Equilibrium effects of public goods

"In this paper we consider how the dental industry responded to the addition of fluoride to public drinking water. We take advantage of the staggered introduction of fluoridation throughout the country to analyze the changes in numbers of within-county dentists relative to physicians in the years surrounding the change in fluoridation status. We find a significant decrease in the number of dental establishments and an even larger reduction in the number of employees per firm following fluoridation. We also find that fluoridation in neighboring markets was associated with an increase in own-market dental supply, suggesting that dentists responded to the demand shock by moving from fluoridated areas to close-by markets. Further analysis suggests that some dentists may have retrained as specialists rather than moving geographically. Our estimates imply that the 8 percentage point change in exposure to water fluoridation from 1974 to 1992 may have led to the loss of as many as 0.6 percent of dental establishments and 2.1 percent of dental employees, suggesting a substantial net impact of this public good on the dental profession since its inception"--National Bureau of Economic Research web site.