Ana Carolina Magalhães

Effect of Salivary Stimulation on Erosion of Human and Bovine Enamel Subjected or Not to Subsequent Abrasion: An in situ/ex vivo Study

This in situ/ex vivo study evaluated whether saliva stimulated by chewing gum could prevent or reduce the wear and the percent change in microhardness (%SMH) of bovine and human enamel submitted to erosion followed by brushing abrasion immediately or after 1 h. During 2 experimental 7-day crossover phases, 9 previously selected volunteers wore intraoral palatal devices, with 12 enamel specimens (6 human and 6 bovine). In the first phase, the volunteers immersed the device for 5 min in 150 ml of cola drink, 4 times per day (at 8, 12, 16 and 20 h). Immediately after the immersions, no treatment was performed in 4 specimens, 4 other specimens were immediately brushed (0 min) using a fluoride dentifrice, and the device was replaced into the mouth. After 60 min, the remaining 4 specimens were brushed. In the second phase, the procedures were repeated, but after the immersions, the volunteers stimulated the salivary flow rate by chewing a sugar-free gum for 30 min. Changes in wear and %SMH were measured. ANOVA and Tukey’s test showed statistical differences (p < 0.05) for the following comparisons. The chewing gum promoted less wear and %SMH. A decreasing %SMH and an increasing enamel wear were observed in the following conditions: erosion only, 60 min and 0 min. The human enamel presented greater %SMH and less wear compared to bovine enamel. The data suggest that the salivary stimulation after an erosive or erosive/abrasive attack can reduce the dental wear and the %SMH.

Influence of Fluoride Dentifrice on Brushing Abrasion of Eroded Human Enamel: An in situ/ex vivo Study

This in situ/ex vivo study assessed the effect of fluoride dentifrice on eroded enamel subjected to brushing abrasion. In a crossover study performed in 2 phases, 10 volunteers wore acrylic palatal appliances, each containing 3 human enamel blocks. Dentifrice was used to brush the volunteers’ teeth and the specimens subjected to abrasion. In phases A and B the dentifrices used had the same formulation, except for the absence or presence of fluoride, respectively. The blocks were subjected to erosion by immersion of the appliances in a cola drink for 5 min, 4 times a day. Then the blocks were brushed, and the appliance was replaced into the mouth. Enamel alterations were determined using profilometry and percentage change in surface microhardness (%SMHC) tests. The data were tested using the paired t test. The mean wear values (±SD, µm) were: group A 6.84 ± 1.72 and group B 5.38 ± 1.21 (p = 0.04). The mean %SMHC values (±SD) were: group A 54.6 ± 16.2 and group B 45.7 ± 6.8 (p = 0.04). Fluoride dentifrice had a protective effect on eroded enamel subjected to brushing abrasion.

The Effect of an Experimental 4% TiF 4 Varnish Compared to NaF Varnishes and 4% TiF 4 Solution on Dental Erosion in vitro

This in vitro study assessed the effect of an experimental 4% TiF4 varnish compared to commercial NaF and NaF/CaF2 varnishes and 4% TiF4 solution on enamel erosion. For this, 72 bovine enamel specimens were randomly allocated to the following treatments: NaF varnish(2.26% F), NaF/CaF2 varnish (5.63% F), 4% TiF4 varnish (2.45% F), F-free placebo varnish, 4% TiF4 solution (2.45% F) and control (not treated). The varnishes were applied in a thin layer and removed after 6 h. The solution was applied to the enamel surface for 1 min. Then, the specimens were alternately de- and remineralized (6 times/day) in an artificial mouth for 5 days at 37°C. Demineralization was performed with the beverage Sprite (1 min, 3 ml/min) and remineralization with artificial saliva (day: 59 min, 0.5 ml/min; during the night: 0.1 ml/min). The mean daily increment of erosion and the cumulative erosion data were tested using ANOVA and ANCOVA, respectively, followed by Tukey’s test (α = 0.05). The mean daily erosion increments and cumulative erosion (micrometers) were significantly less for the TiF4 varnish (0.30 ± 0.11/0.65 ± 0.75) than for the NaF varnish (0.58 ± 0.11/1.47 ± 1.07) or the NaF/CaF2 varnish (0.62 ± 0.10/1.68 ± 1.17), which in turn showed significantly less erosion than the placebo varnish (0.78 ± 0.12/2.05 ± 1.43), TiF4 solution (0.86 ± 0.11/ 2.05 ± 1.49) and control (0.77 ± 0.16/2.06 ± 1.49). In conclusion, the TiF4 varnish seems to be a promising treatment to reduce enamel loss under mild erosive conditions.

