In vitro evaluation of the microhardness of bovine enamel exposed to acid solutions after bleaching

A review on dental whitening

OBJECTIVES

To provide a narrative review on vital dental whitening chemistry, toxicity and safety, vital dental whitening techniques, whitening systems, potential side effects of whitening and cyclic whitening using products with a range of concentrations and pH values. In addition, new developments and recommendations in the field of vital dental whitening will be presented to help clinicians understand the whitening process, its advantages, limitations, and the impact of whitening concentration and pH on enamel providing guidance in tailoring whitening treatments.

DATA

Data were gathered using the following keywords: dental whitening, roughness, hardness, sensitivity, hydrogen peroxide, whitening pH, whitening concentration, whitening chemistry, colour, and toxicity.

SOURCES

An electronic search was performed using PubMed and Scopus databases. Bibliographic material from papers reviewed was then used to find other relevant publications.

CONCLUSIONS

The effectiveness of vital dental whitening depends on many factors, such as the concentration/pH of the whitening agent, application duration, chemical additives, and re-mineralising agents used. Developing new whitening products and technologies such as nano-additives and alternative carrier systems is showing promising results, and might prove efficient in maximising whitening benefits by accelerating the whitening reaction and/or minimising expected reversible/irreversible enamel structural damage.

Chemical, structural and mechanical characterization of bovine enamel

OBJECTIVE

The purpose of this investigation was to establish microstructure, microhardness, fracture toughness, chemical composition, and crack repair of bovine enamel and to compare these features with their human counterparts.

DESIGN

Bovine enamel fragments were prepared and optical microscopy and atomic force microscopy were used to establish microstructure; Raman spectroscopy was used to estimate composition and microindentation using Vickers testing was performed to evaluate hardness.

RESULTS

A strong dependence between indentation load and microhardness values was observed, as was the case in human enamel. Similar microstructure and chemical composition between bovine and human enamel, 7.89% lower microhardness and 40% higher fracture toughness values for bovine enamel were found.

CONCLUSION

From a structural and mechanical standpoint, bovine enamel is a suitable alternative to human enamel for in vitro testing of dental products.

Antibacterial and Remineralization Efficacy of Casein Phosphopeptide, Glycomacropeptide Nanocomplex, and Probiotics in Experimental Toothpastes: An In Vitro Comparative Study

Objective  This article evaluates the antibacterial and remineralization potential of experimentally prepared toothpastes containing different mixtures of nano casein phosphopeptides (nCPP), nano amorphous calcium phosphate (nACP), probiotic ­ Lactobacillus rhamnosus B-445 ( L. rhamnosus ), and nano glycomacropeptide (nGMP).

Materials and Methods  Five experimental toothpaste samples were prepared and grouped, such that group (A0) was the experimental toothpaste base formula. Groups (A1), (A2), (A3), and (A4) were the experimental toothpastes containing: nCPP; nCPP and nACP; nCPP, nACP, and L. rhamnosus , and nCPP, nACP, and nGMP, ­respectively. Group (A5) was the commercial group (GC MI Paste Plus). The five groups were screened against Streptococcus mutans (ATCC 25175) growth, and investigated for their remineralizing potentials on demineralized bovine enamel using Vickers ­microhardness test (Vickers hardness number [VHN]). Scanning electron microscope (SEM) images were obtained for the demineralized and remineralized enamel of the two most effective toothpastes against in vitro bacterial induced enamel demineralization. Statistical analysis was performed using one-way analysis of variance (ANOVA) as well as repeated measures ANOVA followed by Tukey’s post hoc test.

Results  Both (A3) and (A4) were significantly higher in mean inhibition zone ­diameters than group (A1) and (A2). Group (A4) showed the highest statistical ­significance in the mean difference between VHN values of demineralization and 15 days remineralization period. SEM images showed the deposition of nano-sized particles fill the ­microrough surface pattern of the etched enamel.

