The Potential of Hydroxyapatite Toothpaste to Prevent Root Caries: A pH-Cycling Study.

PURPOSE: The effectiveness of a hydroxyapatite (HAP) toothpaste and a fluoride toothpaste in preventing root tissue demineralization (root caries) was compared using an established pH-cycling caries model. MATERIALS AND METHODS: Sixty dentin blocks were produced from the root tissue of extracted human teeth and were assigned to 3 test groups (n=20/group): 10% hydroxyapatite toothpaste (HAP), 1450 ppm fluoride toothpaste (fluoride), and artificial saliva (artsaliva). Early root caries lesions were developed in each sample by 7-day demineralization using a pH-cycling caries model. The daily cyclic treatment regimen consists of two 2-minute toothpaste-slurry treatment periods, one 6-hour acid challenge using acidified gel (pH 4.5), and then storage in remineralizing solution (artsaliva) for the rest of the time. Demineralization was assessed as the amount of mineral loss (∆z) using transverse microradiography (TMR). Pairwise comparisons (between treatments) were performed using analysis of variance (ANOVA), and then Tukey's HSD for multiple comparisons. All p-values are considered significant if p<0.05. RESULTS: Both ANOVA and Tukey's HSD indicated no significant (ANOVA; n=20) difference in mean ∆z among the groups, with least ∆z (±Sd) in the HAP (1117±366) compared to fluoride (1392±334) and artsaliva (1406±223). Relative to control, HAP and fluoride inhibited root demineralization by 21% and 6%, respectively. CONCLUSION: Within the limit of the present study, the tested toothpaste containing 10% HAP is an effective root caries control toothpaste. Toothpaste containing 10% HAP was slightly more effective in preventing tooth demineralization than 1450 ppm fluoride provided as sodium fluoride. Thus, this study shows that HAP toothpastes can serve as an effective alternative to fluoride toothpastes for root caries management.

The effect of flowable composite lining and dentin location on microtensile bond strength and internal fracture formation.

The objective of this study was to determine the effect of flowable composite lining and dentin location on internal dentin fracture formation in the microtensile bond strength (MTBS) test using swept-source optical coherence tomography (SS-OCT). MTBS test beams (1.0×1.0 mm) were prepared from human superficial and deep dentin, which was bonded with a self-etch adhesive (Clearfil SE Bond) and hybrid composite resin (Clearfil AP-X), with or without flowable lining (Clearfil Majesty ES-Flow). We tested 4 groups according to placement technique (with vs. without flowable liner) and dentin (superficial vs. deep) locations. Cross-sectional 2D images of the bonded interface were obtained before and after the MTBS test. Internal dentin fracture after MTBT was observed as a bright zone in SS-OCT. Flowable lining significantly reduced internal fracture formation in dentin (p<0.05). Dentin location significantly influenced MTBS (p<0.05), and this was reduced by flowable lining usage.

Effect of lights with various wavelengths on bleaching by 30% hydrogen peroxide.

The objective of this study was to evaluate the bleaching effect of light sources with various wavelengths using 30% hydrogen peroxide (HP) in vitro. The hematoporphyrin-stained paper was bleached with HP and irradiated for 10 min using LED light sources with 265, 310, 365, 405, or 450 nm respectively. In control group, HP was applied for 10 min without light irradiation. The bleaching procedure was repeated two times. The L*a*b* values of the samples before bleaching and after each bleaching step were measured using a colorimeter. Color changes of specimens were then calculated and statistically analyzed. There was an interaction between light sources and time of irradiation in the color change (p < 0.05). Time and light sources significantly affected ΔE and ΔL (p < 0.05). The light source of 256 nm showed the highest bleaching effect over time followed by that of 310 nm, which were statistically different from other groups (p < 0.001). The 365 nm, 450 nm groups, and control group showed low bleaching effect visually with no significant differences in ΔE and ΔL (p > 0.05). It was concluded that the wavelengths of the light sources affected the bleaching by HP. The 310-nm light can be a potential source for bleaching.

Cross-sectional imaging of tooth bonding interface after thermal stresses and mechanical fracture.

This study determined the influence of thermocycling (TC) and flowable composite on microtensile bond strength (MTBS), crack formation and mechanical properties of the bonding interface using swept-source optical coherence tomography (SS-OCT) and nanoindentation. MTBS test beams prepared from human dentin bonded with self-etch adhesive and hybrid composite with or without flowable lining were aged for either 0 or 10,000 thermocycles, resulting in 4 groups of specimens according to the placement technique and TC (n=10). 2D images were obtained before and after MTBS test to detect crack at interface using SS-OCT. Hardness across resin-dentin bonding area were measured using nanoindentation. Two-way ANOVA showed that flowable lining significantly increased MTBS (p<0.05). TC significantly increased crack percentage in composite while there was no significant difference in dentin crack. Moreover, TC significantly affected the hardness of dentin and resin composites (p<0.05). SS-OCT is effective in detecting internal fracture in substrate.

Fractography of interface after microtensile bond strength test using swept-source optical coherence tomography.

OBJECTIVE: To determine the effect of crosshead speed and placement technique on interfacial crack formation in microtensile bond strength (MTBS) test using swept-source optical coherence tomography (SS-OCT). MATERIALS AND METHODS: MTBS test beams (0.9×0.9mm(2)) were prepared from flat human dentin disks bonded with self-etch adhesive (Clearfil SE Bond, Kuraray) and universal composite (Clearfil AP-X, Kuraray) with or without flowable composite lining (Estelite Flow Quick, Tokuyama). Each beam was scanned under SS-OCT (Santec, Japan) at 1319nm center wavelength before MTBS test was performed at crosshead speed of either 1 or 10mm/min (n=10). The beams were scanned by SS-OCT again to detect and measure cracks at the debonded interface using digital image analysis software. Representative beams were observed under confocal laser scanning microscope to confirm the fractography findings. RESULTS: Two-way ANOVA showed that for MTBS the crosshead speed was not a significant factor (p>0.05), while there was a difference between placement techniques (p<0.001), with flowable lining yielding higher mean values. On the other hand, for crack formation, there was a significant difference between crosshead speeds (p<0.01), while the placement technique did not show up as a statistically significant factor (p>0.05). The interaction of factors were not significant (p>0.05). SIGNIFICANCE: Testing MTBS samples at higher crosshead speeds induced more cracks in dentin. Lining with a flowable composite improved the bonding quality and increased the bond strength. SS-OCT can visualize interfacial cracks after restoration debonding.