Effect of brushing force on the abrasive dentin wear using slurries with different abrasivity values.

OBJECTIVE: The aim of this study was to investigate the resulting abrasive dentin wear using abrasive slurries with different RDA values and applying increasing brushing forces. METHODS: Forty-five bovine incisors were randomly allocated in three groups (A, B, C, n = 15). One hundred and eighty dentin samples were prepared from these incisors and allocated to twelve groups (A1-A4, B1-B4, C1-C4; n = 15). The groups were subjected to a brushing cycle (120 strokes/min, 25 min) as follows: groups A1 to A4 with an abrasive slurry (RDA = 71) applying increasing brushing forces (1, 2, 3 and 4 N). Groups B1 to B4 were brushed using an abrasive slurry (RDA = 85) and C1 to C4 (RDA = 133) applying the same above-mentioned brushing forces. Abrasive dentin wear was recorded using a stylus profilometer and compared amongst the groups using robust models. Pairwise comparisons in each model were tested and corrected after Tukey's method (α = 0.05). RESULTS: Applying 1-N brushing force resulted in the same amount of abrasive dentin wear in all groups regardless of the abrasivity of the used slurry. Increasing the brushing force to 2 N resulted in statistically significantly higher abrasive wear in all groups. This increase in abrasive wear was much higher when the slurry with high abrasivity was used (RDA = 133) compared with the lower abrasive slurry (RDA = 71). CONCLUSION: The abrasivity of the used slurry does not add to the resulting abrasive wear when the brushing force is kept at 1 N. It seems better to advise and help the patients (showing signs of non-carious cervical lesions) calibrating their brushing force to 1 N, than only to advise them to use toothpastes with lower abrasivities.

Green Tea Extract Reduces the Erosive Dentine Wear Caused by Energy Drinks In Vitro.

PURPOSE: To investigate the effect of energy drinks supplementation with green tea extract on the erosive dentine wear. MATERIALS AND METHODS: Six groups of bovine dentine samples (n = 15) were subjected to four cycles erosive attacks (10 min, 25 °C) and remineralisation (artificial saliva, 60 min, 37°C) using the following formulas: tap water; green tea extract; Red Bull; Red Bull supplemented with green tea extract; Red Bull Light; Red Bull Light supplemented with green tea extract. The erosive dentine wear - ie, the irreversible dentine loss - was measured using a stylus profilometer (µm, accuracy = 40 nm). RESULTS: Median and interquartile range (IQR) of erosive dentine wear for the tested energy drinks before and after the supplementation with green tea extract were calculated as follows: Red Bull (before: 3.3 µm (1.0)); after: 1.2 µm (0.6)); Red Bull Light (before: 3.3 µm (0.9)); after: 2.0 µm (0.4)). The difference between the groups before and after the supplementation was statistically significant (P ˂0.05). The erosive dentine wear for the tap water group was calculated at 0.4 µm (0.6) and for the green tea extract group at -1.0 µm (1.3). CONCLUSIONS: Supplementation of energy drinks with green tea extract could reduce the erosive dentine wear caused by energy drink in vitro.

Effect of toothbrush bristle stiffness and toothbrushing force on the abrasive dentine wear.

OBJECTIVE: To investigate the influence of toothbrush bristle stiffness and applied brushing force on the resulting abrasive dentine wear in vitro. METHODS: One hundred sixty bovine dentine samples were randomly allocated in eight groups (n = 20). Groups one to four were brushed with a soft-bristle toothbrush with soft bristles applying 1, 2, 3 and 4 N brushing force, respectively. Groups five to eight were brushed with a medium-bristle toothbrush applying the same aforementioned brushing forces (120 strokes/min, abrasive slurry (RDA = 121), 25 min). Profiles were recorded before and after the brushing sequence, and the median and interquartile range of abrasive dentine wear were calculated and compared using two-way ANOVA and pairwise tests corrected after Tukey (α = 0.05). RESULTS: At 1, 2 and 3 N brushing force, the tested toothbrushes caused no significantly different abrasive dentine wear. At 4 N brushing force, the medium-bristle toothbrush caused statistically significantly higher abrasive force than the soft-bristle toothbrush. Using the medium-bristle toothbrush, abrasive dentine wear statistically significantly increased with increasing brushing force from 1 to 3 N. However, increasing the brushing force to 4 N did not result in statistically significantly higher wear. Using the soft-bristle toothbrush, abrasive dentine wear statistically significantly increased with increasing brushing force from 1 to 2 N. However, increasing the brushing force to 3 or 4 N did not result in statistically significantly higher wear. CONCLUSION: The soft-bristle toothbrush tends to cause less abrasive wear with increasing brushing force than the medium-bristle toothbrush.

Effect of dentin pretreatment on the resulting abrasive dentin wear.

