Effect of opalescent porcelain enamel powder on the chrominance of alumina all-ceramic crowns 
Liu Li, Zhou Qiong-ying, Ding Xiao-qing
Chinese Journal of Tissue Engineering Research . 2012, (12): 2167 -2170 .  DOI: 10.3969/j.issn.1673-8225.2012.12.018