Table 1. Characteristics of the 22 included studies in this meta-analysis.

Reference	Nation	Clinical type	OLP(n/N)	Control(n/N)	Detection method	HPV genotypes
Pol CA et al., 2015	India		21/30	0/30	IHC	HPV16
Arirachakaran P et al., 2013	Thailand		1/37	0/37	PCR	NA
Yildirim B et al., 2011	Turkey		14/65	0/15	IHC	HPV16
Debanth S et al., 2009	India		6/6	3/35	PCR	HPV16, 18, 31, 33, 35, 39, 45, 51,52, 56, 58, 59,68
Fehér E et al., 2009	Hungary		39/119	3/72	PCR	HPV6.11.16.18.31.33
Razavi SM et al., 2009	Iran		9/29	1/14	PCR	HPV18
Szarka K et al., 2009	Hungary		39/119	3/72	PCR	NA
		EA-OLP	26/61	3/72
		non-EA-OLP	13/58	3/72
Yu Hong et al., 2007	China		33/57	3/20	PCR	HPV16
Cianfriglia F et al., 2006	Italy		3/15	2/10	ISH	NA
Giovannelli L et al., 2006	Italy		12/49	11/49	PCR	NA
Campisi G et al., 2004	Italy		14/71	5/90	PCR	HPV16.18.31.6
		EA-OLP	9/44	5/90
		non-EA-OLP	5/27	5/90
Ma Jian et al., 2003	China		26/30	5/18	PCR	NA
OFlatharta C et al., 2003	Ireland		10/38	0/20	PCR	HPV16
Giovannelli L et al., 2002	Italy		9/34	5/90	PCR	NA
Li Hui et al., 2000	China		9/30	3/40	PCR	NA
Sand L et al., 2000	Sweden		6/22	0/12	NA	NA
Qi Yanchun et al., 1999	China		9/30	3/40	PCR	NA
Lei Lei et al., 1997	China		9/22	2/10	PCR	NA
		EA-OLP	3/4	2/10
		non-EA-OLP	6/18	2/10
Vespe M et al., 1997	Germany		3/7	0/33	PCR	HPV16.18.31
Boyd AS et al., 1996	USA		11/13	0/10	PCR	NA
Cox M et al., 1993	UK		3/4	3/5	PCR	HPV16
Maitland NJ et al., 1987	UK		7/8	5/12	PCR	HPV16

n: numbers of HPV positive subjects; N: numbers of total subjects; IHC: immunohistochemical staining; PCR: polymerase chain reaction; ISH: in situ hybridization; NA: not available; EA-OLP: erosive-atrophic oral lichen planus; non-EA-OLP: non-erosive-atrophic oral lichen planus.