STP in Caries Protection: A Study by SEM and EDAX

Objectives: This study utilises scanning electron microscopy (SEM) in back scattering detection (BSD) mode and energy dispersive x-ray analysis (EDAX) to investigate the presence of artificial caries lesions in enamel, formed by cariogenic acid challenge. A comparison was made between human enamel treated and not treated with sodium tripolyphosphate (STP) solutions to investigate the efficacy of STP for the protection of enamel against the formation of caries.

Methods: Human enamel specimens (n=6) were pre-treated with either (i) water (ii) 5.0% STP or (iii) 10% STP for 2 minutes and then an insipient lesion was formed to mimic an in vivo caries using a variation of the FDA caries lesion method #40. Thereafter, enamel specimens were sectioned longitudinally and imaged by SEM using BSD. EDAX was employed to collect elemental maps for calcium and phosphorous to reveal the extent of the sub-surface lesion.

Results: BSD images of the control group showed a morphological re-structuring of the enamel extending some 30 micrometers below the enamel surface. The EDAX analysis mirrored the SEM image showing a dark band, devoid of calcium and phosphorous, that was some 5 micrometers wide and 30 micrometers below the enamel surface. Enamel specimens pre-treated with a 5% STP solution show considerably less sub-surface de-mineralisation when compared to the control group. Enamel treated with 10% STP solution did not provide any significant additional protection.

Conclusion: SEM using back-scattering detection coupled with simultaneous EDAX provides a rapid and compelling method for the study of sub-surface lesions and can be useful as a method for screening new actives. The results after cariogenic acid challenge show that STP solutions may be used to prevent the formation of artificial caries in vitro.