Google uses the old blog title in search results

As a matter of optimization, a few weeks ago I modified the way the titles of my blog posts are displayed (I made a change also in the title of the blog). Then I used the google webmaster tools to re-index the old pages and update titles. Immediately I could update the titles and posts appear correctly on google.

The problem is that now the titles of posts began to appear incorrectly in the search, using the old blog title. Some posts continue to display the updated title, but many recent posts show the old title.

I've tried re-index the pages with google webmaster tools, but the titles remain unchanged in the search results.

Is there any way to "force" google to display the correct titles?