Evaluation of toothpastes for treating root carious lesions - a laboratory-based pilot study.

BACKGROUND: Root caries is preventable and can be arrested at any stage of disease development. The aim of this study was to investigate the potential mineral exchange and fluorapatite formation within artificial root carious lesions (ARCLs) using different toothpastes containing 5,000 ppm F, 1,450 ppm F or bioactive glass (BG) with 540 ppm F. MATERIALS AND METHODS: The crowns of each extracted sound tooth were removed. The remaining roots were divided into four parts (n = 12). Each sample was randomly allocated into one of four groups: Group 1 (Deionised water); Group 2 (BG with 540 ppm F); Group 3 (1,450 ppm F) and Group 4 (5,000 ppm F). ARCLs were developed using demineralisation solution (pH 4.8). The samples were then pH-cycled in 13 days using demineralisation solution (6 h) and remineralisation solution (pH 7) (16 h). Standard tooth brushing was carried out twice a day with the assigned toothpaste. X-ray Microtomography (XMT) was performed for each sample at baseline, following ARCL formation and after 13-day pH-cycling. Scanning Electron Microscope (SEM) and 19F Magic angle spinning nuclear magnetic resonance (19F-MAS-NMR) were also performed. RESULTS: XMT results showed that the highest mineral content increase (mean ± SD) was Group 4 (0.09 ± 0.05), whilst the mineral content decreased in Group 1 (-0.08 ± 0.06) after 13-day pH-cycling, however there was evidence of mineral loss within the subsurface for Groups 1, 3 and 4 (p < 0.05). SEM scans showed that mineral contents within the surface of dentine tubules were high in comparison to the subsurface in all toothpaste groups. There was evidence of dentine tubules being either partially or completely occluded in toothpaste groups. 19F-MAS-NMR showed peaks between - 103 and - 104ppm corresponding to fluorapatite formation in Groups 3 and 4. CONCLUSION: Within the limitation of this laboratory-based study, all toothpastes were potentially effective to increase the mineral density of artificial root caries on the surface, however there was evidence of mineral loss within the subsurface for Groups 1, 3 and 4.

Fabrication of porous carbonate apatite granules using microfiber and its histological evaluations in rabbit calvarial bone defects.

Carbonate apatite (CO3 Ap) granules are known to show good osteoconductivity and replaced to new bone. On the other hand, it is well known that a porous structure allows bone tissue to penetrate its pores, and the optimal pore size for bone ingrowth is dependent on the composition and structure of the scaffold material. Therefore, the aim of this study was to fabricate various porous CO3 Ap granules through a two-step dissolution-precipitation reaction using CaSO4 as a precursor and 30-, 50-, 120-, and 205-µm diameter microfibers as porogen and to find the optimal pore size of CO3 Ap. Porous CO3 Ap granules were successfully fabricated with pore size 8.2-18.7% smaller than the size of the original fiber porogen. Two weeks after the reconstruction of rabbit calvarial bone defects using porous CO3 Ap granules, the largest amount of mature bone was seen to be formed inside the pores of CO3 Ap (120) [porous CO3 Ap granules made using 120-µm microfiber] followed by CO3 Ap (50) and CO3 Ap (30). At 4 and 8 weeks, no statistically significant difference was observed based on the pore size, even though largest amount of mature bone was formed in case of CO3 Ap (120). It is concluded, therefore, that the optimal pore size of the CO3 Ap is that of CO3 Ap (120), which is 85 µm.

Microhardness and SEM-EDX Analysis of Permanent Enamel Surface Adjacent to Fluoride-releasing Restorative Materials Under Severe Cariogenic Challenges.

PURPOSE: In this study, the protective effects of restorative materials with fluoride content, resin-modified glass-ionomer cement (RMGIC), giomer, and glass carbomer against artificial initial caries lesions in a simulated highly cariogenic oral environment were evaluated. Considering the reported recharging abilities of these restorative materials, fluoridated toothpaste was applied to some groups, in which the anti-demineralising effect was also evaluated. MATERIALS AND METHODS: Two enamel blocks were produced from each of 60 sound permanent molars. Sixty specimens were used for microhardness analysis, and the rest were used for SEM-EDX analysis. Enamel specimens were randomly assigned to three groups according to the restorative material: A = resin-modified glass-ionomer cement; B = giomer; C = glass carbomer. Artificial initial caries lesions were created using demineralising solutions, after which specimens were exposed to in vitro pH cycling simulating a highly cariogenic oral environment. Microhardness and mineral analyses were performed on the enamel surrounding the restorative materials at three different times during the experiment: at the beginning of the experiment, then after the creation of the artificial early caries lesions, and finally after pH cycling. RESULTS: Microhardness and SEM-EDX results mostly confirmed each other. RMGIC and glass carbomer groups with added fluoride toothpaste showed statitsically significantly better anti-demineralising effects in comparison to other groups. Neither of the giomer groups performed as well as RMGIC or glass carbomer. CONCLUSION: Because of the similarity between the demineralisation inhibitory activity of glass carbomer and RMGIC, glass carbomer may be preferred as a restorative material in paediatric dentistry.

Regenerating infected bone defects with osteocompatible microspheres possessing antibacterial activity.

Treatment of infected bone defects still remains a formidable clinical challenge, and the design of bone implants with both anti-bacterial activity and -osteogenesis effects is nowadays regarded as a powerful strategy for infection control and bone healing. In the present study, bioresorbable porous-structured microspheres were fabricated from an amphiphilic block copolymer composed of poly(l-lactide) and poly(ethyl glycol) blocks. After being surface coated with mussel-inspired polydopamine, the microspheres were loaded with nanosilver via the reduction of silver nitrate and apatite via biomineralization in sequence. At optimized loading amounts, the nanosilver-loaded microspheres showed no unfavorable effects on the proliferation and differentiation of bone marrow mesenchymal stem cells despite preserving strong antibacterial activity in in vitro evaluations. For the critical-sized defects (φ = 8 mm) in the rat cranium that was pre-infected with Staphylococcus aureus, the filling of the dual-purpose microspheres demonstrated an effective way to kill bacteria in vivo, and in the meantime, it promoted new bone formation efficiently alongside the degradation of microspheres. Thus, the results suggested that bioresorbable microspheres with both osteoconductive and antibacterial activities were a good choice for treating infected bone defects.

Alignment of Biological Apatite c-Axis Under Functional Loading: A Preliminary Report.

PURPOSE: To understand the bone modeling/remodeling process of functionally loaded implants by observing the alignment of the biological apatite (BAp) c-axis. MATERIALS AND METHODS: Commercially available titanium implants with TiO2 grit-blasted surfaces were placed in the fourth premolar and the first molar of the beagle dog and were functionally loaded with casted crowns and were compared to the non-loaded controls. After being killed, the samples were subjected to histological observation and to a microbeam x-ray diffraction (µXRD) analysis with a transmission optical system to evaluate the preferential BAp c-axis alignment. RESULTS: The non-loaded group presented mostly nonoriented BAp c-axis around the implant, whereas for the loaded group, preferential alignment of BAp c-axis was observed along the loading direction of the implant suggesting that the Bap aligned itself based on the direction of the functional mechanical loading. CONCLUSION: The µXRD revealed that the c-axis orientation was perpendicular to the implant thread working against the functional loaded direction, which may contribute in designing an optimal implant macrogeometry.

Are Carious Lesions in Previously Sealed Occlusal Surfaces Detected as well on Colour Photographs as by Visual Clinical Examination?

PURPOSE: To compare the level of agreement between carious lesion assessments according to the visual clinical examination and the colour photograph methods. MATERIALS AND METHODS: Data on the presence of enamel/dentin carious lesions in previously sealed occlusal surfaces in first molars were obtained by two trained and calibrated examiners through visual clinical examination and from colour photographs 4 years after sealing. Kappa statistics were applied to calculate agreement between assessment methods. Data analysis was performed using sign, Bowker symmetry and McNemar's tests. RESULTS: The prevalence of dentin carious lesions was very low. The kappa coefficients for detecting enamel/dentin carious lesions using the two assessment methods were 0.65 (CI: 0.56-0.74) for examiner 1 and 0.70 (CI: 0.62-0.78) for examiner 2. Examiner 2 observed more enamel/dentin carious lesions on colour photographs than did examiner 1 (p = 0.008). Sensitivity analyses did not confirm this outcome. CONCLUSIONS: There was no difference in the detection of enamel/dentin carious lesions in previously sealed occlusal surfaces using colour photographs vs visual clinical examination. The colour photograph method is therefore equivalent to the visual clinical examination in detecting enamel/dentin carious lesions. More studies are required.

