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2. Nolte, W. A. (1977). Oral Microbiology, 3rd edn, C. V. Mosby, St. Louis, ch. 22
3. Dental Estimates Board Annual Reports, Department of Health and Social Security, HMSO, London
4. Office of Health Economics Information Sheets, 162 Regent Street, London WI
5. Health and Personal Social Services Statistics for England 1977 HMSO, London, p. 20