Surface characteristics of aesthetic restorative materials - An SEM study

To determine the degree of surface roughness of glass-ionomer cements (GICs) and polyacid-modified resin composite (PAMRC) after polishing and immersion in various foodstuffs. Three tooth-coloured restorative materials were used: a PAMRC (F2000), a conventional glass-ionomer cement (CGIC) (Fuji IX) and a resin-modified glass-ionomer cements (RM-GIC) (Fuji II LC). Disk-shaped specimens were prepared and tested with either a plastics matrix finish or after polishing with wet silicon carbide papers up to 2000-grit. All specimens were immersed in 37°C-distilled water for 1 week, followed by three different foodstuffs (red wine, coffee or tea) for a further 2 weeks. Replicas of specimens were prepared by taking polyvinyl siloxane impressions, casting in epoxy resin, gold sputter-coating and examining using a Field-Emission Scanning Electron Microscope. The polished and matrix finish specimens of F2000 showed many microcracks at low magnification, and eroded surfaces with missing and protruding particles at high magnification in the polished specimens. The surface-polished specimens of Fuji II LC were considerably rougher than the matrix-finish specimens, with large voids and protruding filler particles. The effects of foodstuffs on Fuji II LC and F2000 were not noticeable. The CGIC became noticeably rougher after exposure to coffee and tea. All specimens had the smoothest surface when they were cured against a plastics matrix strip, and all materials had a rougher surface after polishing. None of the foodstuffs produced a perceptible increase in roughness on RM-GIC and PAMRC surfaces, whereas coffee and tea markedly increased the surface roughness of Fuji IX. © 2007 The Authors.link_to_subscribed_fulltex

Comparison of the effect of storage media on hardness and shear punch strength of tooth-colored restorative materials

Purpose: To measure the surface hardness and shear punch strength of six tooth-colored restorative materials before and after immersion in acidic and alkaline solutions. Methods: Specimens were prepared from three resin composites; Ceram X, Filtek Supreme, Point 4, two polyacid-modified resin composites; Dyract, F2000, and one resin-modified glass-ionomer cement; Fuji II LC, immersed in distilled water for 24 hours at 60°C, polished with silicon carbide papers up to 2000-grit and subjected to baseline measurement for Vickers hardness or shear punch strength. Further specimens were transferred to one of four aqueous media at 60°C for a further 2 weeks; distilled water, 0.01 mol/L lactic acid, 0.1 N NaOH or coffee 15g /500mL, washed, dried and tested for final hardness or shear punch strength. Results: Data analysis using ANOVA and Tukey's test showed that the hardness and shear punch strength values were material and solution dependent. Regardless of the solutions; the hardness of F2000 was the highest and Fuji II LC the lowest; Point 4 and Filtek Supreme had the highest shear punch strength; Fuji II LC and F2000 had lowest. NaOH significantly reduced the hardness of all materials and completely dissolved the structure of Fuji II LC. Lactic acid and coffee significantly increased shear punch strength compared to baseline.link_to_subscribed_fulltex

Subsurface degradation of resin-based composites

Objectives: To determine the depth of a degraded subsurface layer produced in dental composites as a result of exposure to lactic acid or NaOH, by observing the penetration of AgNO3 solution. Methods: Specimens were prepared from four resin composites; Point 4 (Kerr), Premise (Kerr), Filtek Supreme (3M/ESPE), Ceram X (Dentsply), and two polyacid-modified resin composites; Dyract (Dentsply) and F2000 (3M/ESPE). The specimens were immersed in distilled water for 1 week, transferred to one of three aqueous media at 60 °C for 2 weeks; distilled water, 0.01 mol/L lactic acid or 0.1N NaOH, washed and immersed in 50% (w/w) aqueous silver nitrate for 10 days at 60 °C and placed in a photodeveloper solution. After reduction of the silver, specimens were embedded in epoxy resin, sectioned and polished, coated with carbon, and examined by backscattered mode scanning electron microscopy. The depth of silver penetration into the degraded area was measured from the SEM micrographs. Energy dispersive analysis X-ray (EDAX) was used to confirm the presence of silver. Results: NaOH produced the greatest depth of degradation and lactic acid the least. Premise showed the greatest depth of silver penetration when subjected to NaOH, and Filtek Supreme the second with peeling of the surface and cracking, whereas F2000 and Point 4 showed the least in NaOH and lactic acid. Significance: ANOVA and Tukey's test showed that the depth of silver penetration was material and solution dependent, and the differences were significant for most of the materials (P < 0.05). © 2006 Academy of Dental Materials.link_to_subscribed_fulltex

The effect of aging on the fracture toughness of esthetic restorative materials

Purpose: To compare the fracture toughness (KIc) of tooth-colored restorative materials based on a fourpoint bending; to assess the effect of distilled water and a resin surface sealant (G-Coat Plus) on the resistance of the materials to fracture. Methods: Specimens were prepared from six materials: Quix FiI; Dyract (Dentsply), Freedom (SDI), Fuji VII (GC), Fuji IX (GC); Fuji II LC (GC). Fuji II LC and Fuji IX were tested both with and without applying G-Coat Plus (GC). The specimens were divided into the three groups which were conditioned in distilled water at 37°C for 48 hours, 4 and 8 weeks. The specimens were loaded in a four-point bending test using a universal testing machine. The maximum load to specimen failure was recorded and the fracture toughness calculated. Results: There were significant differences among most of the materials (P< 0.001). Quix FiI had the highest mean KIc value and Fuji VII the lowest. Immersion in distilled water for the resin composite and polyacid-modified resin composites caused a significant decrease in KIc as the time interval increased. For glass-ionomer cements, KIc decreased significantly after 4 weeks, and after 8 weeks immersion slightly increased. G-Coat Plus affected Fuji II LC positively while it had no effect on the Fuji IX.link_to_subscribed_fulltex

Comparison of the effect of storage media on shear punch strength of resin luting cements

Objectives: To measure the shear punch strength of eight resin-containing luting cements before and after immersion in acidic solution and ethanol at different temperatures (37° C and 60 °C). Method: Specimens were prepared from six resin luting cements; Set (SDI), Panavia F (Kuraray), RelyX Veneer (3M/ESPE), VarioloinkII (Ivoclar), Maxcem (Kerr), Nexus2 (Kerr) and two Resin-modified glass-ionomer luting cements (RM-GICs); GC Fuji Plus (GC Corporation), RelyX Luting 2 (3 M/ESPE). For each material a total of 114 disc-shaped specimens were prepared. Six specimens were immersed in distilled water for 24 h at 37 °C, polished and subjected to baseline measurement for shear punch strength. The remaining 108 specimens were randomly divided into 18 groups of six, and immersed in three solutions; distilled water, 0.01 mol/L lactic acid, and 50% ethanol at 37 °C or 60 °C, for 1 week, 1 month or 3 months. Specimens were washed, dried and tested for final shear punch strength. Results: Values were material and solution dependent. Values of Nexus 2 and Rely X Veneer are the highest, and Rely X Luting 2 the lowest. Ethanol and lactic acid specimens showed significantly lower values compared with the distilled water specimens. Conclusion: The shear punch strengths of the resin-containing luting cements were affected by time and storage solution. While some of the resin luting cements had significantly higher values compared to that of the RM-GICs, there were no significant differences between the RM-GICs and resin cements such as Panavia F and Set. © 2010 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex