Sequence of stannous and sodium fluoride solutions to prevent enamel erosion.

OBJECTIVES: Investigate the timing of stannous (SnF2) and sodium fluoride (NaF) application with and without salivary pellicle to prevent enamel erosion. METHODS: Human buccal molar enamel samples (n=120, REC ref 12/LO/1836) were randomly assigned to three groups testing SnF2 and NaF basic fluoride formulation and commercial mouthrinses with and without the presence of human saliva. Samples were randomly allocated to 2 subgroups: immersion in either fluoride for 1 min either before or after citric acid immersion (0.3%, pH 3.2, 10 min), and the cycle repeated 5 times. For human saliva group, samples were immersed in 80 ml of natural saliva for 24 h prior to the experiment. Analysis was done using non-contacting profilometry and microhardness change. Data were not normal and were log transformed. A linear model tested statistical differences between the groups. RESULTS: SnF2 application before erosion statistically reduced step height compared to application after erosion for all groups (solutions: 6.5 µm (±1.2), 7.5 µm (±0.8); p=0.01, mouthrinses: 3.2 µm (±0.6), 4.2 µm (±0.7); p<0.0001, mouthrinses with saliva: 2.5 µm (±0.4), 3.1 µm (±0.6); p=0.002, before and after respectively). In contrast, application of NaF before erosion increased step height compared to application after, but this was only statistically significant for the saliva group (before: 5.6 µm (±0.3) and after: 4.9 µm (±0.3); p=0.023). Presence of saliva increased microhardness change (p<0.0001). Within this group, greatest microhardness change was observed when SnF2 was applied before erosion and when NaF was applied after erosion (SnF2: 156.6KHN (±32.8), 123KHN (±20.1); p=0.02. NaF: 119.5KHN (±33.5), 218KHN (±24.9), before, and after respectively). CONCLUSION: SnF2 reduced step height formation overall when compared to NaF, but particularly when applied before citric acid immersion. In contrast, NaF reduced step height when applied after citric acid immersion, but only in the presence of saliva. CLINICAL SIGNIFICANCE: Stannous fluoride can be recommended over sodium fluoride to patients at risk of dental erosion and is optimally applied before erosion occurs. If sodium fluoride is to be used in the presence of saliva it is optimally applied after erosion has occurred.

Effect of Model Variables on in vitro Erosion.

The aim of this study was to investigate the effects of tooth type (molar/premolar), tooth surface (buccal/lingual), smear layer or no smear layer, storage of specimens in deionised water, mode and speed of agitation, and rinsing method between cycles on mean step height loss and Knoop microhardness (KHN) change. Polished human enamel specimens embedded in acrylic resin were prepared from sound permanent molar and premolar tooth surfaces. A 0.3% (pH 3.2) solution of citric acid was used to erode the specimens, in a cycling procedure, consisting of 10 min immersion followed by rinsing in deionised water for 30 s with a spray bottle, for 5 cycles. The specimens were analysed with a non-contact white light profilometer and KHN. Molar teeth (148.99±24.49 KHN) and buccal surfaces (155.62±30.35 KHN) produced significantly less microhardness change compared to premolar (186.40±20.74 KHN) and lingual surfaces (179.76±23.21 KHN; p<0001). The effect of storage and rinsing showed little difference in mean step height loss (<1 µm) and microhardness change. With no smear layer a significantly lower mean step height loss and microhardness change (p<0.001) was observed. Agitation was performed with Orbital, Gyro and See-Saw rockers at 30, 40, 60, and 70 rpm. The mean step height loss was largest for See-Saw at 70 rpm (11.73±0.91 µm) and lowest for Orbital at 30 rpm (2.76±1.12 µm). A statistical difference was found between all types of agitation and speeds (p<0.001). In conclusion, this study has shown that the variables investigated here have a significant impact on the measurable outcome, highlighting the importance of accurate and detailed method sections.

Measuring enamel erosion: a comparative study of contact profilometry, non-contact profilometry and confocal laser scanning microscopy.

OBJECTIVES: To compare three instruments for their ability to quantify enamel loss after acid erosion. METHODS: 6 randomized parallel groups of bovine enamel samples were subjected to citric acid (higher acidity) or orange juice (lower acidity) erosion and remineralisation in a cycling model. Two protected shoulders were created on each of the samples using tape, to serve as reference for analysis. The time of exposure to each acid was varied, along with presence or absence of agitation. After treatment, samples were measured on 3 instruments capable of measuring step height: a contact profilometer (CP); a non-contact profilometer (NCP); and a confocal laser scanning microscope (CLSM) by three different examiners. Additionally, 3D (volume) step height was also measured using the CLSM. RESULTS: Increasing acid concentration and exposure time resulted in greater erosion, as did agitation of samples while in acid solution. All instruments/methods identified the same statistically significant (p<0.05) pair-wise differences between the treatments groups. Further, all four methods exhibited strong agreement (Intra-class correlation ≥ 0.96) in erosion level and were highly correlated, with correlations of 0.99 or higher in all cases. SIGNIFICANCE: All instruments/methods used in this study produced very similar conclusions with regard to ranking of enamel loss, with data showing very high agreement between instruments. All instruments were found to be equally suited to the measurement of enamel erosion.