I am particularly interested in MC3T3-E1 cells (mouse fibroblasts), which are adherent cells. Are hemidesmosomes involved in anchoring the cells to the plastic dish? What (if any) other molecules are involved? What happens at the molecular level?
I doubt that hemidesmosomes are much involved in 3T3 adhesion, just because they are characteristic of epithelial cells and fibroblasts are mesenchymal.
You're also raising an important point for in vitro work, which is that adhesion to plastic is a very imperfect substitute for ECM, and this probably has implications for the behavior of the cells. If you're interested in ECM-dependent processes like migration, adhesion, and invasion, consider coating your plates with collagen or Matrigel.