Conclusion  All these findings suggest the use of probiotic, nCPP–nACP, and nGMP as a dental anticariogenic and remineralizing active agents.

Protective effect of zinc-hydroxyapatite toothpastes on enamel erosion: An in vitro study

BACKGROUND

The aim of the present study was to test the impact of different toothpastes with Zinc-Hydroxyapatite (Zn-HAP) on preventing and repairing enamel erosion compared to toothpastes with and without fluoride.

MATERIAL AND METHODS

The following four toothpastes were tested: two toothpastes with Zn-HAP, one toothpaste with fluoride and one toothpaste without fluoride. An additional control group was used in which enamel specimens were not treated with toothpaste. Repeated erosive challenges were provided by immersing bovine enamel specimens (10 per group) in a soft drink for 2 min (6mL, room temperature) at 0, 8, 24 and 32 h. After each erosive challenge, the toothpastes were applied neat onto the surface of specimens for 3 min without brushing and removed with distilled water. Between treatments the specimens were kept in artificial saliva. Enamel hardness, after the erosive challenge and toothpaste treatment was monitored using surface micro-hardness measurements.

RESULTS

As expected, repeated erosive challenge by a soft drink for total of 8 min significantly reduced enamel surface hardness (ANOVA, p < 0.05). No re-hardening of the surface softened enamel was observed in the group treated with fluoride-free toothpaste. Surface hardness of the softened enamel increased when the specimens were treated with the fluoride toothpaste and the two toothpastes with Zn-HAP (p < 0.05).

CONCLUSIONS

Toothpaste with Zn-HAP resulted in significant enamel remineralisation of erosively challenged enamel, indicating that these toothpastes could provide enamel health benefits relevant to enamel erosion. Key words:Enamel, erosion, remineralization, surface hardness, toothpastes.

An In Situ Study of the Influence of Staining Beverages on Color Alteration of Bleached Teeth

The aim of this study was to evaluate overall color change in bovine tooth fragments submitted to dental bleaching treatment performed simultaneously with the ingestion of beverages containing dyes. For this purpose, tooth fragments assembled into intraoral devices were submitted to at-home dental bleaching using 10% carbamide peroxide (CP) for 14 days and to immersion in staining beverages for 10 minutes daily. The specimens were divided into the following study groups according to bleaching treatment and staining substance (n=12): G I (negative control): no bleaching + distilled water; G II (positive control): bleaching + distilled water; G III: bleaching + coffee; and G IV: bleaching + grape juice. Twelve volunteers used the device continually, except during meals, oral hygiene, dental bleaching, and pigment challenge. Color readings were performed using a spectrophotometer both before the bleaching treatment and after each treatment week. The results were submitted to the normality test. The data obtained were submitted to analysis of variance and the Tukey or Kruskal-Wallis and Dunn tests (α=0.05). All bleached groups showed similar ΔE results at the end of treatment. Staining beverages generated negative ΔL mean values, and the lowest result was obtained in the treatment with coffee after 14 days. The Δa values in the groups that received treatment with staining beverages were higher when compared to the control groups. Dental bleaching associated with the consumption of staining substances may not affect overall tooth color change by the end of the treatment, although the consumption of staining substances did influence the different color dimensions.

Impact of hydrogen peroxide activated by lighting-emitting diode/laser system on enamel color and microhardness: An in situ design

Background:

Hydrogen peroxide (HP) at lower concentration can provide less alteration on enamel surface and when combined with laser therapy, could decrease tooth sensitivity. This in situ study evaluated the influence of 15% and 35% HP gel activated by lighting-emitting diode (LED)/laser light for in-office tooth bleaching.

Materials and Methods:

Forty-four bovine enamel slabs were polished and subjected to surface microhardness (load of 25 g for 5 s). The specimens were placed in intraoral palatal devices of 11 volunteers (n = 11). Sample was randomly distributed into four groups according to the bleaching protocol: 15% HP, 15% HP activated by LED/laser, 35% HP, and 35% HP activated by LED/laser. The experimental phase comprised 15 days and bleaching protocols were performed on the 2^nd and 9^th days. Surface microhardness (KHN) and color changes were measured and data were analyzed by ANOVA (α = 0.05).