Acceleration of bone-defect repair by using A-W MGC loaded with BMP2 and triple point-mutant HIF1α-expressing BMSCs.

BACKGROUND: The goal of this study is to explore the effects of A-W MGC (apatite-wollastonite magnetic bioactive glass-ceramic) loaded with BMP2 (bone morphogenetic protein 2)- and HIF1α(mu) (hypoxia-inducible factor 1 mutation)-expressing BMSCs (bone marrow mesenchymal stem cells) on the bone defect repair. METHODS: (1) BMSCs were infected with viral solution containing BMP2 and HIF1α(mu) with the best MOI (multiplicity of infection). The efficiency was observed via hrGFP (human renilla reniformis green fluorescent protein). (2) The cells were divided into five groups (A-E), and ALP (alkaline phosphatase) activity was measured. (3) BMP2 and HIF1α (hypoxia-inducible factor 1α) protein were measured. (4) A-W MGC was loaded with BMSCs that contain the genes and implanted into the bone defect model. The animals were sacrificed 8 and 12 weeks later. (5) The healing was measured with X-ray, histology, and biomechanics. RESULTS: (1) BMSCs in A-D showed high transfection efficiency. (2) ALP in A and B was higher than the others (p = 0.041 or 0.038); A was higher than B (p = 0.038); (3) BMP2 in A and B was higher than the others (p = 0.014). HIF1α in A and C was higher than the others (p = 0.020). (4) 8 and 12 weeks after, an X-ray indicated that bone defect was nearly fully repaired in A and C. (5) 12 weeks after, the bone remodeling was complete in A and C. (6) The flexural strength in A and C was stronger than the others (p = 0.043). CONCLUSION: Engineered A-W MGC with BMP2 and HIF1α(mu)-expressing BMSCs exhibits comparable therapeutic effects of bone-defect repair as an autologous bone graft.

Desensitizing efficacy of nano-carbonate apatite dentifrice and Er,Cr:YSGG laser: a randomized clinical trial.

OBJECTIVE: The aim of this study was to evaluate the desensitizing effects of a dentifrice containing nano-carbonate apatite (n-CAP) and Er,Cr:YSGG laser in the treatment of dentin hypersensitivity. BACKGROUND DATA: Most studies of hypersensitivity treatment have been conducted with different methods of professional treatment and self-care in each study. Moreover, clinical studies that compare self-care and professional treatment have not yet been published. METHODS: Eighty-two patients with dentin hypersensitivity were divided randomly into three groups: (1) a control group with strontium chloride dentifrice (SC), (2) n-CAP dentifrice (n-CAP), and (3) an Er,Cr:YSGG laser (laser) group. The study was conducted for 4 weeks: a treatment period of 2 weeks and a maintenance period of 2 subsequent weeks. The SC and n-CAP groups were instructed to brush their teeth twice a day for 1 min. The laser group visited twice at 1 week intervals for irradiation of the sensitive teeth. The desensitizing effect was evaluated by assessing the tactile sensitivity using the visual analogue scale (VAS), and evaporative air sensitivity was determined using an air blast score (ABS). RESULTS: The n-CAP group and the laser group showed significantly different desensitizing effects in VAS after 4 weeks (69% and 63%, respectively) and a 33% (p<0.05) and 3% (p>0.05) desensitizing effect, respectively, in VAS during the maintenance period. CONCLUSIONS: The n-CAP and the laser were effective in reducing dentin hypersensitivity. The laser had a superior desensitizing effect at the initial stage, whereas the n-CAP maintained its effect for a relatively longer time in clinical situations.

Biocompatibility and in vivo osteogenic capability of novel bone tissue engineering scaffold A-W-MGC/CS.

