Remineralization of eroded enamel lesions by simulated saliva in vitro

Comparative Effects of CPP-ACP and Xylitol F-Varnishes on the Reduction of Tooth Erosion and Its Progression

Abstract Evaluated the effect of CPP-ACP/NaF and xylitol/NaF varnishes in reduce erosion and progression of erosion. Forty enamel blocks were divided into four groups (n=10): G1=CPP-ACP/NaF varnish (MI varnishTM); G2=xylitol/NaF varnish (Profluorid®); G3=NaF varnish (Duraphat®, positive control) and G4=deionized water (MilliQ®, negative control). Samples were immersed in Sprite ZeroTM (pH 2.58, 4x/day, 3 days), in between immersions, the specimens stayed in artificial saliva. After 3 days of erosion, the eroded area was divided in two (half of one received an additional varnish layer while the other half repeated the same 3-day erosion cycle). The 3D, non-contact profilometry technique was used to determinate tooth structure loss (TSL) and surface roughness (SR). Scanning electron microscopy (SEM) and 3D images were utilized to evaluate the topography of the samples. Mann-Whitney, one-way ANOVA and Tukey tests were used (significance level of 0.05%). SEM and 3D images were descriptively evaluated. After 3 or 6 days of erosion, all tested varnishes were better than G4 (p<0.05) for TSL and SR. In addition, G1 had lower values for TSL than G3 (p<0.05) after 3 days of erosion. Under SEM and 3D images observation, all groups presented porosity, irregularities and depressions on the surface enamel after 3 and 6 days of erosion, more pronounced in G4. An application of topical NaF varnishes was effective in reducing TSL and enamel roughness after erosion challenges, being the CCP-ACP/NaF varnish more effective than NaF varnish and water after 3 days of erosion.

Does delayed toothbrushing after the consumption of erosive foodstuffs or beverages decrease erosive tooth wear? A systematic review and meta-analysis

OBJECTIVE

Controversy exists regarding the effectiveness of delayed toothbrushing in decreasing erosive tooth wear (ETW). The purpose of this systematic review and meta-analysis was to assess the effects of delayed toothbrushing on ETW.

MATERIALS AND METHODS

This systematic review and meta-analysis was conducted according to the PRISMA statement and registered in PROSPERO (CRD42020200463). PubMed, Embase, and Web of Science databases were systematically searched with no publication year limits. Screening and data extraction were performed independently by two reviewers. In situ and in vitro studies comparing ETW after delayed and immediate toothbrushing following an erosive attack were included. Review Manager software 5.3 (The Cochrane Collaboration, Oxford, UK) was used for statistical analyses. Heterogeneity was assessed with the Cochran Q test and I² statistics.

RESULTS

Of the 565 potentially relevant studies, 26 full-text articles were assessed for eligibility. Twelve articles were included in the systematic review, and 11 were included in the qualitative analyses. No significant difference in the ETW of human enamel was observed between delayed and immediate toothbrushing (P = 0.13), whereas significantly less ETW of bovine enamel was observed after delayed toothbrushing (P < 0.001). No significant difference in the ETW of bovine dentin was observed between delayed and immediate toothbrushing (P = 0.34). Studies on human dentin were not available. Subgroup analyses revealed a significant contribution of the use of fluoridated toothpaste to decreasing the ETW of human enamel after erosion and toothbrush abrasion (P = 0.02).

CONCLUSIONS

Bovine and human teeth behaved differently in response to erosion and toothbrush abrasion. Delayed toothbrushing after an erosive attack was not effective at decreasing the ETW of human enamel compared to immediate toothbrushing, whereas it was effective at decreasing the ETW of bovine enamel.

CLINICAL RELEVANCE

Delayed toothbrushing alone after the consumption of erosive foodstuffs or beverages is not capable of preventing erosive enamel wear.

