Aggressive Periodontitis/microbiology; Chronic Periodontitis/microbiology; Dental Plaque/microbiology; Gingivitis/microbiology; Gram-Negative Bacteria/isolation & purification; Herpesviridae/isolation & purification; Adolescent; Adult; Aggregatibacter actinomycetemcomitans/isolation & purification; Aggressive Periodontitis/virology; Bacteroides/isolation & purification; Case-Control Studies; Chronic Periodontitis/virology; Cytomegalovirus/isolation & purification; Dental Plaque/virology; Female; Gingivitis/virology; Herpesvirus 1, Human/isolation & purification; Herpesvirus 4, Human/isolation & purification; Humans; Male; Microbiological Techniques; Middle Aged; Periodontal Attachment Loss/microbiology; Periodontal Attachment Loss/virology; Periodontal Pocket/microbiology; Periodontal Pocket/virology; Polymerase Chain Reaction; Porphyromonas gingivalis/isolation & purification; Prevotella intermedia/isolation & purification; RNA, Bacterial/analysis; RNA, Ribosomal, 16S/analysis; Young Adult