If you have view caching enabled the layout/set output should be cached. The layout/set module view simply internally reruns the url without the layout/set/[layoutname] after setting some parameters so the correct pagelayout is used (it's actually pretty cool how it works)
Are you sure the view cache is not being generated? You should be able to tell if you turn on debugging and access http://dentsply.ca/layout/set/ajax/content/view/ajax/552 a number of times and compare the timing table between accesses.
