Effect of different crown contours on periodontal health in dogs. Microbiological results

Objectives. In some clinical circumstances, i.e. in cases when the upper anterior region has to be restored by prosthetic means, it is necessary to place the margins of crowns and fixed partial dentures subgingivally. In addition, in periodontally compromised patients the restoration sometimes has to be overcontoured in order to replace the lost interdental papilla. The overcontoured crown margin may influence the subgingival bacterial composition. Therefore, the aim of the present investigation was to evaluate the effect of three different subgingival crown contours in dogs on the composition of the subgingival microbiota. Methods. In four adult beagle dogs the second and third premolars were prepared in three quadrants and restored with single gold crowns. The unprepared second and third premolars in the last quadrant served as controls. The crowns had three different emergence profiles including a normal contour, a 30° and a 50° over-contour. During the entire study period, professional oral hygiene was performed seven times a week. Microbiological samples were harvested from four sites of test and control teeth (mesial, distal, buccal and lingual) at baseline, after 3 months, and after 5 months. Results. The microbiological analysis (DNA–DNA hybridization technique) of the subgingival microbial flora revealed a dominance of P. intermedia, T. denticola and C. showae in all test and control groups at baseline. At three months, the total amount of bacteria increased and a broader variety of bacterial species could be detected. The detection frequency of most bacterial species increased from baseline to the 5-month evaluation. The frequency of detection of some species was higher in the 30° and 50° overcontoured test groups compared to the normal contour group and to the natural teeth. Conclusion. It can be concluded within the limits of this investigation that overcontoured gold crowns placed subgingivally have only slight effects on the microbiological composition in dogs when an intensive oral hygiene regimen was executed.