Question regarding mergers, tender offer, and Rule 10b-5?

Basique was a publicly traded corporation engaged in the business of manufacturing chemical refractories for the steel industry. Because Combus desired to acquire Basique, they engaged in merger negotiations. There a merger by tender offer occured. Stockholders who changed their position before the merger when the denial occured brought an action against Basique erting that the denials were false and misleading under Rule 10b-5 and section 10(b). What should be the test to determind whether Basique has violated 10b-5. Does it matter whether the misrepresentation is material?