Diederik Hentenaar

149 General discussion and conclusions air-polishing after a treatment time up to 1 minute, showed a range of pocket depth reductions (between 0.1 mm and 1mm) and changes in average marginal bone loss (0.1mm (±0.8)) comparable to the results of our non-surgical study. In general, it should however be kept in mind that patients characteristics, the presence of suprastructures and anatomical limitations of the oral cavity (e.g. the tongue) are confounders in a clinical setting which could overshadow possible beneficial in-vitro effects. Hence, the true effect of the different parameters mentioned above on the clinical outcome remain to be found. Microbiologically, no significant difference between therapies, neither after the non- surgical nor after the surgical intervention was found. Also no difference in levels of periodontal pathogens were seen when the successfully treated patients in the non- surgical setting were compared to the unsuccessful ones. These relatively unchanged counts 3 and 12 months after respectively a non-surgical and surgical intervention are difficult to understand. Whether for example fast bacterial regrowth or the method of bacterial sampling are underlying causes remain to be found. Moreover, in our studies we used targeted quantitative PCR analysis to investigated the presence of a number of putative bacterial species, both in natural teeth and implants. Although the investigated periodontal species may be considered marker species for periodontitis (Griffen et al., 2012), open-ended microbiome studies have shown that the microbiomes associated with periodontitis and peri-implantitis show major differences (Kumar et al., 2012; Dabdoub et al., 2013; Lafaurie et al., 2017; Sahrmann et al., 2020). The microbiome in peri-implantitis seems associated with predominantly non-cultivable Gram-negative species and is not associated with a uniform microbial profile. Considering this, with our studies an incomplete picture of the potential changes in composition of the peri- implant and periodontal microbiome could have been found. Although for the majority of patients a non-surgical approach seemed to have a limited effect, a small number of patients did seem to benefit from the non-surgical phase in such a way that the burden of surgical follow-up could be prevented. When baseline characteristics of the patients who were considered successfully treated at 3 month follow-up were compared with the characteristics of the unsuccessful ones, lower probing pocket depths, less marginal bone loss and shorter time of implant function before therapy were seen. Moreover, follow-up of the successful patients showed gradual improvement of peri-implant parameters up to 12 months when supportive peri-implant therapy (supragingival instrumentation when plaque/calculus was visible) and oral self-care reinforcement were applied at 6 and 9 months. Hence, the findings of our study underline the importance of early diagnosis and early commencement of non-surgical therapy. Moreover, as shown in the study presented in chapter 3 , and 7