Table 4. The distance between the root apex of impacted third molar and the outer border of the lingual plate as measured on cross-sectional CBCT image (Point A to C in Fig. 2E and Supplementary Fig. 1D).

Type	No. of tooth	Distance(mm)	P-value
Non-contact	99	3.15 ± 0.80	<0.0001#
Contact	145	1.35 ± 0.47
Perforation	120	1.12 ± 0.85*

*Perforation type is defined when the tooth apex perforates beyond the outer border of the lingual plate. The distance between the root apex and the outer border of lingual plate is measured as shown in Supplementary Fig. 1. ^#P-value showed here is the result comparing the distance values between non-contact and contact group by Student-t test.