Results:

There were no significant differences in microhardness values neither in color alteration of enamel treated with 15% HP and 35% HP activated or not by LED/laser system (P > 0.05).

Conclusions:

Both concentrations of HP (15 or 35%), regardless of activated by an LED/laser light, did not affect the surface microhardness and had the same effectiveness in enamel bleaching.

After bleaching enamel remineralization using a bioactive glass-ceramic (BioSilicate®)

Tooth bleaching agents may weaken the tooth structure, therefore, it is important to minimize any risks of enamel and dentine damage caused by them. In this way, different materials have been used to avoid or minimize the tooth damage during bleaching. Recently, bioactive glasses have been demonstrated to be effective in mineralization of dental structures. Therefore, this study evaluated the effect of BioSilicate® (a polycrystalline bioactive glass-ceramic) after bleaching by Laser-induced breakdown spectroscopy (LIBS) technique. Bovine dental blocks with 4 × 4 × 3 mm were obtained (n = 20), sequentially embedded in epoxy resin and then polished. Bleaching was performed using 35% hydrogen peroxide (Whiteness HP). Calcium (Ca) and phosphate (P) intensity values by LIBSwere obtained before the treatment (T0, baseline – control Group), after bleaching (T1), and after BioSilicate® application (T2). The use of BioSilicate® after bleaching showed to be an optimal way to remineralize enamel surface making BioSilicate® application a promising adjunct step to avoid or minimize the mineral loss on enamel surface after bleaching.

Nanotribological and Nanomechanical Properties Changes of Tooth After Bleaching and Remineralization in Wet Environment

Teeth bleaching cases had increased with people's desire for oral aesthetic; however, bleached teeth would still undertake chewing actions and remineralizing process in saliva. Nanotribological and nanomechanical properties are proper displays for dental performance of bleached teeth. The purpose of the research was to reveal the effect of bleaching and remineralization on the nanotribological and nanomechanical properties of teeth in wet environment. The specimens were divided into four groups according to the bleaching products used: 12 % hydrogen peroxide (HP) (12HP group); 15 % carbamide peroxide (CP) (15CP group); 35 % CP (35CP group); and artificial saliva (control group). The nanotribological and nanomechanical property changes of tooth enamel after bleaching and remineralization were evaluated respectively by nanoscratch and nanoindentation tests in wet environment, imitating the wet oral environment. The morphology changes were evaluated by statistical parametric mapping (SPM) and scanning electron microscopy (SEM). After bleaching, 12HP group and 15CP group showed increased scratch depth with more pile ups on the scratch edges, decreased nanohardness, and corroded surface appearance. While the 35CP group showed an increase in nanoscratch depth, no change in nanohardness and surface appearance was observed. The control group showed no change in these measurements. After remineralization, the three bleaching groups showed decreased nanoscratch depth and no change of nanohardness compared with the bleached teeth. And the control group showed no changes in nanotribological and nanomechanical properties. The nanotribological and nanomechanical properties of the 12HP group and 15CP group were affected by bleaching, but the nanotribological properties recovered partly and the nanomechanical properties got no change after 1 week of remineralization. As for the 35CP group, the nanotribological properties were influenced and the nanomechanical properties were not affected. These results remind us of taking actions to protect our teeth during bleaching.

The effect of home-use and in-office bleaching treatments combined with experimental desensitizing agents on enamel and dentin

OBJECTIVE

This study aimed to evaluate in vitro the effect of formulations containing Biosilicate to treat enamel and dentin bovine samples exposed to dental bleaching agents.