BACKGROUND: This study aims to investigate the influence of different dentin pretreatment procedures on the resulting abrasive dentin wear. METHODS: Two groups (A, B) of 60 dentin samples each were prepared. Group A was brushed with an abrasive slurry (RDA = 85) and group B with a different abrasive slurry (RDA = 174). Four subgroups in each group (n = 15) were created (A1-A4) and (B1-B4). The subgroups were pretreated as follows: A1 + B1 with 1200-grit grinding paper, A2 + B2 with 1200- and 2000-grit papers, A3 + B3 with 1200-, 2000-, and 4000-grit papers, A4 + B4 with 1200-, 2000-, 4000-grit papers and with 1000 brushing strokes with a slurry of Elmex toothpaste. All samples were brushed for 25 min at 120 strokes/min. Abrasive dentin wear was measured for each sample profilometrically and the subgroups were compared with each other within the same group. Repeated measures one-way ANOVA was conducted to compare the subgroups and pairwise contrasts were estimated for multiple testing according to Tukey (α = 0.05). RESULTS: The resulting abrasive dentin wear in group A ranged between 15.3 ± 3.4 µm and 17.3 ± 5.5 µm and between 20.3 ± 6.8 µm and 22.5 ± 2.6 µm in group B. No statistically significant difference was noticed between any subgroups within the same group (p ˃ 0.05). CONCLUSIONS: Different dentin pretreatment procedures do not affect the resulting abrasive dentin wear independent of the RDA value of the employed abrasive slurry.

Effect of a sonic toothbrush on the abrasive dentine wear using toothpastes with different abrasivity values.

OBJECTIVE: This in vitro study aimed to investigate the effect of a sonic toothbrush on the resulting abrasive dentine wear using toothpastes with different abrasivities compared to the use of a manual toothbrush. METHODS: Ninety-six bovine dentine samples were divided into six groups and subjected to a brushing sequence (sonic: 20 min, 0.9 N, 10 strokes/min; manual: 20 min, 1.6 N, 60 strokes/min) as follows: group 1: Elmex Sensitive Plus (RDA = 28) + manual toothbrush; group 2: Elmex Sensitive + sonic toothbrush; group 3: Elmex Kariesschutz (RDA = 65) + manual toothbrush; group 4: Elmex Kariesschutz +sonic toothbrush; group 5: Colgate Total Original (RDA = 121) + manual toothbrush; and group 6: Colgate Total Original +sonic toothbrush. The abrasive dentine wear was measured profilometrically. RESULTS: The median (IQR) abrasive dentine wear was as follows: Elmex Sensitive Plus (manual toothbrush: 2.7 µm (0.8), sonic toothbrush: 3.1 µm (1.9)); Elmex Kariesschutz (manual toothbrush: 4.9 µm (1.4), sonic toothbrush: 6.4 µm (2.1)); and Colgate Total Original (manual toothbrush: 5.2 µm (1.1), sonic toothbrush: 9.0 µm (3.1)). Differences in dentine wear between sonic and manual toothbrushes were statistically significant only in the groups brushed with Elmex Kariesschutz and Colgate Total Original (p ≤ 0.05). CONCLUSION: Brushing with a sonic toothbrush could result in a higher abrasive dentine wear compared to manual toothbrush when combined with toothpastes with high abrasivity values.

Prevention of Enamel Softening by Rinsing with a Calcium Solution before Dental Erosion.

OBJECTIVES: This in situ study aimed to evaluate whether rinsing with a calcium-containing solution prior to an erosive attack reduces the softening of enamel. MATERIALS AND METHODS: A total of 240 bovine enamel samples with determined baseline surface microhardness (KHN) were allocated to 5 runs in which each of the 12 volunteers performed the following experiment: 4 enamel samples were inserted in a custom-made intraoral appliance and carried in the mouth (upper jaw) for 30 min before each volunteer either rinsed his mouth for 60 s with a fluoride- and stannous ion-containing dental erosion protection mouth rinse as positive control (run 1), milk (run 2), a solution prepared from a 500-mg calcium effervescent tablet dissolved in 100 mL (run 3) or 200 mL (run 4) water, or did not perform any rinsing with a test solution before the erosive attack (run 5, negative control). To simulate the erosive attack, volunteers rinsed their mouth with a commercial soft drink (Sprite Zero) for 60 s and afterwards with water to stop the erosive process. Finally, surface microhardness was measured again and hardness loss (ΔKHN) calculated. A mixed effect model was fitted to the data set to investigate whether the different runs showed differences with respect to ΔKHN. RESULTS: No significant difference in softening of enamel (mean of ΔKHN; lower confidence level/upper confidence level) was observed between the negative control run 5 (50.7; 60.8/40.6), run 2 (50.7; 60.8/40.6), run 3 (38.7; 48.8/28.6) and run 4 (40.7; 50.8/30.6) (p > 0.05, respectively). Enamel softening in the positive control run 1 (25.4; 35.6/15.3) was significantly lower compared to the softening in run 5 (p < 0.001). No significant difference was observed between run 1 and run 3 (p = 0.09). CONCLUSION: Other than the fluoride- and stannous ion-containing dental erosion protection mouth rinse, none of the investigated calcium-containing solutions is able to significantly reduce erosion-induced softening of enamel.

