How to use LHS Top
The red line in the photograph above shows the incisal edge of the left central incisor - just in case you are visually challenged! The ruler is held with its edge at right angles to, and against, the lower incisors. Clearly the incisal edge of the upper left central incisor is within the "4" zone of the ruler. The IOTN coding is then 4 (the grade) and "a" (the category) i.e. 4a.
Watch Video