bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spinel–cordierite symplectites replacing andalusite: evidence for melt‐assisted diapirism in the Bushveld Complex, South Africa
Authors: Johnson T. , Brown M. , Gibson R. , Wing B. 
Published: August 2004

AbstractSpinel–cordierite symplectites partially replacing andalusite occur in metapelitic rocks within the cores of several country rock diapirs that have ascended into the upper levels of layered mafic/ultramafic rocks in the Bushveld Complex. We investigate the petrogenesis of these symplectites in one of these diapirs, the Phepane dome. Petrographic evidence indicates that at conditions immediately below the solidus the rocks were characterized by a cordierite‐, biotite‐ and K‐feldspar‐rich matrix and 5–10 mm long andalusite porphyroblasts surrounded by biotite‐rich fringes. Phase relations in the MnNCKFMASHT model system constrain the near‐solidus prograde path to around 3 kbar and imply that andalusite persisted metastably into the sillimanite + melt field, where the fringing relationship between biotite and andalusite provided spatially restricted equilibrium domains with silica‐deficient effective bulk compositions that focused suprasolidus reaction. MnNCKFMASHT pseudosections that model these compositional domains suggest that volatile phase‐absent melting reactions consuming andalusite and biotite initially produced a moat of cordierite surrounding andalusite; reaction progressed until all quartz was consumed. Spinel is predicted to grow with cordierite at around 720 °C. Formation of the aluminous solid products was strongly controlled by the receding edge of andalusite grains, with symplectites forming at the andalusite‐cordierite moat interface. Decompression due to melt‐assisted diapiric rise of the floor rocks into the overlying mafic/ultramafic rocks occurred close to the thermal peak. Re‐crossing of the solidus at P = 1.5–2 kbar, T > 700 °C resulted in preservation of the symplectites. Two features of the silica‐deficient domains inhibited resorption of spinel. First, the cordierite moat armoured the symplectites from reaction with crystallizing melt in the outer part of the pseudomorphs. Second, an up‐T step in the solidus at low‐P, which may be in excess of 100 °C higher than the quartz‐saturated solidus, resulted in high‐T crystallization of melt on decompression. Even in metapelitic rocks where melt is retained, preservation of spinel is favoured by decompression.
A method for calculating effective bulk composition modification due to crystal fractionation in garnet‐bearing schist: implications for isopleth thermobarometry
Authors: Evans T. P. 
Published: August 2004

AbstractQuantitative P–T path determination in metamorphic rocks is commonly based on the variation in composition of growth‐zoned garnet. However, some component of growth zoning in garnet is necessarily the result of an effective bulk composition change within the rock that has been generated by crystal fractionation of components into the core of garnet. Therefore, any quantitative calculation of the P–T regime of garnet growth should be completed using an accurate assessment of the composition of the chemical system from which garnet is growing. Consequently, a method for calculating the extent of crystal fractionation that provides a means of estimating the composition of the unfractionated rock at any stage during garnet growth is developed. The method presented here applies a Rayleigh fractionation model based on measured Mn content of garnet to generate composition v. modal proportion curves for garnet, and uses those curves to estimate the vectors of crystal fractionation. The technique is tested by calculating the precision of the equilibrium between three garnet compositional variables within the chemical system determined to be appropriate for each of a series of microprobe analyses from garnet. Application of the fractionation calculations in conjunction with the P–T estimates based on intersecting compositional isopleths provides a means of calculating P–T conditions of garnet growth that is based on individual point‐analyses on a garnet grain. Such spatially precise and easily obtainable P–T data allow for detailed parallel studies of the microstructural, the P–T, and the chemical evolution of metamorphosed pelites. This method provides a means of studying the dynamics of orogenic systems at a resolution that was previously unattainable.
Calculated phase equilibria in K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O for sapphirine‐quartz‐bearing mineral assemblages
Authors: Kelsey D. E. , White R. W. , Holland T. J. B. , Powell R. 
Published: August 2004