BACKGROUND: This study aims to investigate the biocompatibility and in vivo osteogenic capability of the novel bone tissue engineering scaffold apatite-wollastonite-magnetic glass ceramic/chitosan (A-W-MGC/CS). METHODS: Rabbit bone marrow stromal cells (BMSCs) were transfected with adenovirus-human bone morphogenetic protein-2-green fluorescent protein (Ad-hBMP2-GFP). The transfected BMSCs were then inoculated onto the scaffold material A-W-MGC/CS to construct tissue-engineered bone. The attachment and proliferation of BMSCs were observed by scanning electron microscopy (SEM) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) detection, respectively. Rabbit models of bone defects were established and divided into three groups. Experimental group 1 was implanted with prepared tissue-engineered bone. Experimental group 2 was implanted with A-W-MGC/CS without transfected BMSCs. The blank group was injected with transfected BMSCs, without implantation of any scaffold. In the 12th week after surgery, the repair of bone defect was observed by X-ray examination, and histological observations of the area of bone defect were performed. RESULTS: A-W-MGC/CS resulted in good BMSC attachment and had no obvious effects on cell proliferation. In experimental group 1, good repair of bone defect was observed, and the scaffold material degraded completely. In experimental group 2, new bone was formed, but its quality was poor. In the blank group, there was mainly filling of fibrous connective tissues with no observable bone defect repair. CONCLUSION: A-W-MGC/CS possesses good biocompatibility and in vivo osteogenic capability for bone defect repair.

Detoxification of rats subjected to nickel chloride by a biomaterial-based carbonated orthophosphate.

Recently, the therapeutic approaches of the detoxification against the metals (nickel) in the body are the use of biomaterials such as carbonated hydroxyapatite. The aim of this study is therefore to analyze the physiological and physicochemical parameters of strain white rats "Wistar" receiving nickel chloride and to study the protective associative of apatite against adverse effects of this metal, and this in comparison with control rats. Our results showed that the nickel induced in rats an oxidative stress objectified by elevated levels of thiobarbituric acid-reactive substances and conjugated dienes associated with inhibition of the activity of the antioxidant defense system such as glutathione peroxidase, superoxide dismutase and catalase in the liver, kidney, spleen and erythrocyte. Disorders balances of ferric, phosphocalcic, a renal failure and a liver toxicity were observed in rats exposed to nickel. As well as a significant increase in the rate of nickel in the bones and microcytic anemia was revealed. However, the implantation of carbonated hydroxyapatite in capsule form protects rats intoxicated by the nickel against the toxic effects of this metal by lowering the levels of markers of lipid peroxidation and improving the activities of defense enzymes. Our implantation technique is effective to correct ferric balance and phosphocalcic equilibrium, to protect liver and kidney function, to reduce the rate of bone nickel and to correct anemia. They clearly explain the beneficial and protective of our biomaterial which aims the detoxification of rats receiving nickel by substituting cationic (Ca(2+) by Ni(2+)) and anionic (OH(-) by Cl(-)) confirmed by physicochemical characterization like the IR spectroscopy and X-ray diffraction. These techniques have shown on the one hand a duplication of OH(-) bands (IR) and on the other hand the increase of the volume of the apatite cell after these substitutions (X-ray diffraction).

One-year clinical evaluation of a Glass Carbomer fissure sealant, a preliminary study.

Glass Carbomer is a new generation of restorative material developed from glass-ionomer cements with possibility of gradual mineralization into fluorapatite. The aim of this clinical trial was to investigate the retention of Glass Carbomer fissure sealant after 12 months, in comparison to a commonly used conventional resin-based sealant. Forty-eight teeth in 24 patients [mean (SD) = 8 (2.3) years] with well-delineated fissure morphology were randomly divided into two equal groups and sealed with Bis-GMA resin-based Helioseal F (group A, Ivoclar Vivadent, Liechtenstein) and Glass Carbomer (group B, Glass Carbomer Sealant, Glass Carbomer Products, Leiden, Netherlands) using the split mouth design. Materials were placed and set according to the manufacturer's instructions using a polymerization unit Bluephase 16i (Vivadent, Liechtenstein). Complete sealant retentions in both groups were 100% and 75% after 6 and 12 months of clinical service, respectively. There were there were no secondary caries lesions in both groups after 6 months; two new carious lesions were detected in both groups after 12 months. The Mann-Whitney U test revealed no significant difference between the two groups at both evaluations points (P > 0.05). Glass Carbomer material showed a similar retention rate when compared with a resin-based sealant. Future studies are required to examine the long-term performance of Glass Carbomer sealants.

Biomimetic magnesium-carbonate-apatite nanocrystals endowed with strontium ions as anti-osteoporotic trigger.

