More controversy came in 1872, when an amalgam filling was reported as the cause of death of a Nebraska middle-aged man, resulting in a public outcry against the use of amalgam. His physicians reported that the filling caused swelling of his mouth, throat and windpipe, completely hindering respiration. Given that the involved tooth was a lower second molar, it was later considered very likely that the patient died from Ludwig's Angina, which is a type of cellulitis, rather than mercury poisoning. Another alleged case of "pytalism" causing headache, fever, rapid pulse, metallic taste, loss of appetite, and generalized malaise was reported in 1872 in a female patient following the insertion of eight amalgam fillings. Later, however, another dentist examined the fillings and noted they had, in a short period of time, washed away, and that upon gentle pressure the metal crumbled away. He removed all the fillings with an explorer in three minutes; and concluded poor workmanship alone could have explained the patient's symptoms. Alfred Stock was a German chemist who reported becoming very ill in the 1920s and traced his illness to his amalgam fillings and resulting mercury intoxication. He described his recovery after the fillings were removed and believed that amalgam fillings would come to be seen as a "sin against humanity". Stock had also previously been exposed to toxic levels of mercury vapor during the course of his work, due to his use of liquid mercury in some novel laboratory apparatus he invented. 1990s to present In the 1990s, several governments evaluated the effects of dental amalgam and concluded that the most likely health effects would be due to hypersensitivity or allergy. Germany, Austria, and Canada recommended against placing amalgam in certain individuals such as pregnant women, children, those with renal dysfunction, and those with an allergy to metals. In 2004, the Life Sciences Research Office analyzed studies related to dental amalgam published after 1996 and concluded that mean urinary mercury concentration (μg of Hg/L in urine, HgU) was the most reliable estimate of mercury exposure. It found that those with dental amalgam were unlikely to reach the levels where adverse effects are seen from occupational exposure (35 μg HgU). Some 95% of study participants had μg HgU below 4–5. Chewing gum, particularly for nicotine, along with more amalgam, seemed to pose the greatest risk of increasing exposure. One gum-chewer had 24.8 μg HgU. Studies have shown