AbstractSapphirine, coexisting with quartz, is an indicator mineral for ultrahigh‐temperature metamorphism in aluminous rock compositions. Here a new activity‐composition model for sapphirine is combined with the internally consistent thermodynamic dataset used by THERMOCALC, for calculations primarily in K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O (KFMASH). A discrepancy between published experimentally derived FMAS grids and our calculations is understood with reference to H2O. Published FMAS grids effectively represent constant aH2O sections, thereby limiting their detailed use for the interpretation of mineral reaction textures in compositions with differing H2O.For the calculated KFMASH univariant reaction grid, sapphirine + quartz assemblages occur at P–T in excess of 6–7 kbar and 1005 °C. Sapphirine compositions and composition ranges are consistent with natural examples. However, as many univariant equilibria are typically not ‘seen’ by a specific bulk composition, the univariant reaction grid may reveal little about the detailed topology of multi‐variant equilibria, and therefore is of limited use for interpreting the P–T evolution of mineral assemblages and reaction sequences. Calculated pseudosections, which quantify bulk composition and multi‐variant equilibria, predict experimentally determined KFMASH mineral assemblages with consistent topology, and also indicate that sapphirine stabilizes at increasingly higher pressure and temperature as XMg increases. Although coexisting sapphirine and quartz can occur in relatively iron‐rich rocks if the bulk chemistry is sufficiently aluminous, the P–T window of stability shrinks with decreasing XMg. An array of mineral assemblages and mineral reaction sequences from natural sapphirine + quartz and other rocks from Enderby Land, Antarctica, are reproducible with calculated pseudosections. That consistent phase diagram calculations involving sapphirine can be performed allows for a more thorough assessment of the metamorphic evolution of high‐temperature granulite facies terranes than was previously possible. The establishment of a a‐x model for sapphirine provides the basis for expansion to larger, more geologically realistic chemical systems (e.g. involving Fe3+).
Geothermobarometry of UHP and HP eclogites and schists – an evaluation of equilibria among garnet–clinopyroxene–kyanite–phengite–coesite/quartz
Authors: Krogh Ravna E. J. , Terry M. P. 
Published: August 2004

AbstractGeothermometry of eclogites and other high pressure (HP)/ultrahigh‐pressure (UHP) rocks has been a challenge, due to severe problems related to the reliability of the garnet–clinopyroxene Fe–Mg exchange thermometer to omphacite‐bearing assemblages. Likewise, reliable geobarometers for eclogites and related HP/UHP rocks are scarce. In this paper, a set of internally consistent geothermobarometric expressions have been formulated for reactions between the UHP assemblage garnet–clinopyroxene–kyanite–phengite–coesite, and the corresponding HP assemblage garnet–clinopyroxene–kyanite–phengite–quartz. In the system KCMASH, the end members grossular (Grs) and pyrope (Prp) in garnet, diopside (Di) in clinopyroxene, muscovite (Ms) and celadonite (Cel) in phengite together with kyanite and coesite or quartz define invariant points in the coesite and quartz stability field, respectively, depending on which SiO2 polymorph is stable. Thus, a set of net transfer reactions including these end members will uniquely define equilibrium temperatures and pressures for phengite–kyanite–SiO2‐bearing eclogites. Application to relevant eclogites from various localities worldwide show good consistency with petrographic evidence. Eclogites containing either coesite or polycrystalline quartz after coesite all plot within the coesite stability field, while typical quartz‐bearing eclogites with no evidence of former coesite fall within the quartz stability field. Diamondiferous coesite–kyanite eclogite and grospydite xenoliths in kimberlites all fall into the diamond stability field. The present method also yields consistent values as compared with the garnet–clinopyroxene Fe–Mg geothermometer for these kinds of rocks, but also indicates some unsystematic scatter of the latter thermometer. The net transfer geothermobarometric method presented in this paper is suggested to be less affected by later thermal re‐equilibration than common cation exchange thermometers.
Very high‐pressure (>4 GPa) eclogite associated with the Moldanubian Zone garnet peridotite (Nové Dvory, Czech Republic)
Authors: Nakamura D. , Svojtka M. , Naemura K. , Hirajima T. 
Published: August 2004

