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PubMed2003

EXAFS study of Sn(IV) immobilization by hardened cement paste and calcium silicate hydrates.

In this study, the immobilization mechanisms of Sn(IV) onto calcium silicate hydrates (C-S-H) and hardened cement paste (HCP) have been investigated by combining wet chemistry experiments with X-ray absorption spectroscopy (XAS). Evidence is presented which demonstrates the formation of a Sn(IV) inner-sphere surface complex on C-S-H with a CaO/SiO2 weight ratio of 0.7. Two possible structural models, implying a corner sharing between the Sn octahedra and Q1 or Q2b Si tetrahedra, have been developed based on the experimentally determined structural parameters. In HCP, the formation of a different type of Sn(IV) inner-sphere complex has been observed, indicating that C-S-H may not be the uptake-controlling phase for Sn(IV) in the cement matrix. An alternative structural model for Sn(IV) binding in HCP has been developed, assuming that ettringite is the uptake-controlling phase. At high Sn(IV) concentrations, Sn(IV) immobilization in HCP occurs due to the formation of CaSn(OH)6.

Calcium Compounds↗
PubMed1980

The flow properties of dental cements.

The flow properties of several major types of dental cements were investigated using slow compressive strength and creep techniques. Considerable differences were found in their behavior. Whereas the phosphate-bonded and glass-ionomer cements exhibited brittle fracture, the other cements tended to distort to a greater or lesser extent under load. All cements showed some creep under load but the extent of this varied considerably; the creep of phosphate-bonded cements being very small and that of the eugenol and related cements considerable.

Dental Cements↗
PubMed1983

Pulpal responses evaluated by two assessment systems. Use of Nobetec as negative and Super-Syntrex as positive control materials.

In the assessment of pulpal responses to dental materials there is no general agreement regarding which system should be used in the selection of histologic sections for assessment and which negative and positive control materials should be used. The present study is an evaluation, on 227 sections, of two pulpal assessment systems and three section-selection methods using a negative (zinc oxide and eugenol cement) and a positive (silicate) control material. The results indicate that, depending on which system is used, considerable variation in response can be noted. Better standardization of methods is necessary.

Animals↗
PubMed2003

Comparison of retentive systems for composites used as alternatives to porcelain in fixed partial dentures.

STATEMENT OF PROBLEM: The bond strength between framework metals and composites, used as alternatives to porcelain, requires further study because adhesive failures can promote microleakage, discoloration, and stains in composites. PURPOSE: The aim of this in vitro study was to analyze and compare the tensile strength between the base metal Ni-Cr alloys: (Wirocer and Wiron 99) and 2 composites (Artglass and Solidex) with 2 types of mechanical retention (0.4-mm and 0.6-mm beads); 2 types of chemical treatment (Siloc system and Metal Photo Primer system) and the combination of both treatments on a metal framework; to verify whether these composite systems were strong enough to be used as alternatives to porcelain. MATERIAL AND METHODS: A total of 144 specimens, cylindrical metal rods (3 mm diameter x 60 mm length), were cast in Ni-Cr alloy (Wiron 99 or Wirocer), divided into 6 equal groups corresponding to 6 types of retention: airborne particle abrasion/control (A), chemical (C), mechanical with 0.4-mm (M4) and 0.6-mm beads (M6), and chemical/mechanical with 0.4-mm (CM4) and 0.6-mm beads (CM6). Composite rings formed around the rods (6.0 mm diameter X 2.0 mm thickness) of Artglass or Solidex were light polymerized in the UniXS unit (wavelength range of 320-520 nm for 540s) according to the manufacturer's specifications. Specimens were invested, and their tensile strength was measured at fracture with an EMIC-MEM 2000 universal testing machine at a crosshead speed of 2.0 mm/min and 500 kgf load cell. Statistical analysis was carried out with analysis of variance and Tukey's test at significance level P=.01. RESULTS: The highest mean retention values were recorded for groups CM6 (63.57 MPa) and M6 (63.05 MPa). The lowest mean retention values were recorded for groups A (30.63 MPa) and C (25.07 MPa). No significant difference was found regarding the alloys used in this study (P<.01). There was a significant difference in shear strength (P<.01) between Solidex (52.33 MPa) and Artglass (43.18 MPa). CONCLUSION: Within the limitations of this study, mechanical retention with 0.6-mm beads and chemical/mechanical retention with 0.6-mm beads increased the metal-composite tensile bond strength. No significant difference was found between these 2 retention systems. Chemical and airborne particle abrasion/control retentions were statistically weaker than the other types of retention tested. The retention means corresponding to the commercial-grade Ni-Cr alloys used were statistically different. The composite Solidex showed a tensile strength mean statistically higher than Artglass. All values observed were higher than that recommended for metal-ceramic dental restorative systems (25 MPa-ISO 9693).

Analysis of Variance↗
PubMed1999

Depth of cure of prosthetic composite materials polymerized with laboratory and handheld photo-curing units.

