Every year, most unis tend to 'over-offer'. Say there were about 45 spots for dentistry at La Trobe. They may have offered 70 places (I have no idea what it was in reality, this is just a guess), expecting at least ~30 people to reject the offer as tends to happen every year. However, what happened this year was unprecedented; almost everyone ended up accepting the offer, and seeing as dentistry is restricted by the number of dental training chairs available, a uni cannot just take in as many dental students as it wants.
So obviously there's a problem, about 20-30 people aren't able to do dentistry this year after enrolling and taking up their offer. La Trobe generously gave them a guaranteed place in for next year, as well as $30k towards hecs. Basically, if you're trying to get into dent this year at La Trobe, there will probably only be about 5-10 places to compete for as opposed to the normal 30 or so places for metro kids. So yes, if dent at La Trobe was hard to get into in previous years, it will be extremely, extremely difficult to get into this year.