284.3 +/- 38.3; nonbonded composite core, 177.0 +/- 53.7; nonbonded amalgam core, 128.5 +/- 35.0; bonded glass-ionomer core (GIC), 128.0 +/- 24.5; nonbonded GIC, 61.8 +/- 13.3. Two-way ANOVA revealed significant differences between the core material groups and between the bonded and nonbonded groups (P <.001). The interaction between the core material and bond variables was also significant (P =.018). One-way ANOVA revealed statistically significant differences between the bonded (P <.001) and also between the nonbonded core material groups (P <.001). Post hoc multiple comparisons showed that the dowel-head retention of the GIC was significantly weaker than the post-head retention for amalgam and resin composite, whether bonded or not. CONCLUSION: Within the limitations of this study, the adhesive resin luting agent tested appeared to have a significant strengthening effect on the dowel-head retention of the core materials.

Atraumatic restorative treatment (ART): a three-year clinical study in Malawi--comparison of conventional amalgam and ART restorations.

OBJECTIVE: This study compares the quality of class I restorations made with the atraumatic restorative treatment (ART) technique and conventional class I amalgam restorations. METHODS: The study was carried out among secondary school students in Mzuzu, Malawi. First-year students in 1987 who needed at least two class I restorations were selected. Based on a split-mouth design, each participant received both ART and conventional restorations. The 89 pairs of class I cavities were divided randomly into two groups, since two different cermet ionomer cement (CIC) filling materials were used. Impressions of the restorations and subsequent models were made shortly after restoration, after six months, one year, two years, and three years. The quality of the restorations was determined on the models following the US Public Health Service criteria. Bulk fracture, contour, marginal integrity, and surface texture of the restorations were recorded and evaluated separately. Survival rates were determined by the resultant score of all criteria. RESULTS: Though conventional amalgam restorations performed better on all criteria, this difference was significant only for the contour criterion. The survival rates of ART restorations after three years (81.0%) were lower than those of amalgam restorations (90.4%) (P=.067). CONCLUSIONS: The quality of ART class I restorations is competitive with that of conventional amalgam restorations.

A comparative study of plaque mutans streptococci levels in children receiving glass ionomer cement and amalgam restorations.

PURPOSE: The restorative materials amalgam (Standalloy F) and glass ionomer cements (Chelon Silver) were comparatively investigated to determine the number of mutans streptococci METHODS: Saliva and plaque were collected from patients before and 40 days after the insertion of their restorations. RESULTS: Total bateria and mutans streptococci counts were found to be statistically significantly reduced when compared with the prerestoration counts in the saliva samples (P<0.001). Microbiological analysis of the dental plaque showed that the number of mutans streptococci in the glass ionomer cements was significantly lower than in the amalgam restorations (P<0.001). CONCLUSIONS: This study showed that silver glass ionomer cements inhibited the growth of mutans streptococci.

Materiales restauradores convencionales y adhesivos en molares temporarios: adaptación marginal / Conventional and adhesive restorative materials in primary molars: marginal adaptation

La problemática que plantea el reducido espesor de tejidos dentarios en elementos primarios, amplitud y escasa profundidad cavitaria, junto a la necesidad de buscar una "integración diente-restauración", con la mejor adaptacion, sellado marginal, baja incidencia de caries secundaria y la amplia gama de materiales restauradores que nos ofrece el mercado odontológico, motivó la realización del presente trabajo. El propósito de este estudio fue comprobar el grado de adaptación marginal por medio de microscopía electrónica de barrido (M.E.B.). Se emplearon 36 molares temporarios superiores y/o inferiores, recientemente extraídos. Se realizaron prepraaciones cavitarias clase I. Aleatoriamente fueron divididos en 6 grupos según el material restaurador: Grupo I: amalgama convencional; Grupo II: amalgama adherida; grupo III: resina compuesta; Grupo IV: cermet; grupo V: vitro-ionómero-resina; grupo VI: compómero. Posterioremente se obtuvieron réplicas que fueron metalizadas y analizadas con microscopía electrónica de barrido, a diferentes magnificaciones. Las mediciones se realizaron a nivel del BCP, tercio medio de las paredes de contorno y del ángulo axiopulpar. Las pruebas de comparaciones múltiples mostraron que el mejor comportamiento correspondió al compómero, con un valor medio de adaptación de 0,86_m, seguido del grupo III y V con 0,88_m y 1,14_m respectivamente. Los valores medios para el grupo II y IV fueron de 1,31_m en la amalgama adherida y 1,69_m para el cermet. El análisis de varianza determinó que la zona del ángulo axiopulpar mostró la más alta desadaptación en todos los materiales con diferencias significativas (p<0,0005) con respecto al BCP y pared axial que no difieren significativamente entre sí. Puede concluirse que las diferencias histológicas de los elementos temporarios con respecto a los permanentes y las dificultades en la estabilización de uniones fuertes a la dentina primaria serían la causa de las significativamente más bajas fuerzas de adhesión de los sistemas utilizados sobre todo a nivel del ángulo axiopulpar (AU)

Comparative study of the physical properties of core materials.

This study was undertaken to measure physical properties of materials used for direct core buildups, including high-copper amalgam, visible light-cured resin composite, autocured titanium-containing composite, polyacid-modified composite, resin-modified glass-ionomer, and silver cermet cement. Compressive strength, diametral tensile strength, and flexural strength of six core materials of various material classes were measured for each material as a function of time up to 3 months at different storage conditions, using a standard specification test designed for the materials. Three different storage conditions (dry, humid, wet) at 37 degrees C were chosen. Materials were manipulated according to manufacturers' instructions for use as cores. Mean compressive, diametral tensile, and flexural strengths with associated standard deviations were calculated for each material. Multiple comparison and Newman-Keuls tests discerned many differences among materials. All materials were found to meet the minimum specification requirements, except in terms of flexural strength for amalgam after 1 hour and the silver cermet at all time intervals.