Figure 4.

Peptoid induced peritubular mineralization and change in mechanical properties. a–d) SEM images of (a) normal dentin, (b) artificial dentin lesions, (c) lesion remineralized via PILP process (40 ml of solution at 37°C with [Ca²⁺] = 4.5 mM, [HPO₄²⁻] = 2.1 mM in tris buffer with NaN₃ added as a biocide) and (d) via PILP process with pre-incubation in peptoid CC81-3 solution (2 μM peptoid and 100 μg/ml 27 kDa pAsp for 5 days). The addition of the incubation step with peptoid CC81-3 induced the peritubular mineralization (compare insets in (c) and (d)), resembling normal peritubular dentin. (e, f) TEM images with SAED data (g, h) showing (e, g) peritubular minerals generated with addition of peptoid CC81-3 compared with (f, h) normal peritubular dentin. Tb: dentin tubule. Peptoid induced peritubular minerals consist of stack and co-aligned apatite nano-crystals (double head arrow guiding the view of alignment). i–k) AFM images showing peritubular remineralization. (i) Dentin tubule prior to remineralization (j) Dentin tubules 30–50% occluded by peritubular mineralization when the dentin lesion was incubated with 2μM peptoid prior to PILP remineralization. (k) Series of nano-indentations made across the occlusal surface of a remineralized dentin lesion in both the peritubular region and the intertubular region following peptoid-induced remineralization. l) Reduced elastic modulus (E_R) determined from the nano-indentations in (k). Values within the peptoid-induced peritubular mineral ranges from 40–55 GPa, which are markedly higher than the values measured either across the intertubular region or in normal peritubular dentin (28.6 GPa⁵³). AFM image shows triangular indents across the occlusal surface of a remineralized dentin lesion using peptoid+PILP process. The vertical scales of all AFM images are in nm (i – k).