Viscoelastic properties of demineralized dentin matrix.

OBJECTIVES: To evaluate the viscoelastic properties of demineralized dentin matrix. Stress-relaxation studies were done on matrices in tension and strain elongation or creep studies were done in both tension and compression.
METHODS: Mid-coronal dentin disks were prepared from extracted unerupted human third molars. Disks were 0.5 mm thick for stress-relaxation or tensile creep experiments and 0.2-0.3 mm thick for compressive creep studies. 'I' beam specimens were prepared from dentin disks and the middle region was demineralized in 0.5 M EDTA (pH 7) for 4 days. The specimens were held in miniature friction grips in water and pulled at 100 micro m s(-1) to strains of 5, 10, 15 or 20% and then held for 10 min to follow the decay of stress over time. Creep was determined on demineralized dentin immersed in water in tension and in compression. Compressive creep was measured using an LVDT contact probe with loads of 0.02-0.5 N. Strain data were converted to compliance-time curves (strain/stress) and expressed as total compliance (J(t)), instantaneous elastic compliance (J(o)), retarded elastic compliance (J(R)) and viscous response (t/eta) or creep.
RESULTS: The dentin matrix exhibits both stress-relaxation and creep behavior. Stress-relaxation and tensile creep were independent of strain but compressive creep rates were inversely related to compressive strain. Creep values were about 10% at low compressive strains, but fell progressively to 1% at high strains. Compliance-time curves fell with stress and came closer together. However, tensile creep was about 3% regardless of the strain. SIGNIFICANCE: The dentin matrix exhibits viscoelastic properties, but is not linearly viscoelastic. The relatively high creep rates of the matrix under low compressive loads may cause viscous deformations in poorly infiltrated hybrid layers in resin-bonded teeth under function.