The effects of ageing on the biomechanical properties of root dentine and fracture
Abstract
Objectives
Knowledge
of the mechanical behaviour of root dentine can facilitate better
understanding of spontaneous vertical root fracture (VRF), an
age-related disease initiated mainly at the root apex. We tested the
hypothesis that the biomechanical properties of root dentine change with
ageing.
Methods
Sixteen human
premolars were divided into “old” (17–30 years) and “young” (50–80
years) groups. The elastic modulus, nano-hardness, micro-hardness,
elemental contents, tubular density/area of root dentine in cervical,
middle and apical root regions were evaluated using atomic force
microscopy-based nano-indentation, Knoop indentation, scanning electron
microscopy and energy dispersive X-ray spectroscopy, respectively.
Results
The
apical dentine showed a lower nano-hardness, a lower elastic modulus, a
lower calcium content, a lower calcium-to-phosphorus ratio and a
smaller tubular density/area than the cervical dentine in both age
groups, whereas spatial differences in micro-hardness were observed only
in old roots. Compared with young dentine, old dentine showed a greater
hardness, a higher elastic modulus, a greater mineral content and a
smaller tubular size in the cervical portion, whereas the age-induced
changes in tubular density were insignificant. Finite element analysis
revealed that due to its higher elastic modulus, old apical dentine has a
higher stress level than young dentine.
Conclusions
The
intrinsic material properties of root dentine have spatial variations,
and they are altered by ageing. The higher stress level in old apical
dentine may be one reason, if not the most important one, why
spontaneous VRFs are more likely to occur in the elderly population.
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