Effect of different fluoride concentrations of experimental dentifrices on enamel erosion and abrasion.

It has been suggested that fluoride products are able to reduce erosive tooth wear. Thus, the purpose of this in vitro study was to evaluate the effect of dentifrices with different fluoride concentrations as well as of a low-fluoridated dentifrice supplemented with trimetaphosphate (TMP) on enamel erosion and abrasion. One hundred twenty bovine enamel blocks were assigned to the following experimental dentifrices: placebo, 1,100 µg F/g, 500 µg F/g plus 3% TMP and 5,000 µg F/g. The groups of enamel blocks were additionally subdivided into conditions of erosion (ERO) and of erosion plus abrasion (ERO + ABR). For 7 days, the blocks were subjected to erosive challenges (immersion in Sprite® 4 times a day for 5 min each time) followed by a remineralizing period (immersion in artificial saliva between erosive challenges for 2 h). After each erosive challenge, the blocks were exposed to slurries of the dentifrices (10 ml/sample for 15 s). Sixty of the blocks were additionally abraded by brushing using an electric toothbrush (15 s). The alterations of the enamel were quantified using the Knoop hardness test and profilometry (measurements in micrometers). The data were analyzed using a 2-way ANOVA test followed by a Bonferroni correction (p < 0.05). In in vitro conditions, the 5,000 µg F/g and 500 µg F/g plus 3% TMP dentifrices had a greater protective effect when compared with the 1,100 µg F/g dentifrice, under both ERO and ERO + ABR conditions. The results suggest that dentifrices alone are not capable of completely inhibiting tooth wear.

Effect of Different Concentrations of Fluoride in Dentifrices on Dentin Erosion Subjected or Not to Abrasion in situ/ex vivo

This in situ/ex vivo study assessed the effect of different concentrations of fluoride in dentifrices on dentin subjected to erosion or to erosion plus abrasion. Ten volunteers took part in this crossover and double-blind study performed in 3 phases (7 days). They wore acrylic palatal appliances containing 4 bovine dentin blocks divided in two rows: erosion and erosion plus abrasion. The blocks were subjected to erosion by immersion ex vivo in a cola drink (60 s, pH 2.6) 4 times daily. During this step, the volunteers brushed their teeth with one of three dentifrices D (5,000 ppm F, NaF, silica); C (1,100 ppm F, NaF, silica) and placebo (22 ppm F, silica). Then, the respective dentifrice slurry (1:3) was dripped on dentin surfaces. While no further treatment was performed in one row, the other row was brushed using an electric toothbrush for 30 s ex vivo. The appliances were replaced in the mouth and the volunteers rinsed with water. Dentin loss was determined by profilometry and analyzed by 2-way ANOVA/Bonferroni test (a = 0.05). Dentin loss after erosive-abrasive wear was significantly greater than after erosion alone. Wear was significantly higher for the placebo than for the D and C dentifrices, which were not significantly different from each other. It can be concluded that the presence of fluoride concentrations around 1,100 ppm in dentifrices is important to reduce dentin wear by erosion and erosion + abrasion, but the protective effect does not increase with fluoride concentration.

