Therapeutic mineral enrichment of dental plaque visualized by transmission electron microscopy

The form, location, and distribution of fluorhydroxyapatite deposited in dental plaque by a urease-mediated mineral enrichment process have been studied by transmission electron microscopy. Artificial plaque was formed in terylene gauze in the mouth of one subject and immersed for five min four times per day in a mineral-enriching solution. Contralateral control plaque remained untreated. The effect on natural plaque was studied in two subjects who withheld oral hygiene for four days and mouthrinsed with this solution for two min four times per day during the last two days. Mineral deposits were seen in all plaque samples exposed to the test solution. None was detected in any control sample. The deposits were scattered in the interbacterial matrix as needle-shaped crystals, the size and shape of apatite, together with amorphous material. The crystals appeared larger and more perfect, and the amorphous material less conspicuous, with longer in vivo rinsing periods. Platelet-shaped crystals of octacalcium phosphate were never seen. Mineral was also seen within the remnants of dead bacterial cells and within degenerating epithelial cells. Crystals were never seen within intact bacterial cells, as in calculus formation. The presence of a single crystal type and the relative absence of densely-mineralized foci are other differences between this mineral-enrichment process and supra-gingival calculus formation. A longer-term study is necessary to determine whether the solution promotes calculus by providing nucleation seeds.