## 3 Results  
Age, sex, income, and region of residence were matched between tonsillectomy and control participants exactly (\(p=1.000\)), while obesity, smoking, and CCI were different (\(p<0.05\), Table 1). The number of CP treatments prior to the index date were matched as the categorical variable. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Characteristics**} & \multicolumn{3}{c}{**Total Participants**} \\ \cline{2-4}  & **Tonsilllectomy (n, \%)** & **Control (n, \%)** & \(p\)**-Value** \\ \hline Age (years old) & & & 1.000 \\ \hline
40–44 & 74 (7.1) & 296 (7.1) & \\
45–49 & 252 (24.1) & 1008 (24.1) & \\
50–54 & 324 (31.0) & 1296 (31.0) & \\
55–59 & 226 (21.7) & 904 (21.7) & \\
60–64 & 100 (9.6) & 400 (9.6) & \\
65–69 & 46 (4.4) & 184 (4.4) & \\
70–74 & 13 (1.3) & 52 (1.3) & \\
75–79 & 6 (0.6) & 24 (0.6) & \\
80–84 & 3 (0.3) & 12 (0.3) & \\ \hline Sex & & & 1.000 \\ \hline Male & 720 (69.0) & 2880 (69.0) & \\ Female & 324 (31.0) & 1296 (31.0) & \\ \hline Income & & & 1.000 \\ \hline
1 (lowest) & 114 (10.9) & 456 (10.9) & \\
2 & 105 (10.1) & 420 (10.1) & \\
3 & 127 (12.2) & 508 (12.2) & \\
4 & 216 (20.7) & 864 (20.7) & \\
5 (highest) & 482 (46.2) & 1928 (46.2) & \\ \hline Region of residence & & & 1.000 \\ \hline Urban & 527 (50.5) & 2108 (50.5) & \\ Rural & 517 (49.5) & 2068 (49.5) & \\ \hline Pre index date of CP & & & 1.000 \\ \hline
0 time & 701 (67.2) & 2804 (67.2) & \\
1 time & 145 (13.9) & 580 (13.9) & \\ \(\geq\)2 times & 198 (19.0) & 792 (19.0) & \\ \hline Obesity \({}^{\ddagger}\) & & & \textless{}0.001 \({}^{*}\) \\ \hline Underweight & 6 (0.6) & 61 (1.5) & \\ Normal & 245 (23.5) & 1436 (34.4) & \\ Overweight & 286 (27.4) & 1143 (27.4) & \\ Obese I & 442 (42.3) & 1427 (34.2) & \\ Obese II & 65 (6.2) & 109 (2.6) & \\ \hline Smoking status & & & 0.019 \({}^{*}\) \\ \hline Nonsmoker & 611 (58.5) & 2483 (59.5) & \\ Past smoker & 193 (18.5) & 633 (15.2) & \\ Current smoker & 240 (23.0) & 1060 (25.4) & \\ \hline Alcohol consumption & & & 0.219 \\ \hline \(<\)1 time a week & 647 (62.0) & 2501 (59.9) & \\ \(\geq\)1 time a week & 397 (38.0) & 1675 (40.1) & \\ \hline CCI score & & & \textless{}0.001 \({}^{*}\) \\ \hline
0 & 713 (68.3) & 3,275 (78.4) & \\
1 & 168 (16.1) & 448 (10.7) & \\
2 & 85 (8.1) & 240 (5.8) & \\
3 & 29 (2.8) & 91 (2.2) & \\ \(\geq\)4 & 49 (4.7) & 122 (2.9) & \\ \hline \hline \end{tabular} Abbreviations: CCI, Charlson comorbidity index: CP, chronic periodontitis. \({}^{*}\) Chi-square test. Significance at \(p<0.05\). \({}^{*}\) Obesity (BMI, body mass index, kg/m\({}^{2}\)) was categorized as \(<\)18.5 (underweight), \(\geq\)18.5 to \(<\)23 (normal), \(\geq\)23 to \(<\)25 (overweight), \(\geq\)25 to \(<\)30 (obese I), and \(\geq\)30 (obese II).  
\end{table} 
Table 1: General Characteristics of Participants. The adjusted estimated value (EV) of the number of post-ID CP did not reach statistical significance in any post-ID year (each of \(p>\) 0.05, Table 2). In the subgroup analyses according to age and sex, statistical significance was only reached in \(\geq\)60-year-old men in post ID 2 y (EV = 0.561, 95% CI = 0.156-0.967, \(p\) = 0.007, Figure 2). In another subgroup analysis according to the number of pre-ID CP, statistical significance was not found in any analysis, see Figure 3.