I occasionally hear people saying that coffee has bad implications for the health of teeth. Are there any significant dental studies proving/disproving this statement?
A recent study published in Letters in Applied Microbiology suggests that coffee can break down bacterial plaques that form on teeth. These studies were done in a lab on extracted teeth, using moderate amounts of coffee on lab-grown plaques formed by bacteria from saliva. Antibacterial effect of coffee: calcium concentration in a culture containing teeth/biofilm exposed to Coffea Canephora aqueous extract, Letters in Applied Microbiology, Volume 59, Issue 3, September 2014, Pages: 342–347, N. Meckelburg et al.
Coffee can stain teeth. Is that a health issue? It's often listed with other dental health issues but I'm not sure why.
The acidity of coffee may wear down teeth over time, but it's not a prime suspect. The acidity of coffee generally falls somewhere between that of pure water and cow's milk, according to one article. Fruit juice and soft drinks are far more acidic (pH < 3). Coffee is only slightly more acidic than saliva. There is no shortage of articles claiming high acidity of coffee but a pH of 5--a plausible average--is not very high.
There are probably hundreds of studies in English alone on the effect of coffee on dental health. In terms of acidity it's not as bad as juice and not as benign as water. The plaque-preventive effect is something new to consider. There is also a 2012 study by the American Cancer Society suggesting that coffee lowers the risk of oral cancer. Those who drank 4+ cups of coffee a day were about half as likely to die of oral/pharyngeal cancer as those who drank occasionally or not at all. Coffee, Tea, and Fatal Oral/Pharyngeal Cancer in a Large Prospective U.S. Cohort, American Journal of Epidemiology, Dec. 2012 (online), Hildebrand et al. To the extent that oral cancer is a dental health issue this is also something to weigh.
Science doesn't necessarily furnish a simple answer. It appears that the mildly corrosive effect of coffee may be offset by a tendency to reduce plaque. If coffee helps reduce the risk of oral cancer one could argue that, overall, the benefits of coffee for dental health outweigh the risks.