4Quek SL, Tay CK,Tay KH,et al. Pattern of third molar impaction in a Singapore Chinese population: A retrospective radiographic survey [J]. Int J Oral Maxillofae Surg 2003,32(5) :548-552.
5Morris CR,Jerman AC. Panoramic radiographic survey: A study of embedded third molars[J]. J Oral Surg, 1971,29(2) : 122-125.
6Chu FC, Li TK, Lui VK,et al. Prevalence of impacted teeth and asso- dated pathologies-a radiographic study of the Hong Kong Chinese population[J]. Hong Kong Med J,2003,9(3) :158-163.