Evaluation of Fluoride Rinses Employing an in vitro Remineralization/Demineralization Model

Objective: Determine the impact of phosphate and sodium lauryl sulfate (SLS) on enamel fluoride uptake; lesion remineralization; and prevention of demineralization on acid challenge.

Method: Artificial lesions were formed in human enamel specimens by immersion in lactic acid/Carbopol, 50% saturated with hydroxyapatite(pH 5.0).  A remineralizing solution was used as the medium in all treatment groups.  After initial surface microhardness (SMH), specimens were treated in the following sequence for 15-days: (1 min treatment, remineralization, 1 min treatment, remineralization, acid challenge, remineralization, 1 min treatment, remineralization, 1 min treatment followed by remineralization overnight).  Specimens were analyzed for SMH (5, 10, and 15-days) and lesion fluoride content (microdrilling method; 15-days).  Following the fluoride analyses, specimens were subjected to a simulated plaque acid challenge (SPAC).  The control rinse (CR) consisted of 21.6%v/v ethanol, 0.0221%w/v NaF ( pH=3.5).  The other treatment samples were CR+0.1M Phosphate ^and CR+0.1M Phosphate+0.1%w/w SLS. 

Result:

Treatment Group	Δ Surface Microhardness (Mean+/-SD)				Fluoride Content mgF/cm3
	5-Day	10-Day	15-Day	SPAC
H2O	2.8±1.4	2.3±1.9	0.5±1.5	-7.5±1.4	217±7
CR	10.4±1.5a	12.2±1.6a	20.3±1.9a	6.1±1.5a	2,579±101a
CR+Phosphate	15.9±1.8a	20.1±1.9b	25.4±2.1a	13.6±2.2b	2,920±134b
CR+Phosphate+SLS	11.9±1.5a	15.9±1.5a,b	22.7±1.6a	9.9±1.6a,b	3,132±127b

All three rinses remineralized lesions significantly better than H₂O at all time points.  For each column, values with identical letters do not differ significantly (p>0.05) as determined by SNK analysis.  Both phosphate-containing rinses were significantly more effective in promoting fluoride uptake.  CR+Phosphate was more effective remineralizing lesions than the control at 10-days and in the SPAC.  No significant differences were found between the CR+Phosphate and CR+Phosphate+SLS mouthrinses. 

Conclusion: The addition of sodium lauryl sulfate did not impede fluoride efficacy in these low pH, hydroalcoholic mouthrinses.  When phosphate was present (with and without SLS), rinses displayed a superior benefit in fluoride uptake compared to the positive control.