AbstractEquilibrium pressure–temperature (P–T) conditions were estimated for kyanite‐bearing eclogite from Nové Dvory, Czech Republic, by using garnet–clinopyroxene thermometry and garnet–clinopyroxene–kyanite–coesite (or quartz) barometry. The estimated P–T conditions are 1050–1150 °C, 4.5–4.9 GPa, which are mostly the same as previously estimated values for garnet peridotite from Nové Dvory (∼1100–1250 °C, 5–6 GPa). Such very high‐P conditions, which correspond to about 150‐km depth, have been obtained for some garnet peridotites in the Gföhl Unit of the Bohemian Massif, but pressure conditions of eclogites associated with the garnet peridotites have not been so well constrained. This is the first substantial finding of eclogite that gives such very high‐P conditions in the Gföhl Unit of the Bohemian Massif. The Gföhl Unit mainly consists of felsic granulite or migmatitic gneiss, but these rock types do not display high‐P (>2.5 GPa) evidence. It is unclear whether both the peridotite body and surrounding felsic rocks in the Gföhl Unit were buried to very deep levels, but at least some garnet peridotites and associated eclogites in the Gföhl Unit have ascended from about 150‐km depth.
Candida albicans colonization of surface‐sealed interim soft liners
Authors: Olan‐Rodriguez Luciano , Minah Glenn E. , Driscoll Carl F. 
Published: August 2004

Purpose This in‐vivo investigation evaluated the effect of 2 denture sealer agents on the microbial colonization of a newly placed soft interim denture liner during a period of 14 days.Materials and Methods An interim soft denture liner (Coe‐Soft; GC America, Alsip, IL) was coated with 2 different denture surface sealants (Palaseal [Heraeus Kulzer, Irvine, CA] and Mono‐Poly [Plastodent, New York, NY]). Three rectangular wells of 1 cm wide × 2 cm long × 2 mm deep were placed in the intaglio of 10 maxillary complete dentures and filled with the soft liner material. The soft liner surface was treated with Palaseal (first well) and Mono‐Poly (second well), and the unsealed (third well) was used as a control. These were exposed to the oral cavity for 14 days. The effect the sealant had in the prevention of Candidal colonization in vivo of the soft liner material was evaluated. Microbiological specimens were recovered from all samples and cultivated. Microbiological data from the control and 2‐test samples in each denture were tabulated, and statistical analyses were performed.Results This investigation showed clear differences (p < .001) between the sealed and unsealed soft liners. The sealed material showed significantly less colonization by yeast and bacteria. Intercomparison of the surface denture sealers, Palaseal versus Mono‐Poly, showed no statistically significant differences (p < .005) in total yeast or bacterial colonization.Conclusion Coating of Coe‐Soft denture liner with either Palaseal or Mono‐Poly significantly decreased yeast and bacterial colonization.
Tensile bond strength of resin‐modified glass‐ionomer cement to microabraded and silica‐coated or tin‐plated high noble ceramic alloy
Authors: Swartz Jeffrey M. , Davis Richard D. , Overton Johnnie D. 
Published: August 2004

