Directed acyclic graph (DAG).

<p>A = Material group characteristics; B = Measured laboratory outcome; C = True clinical outcome; D = Type of dentition; E = Type of tooth; F = Position of tooth in oral cavity; G = Type/Size of tooth cavity; H = Oral hygiene/habits of patient(s); I = Unknown influencing factors; J = Number of units evaluated (laboratory); K = Specimen selection process; L = Type of measurement; M = Quality /Characteristics of measurement procedure/evaluation process; N = Foreknowledge; O = Measured clinical outcome; P = Group characteristics; Q = Group selection process (randomisation); R = Number of units at baseline; S = Number of units evaluated (clinical); T = Number of units lost-to-follow-up.