A Twitter button or widget loads on your page by Twitter’s JavaScript scanning the DOM for an element + classname it recognizes and interpreting the result. You may also dynamically insert using our JavaScript factory functions.
If you are inserting new HTML into a page after Twitter’s widgets JavaScript has loaded and performed its initial scan of the page you’ll need to trigger a new scan by calling twttr.widgets.load().
You may also use a JavaScript factory function such as twttr.widgets.createTweet() to insert a single Tweet.