FLUID-DYNAMICS OF GINGIVAL TISSUES

Gingival hydraulic interstitial pressure was measured with glass micro pipettes in 18 anesthetized rabbits at the level of the free gingiva, attached gingiva and oral mucosa facing the incisors and molar teeth. Samples of gingival interstitial tissue fluid were also collected by i nserting nylon wicks in the subepithelial layer of the oral mucosa. Co lloid osmotic pressure of interstitial fluid samples was measured with an osmometer whose membrane had a molecular cutoff of 30 kD. Hydrauli c interstitial pressure from the free gingiva, at an average distance of 300 mu m from sulcular space, was -1.3 +/- 0.9 (SD) cmH(2)O. Mean c olloid osmotic pressure of gingival tissues interstitial fluid was 13. 1 cmH(2)O, corresponding to a protein concentration of 2.8 g/dl. The t hickness of the sulcular epithelium and of the oral gingival epitheliu m (data from 2 rabbits) were approximate to 100 mu m; the minimal dist ance of microvessels from the surface of the sulcular epithelium was a pproximate to 150 mu m. Based on hydraulic and colloid osmotic data, t he Starling balance of pressures causes fluid filtration from gingival capillaries to gingival interstitium; however, across the sulcular ep ithelium, the pressure gradient sustains fluid absorption from the sul cus into the gingival interstitium. Plasma proteins may leak from micr ovessels into gingival interstitium, down convective bulk flow and via a concentration dependent diffusive component. At sulcular level, pro teins may leak into the sulcus down a concentration gradient. Thus. at sulcular level a peculiar condition occurs in that there is an absorp tion gradient for water but a filtration gradient for plasma proteins.