Even if other manufacturers or retailers are available to distribute AMD products, that does not end the inquiry. For example, in Dentsply, the 3d Circuit concluded that a dominant artificial-tooth manufacturer's exclusivity agreements with key dealers harmed competition by keeping its competitors' sales from posing a genuine threat to the monopolist's overwhelming share of the market. The court instructed that the "test is not total foreclosure, but whether the challenged practices bar a substantial number of rivals or severely restrict the market's ambit." Similarly, in the Microsoft case, the court held that exclusion from certain key, cost-efficient manufacturers was exclusionary even though other forms of distribution were available. As former Judge Robert Bork observed more than 30 years ago, "By disturbing optimal distribution patterns one rival can impose costs upon another, that is, force the other to accept the higher costs." See Robert Bork, The Antitrust Paradox 156 (1978).