PubMed · 10036837
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
S Carstensen. 1999. Orthodontic separators.. https://doi.org/10.14219/jada.archive.1999.0148
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The aim of our study was to investigate the effect of resin composite components on glucan synthesis by glucosyltransferase (GTase) derived from a cariogenic bacterium, Streptococcus sobrinus B13. The eluates from cured composites stored in 0.05 mol/L potassium phosphate buffer (KPB) (pH 6.8) for 2 weeks at 37 degrees C stimulated the formation of water-insoluble glucan, whereas those from amalgam inhibited it. This finding suggests that the eluates from the resin composites enhance GTase activity and contribute to plaque formation. In the individual resin components, a diglycidyl methacrylate and triethylene glycol dimethacrylate significantly enhanced GTase activity. However, most polymerization inhibitors and accelerators were potent inhibitors of enzyme activity. Thus, GTase stimulation by eluates from resin composites is hypothesized to be heavily dependent on the effect of the eluated resin monomers, even though the other eluting components had inhibitory effects on GTase.
OBJECTIVE: Determination of flexural strength, flexural modulus, fracture toughness, Vickers hardness, and wear resistance of condensable composites (Solitaire, Surefil, Alert) and an ormocer (Definite) in comparison with a hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc). METHODS: Flexural strength, flexural modulus, and fracture toughness were determined in 3-point bending. Single-edge notched-bend specimens were used to evaluate fracture toughness. Microhardness was measured with a Vickers indenter. Wear was determined in a pin-on-block-design with a Degusit antagonist at 50 N load and quantified by a replica technique after 6000, 10000, 30000, and 50000 load cycles using a 3D-laser scanner. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests. RESULTS: Alert exhibited the highest flexural modulus, K(IC), and hardness, but lowest wear resistance. Solitaire presented the highest wear resistance, but significantly lower flexural strength, flexural modulus, K(IC), and hardness than all other materials. No significant correlation could be detected between hardness and wear of the tested composites with Pearson's correlation coefficient. SIGNIFICANCE: The condensable composites differed significantly in their mechanical properties. This study suggested that, besides the filler content level and filler size, other factors like matrix-filler interactions highly influence the fracture and wear behavior of the materials.
The internal corrosion of dental resin composites is associated with water-sorption and leads to (1) interfacial debonding, (2) filler dissolution, (3) matrix cracking, and (4) subsurface damage. The last factor creates a condition for "corrosive-wear" in which the damaged layer is worn with ease exposing a new surface and perpetuating the cycle of corrosion and wear. Central to the simulation of in vivo corrosive-wear is the recreation of the subsurface damage layer. To produce this layer in water, artificial saliva, and in media of low pH is time-consuming, because the degradation process in these environments is extremely slow. In laboratory wear tests using aqueous environments, the contact time of resin composites with water is too short to cause significant internal degradation. Thus, data obtained from such tests represent abrasive and not corrosive-wear, and do not correlate well with in vivo wear data. In considering this limitation of the above media for accelerated wear tests, an alkaline medium has been used in this study to simulate corrosive-wear of eleven commercial composites. The procedure consists of exposing each material to 0.1 N NaOH at 60 degrees C for 2 weeks followed by abrasion in a tooth brushing machine. The medium choice is based on the rationale that in vivo degradation arises from reaction with the OH(-), and this reaction can be enhanced by raising the pH and the temperature of the medium. The warm NaOH solution satisfies both these conditions. Parameters examined to evaluate the resistance of each composite to corrosion and wear were (1) mass loss, (2) Si-loss, (3) degradation depth, and (4) wear depth, respectively. A highly significant correlation has been observed among various corrosion and wear parameters. SEM examination indicated degradation to be associated with interfacial separation, filler dissolution, matrix cracking, and subsurface damage. These features are characteristics of in vivo worn composite restorations. Time is of utmost importance in laboratory evaluation of restorative materials. The ability of NaOH to meet this expediency and to mimic the in vivo degradation process makes it a useful medium for corrosive-wear studies of dental composites.