3D-position and Pose of Lower Third Molars

Objectives: Surgical removal of wisdom teeth is among the most common procedures in oral surgery. Basing on 3D-radiography, the goal of this research was to develop a systematic classification describing the variation in anatomical position and pose of lower wisdom teeth and their spatial relation to the mandibular canal, to which injuries rank among the most pertinent surgical complications.
Methods: An innovative classification concentrating on the angular position, root structure, and cranio-caudal height of mandibular wisdom teeth and the spatial relationship to the nerve canal was developed. From our database of existing CBCT scans, a sample comprising 483 CBCTs containing lower third molars were selected. The classification was applied to the data and statistically evaluated.
Results: Our classification comprises three main classes describing the position of the crown in relation to the mandibular bone. Six sub-classes describing the vertical and horizontal position in the mandible plus the angulation of the tooth were established per class. The vertical position was most common (39.8%), followed by vertical mesio-angular (28.6%) and vertical lingual-angular (14.1%) positions. In 41.8% no direct contact to the mandibular nerve was found. Patients with more roots were more likely to experience contact to the nerve: 44.8% of single-root, 55.3% of double-root, 84.6% of triple-root, and 100% of quad-root teeth. The number of contacts decreased the closer the wisdom toothwas to the occlusal plane. Should the wisdom tooth be encompassed by bone, 12.1% exhibit no contact; if it reaches the occlusal plane the likelihood rises to 84.5%.
Conclusions: By implementing the third-dimension, our classification should allow more accurate and realistic position and pose information compared to earlier classifications based on conventional 2D-x-rays. Evaluating patient data using 3D-classification provides surgeons with a statistical overview of potential constellations of lower wisdom teeth and indicates when a higher risk for complication exists.