In situ efficacy of an experimental toothpaste on enamel rehardening and prevention of demineralisation: a randomised, controlled trial

Abstract

Background: A novel sodium fluoride toothpaste containing lactate ion and polyvinylmethylether-maleic anhydride has been developed to promote enamel remineralisation and resistance to demineralisation. In this in situ study, we compared this toothpaste ('Test') with a stannous fluoride-zinc citrate (SnF 2-Zn) toothpaste ('Reference') (both 1100-1150 ppm fluoride) and a fluoride-free toothpaste ('Placebo') using an enamel dental erosion-rehardening model. Methods: In each phase of this randomised, investigator-blind, crossover study, participants wore palatal appliances holding bovine enamel specimens with erosive lesions. They brushed their natural teeth with either the Test, Reference or Placebo toothpastes, then swished the resultant slurry. Specimens were removed at 2 h and 4 h postbrushing and exposed to an in vitro acid challenge. Surface microhardness was measured at each stage; enamel fluoride uptake was measured after in situ rehardening. Surface microhardness recovery, relative erosion resistance, enamel fluoride uptake and acid resistance ratio were calculated at both timepoints. Results: Sixty two randomised participants completed the study. Test toothpaste treatment yielded significantly greater surface microhardness recovery, relative erosion resistance and enamel fluoride uptake values than either Reference or Placebo toothpastes after 2 and 4 h. The acid resistance ratio value for Test toothpaste was significantly greater than either of the other treatments after 2 h; after 4 h, it was significantly greater versus Placebo only. No treatment-related adverse events were reported. Conclusions: In this in situ model, the novel-formulation sodium fluoride toothpaste enhanced enamel rehardening and overall protection against demineralisation compared with a fluoride-free toothpaste and a marketed SnF 2-Zn toothpaste. Trial registration: ClinicalTrials.gov; NCT03296072; registered September 28, 2017.

The effect of dentifrice ingredients on enamel erosion prevention and repair

“…A recent clinical study, in which 'in situ' enamel specimens were mounted in an intra-oral appliance, 15 showing the highest uptake in all three study groups. Notably, 44 Ca uptake confirm the role of free fluoride ion in promoting remineralisation, as reported previously by the present authors.…”

“…It has already been established that fluoride is a key ingredient in dentifrices for mitigation of dental erosion by inhibition of demineralisation and promotion of remineralisation. The delivery of fluoride to the tooth surface from a dentifrice is optimal when ingredients which interfere with fluoride delivery are removed from formulation 16 and agents which can increase uptake of fluoride are present 15,17 …”

“…A recent clinical study, in which ‘in situ’ enamel specimens were mounted in an intra‐oral appliance, 15 used surface microhardness measurements to compare a sodium fluoride‐based dentifrice, containing PVM/MA copolymer and sodium lactate with the formulation pH controlled to 6.2 (NaF/CL in this study), with a control formulation containing stannous fluoride and zinc citrate. The NaF/CL formulation was found to increase fluoride uptake, remineralisation and overall fluoride‐mediated protection against dietary acid compared to the control.…”

“…The delivery of fluoride to the tooth surface from a dentifrice is optimal when ingredients which interfere with fluoride delivery are removed from formulation 16 and agents which can increase uptake of fluoride are present. 15,17 In this study two key aspects of dentifrice development have been addressed, that is, iterative formulation improvement and a comparison of a range of competitive formulations which have been designed to provide improved resistance to dental erosion through enhanced fluoride uptake and repair demineralised enamel through remineralisation.…”

“…However, dentifrices are complex vehicles for therapeutic agents, and several ingredients commonly found in formulations can interfere with fluoride action. This may occur by direct precipitation of fluoride ion via certain polyvalent metal ions; reduction of fluoride binding to enamel surfaces by ionic surfactants, for example, sodium lauryl sulfate; 14 or interference with fluoride‐promoted remineralisation processes by polyvalent metal ions and polyphosphates 15,16 . It is not possible to simply add more fluoride to formulations to offset these losses because national and international regulatory bodies set limits to dentifrice fluoride content in order to avoid harmful over‐exposure from ingested product.…”