Parameters Severity criteria
Anatomical
Size of periapical radiolucencya (S) S0: radiolucency does not exceed 2 times the width of the lateral periodontal ligament space;
S1: diameter of well-defined radiolucency up to 3 mm;
S2: diameter of well-defined radiolucency 3 : 5 mm;
S3: diameter of well-defined radiolucency > 5 mm
Relationship between dental root and periapical radiolucency (R) R1: radiolucency appears on one root;
R2: radiolucency appears on more than one root;
R3: radiolucency involves furcation area
Location of radiographically detected bone destruction (D) D1: radiolucency around root apex;
D2: radiolucency is in contact with important anatomical structures;
D3: destruction of cortical bone
Treatment-related
Canal obturation length (L) L0: no obturation material radiographically visible in pulp chamber and in root canal space;
L1: obturation material visible in root canal space, 0 : 2 mm from radiographic root apex;
L2: obturation material visible in root canal space, > 2 mm from radiographic root apex;
L3: extrusion of obturation material through root apex;
L4: obturation material radiographically visible only in pulp chamber
Obturation homogeneity (H) H0: no obturation material radiographically visible in root canal;
H1: homogenous appearance of obturation material in root canal space;
H2: voids and porosity of obturation material in root canal space
Coronal seal (CS) CS0: no coronal restoration;
CS1: adequate/coronal restoration appears intact radiographically;
CS2: inadequate (detectable radiographic signs of overhangs, open margins, recurrent caries, or lost coronal restoration)

Presence of complications/failures (root perforation,
untreated/missed root canal, root resorption, root/tooth fracture,
endodontically treated root with radiolucency, instrument fracture in root canal) (CF)

CF0: no;
CF1: yes
Post inside root canal (P) P0: no;
P1: yes

Assessment criteria of anatomical and treatment-related parameters adapted from Venskutonis et al. [17]
aPeriapical lesion on the digital periapical radiography was defined as a radiolucency located in the periapical area of the tooth in connection with the apical part of the root exceeding at least twice the width of the periodontal ligament space [5].
For the cone-beam computed tomography images, the same criterion was applied, and the radiolucency had to be visible at least in two image planes.