PubMed · 3477249
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S Carossa, P Pera, C Antonelli. 1987-01-25. [Etchable splints in chromium-cobalt].. https://pubmed.ncbi.nlm.nih.gov/3477249/
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Atomic force microscopy (AFM) combined with a nano-indentation technique was used to reveal the structure and to perform site-specific mechanical testing of the enamel of third molars. Nano-indentations (size<500 nm) were made in the cusp area to measure the mechanical properties of single enamel rods at different orientations. The influence of etching on the physical properties was studied and etching conditions that did not significantly alter the plastic-elastic response of enamel were defined. Elasticity and hardness were found to be a function of the microstructural texture. Mean Young's moduli of 87.5 (+/-2.2) and 72.2 (+/-4.5) GPa and mean hardness of 3.9+/-0.3 and 3.3+/-0.3 GPa were measured in directions parallel and perpendicular to the enamel rods, respectively. Analysis of variance showed that the differences were significant. The observed anisotropy of enamel is related to the alignment of fibre-like apatite crystals and the composite nature of enamel rods. Mechanical properties were also studied at different locations on single enamel rods. Compared to those in the head area of the rods, Young's moduli and hardness were lower in the tail area and in the inter-rod enamel, which can be attributed to changes in crystal orientation and the higher content of soft organic tissue in these areas.
OBJECTIVE: Gallium and indium-containing alloys have demonstrated an ability to wet and bond to many types of materials including enamel. The purpose of this study was to evaluate and compare the bond strengths of a gallium-and-indium-containing alloy and a dental amalgam to human enamel surfaces. METHOD: A flat enamel bonding surface was created by slicing recently extracted human molars with a 180-grit diamond wheel. Cylinders of amalgam or a gallium-indium alloy were bonded to the as-cut surfaces or to as-cut surfaces that had been pumiced, air-abraded or acid-etched for various times. Before testing, samples were stored under different conditions (100% humidity, immersed in water, thermocycled). The shear-bond strength was determined using a crosshead speed of 0.1 mm x min(-1). Sample size was 10. Data was subjected to ANOVA and a post-hoc Tukey's test. RESULTS: The bond strength of amalgam to enamel was zero. The bond strength of the gallium-indium alloy ranged between 6.5 MPa (10s etch with 10% phosphoric acid) and 4.2 MPa (pumiced enamel). Acid-etching significantly increased the bond strength (P>0.0001) The bond strength was not significantly affected by the type of mechanical surface preparation, storage conditions, thermocycling, etching times or acid concentrations. SIGNIFICANCE: Bonding, particularly chemical bonding, suggests a greater potential for better wetting and therefore better sealing of a cavity. Since microleakage of restorations is one of the principal causes of restoration failure, materials that can bond may in turn posses enhanced resistance to microleakage and ultimately, resistance to restoration failure. The gallium-indium alloy evaluated in this study may be such an alloy.
OBJECTIVE: The purpose of this study was to investigate the effect of smear layers on the tensile bond strength to human dentin. Bond strength was determined on dumbbell-shaped specimens to determine the feasibility for clinical use of a self-etching primer. METHODS: The dentin of extracted human teeth was exposed by grinding with either #180 or #600 abrasive paper. A self-etching primer was then applied to the prepared dentinal surfaces and left undisturbed for 30s. It was then air-dried and a photocured bonding agent applied and irradiated for 20s. A composite resin was then added to the primed dentin and light-cured for 60s to complete the bonded assemblies. Mini-dumbbell specimens (3.0 x 2.0 mm2) were prepared from the bonded samples. These specimens were stored in 37 degrees C water for 24h before tensile loading to failure at a crosshead speed of 1.0 mm/min. Surfaces of fractured specimens, both resin and dentin, were examined under a scanning electron microscope (SEM). RESULTS: Significantly different tensile bond strengths (TBS) of 10.0+/-7.2 and 28.5+/-5.2MPa were found for #180- and #600-prepared dentin, respectively (p<0.01). The former specimens fractured within the hybridized, relatively coarse smear layer, while the latter demonstrated adhesive failure between the composite resin and an attached PMMA rod, not between the dentin and applied adhesive agent. SIGNIFICANCE: The presence and quality of a smear layer yields significantly different bond strengths to prepared human dentin, in vitro. However, a TBS of 10+/-7MPa is evidently adequate, since self-etching primers have been well accepted in dental clinics.