Measurement of erosion depth using microcomputed tomography and light microscopy

Tooth-erosion is the surface loss of dental hard tissue mostly associated with an acid attack. The aim was to compare dentin and enamel erosion depth measurements using micro-computed tomography (microCT) and light microscopy (LM). Enamel/dentin blocks were prepared from caries-free human molar-teeth (N = 12). Teeth were sectioned to a rectangular shape of 4 × 4 × 6 mm. Specimens were treated with water (NC) or 1.0% citric-acid solution (PC). After treatment, specimens were scanned with micro-computed tomography. On completion, specimens were sectioned and observed under a light-microscope. Lesion depth was observed with 10× magnification and images transferred to Simpleware software. Vertical distance from lesion surface to bottom was measured. Pearson correlation test was used to evaluate correlation and Wilcoxon Signed Rank test to evaluate differences in the two-analysis methods. Mean enamel erosion depth was 0.63 and 38.38 μm (microCT) and 0.54 and 39.43 μm (LM) for NC and PC, respectively. Dentin erosion depth was 0.72 and 48.05 μm (microCT) and 0.56 and 49.92 μm (LM) for NC and PC, respectively. There was a significant correlation between the two-analysis methods (r = 0.998; p < .001). No statistically significant difference in results were obtained when microCT and LM were compared (p = .584). This results obtained from the current study suggested that erosion depth measurements made using microCT and LM yielded comparable results. The microCT method is preferred if the conservation of specimens is desired.

The effect of Er,Cr:YSGG laser, fluoride, and CPP-ACP on caries resistance of primary enamel

The aim of this in vitro study was to determine the effect of different remineralization agents and laser on caries resistance of primary enamel. In the study, 150 sound primary molars were used. The initial microhardness values were measured and the teeth were randomly assigned to ten treatment groups (n = 15): no treatment/negative control (C), NaF, APF, fluoride varnish (FV), CPP-ACP, laser (L), L + NaF, L + APF, L + FV, L + CPP-ACP. The microhardness values were measured after the treatments and the pH cycle. The obtained data were analyzed statistically. One sample from each group was examined before treatment, after treatment, and after the pH cycle with a scanning electron microscope. While microhardness values after treatment compared to baseline increased, microhardness after the pH cycle decreased compared to after treatment values in all experimental groups (p < 0.05). In regard to the difference in microhardness after the pH cycle and baseline, there were no statistically significant differences between groups C and NaF and between C and CPP-ACP (p > 0.05). There was a significant difference between groups L and L + FV (p < 0.05), while no significant difference was noted between groups L and L + NaF, L + APF, L + CPP-ACP (p > 0.05). As a conclusion, FV is more effective when used in combination with laser than laser alone. NaF, CPP-ACP, and laser may be insufficient in protecting the primary teeth against acid attacks compared to FV used with laser.

Saliva with reduced calcium and phosphorous concentrations: Effect on erosion dental lesions

OBJECTIVES

To investigate whether saliva formulations with reduced calcium (Ca) and inorganic phosphorous (Pi) concentration would affect dental erosion caused by hydrochloric acid (HCl).

METHODS

Enamel and root dentine bovine slabs were embedded, polished, and measured for surface Knoop microhardness (SMH). After reference areas were created, specimens were exposed to HCl solution (0.01 M; pH 2; 120 s) and immersed in artificial salivas (6 hr) containing three different Ca/Pi concentrations (n = 15), which simulate serum conditions of normo-, mild, or severe hypocalcemia. The control group was immersed in Ca/Pi-free saliva. The study protocol was carried out 2×/day for 5 days. Surface loss of enamel and root dentine was assessed using an optical profilometer, and SMH was remeasured for enamel.

RESULTS

One-way analysis of variance (p < .001) and Tukey's test showed that enamel loss in groups subjected to artificial salivas that simulated mild or severe hypocalcemia did not differ from that resembling normocalcemia. %SMH was lower when saliva was mildly and normally concentrated in Ca/Pi (p < .001). Root dentine loss was higher in saliva simulating severe hypocalcemia than in those referring to mild, hypo-, and normocalcemia.

CONCLUSIONS

Depending on the dental substrate, salivary formulations resembling serum hypocalcemia affected surface loss due to erosion and rehardening thereof.

