Apical constriction (Physiological foramen)
- is considered narrowest diameter of root canal.
- located at the cementum-dentinal junction.
- is the apical limit of the root canal preparation.
- is also known as the histological foramen, because it is located at the junction between the pulpal connective and interstitial loose connective tissues of the periodontal ligament.
- not visible on x-ray (we may find it only using WL determination methods).
Apical foramen (Anatomical foramen)
- Opening at the root surface through which pass nerves and blood vessels.
Between apical constriction and apical foramen, cell-rich connective (periodontal) tissue is found. After proper RCT, this tissue may start the apposition of cementum like cells to create hard tissue for closure of the root canal apically.
Radiographic apex (Anatomical apex), Radiographic vertex (True apex)
- highest point of the root seen on X-ray.
- may correspond to apical foramen or (usually) not.
According to research the average distances are:
- apical constriction–apical foramen ~0.5-0.8mm.
- apical foramen–radiographic apex ~0-0.3mm.
- apical constriction–radiographic apex ~up to 1.1mm.