Effect of pH on Remineralization Efficacy of Over-the-counter Fluoride Mouthrinses

Objective:  Determine the effect of pH on the enamel remineralization efficacy of fluoride mouthrinses on non-cavitated lesions with different levels of demineralization.  It has been hypothesized that lower pH fluoride treatments enhance remineralization, particularly in less demineralized non-cavitated early lesions.

Method: Human enamel specimens were demineralized to create three groups each of “early” (EL) and “advanced” (AL) non-cavitated caries-like lesions (N=18/group).  After being analyzed for surface microhardness (SMH), specimens were exposed for 20 days to a pH-cycling remineralization/demineralization model.  During the cycling period, EL and AL groups were treated 4 times/day for one minute with either LISTERINE® TOTAL CARE with 0.0221% NaF at pH 3.5 (LpH) or ACT® TOTAL CARE with 0.02% NaF at pH 6.5 (NpH), or deionized water at pH 7.0 (H₂O).  SMH (10d, 20d) and lesion fluoride content (microdrilling method; 20d) were determined.  Lastly, specimens were demineralized again for two hours to determine resistance to a simulated plaque acid challenge (SPAC).  Data were analyzed using ANCOVA (α=0.05). 

Result:

 

Lesion	Treatment	Surface Microhardness Number (Mean+/-SD)				Fluoride
Type	Group	Baseline	10-day	20-day	SPAC	Content
EL	H2O	109±7	86±10	83±10	76±11	50±12
EL	LpH	113±8	127±16	144±22	136±20	221±94
EL	NpH	113±8	122±12	131±13	126±14	171±45
AL	H2O	37±6	45±8	48±8	42±9	62±20
AL	LpH	37±5	59±11	68±9	62±8	520±103
AL	NpH	37±6	57±10	68±11	64±11	506±123

Both LpH and NpH  rinses remineralized early and advanced lesions significantly better than H₂O(p<0.001) at both 10 and 20 days.  LpH was significantly more effective than NpH in remineralizing(p =0.006), promoting fluoride uptake(p=0.017), and resisting SPAC(p=0.03) in EL after 20 days of cycling.  No significant differences were found between LpH and NpH treatments in AL. 

Conclusion: While both fluoride mouthrinses showed remineralization and fluoride uptake promotion potential, LpH demonstrated significantly enhanced efficacy in less demineralized non-cavitated lesions.