Abstract
It was hypothesized that applying the polymer-induced liquid-precursor (PILP) system to artificial lesions would result in time-dependent functional remineralization of carious dentin lesions that restores the mechanical properties of demineralized dentin matrix. 140 µm deep artificial caries lesions were remineralized via the PILP process for 7–28 days at 37°C to determine temporal remineralization characteristics. Poly-L-aspartic acid (27 KDa) was used as the polymeric process-directing agent and was added to the remineralization solution at a calcium-to-phosphate ratio of 2.14 (mol/mol). Nanomechanical properties of hydrated artificial lesions had a low reduced elastic modulus (ER = 0.2 GPa) region extending about 70 μm into the lesion, with a sloped region to about 140 μm where values reached normal dentin (18–20 GPa). After 7 days specimens recovered mechanical properties in the sloped region by 51% compared to the artificial lesion. Between 7–14 days, recovery of the outer portion of the lesion continued to a level of about 10 GPa with 74% improvement. 28 days of PILP mineralization resulted in 91% improvement of ER compared to the artificial lesion. These differences were statistically significant as determined from change-point diagrams. Mineral profiles determined by micro x-ray computed tomography were shallower than those determined by nanoindentation, and showed similar changes over time, but full mineral recovery occurred after 14 days in both the outer and sloped portions of the lesion. Scanning electron microscopy and energy dispersive x-ray analysis showed similar morphologies that were distinct from normal dentin with a clear line of demarcation between the outer and sloped portions of the lesion. Transmission electron microscopy and selected area electron diffraction showed that the starting lesions contained some residual mineral in the outer portions, which exhibited poor crystallinity. During remineralization, intrafibrillar mineral increased and crystallinity improved with intrafibrillar mineral exhibiting the orientation found in normal dentin or bone.
Highlights
Replacing mineral within type I collagen is critical to establishing the normal mechanical properties of calcified tissues such as dentin that forms the bulk of the tooth [1,2]
Subsequent analyses by nanoindentation and MicroXCTTM suggest that the lesions have a highly demineralized region that extended approximately 80 mm followed by a gradual rise to normal dentin values at a depth of 140– 150 mm
This work determined that substantial restoration of the mechanical properties of hydrated carious dentin tissue occurred with the polymer-induced liquid- precursor (PILP) process, providing functional remineralization [1,2] in artificial lesions
Summary
Replacing mineral within type I collagen is critical to establishing the normal mechanical properties of calcified tissues such as dentin that forms the bulk of the tooth [1,2]. Several other groups have suggested that amorphous inorganic precursors may be a critical stage in biomineralization, Gower’s group pioneered the concept that formation of liquid nanoprecursors encapsulated by polyanionic polymers may be a fundamental step in many forms of biomineralization [6,7,8]. These studies have shown significant success in mineralizing a variety of organic matrices with both calcium carbonate and calcium phosphates including collagen matrices mineralized by formation of hydroxyapatite [9]. This study exploits the concept of ‘‘biologically induced mineralization’’ using PILP mechanism for remineralization of dental carious lesions
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