Table 1. Characteristics of the included studies.

No	Author	Year	Sample	Age	Gender	Country	Region	Race	Population
1	Massler and Frankel 6	1951	2758	14-18	M=1238, F=1520	America	America	Caucasian	Schoolchildren
2	Goose et al. 7	1957	2956	7-15	Not mentioned	Britain	Europe	Caucasian	Schoolchildren
3	Mills 8	1966	1455	8-17	M=719, F=736	America	America	Caucasian	Schoolchildren
4	Grewe et al. 9	1968	651	9-14	M=322, F=329	America	America	Caucasian	Community
5	Helm 10	1968	1700	6-18	M=742, F=958	Denmark	Europe	Caucasian	Schoolchildren
6	Thilander and Myrberg 11	1973	6398	7-13	M=3093, F=3305	Sweden	Europe	Caucasian	Schoolchildren
7	Foster and Day 12	1974	1000	12	Not mentioned	Britain	Europe	Caucasian	Schoolchildren
8	Ingervall et al. 13	1978	389	21-54	M=389, F=0	Sweden	Europe	Caucasian	Military service
9	Helm and Prydso 14	1979	1536	14-18	Not mentioned	Denmark	Europe	Caucasian	Schoolchildren
10	Lee et al. 15	1980	2092	17-21	M=1281, F=811	Korea	Asia	Mongoloids	Community
11	Gardiner 16	1982	479	10-12	Not mentioned	Libya	Africa	Caucasian	Community
12	De Muňiz 17	1986	1554	12-13	M=655, F=899	Argentine	America	Caucasian	Schoolchildren
13	Kerosuo et al. 18	1988	642	11-18	M=340, F=302	Tanzania	Africa	Africans	Schoolchildren
14	Woon et al. 19	1989	347	15-19	Not mentioned	China	Asia	Mongoloids	Community
15	Al-Emran et al. 20	1990	500	14	M=500, F=0	Saudia	Asia	Caucasian	Schoolchildren
16	El-Mangoury and Mostafa 21	1990	501	18-24	M=231, F=270	Egypt	Africa	Caucasian	Community
17	Lew et al. 22	1993	1050	12-14	Not mentioned	China	Asia	Mongoloids	Schoolchildren
18	Tang 23	1994	201	20	Not mentioned	China	Asia	Mongoloids	Community
19	Harrison and Davis 24	1996	1438	7-15	Not mentioned	Canada	America	Caucasian	Community
20	Ng’ang’a et al. 25	1996	919	7-15	M=468, F=451	Kenya	Africa	Africans	Community
21	Ben-Bassat et al. 26	1997	939	6-13	M=442, F=497	Israel	Asia	Caucasian	Schoolchildren
22	Proffit et al. 27	1998	14000	8-50	Not mentioned	America	America	Caucasian	Community
23	Dacosta 28	1999	1028	11-18	M= 484, F=544	Nigeria	Africa	Africans	Community
24	Saleh 29	1999	851	9-15	M=446, F=405	Lebanon	Asia	Caucasian	Schoolchildren
25	Esa et al. 30	2001	1519	12-13	M=772, F=747	Malaysia	Asia	Mongoloids	Schoolchildren
26	Thilander et al. 31	2001	4724	5-17	M=2371, F=2353	Colombia	America	Caucasian	Heath center
27	Freitas et al. 32	2002	520	11-15	M=250, F=270	Brazil	America	Caucasian	Schoolchildren
28	Bataringaya 33	2004	402	14	M=141, F=261	Uganda	Africa	Africans	Schoolchildren
29	Onyeaso 34	2004	636	12-17	M=334, F=302	Nigeria	Africa	Africans	Schoolchildren
30	Tausche et al. 35	2004	197	6-8	M=970, F=1005	Germany	Europe	Caucasian	Schoolchildren
31	Abu Alhaija et al. 36	2005	1003	13-15	M=619, F=384	Jordan	Asia	Caucasian	Schoolchildren
32	Ali and Abdo 37	2005	1000	7-12	M=501, F=499	Yemen	Asia	Caucasian	Schoolchildren
33	Behbehani et al. 38	2005	1299	13-14	M=674, F=625	Kuwait	Asia	Caucasian	Schoolchildren
34	Ciuffolo et al. 39	2005	810	11-14	M=434, F=376	Italy	Europe	Caucasian	Schoolchildren
35	Karaiskos 40	2005	395	9	Not mentioned	Canada	America	Caucasian	Schoolchildren
36	Ahangar Atashi 41	2007	398	13-15	Not mentioned	Iran	Asia	Caucasian	Community
37	Gelgör et al. 42	2007	810	11-14	M=1125, F=1204	Turkey	Europe	Caucasian	Health center
38	Jonsson et al. 43	2007	829	31-44	M=342, F=487	Iceland	Europe	Caucasian	Schoolchildren
39	Josefsson et al. 44	2007	493	12-13	Not mentioned	Sweden	Europe	Caucasian	Schoolchildren
40	Ajayi 45	2008	441	11-18	M=229, F=212	Nigeria	Africa	Africans	Schoolchildren
41	Mtaya 46	2008	1601	12-14	M=632, F=969	Tanzania	Africa	Africans	Schoolchildren
42	Borzabadi-Farahani et al. 47	2009	502	11-14	M=249, F=253	Iran	Asia	Caucasian	Schoolchildren
43	Daniel et al. 48	2009	407	9-12	M= 191, F=216	Brazil	America	Caucasian	Schoolchildren
44	Šidlauskas and Lopatienė 49	2009	1681	7-15	M=672, F=1009	Lithuania	Europe	Caucasian	Schoolchildren
45	Alhammadi 50	2010	1000	18-25	M=500, F=1000	Yemen	Asia	Caucasian	Schoolchildren
46	Bhardwaj et al. 51	2011	622	16-17	M= 365, F=257	India	Asia	Caucasian	Schoolchildren
47	Nainani and Relan 52	2011	436	12-15	M= 224, F=212	India	Asia	Caucasian	Schoolchildren
48	Bugaighis et al. 53	2013	343	12-17	M=169, F=174	Libya	Africa	Caucasian	Schoolchildren
49	Kaur et al. 54	2013	2400	13-17	M=1192, F=1208	India	Asia	Caucasian	Schoolchildren
50	Reddy et al. 55	2013	2135	6-10	M=1009, F=1126	India	Asia	Caucasian	Schoolchildren
51	Bilgic F et al. 56	2015	2329	12.5-16.2	M=1125, F=1204	Turkey	Europe	Caucasian	Schoolchildren
52	Gupta et al. 57	2016	500	12-17	M=1125, F=1204	India	Asia	Caucasian	Schoolchildren
53	Narayanan et al. 58	2016	2366	10-12	M=1281, F=1085	India	Asia	Caucasian	Schoolchildren

M = male; F = female.