An In Vitro Evaluation of Human Enamel Surfaces Subjected to Erosive Challenge After Bleaching

OBJECTIVES

This study aimed to evaluate whether tooth enamel bleached with hydrogen peroxide (H₂ O₂ ) is more susceptible to erosion when compared with unbleached tooth enamel; and whether the presence of calcium (Ca) in the bleaching gel influenced this process.

MATERIALS AND METHODS

Enamel blocks were prepared from human molars, and submitted to surface microhardness analysis (baseline). Blocks were prepared and randomly divided into four treatment groups (n = 20): G1 and G2-bleached with 7.5% H₂ O₂ , with and without Ca, respectively; G3 and G4-bleached with 35% H₂ O₂ , with and without Ca, respectively. After bleaching, these groups were submitted to an erosive challenge with 1% citric acid. G5 and G6 (n = 20, each) were the negative (without bleaching) and positive controls (without bleaching, but with erosion), respectively. The percentage of surface hardness loss (%SHL), the 3D non-contact profilometry and Scanning Electron Microscopy (SEM) analyses were performed.

RESULTS

G2 showed the highest %SHL after bleaching. G1 presented the lowest %SHL in comparison with G2, G3, G4, and G6 after erosion (p < 0.05), which was confirmed only by the SEM analysis.

CONCLUSION

It is suggested that low concentration of H₂ O₂ with calcium can be recommended for at-home bleaching agents, which may avoid the mineral loss of bleached enamel after an erosive challenge.

CLINICAL SIGNIFICANCE

Low concentration of H₂ 0₂ with calcium can be recommended for at-home bleaching agents, which may avoid the mineral loss of bleached enamel after an erosive challenge. (J Esthet Restor Dent 29:128-136, 2017).

Effect of Different Light Sources and Enamel Preconditioning on Color Change, H2O2 Penetration, and Cytotoxicity in Bleached Teeth

This study evaluated the effects of acid etching of the enamel and the combination of different light sources (halogen light, light-emitting diodes [LEDs], and LED/Laser) and the bleaching product on color change, penetration of hydrogen peroxide (H2O2), and cytotoxicity over time. The color change (ΔE) and the amount of H2O2 that permeated the tooth tissue were analyzed using a spectrophotometer. Cell metabolism and morphology were evaluated using the methylthiazol tetrazolium assay and scanning electron microscopy, respectively. The ΔE values and H2O2 permeation were not significantly different under any of the experimental conditions. Tooth whitening significantly reduced cell metabolism, regardless of whether a light source was used. Preconditioning the enamel did not influence the cellular metabolism in any group. In conclusion, combining the bleaching product with different light sources and/or preconditioning the enamel resulted in few significant changes in color, transenamel and transdentinal penetration of H2O2, or cytotoxicity and cell morphology.

Demineralization and hydrogen peroxide penetration in teeth with incipient lesions

The aim of this study was to evaluate the demineralization and hydrogen peroxide (HP) penetration in teeth with incipient lesions submitted to bleaching treatment. For analysis of HP penetration, sound and demineralized enamel/dentin discs were placed in artificial pulp chambers containing acetate buffer solution. After bleaching treatment, this solution was subjected for analysis of optical density by spectrophotometry and the disc surfaces were analyzed with scanning electron microscopy (SEM) and polarized light microscopy (PLM). The remaining discs were subjected for cross-sectional hardness analysis at different depths. Data were analyzed by repeated measures ANOVA and PLSD Fisher test (a=0.05). It was observed that previously demineralized teeth showed greater HP penetration (p<0.05). The bleaching treatment caused changes to a depth of 20 µm in sound enamel and up to 90 µm in demineralized enamel. SEM and PLM images revealed that the bleaching treatment caused superficial changes that were considerably more accentuated in previously demineralized teeth. It may be concluded that the enamel mineralization level influences HP penetration and the bleaching agent contributed to increase the demineralization depth.

Effect of erbium, chromium: yttrium, scandium, gallium, garnet laser and casein phosphopeptide-amorphous calcium phosphate on surface micro-hardness of primary tooth enamel

Objective:

The aim was to evaluate the effect of Er, Cr: YSGG laser and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on surface micro-hardness of primary tooth enamel.