This study examined depth of cure of two prosthetic composite materials (Artglass(R) and Dentacolor(R)) polymerized by means of four photo-curing units for the purpose of comparing the curing performance of laboratory and handheld curing units. Each composite material was photo-exposed either with one of two laboratory photo-curing units (Dentacolor XS(R) and UniXS(R)) or with one of two handheld photo-curing units (Translux CL(R) and Translux EC(R)). The light sources were differently shaped xenon stroboscopic lamps for the laboratory units, and halogen lamps of differing intensity for the handheld units. Exposure periods were 20, 30, 60, and 90 s, and depth of cure of the materials was determined with a scraping technique. The two handheld curing units generated significantly greater depth of cure for both materials than either of the two laboratory curing units. Of the two laboratory units, the Dentacolor XS(R) unit produced somewhat greater depth of cure for all combinations than the UniXS(R) unit, whereas the differences in depth of cure of the two materials exposed with the two handheld units were not significant when the exposure time period was 60 s or more. The Dentacolor(R) composite generally demonstrated greater depth of cure than the Artglass(R) composite under identical curing conditions.

Chemical Phenomena↗
PubMed2000

Comparative evaluation of secondary heat treatment and a high intensity light source for the improvement of properties of prosthetic composites.

This study determined the hardness and water solubility of two prosthetic composites polymerized with three curing modes for the purpose of evaluating the influence of secondary heating and a high intensity light source on resulting material properties. Two prosthetic composite materials (Artglass and Dentacolor) were cured with the following methods: (1) exposure by means of a photo-curing unit with a xenon stroboscopic light source (Dentacolor XS) for 120 s; (2) exposure with the xenon unit for 120 s, followed by heating in an oven (KL 100) at 100 degrees C for 15 min; and (3) exposure by means of a photo-curing unit with two metal halide lamps (Hyper LII) for 120 s. Knoop hardness and water solubility were determined according to standardized testing methods. Although post-cure heat treatment considerably elevated the Knoop hardness number for both materials, the greatest hardness number was generated with the use of the metal halide unit. Water solubility of the Dentacolor material was lowest when the material was cured with the metal halide unit, followed by the secondary heated group, whereas, solubility of the Artglass material was unaffected by the curing modes. This suggests that the use of a high intensity light source is more effective than the application of secondary heating for improving the post-curing properties of composites.

Analysis of Variance↗
PubMed2001

Influence of thermal cycles in water on flexural strength of laboratory-processed composite resin.

Recently a new generation of laboratory-processed composite resins containing submicron glass fillers was introduced, with claims of high strength. The purpose of this study was to evaluate the effect of thermal cycling in water on the flexural strength and hardness of several laboratory composite systems. The flexural strength of the new laboratory processed composite resins (Artglass [AG], Targis [TR] and Estenia [ES]) was significantly higher than that of conventional resins (Dentacolor [DC] and Cesead II [CS]). Thermocycling caused a reduction of the flexural strength but not a reduction of the hardness for most of materials tested. It was concluded that thermocycling affected the properties of the laboratory-processed hybrid type composite resin, ES, AG and TR. However, the changes of these properties were smaller than those of microfine type composite resin DC. Thus, ES, AG and TR may maintain better properties during service compared with DC.

Analysis of Variance↗
PubMed2003

Influence of fibre position on the flexural properties and strain energy of a fibre-reinforced composite.

The introduction of laboratory-processed composite systems and fibre reinforcement techniques have increased the possibilities for the prosthetic replacement of missing tooth tissues. Laboratory fabrication variables may significantly influence the properties of the final prosthesis. During the construction of a fibre-reinforced bridge it is necessary to place the fibre at some distance from the fitting surface of the restoration in the pontic region. No guidelines are available for optimal fibre placement in this respect. The purpose of this study was to assess the influence of placing ultra high molecular weight polyethylene (UHMWPE) fibre at five different distances from the tensile side of test samples on flexural properties and the strain energy stored within the dental composite. The results of this investigation showed that whilst moving the fibre reinforcement away from the tensile side by up to 1.5 mm led to a significant reduction in flexural strength, there was no significant decline in the increase in strain energy stored within the tested composite until this distance was exceeded.

Composite Resins↗
PubMed1977

Linear dimensional changes of three luting agents.

The linear dimensional changes during setting of a reinforced zinc oxide eugenol cement (Alumina EBA Crown and Bridge Cement), a composite resin cement (Epoxylite 9080 Crown and Bridge Adhesive) and a zinc silico phosphate cement (Fluoro-Thin cement), have been studied. The measurements were were performed on specimens placed on a mercury bath. The cements were allowed to set under various environmental humidity. The measurements of specimen length started 3 or 5 min after commencing the mix. The EBA-cement showed a maximum contraction of 0-4 percent after 7 days when setting under dry conditions. Under wet conditions the cement had an initial contraction the first day of setting, and thereafter an expansion. After 21 days specimens setting under 100 percent relative humidity showed 0-3 percent expansion, whereas specimens immersed in water attained the initial length. The composite resin cement showed a contraction of 1-0 percent after 1 day when setting under dry conditions. Under wet conditions the specimens had an initial contraction of 0-8 percent the first day of setting being reduced to 0-4 percent during the next 20 days. The zinc silico phosphate cement showed a maximum contraction of 3-0 percent after 7 days under dry conditions and 0-5 percent after 1 day under wet conditions.

