BACKGROUND: An increase in gingival sulcular fluid filtration is a common clinical sign of early gingivitis. The aim of this study was to describe the fluid dynamics of the gingival interstitial tissues at the level of the sulcus in the transition towards inflammation. METHODS: In 13 anesthetized rabbits, a silk ligature was placed around incisors close to the gingival margin, in order to prevent mechanical cleaning of plaque deposition. After 2 to 7 days, animals were anesthetized and interstitial fluid pressure measured using glass micropipettes connected to a servonull pressure system at the level of the free and attached gingiva. RESULTS: Interstitial pressure was 3.8 +/- 2.9 cmH2O, significantly higher than the normal physiological value (about -1 cmH2O). Colloid osmotic pressure of interstitial fluid samples collected using the wick technique was measured using an osmometer whose membrane had a molecular cut-off of 30 kD and averaged 12.8 +/- 2.8 cmH2O (unchanged relative to control). Mean gingival sulcular fluid flow, measured by placing a PE tube (0.5 mm OD, 0.28 mm ID) in the sulcus, was 0.16 +/- 0.12 microl/h; the mean colloid osmotic pressure was 13.6 +/- 6.6 cmH2O, corresponding to a protein concentration of approximately 2.8 g/dl. Proteins of gingival fluid may leak from inflamed gingival interstitium or derive from bacteria of dental plaque. Histological analysis of gingival biopsies showed neutrophilic polymorphonuclear leukocyte infiltrates in both the dermis and epidermis layer. CONCLUSIONS: Based on hydraulic and colloid osmotic data, the Starling pressure gradient favored filtration from gingival interstitium to the sulcular space, a condition opposite to that observed in healthy gingiva where fluid filtration is absent.
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