Effect of Topical Fluoride Application Temperature on Recharge and Rerelease in Different Restorative Materials

Abstract

Introduction and aims: This study aimed to evaluate the influence of topical fluoride application temperature on the recharge and rerelease behaviour of three fluoride-containing restorative materials treated with 1.23% acidulated phosphate fluoride (APF) gel and 8% stannous fluoride (SnF₂).

Methods: Specimens of an alkasite-restorative material (Cention N), a resin-modified glass ionomer (Fuji II LC), and a conventional glass ionomer (Fuji IX GP) were prepared (n = 32 per material; n = 8 for each combination of fluoride agent and temperature). After an initial 64-day fluoride release phase in deionized water, samples were recharged with APF gel or SnF₂ at room temperature (23 ± 2°C) or high temperature (HT) (55 ± 2°C) for 4 minutes. Subsequent fluoride rerelease was measured for 32 days. Physicochemical properties of fluoride agents, including viscosity, temperature, and pH, were analysed. Elemental mapping of fluoride and tin distribution was performed using scanning electron microscope-energy-dispersive X-ray spectroscopy.

Results: All restorative materials initially showed rapid fluoride release that decreased over 64 days. After topical application, cumulative fluoride rerelease was significantly higher under HT than room temperature across all groups (P < .05), particularly with APF gel. RMGI demonstrated the greatest fluoride rerelease, while CGI showed the highest initial release. Scanning electron microscope-energy-dispersive X-ray spectroscopy revealed higher fluoride content at HT across all materials in both surface and cross-sectional analyses, regardless of the fluoride agent used. Tin distribution was detected only in SnF₂-treated groups.

Conclusion: Elevated application temperature significantly improves the fluoride recharge and sustained release capacity of restorative materials, with outcomes depending on the fluoride agent and material type.

Clinical relevance: Applying topical fluoride at higher temperatures may enhance its anticariogenic efficacy by promoting greater fluoride uptake and prolonged release from restorative materials. These findings highlight the importance of considering application conditions when optimizing preventive protocols in clinical practice.

Keywords: Acidulated phosphate fluoride gel; Fluoride application; Fluoride ion release; Fluoride uptake; Fluoride-containing restorative material; Stannous fluoride.

Fig. 1

Flowchart depicting the study design and experiment workflow.

Fig. 2

(A) Change in the viscosity of 1.23% acidulated phosphate fluoride (APF) gel as a function of shear rate at room temperature (RT) and high temperature (HT). (B and C) Temperature and pH changes of SnF₂ and APF gel: (B) temperature was measured after transferring samples from HT storage to a 37 ± 1°C environment; (C) pH was measured for samples stored under HT and RT conditions.

Fig. 3

Fluoride ion rerelease (ppm) from ARM, RMGI, and CGI measured on days 1, 2, 4, 8, 16, 32, and 64. Different uppercase letters indicate statistically significant differences in fluoride release within each material group over time (P < .05). ARM, alkasite-restorative material; CGI, conventional glass-ionomer cement; RMGI, resin-modified glass-ionomer cement.

Fig. 4

Cumulative fluoride rerelease (ppm) measured on days 1, 2, 4, 8, 16, and 32 after topical application of 1.23% acidulated phosphate fluoride gel (APF gel) or 8% stannous fluoride (SnF₂). (A-C) Cumulative rerelease after fluoride uptake with APF gel, (D-F) Cumulative rerelease after fluoride uptake with SnF₂. ARM, alkasite-restorative material; CGI, conventional glass-ionomer cement; HT, high temperature; RMGI, resin-modified glass-ionomer cement; RT, room temperature.