Purpose: The aim of this study was to verify how the prevalence of viridans-streptococci is changed by two appointments of professional prophylaxis and after the subgingival instrumentation via scaling and root planing (SRP). Material and Methods: Samples of the subgingival biofilm were collected from 19 individuals with periodontitis receiving two appointments of professional prophylaxis and SRP before and after the treatment procedures and the presence of viridans-streptococci was analysed by microbiological cultivation. Non-parametric statistical testing using Friedman/Wilcoxon tests and chi-square testing was used for statistical analysis. Results: No statistically significant changes over time were found for the mutans-group. The prevalence of Streptococcus mitis decreased after two appointments of professional prophylaxis (p = 0.013). The prevalence of S. mitis decreased again after SRP (p <0.001). The prevalence of Streptococcus anginosus decreased after two appointments of professional prophylaxis (p = 0.002). After SRP five positive results for S. anginosus were detected (p = 0.026). For Streptococcus oralis and Streptococcus gordonii tendencies to statistical significance were found. The number of positive results for S. oralis increased after the first appointment of professional oral prophylaxis (p = 0.055). The number of positive results for S. gordonii increased after the first appointment of professional oral prophylaxis (p = 0.055). Conclusion: The step-wise periodontal therapy influences the prevalence of viridans-streptococci, especially S. mitis and S. anginosus. No tremendous increase of streptococci especially related to the carious process occurs in the subgingival biofilm. Clinical Relevance: The study reveals knowledge on changes of the composition of the subgingival biofilm due to different steps of periodontal therapy.
Keywords: periodontitis; professional dental prophylaxis; subgingival biofilm; subgingival instrumentation; viridans-streptococci.