Materials and Methods:

A total of 30 freshly extracted caries free primary anterior teeth were cleaned and stored in 1% thymol. Teeth were embedded in acrylic resin such that only their buccal surfaces were exposed and were divided into four groups. Group I: Five intact teeth (negative control). The remaining 25 teeth were immersed for 30 min in 1% citric acid for demineralization. Group II: Five demineralized teeth (positive control), Group III: CPP-ACP (GC tooth mousse-GC International, Itabashi-Ku, Tokyo, Japan) application and Group IV: Etching using Er, Cr: YSGG laser + CPP-ACP application. Groups III and IV were subjected to pH cycling for 5 days. Surface micro-hardness of all the teeth was measured using Brinell hardness tester (Fuel Instruments and Engineers Pvt. Ltd.). Data were analyzed using ANOVA.

Results:

Mean surface micro-hardness of Groups I and II were 177.43 kgf/mm² and 164.86 kgf/mm², respectively. Group IV showed a higher mean surface micro-hardness (230.68 kgf/mm²) compared with that of Group III (190.28 kgf/mm²). In comparison to all other groups, laser etching prior to CPP-ACP application increased surface micro-hardness significantly (P < 0.001).

Conclusion:

Laser irradiation of primary teeth followed by CPP-ACP application increased surface micro-hardness of enamel.

Penetration of hydrogen peroxide and degradation rate of different bleaching products

This study's aim was to evaluate the degradation rate of hydrogen peroxide (H2O2) and to quantify its penetration in tooth structure, considering the residence time of bleaching products on the dental enamel. For this study, bovine teeth were randomly divided according to the bleaching product received: Opalescence Xtra Boost 38%, White Gold Office 35%, Whiteness HP Blue 35%, Whiteness HP Maxx 35%, and Lase Peroxide Sensy 35%. To analyze the degradation of H2O2, the titration of bleaching agents with potassium permanganate was used, while the penetration of H2O2 was measured via spectrophotometric analysis of the acetate buffer solution, collected from the artificial pulp chamber. The analyses were performed immediately as well as 15 minutes, 30 minutes, and 45 minutes after product application. The data of degradation rate of H2O2 were submitted to analysis of variance (ANOVA) and Tukey tests, while ANOVA and Fisher tests were used for the quantification of H2O2, at the 5% level. The results showed that all products significantly reduced the concentration of H2O2 activates at the end of 45 minutes. It was also verified that the penetration of H2O2 was enhanced by increasing the residence time of the product on the tooth surface. It was concluded that the bleaching gels retained substantial concentrations of H2O2 after 45 minutes of application, and penetration of H2O2 in the dental structure is time-dependent.

Transenamel and transdentinal penetration of hydrogen peroxide applied to cracked or microabrasioned enamel

The present study evaluated transenamel and transdentinal penetration of hydrogen peroxide during tooth whitening recognized in altered enamel by the presence of cracks or microabrasion. We used 72 experimental units (n=20) obtained from bovine incisors: GI-sound enamel; GII-teeth showing visible enamel cracks (4 mm to 5.7 mm in length); and GIII-microabrasioned enamel. The 12 remaining specimens were used to analyze the enamel surface morphology using scanning electron microscopy. The specimens were cylindrical and 5.7 mm in diameter and 3.5 mm thick. A product based on 35% hydrogen peroxide was used for bleaching, following the manufacturer's recommendations for use. To quantify the H2O2 penetration, the specimens were placed in artificial pulp chambers containing an acetate buffer solution. After bleaching, the solution was collected and adequately proportioned with leucocrystal violet, peroxidase enzyme, and deionized water. The resulting solution was evaluated using ultraviolet visible reflectance spectrophotometer equipment. The data were analyzed by analysis of variance (ANOVA) and Fisher's PLSD at a significance level of 0.05, and significant differences in the penetration of peroxide in different substrate conditions were observed (p<0.0001). The penetration of hydrogen peroxide was more intense in cracked teeth. The group in which the enamel was microabraded showed intermediate values when compared to the control group. Microabrasion and the presence of cracks in the enamel make this substrate more susceptible to penetration of hydrogen peroxide during in-office whitening.