To observe whether preserved healthy cementum could promote
differentiation of human periodontal ligament cells to
cementoblasts.  Materials and methods  Symmetrical root slices
from each healthy premolar were distributed into either the
control group (cementum removed) or test group (cementum
preserved). After isolation and characterization, human
periodontal ligament cells were inoculated onto root slices for
7 days co-culture. Two slices per group were studied for cell
morphology by scanning electronic microscopy. Twenty-three
slices were detected for expression of cementum attachment
protein and cementum protein 23, two putative cementoblast
markers, by real-time polymerase chain reaction. Twenty slices
were transplanted into nude mice and analysed using histology
and immunohistochemistry for osteopontin and bone sialoprotein
expression after 8 weeks.   Cells of the test group had smoother
fibroblast morphology and higher cementum protein 23 and
cementum attachment protein expression than those of the con