Purpose The purpose of this study was to evaluate the influence of alloy surface microabrasion, silica coating, or microabrasion plus tin plating on the tensile bond strengths between a resin‐modified glass‐ionomer luting cement and a high‐noble alloy. Bond strength between the microabraded alloy specimens and conventional glass‐ionomer cement or resin cement were included for comparison.Materials and Methods One hundred twenty uniform size, disk‐shaped specimens were cast in a noble metal alloy and divided into 6 groups (n = 10 pairs/group). The metal surfaces of the specimens in each group were treated and cemented as follows. Group 1: No surface treatment (as cast, control), cemented with a resin‐modified glass‐ionomer cement. Group 2: Microabrasion with 50‐μm aluminum oxide particles, resin‐modified glass‐ionomer cement. Group 3: A laboratory microabrasion and silica coating system, resin‐modified glass‐ionomer cement. Group 4: Microabrasion and tin‐plating, resin‐modified glass‐ionomer cement. Group 5: Microabrasion only, conventional glass‐ionomer cement. Group 6: Microabrasion and tin‐plating, conventional resin cement. The uniaxial tensile bond strength for each specimen pair was determined using an Instron Universal Testing Machine (Instron Corp, Canton, MA). Results were analyzed using a one‐way analysis of variance (α= 0.05) and a Tukey post‐hoc analysis.Results Mean bond strength: Group 1: 3.6 (±1.5) MPa. Group 2: 4.2 (±0.5) MPa. Group 3: 6.7 (±0.9) MPa. Group 4: 10.6 (±1.8) MPa. Group 5: 1.1 (±0.4) MPa. Group 6: 14.6 (±2.3) MPa. Group 6 was significantly stronger than Group 4. The bond strength of specimens cemented with the resin‐modified glass‐ionomer cement using microabrasion and tin‐plating (Group 4) was significantly stronger than all other groups except the resin cement with microabrasion and tin‐plating (Group 6).Conclusion Microabraded and tin‐plated alloy specimens luted with the resin‐modified glass‐ionomer cement resulted in the greatest mean tensile strengths for the resin‐modified glass‐ionomer cement groups. This strength was 73% of the mean tensile strength of microabraded specimens luted with resin cement.
Predictions of cement microfracture under crowns using 3D‐FEA
Authors: Kamposiora Phophi , Papavasiliou George , Bayne Stephen C. , Felton David A. 
Published: August 2004

Purpose The objective of this research study was to test the effects of (1) crown margin type, (2) cement type, (3) cement thickness, (4) loading direction, and (5) loading magnitude on stress levels and distributions within luting cement that might lead to cement microfracture using three‐dimensional Finite Element Analysis techniques.Materials and Methods Thirty‐two three‐dimensional computer models, as well as models for standards, were generated for a mandibular first premolar. Crown preparations exhibited shoulder or chamfer margin configurations, and zinc phosphate, zinc polycarboxylate, glass ionomer, and resin cements were used in thicknesses of 25 or 100 μm. Modeled crowns were loaded axially or obliquely at 10 and 100 MPa. Areas and levels of stress concentrations within the cement were determined.Results Stresses in the cement were low for all situations except 100 MPa oblique stressing. Stresses at the margins of crowns with chamfer marginal configuration were higher than those with shoulder margins. Stresses under oblique stressing were 10 to 150 times higher than under axial stressing. Except for Zn phosphate cement, cement thickness minimally affected stress levels and distributions. Greater stresses were found in cements with the greater Young's modulus.Conclusions Although the chamfer margin design could lead to greater stresses near the margins that places the cement at risk for microfracture and possible crown failure, glass‐ionomer and composite resin cements have more favorable mechanical properties for resisting microfracture.
A prospective 5‐year study of fixed partial prostheses supported by implants with machined and TiO2‐blasted surface
Authors: Gotfredsen Klaus , Karlsson Ulf 
Published: August 2004

Purpose The aim of the present study was to evaluate whether there was a difference between machined and TiO2‐blasted implants regarding survival rate and marginal bone loss during a 5‐year observation period.Materials and Methods A total of 133 implants (Astra Tech Dental Implants; Astra Tech AB, Mölndal, Sweden) were placed in 50 patients at 6 centers in 4 Scandinavian countries. Forty‐eight implants were installed in the maxilla and 85 implants in the mandible. A randomization and a stratification were done, so that each fixed partial prosthesis was supported by at least 1 machined and 1 TiO2‐blasted implant. The implant‐supported fixed partial prostheses (ISFPP) were fabricated within 2 months after postoperative healing. A total of 52 ISFPP (17 maxillary, 35 mandibular) were inserted. The patients were clinically examined once a year for 5 years. At the annual follow‐up, biological as well as technical complications were recorded.Results Of the 133 implants placed, 3 were reported as failed after 5 years of follow‐up, resulting in an overall cumulative survival rate of 97.6%. The cumulative implant survival rates were 100% for the TiO2‐blasted implants and 95.1% for the machined implants. No significant difference in survival was, however, found between the machined and TiO2‐blasted implants after 5 years. The mean marginal bone loss in the maxilla was 0.21 ± 0.83 mm (SD) for the machined implants and 0.51 ± 1.11 mm (SD) for the TiO2‐blasted implants during the 5‐year observation period. In the mandible, the mean marginal loss was 0.22 ± 1.13 mm for the machined implants and 0.52 ± 1.07 mm for the TiO2‐blasted implants from baseline to the 5‐year examination. No significant difference in marginal bone loss between the 2 surface groups was found during the 5‐year observation period.Conclusions The present study shows good 5‐year results with small ISFPP in the mandible, as well as in the maxilla. No significant differences were found in failure rate and marginal bone loss around implants with a machined rather than a TiO2‐blasted surface.
Wear of enamel opposing low‐fusing and conventional ceramic restorative materials
Authors: Clelland Nancy L. , Agarwala Vaishali , Knobloch Lisa A. , Seghi Robert R. 
Published: August 2004