Composite Resins↗
PubMed1989

Increase in compressive strength of glass ionomer restorative materials with respect to time: a guide to their suitability for use in posterior primary dentition.

Glass ionomer restorative cements have been used in anterior restorations for a number of years but have not been considered strong enough for use in posterior restorations. The compressive strengths of a number of materials currently available were measured at 30 min, 1 hour and 24 hours. It was concluded that some of the materials might be considered for posterior restorations in deciduous teeth where no other considerations, such as radiopacity, apply.

Dental Cements↗
PubMed1990

An evaluation of a rapid setting glass ionomer cement used by general dental practitioners to restore deciduous teeth.

Twenty-one general dental practitioners evaluated the clinical handling properties and performance of a newly formulated glass ionomer cement of the powder/water type. One hundred and eighteen restorations were placed. Sixty-nine restorations were reviewed, on average, after 6 months by 17 practitioners who completed the trial. This formulation set rapidly. Approximately 90% of the restorations that were reviewed performed well over the period of assessment. The results of the trial were compared with those of trials on earlier glass ionomer cements used to restore deciduous teeth. The main advantage of the new formulation was the improvement in handling properties.

Child↗
PubMed1999

Effect of two abrasive systems on resin bonding to laboratory-processed indirect resin composite restorations.

PURPOSE: This study compared two methods of surface roughening or preparation, with or without the use of proprietary surface wetting agents, to evaluate their effect on resin cement adhesion to the following laboratory-processed, indirect restorations: Artglass (AG), belleGlass HP (BG), Concept (C), and Targis (T). Methods of surface roughening or preparation included microetching with aluminum oxide (AO): 50 microns at 34 psi and silanized silica coating, CoJet-Sand (CJ): 30 microns at 34 psi. Artglass and Concept were tested with and without the use of their respective surface wetting agents: Artglass Liquid (AGL) and Special Bond II (SB). MATERIALS AND METHODS: One hundred twenty specimens, each consisting of a pair of cylinders (7.0 x 3 mm and 4.3 x 3 mm) were fabricated. The larger cylinder or base was embedded in self-curing resin in a phenolic ring, and bonding surfaces were finished with 320-grit silicon carbide paper. Specimen pairs for each restorative material were randomly assigned to treatment groups (n = 10) and received the following surface treatments prior to cementation: group 1 (AG/AO/+AGL), group 2 (AG/AO/-AGL), group 3 (AG/CJ/+AGL), group 4 (AG/CJ/-AGL), group 5 (BG/AO), group 6 (BG/CJ), group 7 (C/AO/+SB), group 8 (C/AO/-SB), group 9 (C/CJ/+SB), group 10 (C/CJ/-SB), group 11 (T/AO), and group 12 (T/CJ). Specimen pairs were cemented with a dual-cure resin cement (Dual) and a standardized force of 1 MPa. Specimens were light-cured 40 seconds per side (80 s total), then thermocycled 300 times at between 5 degrees and 55 degrees C. Shear bond strengths (MPa) were determined using a Zwick Materials Testing Machine at a crosshead speed of 5 mm per minute. RESULTS: One-way analysis of variance (ANOVA) and Duncan's multiple range test (alpha = 0.05) by restoration type indicated no significant differences in shear bond strength between BG group 5 (29.8 +/- 5.8), BG group 6 (28.3 +/- 4.3), T group 11 (29.3 +/- 4.9), and T group 12 (29.0 +/- 4.4). Shear bond strength in AG group 3 (35.9 +/- 3.4) was significantly higher than in AG group 4 (32.4 +/- 4.0) and equal to that in AG group 2 (31.9 +/- 3.9) and AG group 1 (30.0 +/- 3.6). Shear bond strength in C group 10 (24.8 +/- 5.7) was equal to that in C group 9 (21.5 +/- 2.9), but was higher than in C groups 7 (19.4 +/- 3.1) and 8 (19.3 +/- 3.4). CLINICAL SIGNIFICANCE: Under the conditions of this study, the combination of CoJet-Sand and Artglass Liquid resulted in the highest bond strength for Artglass restorations. Microetching with CoJet-Sand or aluminum oxide followed by wetting with an unfilled adhesive was an effective surface pretreatment for dual-cure resin cementation of the four proprietary indirect resin-ceromer restorations tested.

Acid Etching, Dental↗
PubMed1980

Rheology of luting cements.

A rheometer has been developed to simulate the extrusion of luting cement from beneath a full crown during seating using clinically realistic shear rates. Five luting cements were studied, and differences in rheological behavior were illustrated. These measurements demonstrate the importance of consideration of the effects of shear rate on viscosity when evaluating a cement for optimal clinical utilization.

Cold Temperature↗