Shanshan Liang

Surface alteration of human tooth enamel subjected to acidic and neutral 30% hydrogen peroxide

OBJECTIVES To investigate the effects of acidic and neutral 30% hydrogen peroxide (HP) on human tooth enamel in terms of chemical structure, mechanical property, surface morphology and tooth colour. METHODS Twenty-seven human dental blocks were obtained from premolars and randomly divided into three groups (n=9): Group acidic HP (30% HP, pH≈3.6), Group neutral HP (30% HP, pH≈7.0) and Group DW (distilled water, pH≈6.8). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, atomic force microscopy (AFM) investigation, microhardness test and colour measurements were carried out before and after treatments. ATR-FTIR and Raman spectroscopy were analysed and then the carbonate:mineral ratio (C:M), Raman absolute intensity (RAI), Raman relative intensity (RRI), and laser-induced fluorescence intensity (FI) were obtained for evaluation. RESULTS The C:M, percentage microhardness and percentage RRI of group acidic HP decreased more significantly than those of group neutral HP (P=0.02, P=0.001, P<0.001, respectively) and group DW (P=0.01, P=0.008, P<0.001, respectively). Whilst group neutral HP and group DW had no statistical difference in above terms (P=0.818, P=0.528, P=0.158, respectively). Significant morphological alterations were observed in group acidic HP. Group acidic HP and neutral HP had no significant difference in percentage FI (P=0.652) and ΔE (P=0.906). CONCLUSIONS This study suggested that neutral 30% HP had the same efficiency in tooth bleaching and it caused less deleterious effects on enamel than acidic 30% HP.

The dentine remineralization activity of a desensitizing bioactive glass‐containing toothpaste: an in vitro study

BACKGROUND Dentine hypersensitivity occurs easily on exposed dentine. This study aimed to evaluate the effectiveness of a novel bioactive glass-containing toothpaste on dentine permeability and remineralization. METHODS Thirty dentine discs were divided into three groups of 10 specimens each. The groups corresponded to the following brushing treatments: no brush, distilled water, and bioactive glass-containing toothpaste (Novamin). The toothpaste was applied twice a day for 7 days. Dentine permeability was measured after ethylene-diamine-tetraacetic acid (EDTA) etching, initial application, 3-day application, 7-day application and citric acid challenge, respectively. The dentine morphology was investigated using scanning electron microscopy (SEM). Attenuated total reflection Fourier transform infrared (ATR/FTIR) spectroscopy was performed to monitor the mineral variation on demineralized dentine. Qualitative information of elemental variation before and after treatments on completely demineralized dentine was detected by energy dispersive X-ray (EDX) analysis. RESULTS The bioactive glass-containing toothpaste significantly reduced dentine permeability after the 7-day treatment and showed, under SEM, excellent resistance to acid challenge compared to the other groups. ATR/FTIR and EDX revealed increased mineral content after treatment with Novamin. CONCLUSIONS As the innovative bioactive glass-containing toothpaste occlude dentinal tubules and resist acid challenge, it may be useful for the treatment of dentine hypersensitivity and dentine remineralization.

Evaluation of the esthetic effect of resin cements and try-in pastes on ceromer veneers

OBJECTIVE To evaluate the influence of various shades of resin cements on the final color of ceromer veneers and analyse the agreement of resin cements and corresponding try-in pastes. METHODS Ceromer disks (Ceramage, 1.0mm×10mm diameter) were bonded to resin background disks (3.0mm×10mm diameter) using five shades of resin cements (RelyX Veneer), whilst butylphthalate was placed between ceromer and resin background as the control group (n=5). The corresponding try-in pastes were placed between ceromer and resin background disks using the specimens of the control group. After colorimetric evaluations, the thickness of ceromer disks was reduced to 0.8 and 0.5mm. Color measurements were repeated at each thickness. To analyse masking ability of the cement, resin background disks with 0.1mm thick cement layer were fabricated using five shades of resin cements (n=5). RESULT Two-way ANOVA of ΔE values of cement shades and control group revealed significant differences in cement shade and thickness, and their interaction (p<0.001). The 0.5mm thick Ceramage specimens yielded the highest mean ΔE values (2.44±1.12) for all cement shade groups. A3, WO, and B05 shade of resin cements created perceptible color differences (ΔE>2.0) in 0.5mm thick specimens and WO shade in 0.8mm thick specimens. There were no perceptible color differences between resin cements and corresponding try-in pastes. CONCLUSION The effect of resin cements on the final color of ceromer veneers depended on cement shades and thickness of ceromer. The color of resin cements and corresponding try-in pastes achieved high agreement.

