Table 3. The thickness of the lingual plate at the level of the root apex of impacted third molar as measured on cross-sectional CBCT image (Point B to C in Fig. 2E).

Type	No. of tooth	Thickness (mm)	P-value
Non-contact	99	1.77 ± 0.50	<0.0001#
Contact	145	1.35 ± 0.47
Perforation	120	0.00 ± 0.00*

*When the tooth apex perforates beyond the outer border of lingual plate as defined as perforation type, the thickness of lingual plate is record as 0 mm. ^#P-value showed here is the result comparing the distance values between non-contact and contact group by Student-t test.