## 4 Discussion  
The hypothesis of this study, based on previous research that suggests a link between peritonsillar infection and periodontitis, was that the bacteriological and clinical outcomes of tonsillectomy could influence the diagnosis and treatment of CP [29]. It has previously been suggested that the niches around the palatine tonsils are the sources of bacterial infection for the periodontal area [18; 23]. Unexpectedly, this study revealed that the adjusted EV of the number of post-ID CP did not reach statistical significance in any post-ID year. In another subgroup analysis according to the number of pre-ID CP, statistical significance was not found in any analysis. These findings oppose the assumption made by [PERSON] et al., although limitations of this study should be further discussed [18]. Tonsillectomy, including removal of the biofilm, has a positive effect on the intraoral areas such as the gingiva and tongue. A previous study reported that the microorganisms in the tongue area were altered following tonsillectomy [26]. The study showed that _Tannerella forythia_ and _Porphyomonas gingivalis_ levels decreased in samples taken from the tongue after tonsillectomy [26]. This result could be explained by how anatomically close the tongue and tonsils are, and the fact that saliva is exchanged between them while speaking and swallowing. On the contrary, the same study reported that lesser changes occurred in other bacteria levels in the periodontal pocket following tonsillectomy [26]. They suggested that, with regards to the tonsillar area, the periodontal pocket would be more distant and difficult to access than the tongue area. As such, other bacteria in the periodontal pocket may be less affected. We also believe that the risk of developing CP after tonsillectomy was not reduced in our study for this reason. Another reason for the discrepancy between the diagnosis and treatment of CP and tonsillectomy is that the major bacteria in culture-dependent studies of tonsils and the microbiome in culture-independent 16 s sequencing studies are _Streptococcus_ and _Haemophilus influenzae_[8; 30]. However, the essential microbiome in CP was _Porpyomonas gingivalis_, which can increase the activity of biofilm bacteria by interrupting homeostasis in the host. Our findings could be explained by the improvements that occur with regards to mouth breathing following tonsillectomy. Tonsillectomy can eliminate breathing problems such as snoring or mouth  
Figure 3: Subgroup analyses of simple and multiple linear regression models (estimated value [95% confidence interval]) for post-index date of CP (post-ID CP) periods in tonsillectomy and control groups according to pre-index date of CP (pre-ID CP) for 2 years. breathing [31], which is likely to increase the risk of periodontitis. [PERSON] et al. have reported that a patient's periodontal condition is influenced by mouth breathing even after periodontal treatment such as scaling and root planning [32]. Mouth breathing also induces a dry condition in the intraoral area, which could increase the possibility of periodontitis. This hypothesis was explained in another study, suggesting that the salivary substitute had a positive effect on the periodontal condition in mouth breathing patients with CP [33]. According to these studies, tonsillectomy might reduce mouth breathing, and improved mouth breathing could have a beneficial effect on periodontitis. This study has four advantages. The first is the large number of study participants (n = 5220). Participants were followed up for a maximum of 13 years following tonsillectomy, whereas a similar study only conducted a 3-year follow-up [29]. Secondly, the Korean National Health Insurance Service-Health Screening Cohort dataset is a large national survey that is representative of the Korean population. These cohort records were available for each participant, and the records used in our study were not distorted by the memory of participants.