Investigation of three home-applied bleaching agents on enamel structure and mechanical properties: an in situ study.

The safety of at-home tooth bleaching, based upon carbamide peroxide (CP) or hydrogen peroxide (HP) as the active agent, has been questioned. The aim of the present study was to investigate the effects of three differently concentrated home-applied bleaching agents on human enamel under in situ conditions. Sixty specimens were divided randomly into four groups and treated with 10% CP, 15% CP, 20% CP, and distilled water, respectively. Raman spectroscopy, attenuated total reflectance-infrared (ATR-IR) spectroscopy, atomic force microscopy (AFM), microhardness, and fracture toughness (FT) measurements were conducted to determine variations on enamel structure and mechanical properties before and after the bleaching process. Raman revealed little variation of Raman relative intensity after treatment with CP, which was consistent with the results of ATR-IR, AFM, and microhardness analyses. In addition, laser-induced fluorescence (LIF) intensity, and FT showed significant decreases on CP-treated specimens. These findings suggested there were minimal demineralization effects of the three at-home bleaching agents on enamel in situ. However, the decrease of LIF intensity and FT on enamel seemed to be inevitable.

Separate contribution of enamel and dentine to overall tooth colour change in tooth bleaching

OBJECTIVES The aim of this study was to evaluate the separate contribution of enamel (E) and dentine (D) to the colour change of tooth which subjected to 10% carbamide peroxide (CP) gels using a novel recombined enamel-dentine (Recombined-ED) study model. METHODS 120 enamel-dentine (ED) samples (four homogeneous premolar ED from each patient; total=30×4 ED) were involved in the present study. Two homogeneous ED samples were bleached with 10% CP and the other two ones were stored in artificial saliva for one, two or four weeks. After treatment, four kinds of layers were prepared from each four homogeneous ED samples by removing enamel or dentine part: bleached-enamel (BE), bleached-dentine (BD), control-enamel (CE) and control-dentine (CD). Initial and final colour records of samples were taken with a spectrophotometer in CIELab system. The contribution of enamel/dentine to the colour change of tooth (CTCC) was calculated by measuring the colour difference ΔE between two different enamel-dentine combinations (ΔE between BE/BD and CE/BD for enamel; ΔE between BE/BD and BE/CD for dentine). Translucency parameter (TP) was obtained by calculating the colour difference between enamel on black and white backings. RESULTS ED and recombined-ED were significantly correlated in L(*)a(*)b(*) values both for unbleached samples and bleached samples. Bleaching resulted in a significant colour change (ΔE) of E, D and ED samples. The TP of BE was significantly lower than that of CE. The CTCC of enamel was significantly higher than that of dentine all through the time points. CONCLUSIONS Enamel played a more important role than dentine in tooth bleaching due to the changes in translucency and colour.

Compositional, structural and mechanical comparisons of normal enamel and hypomaturation enamel.

Hypomaturation amelogenesis imperfecta is a hereditary disorder of the enamel that severely influences the function, aesthetics and psychosocial well-being of patients. In this study, we performed a thorough comparison of normal and hypomaturation enamel through a series of systematical tests on human permanent molars to understand the biomineralization process during pathological amelogenesis. The results of microcomputed tomography, scanning electron microscopy, Fourier transform infrared, Raman spectroscopy, microzone X-ray diffraction, thermal gravimetric analysis, energy diffraction spectrum and Vickers microhardness testing together show dramatic contrasts between hypomaturation enamel and normal enamel in terms of their hierarchical structures, spectral features, crystallographic characteristics, thermodynamic behavior, mineral distribution and mechanical property. Our current study highlights the importance of the organic matrix during the amelogenesis process. It is found that the retention of the organic matrix will influence the quantity, quality and distribution of mineral crystals, which will further demolish the hierarchical architecture of the enamel and affect the related mechanical property. In addition, the high carbonate content in hypomaturation enamel influences the crystallinity, crystal size and solubility of hydroxyapatite crystals. These results deepen our understanding of hypomaturation enamel biomineralization during amelogenesis, explain the clinical manifestations of hypomaturation enamel, provide fundamental evidence to help dentists choose optimal therapeutic strategies and lead to improved biofabrication and gene therapies.

Minimally invasive treatment for esthetic management of severe dental fluorosis: a case report.