The present work investigates the preparation of biomimetic nanocrystalline apatites co-substituted with Mg, CO3 and Sr to be used as starting materials for the development of nanostructured bio-devices for regeneration of osteoporotic bone. Biological-like amounts of Mg and CO3 ions were inserted in the apatite structure to mimic the composition of bone apatite, whereas the addition of increasing quantities of Sr ions, from 0 up to 12 wt.%, as anti-osteoporotic agent, was evaluated. The chemical-physical features, the morphology, the degradation rates, the ion release kinetics as well as the in vitro bioactivity of the as-prepared apatites were fully evaluated. The results indicated that the incorporation of 12 wt.% of Sr can be viewed as a threshold for the structural stability of Mg-CO3-apatite. Indeed, incorporation of lower quantity of Sr did not induce considerable variations in the chemical structure of Mg-CO3-apatite, while when the Sr doping extent reached 12 wt.%, a dramatically destabilizing effect was detected on the crystal structure thus yielding alteration of the symmetry and distortion of the PO4. As a consequence, this apatite exhibited the fastest degradation kinetic and the highest amount of Sr ions released when tested in physiological conditions. In this respect, the surface crystallization of new calcium phosphate phase when immersed in physiological-like solution occurred by different mechanisms and extents due to the different structural chemistry of the variously doped apatites. Nevertheless, all the apatites synthesized in this work exhibited in vitro bioactivity demonstrating their potential use to develop biomedical devices with anti-osteoporotic functionality.

Synergistic effect of dentinal tubule occlusion by nano-carbonate apatite and CO2 laser in vitro.

OBJECTIVE: The aim of this study was to evaluate the occluding effects of a combination of dentifrice containing nano-carbonate apatite (n-CAP) and a CO2 laser on dentinal tubules, and to assess the acid resistance of the occluded dentinal tubules produced. BACKGROUND DATA: A number of experiments have been conducted recently to relieve the symptoms of dentin hypersensitivity (DH) using a laser in combination with desensitizing products. MATERIALS AND METHODS: One hundred and twenty specimens with exposed dentinal tubules were divided into four groups: the control, n-CAP, laser, and combined groups. Thirty specimens in each group were reassigned into three different conditions: baseline, treatment for occluding dentinal tubules, and acid challenge (pH 4.0 acetate buffer solution for 3 min). At the end of each phase, all specimen surfaces were evaluated by scanning electron microscope (SEM). RESULTS: The combined group had a significantly smaller mean dentinal tubule area than the control group, and the fewest reopened dentinal tubules after acid challenge. CONCLUSIONS: The combined therapy is a promising means of treating DH patients in the clinic.

Combined effects of Er:YAG laser and nano-carbonate apatite dentifrice on dentinal tubule occlusion: in vitro study.

OBJECTIVE: The aim of this study was to evaluate the occluding effects of Er:YAG laser and dentifrice containing nano-carbonate apatite (n-CAP) on the dentinal tubules. BACKGROUND DATA: Although there are various treatment methods for dentin hypersensitivity (DH), more effective methods are still being sought. METHODS: Sound human root dentin specimens were etched with 6% citric acid to open the dentinal tubules. The specimens were divided randomly into four groups: no treatment (control group), toothbrushing using 20% n-CAP dentifrice (n-CAP group), Er:YAG laser irradiation (LI group), and LI after n-CAP (combined group). The degree of occlusion of the dentinal tubules and the thickness of the deposition layer were evaluated by scanning electron microscopy and an image analyzer. RESULTS: It was shown that the occlusion effect of the n-CAP group was 87%, that of the combined group was 54%, and that of the LI group was 52%, compared with that of the control group. And the n-CAP particles were observed not only under the irradiated surface and but also above the surface in the combined group. CONCLUSIONS: This combination method has the potential for enhancement of the dentinal tubule occlusion. However, further study is needed to present the combination effects with additional analysis, and the long-term effects.

Nanotechnology and its role in caries therapy.

The purpose of this review is to highlight recent nanotechnological developments for remineralization of incipient caries lesions as well as biomimetic strategies for enamel synthesis based on the application of nanotechnology. Analysis of in vitro data indicates that apatite nanoparticles might be effective in reversing lesion progression in the outer but not in the deeper part of early caries lesions. To control caries-induced demineralization, investigators have developed calcium and phosphate or fluoride ion-releasing nanofillers, enabling resin composites to release ions, if the pH decreases under in vitro conditions. Extensive in vitro investigations of apatite crystallization have been performed to mimic the hierarchical topology of natural enamel. Strategies for formation of highly organized biomineralized structures include oriented aggregation of nanocrystallites or the assembly of apatite nanoparticles mediated by organic scaffolds. Despite all these promising in vitro experiments, the effectiveness of such strategies for the control of demineralization processes as well as for caries therapy still needs validation by clinical studies.