Methods for assessment of dental erosion.

Various assessment techniques have been applied to evaluate the loss of dental hard tissue and the surface-softened zone in enamel induced by erosive challenges. In this chapter, the most frequently adopted techniques for analyzing the erosively altered dental hard tissues are reviewed, such as profilometry, measuring microscope techniques, microradiography, scanning electron microscopy, atom force microscopy, nano- and microhardness tests and iodide permeability test. Moreover, methods for chemical analysis of minerals dissolved from dental hard tissue are discussed. It becomes evident that the complex nature of erosive mineral loss and dissolution might not be comprehended by a single technique, but needs application of different approaches for full understanding.

Stability of two resin combinations used as sealants against toothbrush abrasion and acid challenge in vitro.

OBJECTIVE: To test the stability of two conventional adhesives when combined with a low-viscosity caries infiltrant used for sealing sound enamel against toothbrush abrasion and acid challenge in vitro. MATERIALS AND METHODS: Bovine enamel discs (Ø = 3 mm) randomly assigned to three groups (n = 10/group) were etched with 37% phosphoric acid for 30 s and treated with resins of different monomer contents forming three test groups: (1) Untreated specimens (Control); (2) Infiltrant (Icon, DMG) + conventional enamel bonding adhesive (Heliobond, Ivoclar Vivadent); and (3) Infiltrant + conventional orthodontic adhesive (Transbond XT Primer, 3M Unitek). All specimens were immersed in hydrochloric acid (pH 2.6) for up to 9 days, during which they were exposed to 1825 toothbrush-strokes per day. Calcium dissolution was assessed using Arsenazo III method at 24-h intervals. Data were analyzed by Kruskal-Wallis and Wilcoxon signed ranks tests. RESULTS: Cumulative calcium dissolution for the untreated specimens (39.75 ± 7.32 µmol/ml) exceeded the sealed groups (Icon + Heliobond: 23.44 ± 7.03 µmol/ml; Icon + Transbond XT Primer: 22.17 ± 5.34 µmol/ml). Untreated specimens presented a relatively constant calcium dissolution rate throughout the experimental period, whereas the sealed groups presented a gradual increase indicating weakening of the seal by toothbrush abrasion. Both sealed groups presented significantly lower daily calcium dissolution at all time points compared to the control, except for Group 2 on the last measurement day. CONCLUSIONS: Low-viscosity caries infiltrant application on sound enamel prior to conventional resin application provided a protective effect against enamel demineralization, but this effect was not stable when challenged mechanically by toothbrush abrasion.

Effect of a low-viscosity adhesive resin on the adhesion of metal brackets to enamel etched with hydrochloric or phosphoric acid combined with conventional adhesives.

PURPOSE: This study investigated the effect of a low-viscosity adhesive resin (Icon) applied after either hydrochloric (HCl) or phosphoric acid (H3PO4) on the adhesion of metal brackets to enamel. Failure types were analyzed. MATERIALS AND METHODS: The crowns of bovine incisors (N = 20) were sectioned mesio-distally and inciso-gingivally, then randomly assigned to 4 groups according to the following protocols to receive mandibular incisor brackets: 1) H3PO4 (37%)+TransbondXT (3M UNITEK); 2) H3PO4 (37%)+Icon+TransbondXT; 3) HCl (15%)+Icon (DMG)+TransbondXT 4) HCl (15%)+Icon+Heliobond (Ivoclar Vivadent)+TransbondXT. Specimens were stored in distilled water at 37°C for 24 h and thermocycled (5000x, 5°C to 55°C). The shear bond strength (SBS) test was performed using a universal testing machine (1 mm/min). Failure types were classified according to the Adhesive Remnant Index (ARI). Contact angles of adhesive resins were measured (n = 5 per adhesive) on ceramic surfaces. RESULTS: No significant difference in SBS was observed, implying no difference between combinations of adhesive resins and etching agents (p = 0.712; ANOVA). The Weibull distribution presented significantly lower Weibull modulus (m) of group 3 (m = 2.97) compared to other groups (m = 5.2 to 6.6) (p < 0.05). The mean SBS results (MPa) in descending order were as follows: group 4 (46.7 ± 10.3) > group 1 (45.4 ± 7.9) > group 2 (44.2 ± 10.6) > group 3 (42.6 ± 15.5). While in groups 1, 3, and 4 exclusively an ARI score of 0 (no adhesive left on tooth) was observed, in group 2, only one specimen demonstrated score 1 (less than half of adhesive left on tooth). Contact angle measurements were as follows: Icon (25.86 ± 3.81 degrees), Heliobond (31.98 ± 3.17 degrees), TransbondXT (35 ± 2.21 degrees). CONCLUSION: Icon can be safely used with the conventional adhesives tested on surfaces etched with either HCl or H3PO4.