Dental fluorosis is a developmental disturbance of enamel caused by excessive fluoride on ameloblasts during enamel formation. Patients often present to the dentist with a main goal of improving their esthetic appearance. This case report describes a minimally invasive technique for treating a severe case of enamel fluorosis with brown surface aspect and small defects. A selective mega-abrasion and microabrasion were used to recreate macro- and micro- surface morphology, followed by power bleaching, home bleaching, and resin infiltration to improve the esthetic appearance.

Optical properties of enamel and translucent composites by diffuse reflectance measurements.

OBJECTIVES The aim of this study was to evaluate the optical properties of natural enamel and translucent composites by diffuse reflectance measurements and Kubelka-Munks theory. METHODS Twenty natural enamel slabs and 80 composite replicas using four brands of translucent composites (Gradia Direct, Venus, Brilliant New line and Beautiful II; n=20) were evaluated at thicknesses of 1.0mm. The spectral distributions of enamel and composites were measured by means of a reflectance spectrophotometer. Optical constants including scattering coefficient (S), absorption coefficient (K), light reflectivity (RI) and infinite optical thickness (X(∞)) were calculated from the spectral reflectance data using Kubelkas equations. Paired t-tests were performed to evaluate the differences of optical constants (S, K, RI and X(∞)) between natural enamel and composites. RESULTS The optical constants S and K decreased with increasing wavelength, while RI and X(∞) increased with increasing wavelength within the visible spectrum. The values of enamel were in the range of the optical constants of these composites within the visible spectrum. However, there were significant differences of optical constants (S, K, RI and X(∞)) between enamel and translucent composites (p<0.05). CONCLUSIONS The optical constants of translucent composites were not completely consistent with that of natural enamel. In addition, the optical properties of these translucent composites varied with the brands of the composites.

In vitro evaluation of halogen light-activated vs chemically activated in-office bleaching systems

Abstract Objectives. To compare the tooth whitening efficacy, temperature and HP concentration changes induced by halogen light-activated and chemically activated in-office bleaching systems. Materials and methods. Twenty-four extracted premolars were randomly divided into two groups (n = 12): Group BL (35% HP with halogen light activation) and Group OP (38% HP with chemical activation). Tooth color was measured by a spectrophotometer according to the CIE L*a*b* color space system. Temperatures of bleaching gels and pulp chambers during the bleaching process were monitored and recorded by a digital multimeter with K-type thermocouple. HP concentrations were tested before and after treatments by iodometry. ANOVA and paired t-test were used for statistical analyses at the significance of p < 0.05. Results. Tooth whitening resulted in the increase of ΔL* and ΔE and reduction of Δb*. Paired t-tests revealed groups BL had greater ΔE than group OP, however, there was no statistically significant difference in ΔE between them after 3 weeks post-treatment. Maximal temperature rise (ΔT) was found only in group BL, showing the increment of 2.55 and 2.02°C for bleaching gels and pulp chambers, respectively. HP concentrations were higher than baseline values for group OP (p < 0.001) rather than group BL. Conclusions. Halogen light and chemically activated in-office bleaching systems were both effective for tooth whitening, but halogen light activation could improve the immediate whitening effect. In contrast, chemical activation was a more conservative method due to the little temperature rise in pulp chambers.

Effect of halogen light irradiation on hydrogen peroxide bleaching: an in vitro study

BACKGROUND The aim of this study was to evaluate the effect of halogen light irradiation on hydrogen peroxide (HP) bleaching by assessing HP concentrations, tooth whitening efficacy, and temperature variations in bleaching agents and pulp chambers. METHODS Sixteen premolars were randomly divided into two groups: Group BL (bleaching agent with halogen light irradiation for 3 × 10 minutes) and Group B (bleaching agent alone). HP concentrations were tested before and after treatment. CIE L*a*b* values of specimens were obtained using a spectrophotometer. Temperatures of bleaching gels and pulpal chambers were recorded by a digital multimeter with K-type thermocouple. Data were analysed using ANOVA and paired t-test. RESULTS After treatment, HP concentration in group BL was slightly higher than that in group B. Paired t-tests revealed significant differences of ΔE between groups BL and B in all time intervals except at day 35. The temperature rise of bleaching gels and pulpal chambers in group BL was significantly higher than that in group B. CONCLUSIONS In-office bleaching was effective for tooth whitening. The involvement of halogen light was beneficial for the immediate whitening effect but had little impact on the long-term whitening effect.