Nucleating Properties of Hydroxyapatite-Protein-Composites in Human Saliva

Objectives: Toothpastes containing a Hydroxyapatite-Protein-Composite (HPC) have recently been found to restore eroded enamel in vitro, using calcium and phosphate ions from simulated saliva to build up a firmly bound layer of calcium phosphate. Objective of this study was to investigate the restoring properties of HPC using the more complex human saliva.

Methods: An HPC containing toothpaste served as test (TP), an HPC free paste as control (CP), both containing 1450ppm Fluoride. 24 bovine enamel specimens were mounted in cold cure acrylic, polished flat, eroded (6h, lactic acid buffer, pH=4.6) and randomly divided into 2 groups. Specimens were brushed with 1:1 slurries of either TP or CP in water (1min, 150g load, twice daily, 15d). In between treatments specimens were stored in non-pooled human saliva of 6 volunteers (37°C, 2ml/sample, 2 samples per group and volunteer). Specimens were examined by electron microscopy before and after treatment. Image analysis was done by 3 examiners trained with exemplary images. Surface restoration was assessed by a three step classification systems on the visibility of enamel prisms.

Results: Before treatment all specimens showed clearly visible prisms. After treatment specimens were classified as follows

	prism visibility
Product	clearly visible	visible	not visible
TP (% of specimens)	0	40	60
CP (% of specimens)	25	75	0

Cross sectioning of samples with non visible prisms showed the formation of a layer 1.3µm in thickness.

Conclusion: Most specimens showed a slight smoothening of the surface due to saliva.

TP additionally restores eroded enamel surfaces by forming a solid layer of calcium phosphate also with human saliva as calcium and phosphate source. However, the intensity of this effect varies from individual to individual.