Comparison of the Effects of TiF4 and NaF Solutions at pH 1.2 and 3.5 on Enamel Erosion in vitro

This study aimed to analyse and compare the protective effect of buffered (pH 3.5) and native (pH 1.2) TiF4 in comparison with NaF solutions on enamel erosion. Bovine samples were pretreated with 1.50% TiF4 or 2.02% NaF (both 0.48 M F) solutions, each at a pH of 1.2 and 3.5. The control group received no fluoride pretreatment. Twenty samples per group were eroded with HCl (pH 2.6) for 10 × 60 s. Erosion was either investigated by profilometry (n = 10) or by determination of calcium release into the acid (n = 10). Additionally, the elemental surface composition was quantified by X-ray energy-dispersive spectroscopy in fluoridated but not eroded samples (6 samples per group). Scanning electron microscopy was performed prior and after erosion (2 samples per group). Cumulative enamel loss (μm) and calcium release (nmol/mm2) were analysed by repeated-measures ANOVA. The Ti and F surface composition was analysed by one-way ANOVA separately for each element. Only TiF4 at pH 1.2 reduced enamel surface loss significantly. Calcium release was significantly reduced by TiF4 and NaF at pH 1.2, but not by the solutions at pH 3.5. Samples pretreated with TiF4 at pH 1.2 showed a significant increase in Ti, while NaF increased F concentration significantly. Only TiF4 at pH 1.2 induced the formation of a glaze-like layer, which was still present after erosion. Enamel erosion can be significantly reduced by TiF4 at pH 1.2 but not at pH 3.5. TiF4 at pH 1.2 was more effective in protecting against enamel erosion than NaF.

Protective Effect of Different Tetrafluorides on Erosion of Pellicle-Free and Pellicle-Covered Enamel and Dentine

The aim was to analyze the protective effects of titanium, zirconium and hafnium tetrafluorides on erosion of pellicle-free and pellicle-covered enamel and dentine in vitro. Eight groups of 20 specimens each of bovine enamel and bovine dentine were prepared. Half the specimens in each group were immersed in human saliva for 2 h for pellicle formation. Specimens were then left untreated (controls) or were treated for 120 s with TiF4, ZrF4 or HfF4 solutions (0.4 or 1%) or 1.25% AmF/NaF gel. All specimens were eroded by exposure to hydrochloric acid, pH 2.6, for 25 min. Cumulative calcium release into the acid was monitored in consecutive 30-second intervals for 5 min, then at 2-min intervals up to a total erosion time of 25 min using the Arsenazo III procedure. Data were analyzed by ANOVA. 1% TiF4 solution offered the best protective effect, especially in dentine (reduction of calcium loss about 50% at 25 min). 1% ZrF4, 1% HfF4 and 0.4% TiF4 also reduced calcium loss, but to a lesser extent. Long-term effects were limited to dentine, while reduction of enamel erosion (about 25%) was restricted to 1-min erosion. The fluoride gel had a protective effect only in dentine. The efficacy of the tetrafluorides was influenced by the presence of the pellicle layer, in that the protection against dentine erosion by TiF4 and ZrF4 was greater on pellicle-covered specimens. Tetrafluoride solutions, especially 1% TiF4, could decrease dental erosion, but were more effective on dentine than on enamel.

Comparison of Cross-Sectional Hardness and Transverse Microradiography of Artificial Carious Enamel Lesions Induced by Different Demineralising Solutions and Gels