Caries infiltrant combined with conventional adhesives for sealing sound enamel in vitro.

OBJECTIVE: To test the null hypothesis that combining low-viscosity caries infiltrant with conventional adhesive resins would not improve sealing of sound enamel against demineralization in vitro. MATERIALS AND METHODS: Bovine enamel discs (N = 60) with diameter of 3 mm were randomly assigned to six groups (n = 10). The discs were etched with 37% phosphoric acid for 30 seconds and treated with resins of different monomer content forming the following groups: (1) Icon (DMG), (2) Transbond XT Primer (3M ESPE), (3) Heliobond (Ivoclar Vivadent), (4) Icon + Transbond XT Primer, and (5) Icon + Heliobond. Untreated etched samples served as the negative control. Specimens were subjected to demineralization by immersion in hydrochloric acid (pH 2.6) for 80 hours. Calcium dissolution into the acid was assessed by colorimetric analysis using Arsenazo III method at 16-hour intervals. Groups presenting high protection against demineralization were subjected to further acidic challenge for 15 days with calcium measurements repeated at 24-hour intervals. Data were analyzed by Kruskal-Wallis test and Mann-Whitney U-test. RESULTS: Untreated specimens showed the highest amount of demineralization. Icon and Transbond XT primer decreased the mineral loss significantly compared to the control. Heliobond performed significantly better than both Icon and Transbond XT primer. Combination of Icon both with Transbond XT primer or Heliobond served as the best protective measures and maintained the protective effect for the additional 15-day acidic challenge. CONCLUSIONS: Within the limitations of this in vitro study, it could be concluded that the use of low-viscosity caries infiltrant prior to application of the tested conventional adhesives increases their protective effect against demineralization.

Effect of sodium hypochlorite contamination on microhardness of dental core build-up materials.

This study aimed to determine the influence of sodium hypochlorite (NaOCl) contamination on the microhardness of build-up composites. Fifty-two samples, from each of three build-up materials (LuxaCore Dual, MultiCore flow and Rebilda DC) were prepared. Half of the samples from each material were stored in physiologic saline (baseline control) while the other halves were stored in NaOCl. After 1 h, the samples were rinsed with tap water, cut axially and measured for Knoop hardness at different depth levels. The results were analysed by ANOVA and unpaired t-tests (p<0.05). Significant differences in microhardness were observed for LuxaCore Dual up to 0.2 mm, Rebilda DC up to 0.3 mm, and for MultiCore flow up to 0.4 mm under the surface level. Contact with sodium hypochlorite on build-up materials causes reduction of the microhardness. The softening is not only limited on the surface, but can also be found in deeper layers of build-up materials.

Erosion-inhibiting potential of a stannous chloride-containing fluoride solution under acid flow conditions in vitro.

OBJECTIVES: This study aimed to analyse the erosion-inhibiting potential of a single application of stannous chloride-containing fluoride solution on pellicle-covered enamel and dentine under constant acid flow conditions in vitro. DESIGN: Bovine enamel (n=60) and dentine (n=60) samples were exposed 1h to the oral cavity of 4 healthy volunteers to allow for in situ pellicle formation. Pellicle-covered samples were randomly assigned to three groups (each n=20 enamel and n=20 dentine samples; 5 enamel and 5 dentine samples/volunteer) and treated once with a SnCl2/AmF/NaF (800 ppm Sn(II), 500 ppm F, pH 4.5) or a NaF solution (500 ppm F, pH 4.5) for 2 min or remained untreated (controls). Samples were eroded with hydrochloric acid (pH 2.6) in a small erosion chamber at 60 microl/min for 25 min. Calcium release into the acid was monitored in consecutive 30s intervals for 5 min, then at 1 min intervals up to a total erosion time of 25 min using the Arsenazo III procedure. Data were statistically analysed by random-effects linear models (p<0.05). RESULTS: The stannous chloride-containing fluoride solution reduced calcium loss of enamel and dentine to up to 6 min and 3.5 min, respectively. Calcium loss (% of control) amounted from 24+/-7 (30s) up to 93+/-14 (6 min) in enamel and from 38+/-13 (30s) to 87+/-15 (3.5 min) in dentine. The sodium fluoride solution was unable to reduce enamel and dentine erosion at any time point. CONCLUSION: A single application of a stannous chloride-containing fluoride solution reduced enamel and dentine erosion up to 6 min and 3.5 min of constant acid flow, respectively.