MATERIALS AND METHODS

On enamel and dentin bleached with commercial gels containing 16% carbamide peroxide (CP) (14 days/4 h) or 35% hydrogen peroxide (single session/45 min), desensitizing dentifrices (Sensodyne(®); experimental dentifrice of Biosilicate(®); Odontis RX(®); Sorriso(®)) were applied along 14 days and desensitizing pastes (Biosilicate(®)/water 1:1; Dessensebilize NanoP(®); Bioglass type 45S5/water 1:1) were applied on days 1, 3, 7, 10 and 14. Distilled water was the control. Microhardness (MH) and roughness measurements were the variables measured on the samples before and after the treatments. Student's t-test analyzed differences before and after the treatments. Two-way analysis of variance and post-hoc Tukey test analyzed differences among the factors desensitizing, bleaching agents and substrate.

RESULTS

Tukey test showed no differences in roughness for both bleaching treatments and among the desensitizing agents (P > 0.05). Differences in MH appeared on enamel treated with in-home bleaching when control group (lower values) was compared with Sensodyne, Biosilicate dentifrice, Biosilicate paste, and Bioglass paste (higher values). Comparisons between desensitizing agents on dentin treated with both bleaching gels showed no statistical differences.

CONCLUSIONS

The effect of formulations containing Biosilicate (Biosilicate dentifrice and paste) was significant in the MH of enamel bleached with 16% CP.

Effect of fluoride gels on microhardness and surface roughness of bleached enamel

The effect of bleaching treatments containing added calcium and combined with neutral or acidic fluoride gels on tooth enamel was investigated in vitro through Knoop microhardness (KHN) and surface roughness (SR) measurements. A total of 60 bovine incisors were tested, including 30 for SR measurements and 30 for KHN measurements. The specimens were divided into 12 groups and subjected to a bleaching agent with hydrogen peroxide 35% (Whiteness HP 35% Maxx, FGM) or hydrogen peroxide 35% with calcium (Whiteness HP 35% Blue Calcium, FGM) and a fluoride treatment flugel acidulated phosphate fluoride (APF) or flugel neutral fluoride (NF). Control specimens were submitted to bleaching treatments without fluoride. Microhardness tests were performed using a Knoop indentor. Roughness measurements were obtained using a roughness analyzer. Measurements were obtained before and after treatment. The specimens were stored in distilled water at 37 °C between treatments. The results were analyzed using descriptive and inferential statistics. Treatments using APF combined with 35% HP caused a decrease in microhardness, while NF combined with HP 35% Ca increased the enamel hardness. Fluoride gels did not alter the SR of the bleached enamel.

Effects of a bleaching agent with calcium on bovine enamel

Objective:

This in vitro study analyzed the effects of a bleaching treatment containing 35% hydrogen peroxide (HP) with or without calcium on bovine enamel, using the Knoop hardness number (KHN), tristimulus colorimetry (TC), and scanning electron microscopy.

Materials and Methods:

Forty-five specimens were randomly divided into groups (n = 5), which included artificial saliva (negative control [NC]), 35% HP (positive control [PC]), and 35% HP Blue Calcium (HP Blue). The specimens were subjected to three bleaching sessions. During the sessions, the specimens were immersed in artificial saliva at 37°C. Before and after bleaching, KHN tests were conducted using a force of 25 gf for 5 s. TC was performed using the CIE-L*a*b* system and readouts were obtained at the following 4 time points: Before the bleaching treatment; after the first session, the second session, and the third session. The specimens were dehydrated and coated with gold, and the photomicrographs were analyzed in a double-blind manner with a LEO microscope.

Results:

Using one-way analysis of variance and Tukey's test (P < 0.05), a statistically significant difference was identified between the initial and final mean KHNs of the NC and PC groups, while the initial and final mean KHNs were not significantly different in the HP Blue group. The final mean values of ΔE, ΔL, and Δb of the PC and HP Blue groups were significantly higher than the initial values (P < 0.01 for both). The photomicrographs revealed no differences among the groups.

Conclusions:

Therefore, treatment with HP Blue prevented changes in the KHN without reducing the efficacy of bleaching.