Assessment of the proximal periodontal bone height from radiographs with partial reproduction of the teeth. A methodological study.

Difficulties arise in radiographic assessment of the proximal periodontal bone height in cases where the whole of the teeth is not reproduced on the films. To overcome this, a study was made of the ratio between the crown height and the total tooth length of mandibular molars and premolars. This ratio was found to be about 35:100 with slight differences between the different types of those teeth. The study was preceded by an evaluation of the precision in single measurements of the quotient between the crown and the tooth length. The intra- as well as the inter-observer reliability was found to be high. Based on these results scales were devised which were engraved in rulers of plastic material, one type for mandibular premolars and one for each of first and second molars. These rulers make possible an assessment of the periodontal bone height even if the crown tips or the apices are not depicted in the radiographs. Since differences between these rulers are slight, one ruler based on mean values may be enough for practical purposes. In the next step of our investigation the agreement between assessments from bite-wing films and those from periapical films was found to be good. Since bite-wing radiography gives information not only about the periodontal bone level but also about proximal caries and calculus as well as the state of restorations, much information may be gathered with use of a minimum of radiation.