Quantitative/qualitative analysis of adhesive-dentin interface in the presence of 10-methacryloyloxydecyl dihydrogen phosphate.

Dental adhesive provides effective retention of filling materials via adhesive-dentin hybridization. The use of co-monomers, such as 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), is thought to be crucial for hybridization owing to their ionic-binding to calcium and co-polymerization in the polymerizable adhesives. Optimal hybridization partly depends on the mechanical properties of polymerized adhesives, which are likely to be proportional to the degree of conversion ratio. This study assessed the correlation between polymerization quality and mechanical properties at the adhesive-dentin interfaces in the presence or absence of 10-MDP. In situ Raman microspectroscopy and nanoindentation tests were used concurrently to quantify the degree of conversion ratio and dynamic mechanical properties across the adhesive-dentin interfaces. Despite the excellent diffusion and apparent higher degree of co-polymerization, 10-MDP reduced the elastic modulus of the interface. The higher viscoelastic properties of the adhesive are suggestive of poor polymerization, namely polymerization linearity related to the long carboxyl chain of 10-MDP. Such reduced mechanical integrity of hybridization could also be associated with the inhibition of nano-layering between 10-MDP and mineralized tissue in the presence of hydroxyethyl methacrylate (HEMA). This potential drawback of HEMA necessitates further qualitative/quantitative characterization of adhesive-dentin hybridization using a HEMA-free/low concentration experimental 10-MDP monomer, which theoretically possesses superior chemical bonding potential to the current HEMA-rich protocol.

Exceptional contact elasticity of human enamel in nanoindentation test.

OBJECTIVE: Tooth enamel has unsurpassed hardness and stiffness among mammalian tissue structures. Such stiff materials are usually brittle, yet mature enamel can survive for a lifetime. Understanding the nanoscale origin of enamel durability is important for developing advanced load-bearing biomaterials. Here, nanoscale exceptional contact elasticity of the human tooth enamel, based on nanoindentation tests, is reported. METHODS: Spherical indenter tips with radii of 243 and 1041nm were used to determine stress-strain curves of enamel. Force-displacement curves were recorded using quasi-static loading strain rates of 0.031, 0.041, and 0.061s-1. The storage moduli from a superimposed signal amplitude (dynamic strain at 220Hz) embedded during primary quasi-static loading and from quasi-static elastic theory were simultaneously measured. Modulus mapping was considered to be an extremely low quasi-static loading strain rate indentation test. RESULTS: The elastic limits were 7-9GPa and 5-6GPa for the small and large indenters, respectively. The elastic-plastic transition point and elastic modulus value increased with substantially increased quasi-static loading strain rate. The results suggested that the increase of the elastic limit during high-loading strain was associated with exceptional contact elasticity at the nanoscale of the enamel structure and the consequent extension of the contact area (i.e., a temporary pile-up response, dependent on the enamel nanocrystals and protein glue). SIGNIFICANCE: Structural modification at this scale effectively prevents the initiation of cracking from localized strain, thus reinforcing the bulk structure. These results may provide valuable insight for conceptualizing bio-inspired nanocomposites.

Nanomechanical characterization of time-dependent deformation/recovery on human dentin caused by radiation-induced glycation.

An increase in non-enzymatic collagen matrix cross-links, such as advanced glycation end-products (AGEs), is known to be a major complication in human mineralized tissues, often causing abnormal fractures. However, degradation of mechanical properties in relation to AGEs has not been fully elucidated at the material level. Here, we report nanoscale time-dependent deformation and dimensional recovery of human tooth dentin that has undergone glycation induced by x-ray irradiation. The reduction in enzymatic collagen cross-linking and the increased level of AGEs with concomitant growth of disordered collagen matrix diminished creep deformation recovery in the lower mineralized target region. However, the elevated AGEs level alone did not cause a reduction in time-dependent deformation and its recovery in the higher mineralized target region. In addition to the elevated AGEs level, the degradation of the mechanical properties of mineralized tissues should be assessed with care in respect to multiple parameters in the collagen matrix at the molecular level.

Rapid GC-MS analysis of methamphetamine and its metabolites in urine--application of a short narrow-bore capillary column to GC-MS.

A rapid analysis of methamphetamine and its metabolites in urine was performed by gas chromatography-mass spectrometry (GC-MS) using a short narrow-bore capillary column (NBC) (5 m x 0.1 mm I.D.). For detection, selected ion monitoring (SIM) was performed for the characteristic ions of each of the compounds. The analytes were independently detected within 2 min. Linearity was demonstrated over a range from 25-2500 ng/ml. As an application of this study, a urine sample from a drug-abuse suspect was analyzed. The analytes from the actual sample were detected with reasonable reproducibility. The results indicate the possibility of rapid analysis using a conventional GC-MS with a short NBC at a relatively low inlet pressure.