[Darkfield or phase contrast microscopy. Usefulness in periodontology]

Microscopic evaluation of a dental plaque sample is not very useful, since the bacteria are difficult to distinguish from the diluent (same refractive index). Two types of microscopic analyses try to solve this problem in a different way. Using a darkfield microscope, the object is illuminated by slanting rays of light, that are then dispersed or bent away and enter the object. In this way, a shining image on a dark background is formed. The phase contrast microscope uses two principles of the geometry (wave length and amplitude) to create an image of the illuminated cells. Methodologically the next aspects are important, since they strongly influence the outcome of the analysis: contamination of the sample, technique of sampling and preparation of the sample. The reproducibility of the above mentioned techniques is high when a great number of parameters is kept constant. The analysis of the sample give us some clinically relevant information.