polysaccharides

Dental Biofilms

This is an exercise which can be carried out to illustrate the presence of biofilms on the teeth of students. It requires no special equipment and very little time. It could be included in a class on oral microbiology or as an object lesson for introductory microbiology students.

The minimal requirement in time and equipment makes this an excellent choice for a lesson in a health related class at the elementary or middle school level. The only material required, is a Dental Plaque Disclosing Agent such as Trace Disclosing Tablets which can be obtained from a local dentist. These tablets are chewed by the student and plaque is revealed as a red stain on the teath. This stain is subsequently removed by brushing. The active ingredients in the Trace product are D and C Red #28.

Addy et al. (1993) describe a number of methods by which the amount of plaque can be quantified. One of these is a modification of the Quigleyand Hine plaque index.

This index evaluates the plaque revealed on the cheek (buccal) side and the tongue (lingual) side of the teeth on a scale from 0 - 5 where:

0 = no plaque
1 = isolated flecks of plaque near the gingival (gum) margin
2 = a 1 mm band of plaque at the gingival margin
3 = up to one-third of the surface covered with plaque
4 = disclosed plaque from one-third to two-thirds of the surface
5 = disclosed plaque on more than two-thirds of the surface

This image shows human dental plaque exposed to 5% sucrose in situ for 5 minutes, after which Gram's iodine (0.33% Iodine in 0.66% KI) was applied.

The sucrose solution was applied to the cheek side of the upper left central incisor while the upper right central incisor served as a control.

Iodine selectively binds to alpha-1,4 glucans such as glycogen or amylose and this results in brown to purple staining.

Safety Note: Please do not use iodine on students. Due to its toxicity, Iodine/Potassium iodide solutions used to reveal plaque should be left in the hands of dental professionals. Obtain nontoxic dental plaque disclosing agents such as "Trace Disclosing Agents" to reveal plaque in students.

The ability of oral bacteria to store iodophilic polysaccharide or glycogen-like molecules inside their cells is associated with dental caries since these storage compounds may extend the time during which lactic acid formation can occur. It is the formation of lactic acid which decalcifies tooth structure.

Many other polysaccharides will stain with Lugol or other iodine preparations so you might try iodine on other sorts of biofilms.

Reference:

Addy, M., M.A.Slayne and W.G. Wade, 1993. Methods for the Study of Dental Plaque Formation and Control, IN Denyer, S.P., S.P. Gorman and M. Sussman, Microbial Biofilms: Formation and Control, Blackwell Scientific Publications, Oxford.