The aims of this study were: (1) to correlate surface (SH) and cross-sectional hardness (CSH) with microradiographic parameters of artificial enamel lesions; (2) to compare lesions prepared by different protocols. Fifty bovine enamel specimens were allocated by stratified randomisation according to their initial SH values to five groups and lesions produced by different methods: MC gel (methylcellulose gel/lactic acid, pH 4.6, 14 days); PA gel (polyacrylic acid/lactic acid/hydroxyapatite, pH 4.8, 16 h); MHDP (undersaturated lactate buffer/methyl diphosphonate, pH 5.0, 6 days); buffer (undersaturated acetate buffer/fluoride, pH 5.0, 16 h), and pH cycling (7 days). SH of the lesions (SH1) was measured. The specimens were longitudinally sectioned and transverse microradiography (TMR) and CSH measured at 10- to 220-μm depth from the surface. Overall, there was a medium correlation but non-linear and variable relationship between mineral content and √CSH. √SH1 was weakly to moderately correlated with surface layer properties, weakly correlated with lesion depth but uncorrelated with integrated mineral loss. MHDP lesions showed the highest subsurface mineral loss, followed by pH cycling, buffer, PA gel and MC gel lesions. The conclusions were: (1) CSH, as an alternative to TMR, does not estimate mineral content very accurately, but gives information about mechanical properties of lesions; (2) SH should not be used to analyse lesions; (3) artificial caries lesions produced by the protocols differ, especially considering the method of analysis.

Effect of erosive pH cycling on different restorative materials and on enamel restored with these materials

This in vitro study evaluated the effect of erosive pH cycling on the percentage of surface micro-hardness change (%SMHC) and wear of different restorative materials and bovine enamel restored with these materials. Eighty enamel specimens were randomly divided into eight groups according to the restorative materials and immersion media used: GI/GV-resin-modified glass-ionomer, GII/GVI-conventional glass-ionomer, GIII/GVII-resin composite and GIV/GVIII-amalgam. Over a period of seven days, groups GI to GIV were immersed in a cola drink (ERO) for 5 minutes, 3x/day and kept in artificial saliva between erosive cycles. Groups GV to GVIII were immersed in artificial saliva (SAL) throughout the entire experimental period (control). Data were tested for significant differences using ANOVA and Tukeys tests (p<0.05). For %SMHC, considering the restorative materials, no significant differences were detected among the materials and immersion media. Mean wear was higher for the resin modified glass ionomer cement when compared to conventional cement, but those materials did not significantly differ from the others. For enamel analyses, erosive pH cycling promoted higher wear and %SMHC compared to saliva. There were no significant differences in wear and %SMHC of enamel around the different restorative materials, regardless of the distance from the restorative material (50, 150 or 300 microm). In conclusion, there were only subtle differences among the materials, and these differences were not able to protect the surrounding enamel from erosion.

Impact of toothpaste slurry abrasivity and toothbrush filament stiffness on abrasion of eroded enamel – an in vitro study

Objective. Toothbrush abrasion is significant in the development of tooth wear, particularly when combined with erosion. This in vitro study aimed to evaluate the impact of toothpaste slurry abrasivity and toothbrush filament stiffness on abrasion of eroded enamel. Material and methods. Eroded enamel samples (hydrochloric acid, pH: 2.6, 15 s) were brushed with 40 strokes in an automatic brushing machine using manual toothbrushes with different filament stiffness (filament diameter: 0.15, 0.20, or 0.25 mm). A paste-free control slurry (relative enamel abrasion (REA) value 2) and toothpaste slurries with different abrasivity (REA values 6 or 9) were used for brushing. Erosion and abrasion were followed by storing the enamel samples in artificial saliva for 3 h. After each 4th cycle, the samples were stored in artificial saliva for 15 h. After 60 cycles, enamel loss was measured by profilometry and statistically analyzed by two-way and one-way ANOVA and Bonferroni/Dunn post-hoc tests. Results. Loss of enamel (mean, µm) was influenced mainly by the abrasivity of the slurry and increased along with REA value (REA 2: 0.0–0.2, REA 6: 2.1–3.3, REA 9: 2.9–3.7). Abrasion of eroded enamel was also affected by filament stiffness of the toothbrush, but only groups brushed with toothpaste slurry of REA 6 showed any significant difference between the different toothbrushes. Thereby, toothbrushes with 0.2 mm filament diameter caused higher enamel loss than 0.15 and 0.25 mm filaments. Conclusions. Toothbrush abrasion of eroded enamel is influenced mainly by the abrasivity of the toothpaste slurry, but is also modified by toothbrush filament stiffness.