Furthermore, the present analysis failed to identify any significant correlation of either fungal organisms or disease severity with opportunistic bacteria, such as M. salivarium, V. parvula, and S. aureus. At tooth sites, M. salivarium was mainly isolated from the sulcus area and associated with gingivitis lesions [27]. Interestingly, S. aureus has only been identified at one single peri-implantitis - but several healthy implant sites, which is contradictory to the higher prevalence at peri-implantitis sites noted in larger cohorts [4,7,9]. When further analyzing the present data, it was also noted that at several sites, the frequency of selected periodontopathogenic bacteria was below the detection thresholds, irrespective of disease severity. These findings clearly corroborate previous data indicating that these periodontopathogenic bacteria may not necessarily be related to peri-implantitis [6].

Fungal organisms have also been isolated from periodontal pockets in chronic periodontitis patients. The reported prevalence of yeast-positive samples varied between 15.6% and 17.5% [28,29]. These untreated periodontal pockets were also dominated by C. albicans. Other species, such as Candida parapsilosis, C. dubliniensis, Candida tropicalis, and Rhodotorula spp., were rarely observed [30]. Even though the prevalence of C. albicans tended to be higher in chronic periodontitis (30%) when compared with healthy patients (15%), this difference did not reach statistical significance [30]. The present frequency of fungal organisms in subgingival plaque samples obtained from teeth with a history of periodontitis basically corroborates the above reported data but was markedly lower when compared with all implant sites investigated. However, the frequency distribution of periodontopathogenic and opportunistic bacteria did not seem to differ between tooth and implant sites, which is basically in line with a recent analysis assessing Aggregatibacter actinomycetemcomitans, Pg, Prevotella intermedia, Tf, Treponema denticola, S. aureus, enteric bacteria, and P. aeruginosa [10]. In this context, it must be emphasized that the present analysis just focused on the most relevant periodontopathogens associated with peri-implantitis [4] as well as a few opportunistic bacteria [4,7,9,27] that were linked to the oral cavity. Therefore, future analyses should consider a broader spectrum of potential pathogens.