 This was called the "focal infection theory", and it led some dentists to advocate dental extraction.In the 1930s, this theory was discredited, but the theory was recently revived by a book entitled "Root Canal Cover-Up Exposed" which used the early discredited research, and further complicated by epidemiological studies which found correlations between periodontal disease and heart disease, strokes, and preterm births.The book's author, George Meinig, has been a strong advocate against endodontic therapy for years; he has since lost his dental license for gross negligence and "Root Canal Cover-Up Exposed" has come under great criticism.