Seems like a problem for jQuery. Check this answer for the entire-element capitalization, then you can parse the first sentence by using something like:
var setval = $('#my_paragraph').html();
var firstSentence = setval.substring(0, setval.indexOf('.'));
firstSentence = toProperCase(firstSentence);
var theRest = setval.substring(setval.indexOf('.') + 1);
$('#my_paragraph').html(firstSentence + theRest);