Effects of osmotic stimuli on fluid flow after self-etching adhesive

Objective: To determine in vitro the dentinal fluid movement produced by various osmotic stimuli, and evaluate fluid movement across human dentin in response to the application of various osmotic stimuli before and after bonding. Methods: The experiments were carried out on 10 recently extracted premolars. The teeth were scheduled for extraction as part of orthodontic treatment. Each tooth was sectioned transversely below to the cemento-enamel junction 1-2mm with a diamond disc and water coolant. Dentine was exposed at the tip of the buccal cusp of a premolar on one side by cutting a cavity (diam. 3 mm, depth 3 mm) and was etched with 35% phosphoric acid for 30s. The solutions of saturated CaCl₂, sugar syrup, chocolate, and sweet Thai dessert were used as osmotic test solutions, and randomly applied through dentin. The fluid flow through dentine obtained at 15s during application of each osmotic stimulus was measured before and after bonding with self-etching system (Clearfil^® S3 bond single-dose). Results: Before bonding procedures, CaCl₂ significantly produced peak rate of fluid flow (1.15±0.37 nLs^-1mm^-2), when compared with normal saline solution (NSS: 0.42±0.14), sugar syrup (0.8±0.22), chocolate (0.65±0.22), and sweet Thai dessert (0.55±0.19, 1-way RM ANOVA and Holm-Sidak method, P<0.05). During the applications of all osmotic stimuli, the amount of fluid movement across resin-bonded dentin was significantly lower than that without adhesive. There were no significant differences of fluid shifts across conditioned dentin obtained during the application of all osmotic stimuli (NSS:0.2±0.1; CaCl₂:0.25±0.15; sugar syrup:0.2±0.15; chocolate:0.2±0.14; Thai Dessert:0.2±0.13 nLs^-1mm^-2, P>0.05). Conclusion: It appears that different osmotic stimuli produced different rates of outward fluid flow through dentin. The application of self-etching adhesive significantly produced similar reduction of fluid movement in response to osmotic stimulation, irrespective of the chemical composition, or the osmotic pressure of stimuli. This study was supported by Thailand Research Fund.