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. 2021 Dec 15;21:641. doi: 10.1186/s12903-021-01996-0

Fig. 1.

Fig. 1

Left: An example of single root tooth measurement. Ai, i = 1, …,5 (teeth with one root), is the distance between the inner sides of the open apex; Right: An example of multiple root tooth measurement. Ai, i = 6,7 (teeth with two open apices) is the sum of the distances between the inner sides of the two open apices; and Li, i = 1,…,7, is the length of the seventh teeth