Oral bone loss induced by mineral deficiency in a rat model: effect of a synthetic bone mineral (SBM) preparation.

UNLABELLED: Osteoporosis affects the craniofacial and oral structures and has been associated with periodontal bone loss, tooth loss and reduced jaw bone mass. OBJECTIVE: This study aimed to test the therapeutic efficacy of synthetic bone mineral (SBM) in minimizing alveolar bone loss induced by mineral deficiency in a rat model. SBM consists of a calcium carbonate apatite (similar to bone apatite) matrix incorporating magnesium, zinc, and fluoride ions. DESIGN: Thirty female Sprague Dawley rats (2 months old) were randomly distributed into 3 groups (10 rats per group): GA (control), on basic diet; GB, on mineral deficient (MD) diet; and GC, on MD+SBM. The rats were sacrificed after 3 months, the jawbones were isolated and the soft tissues removed. Bone density was determined using X-ray radiography (Faxitron); mandibular cortical width, panoramic mandibular index, and alveolar resorption degree (M/M ratio) using BioquantOsteo; and bone micro-architecture micro-computed tomography and scanning electron microscopy. RESULTS: Compared to control (GA), the rats on MD diet (GB) experienced significant mandibular bone loss while the rats on MD+SBM diet (GC) experienced significantly less bone loss compared to the GB group. CONCLUSION: SBM, administered orally, may have the potential as an osteoporosis therapeutic agent in minimizing or preventing alveolar bone loss induced by mineral deficiency.

Effect of white mineral trioxide aggregate compared with biomimetic carbonated apatite on dentine bridge formation and inflammatory response in a dental pulp model.

AIM: To evaluate the effects of apatite precipitation on the biocompatibility and hard tissue induction properties of white mineral trioxide aggregate (WMTA) in a dental pulp model. METHODOLOGY: Pulp exposures were created on the axial walls of 32 sound canine teeth of eight dogs. Four additional sound teeth served as controls. The pulps were capped either with WMTA or apatite derivatives [biomimetic carbonated apatite (BCAp)] in the interaction of WMTA with a synthetic tissue fluid and restored with zinc oxide-eugenol cement. After 7 and 70 days, the animals were killed, and the histological specimens taken from the teeth were stained with haematoxylin and eosin for histomorphological evaluation. The Brown and Brenn technique was employed to stain bacteria. The data were subjected to nonparametric Kruskall-Wallis analysis and Mann-Whitney U_tests. RESULTS: Biomimetic carbonated apatite did not induce hard tissue bridge formation. WMTA performed significantly better than BCAp in this respect at both periods (P < 0.05). BCAp was associated with a significantly greater inflammatory response as compared with WMTA after 7 days (P < 0.05). Both materials were associated with similar reactions after 70 days (P >0.05). CONCLUSIONS: White mineral trioxide aggregate induced hard tissue formation via a mechanism other than that postulated via apatite formation.

Effect of nano-carbonate apatite to prevent re-stain after dental bleaching in vitro.

OBJECTIVES: This study examined the effect of nano-carbonate apatite (n-CAP) to prevent re-staining and the change of enamel surface after dental bleaching in vitro. METHODS: Twenty-four bovine specimens were bleached for 2 weeks with 10% carbamide peroxide (CP). After bleaching, the specimens were divided into the following four groups: distilled and deionized water (DDW, negative control), 10% n-CAP, NaF (positive control) and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP, positive control). Each group was subjected to pH cycling for 7 days. The specimens were treated for 4 min 3 times per day and re-staining was induced naturally by artificial saliva in the remineralization process. After pH cycling, the changes in colour were evaluated with spectrophotometry and scanning electron microscopy (SEM). The difference in colour between before and after pH cycling was evaluated using an ANOVA and Tukey test. RESULTS: After pH cycling, the colour difference of n-CAP group was significantly lower than that of the DDW and CPP-ACP groups (p<0.05). SEM showed that n-CAP particles were deposited regularly on the damaged surface compared to the other groups. CONCLUSION: 10% n-CAP could significantly maintain the initial colour and protect the damaged enamel structure after bleaching.