Despite their widespread use, dental radiographs have numerous shortcomings for measuring alveolar bone changes. In order to develop guidelines for improving the reliability of radiographic measurements, factors affecting the formation of an image were reviewed. These were considered regarding the design of a clinical monitoring system, capable of detecting the loss of small amounts of alveolar bone crest from serial films. Dentists need a monitoring system to assess whether bone loss is progressing or to judge whether a treatment is successful. 2 models were constructed to predict how long it would take to detect marginal bone loss occurring at a linear rate of 0.1 mm/year. The 1st model assumed a CEJ-crest measurement error of +/- 0.3 mm and the second +/- 0.9 mm, both using a 0.1 mm measuring interval. These error values were derived from the literature. The 1st model predicted it would take between 7 and 13 years for the system to measure a 1.0 mm loss in crest height caused by an actual loss of between 0.7 and 1.3 mm. The 2nd model predicted that a 1.0 mm measurement would occur between 1 and 19 years, caused by an actual crestal bone loss of between 0.1 and 1.9 mm. From these models, it appears that routine screening of patients by general dental practitioners for small amounts of bone loss is unlikely to be successful without the use of (i) repositionable stentless film holders to standardise the irradiation geometry, (ii) a very accurate reproducible measuring technique which (iii) will probably require an automatic computer-based measuring system.(ABSTRACT TRUNCATED AT 250 WORDS)