Some warn about keeping ascorbic acid in the mouth too long out of fear it might hurt the tooth enamel. Don't believe there is much difference in absorption with a tablet. Personally need many grams to alleviate rhinitis symptoms. In that range one better avoids tablets and capsules for avoiding too many binders and fillers (which aren't that healthy in the long run). I only use pure ascorbic acid powder in water.
One thing which isn't true for ascorbic acid but gets repeated many times, is that there isn't saturation of serum levels at low intakes, but it does increase gradually with higher intakes. For example, one study found that with 20g per day serum ascorbic acid levels are about 10 times higher at all times, than in average without supplementing. Though admittedly that's a 200 times higher intake than from diet. Such levels are still not possible to even reach with a few grams per day.
As both andy and pamojja have already stated, while holding it in your mouth won't increase its absorption rate or improve Vit C's bioavailability, it will melt you molars. And your other teeth, as well. Don;t recommend.