Purpose This study evaluated the wear area of human enamel opposing 2 conventional and 2 low‐fusing dental porcelains, as well as abrasive wear, attrition, surface hardness, and fracture toughness for the 4 porcelain substrates.Materials and Methods Two low‐fusing and 2 conventional metal‐ceramic porcelains were used to form 15‐mm‐diameter disks (n = 10), which were fired according to manufacturer's recommendations. Enamel cusps (n = 40) were formed from extracted third molars. All ceramic and enamel specimens were finished to a 1000‐grit silicon carbide surface. The Oregon Health Sciences University (Portland, OR) oral wear simulator was used to deliver a 20‐N load from the cusps to the ceramic substrates through a food‐like slurry. The sliding action of the cusps over an 8‐mm linear path produced abrasive wear. A static 70‐N load was applied at the end of the path to create attrition. This sequence was repeated at 1.0 Hz for 50,000 cycles. Ceramic wear was measured with a profilometer (±2 micrometers), and enamel wear was evaluated using optical scanning methods. After wear testing, the hardness and fracture toughness of the ceramic surfaces were determined, and scanning electron photomicrographs were made using representative ceramic and enamel specimens from each group. Enamel wear areas, abrasion and attrition depths, hardness, and fracture toughness values were subjected to analysis of variance and Tukey‐Kramer post hoc tests to determine significant differences.Results Enamel wear was not significantly different for low‐fusing and conventional porcelains (p= .29). The wear of conventional and low‐fusing ceramic substrates was also not significantly different (p= .79). However, depth of porcelain wear caused by attrition was in general significantly greater than abrasive wear (p= .0004). Although no significant differences were found in the measured porcelain hardness values (p= .08), 1 conventional porcelain exhibited fracture toughness significantly greater than 1 low‐fusing porcelain (p < .01).Conclusions No differences in wear patterns were noted among low‐fusing compared with conventional metal‐ceramic porcelains, but static loading resulted in significantly greater attrition compared with the observed sliding abrasive wear.
Effect of abutment tooth reinforcement techniques on the fracture resistance of removable partial denture master casts
Authors: Sato Yuuji , Takaki Naomi , Tsuga Kazuhiro , Hosokawa Ryuji 
Published: August 2004

Purpose The purpose of this study was to compare the mean loads required to fracture an isolated stone abutment tooth when various reinforcement techniques were used: (A) no reinforcement, (B) surface hardening, (C) impression trimming, (D) dowel placement, and (E) impression trimming plus dowel placement.Materials and Methods Die stone premolar specimens for each group (n = 4) were loaded perpendicular to the tooth long axis in 100‐g increments 25 hours after pouring the impression. Mean load to failure was determined for each group. Data were evaluated with a one‐way analysis of variance (α= 0.05) to determine differences among groups. Paired comparisons of factor level means were made with Tukey's q‐test.Results The mean fracture load for Group E (7.6 kg) was significantly greater than Groups A (2.0 kg), B (2.1 kg), and C (3.4 kg). No significant difference was found between Groups D (6.0 kg) and E.Conclusions Dowel reinforcement with impression trimming at the cervical portion of the abutment tooth resulted in significantly greater fracture resistance than the control, surface model hardener, or impression trimming alone.