Sealing of open dentinal tubules by laser irradiation: AFM and SEM observations of dentine surfaces

Measurement of eroded dentine tubule patency and roughness following novel dab-on or brushing abrasion

OBJECTIVES

To investigate the effect of dab-on or brushing of stannous-fluoride SnF2 or sodium-fluoride NaF dentifrice on eroded dentine tubule patency, surface and inter-tubular dentine roughness, using Confocal-Laser-Scanning-Microscopy (CLSM), Atomic-Force-Microscopy (AFM), Energy-Dispersive-X-ray-Spectroscopy (EDX), Scanning-Electron-Microscopy (SEM) and Contact-Profilometry (CP).

METHODS

75-polished human dentine samples were prepared and eroded in agitated 6% citric acid to expose patent tubules and 'initiate' DH. Samples were randomly allocated into 5 intervention groups; artificial saliva control (1); electric tooth-brushing with NaF (2) or SnF2 (3), and dab-on application of NaF (4) or SnF2 (5). Samples underwent three cycles of intervention followed by further acid challenge. Patent tubules, likely to cause DH clinically, were measured using validated biocomputational methods with CLSM images of dentine surfaces taken baseline and post-intervention. Randomised samples (n = 15, 20 %) were investigated using AFM, EDX and SEM to study surface and sub-surface tubular occlusion. Dentine surface and inter-tubular roughness were measured using CP and AFM respectively.

RESULTS

At baseline, mean tubule patency in all samples was 216 (SD 58) with no significant inter-group differences. Post-intervention, the mean patency was 220 (40) and 208 (35) in groups 1 and 2 respectively (p ≥ 0.06), but decreased to 62 (41), 62 (21) and 63 (19) in groups 3, 4 and 5 respectively (p < 0.0001). Patency was confirmed using AFM, SEM and EDX. SnF2 interventions created greater sub-surface occlusion (p < 0.01), and increased CP surface roughness (p = 0.015). Significant negative correlation (-0.6) existed between CP surface roughness and tubule patency (p = 0.009).

CONCLUSIONS

Dab-on with NaF and SnF2 or brushing with SnF2 reduces DH in eroded dentine with ongoing acid challenges. Contacting surface roughness measures indicate risk of DH.

CLINICAL SIGNIFICANCE

Dab-on is a convenient supplementary method of dentifrice application to reduce DH; it beneficially avoids brushing post-erosion or overzealous brushing, enables re-establishment of an appropriate brushing regime post-DH and supports oral health. Significant modes of action of SnF2 in reducing DH are revealed. Finally, CP roughness measures provide indication of dentine lesions that may cause DH clinically.

Atomic force microscopy visualization of injuries in Enterococcus faecalis surface caused by Er,Cr:YSGG and diode lasers

Aim: To visualize by Atomic Force Microscopy the alterations induced on Enterococcus. faecalis surface after treatment with 2 types of laser: Erbium chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser and Diode laser. Material and Methods: Bacterial suspensions from overnight cultures of E. faecalis were irradiated during 30 seconds with the laser-lights at 1 W and 2 W of power, leaving one untreated sample as control. Surface alterations on treated E. faecalis were visualized by Atomic Force Microscopy (AFM) and its surface roughness determined. Results: AFM imaging showed that at high potency of laser both cell morphology and surface roughness resulted altered, and that several cell lysis signs were easily visualized. Surface roughness clearly increase after the treatment with Er,Cr:YSGG at 2W of power, while the other treatments gave similar values of surface roughness. The effect of lasers on bacterial surfaces visualized by AFM revealed drastic alterations. Conclusions: AFM is a good tool to evaluate surface injuries after laser treatment; and could constitute a measure of antimicrobial effect that can complete data obtained by determination of microbial viability.

Key words:Atomic force microscopy, Er,Cr:YSGG laser, diode laser, Enterococcus faecalis, surface roughness.