Comparison of an experimental single application two-step 25600 ppm Ammonium Fluoride / 34100 - 48600 ppm Nano-Calcium Fluoride solution vs. a one-step 7700 ppm Ammonium Fluoride varnish for Preventing Enamel Loss from Erosion and Attrition in vitro

Abstract

Introduction: The potential for high-fluoride treatments to prevent progression of erosion and attrition is not fully understood. This thesis investigated the effect of an experimental two-step ammonium fluoride/nano-calcium fluoride formulation (25600 ppm NH4F plus 34100 - 48600 ppm CaF2) versus a single-application one-step 7700 ppm ammonium fluoride (NH4F) varnish on step height loss (μm) of polished and natural human enamel undergoing erosion and attrition in vitro. Material and methods: Three restorative dental materials and human enamel (Occlusal vs. Buccal) samples were used to validate the attrition simulation method. Samples were subjected to attritional wear using leucite-reinforced CAD/CAM ceramic antagonists in an electrodynamic wear simulator (200 cycles, 80 N load, 0.7 mm horizontal slide). Following validation, polished and natural (unpolished) enamel samples were pre-treated with either deionized water (DIW negative control), NH4F varnish (positive control) or a two-step NH4F/CaF2 solution. After surface wiping, samples were subjected to erosion (0.3% citric acid solution immersion, pH 3.8, for 5, 10, 15, 20 and 60 minutes) and attrition (200 strokes). Enamel wear was measured using non-contact laser profilometry (NCLP). Enamel surface and sub-surface mechanical testing was conducted using micro- and nanoindentation. Enamel surface and sub-surface qualitative examination was conducted using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Results: The attrition method revealed that the glass ionomer material experienced the most wear, measuring 177.8 μm (±16.9). This was significantly more than the fine particle composite, which showed 22.2 μm (±1.3) of wear, and the micro-filled composite, which had the least wear at 13.6 μm (±1.02) (P < 0.001). Enamel samples from buccal vs. occlusal sources experienced non-significantly different step height enamel wear (P<0.05). The attrition wear generation was consistent with co-efficient of variation <10%. Polished enamel samples treated with surface fluoride treatments showed significantly reduced step height enamel loss vs. control (p<0.001): Mean (SD) enamel loss for DIW treatment was 1.97 μm (±0.14) after erosion and 36.55 μm (±1.79) after erosion/attrition. NH4F treatment reduced loss to 0.58 μm (±0.08) after erosion and 32.71 μm (±2.63) after erosion/attrition (p<0.001). NH4F/CaF2 treatment further reduced loss to 0.41 μm (±0.06) after erosion and 24.08 μm (±3.15) after erosion/attrition (p<0.001). This was supported by the microhardness data: fluoride-treated enamel experienced reduced hardness changes following both erosion and erosion/attrition vs. non-fluoride treated enamel (p<0.001). For natural enamel, the experimental NH4F/CaF2 solution significantly reduced enamel loss after all erosion durations (5, 20, 60 minutes) and after 200 strokes of attrition. After 5 minutes of erosion, enamel loss compared to DIW was significantly reduced (p<0.001). Mean (SD) enamel loss in the NH4F/CaF2 treated group was reduced to 0.21 μm (±0.13) after erosion and 9.82 μm (±1.46) after erosion/attrition in comparison with DIW treated groups which was 0.79 μm (±0.32) after erosion and 15.58 μm (±2.49) after erosion/attrition. The surface and sub-surface SEM and EDS data supported these findings. Conclusion: The two-step ammonium fluoride solution (NH4F/CaF2) reduced step height enamel loss and hardness changes occurring in polished and natural enamel during simulated erosion and attrition in vitro.