Amelogenin-inspired peptide, calcium phosphate solution, fluoride and their synergistic effect on enamel biomimetic remineralization: an in vitro pH-cycling model.

BACKGROUND: Several methods were introduced for enamel biomimetic remineralization that utilize a biomimetic analogue to interact and absorb bioavailable calcium and phosphate ions and induce crystal nucleation on demineralized enamel. Amelogenin is the most predominant enamel matrix protein that is involved in enamel biomineralization. It plays a major role in developing the enamel's hierarchical microstructure. Therefore, this study was conducted to evaluate the ability of an amelogenin-inspired peptide to promote the remineralization potential of fluoride and a supersaturated calcium phosphate solution in treating artificially induced enamel carious lesions under pH-cycling regimen. METHODS: Fifty enamel slices were prepared with a window (4*4 mm2 ) on the surface. Five samples were set as control healthy enamel and 45 samples were subjected to demineralization for 3 days. Another 5 samples were set as control demineralized enamel and 40 enamel samples were assigned into 8 experimental groups (n=5) (P/I, P/II, P/III, P/AS, NP/I, NP/II, NP/III and NP/AS) according to peptide treatment (peptide P or non-peptide NP) and remineralizing solution used (I; calcium phosphate solution, II; calcium phosphate fluoride solution, III; fluoride solution and AS; artificial saliva). Samples were then subjected to demineralization/remineralization cycles for 9 days. Samples in all experimental groups were evaluated using Raman spectroscopy for mineral content recovery percentage, microhardness and nanoindentation as healthy, demineralized enamel and after pH-cycling. Data were statistically analysed using two-way repeated measures Anova followed by Bonferroni-corrected post hoc test for pairwise multiple comparisons between groups. Statistical significance was set at p= 0.05. Additionally, XRD, FESEM and EDXS were used for crystal orientation, surface morphology and elemental analysis after pH-cycling. RESULTS: Nanocrystals clumped in a directional manner were detected in peptide-treated groups. P/II showed the highest significant mean values in mineral content recovery (63.31%), microhardness (268.81±6.52 VHN), elastic modulus (88.74±2.71 GPa), nanohardness (3.08±0.59 GPa) and the best crystal orientation with I002/I300 (1.87±0.08). CONCLUSION: Despite pH changes, the tested peptide was capable of remineralizing enamel with ordered crystals. Moreover, the supplementary use of calcium phosphate fluoride solution with peptide granted an enhancement in enamel mechanical properties after remineralization.

Physical and mechanical evaluation of dental resin composite after modification with two different types of Montmorillonite nanoclay.

OBJECTIVES: Evaluation of degree of conversion (DC), flexural properties, micro-hardness and color change (ΔE00) of dental resin composite after modification with two types of organo-modified Montmorillonite (MMT) nanoclay; an experimentally synthesized polymethyl-methacrylate modified MMT nanoclay (PMMA/MMT), and a commercially available one (Cloisite20A). METHODS: MMT was synthesized by sol-gel technique, organo-modified with polymethyl-methacrylate and characterized using EDX, XRD and FTIR. PMMA/MMT and Cloisite20A nanoclay were added to flowable resin composite in 0.5, 1 and 1.5 wt% concentrations. Unmodified resin composite was used as control group. DC was assessed by FTIR, flexural properties were tested by three-point bending test using a universal testing machine, micro-hardness was analyzed by Vickers micro-hardness tester and color change (ΔE00) was evaluated using a reflective spectrophotometer. SEM and elemental mapping assessment were performed to evaluate nanoclay distribution in resin composite. Data were analyzed using One-way ANOVA followed by Tukey's post hoc test, in addition to Two-way ANOVA (p ≤ 0.05). Weibull analysis was used to analyze flexural strength results. RESULTS: Characterization results revealed successful preparation of PMMA/MMT. DC results showed insignificant difference up to 1 wt% of nanoclay concentration. Addition of 0.5 wt% of PMMA/MMT significantly increased flexural properties, while addition of 1.5 wt% of PMMA/MMT significantly decreased flexural properties. Micro-hardness results revealed a significant increase in PMMA/MMT groups in all tested concentrations. ΔE00 results showed that color change was clinically acceptable on adding 0.5 wt% nanoclay. CONCLUSION: PMMA/MMT in 0.5 wt% is a promising nanofiller for resin composite that significantly enhanced flexural strength and micro-hardness without compromising DC and color.

Effect of surface area and air-drying distance on shear bond strength of etch-and-rinse adhesive

We evaluated the effects of air-drying distance and bond surface area on the shear bond strength of a 2-step etch-and-rinse adhesive. A total of 120 bovine anterior teeth were equally divided into 6 main groups based on bonding surface area. The main groups were divided into sub-groups (n = 5) according to air-drying distance. The shear strength was determined using a universal testing machine at a crosshead speed of 0.5 mm/min. The averaged results were subjected to two-way ANOVA and Tukey's test (α = 0.05). Two-way ANOVA testing identified no significant cross-product interactions (p > 0.05), but the main factors of area (p < 0.0001) and air-drying distance (p < 0.00001) significantly affected the mean bond strength. Shorter air-drying distances improved bond strength, and increased surface area decreased the bond strength.

Effect of surface area and air-drying distance on shear bond strength of etch-and-rinse adhesive.

We evaluated the effects of air-drying distance and bond surface area on the shear bond strength of a 2-step etch-and-rinse adhesive. A total of 120 bovine anterior teeth were equally divided into 6 main groups based on bonding surface area. The main groups were divided into sub-groups (n = 5) according to air-drying distance. The shear strength was determined using a universal testing machine at a crosshead speed of 0.5 mm/min. The averaged results were subjected to two-way ANOVA and Tukey's test (α = 0.05). Two-way ANOVA testing identified no significant cross-product interactions (p > 0.05), but the main factors of area (p < 0.0001) and air-drying distance (p < 0.00001) significantly affected the mean bond strength. Shorter air-drying distances improved bond strength, and increased surface area decreased the bond strength.