@Praveen.S
Acrodonts are attached on the top surface of the jaw bone as in fish and amphibians. This type of attachment is not very strong and teeth are lost easily and are replaced by new ones.
Pleurodont: These are attached on the inner side and uppper side of the jawbone that brings larger surface area of tooth in contact with jawbone and hence attachment is stronger, as in lizards and urodeles (salamander). But this attachment is also not as strong as thecodont.
Thecodont are those which is completely enclosed in a deep socket of bone, as seen in crocodile, dinosaurs and mammals. It makes the attachment stronger in vertebrates as compare to pleurodont and acrodont.