How did the genes develop that code for dental tissues?

There is growing evidence that genes encoding extracellular
matrix proteins involved in the biomineralization
of bone, dentin, and enamel diverged from a common
ancestor gene. The initial event was the generation of
SPARCL1 (Sparc-like 1) from SPARC (secreted protein,
acidic and rich in cysteine; BM-40/osteonectin) in a chromosome-
wide large segmental duplication that spawned
the chromosomal region ancestral to the long arm of human
chromosome 4. The new gene (SPARCL1) gave rise
to the secretory calcium-binding phosphoprotein (SCPP)
gene family. In the first paper, Kawasaki et al. (Pennsylvania
State University) advance their theory of the evolution
of the SCPP gene family in Gene Duplication and the
Evolution of Vertebrate Skeletal Mineralization.

Source:

Molecular Evolution and Genetic Defects of Teeth, Cells Tissues Organs, 2007