Figure 4. Collagen birefringence and PDL directionality across groups and age.

a) Histology sections were stained with picrosirius red. b) Imaging was primarily focused around the furcation and root-PDL (R-PDL) surrounding the distal root of the 2^nd molar. c) Birefringence signal was measured in the following regions: interradicular bone (IR-B), interradicular periodontal ligament (IR-PDL), and R-PDL. IR-PDL revealed a sponge-like configuration while R-PDL illustrated an increased collagen fiber orientation. Under polarized light, collagen orientation was quantified within IR-PDL, IR-B, and R-PDL. White bars are 100 µms. Trends show increased birefringence as a function of age within PDL regions and a decrease in birefringence as a function of age within interradicular bone. Statistical significance in birefringence between SD and HD is indicated with an (*) (p<0.05) and was only observed in the PDL of 8 week old. Graphical representation of averages and standard deviations show no age-related trends for both hard and soft diet groups. (d) Images using polarized light microscopy show regions of distal (yellow box) and mesial (red box) regions used to calculate fiber orientation. Representative histogram distributions of fiber orientation in (e) hard diet and (f) soft diet are shown for 8, 16, and 24 weeks with total group average and standard deviations are shown. g) As a function of age trends included a decreasing difference in distal- and mesial-PDL orientation within and across hard and soft diet groups with age.