Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): Incisor enamel defects in peri^lacZ null mice. Backscatter scanning electron microscopy images of wild-type (upper) and null (lower) 3-month-old maxillary incisors show clefting of the enamel surface in only the periostin-deficient incisors. Note that the null teeth exhibit a complete deformation of the enamel surface that affects the incisor from the apex to the incisal edge. (See related article on p. 11131.)