The findings in the York Review [ 28 ] that children in fluoridated regions had an average of % less dental caries is in part reflection of increasing critical assessment of the benefits of community water fluoridation and the impact of improved oral hygiene or other factors. A survey of 55 reputable oral health specialists on the impacts of artificial water fluoridation and other preventive technologies on the decline in dental caries prevalence over the past four decades in most nations revealed that, apart from fluoridated toothpaste, there were conflicting responses on the impact of artificial water fluoridation and other fluoride-based technologies [ 32 ]. Studies focused on dental caries trends following cessation of fluoridation have produced contradictory results, in part due to study technique, availability of other fluoride sources, and consumption patterns of cariogenic foods [ 33 , 34 ].
Many web sites benefit from a network effect. One example is web marketplaces and exchanges. For example, eBay would not be a particularly useful site if auctions were not competitive. However, as the number of users grows on eBay, auctions grow more competitive, pushing up the prices of bids on items. This makes it more worthwhile to sell on eBay and brings more sellers onto eBay, which drives prices down again as this increases supply, while bringing more people onto eBay because there are more things being sold that people want. Essentially, as the number of users of eBay grows, prices fall and supply increases, and more and more people find the site to be useful.