Table 1 The demographic data and variables assignment of this study

Patient level (third level)

N = 58

 Age, years

Continuity variable

45.00 ± 12.56

 Gender

Male = 1/female = 2

34/24

 Smoking

Smoking = 0/non-smoking = 1

40/18

 BMI, kg/m²

Continuity variable

24.97 ± 2.57

 Compliance

Complete compliance = 1/irregular compliance = 2

32/26

 Percentage of baseline PD ≥ 5 mm

Continuity variable

34.75 ± 16.24

 OHA score, point

Continuity variable

6.52 ± 1.23

 Education

High school degree or below = 1/bachelor's degree = 2/postgraduate degree or above = 3

27/24/7

Tooth level (second level)

N = 1162

 Baseline BI

0/1/2/3/4/5

0/102/342/450/268/0

 Tooth type

Single tooth = 1/multiple teeth = 2

708/454

 TM, degree

0 degree = 0/I degree = 1/II degree = 2/III degree = 3

936/138/71/17

 CAL, mm

Continuity variable

4.26 ± 1.22

Site level (first level)

N = 3126

 Baseline PD

Continuity variable

5.69 ± 1.08

 Site location

Mesio-buccal, disto-buccal, mesio-lingual, disto-lingual sites = 1/mid-buccal, mid-lingual site = 2

2714/412