Injection of BPA restores collagen in SPARC-null PDL. (A) PSR-stained sections of either DMSO (Control, top panels) or BPA-injected (bottom panels) WT and SPARC-null PDL. BPA-injected SPARC-null PDL appeared to have an increase in thick collagen, as well as increases in total collagen over control sections. BPA-injected WT also had apparent increases in thick collagen. (B) WT and SPARC-null PDL had significant increases in the percent volume fraction of thick collagen following BPA injections versus control values. (C) In SPARC-null PDL, but not WT, BPA injection significantly increased total collagen volume fractions over that of control values. (D) The molar extraction force of WT and SPARC-null PDL was increased in BPA-injected mice versus vehicle control. *p < 0.05 between the DMSO injected and BPA injected for each genotype, n = 8 mice per genotype per condition for measurements of total collagen and fiber thickness, n = 5 mice per genotype for mechanical strength measurements. SPARC = SP = secreted protein acidic and rich in cysteine; PDL = periodontal ligament; PSR = Picrosirius red; B = bone; T = tooth; BPA = 5-(Biotinamido) pentylamine; DMSO = dimethylsulfoxide.